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WO2008036959A2 - dispositif matriciel à micromiroirS comprenant une couche de métal réfléchissante encapsulée et son procédé de fabrication - Google Patents

dispositif matriciel à micromiroirS comprenant une couche de métal réfléchissante encapsulée et son procédé de fabrication Download PDF

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Publication number
WO2008036959A2
WO2008036959A2 PCT/US2007/079256 US2007079256W WO2008036959A2 WO 2008036959 A2 WO2008036959 A2 WO 2008036959A2 US 2007079256 W US2007079256 W US 2007079256W WO 2008036959 A2 WO2008036959 A2 WO 2008036959A2
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WO
WIPO (PCT)
Prior art keywords
micromirror
coating layer
metal layer
array device
micromirror array
Prior art date
Application number
PCT/US2007/079256
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English (en)
Other versions
WO2008036959A3 (fr
Inventor
Jin Young Sohn
Gyoung Il Cho
Cheong Soo Seo
Original Assignee
Stereo Display, Inc.
Angstrom, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US11/534,620 external-priority patent/US7589885B2/en
Priority claimed from US11/534,613 external-priority patent/US7589884B2/en
Application filed by Stereo Display, Inc., Angstrom, Inc. filed Critical Stereo Display, Inc.
Publication of WO2008036959A2 publication Critical patent/WO2008036959A2/fr
Publication of WO2008036959A3 publication Critical patent/WO2008036959A3/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
    • B81B7/0009—Structural features, others than packages, for protecting a device against environmental influences
    • B81B7/0012—Protection against reverse engineering, unauthorised use, use in unintended manner, wrong insertion or pin assignment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B2201/00—Specific applications of microelectromechanical systems
    • B81B2201/04—Optical MEMS
    • B81B2201/042—Micromirrors, not used as optical switches

Definitions

  • the present invention relates to fabrication of micromirror device, more specifically, micromirror array fabrication and structure.
  • Micromirror related devices are usually light reflecting and light modulating devices. Especially controlling light and having a good quality of reflectivity is essential to the device as well as the operation of the micromirror devices.
  • Hornbeck discloses a micromirror array device with metal layer made of aluminum alloy in US Patent No. 5,083,857. Since the micromirror array was made by the aluminum alloy, the micromirror array device has a reflectivity of metal. It has a good performance of light reflecting and modulating. Even though aluminum alloy has a high reflectivity, the metal surface is degraded by oxidation. Since the metal layer was exposed to the environments, the reflectivity of the micromirror was slowly degraded by oxidation.
  • anti-reflective coatings are also investigated. Some example can be found in the US Patent No. 6,282,010 to Sulzbach, and the US Patent No. 7,009,745 to Miller. In those patents, the structures under the reflective surface are coated with anti-reflective materials. Since the structure of the micromirror device was made with metal or metal alloy, the structure itself has a relatively high reflectivity. The residual light reflected from the metal surface other than reflective mirror surface made serious problems for generating images with high resolution and high quality. The anti-reflection coating for the structure enhanced the optical quality of the micromirror device. But the enhancement was not enough and the process for anti-reflective coating was complex and difficult.
  • micromirror device By introducing wafer bonding and transparent substrates, a different structure for micromirror device was disclosed by Huibers in the US Patent No. 5,835,256. The device has a better protection for reflective mirror surface, but the fabrication of the device becomes considerably difficult with fabrication on the transparent wafer and wafer bonding of two different wafers. One more problem is that this structure experiences a thermal degradation of the reflectivity. [0006] More recently, another micromirror array device was disclosed in US Patent
  • the Micromirror Array Lens acts as a variable focusing lens by controlling micromirrors in the Micromirror Array Lens.
  • the micromirrors in the Micromirror Array Lens need a good quality of optical coating as well as protection for the micro-mechanical structures.
  • the present invention is dedicated to solve the following problems: oxidation of the metal coating, degradation of the reflective coating layer, protection of micro-mechanical structures and reflective surface from the acid or base, protection of reflective surface from severe environments, providing the anti-reflective coating for optically non-effective area, providing protective layer for reflective surface, and simplifying the process of fabrication.
  • the object of the present invention is to provide a micromirror device, a micromirror array device and a method for making the same. While fabricating the micromirror device and the micromirror array device, there remain lots of obstacles for having a good quality of operation. Especially providing a good optical quality is very important in making micromirror and micromirror array device.
  • the present invention provides a micromirror array device with special coating structures. By introducing a sub coating layer and an over coating layer with a high reflective metal layer, the reflectivity of the micromirrors in the micromirror array device is preserved and protected from environmental circumstances, oxidation, degradation, acid, base, and galvanic corrosion of the micro-mechanical structures.
  • micromirror array device with optical performance and its structures can be found in US Patent Publication No. 20050280883 Al, US Patent Publication No. 20060012852 Al, US Patent Publication No. 20060152792 Al, US Patent Publication No. 20060203358 Al, US Patent App. Ser. No. 11/426,565 filed on June 26, 2006, and US Patent
  • Micromirror Array Lens By using a micromirror array, a Micromirror Array Lens was developed as one of the micromirror array applications. The details of the Micromirror Array Lens is disclosed in US Patent No. 6,970,284 to Kim, US Patent No. 7,031,046 to Kim, US Patent No.
  • the micromirror array device of the present invention comprises a plurality of micromirrors.
  • Each micromirror in optically effective area comprises a substrate with at least one electrode and at least one actuation element, a micromirror structure, a sub coating layer, a metal layer, and an over coating layer.
  • the effective area is the area where the actual spatial light modulating is performed or where focusing of the Micromirror Array Lens is performed.
  • the substrate has at least one electrode to provide actuation force for micromirror motion.
  • the actuation elements make micromirror motion controlled by electrostatic force induced between the electrodes in the substrate and the micromirror structure. All the elements which are related with the motion of the micromirror can be actuation elements.
  • the micromirror structure has rotational and/or translational motions controlled by the actuation elements.
  • the sub coating and the over coating layers encapsulate the metal layer to prevent the metal layer from oxidation and to prevent the micromirror structure and the actuation elements from galvanic corrosion.
  • the metal layer makes the micromirror structure have high reflectivity. The encapsulation of the metal layer considerably reduces degradation of reflectivity by the metal layer.
  • the shape of the micromirrors can be varied with geometry of the micromirror array device.
  • the micromirrors in the effective area have a shape selected from the group consisting of fan, rectangular, square, hexagonal, and triangular shapes.
  • a fan shape for micromirrors is a good choice for effective fabricating the micromirror array device such as the Micromirror Array Lenses.
  • micromirrors with rectangular or square shapes can be selected to have a proper geometry of the optical system.
  • the hexagonal and triangular shape micromirrors are also used for systems with rotational symmetry (axis-symmetry), especially with six-fold rotational symmetry (three-fold rotational symmetry). Hexagonal micromirrors can be used for highly dense system. Again, the selection of the micromirror shapes is highly dependent on the optical system geometry and the devices.
  • the micromirror array device can be extended to have a function of a lens and act as a Micromirror Array Lens.
  • the micromirror array for Micromirror Array Lens should satisfy two conditions to form a good lens.
  • One is the convergence condition that every light should be converged into a focal point.
  • the other is the phase matching condition that the phase of the converged light should be the same.
  • the phase matching condition is that all the light passing through a lens should have the same optical path length to the focal point.
  • the Micromirror Array Lens arranged in a flat surface uses the periodicity of the light to satisfy the phase matching condition. Since the same phase condition occurs periodically, the phase matching condition can be satisfied even though the optical path length is different.
  • Each micromirror in the Micromirror Array Lens can be controlled independently to satisfy the phase matching condition and the convergence condition. [0016] Only after satisfying the convergence and the phase matching conditions, the micromirror array device can perform its function as a Micromirror Array Lens and build a lens with an optical surface profile.
  • An optical surface profile is the surface shape of the micromirror array which meets the lens conditions of convergence and phase matching.
  • Each micromirror in the effective area is independently controlled to form at least one optical surface profile.
  • the Micromirror Array Lens can have a plurality of optical surface profiles to have a variable focusing property. By changing the optical surface profile, the Micromirror Array Lens can change its focal length, optical axis, and focusing properties.
  • the Micromirror Array Lens can be a variable focusing lens having lots of optical profiles.
  • the substrate has at least one electrode, usually a plurality of electrodes for providing actuation force for micromirror motion. Each electrode is used for generating motion for micromirror. Sometimes groups of electrodes are used for micromirror motion.
  • a control circuitry should be constructed.
  • the substrate comprises a control circuitry constructed by using semiconductor microelectronics technologies such as MOS and CMOS technologies. By providing semiconductor microelectronics, the micromirror array device can have high flexibility in motion control with convenience.
  • the electrodes should have a different electric potential from the electric potential of the actuation elements or the micromirror structure.
  • the electrodes are protected by passivation layer.
  • the passivation layer prevents the electrodes from possible electric contact or problems with other structures in the micromirror structure.
  • the passivation layer can be built with silicon oxide or low-stressed silicon nitride (LSN) since they have high electrical resistance and easy accessibility for fabrication.
  • the micromirror array device can be built so that the micromirrors in the micromirror device are controlled together and has their respective motions with a common input signal.
  • the micromirrors in the effective area are controlled to form an optical surface profile by a common electrical signal to the corresponding electrodes.
  • the Micromirror Array Lens can be digitally or discretely controlled to have an optical surface profile with corresponding optical properties.
  • the number of the inputs can be reduced by using common input signal down to the number of optical surface profiles. To control a certain amount of the optical surface profiles, only the same number of the electrical inputs is needed. Also the operating circuitry becomes extremely simple.
  • the sub coating and the over coating layers encapsulate the metal layer to prevent the metal layer from oxidation and to prevent the micromirror structure and the actuation elements from galvanic corrosion.
  • the encapsulated metal layer is protected by the sub coating layer and the over coating layer from degradation of reflectivity and also from acid, base, or severe environments.
  • the sub coating layer is deposited on the micromirror structure with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI2O3), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the sub coating layer prevents the metal layer from electrical contacting with micromirror structure. Since the galvanic corrosion can only occur if the dissimilar metals are in electrical contact. When the dissimilar metals are insulated from each other by suitable plastic strips, washers or sleeves, the galvanic corrosion cannot occur. Thus the sub coating layer prevents the micromirror structure and the actuation elements from galvanic corrosion by electrically separating the micromirror structure and the metal layer. For micromirror array devices with electrostatic force actuation, the electrical separation is especially important.
  • the sub coating material should be highly electrically insulating and also consistent with the fabrication processes. To have sufficient electrical separation and optical properties, the thickness of the sub coating layer should be controlled to have between 20 nm and 500 nm preferably lOOnm.
  • the metal layer is made of material selected from the group consisting of silver
  • the thickness of the metal layer is controlled to have between 20 nm and 1000 nm preferably 100 nm.
  • the thickness should be controlled to have high reflectivity of the micromirrors in the micromirror array device.
  • the material of the metal layer should be selected by considering the required reflectivity, operating wavelength, operating environment, and others. Also since the metal layer is easy to be attacked from acid or base or other environmental reasons, the metal layer should be protected from them.
  • the sub coating layer and the over coating layer provide a strong protection for the metal layer from oxidation, acid, base and galvanic corrosion by encapsulating the metal layer.
  • the over coating layer and the sub coating layer prevent the metal layer from oxidation by encapsulating the metal layer.
  • the over coating layer and the sub coating layer protect the metal layer from acid or base to maintain reflectivity of the micromirrors by encapsulating the metal layer.
  • the degradation of the reflectivity is considerablely reduced by encapsulation of the metal layer by the sub coating layer and the over coating layer.
  • One more thing is that the over coating layer and the sub coating layer protect the metal layer from etchants while removing sacrificial layer or layers of the micro-mechanical structure.
  • the over coating layer provides a protection for metal layer from the operating environments. Since the metal layer should have high reflectivity, the thickness of the over coating layer should be controlled to maximize reflectivity of the metal layer. The maximized reflectivity enhances the performance of the Micromirror Array Lens.
  • the thickness of the over coating layer is controlled to have between 20 nm and 500 nm preferably 100 nm. Since the over coating layer is directly exposed to the operating environment, the thickness of the over coating layer is more important than that of the sub coating layer, especially to control the reflectivity of the micromirrors.
  • the sub coating layer is deposited on the micromirror structure with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the micromirror array device further comprises an optically non-effective area which is other than the controlled micromirror area.
  • the non-effective area comprises a substrate, at least one dummy structure, a sub coating layer, and an over coating layer.
  • the sub coating and the over coating layers are fabricated together with the layers in the micromirrors in the effective area.
  • the micromirror array device is a fragile one, the micromirrors should be protected during the fabrication and the usage.
  • the dummy structures are introduced and fabricated with the micromirror structures. The dummy structures protect the micromirrors in the effective area from external perturbation.
  • the external perturbation can be occurred during fabrication of the micromirror array device and operation of the micromirror array device.
  • the dummy structures enclose the effective area and act as a buffer area of the device.
  • the dummy structures are also fabricated with the micromirror structures or elements in the effective area.
  • the non- effective area should not be optically active.
  • the anti-reflective coating enhances the optical performance of the micromirror array device. Since the dummy structures do not have metal layer, the structures do not have high reflectivity, but still the dummy structures make effects on the optical quality. To enhance the optical performance, it is highly desired that the noneffective area has as low reflectivity as possible.
  • An anti-reflective coating for the non-effective area is one solution.
  • the non-effective area can have anti-reflective coating.
  • two layers of sub coating and over coating layers are applied to the dummy structures.
  • the total thickness of the sub coating and over coating layers can be controlled to have anti- reflective coating properties.
  • the method for fabricating the micromirror device comprises the steps of forming electrodes and control circuitry on a substrate, building micromirror actuation elements with sacrificial layer or layers, applying a micromirror structure layer, applying a sub coating layer to the micromirror structure, applying a metal layer to the sub coating layer on effective area, applying an over coating layer, selectively etching the sub coating layer, the over coating layer and the micromirror structure layer to make micromirror structures with coating layers, removing the sacrificial layers and releasing the actuation elements and the micromirror structures.
  • the metal layer is encapsulated by the sub coating layer and the over coating layer to prevent the metal layer from oxidation and to prevent the micromirror structures and the actuation elements from galvanic corrosion.
  • non-effective area can be made without extra process of fabrication. The only differences are that the non-effective area does not have metal layer since it does not need high reflectivity and that the non-effective area does not have actuation elements. The dummy structures in the non-effective area are more likely the micromirror structure without actuation part.
  • advantages for the method of the present invention By applying the sub coating layer and the over coating layer, the metal layer can be protected from severe environments, oxidation, degradation of reflectivity, acid, base, and galvanic corrosion.
  • the sub coating layer and the over coating layer can provide optical properties to the effective and non-effective area as much as protection to the metal layer.
  • the thickness of the over coating layer is controlled to have high reflectivity along with the protection of the metal layer.
  • the over coating layer and the sub coating layer are combined together since there is no metal layer.
  • the total thickness of the sub coating layer and the over coating layer is controlled to have anti- reflective property.
  • the coating layer and the micromirror structure can be etched together. After depositing the micromirror structure together with dummy structures in the noneffective area, the sub coating layer is deposited. Next the metal layer is deposited with patterning the shape of micromirrors.
  • the over coating layer is followed by the metal layer to encapsulate the metal layer with the sub coating layer.
  • the layers are patterned and etched. The etching processes can be performed altogether with the same patterning process, which reduces the process of the fabrication considerably.
  • an optical micromirror device can be built with the same advantages of the micromirror array device explained the above.
  • the optical micromirror device of the present invention comprises a micromirror.
  • the micromirror comprises a substrate with at least one electrode and at least one actuation element, a micromirror structure, a sub coating layer, a metal layer, and an over coating layer.
  • the substrate has at least one electrode to provide actuation force for micromirror motion.
  • the actuation elements make micromirror motion controlled by electrostatic force induced between the electrodes in the substrate and the micromirror structure.
  • the micromirror structure has rotational and/or translational motions controlled by the actuation elements.
  • the sub coating and the over coating layers encapsulate the metal layer to prevent the metal layer from oxidation and to prevent the micromirror structure and the actuation elements from galvanic corrosion.
  • the metal layer makes the micromirror structure have high reflectivity.
  • the shape of the micromirror can be varied with object of the optical micromirror device.
  • the micromirror has a shape selected from the group consisting of fan, rectangular, square, hexagonal, and triangular shapes. The selection of the micromirror shapes is highly dependent on the optical system geometry and the device itself.
  • the substrate has at least one electrode, usually a plurality of electrodes for providing actuation force for micromirror motion. Each electrode is used for generating motion for the micromirror. Sometimes groups of electrodes are used for micromirror motion.
  • the substrate comprises a control circuitry constructed by using semiconductor microelectronics technologies such as MOS and CMOS technologies. By providing semiconductor microelectronics, the control of the optical micromirror device becomes much easier.
  • the electrodes should have a different electric potential from the electric potential of the actuation elements or the micromirror structure.
  • the electrodes are protected by passivation layer.
  • the passivation layer prevents the electrodes from possible electric contact or problems with other structures in the micromirror structure.
  • the passivation layer can be built with silicon oxide or low-stressed silicon nitride (LSN) since they have high electrical resistance and easy accessibility for fabrication.
  • the sub coating and the over coating layers encapsulate the metal layer to prevent the metal layer from oxidation and to prevent the micromirror structure and the actuation elements from galvanic corrosion.
  • the encapsulated metal layer is protected by the sub coating layer and the over coating layer from degradation of reflectivity and also from acid, base, or severe environments.
  • the sub coating layer is deposited on the micromirror structure with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI2O3), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the sub coating layer prevents the metal layer from electrical contacting with micromirror structure.
  • the sub coating layer prevents the micromirror structure and the actuation elements from galvanic corrosion by electrically separating the micromirror structure and the metal layer.
  • the electrical separation is especially important.
  • the sub coating material should be highly electrically insulating and also consistent with the fabrication processes. To have sufficient electrical separation and optical properties, the thickness of the sub coating layer should be controlled to have between 20 nm and 500 nm preferably lOOnm.
  • the metal layer is made of material selected from the group consisting of silver
  • the thickness of the metal layer is controlled to have between 20 nm and 1000 nm preferably 100 nm.
  • the thickness should be controlled to have high reflectivity of the micromirror device.
  • the material of the metal layer should be selected by considering the required reflectivity, operating wavelength, operating environment, and others. Also since the metal layer is easy to be attacked from acid or base or other environmental reasons, the metal layer should be protected from them.
  • the sub coating layer and the over coating layer provide a strong protection for the metal layer from oxidation, acid, base and galvanic corrosion by encapsulating the metal layer.
  • the over coating layer and the sub coating layer prevent the metal layer from oxidation by encapsulating the metal layer.
  • the over coating layer and the sub coating layer protect the metal layer from acid or base to maintain reflectivity of the micromirrors by encapsulating the metal layer.
  • the degradation of the reflectivity is considerable reduced by encapsulation of the metal layer by the sub coating layer and the over coating layer.
  • the over coating layer and the sub coating layer protect the metal layer from etchants while removing sacrificial layer or layers of the micro-mechanical structure. Usually while removing sacrificial layer or layers, a strong acid or base such as fluoric acid is applied to dissolve the sacrificial layers made of such as silicon oxide.
  • the over coating layer provides a protection for metal layer from the operating environments. Since the metal layer should have high reflectivity, the thickness of the over coating layer should be controlled to maximize reflectivity of the metal layer. The maximized reflectivity enhances the performance of the optical micromirror device.
  • the thickness of the over coating layer is controlled to have between 20 nm and 500 nm preferably 100 nm. Since the over coating layer is directly exposed to the operating environment, the thickness of the over coating layer is more important than that of the sub coating layer, especially to control the reflectivity of the micromirror.
  • the over coating layer is deposited on the micromirror structure with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI2O3), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the optical micromirror device further comprises an optically non-effective area which is other than the micromirror itself. Since the structure in the non-effective area does not need actuation parts, the structure of the non-effective area is somewhat different from that of the micromirror.
  • the non-effective area comprises a substrate, at least one dummy structure, a sub coating layer, and an over coating layer. The sub coating and the over coating layers are fabricated together with the layers in the micromirror.
  • the optical micromirror device is a fragile one, the micromirror should be protected during the fabrication and the usage. To protect the micromirror, the dummy structures are introduced and fabricated with the micromirror structures.
  • the dummy structures protect the micromirror from external perturbation.
  • the external perturbation can be occurred during fabrication of the micromirror device and operation of the micromirror device.
  • the dummy structures enclose the micromirror and act as a buffer area of the micromirror device.
  • the dummy structures are also fabricated with the micromirror structures or elements in the micromirror itself.
  • the noneffective area should not be optically active.
  • the anti-reflective coating enhances the optical performance of the optical micromirror device. Since the dummy structures do not have metal layer, the structures do not have high reflectivity, but still the dummy structures make effects on the optical quality.
  • the non-effective area has as low reflectivity as possible.
  • An anti-reflective coating for the noneffective area is one solution.
  • the non-effective area can have anti-reflective coating.
  • two layers of sub coating and over coating layers are applied to the dummy structures.
  • the total thickness of the sub coating and over coating layers can be controlled to have anti- reflective coating properties.
  • the method for fabricating the optical micromirror device is also provided.
  • the method for fabricating the optical micromirror device comprises the steps of forming electrodes and control circuitry on a substrate, building micromirror actuation elements with sacrificial layer or layers, applying a micromirror structure layer, applying a sub coating layer to the micromirror structure, applying a metal layer to the sub coating layer on effective area, applying an over coating layer, selectively etching the sub coating layer, the over coating layer and the micromirror structure layer to make micromirror structures with coating layers, removing the sacrificial layers and releasing the actuation elements and the micromirror structures just like the method for fabricating the micromirror.
  • the metal layer is encapsulated by the sub coating layer and the over coating layer to prevent the metal layer from oxidation and to prevent the micromirror structures and the actuation elements from galvanic corrosion.
  • non-effective area can be made without extra process of fabrication. The only differences are that the non-effective area does not have metal layer since it does not need high reflectivity and that the non-effective area does not have actuation elements. The dummy structures in the non-effective area are more likely the micromirror structure without actuation part.
  • advantages for the method of the present invention By applying the sub coating layer and the over coating layer, the metal layer can be protected from severe environments, oxidation, degradation of reflectivity, acid, base, and galvanic corrosion.
  • the sub coating layer and the over coating layer can provide optical properties to the effective and non-effective area as much as protection to the metal layer.
  • the thickness of the over coating layer is controlled to have high reflectivity along with the protection of the metal layer.
  • the over coating layer and the sub coating layer are combined together since there is no metal layer.
  • the total thickness of the sub coating layer and the over coating layer is controlled to have anti- reflective property.
  • the coating layer and the micromirror structure can be etched together.
  • the Micromirror Array Lens as one of applications of the micromirror array device comprises a plurality of micromirrors.
  • Each micromirror in optically effective area comprises a substrate with at least one electrode and at least one actuation element, a micromirror structure, a sub coating layer, a metal layer, and an over coating layer.
  • the effective area is the area where the actual focusing of the Micromirror Array Lens is performed.
  • the substrate has at least one electrode to provide actuation force for micromirror motion.
  • the actuation elements make micromirror motion controlled by electrostatic force induced between the electrodes in the substrate and the micromirror structure. All the elements which are related with the motion of the micromirror can be actuation elements.
  • the micromirror structure has rotational and/or translational motions controlled by the actuation elements.
  • the sub coating and the over coating layer encapsulate the metal layer to prevent the metal layer from oxidation and to prevent the micromirror structure and the actuation elements from galvanic corrosion.
  • the metal layer makes the micromirror structure have high reflectivity. The encapsulation of the metal layer considerably reduces degradation of reflectivity by the metal layer.
  • the sub coating and the over coating layer provide good protective layers for the metal layer.
  • the shape of the micromirrors can be varied with geometry of the Micromirror
  • the micromirrors in the effective area have a shape selected from the group consisting of fan, rectangular, square, hexagonal, and triangular shapes.
  • a fan shape for micromirrors is a good choice for effective fabricating the Micromirror Array Lenses.
  • micromirrors with rectangular or square shapes can be selected to have a proper geometry of the optical system.
  • the hexagonal and triangular shape micromirrors are also used for systems with rotational symmetry, especially with six-fold rotational symmetry. Hexagonal micromirrors can be used for highly dense system.
  • the selection of the micromirror shapes is highly dependent on the optical system geometry and the devices.
  • the substrate has at least one electrode, usually a plurality of electrodes for providing actuation force for micromirror motion. Each electrode is used for generating motion for micromirror. Sometimes groups of electrodes are used for micromirror motion.
  • a control circuitry should be constructed.
  • the substrate comprises a control circuitry constructed by using semiconductor microelectronics technologies such as MOS and CMOS technologies. By providing semiconductor microelectronics, the Micromirror Array Lens can have high flexibility in motion control with convenience.
  • the electrodes should have a different electric potential from the electric potential of the actuation elements or the micromirror structure.
  • the electrodes are protected by passivation layer.
  • the passivation layer prevents the electrodes from possible electric contact or problems with other structures in the micromirror structure.
  • the passivation layer can be built with silicon oxide or low-stressed silicon nitride (LSN) since they have high electrical resistance and easy accessibility for fabrication.
  • LSN low-stressed silicon nitride
  • Micromirror Array Lens should satisfy two conditions to form a good lens.
  • One is the convergence condition that every light should be converged into a focal point.
  • the other is the phase matching condition that the phase of the converged light should be the same.
  • the phase matching condition is that all the light passing through a lens should have the same optical path length to the focal point.
  • the Micromirror Array Lens arranged in a flat surface uses the periodicity of the light to satisfy the phase matching condition. Since the same phase condition occurs periodically, the phase matching condition can be satisfied even though the optical path length is different.
  • Each micromirror in the Micromirror Array Lens can be controlled independently to satisfy the phase matching condition and the convergence condition.
  • Micromirror Array Lens can build a lens with an optical surface profile.
  • An optical surface profile is the surface shape of the micromirror array which meets the lens conditions of convergence and phase matching.
  • Each micromirror in the effective area is independently controlled to form at least one optical surface profile.
  • the Micromirror Array Lens has a plurality of optical surface profiles to have a variable focusing property. By changing the optical surface profile, the Micromirror Array Lens can change its focal length, optical axis, and focusing properties.
  • the Micromirror Array Lens can be a variable focusing lens having lots of optical profiles.
  • the Micromirror Array Lens can be built so that the micromirrors in the effective area are controlled by a common input signal to the electrodes to form an optical surface profile.
  • the Micromirror Array Lens can be digitally or discretely controlled to have an optical surface profile with corresponding optical properties.
  • the number of the inputs can be reduced by using common input signal down to the number of optical surface profiles. To control a certain amount of the optical surface profiles, only the same number of the electrical inputs is needed. Also the operating circuitry becomes extremely simple.
  • the sub coating and the over coating layers encapsulate the metal layer to prevent the metal layer from oxidation and to prevent the micromirror structure and the actuation elements from galvanic corrosion.
  • the encapsulated metal layer is protected by the sub coating layer and the over coating layer from degradation of reflectivity and also from acid, base, or severe environments.
  • the sub coating layer is deposited on the micromirror structure with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the sub coating layer prevents the metal layer from electrical contacting with micromirror structure.
  • the sub coating layer prevents the micromirror structure and the actuation elements from galvanic corrosion by electrically separating the micromirror structure and the metal layer.
  • the sub coating material should be highly electrically insulating and also consistent with the fabrication processes. To have sufficient electrical separation and optical properties, the thickness of the sub coating layer should be controlled to have between 20 nm and 500 nm preferably lOOnm.
  • the metal layer is made of material selected from the group consisting of silver
  • the thickness of the metal layer is controlled to have between 20 nm and 1000 nm preferably 100 nm.
  • the thickness should be controlled to have high reflectivity of the micromirrors in the Micromirror Array Lens.
  • the material of the metal layer should be selected by considering the required reflectivity, operating wavelength, operating environment, and others. Also since the metal layer is easy to be attacked from acid or base or other environmental reasons, the metal layer should be protected from them.
  • the sub coating and the over coating provide a strong protection for the metal layer from oxidation, acid, base and galvanic corrosion by encapsulating the metal layer.
  • the over coating layer and the sub coating layer prevent the metal layer from oxidation by encapsulating the metal layer.
  • the over coating layer and the sub coating layer protect the metal layer from acid or base to maintain reflectivity of the micromirrors by encapsulating the metal layer.
  • the degradation of the reflectivity is considerably reduced by encapsulation of the metal layer by the sub coating layer and the over coating layer.
  • One more thing is that the over coating layer and the sub coating layer protect the metal layer from etchants while removing sacrificial layer or layers of the micro- mechanical structure.
  • the over coating layer provides a protection for metal layer from the operating environments. Since the metal layer should have high reflectivity, the thickness of the over coating layer should be controlled to maximize reflectivity of the metal layer. The maximized reflectivity enhances the performance of the Micromirror Array Lens.
  • the thickness of the over coating layer is controlled to have between 20 nm and 500 nm preferably 100 nm. Since the over coating layer is directly exposed to the operating environment, the thickness of the over coating layer is more important than that of the sub coating layer, especially to control the reflectivity of the micromirrors.
  • the over coating layer is deposited on the micromirror structure with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI2O3), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the Micromirror Array Lens further comprises an optically non-effective area which is other than the controlled micromirror area.
  • the non-effective area comprises a substrate, at least one dummy structure, a sub coating layer, and an over coating layer.
  • the sub coating and the over coating layers are fabricated together with the layers in the micromirrors in the effective area.
  • the Micromirror Array Lens is a fragile device, the micromirrors should be protected during the fabrication and the usage.
  • the dummy structures are introduced and fabricated with the micromirror structures.
  • the dummy structures protect the micromirrors in the effective area from external perturbation. The external perturbation can be occurred during fabrication of the Micromirror Array Lens and operation of the Micromirror Array Lens.
  • the dummy structures enclose the effective area and acts as a buffer area of the device.
  • the dummy structures are also fabricated with the micromirror structures or elements in the effective area.
  • the noneffective area should not be optically active.
  • the anti-reflective coating enhances the optical performance of the Micromirror Array Lens. Since the dummy structures do not have metal layer, the structures do not have high reflectivity, but still the dummy structures make effects on the optical quality. To enhance the optical performance, it is highly desired that the noneffective area has as low reflectivity as possible.
  • An anti-reflective coating for the noneffective area is one solution. By controlling the thickness of the existing layers for the micromirrors, the non-effective area can have anti-reflective coating. In the non-effective area, two layers of sub coating and over coating layers are applied to the dummy structures.
  • the total thickness of the sub coating and over coating layers can be controlled to have anti- reflective coating properties.
  • To provide anti-reflective coating for non-effective area along with protection of the metal layer is the one of main ideas and advantages of the present invention. [0063] In the present invention, the method for fabricating the Micromirror Array Lens is also provided.
  • the method for fabricating the Micromirror Array Lens comprises the steps of forming electrodes and control circuitry on a substrate, building micromirror actuation elements with sacrificial layer or layers, applying a micromirror structure layer, applying a sub coating layer to the micromirror structure, applying a metal layer to the sub coating layer on effective area, applying an over coating layer, selectively etching the sub coating layer, the over coating layer and the micromirror structure layer to make micromirror structures with coating layers, removing the sacrificial layers and releasing the actuation elements and the micromirror structures.
  • the metal layer is encapsulated by the sub coating layer and the over coating layer to prevent the metal layer from oxidation and to prevent the micromirror structures and the actuation elements from galvanic corrosion.
  • non-effective area can be made without extra process of fabrication. The only differences are that the noneffective area does not have metal layer since it does not need high reflectivity and that the non-effective area does not have actuation elements. The dummy structures in the noneffective area are more likely the micromirror structure without actuation part.
  • advantages for the method of the present invention By applying the sub coating layer and the over coating layer, the metal layer can be protected from severe environments, oxidation, degradation of reflectivity, acid, base, and galvanic corrosion.
  • the sub coating layer and the over coating layer can provide optical properties to the effective and non-effective area as much as protection to the metal layer.
  • the thickness of the over coating layer is controlled to have high reflectivity along with the protection of the metal layer.
  • the over coating layer and the sub coating layer are combined together since there is no metal layer.
  • the total thickness of the sub coating layer and the over coating layer is controlled to have anti- reflective property.
  • the coating layer and the micromirror structure can be etched together.
  • the sub coating layer is deposited.
  • the metal layer is deposited with patterning the shape of micromirrors.
  • the over coating layer is followed by the metal layer to encapsulate the metal layer with the sub coating layer.
  • the layers are patterned and etched. The etching processes can be performed altogether with the same patterning process, which reduces the process of the fabrication considerably.
  • the optical micromirror device and the micromirror array device of the present invention has advantages: (1) the high reflective metal layer is protected from oxidation; (2) the reflective metal layer is protected from acid or base; (3) the degradation of the reflective metal layer is reduced; (4) the micro-mechanical structures are protected from galvanic corrosion; (5) the metal layer can have high reflectivity with protection; (6) the non-effective area has anti-reflective coating to enhance optical performance; (7) anti-reflection and protection coating are deposited altogether; (8) the coating layers and the micromirror structure can be etched together; (9) the process of fabrication is simple.
  • FIG. 1 shows structure of a micromirror in a micromirror array device with sub coating and over coating layers altogether with the metal layer;
  • FIG. 2 shows structure of a micromirror in a micromirror array device before removing the sacrificial layers;
  • FIGS. 3A-3I shows fabrication process of the micromirror array device with effective and non-effective area
  • FIG. 4 shows how the light modulation of the micromirror array device and the anti-reflective coating in non-effective area work.
  • FIG. 5 illustrates an optical system of a Micromirror Array Lens having line symmetry as an example of the micromirror array device
  • FIG. 6 illustrates effective and non-effective area determined by the optical geometry with line symmetry in a Micromirror Array Lens.
  • FIG. 7 illustrates an optical system of a Micromirror Array Lens having symmetry of revolution;
  • FIG. 8 illustrates effective and non-effective area determined by the optical geometry with symmetry of revolution.
  • FIG. 1 shows the structure of a micromirror with sub coating layer 17 and over coating layer 19 altogether with the metal layer 18.
  • the substrate 11 has at least one electrode 12 to build electrostatic force between the substrate 11 and the micromirror structure 16.
  • the corresponding electrode 12 for motion has an electric potential different from the electric potential of the micromirror structure 16.
  • the electrically charged structure makes the capacitive force between the electrodes 12 and the micromirror structure 16.
  • some structures work together and make actuation force to the micromirror.
  • the pillar structure 13 gives a rigid rotational or translational center to the micromirror structure 16.
  • the flexible spring structure 14 connects the rigid bodies and the moving structures.
  • the top electrode 15 gives enhancement on the electrostatic force and on the structural stability.
  • the pillar structure 13, the flexible spring structure 14, the top electrode 15, and other components for actuation can be actuation components.
  • the micromirror structure 16 is built for the base of the micromirror motion and the reflective surface of the micromirror device.
  • the sub coating layer 17 is applied to build insulation between the micromirror structure 16 and the metal layer 18.
  • the metal layer 18 lies on top of the sub coating layer 17 and gives high reflectivity to the micromirror structure 16.
  • the micromirror structure 16 with high reflectivity plays a role of a high reflector, thus the micromirror array plays a role of a spatial light modulator.
  • the over coating layer 19 is applied to encapsulate the metal layer 18 with the sub coating layer 17 and to prevent the exposure of the metal layer 18 direct to the operational environment, oxidation, acid, base, or galvanic corrosion.
  • the sub coating layer 17 and the over coating layer 19 encapsulate the metal layer 18 to prevent the metal layer 18 from oxidation and degradation of the high reflectivity and also to prevent the micromirror structure 16 and the actuation elements 13, 14, 15 from galvanic corrosion.
  • the encapsulated metal layer 18 is protected by the sub coating layer 17 and the over coating layer 19.
  • the sub coating layer 17 and the over coating layer 19 is deposited on the micromirror structure 16 with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI2O3), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the sub coating layer 17 prevents the metal layer 18 from electrical contacting with micromirror structure 16.
  • the galvanic corrosion can only occur if the dissimilar metals are in electrical contact.
  • the micromirror structure 16 and the metal layer 18 are the dissimilar metals for possible galvanic corrosion. If the dissimilar metals are insulated from each other by suitable plastic strips, washers or sleeves then galvanic corrosion cannot occur.
  • the sub coating layer 17 prevents the micromirror structure 16 and the actuation elements 13, 14, 15 from galvanic corrosion by electrically separating the micromirror structure 16 and the metal layer 18.
  • the sub coating layer 17 materials should be highly electrically insulating and also consistent with the fabrication processes. While selecting the material for the coating layers
  • the thickness of the sub coating layer 17 should be controlled to have between 20 nm and 500 nm preferably 100 nm.
  • the over coating layer 19 provides a protection for metal layer 18 from the operating environments. Since the metal layer 18 should have high reflectivity, the thickness of the over coating layer 19 should be controlled to maximize reflectivity of the metal layer 18. The maximized reflectivity enhances the efficiency of the micromirror array device.
  • the thickness of the over coating layer 19 is controlled to have between 20 nm and 500 nm preferably 100 nm. Since the over coating layer 19 is directly exposed to the operating environment, the thickness of the over coating layer 19 is more important than that of the sub coating layer 17, especially to have high reflectivity of the micromirrors.
  • the metal layer 18 is made of material selected from the group consisting of silver (Ag), aluminum (Al), gold (Ag), nickel (Ni), chromium (Cr), and platinum (Pt) to have high reflectivity.
  • the thickness of the metal layer 18 is controlled to have between 20 nm and 1000 nm preferably 100 nm. The thickness should be selected to have high reflectivity of the micromirrors. Also the material of the metal layer 18 should be selected by considering the required reflectivity, operating wavelength, operating environment and others. Also since the metal layer 18 is easy to be attacked from acid or base or other environmental reasons, the metal layer 18 should be protected.
  • the sub coating layer 17 and the over coating layer 19 provide a strong protection for the metal layer 18 from oxidation, acid, base and galvanic corrosion.
  • the over coating layer 19 and the sub coating layer 17 prevent the metal layer 18 from oxidation by encapsulating the metal layer 18.
  • the over coating layer 19 and the sub coating layer 17 protect the metal layer 18 from acid or base to maintain reflectivity of the micromirror by encapsulating the metal layer 18.
  • One more thing is that the over coating layer 19 and the sub coating layer 17 protect the metal layer 18 from etchants while removing sacrificial layers. Usually while removing sacrificial layer, a strong acid or base such as fluoric acid is applied to dissolve the sacrificial layer such as silicon oxide. [0082] FIG.
  • the micromirror in the micromirror array device is fabricated with layer by layer.
  • the electrical circuitry and the electrodes for micromirror motion generation are laid on top of the substrate 21.
  • the actuation elements 22, 23, 25 are fabricated on the substrate 21 with electrodes.
  • the actuation elements are the pillar structure 22, the flexible spring structure 23, the top electrode 25, and etc.
  • the actuation elements 22, 23, 25 are built with the sacrificial layer 24 to make the structure become layer by layer flat.
  • the micromirror structure 26 is made with connection to the actuation elements 22, 23, 25.
  • the micromirror structure 26 has a high reflectivity by depositing the metal layer 28.
  • This metal layer 28 is encapsulated and protected by the sub coating layer 27 and the over coating layer 29 while releasing process for removing the sacrificial layer 24 and while the operation of the micromirror array device. Since the metal layer 28 is extremely reactive in some cases, the layer should be protected from oxidation, degradation, acid, and base.
  • the substrate 21 has at least one electrode, usually a plurality of electrodes for providing actuation force for micromirror motion. Each electrode is used for generating motion for micromirror. Sometimes groups of electrodes are used for micromirror motion.
  • the electrical circuitry in the substrate 21 gives the controllability of the micromirror device.
  • the control circuitry becomes more complex.
  • the electrical control circuitry has its controllability of each micromirror.
  • a control circuitry should be constructed.
  • the substrate 21 comprises a control circuitry constructed by using semiconductor microelectronics technologies such as MOS and CMOS technologies. By providing semiconductor microelectronics, the micromirror array device can have high flexibility in motion generation with easy control. [0084] To build electrostatic force between the electrodes and the actuation elements
  • the electrodes should have a different electric potential from the electric potential of the actuation elements 22, 23, 25 or micromirror structure 26.
  • the electrodes are protected by passivation layer (not shown in the figure).
  • the passivation layer prevents the electrodes from possible electric contact with other structures 22, 23, 25, 26 in the micromirror.
  • Passivation layer can be built with silicon oxide or low-stressed silicon nitride since they have high electrical resistance.
  • the micromirror array should satisfy two conditions to form a good lens.
  • One is the convergence condition that every light should be converged into a focal point.
  • the other is the phase matching condition that the phase of the converged light should be the same.
  • the phase matching condition is that all the light passing through a lens should have the same optical path length to the focal point.
  • the Micromirror Array Lens arranged in a flat surface uses the periodicity of the light to satisfy the phase matching condition. Since the same phase condition occurs periodically, the phase matching condition can be satisfied even though the optical path length is different.
  • Micromirror Array lens can be controlled independently to satisfy the phase matching condition and the convergence condition.
  • Micromirror Array Lens can build a lens with an optical surface profile.
  • An optical surface profile is the surface shape of the micromirror array which meets the lens conditions of convergence and phase matching.
  • Each micromirror in the effective area is independently controlled to form at least one optical surface profile.
  • the Micromirror Array Lens has a plurality of optical surface profiles to have a variable focusing property. By changing the optical surface profile, the Micromirror Array Lens can change its focal length, optical axis, and focusing properties.
  • the Micromirror Array Lens can be a variable focusing lens having lots of optical profiles.
  • the Micromirror Array Lens can be built so that the micromirrors in the effective area are controlled by a common input signal to the electrodes to form an optical surface profile.
  • the Micromirror Array Lens can be digitally or discretely controlled to have an optical surface profile with corresponding optical properties.
  • the number of the inputs can be reduced by using common input signal down to the number of optical surface profiles.
  • the operating circuitry becomes extremely simple.
  • the motion of the Micromirror Array Lens is activated by applying voltages to the corresponding electrodes through the control circuitry. The motion can be made only after the releasing process by removing the sacrificial layer or structures in the micromirror array device.
  • FIGS. 3A-3I shows the fabrication process of micromirror device with effective area 39A and non-effective area 39B.
  • the method for fabricating the micromirror array device comprises the steps of forming electrodes 31A, 31B and control circuitry on a substrate 31C, building micromirror actuation elements 32A, 32B, 32C, 32D, 32E with sacrificial layer or layers 37, applying a micromirror structure layer 33C, applying a sub coating layer 34C to the micromirror structure layer 33C, applying a metal layer 35 to the sub coating layer 34C on effective area 39A, applying an over coating layer 36C, selectively etching the sub coating layer 34C, the over coating layer 36C and the micromirror structure layer 33C to make micromirror structures 33A, 33B with coating layers 34A, 34B, 36A, 36B, removing the sacrificial layers 37 and releasing the actuation elements 32A, 32B, 32C, 32D, 32E and the micromirror
  • the metal layer 35 is encapsulated by the sub coating layer 34A and the over coating layer 36A to prevent the metal layer 35 from oxidation and to prevent the micromirror structures 33A, 33B and the actuation elements 32A, 32B, 32C, 32D, 32E from galvanic corrosion.
  • Non-effective area 39B can be made without extra process of fabrication. The differences from the effective area 39A are that the non-effective area 39B does not have metal layer 35 since it does not need high reflectivity and that the non-effective area 39B does not have actuation elements 32A, 32C, 32D, 32E. The dummy structures 33B are more likely the micromirror structures 33A without actuation part. There are lots of advantages for the method of the present invention. By applying sub coating layer 34A and over coating layer 36A, the metal layer 35 can be protected from severe environments, oxidation, degradation, acid, base, and galvanic corrosion.
  • the sub coating layers 34A, 34B and the over coating layers 36A, 36B can provide optical properties to the effective area 39A and non-effective area 39B as much as protection to the metal layer 35.
  • the thickness of the over coating layer 36A is controlled to have high reflectivity along with the protection of the metal layer 35.
  • the over coating layer 36B and the sub coating layer are controlled to have high reflectivity along with the protection of the metal layer 35.
  • the coating layers 34C, 36C and the micromirror structure layer 33C can be etched together. After depositing the micromirror structure layer 33C including micromirror structure 33A in the effective area 39A together with the dummy structures 33B in the non-effective area 39B, the sub coating layer 34C is deposited. Next the metal layer 35 is deposited with patterning with the shape of micromirrors. The over coating layer 36C is followed by the metal layer 35 to encapsulate the metal layer 35 with the sub coating layer 34C.
  • FIG. 3 A shows the first step of building the micromirror array device, which is making the electrodes 31A, 31B on the substrates 31C.
  • the substrate 31C has at least one electrode 3 IA, 3 IB usually a plurality of electrodes 3 IA, 3 IB for providing actuation force for micromirror motion.
  • Each electrode 31 A is used for generating motion for micromirror.
  • groups of electrodes 31 A are used for micromirror motion.
  • the substrate 31C comprises a control circuitry constructed by using semiconductor microelectronics technologies such as MOS and CMOS technologies.
  • semiconductor microelectronics By providing semiconductor microelectronics, the micromirror array device can have high flexibility in motion with easy control.
  • FIG. 3B the fabrication of the actuation elements 32A, 32B, 32C, 32D, 32E with sacrificial layers 37 are illustrated. To build electrostatic force between the electrodes
  • the electrodes 31 A should have a different electric potential from the actuation elements 32 A, 32B, 32C, 32D, 32E or micromirror structure 33A.
  • the electrodes 31A, 31B are protected by passivation layer (not shown in the figure).
  • the passivation layer prevents the electrodes 3 IA, 3 IB from possible electric contact with other structures in the micromirror array device.
  • Passivation layer can be built with silicon oxide or low-stressed silicon nitride since they have high electrical resistance.
  • the actuation elements 32A, 32B, 32C, 32D, 32E are built with sacrificial layer 37.
  • the pillar structure 32A, 32B gives a rigid rotational or translational center to the micromirror structures 33A.
  • the flexible spring structure 32C connects the rigid bodies and the moving structures and also the restoration force to the system.
  • the top electrode 32D gives enhancement on the electrostatic force and on the structural stability.
  • micromirror structure 33A is connected by the post structure 32E. Since there should be space for the moving structures and elements 32A, 32B, 32C, 32D, 32E, 33A, the structure are fabricated with sacrificial layer 37, which will be removed after fabrication process before operating the device. [0094] Actuation elements 32A, 32B, 32C, 32D, 32E are followed by micromirror structure layer 33C including the micromirror structure 33A and the dummy structures 33B. The process for building the micromirror structure layer 33C is shown in FIG. 3C. Especially the micromirror structure 33A should be the base structure for the optical reflectivity. The structure can be planarized by applying Chemical Mechanical Polishing (CMP) process.
  • CMP Chemical Mechanical Polishing
  • the CMP process can be applied to the over-grown sacrificial layer 37 before depositing the micromirror structure layer 33C or can be applied to the micromirror structure layer 33C after depositing the micromirror structure layer 33C to have flat surface micromirrors for the reflection. While the CMP process, it is desirable to have the mechanical structures to be protected by other structure 33B from the external shock or force. To protect the micromirror structure 33A during the CMP process and other processes, the present invention introduces the dummy structures 33B in the optically non-effective area 39B. The dummy structures 33B are located in the optically non-effective area 39B and do not have actuation elements. The dummy structures 33B are rather fixed structures than structures with free moving.
  • the dummy structures 33B in the non-effective area 39B are fixed and protect the micromirrors in the effective area 39A from external perturbation.
  • the external perturbation can be occurred during fabrication of the micromirror array device and operation of the micromirror array device.
  • the micromirror array device in the present invention comprises optically noneffective area 39B which is other than the controlled micromirror area 39A. Since the structure 33B in the non-effective area 39B does not need actuation parts, the structure 33B of the non-effective area 39B is somewhat different from that 33A of effective area 39A.
  • the structure 33B in the optically non-effective area 39B mainly protects the micromirrors 33A in the effective area 39A.
  • the micromirrors 33A in the effective area 39A should be protected during the fabrication and the usage.
  • the dummy structures 33B protect the micromirrors 33A in the effective area 39A.
  • the dummy structures 33B encircle the effective area 39A and act as a buffer area of the device.
  • the dummy structures 33B are also fabricated with the micromirror structures 33A or elements 32C, 32D, 32E in the effective area 39A.
  • the micromirror structure 33A and the dummy structure 33B are not separated and the only difference between them is the presence of the actuation elements 32C, 32D, 32E. Since the dummy structures 33B do not need to move, the dummy structures 33B do not have movable actuation structure. The dummy structures 33B rather have the fixed rigid structures to have rigidity than movable structures. Also the structure 33B is not distinguished until the etching process of the micromirror gap 38 between the micromirror structures 33A and the dummy structures 33B. [0097] After depositing the micromirror structure layer 33C, the sub coating layer 34C is applied. The process is shown in FIG. 3D. Since the sub coating layer 34C can also be etched together with over coating layer 36C and the micromirror structure layer 33C, the layer 34C does not has any pattern until now, either.
  • the sub coating layer 34A encapsulate the metal layer 35 to prevent the metal layer 35 from oxidation and to prevent the micromirror structure 33A and the actuation elements 32B, 32C, 32D, 32E from galvanic corrosion with the over coating layer 36A.
  • the sub coating layer 34C is deposited on the micromirror structure layer 33C with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI2O3), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride (Si 3 N 4 ), titanium nitride (TiN), magnesium fluoride (MgF 2 ), zinc sulfide (ZnS), zinc selenide (ZnSe), polycarbonate, polyester, polyethylene naphthalate, and fluoropolymer.
  • the sub coating layer 34A prevents the metal layer 35 from electrical contacting with micromirror structure 33A. Since the galvanic corrosion can only occur if the dissimilar metals are in electrical contact.
  • the micromirror structure 33A and the metal layer 35 are the dissimilar metals for possible galvanic corrosion. If the dissimilar metals are insulated from each other by suitable plastic strips, washers or sleeves then galvanic corrosion cannot occur.
  • the sub coating layer 34A prevents the micromirror structure 33A and the actuation elements 32B, 32C, 32D, 32E from galvanic corrosion by electrically separating the micromirror structure 33A from the metal layer 35.
  • the sub coating layer 34A material should be highly electrically insulating and also consistent with the fabrication processes.
  • the thickness of the sub coating layer 34C, 34 A should be controlled to have between 20 nm and 500 nm preferably 100 nm.
  • the sub coating layer 34C, 34B is also used for providing anti-reflective coating for the dummy structures 33B in the optically non-effective area 39B.
  • the over coating layer 36B and the sub coating layer 34B are combined together since there is no metal layer.
  • the total thickness of the sub coating layer 34B and the over coating layer 36B can be controlled to have anti-reflective property in the non-effective area 39B.
  • the anti-reflective property should be obtained by controlling the sub coating layers 34C, 34B without providing extra layer structure.
  • the non-effective area 39B should not be optically active, the anti- reflective coating for the non-effective area 39B enhances the performance of the micromirror array device. Since the dummy structures 33B do not have metal layer, the structure 33B does not have high reflectivity. To enhance the optical performance, it is much better that the noneffective area 39B has as low reflectivity as possible. An anti-reflective coating for the non- effective area 39B is one solution.
  • the non-effective area 39B can have anti-reflective coating.
  • two layers of sub coating layer 34B and over coating layer 36B are applied to the dummy structures 33B.
  • the total thickness of the sub coating layer 34B and over coating layer 36B can be controlled to have anti-reflective coating properties.
  • FIG. 3E the process with the patterned metal layer 35 is presented.
  • the metal layer 35 is patterned with the mask of the micromirror shapes. Only on top of the movable and optically effective area 39A, the metal layer 35 is applied to have high reflectivity.
  • the well known lift-off process and evaporation or sputtering process with micro lithography can be applied to make the metal layer with micromirror patterning.
  • the metal layer 35 is made of material selected from the group consisting of silver (Ag), aluminum (Al), gold (Ag), nickel (Ni), chromium (Cr), and platinum (Pt) to have high reflectivity.
  • the thickness of the metal layer is controlled to have between 20 nm and
  • the thickness should be selected to have high reflectivity of the micromirrors.
  • the material of the metal layer 35 should be selected by considering the required reflectivity, operating wavelength, operating environment and others. Also since the metal layer 35 is easy to be attacked from acid or base or other environmental reasons, the metal layer 35 should be protected.
  • the sub coating layer 34A and the over coating layer 36A provide a strong protection for the metal layer 35 from oxidation, acid, base and galvanic corrosion. The over coating layer 36A and the sub coating layer 34A prevent the metal layer 35 from oxidation by encapsulating the metal layer 35.
  • the over coating layer 36A and the sub coating layer 34A protect the metal layer 35 from acid or base to maintain reflectivity of the micromirror by encapsulating the metal layer 35. Also the over coating layer 36A and the sub coating layer 34A reduces degradation of reflectivity of the micromirrors provided by the metal layer 35.
  • the over coating layer 36A and the sub coating layer 34A protect the metal layer 35 from etchants while removing sacrificial layers 37. Usually while removing sacrificial layers 37, a strong acid or base such as fluoric acid is applied to dissolve the sacrificial layer such as silicon oxide. The protection from a strong acid and a strong base is another purpose of the present invention.
  • Deposition of the over coating layer 36C is illustrated in FIG. 3F.
  • the over coating layer 36A provides a protection for metal layer 35 from the operating environments.
  • the thickness of the over coating layer 36A should be controlled to maximize reflectivity of the metal layer 35.
  • the maximized reflectivity enhances the optical performance of the micromirror array device.
  • the thickness of the over coating layer 36A is controlled to have between 20 nm and 500 nm preferably 100 nm. Since the over coating layer 36A is directly exposed to the operating environment, the thickness of the over coating layer 36A is more important than that of the sub coating layer 34 A, especially to maximize the reflectivity of the micromirrors.
  • the sub coating layer 34C is deposited on the micromirror structure layer 33C with material selected from the group consisting of silicon oxide (SiO 2 ), aluminum oxide (AI 2 O 3 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), cesium oxide (CeO 2 ), silicon nitride
  • FIG. 3G illustrates the etching process of the micromirror device.
  • the micromirror gap 38 between micromirrors 33A and the dummy structure 33B is etched.
  • the micromirror structure layer 33C now has its own separated structures for micromirrors 33A and dummy structures 33B.
  • the micromirror array device comprises optically non-effective area 39B which is other than the controlled micromirror area 39A. Now the effective area 39A and the non-effective area 39B can be differentiated. Since the structure 33B in the noneffective area 39B does not need actuation parts, the structure 33B of the non-effective area 39B is somewhat different from that 33A of effective area 39A.
  • the non-effective area 39B comprises a substrate 31C, at least one dummy structure 33B, a sub coating layer 34B, and an over coating layer 36B.
  • the sub coating layer 34B and the over coating layer 36B are fabricated together with the layers 34A, 36A in the micromirrors in the effective area 39A as one layer 34C and 36C.
  • the structures in non-effective area 39B protect the micromirror structures 33A in the effective area 39A.
  • the dummy structures 33B encircle the effective area 39A and act as a buffer area 39B of the device.
  • the dummy structures 33B are also fabricated with the micromirror structures 33A or elements 32C, 32D, 32E in the effective area 39A.
  • the non-effective area 39B should not be optically active.
  • the anti-reflective coating enhances the performance of the micromirror array device. Since the dummy structures 33B do not have metal layer 35, the structure 33B does not have high reflectivity.
  • the non-effective area 39B has as low reflectivity as possible.
  • An anti-reflective coating for the non-effective area 39B is one solution.
  • the non-effective area 39B can have anti-reflective coating.
  • two layers of sub coating layer 34B and over coating layer 36B are applied to the dummy structures 33B.
  • the total thickness of the sub coating layer 34B and over coating layer 36B can be controlled to have anti-reflective coating properties.
  • To provide anti-reflective coating for non-effective area 39B along with protection of the metal layer 35 is the one of main ideas and advantages of the present invention.
  • FIG. 3H the released structure of the micromirror array device without the sacrificial layer 37 is shown. Since there should be space for the moving structures and elements 32B, 32C, 32D, 32E, the structures for the micromirror array device are fabricated with sacrificial layer 37, which will be removed after fabrication process before operating the device. Usually while removing sacrificial layers 37, a strong acid or base such as fluoric acid is applied to dissolve the sacrificial layers 37 such as silicon oxide. After removing the sacrificial layers 37, the micromirror array device is ready for usage. [00110] In FIG.
  • the micromirror array device which has the same material for the sub coating layers 34A, 34B and the over coating layers 36A, 36B in the structure. Since the material of the sub coating layers 34A, 34B and the over coating layers 36A, 36B is the same.
  • the process for the micromirror array device can made simplified and compact.
  • the thickness of the over coating layers 36A, 36B should be determined by considering the optical reflectivity of the metal layer 35 in the effective area 39A.
  • the thickness of the sub coating layer 34 A, 34B should be determined by considering the anti-reflective property of the dummy structures 33B in the optically non-effective area 39B.
  • FIG. 4 shows how the light modulation of the micromirror array device and the anti-reflective coating in non-effective area work.
  • the incident light 41 comes from the left and incidents on the micromirrors 42 in the effective area and the dummy structures 43 in the non-effective area.
  • the modulated light 44 are modulated by the micromirror motion in the effective area.
  • the modulated light finally arrives onto the screen 46.
  • the light incident on the non-effective area are absorbed or reduced by the anti-reflective coating.
  • the reduced light 45 by the anti-reflective coating on the dummy structures in the non-effective area is aimed out of the screen.
  • the anti-reflective coating reduces the incident light and gives reduced light 45.
  • the shape of the micromirror can be varied with optical system.
  • the micromirror has a shape selected from the group consisting of fan, rectangular, square, hexagonal, triangular, and circular shapes. For an optical system with line symmetry, the micromirror with rectangular or square shape can be selected.
  • the hexagonal and triangular shape micromirror is also used for systems with the rotational symmetry, especially with sixfold rotational symmetry.
  • Circular micromirror can be used for systems with symmetry of revolution.
  • the selection of the micromirror shape is highly dependent on the optical system geometry and the device.
  • FIG. 5 shows a Micromirror Array Lens as an example of the micromirror array device.
  • the Micromirror Array Lens has a different geometry depending on applications.
  • the geometry of the example can be used as an automatic focusing system as an application of the Micromirror Array Lens.
  • the incident light 56 comes from the left and passes through an auxiliary lens 55.
  • the auxiliary lens 55 changes optical power of the system.
  • the Micromirror Array Lens 51 changes the focal length, optical axis and other focusing properties of the optical system to make images 54 onto the image sensor 53 by controlling each micromirror 52 in the Micromirror Array Lens 51 independently.
  • the Micromirror Array Lens 51 has line symmetry about the y-axis.
  • the coordinate configuration is shown in the figure. Since the system has line symmetry, the shape of the micromirror 52 can be determined by considering the line symmetry of the optical system. To have an automatic function, the control process of the Micromirror Array Lens 51 according to the image quality on the image sensor 53 should be added.
  • the shape of the micromirrors 52 can be varied with geometry of the
  • the micromirrors 52 in the effective area have a shape selected from the group consisting of fan, rectangular, square, hexagonal, and triangular shapes.
  • the micromirrors with rectangular or square shapes can be selected to have a proper geometry of the optical system.
  • the hexagonal and triangular shape micromirrors are also used for systems with the rotational symmetry, especially with six-fold rotational symmetry. Hexagonal micromirrors can be used for highly dense system. Again, the selection of the micromirror shapes is highly dependent on the optical system geometry and the devices.
  • FIG. 6 a Micromirror Array Lens 61 as an example of the micromirror array device is shown for the line symmetry system shown in FIG. 5.
  • the coordinate of the Micromirror Array Lens 61 is the same as the one in FIG. 5.
  • the non-effective area 65 has a plurality of dummy structures 63 to protect the micromirrors 62 in the effective area 64.
  • the Micromirror Array Lens 61 has also line symmetry about the y- axis.
  • the micromirrors 62 in the optically effective area 64 only make their own motion to build an optical surface profile.
  • the optical surface profile satisfies convergence and phase matching conditions for forming a lens.
  • Micromirror Array Lens should satisfy two conditions to form a good lens.
  • One is the convergence condition that every light should be converged into a focal point.
  • the other is the phase matching condition that the phase of the converged light should be the same.
  • the phase matching condition is that all the light passing through a lens should have the same optical path length to the focal point.
  • the Micromirror Array Lens arranged in a flat surface uses the periodicity of the light to satisfy the phase matching condition. Since the same phase condition occurs periodically, the phase matching condition can be satisfied even though the optical path length is different.
  • Each micromirror in the Micromirror Array Lens can be controlled independently to satisfy the phase matching condition and the convergence condition.
  • Micromirror Array Lens can build a lens with an optical surface profile.
  • An optical surface profile is the surface shape of the micromirror array which meets the lens conditions of convergence and phase matching.
  • Each micromirror in the effective area is independently controlled to form at least one optical surface profile.
  • the Micromirror Array Lens has a plurality of optical surface profiles to have a variable focusing property. By changing the optical surface profiles, the Micromirror Array Lens can change its focal length, optical axis, and other focusing properties.
  • the Micromirror Array Lens can be a variable focusing lens having lots of optical surface profiles. For having an automatic focusing function, the system can have pre-determined optical surface profiles according to the object distance. The different optical surface profiles are controlled with the signal from the image sensor. [00118] FIG.
  • the incident light 71 comes from the left and passes through an auxiliary lens 72.
  • the auxiliary lens 72 changes optical power of the system.
  • cube beam splitter 73 change the incident light 71 direction down to the Micromirror Array Lens 74.
  • the Micromirror Array Lens 74 changes the focusing properties of the optical system to make images 77 onto the image sensor 76 by controlling each micromirror 75 in the Micromirror Array Lens 74 independently.
  • the Micromirror Array Lens 74 has symmetry of revolution about the center of the Micromirror Array Lens 74.
  • the shape of the micromirror 75 can be determined by considering the symmetry of revolution of the optical system. With an optical geometry with symmetry of revolution such as shown in FIG 7, the micromirrors 75 with a fan shape can be used as a good candidate for effective unit micromirror for making a Micromirror Array Lenses 74.
  • the hexagonal and triangular shape micromirrors can also be used for system with rotational symmetry. Hexagonal micromirrors can be used for highly-dense system. Again the selection of the micromirror shape is highly dependent on the optical system geometry and the devices.
  • FIG. 8 another example of the Micromirror Array Lens 81 is shown for a system with symmetry of revolution shown in FIG. 7.
  • the optically effective area 84 in the center and also the optically non-effective area 85 can be found around the effective area 84.
  • the non-effective area 85 has two dummy structures 83 encircled the effective area 84 to protect the micromirrors 82 in the effective area 84.
  • the Micromirror Array Lens 81 has also symmetry of revolution about the center.
  • the micromirrors 82 with a fan shape are used for the Micromirror Array Lenses 81.

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
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  • Mechanical Light Control Or Optical Switches (AREA)

Abstract

La présente invention porte sur un dispositif à micromiroirs optiques et son dispositif matriciel et son procédé de fabrication. Grâce à l'introduction d'une couche de sous-revêtement et une couche de revêtement externe avec une couche de métal fortement réfléchissante, la couche réfléchissante des micromiroirs est protégée de l'environnement, d'une oxydation, d'une dégradation, des acides, des bases, et d'une corrosion galvanique des structures micromécaniques. De même la nouvelle structure d'enduction améliore les performances du dispositif matriciel à micromiroirs en réduisant la dégradation de la réflectivité de la couche de métal, en produisant un effet anti-reflet dans la zone non efficace optiquement, et en protégeant les structures micromécaniques.
PCT/US2007/079256 2006-09-22 2007-09-22 dispositif matriciel à micromiroirS comprenant une couche de métal réfléchissante encapsulée et son procédé de fabrication WO2008036959A2 (fr)

Applications Claiming Priority (4)

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US11/534,613 2006-09-22
US11/534,620 2006-09-22
US11/534,620 US7589885B2 (en) 2006-09-22 2006-09-22 Micromirror array device comprising encapsulated reflective metal layer and method of making the same
US11/534,613 US7589884B2 (en) 2006-09-22 2006-09-22 Micromirror array lens with encapsulation of reflective metal layer and method of making the same

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103137884A (zh) * 2011-11-25 2013-06-05 海洋王照明科技股份有限公司 一种有机电致发光器件的复合封装结构及其封装方法

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JP4300766B2 (ja) * 2002-08-01 2009-07-22 株式会社ニコン 立体構造素子およびその製造方法、光スイッチ、マイクロデバイス
US6891655B2 (en) * 2003-01-02 2005-05-10 Micronic Laser Systems Ab High energy, low energy density, radiation-resistant optics used with micro-electromechanical devices
US6903860B2 (en) * 2003-11-01 2005-06-07 Fusao Ishii Vacuum packaged micromirror arrays and methods of manufacturing the same
US7068416B2 (en) * 2004-04-12 2006-06-27 Angstrom Inc. Three-dimensional imaging device

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103137884A (zh) * 2011-11-25 2013-06-05 海洋王照明科技股份有限公司 一种有机电致发光器件的复合封装结构及其封装方法

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