DE102022005022A1 - MICROSCANNER WITH A DEFLECTION ELEMENT AND SPRING ELEMENTS CURVED TOWARDS THIS FOR VIBRATING SUSPENSION OF THE DEFLECTION ELEMENT - Google Patents

Abstract

A microscanner for projecting electromagnetic radiation onto an observation field has: a deflection element with a mirror surface designed as a micromirror for deflecting an incident electromagnetic beam; a support structure surrounding the deflection element at least in sections; and (iii) a spring device by means of which the deflection element is suspended on the support structure in such a way that it can oscillate in such a way that it can simultaneously carry out a first rotational oscillation about a first oscillation axis and a second rotational oscillation about a second oscillation axis orthogonal thereto relative to the latter in order to, by reflection, a to effect a Lissajous projection into an observation field during the simultaneous oscillations of the electromagnetic beam incident on the deflection element. The spring device has a plurality of spring elements arranged together in a ring shape around the deflection element, which are each anchored on the one hand at a first anchoring point on the support structure and on the other hand are anchored directly or indirectly at a second anchoring point on the deflection element. In between, they each have an arcuate course, at least in sections, which is curved in the direction of the deflection element. The course of the shape of each spring element is chosen so that its respective arc is given by a section of the course lying between two turning or end points delimiting it and a straight line running orthogonally to a connecting line through the two turning points and through a vertex of the arc runs through the geometric center or center of mass of the deflection element.

Description

The present invention relates to a microscanner for projecting electromagnetic radiation onto an observation field.

In the case of microscanners, which in technical language are also referred to as “MEMS scanners”, “MEMS mirrors” or “micro mirrors” or in English in particular as “microscanners” or “micro-scanning mirrors” or “MEMS mirrors”, These are micro-electro-mechanical systems (MEMS) or more precisely micro-opto-electro-mechanical systems (MOEMS) from the class of micromirror actuators for the dynamic modulation of electromagnetic radiation, in particular visible light. Depending on the design, the modulating movement can of an individual mirror in translation or rotation around at least one axis. In the first case, a phase-shifting effect is achieved, in the second case, the deflection of the incident electromagnetic radiation is achieved. In the following, microscanners are considered in which the modulating movement of an individual mirror is rotational. In microscanners The modulation, in contrast to mirror arrays, in which the modulation of incident light takes place via the interaction of several mirrors, is generated via a single mirror.

Microscanners can be used in particular to deflect electromagnetic radiation in order to modulate an incident electromagnetic beam with respect to its deflection direction by means of a deflection element (“mirror”). This can be used in particular to effect a Lissajous projection of the beam into an observation field or projection field. For example, imaging sensory tasks can be solved or display functionalities can be implemented. In addition, such microscanners can also be used to irradiate materials in an advantageous manner and thus process them. Possible other applications are in the area of lighting or illuminating certain open or closed rooms or areas of space with electromagnetic radiation, for example in the context of headlight applications.

In many cases, microscanners consist of a deflection element (mirror or mirror plate) that is suspended laterally on elastically deformable springs. A distinction is made between single-axis mirrors, which should preferably only be suspended about a single axis, from two-axis and multi-axis mirrors.

Both in the case of imaging sensors and in the case of a display function, a microscanner is used to deflect electromagnetic radiation such as a laser beam or a shaped beam from any other source of electromagnetic radiation at least one-dimensionally, for example horizontally and/or vertically, in order to achieve a To scan or illuminate the object surface at least in sections within an observation field. In particular, this can be done in such a way that the scanned laser beam sweeps over a rectangular area on a projection surface in the projection field. In these applications, microscanners with at least two-axis mirrors or single-axis mirrors connected in series in the optical path are used. The wavelength range of the radiation to be deflected can in principle be selected from the entire spectrum from short-wave UV radiation, through the VIS range, NIR range, IR range, FIR range to long-wave terrestrial and radar radiation.

Microscanners are often manufactured using semiconductor technology methods. Based on semiconductor wafer substrates, in particular silicon wafer substrates, layer deposition, photolithography and etching techniques serve to form microstructures in the substrate and thereby realize microscanners with movable MEMS mirrors, in particular as a chip. In addition to silicon, other semiconductor materials are also possible.

In many known cases, microscanner-based laser projection displays are so-called raster scan displays, in which a first beam deflection axis is operated at high frequency in resonance (typically 15 kHz to 30 kHz) (fast axis), the horizontal deflection and a second axis is operated quasi-statically (=non-resonantly) at low frequency (typically 30 Hz to 60 Hz) in order to generate the vertical deflection. A fixed grid-like line pattern (trajectory) is typically reproduced 30 to 60 times per second.

A different approach is used in the so-called Lissajous microscanners, especially in Lissajous scan displays. There, both axes are usually operated in resonance, ie by excitation with at least one resonance frequency of the mirror, thereby generating a scan path in the form of a Lissajous figure. In this way, large amplitudes can be achieved in both axes. The vertical deflection in particular can therefore be much larger than with a raster scanner. Accordingly, a Lissajous microscanner, especially a Lissajous scan display, can usually have a significantly higher optical resolution solution can be achieved than with a raster scan display, especially in the vertical direction.

From the EP 2 514 211 B1 a deflection device for a projection system for projecting Lissajous figures onto an observation field is known, which is designed to deflect a light beam about at least a first and a second deflection axis to generate the Lissajous figures.

DE 10 2011 104 556 A1 discloses a deflection device for a scanner with Lissajous scanning with a micromirror oscillating in at least two deflection axes, which has a frame and a mirror plate movably arranged via a suspension, and with a control device for generating control signals for a resonant operation of the micromirror in the at least two deflection axes. The suspension of the mirror plate has at least one spring, which is connected on the one hand to the mirror plate and on the other hand to the fixed frame. The frequencies of the control signals for the resonant operation of the micromirror in the at least two deflection axes are essentially the same, but differ at least by the predetermined sampling repetition rate. The level of the resonance frequencies of the deflection axes and thus the frequencies of the control signals are determined by a predetermined sampling resolution and a predetermined sampling repetition rate.

US 2020/386985 A1 discloses microelectromechanical systems (MEMS), in particular a mirror system that is used, for example, in LiDAR (Light Detection and Ranging). The MEMS mirror system of the invention uses four suspensions, each connected to a reflector body at two separate connection points that can be independently displaced by piezoelectric actuators. By actuating adjacent and opposing pairs of piezoelectric actuators, the reflector body can be excited to oscillate about two orthogonal axes.

US 2021/223539 A1 discloses a micromirror device. It includes: a mirror portion having a reflective surface that reflects incident light; a first actuator having an annular shape and disposed around the mirror portion; a second actuator having an annular shape and disposed around the first actuator; a first connection portion that connects the mirror portion and the first actuator on a first axis lying in a plane including the reflecting surface of the mirror portion in a stationary state and that rotatably supports the mirror portion about the first axis; a second connecting portion connecting the first actuator and the second actuator on a second axis lying in a plane including the reflecting surface of the mirror portion in a stationary state and orthogonal to the first axis, and rotating the first actuator about the second axis rotatable; a third connection portion connected to an outer periphery of the second actuator on the second axis; and a fixed portion connected to the third connection portion and supporting the second actuator through the third connection portion.

US 2019/068934 A1 discloses a MEMS device having a fixed structure, a movable structure, and deformable structures extending therebetween. The deformable structures have first ends anchored along the X and Y axes of the fixed structure and second ends anchored offset from the X and Y axes of the fixed structure. The deformable structures are shaped to curve from their anchor points along the movable structure back to the movable structure, extend along the perimeter of the movable structure, and then curve away from the movable structure and to their anchor points along the fixed structure. Each deformable structure has two piezoelectric elements extending along the length of that deformable structure, with one piezoelectric element having a greater length than the other piezoelectric element.

To drive a microscanner, i.e. the oscillations of its deflection element or mirror, electrostatic, electromagnetic, piezoelectric, thermal and other actuator principles are typically used. The mirror movement can in particular be quasi-static or resonant. The latter can be used in particular to achieve larger vibration amplitudes, larger deflections and higher optical resolutions. In addition, in resonant operation, energy consumption can generally be minimized or advantages can be achieved, particularly in terms of stability, robustness, production yield, etc. Scan frequencies from 0 Hz (quasi-static) to over 100 kHz (resonant) are typical.

However, various desirable properties of microscanners for biaxially resonant Lissajous operation are often difficult to reconcile. In particular, it is challenging to realize microscanners with mirror diameters between 0.5 mm and 30 mm, which on the one hand have large optical scanning angles (e.g. in the range of at least 20° to 90°) On the other hand, high scanning frequencies (eg between 2 kHz and 90 kHz) can be achieved and, for cost reasons, no longer require a MEMS chip edge length than approximately twice or three times the mirror diameter.

High-performance MEMS mirror chips often have edge lengths that are 4-10 times as large as the mirror diameter, which is not only expensive to produce but can also severely limit the possible applications, for example when it comes to installation in a mobile consumer end product is possible. The problem described increases in particular when not only a single-axis MEMS mirror, but a two- or multi-axis mirror is to be designed.

In order to achieve the large scanning angles despite the high scanning frequencies required, the MEMS designer is faced with the problem of having to create very long, wide springs to suspend the mirror so that it can oscillate and accommodate them on the MEMS chip. Very wide springs (e.g. with a width and thickness between 50µm and 1500µm and a length of 500µm to 10,000µm) are often required to bring the mirrors to high resonance frequencies and scanning frequencies despite large scanning angles and mirror diameters.

The goal of achieving high scanning frequencies, combined with the requirement to occupy as little chip area as possible, inevitably leads to the use of very stiff spring structures. However, particularly in areas in which the structure of the suspension has narrow radii, high mechanical stresses regularly arise during operation of the mirror due to the deformation of the suspension.

Another problem that occurs with mirrors that are intended to combine high scanning frequencies with a small size is mechanical crosstalk between the axes, especially with mirrors in which the mirror movement in both axes is caused by deformation of the same spring structure (“gimballless” design), since here the deflection of the mirror in one direction brings with it a preload on the suspension, which influences the movement of the mirror in the other axis (and vice versa).

The use of a rigid, solid gimbal known from the prior art (gimbal = gimbal suspension) can at least largely prevent this mechanical crosstalk, since it separates the suspensions of the two axes. However, the high mass of such a gimbal ensures that the scanning axis, which is created by the movement of the gimbal itself, can only achieve relatively low scanning frequencies.

It is an object of the invention to provide an improved microscanner which combines high scanning frequencies, large scanning angles, a small design and mechanically, at least largely, independent axes.

The solution to this problem is achieved in accordance with the teaching of the independent claim. Various embodiments and developments of the invention are the subject of the subclaims.

One aspect of the solution presented here concerns a microscanner for projecting electromagnetic radiation onto an observation field. The microscanner has: (i) a deflection element with a mirror surface designed as a micromirror for deflecting an incident electromagnetic beam; (ii) a support structure surrounding the deflection element at least in sections, which can in particular be frame-shaped and in particular can be made from a semiconductor substrate; and (iii) a spring device by means of which the deflection element is suspended on the support structure in such a way that it can oscillate in such a way that it can simultaneously carry out a first rotational oscillation about a first oscillation axis and a second rotational oscillation about a second oscillation axis orthogonal thereto relative to the latter in order to, by reflecting a to effect a Lissajous projection into an observation field during the simultaneous oscillations of the electromagnetic beam incident on the deflection element. The spring device has a plurality of spring elements arranged together in a ring shape around the deflection element, in particular four such spring elements. The spring elements are each anchored on the one hand at a first anchoring point on the support structure and on the other hand (i) indirectly, in particular via a torsion spring (hereinafter also referred to as “first” torsion spring), or (ii) anchored directly at a second anchoring point on the deflection element. In between (ie between the respective first anchoring point and the respective second anchoring point) they each have an at least partially arcuate course such that this arcuate course is curved towards the deflection element (i.e. is convex as seen from this), the course The shape of each spring element is chosen so that its respective arc is given by a section of the course lying between two turning or end points delimiting it and a straight line running orthogonally to a connecting line through the two turning points and through a vertex of the arc through the geometric central center or center of mass of the deflection element.

The term “deflection element”, as used here, is to be understood in particular as meaning a body that has a reflecting surface (mirror surface) that is smooth enough that reflected electromagnetic radiation, e.g. visible light, maintains its parallelism according to the law of reflection and thus a image can emerge. The roughness of the mirror surface must be smaller than approximately half the wavelength of the electromagnetic radiation. The deflection element can in particular be designed as a mirror plate with at least one mirror surface or have one. In particular, the mirror surface itself can consist of a different material, for example of a metal, in particular deposited, than the other body of the deflection element.

The term “oscillation axis” or, equivalently, “axis”, as used herein, is to be understood in particular as an axis of rotation (axis of rotation) of a rotary movement. It is a straight line that defines or describes a rotation or rotation.

The term “Lissajous projection” (and modifications thereof), as used herein, is understood to mean, in particular, a scanning of an observation field with the aid of electromagnetic radiation, which is caused by at least two mutually orthogonal harmonic oscillations (oscillations) of the radiation in a deflection device that deflects the observation field, in particular a single deflection element or a combination of at least two deflection elements.

The terms “comprises,” “includes,” “includes,” “has,” “has,” “with,” or any other variation thereof, as may be used herein, are intended to cover non-exclusive inclusion. For example, a method or device that includes or has a list of elements is not necessarily limited to those elements, but may include other elements that are not expressly listed or that are inherent to such method or device.

Furthermore, unless expressly stated to the contrary, “or” refers to an inclusive or and not an exclusive “or”. For example, a condition A or B is satisfied by one of the following conditions: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

The terms “a” or “an” as used herein are defined to mean “one or more”. The terms “another” and “another” as well as any other variant thereof are to be understood in the sense of “at least one further”.

The term “plurality,” as used herein where appropriate, is to be understood in the sense of “two or more.”

The term “configured” or “set up” to fulfill a specific function (and respective modifications thereof), as used here where appropriate, is to be understood as meaning that a relevant device or component thereof already exists in a configuration or setting , in which it can carry out the function or at least it can be set - i.e. configurable - in such a way that it can carry out the function after the appropriate setting. The configuration can be carried out, for example, by appropriately setting parameters of a process flow or switches or the like to activate or deactivate functionalities or settings. In particular, the device can have several predetermined configurations or operating modes, so that the configuration can be carried out by selecting one of these configurations or operating modes.

With a microscanner according to the solution, the axis-dependent mechanical stresses are separated into different areas of the spring device. This results in an, at least extensive, decoupling of the two oscillation axes in the sense that an interaction (“crosstalk”) between the two oscillation axes is reduced and largely eliminated. In this way, the advantages of a rigid gimbal can be achieved without having to use one. In particular, a particularly compact design of the suspension and thus of the microscanner as a whole can be achieved.

Due to the special arc shape of the spring devices, their masses are arranged particularly close to the oscillation axes, which means that a particularly low moment of inertia of the spring device with respect to the two oscillation axes can be achieved. This in turn promotes or enables high scanning frequencies and scanning angles for a given drive.

In addition, there are advantages in terms of the variability of the aforementioned microscanner design, in particular for the purpose of adapting to different intended frequency ratios (ie ratios of the resonance frequency of the first, ins special “faster” oscillation axis and the resonance frequency of the second, especially “slower”, oscillation axis. A specific desired frequency ratio can be achieved comparatively easily, depending on the desired use of the microscanner, by appropriately designing the design during the design phase of the microscanner. The configuration of the resonance frequencies of the two axes and thus the frequency ratio can be carried out in particular by adjusting lengths, curvatures of the arch shape, and/or stiffness of the spring elements, in particular by means of geometry adjustments.

In particular, exemplary embodiments of such microscanners are possible which, on the one hand, have large optical scanning angles in the range of at least 20° and, for example, up to 90°, and on the other hand, scanning frequencies between 2 kHz and 90 kHz can be achieved and, for cost reasons, do not require more (chip) edge length than about twice or three times the mirror diameter. This also opens up wide use in a wide variety of possible applications, for example when it comes to installing the microscanner in a mobile consumer end product, such as a smartphone, a portable computer or even a so-called “wearable” device ( e.g. “Smart Watch”).

Various exemplary embodiments of the microscanner are described below, each of which can be combined with one another in any way, unless this is expressly excluded or is technically impossible.

In some embodiments, the spring elements have the same shape with one another and their annular arrangement with respect to a geometric center of the deflection element has rotational symmetry. By means of such a symmetrical structure, the complexity of the design of the microscanner in its design, in particular with regard to the desired resonance frequencies of the oscillation axes and/or their frequency ratio or frequency difference, is simplified. In addition, particularly stable vibration behavior can be achieved with particularly good decoupling of the two vibration axes.

In some embodiments, two of the spring elements are mechanically connected to one another at a point that does not coincide with their first anchoring points (i) or (ii) formed together in one piece and from a coupling point lying between their first anchoring points, in particular in the middle between them, indirectly using a first torsion spring are anchored together on the deflection element. In case (i), the coupling point can in particular coincide with a connection point at which the two spring elements are mechanically connected to one another.

In this way, the direction and the resonance frequency of one of the oscillation axes could be essentially determined by the first torsion spring(s). Due to the design-related mass distribution of the torsion springs, which is close to the oscillation axis, particularly low moments of inertia and thus high resonance frequencies (and thus corresponding scan frequencies in resonant operation) and large scan angles with respect to this oscillation axis can be achieved. This oscillation axis can therefore be designed in particular as the faster of the two oscillation axes if their resonance frequencies differ.

In addition, when designing the microscanner, the moment of inertia of the oscillation axis determined by the first torsion springs, which can be designed in particular as the slow axis in the case of different resonance frequencies of the two oscillation axes, can be strongly influenced by a length adjustment and thus an adjustment of the resonance frequency of the oscillation axis towards a desired frequency ratio of both oscillation axes, more precisely of their resonance frequencies. The length of the first torsion springs can therefore largely be freely selected within the scope of the design. This option makes it possible to avoid unfavorable frequency conditions, which could, among other things, lead to mechanical crosstalk.

A high level of resistance to mechanical stress can also be achieved in this way, since the stress is well distributed along the respective course of the spring element, since smaller radii of curvature, especially at turning points of the curved course of the spring elements, can be avoided more easily than in the case of their direct anchoring on the deflection element.

In some embodiments, the arcuate course of at least one, in particular all, of the spring elements is circular or elliptical. This shape is particularly advantageous with regard to high resistance to mechanical stress, since the stress is well distributed along the respective course of the spring element, since smaller radii of curvature can be avoided. Also have Circular or elliptical curves when designing a microscanner design have the advantage that they are usually easier to simulate than more complex shapes.

In some of these embodiments, the arcuate course of the spring element spans an angle between 0° and 360°, in particular between 65° and 115°, relative to a center point of the circular arc or a focal point of the elliptical arc. For reasons of space, in particular angles in the range between 85° and 95° (approx. 90°) represent a practical size in which there is still sufficient spring length to accommodate even very large deflection angles of the deflection element and thus very large scanning angles, in particular up to 180 ° or even more.

In some embodiments, at least one of the spring elements, in particular all of them, has a variable strength along its arcuate course, in particular with regard to at least one spatial dimension (width and/or thickness), which is monotonous, in particular uniform, at least in the area of the arcuate course of the respective spring element ( i.e. linear) increases or decreases along the course.

In some embodiments (i) a plumb line on the mirror surface of the deflection element, when it is in its stable rest position relative to the support structure without vibration, defines a first direction and (ii) in the case of at least one of the spring elements, its maximum and/or or average thickness (“width”) in a plane orthogonal to the first direction greater than its maximum or average strength (“thickness”) along the first direction. In particular, the strength in a plane orthogonal to the first direction and/or the strength along the first direction can also be constant. These embodiments offer the advantage that process-related width-related tolerances when structuring wide springs are less relevant with regard to maintaining the desired spring properties than with narrower springs. The thickness of the spring elements can be determined in particular by a layer thickness or substrate thickness of a semiconductor body (e.g. wafer, for example with a thickness of 80 μm), from which the spring device and optionally also the deflection element and the support structure are formed by means of structuring, in particular by etching. In such etching processes, however, the side wall roughness of the structures produced by etching can often be influenced less easily than their surface roughness. In the case of spring elements whose thickness is less than their width, the mechanical stress that occurs in the spring elements during operation of the microscanner can be easily transferred to the smooth surface that can be controlled with regard to their exact shape, in particular surface roughness, whereby the breaking strength of the spring element(s) can be increased .

In some embodiments, two of the spring elements, whose second anchoring points (on the deflection element) do not coincide, have a common section in which the two spring elements are mechanically connected to one another or are formed in one piece together. This course section forms a (second) torsion spring, by means of which these two spring elements are suspended together on the support structure at at least one assigned first anchoring point. With regard to this second torsion spring(s), there is also the advantage that the resonance frequency of the associated oscillation axis can be easily adjusted within the scope of the microscanner design by choosing their length.

In some embodiments, the spring device is designed in such a way, in particular with regard to its geometry and/or its material, that the second oscillation axis is defined by the position of the second anchoring points on the deflection element, in particular coincides with or runs parallel to a connecting straight line through the second anchoring points, and has a higher resonance frequency (or equivalently: natural frequency) with respect to its rotary oscillation than the first oscillation axis orthogonal to it with respect to its rotary oscillation.

In particular, in some of these embodiments, the ratio of the higher to the lower resonance frequencies is not an integer, but differs by at most 10%, preferably at most 5%, from the ratio of the closest integer value. In such cases, a Lissajous trajectory results in the observation field, or on an object surface (e.g. screen) lying in the observation field transverse to the optical axis of the projection, which can fill or illuminate the image field in a very short time, especially in the context of a digital image can represent pixels of the image field. The time required for this is largely determined by the choice of resonance frequencies. The closest integer value can in particular be 1, 2, 3, 4 or 5.

In some embodiments, the microscanner further has a drive device for directly or indirectly driving the oscillations of the deflection element around the two Oscillation axes. In particular, electrostatic, piezoelectric, electromagnetic and thermal drives come into consideration as drives, which can be fully or partially provided and manufactured as part of MEMS production at wafer level. In addition, so-called external drives are also possible, which supply the component with vibration energy in the appropriate frequency range from an external non-MEMS actuator, such that the MEMS mirror begins to oscillate in one or both axes.

In particular, the drive device according to some of these embodiments can have at least one drive element with a piezo actuator, which is arranged on one of the spring elements in order to cause it to vibrate. This represents a particularly space-saving and, due to the direct coupling of the piezo actuator with the spring element, particularly effective and, in particular, energy-efficient option for implementing a drive device for the microscanner.

In some embodiments, the drive device is configured so that it can cause the deflection element to oscillate in a double-resonant manner with respect to the first and second oscillation axes. For this purpose, the actuator system can in particular have or consist of one or more actuators. This enables particularly low-energy operation of the microscanner as well as large scanning angles and, depending on the choice of resonance frequencies, also high scanning frequencies.

In some of these embodiments, the drive device is configured so that it can set the deflection element into a double resonant oscillation with respect to the first and second oscillation axes such that for the frequency ratio of the resonance frequency f ₁ with respect to the faster of the two oscillation axes to the resonance frequency f ₂ with respect to the slower one The following applies to both oscillation axes: f ₁ /f ₂ = F + v, where F is a natural number and the following applies to the detuning v: v = (f ₁ -f ₂ )/f ₂ with (f ₁ -f ₂ ) < 200 Hz , where v is not an integer. This results in a frequency ratio f ₁ /f ₂ close to 1, 2, 3, or 4, etc.

The detuning v can in particular be achieved in such a way that only one of the two oscillation frequencies or both differ or differ from the respective resonance frequency to the associated oscillation axis. The detuning v compared to an integer frequency ratio plays a major role, because this detuning of the frequency determines how quickly the Lissajous trajectory moves spatially. With an integer ratio, the detuning is zero and the trajectory is stationary and constantly reproduces itself in this form.

With a non-integer detuning v > 0, the trajectory begins to move, and within a certain interval the faster the greater the detuning v is compared to the integer ratio. The speed of progress at which the trajectory continues to move can advantageously be chosen so that a specific trajectory repetition rate (complete phase cycles/time), e.g. from the frequency range of 30 Hz to 100 Hz, is set with which the trajectory reproduces itself or under ideal conditions reproduced in undisturbed conditions. (For explanation: Exact reproduction is often not possible, especially when using phase-locked loops or other control loops. However, the advantages of a well-chosen detuning and an associated favorable rate of progression of the trajectory remain). On the basis of a detuning v selected in this way, an improved, i.e. increased line density, at least on average over time, can also be achieved.

In some embodiments, at least two of the following functional elements of the microscanner are at least partially made from the same plate-shaped substrate: the spring device, the deflection element, the support structure. In particular, the substrate can be a semiconductor substrate, such as a silicon substrate, from which at least two, preferably all, of the aforementioned functional elements are made. On the one hand, this has the advantage that the microscanner, or the functional elements mentioned thereof, can be produced within the scope of the same substrate processing, instead of being initially produced as separate components in separate processes and subsequently assembled to form microscanners. On the other hand, the production of the microscanner or the functional elements mentioned from a single substrate allows a particularly spatially or surface-efficient solution, since the manufacturing processes known from semiconductor or microsystem technology can be used here, in particular the targeted production of the smallest structures allow.

Further advantages, features and possible applications of the present solution result from the following detailed description in connection with the figures.

• 1 schematisch eine erste Ausführungsform eines zweiachsigen Mikroscanners mit einer Federeinrichtung mit vier Federelementen und zwei am Ablenkelement verankerten Torsionsfedern;
• 2 schematisch eine zweite Ausführungsform eines zweiachsigen Mikroscanners, mit einer Federeinrichtung mit vier Federelementen und zwei (weiteren) an der Tragestruktur verankerten Torsionsfedern;
• 3 schematisch eine dritte Ausführungsform eines zweiachsigen Mikroscanners, bei der die bogenförmigen Abschnitte der Federelemente jeweils einen spitzen Winkel kleiner 90°, insbesondere von 32°, einschließen; und
• 4 schematisch eine dritte Ausführungsform eines zweiachsigen Mikroscanners, bei der die bogenförmigen Abschnitte der Federelemente jeweils einen Winkel von mehr als 90°, insbesondere von 160°, einschließen.

This shows:

• 1 schematically a first embodiment of a two-axis microscanner with a spring device with four spring elements and two torsion springs anchored to the deflection element;
• 2 schematically a second embodiment of a two-axis microscanner, with a spring device with four spring elements and two (further) torsion springs anchored to the support structure;
• 3 schematically a third embodiment of a two-axis microscanner, in which the arcuate sections of the spring elements each enclose an acute angle of less than 90°, in particular of 32°; and
• 4 schematically a third embodiment of a two-axis microscanner, in which the arcuate sections of the spring elements each enclose an angle of more than 90°, in particular of 160°.

In the figures, the same reference numerals denote the same, similar or corresponding elements. Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are reproduced in such a way that their function and general purpose are understandable to those skilled in the art. Connections and couplings between functional units and elements shown in the figures can also be implemented as indirect connections or couplings, unless expressly stated otherwise. Functional units can in particular be implemented as hardware, software or a combination of hardware and software.

1 shows schematically a two-axis microscanner 10 according to a first embodiment of the present solution. The microscanner 10 is manufactured as a MEMS from a plate-shaped substrate, in particular a semiconductor substrate such as a silicon substrate, in particular by structuring the substrate, typically using lithography and etching processes.

The microscanner 10 has a deflection element 1 in the form of a mirror plate, which, by means of a spring device which has four spring elements 4 arranged in a ring shape around the deflection element, is attached to a frame-shaped, flat support structure 7 surrounding the deflection element 1 on all sides around two mutually orthogonal oscillation axes 8a and 8b is suspended so that it can oscillate. The spring elements 4 each have a course that is curved at least in sections towards the deflection element 1 and are each individually anchored with one of their ends at a respective first anchoring point 6 on the support structure 7. The arch shape can in particular be circular or elliptical.

The course of the shape of each spring element 4 is chosen so that its respective arc is given by a section of the course lying between two turning or end points delimiting it (whereby in the microscanner 10 each arc passes through an end point of the respective spring element 4 at its anchoring point 6 on the chip frame and by a turning point on the other side of the arc), and a straight line 4c running orthogonally to a connecting line 4a through the two turning points and through the apex 4b of the arc (or a perpendicular projection thereof onto that defined by the chip frame 7 Plane) runs through the deflection element 1, in particular through its geometric center or its center of mass.

The width of the spring elements (in the plane defined by the chip frame 7), in particular the width of their arcuate sections, can in particular be chosen to be larger than their thickness (measured orthogonally to the plane defined by the chip frame 7). Overall, the ring-shaped arrangement of the spring elements 4 has a rotational symmetry with respect to a geometric center of the (here, for example, circular) deflection element 1, specifically a four-fold symmetry.

The support structure 7, which can also be referred to as a chip frame, has a high level of rigidity, so that when the deflection element 1 vibrates, it essentially acts as a rigid structure for anchoring the spring device. In particular, it can have a rectangular shape. In particular in the case of rotationally symmetrical (e.g. four-fold rotational symmetry) it can, as in 1 shown to be specifically square.

Each of the spring elements 4 is connected at its other end to an associated second spring element 4 at a coupling point 9, so that the microscanner 10 has a total of two separate spring structures, each having two spring elements 4 (in 1 The two spring elements to the left of the axis 8a together form a first spring structure and the two spring elements to the right of the axis 8a form a second spring structure). The suspension of the deflection element 1 is achieved in each of the two spring structures by means of a respective torsion spring 3, which extends between the respective coupling point 9 and the deflection element 1, to which it is anchored at a respective second anchoring point 2. The respective two spring elements 4 and the respective torsion spring 9 of each of the spring structures can in particular which can also be designed integrally, ie in one piece. This can be caused in particular by appropriate structuring of a common substrate from which the microscanner 10 is made. In addition, the deflection element 1 and/or the support structure 7 can also be designed integrally with the spring structures, in particular in such a way that the in 1 The structure of the microscanner 10 shown is in one piece overall.

On the one hand, the deflection element 1 can oscillate rotationally about a first oscillation axis 8a, whereby in addition to the deflection element 1, the two spring structures and the two torsion springs 3 are deflected relative to the plane defined by the chip frame 7. The spring force for this first oscillation is caused primarily by a deformation of the spring elements 4, in particular of their sections close to the frame.

On the other hand, the deflection element 1 can also oscillate rotationally about the second oscillation axis 8b, with the deflection element 1 in particular being deflected relative to the plane defined by the chip frame 7 and, in particular, the two torsion springs 9 and the adjoining sections of the spring elements 4 being for this second Provide the spring force required for oscillation. The microscanner 10 can in particular be designed so that the oscillation axis 8a is slower than the oscillation axis 8b, i.e. that it has a lower resonance frequency compared to the latter. The design of the microscanner 10 favors such an assignment of fast and slow axes, in particular in that the torsion springs 9, which oscillate significantly next to the deflection element 1, lie essentially on or very close to the oscillation axis 8b and therefore have a very low moment of inertia. In contrast, when oscillating about the oscillation axis 8a, the entire spring structures oscillate, some of which are located relatively far away from the oscillation axis 8a and thus have a larger moment of inertia with respect to this axis 8a. However, in order to enable high oscillation frequencies and thus scanning frequencies even with this slower oscillation axis, the spring elements 4 have the above-mentioned arcuate sections which are curved towards the deflection element 1. This ensures that as much of the mass as possible of the spring elements 4 is displaced in the direction of the oscillation axis 8a and the moment of inertia is therefore reduced overall.

The spring device, i.e. H. The suspension of the deflection element 1 provided by the two spring structures acts like a gimbal (gimbal suspension), in that the mechanical crosstalk between the two vibrations is minimized by separating the axis-dependent mechanical stresses so that they occur, at least largely, in different sections of the spring elements 4 or vibration axes 8A and 8b, is achieved. This type of suspension of the deflection element 1 with extensive decoupling of the axes acts as a spring and therefore differs fundamentally from known suspensions using a, in particular rigid, gimbal.

In a possible variant of the microscanner 10, the spring elements 7 are each anchored individually to the deflection element 1. Instead of a single torsion spring 9 per spring structure, the ones anchored directly on the deflection element 1 form 1 Sections 3a of the spring elements 4 shown in dashed lines each have a torsion spring. This variant can in particular also be based on the embodiments shown below 2 until 4 be applied.

To drive it, the microscanner 10 can in particular have one or more piezo elements (not shown in the figures for the sake of clarity). In particular, they can be arranged on one or more, in particular all, of the spring elements 4 in order to specifically deform them when activated accordingly and thus to provide them with energy to drive the oscillations. In order to achieve the smallest possible effect on the moment of inertia of the spring elements 4 with respect to the oscillation axes, the piezo elements can be arranged in particular on the arcuate sections of the spring elements 4 where they are closest to the center, center of mass or edge of the deflection element 1, i.e. in In the case of a circular deflection element 1, where the arcuate section comes closest to the deflection element 1 (see tip of the arrow for reference number 4).

The type of suspension described results in two mutually perpendicular oscillation axes 8a and 8b, about which the deflection element 1 can oscillate resonantly in both axes. This operating mode can be particularly advantageous in laser projection displays and imaging sensors such as 3D cameras, LIDAR sensors (LIDAR = Light imaging, detection and ranging), OCT devices (OCT = optical coherence tomography), etc .as well as in laser material processing.

2 shows schematically a two-axis microscanner 20 according to a second embodiment of the present solution. The microscanner 20 largely corresponds to the microscanner 10, so that only the relevant sub-sections will be discussed below Differences are entered into and otherwise that too 1 or to the microscanner 10 What was said also applies to the microscanner 20. The same also applies with regard to the 3 and 4 .

A significant difference between embodiments 10 and 20 is that in the microscanner 20 on each relevant side of the chip frame 7 (in 2 i.e. top and bottom) the spring structures or their spring elements 4 are no longer individually, but jointly anchored via a common spring section 5, which forms a (second) torsion spring, to the chip frame 7 at a respective (first) anchoring point. How out 2 can be seen, here are the two in the 2 The upper ends of the two spring structures, ie the two spring elements 4 lying above the oscillation axis 8b, are connected to one another in the section 5 forming a (second) torsion spring or are designed integrally and are anchored together on the chip frame 7. The same applies to the two spring elements 4 located below the oscillation axis 8b.

With this embodiment 20, a further minimization of the mechanical stress in the spring elements 4 and consequently an increased robustness and service life of the microscanner can be promoted. The risk that the microscanner, in particular its delicate spring elements 4, comes close to its breaking limit when operating at high frequencies and/or large deflections can thus be effectively countered. Looking at it the other way around, it allows. Such a design of a microscanner makes the spring structures correspondingly more delicate and therefore with less mass, which in turn is advantageous with regard to high operating frequencies and large deflection angles.

With such a design, the spring characteristics of the torsion springs 5 can also be assumed to be linear over a wide range, which makes it easier to control the microscanner for its operation, since less complex controls can be used.

Another change to the design of the microscanner 10 1 can optionally consist of adapting the shape of the support structure or the chip frame seven of FIG. 7, in particular choosing a rectangular shape that deviates from a square. This is particularly advantageous with regard to a suitable choice of the length of the second torsion spring 5 with a view to tuning the resonance frequency, in particular the oscillation axis 8a.

3 schematically illustrates a two-axis microscanner 30 according to a third embodiment of the present solution, which is a special design of the microscanner 10 1 corresponds, but also to the microscanner 20 2 is applicable.

It is characterized in particular by the fact that the arcuate sections of the spring elements 4 each enclose an acute angle Φ <90°, in particular of 32°, for example. Such variants are characterized in particular by the fact that strong curvatures can be largely avoided in the course of the spring elements 4, which is advantageous with regard to a high breaking point and thus a high level of robustness and service life.

4 schematically illustrates a two-axis microscanner 40 according to yet another, fourth embodiment of the present solution, which in turn is based on a special design of the microscanner 10 1 corresponds, but also to the microscanner 20 2 is applicable.

It is characterized in particular by the fact that the arcuate sections of the spring elements 4 each enclose an obtuse angle Φ > 90°, in particular 160°, for example. Such variants are characterized in particular by the fact that the strongly pronounced arcuate shape of the spring elements 4 promotes a mass distribution in which the mass of the spring elements lies particularly close to the oscillation axis 8a. Consequently, high resonance frequencies with respect to this oscillation axis can be achieved particularly well here.

For reasons of space, angles Φ in the range from 85° to 95°, in particular Φ ≈ 90°, represent an appropriate size in which there is still sufficient spring length to enable large deflection angles.

Unless otherwise stated, the following explanations are independent of a specific embodiment of a microscanner according to the solution and therefore apply in particular to all embodiments 10 to 40 from the 1 until 4 and their mentioned variants are applicable, which will continue to be referred to below for the purpose of explanation.

Microscanners with two fast axes, in which the resonance frequency f ₁ for the faster one of the axes and f ₂ for the slower one of the axes almost but not exactly form an integer ratio to one another, are particularly advantageous, especially for Lissajous operation with two axes the. So: f ₁ /f ₂ = 1, 2, 3, 4, 5 etc., because then a Lissajous trajectory always occurs, which advantageously efficiently fills the image field in a very short time that can be set by choosing the resonance frequencies themselves can.

A microscanner according to the solution can be easily adapted to different frequency ratios during its design. For example, for a specific frequency ratio, you can set a difference frequency of the two oscillation axes 8a and 8b so that this difference corresponds to the desired image repetition rate, regardless of the integer ratio. For example, for a frequency ratio f ₁ /f ₂ ≈ 2, the slower first axis 8a can be tuned to 10 kHz and the faster second axis 8b to 20.2 kHz in order to realize a refresh rate of 200 Hz. Likewise, for example, a frequency ratio f ₁ /f ₂ ≈ 3 could be realized by tuning the axes to f ₁ = 5 kHz and f ₂ = 15.2 kHz. For a frequency ratio f ₁ /f ₂ ≈ 4, for example, the axes would be designed for f ₁ = 5 kHz and f ₂ = 20.2 kHz (etc.).

• - die Länge der (ersten) Torsionsfedern 3 (bzw. 3a) am Ablenkelement 1 und damit das Trägheitsmoment, welches auf die dazu quer stehende Achse 8a wirkt, angepasst wird.
• - die Breite der (ersten) Torsionsfedern 3 (bzw. 3a) am Ablenkelement 1 und damit deren Steifigkeit angepasst wird (dasselbe gilt gegebenenfalls für die zweite Torsionsfeder 5 zur Aufhängung an der Tragestruktur 7).
• - die Breite der Federelemente 4, insbesondere von deren bogenförmigen Abschnitten, und damit deren Steifigkeit variiert wird.
• - die Dicke und damit die Steifigkeit der Federelemente 4 variiert wird.
• - gegebenenfalls die Geometrie einer Stützstruktur auf der der Spiegelfläche gegenüberliegenden Seite des Ablenkelements 1 und damit dessen Trägheitsmoment angepasst wird.

The setting of the resonance frequencies to the two oscillation axes 8a and 8b, in particular their ratio and, if necessary, detuning compared to an integer ratio, can be achieved in particular by (if available for the respective microscanner design):

• - the length of the (first) torsion springs 3 (or 3a) on the deflection element 1 and thus the moment of inertia, which acts on the axis 8a located transversely thereto, is adjusted.
• - the width of the (first) torsion springs 3 (or 3a) on the deflection element 1 and thus their stiffness is adjusted (the same applies if necessary to the second torsion spring 5 for suspension on the support structure 7).
• - The width of the spring elements 4, in particular of their arcuate sections, and thus their rigidity is varied.
• - the thickness and thus the rigidity of the spring elements 4 is varied.
• - If necessary, the geometry of a support structure on the side of the deflection element 1 opposite the mirror surface and thus its moment of inertia is adjusted.

Electrostatic, piezoelectric, electromagnetic and thermal drives come into consideration as drives for the microscanners, which are already fully or partially planned and manufactured as part of MEMS production at wafer level. In addition, so-called external drives are also possible, which supply the microscanner with vibration energy in the appropriate frequency range from an external non-MEMS actuator, such that the deflection element 1 begins to oscillate in one or both oscillation axes 8a and 8b. As already mentioned, piezoelectric actuators can be arranged particularly advantageously on the spring elements themselves, where they can stimulate the vibration of the deflection element 1 in a particularly (energy) efficient manner.

While at least one exemplary embodiment has been described above, it should be noted that a large number of variations exist. It should also be noted that the exemplary embodiments described are only non-limiting examples and are not intended to limit the scope, applicability, or configuration of the devices and methods described herein. Rather, the foregoing description will provide guidance to those skilled in the art for implementing at least one exemplary embodiment, with the understanding that various changes in the operation and arrangement of the elements described in an exemplary embodiment may be made without departing from that set forth in the appended claims the specified subject matter and its legal equivalents are deviated from.

REFERENCE SYMBOL LIST

1

Deflection element, especially mirror plate

2

second anchor point, on mirror plate

3

(first) torsion spring, anchored to mirror plate

3a

Section of a spring element 4 anchored directly from the deflection element

4

Spring element with an arcuate section

4a

Straight through the turning or end points delimiting the arch

4b

Vertex of the arc

4c

Straight through the vertex 4b and orthogonal to straight line 4a

5

(second) torsion spring, anchored to the support structure (chip frame).

6

first anchoring point(s), on the support structure (chip frame)

7

Support structure, especially rigid chip frame

8a

first (especially slower) axis of oscillation

8b

second (especially faster) axis of oscillation

9

Crosspoint

10

first embodiment of a two-axis microscanner

20

second embodiment of a two-axis microscanner

30

Third embodiment of a two-axis microscanner

40

fourth embodiment of a two-axis microscanner

Φ

Angle spanned by an arcuate section of a spring element

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2514211 B1 [0009]
• DE 102011104556 A1 [0010]
• US 2020386985 A1 [0011]
• US 2021223539 A1 [0012]
• US 2019068934 A1 [0013]

Claims (16)

Microscanner (10; 20; 30; 40) for projecting electromagnetic radiation onto an observation field, the microscanner (10; 20; 30; 40) having: a deflection element (1) with a mirror surface designed as a micromirror for deflecting an incident electromagnetic beam; a support structure (7) surrounding the deflection element (1) at least in sections; and a spring device by means of which the deflection element (1) is suspended from the support structure (7) so that it can oscillate in such a way that, relative to it, there is simultaneously a first rotational oscillation about a first oscillation axis (8a) and a second rotational oscillation about a second oscillation axis (8b) orthogonal thereto ) can be carried out in order to effect a Lissajous projection into an observation field by reflecting an electromagnetic beam incident on the deflection element (1) during the simultaneous oscillations; wherein the spring device has a plurality of spring elements arranged together in a ring shape around the deflection element (1), each of which is anchored on the one hand at a first anchoring point (6) on the support structure (7) and on the other hand directly or indirectly at a second anchoring point (2). are anchored to the deflection element (1) and in between have an at least partially arcuate course such that this arcuate course is curved towards the deflection element (1); and wherein the course of the shape of each spring element (4) is selected so that its respective arc is defined by a turning or Section of the course lying at the end points is given and a straight line (4c) running orthogonally to a connecting line (4a) through the two turning points and through a vertex (4b) of the arc runs through the geometric center or center of mass of the deflection element (1). Microscanner (10; 20; 30; 40) after Claim 1 , wherein the spring elements (4) have the same shape among themselves and their ring-shaped arrangement has rotational symmetry with respect to a geometric center of the deflection element (1). Microscanner (10; 20; 30; 40) according to one of the preceding claims, wherein two of the spring elements (4) are mechanically connected to one another at a point that does not coincide with their first anchoring points (6) or are formed in one piece and by one between their first Anchoring points (6) lying coupling point are indirectly anchored together on the deflection element (1) using a first torsion spring (3). Microscanner (10; 20; 30; 40) according to one of the preceding claims, wherein the arcuate course of at least one of the spring elements (4) is in the shape of a circular arc or an elliptical arc. Microscanner (10; 20; 30; 40) after Claim 4 , wherein the arcuate course of the spring element (4) spans an angle between 0° and 360° relative to a center of the circular arc or a focal point of the elliptical arc. Microscanner (10; 20; 30; 40) according to one of the preceding claims, wherein at least one of the spring elements (4) each has a variable strength along its arcuate course, which is monotonically along the at least in the area of the arcuate course of the respective spring element (4). increases or decreases over time. Microscanner (10; 20; 30; 40) according to one of the preceding claims, wherein: a plumb line on the mirror surface of the deflection element (1), when it is in its stable rest position relative to the support structure (7) without vibration, defines a first direction; and in at least one of the spring elements (4) whose maximum and/or average strength determined along its arcuate course in a plane orthogonal to the first direction is greater than its maximum or average strength along the first direction. Microscanner (20) according to one of the preceding claims, wherein two of the spring elements, whose second anchoring points (2) do not coincide, have a common section in which the two spring elements (4) are mechanically connected to one another or formed in one piece, this section forms a second torsion spring (5), by means of which these two spring elements (4) are suspended together on the support structure (7) at at least one assigned first anchoring point (6). Microscanner (10; 20; 30; 40) according to one of the preceding claims, wherein the spring device is designed such that the second axis of oscillation (8b) is defined by the position of the second anchoring points (2) on the deflection element (1), and has a higher resonance frequency with respect to its rotary oscillation than the orthogonal first oscillation axis (8a) with respect to its rotary oscillation. Microscanner (10; 20; 30; 40) after Claim 9 , whereby the ratio of the higher to the lower of the resonance frequencies is not an integer but deviates by a maximum of 10%, preferably a maximum of 5%, from the ratio of the closest integer value. Microscanner (10; 20; 30; 40) after Claim 10 , where the nearest integer value is 1, 2, 3, 4 or 5. Microscanner (10; 20; 30; 40) according to one of the preceding claims, further comprising a drive device for directly or indirectly driving the oscillations of the deflection element (1) about the two oscillation axes. Microscanner (10; 20; 30; 40) after Claim 12 , wherein the drive device has at least one drive element with a piezo actuator which is arranged on one of the spring elements (4) in order to cause it to vibrate. Microscanner (10; 20; 30; 40) after Claim 12 or 13 , wherein the drive device is configured so that it can set the deflection element (1) into a double-resonant oscillation with respect to the first and second oscillation axes. Microscanner (10; 20; 30; 40) after Claim 14 , wherein the drive device is configured so that it can set the deflection element (1) into a double-resonant oscillation with respect to the first and second oscillation axes such that for the frequency ratio of the resonance frequency f ₁ with respect to the faster of the two oscillation axes to the resonance frequency f ₂ with respect to the slower one of the two oscillation axes: f ₁ /f ₂ = F + v, where F is a natural number and for the detuning v the following applies: v = (f ₁ -f ₂ )/f ₂ with (f ₁ -f ₂ ) < 200 Hz, where v is not an integer. Microscanner (10; 20; 30; 40) according to one of the preceding claims, wherein at least two of the following functional elements of the microscanner are at least partially made from the same plate-shaped substrate: the spring device, the deflection element, the support structure (7).

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