JP7651230B2 - Laminated structure, electronic device, electronic equipment and system - Google Patents

Description

The present invention relates to piezoelectric bodies, laminated structures, electronic devices, electronic equipment and methods for manufacturing these.

Thin films made of lead zirconate titanate (Pb(Zr,Ti) _O3 ) (hereinafter also referred to as PZT), which has excellent piezoelectric and ferroelectric properties, are used in memory elements such as non-volatile memories (FeRAM), as well as in MEMS (Micro Electro Mechanical Systems) technology such as inkjet heads and acceleration sensors, taking advantage of their ferroelectric properties.

In recent years, it has been considered to form a piezoelectric film having good piezoelectric properties on a Pt film by forming a Pt film oriented in (200) on a Si substrate oriented in (100) via a ZrO ₂ film oriented in (200) or the like (Patent Document 1). However, the adhesion and crystallinity at the interface are still not satisfactory, and there are problems such as relatively many defects, imprinting, and easy loss of polarization when voltage is applied, and excellent hysteresis characteristics cannot be obtained. Therefore, for example, the center of hysteresis of the polarization amount against the applied voltage is shifted to the positive applied voltage side, and the remanent polarization Pr ⁺ at the applied voltage of 0 V is high in reliability such as 20 μC/cm ² or more, and excellent hysteresis characteristics can be obtained, and measures to further improve the piezoelectric properties of the piezoelectric film have been awaited.

JP 2015-154015 A

The present invention aims to provide a piezoelectric material having excellent hysteresis characteristics, a laminated structure containing the piezoelectric material, an electronic device, an electronic instrument, and a manufacturing method for obtaining these in an industrially advantageous manner.

As a result of intensive research to achieve the above-mentioned object, the present inventors have found that, by forming at least a compound film on a crystal substrate, then laminating an epitaxial film containing a crystalline compound, and then laminating a single crystal film made of a conductive metal on the epitaxial film, either directly or via another layer, and then laminating a piezoelectric film on the single crystal film, either directly or via another layer, the epitaxial film is formed by using a compound element in the compound film and the piezoelectric film is laminated by vapor deposition or sputtering, a piezoelectric body in which the center of hysteresis of the polarization amount with respect to an applied voltage has shifted to an applied voltage range of 100 to 300 V can be easily obtained, and the obtained piezoelectric body has excellent hysteresis characteristics without problems such as imprinting, and have found that such a piezoelectric body and a manufacturing method thereof can solve the above-mentioned conventional problems in one fell swoop.
After obtaining the above findings, the present inventors conducted further studies and completed the present invention.

That is, the present invention relates to the following inventions.
[1] A piezoelectric body, characterized in that the center of hysteresis of the amount of polarization with respect to an applied voltage is shifted toward a positive applied voltage, and the remanent polarization Pr ⁺ at an applied voltage of 0 V is 20 μC/ ^cm2 or more.
[2] The piezoelectric body according to [1], wherein the center of hysteresis of the amount of polarization with respect to the applied voltage is shifted to a range of applied voltage of 100 to 300 V.
[3] The piezoelectric body according to [1] or [2], wherein the remanent polarization Pr ⁺ at an applied voltage of 0 V is 75 μC/ ^cm2 or more.
[4] The piezoelectric body according to any one of [1] to [3], wherein the remanent polarizations Pr ⁺ and ^Pr- at an applied voltage of 0 V have approximately the same absolute value.
[5] The piezoelectric body according to any one of [1] to [4] above, which is a PZT-based piezoelectric body.
[6] A method for manufacturing a laminated structure, comprising forming at least a compound film on a crystal substrate, laminating an epitaxial film containing a crystalline compound, laminating a single crystal film made of a conductive metal on the epitaxial film directly or via another layer, and then laminating a piezoelectric film on the single crystal film directly or via another layer, wherein the epitaxial film is formed by using a compound element in the compound film, and the piezoelectric film is laminated by sputtering.
[7] The manufacturing method according to [6], further comprising the steps of: using the compound element in the compound film; introducing a compound element gas; and depositing the epitaxial film in the presence of the compound element gas.
[8] A laminated structure including at least a crystal substrate, an epitaxial film containing a crystalline compound, an electrode, and a piezoelectric body, the piezoelectric body being the piezoelectric body according to any one of [1] to [5] above, and the epitaxial film being formed by incorporating a compound element in a compound film laminated on the crystal substrate into the crystalline compound.
[9] The laminated structure according to [8], wherein the epitaxial film constitutes a part or the whole of a buffer layer and is a substrate for crystal growth.
[10] A piezoelectric element including a laminated structure, characterized in that the laminated structure is the laminated structure according to [8] or [9] above.
[11] A method for manufacturing a piezoelectric element using a laminated structure, characterized in that the laminated structure is the laminated structure according to [8] or [9] above.
[12] An electronic device including a laminated structure, the laminated structure being the laminated structure according to [8] or [9].
[13] The electronic device according to [12] above, which is a piezoelectric device.
[14] A method for producing an electronic device using a laminated structure, wherein the laminated structure is the laminated structure according to [8] or [9].
[15] An electronic device including an electronic device, the electronic device being the electronic device according to [13] or [14].
[16] A method for manufacturing an electronic device using a laminated structure or an electronic device, the laminated structure being the laminated structure described in [8] or [9] above, and the electronic device being the electronic device described in [13] or [14] above.
[17] A system including an electronic device, the electronic device being the electronic device described in [15] above.
[18] The laminate structure according to [8], further comprising: an amorphous thin film containing a constituent metal of the epitaxial film and/or the crystal substrate and/or one or more embedded layers containing the constituent metal embedded in a portion of the crystal substrate, between the crystal substrate and the epitaxial film.
[19] The laminate structure according to [18], further comprising an amorphous thin film between the crystal substrate and the epitaxial film, the amorphous thin film containing a constituent metal of the epitaxial film, and/or one or more buried layers embedded in a portion of the crystal substrate and containing a constituent metal of the epitaxial film.
[20] The laminate structure according to [18], further comprising: an amorphous thin film between the crystal substrate and the epitaxial film, the amorphous thin film containing a constituent metal of the epitaxial film and/or the crystal substrate; and one or more buried layers embedded in a portion of the crystal substrate and containing the constituent metal.
[21] The laminate structure according to any one of [18] to [20], wherein the constituent metal comprises Hf.
[22] The laminate structure according to any one of [18] to [21], wherein the amorphous thin film has a thickness of 1 nm to 10 nm.
[23] The laminated structure according to any one of [18] to [22], wherein the embedded layer has a cross-sectional shape of a substantially inverted triangle.
[24] An electronic device, an electronic equipment, or a system including a laminate structure, the laminate structure being characterized in that the laminate structure is the laminate structure according to any one of [18] to [23] above.

The laminated structure, electronic device, and electronic equipment of the present invention contain a piezoelectric material having excellent hysteresis characteristics, and the manufacturing method of the present invention has the effect of enabling the piezoelectric material, the laminated structure, the electronic device, and the electronic equipment to be obtained in an industrially advantageous manner.

FIG. 1 is a diagram showing a schematic diagram of an example of a preferred embodiment of a precursor of a laminated structure of the present invention. FIG. 2 is a diagram showing a schematic diagram of another preferred embodiment of the laminated structure of the present invention. 1A to 1C are diagrams illustrating an example of an oxide film forming step in a preferred method for producing a laminated structure of the present invention. 1A to 1C are diagrams illustrating an example of an epitaxial film formation step in a preferred method for producing a laminated structure of the present invention. 1 shows cross-sectional STEM images observed in examples. 1 shows cross-sectional STEM images observed in examples. 1 shows STEM images observed in the examples. 1 shows STEM images observed in the examples. 1A and 1B are diagrams illustrating a preferred embodiment of a MEMS transducer according to the present invention. FIG. 1 is a schematic diagram showing an example of a cross-sectional view of a portion of a wafer provided with a piezoelectric actuator, as a suitable application example of the present invention to a fluid discharge device. 1 is a diagram showing hysteresis curves measured in the examples, with the vertical axis showing remanent polarization and the horizontal axis showing applied voltage. FIG. 2 is a diagram showing the results of XPS measurement in an example. FIG. 2 is a diagram showing the results of XPS measurement in an example. FIG. 2 is a schematic diagram showing a film forming apparatus preferably used in the examples. 1 shows a cross-sectional STEM image measured in an example. 1 shows an STEM image measured in an example. 1 shows an STEM image of a buried layer measured in an example.

The piezoelectric body of the present invention is characterized in that the center of hysteresis of the polarization amount with respect to the applied voltage is shifted to the positive applied voltage side, and the remnant polarization Pr ⁺ at the applied voltage of 0V is 20 μC/ ^cm2 or more. In the present invention, it is preferable that the center of hysteresis of the polarization amount with respect to the applied voltage is shifted to the range of applied voltage of 100 to 300V, and the remnant polarization Pr ⁺ at the applied voltage of 0V is preferably 75 μC/ ^cm2 or more, and more preferably 95 μC/ ^cm2 or more. In the present invention, it is preferable that the remnant polarizations Pr ⁺ and ^Pr- at the applied voltage of 0V have approximately the same absolute values. "Approximately the same absolute values" means that the absolute values of the remnant polarizations Pr ⁺ and ^Pr- are completely the same, or the difference between them is within 5% (preferably within 1%). In the present invention, the absolute values of the remanent polarizations Pr ⁺ and ^Pr- at an applied voltage of 0 V are preferably 20 μC/ ^cm2 or more, more preferably 75 μC/ ^cm2 or more, and most preferably 95 μC/ ^cm2 or more.

The piezoelectric body can be easily obtained by forming at least a compound film on a crystal substrate, then laminating an epitaxial film containing a crystalline compound, and then laminating a single crystal film made of a conductive metal on the epitaxial film directly or through another layer, and then laminating a piezoelectric film on the single crystal film directly or through another layer, by forming the epitaxial film using a compound element in the compound film, and laminating the piezoelectric film by vapor deposition or sputtering. The crystalline compound is not particularly limited and may be a known crystalline compound, but in the present invention, it is preferable that the crystalline compound is a metal compound, and the metal of the metal compound may also be a known metal. Examples of the metal include D block metals in the periodic table. The compound of the metal compound may also be a known compound, and examples of the compound in the crystalline compound include oxides, nitrides, oxynitrides, sulfides, oxysulfides, borides, oxyborides, carbides, oxycarbides, borocarbides, boronitrides, borosulfides, carbonitrides, carbosulfides, and carboborides. In the present invention, oxides or nitrides are preferred because, for example, they can provide better stress relaxation and warpage reduction in heteroepitaxial growth as a buffer layer, and can further provide better electrical properties (particularly the interface between the conductor layer and the insulating layer). In addition, the crystalline compound is preferably a crystalline oxide, the compound film is preferably an oxide film, and the compound element is preferably oxygen. In the present invention, the crystalline compound is preferably a crystalline nitride, the compound film is preferably a nitride film, and the compound element is preferably nitrogen.

Figure 1 shows a suitable example of the precursor of the laminated structure. In the precursor of the laminated structure of Figure 1, an epitaxial layer 3 is laminated on a crystal substrate 1 using an oxide film 2, and a second epitaxial layer 4 is further laminated on the epitaxial layer 3. In this specification, the terms "film" and "layer" may be interchanged depending on the case or situation. In addition, although oxides are given as suitable examples of the laminated structure, the present invention is not limited to these suitable examples, and the present invention can also be suitably applied to various compounds such as nitrides.

The precursor can be easily manufactured by forming an oxide film 2 of the crystal substrate 1 on the crystal substrate 1 as shown in FIG. 3, and then using the oxygen in the oxide film 2 to form an epitaxial film 3 made of a crystalline oxide on the crystal substrate 1 as shown in FIG. 4. In the present invention, the precursor may have the oxide film 2 on the crystal substrate 1, or the oxide film 2 may disappear when the epitaxial film 3 is formed by taking in all the oxygen in the oxide film 2. Each of these will be described in more detail below, but the present invention is not limited to these specific examples.

The crystal substrate (hereinafter, also simply referred to as "substrate") is not particularly limited as long as it does not impede the object of the present invention, such as the substrate material, and may be a known crystal substrate. It may be an organic compound or an inorganic compound. In the present invention, it is preferable that the crystal substrate contains an inorganic compound. In the present invention, it is preferable that the substrate has crystals on a part or all of its surface, more preferably a crystal substrate having crystals on all or a part of the main surface on the crystal growth side, and most preferably a crystal substrate having crystals on the entire main surface on the crystal growth side. The crystal is not particularly limited as long as it does not impede the object of the present invention, and the crystal structure is not particularly limited, but it is preferable that it is a crystal of a cubic system, a tetragonal system, a trigonal system, a hexagonal system, an orthorhombic system, or a monoclinic system, and more preferably a crystal oriented in (100) or (200). In addition, the crystal substrate may have an off angle, and the off angle may be, for example, an off angle of 0.2° to 12.0°. Here, the "off angle" refers to the angle between the substrate surface and the crystal growth surface. The substrate shape is not particularly limited as long as it is plate-like and serves as a support for the epitaxial film. It may be an insulating substrate or a semiconductor substrate, but in the present invention, the substrate is preferably a Si substrate, more preferably a crystalline Si substrate, and most preferably a crystalline Si substrate oriented in (100). In addition to the Si substrate, examples of the substrate material include one or more metals belonging to Groups 3 to 15 of the periodic table or oxides of these metals. The shape of the substrate is not particularly limited, and may be an approximately circular shape (e.g., a circular shape, an elliptical shape, etc.) or a polygonal shape (e.g., a triangular shape, a square shape, a rectangular shape, a pentagonal shape, a hexagonal shape, a heptagonal shape, an octagonal shape, a nonagonal shape, etc.), and various shapes can be suitably used. In addition, in the present invention, a large-area substrate can be used, and the area of the epitaxial film can be increased by using such a large-area substrate.

In addition, in the present invention, it is preferable that the crystal substrate has a flat surface, but it is also preferable that the crystal substrate has an uneven shape on a part or all of the surface, since this improves the quality of the crystal growth of the epitaxial film. The crystal substrate having the uneven shape may have an uneven portion consisting of a concave or convex portion formed on a part or all of the surface, and the uneven portion is not particularly limited as long as it is composed of a convex portion or a concave portion, and may be an uneven portion consisting of a convex portion, an uneven portion consisting of a concave portion, or an uneven portion consisting of a convex portion and a concave portion. The uneven portion may be formed from regular convex portions or concave portions, or may be formed from irregular convex portions or concave portions. In the present invention, it is preferable that the uneven portion is formed periodically, and it is more preferable that the uneven portion is patterned periodically and regularly. The shape of the uneven portion is not particularly limited, and examples thereof include a stripe shape, a dot shape, a mesh shape, and a random shape, but in the present invention, a dot shape or a stripe shape is preferable, and a dot shape is more preferable. In addition, when the unevenness is patterned periodically and regularly, the pattern shape of the unevenness is preferably a triangle, a quadrangle (for example, a square, a rectangle, or a trapezoid), a polygon such as a pentagon or a hexagon, a circle, an ellipse, or the like. In addition, when the unevenness is formed in a dot shape, the lattice shape of the dots is preferably a lattice shape such as a square lattice, an oblique lattice, a triangular lattice, or a hexagonal lattice, and more preferably a triangular lattice shape. The cross-sectional shape of the concave or convex part of the unevenness is not particularly limited, but examples thereof include a U-shape, a U-shape, an inverted U-shape, a wave shape, or a polygon such as a triangle, a quadrangle (for example, a square, a rectangle, or a trapezoid), a pentagon, or a hexagon, and the like. In addition, the thickness of the crystal substrate is not particularly limited, but is preferably 50 to 2000 μm, more preferably 100 to 1000 μm.

The oxide film is not particularly limited as long as it is an oxide film that can incorporate oxygen atoms into the epitaxial film, and usually contains an oxide material. The oxide material is not particularly limited as long as it does not hinder the object of the present invention, and may be a known oxide material. Examples of the oxide material include oxides of metals or semimetals. In the present invention, it is preferable that the oxide film contains the oxide material of the crystal substrate, and examples of such oxide films include a thermal oxide film of the crystal substrate and a natural oxide film. In addition, in the present invention, the oxide film may be a sacrificial layer in which a part or all of the film disappears or is destroyed when oxygen atoms are incorporated, and in the present invention, it is preferable that the oxide film is an oxygen supply sacrificial layer in which oxygen atoms are incorporated and the oxide film itself disappears during the crystal growth of the epitaxial layer. In addition, the oxide film may be patterned, for example, in a striped, dotted, meshed, or random pattern. The thickness of the oxide film is not particularly limited, but is preferably more than 1 nm and less than 100 nm.

The epitaxial layer is not particularly limited as long as it includes an epitaxial film incorporating oxygen atoms from the oxide film. The "epitaxial film incorporating oxygen atoms from the oxide film" means that oxygen atoms from the oxide film are taken by the epitaxial film during the crystal growth of the epitaxial film. The epitaxial film is not particularly limited as long as it is an epitaxial film that has grown as a crystal by incorporating oxygen atoms from the oxide film, but in the present invention, it is preferable that it includes a metal or a metal oxide. The metal is preferably, for example, one or more metals belonging to the d block of the periodic table. The metal oxide is preferably, for example, an oxide of one or more metals belonging to the d block of the periodic table. In the present invention, it is preferable that the epitaxial film includes a dielectric. In addition, in the present invention, it is preferable that the epitaxial film includes a neutron absorbing material. The neutron absorber may be a known neutron absorber, and in the present invention, by using such a neutron absorber to capture oxygen from the oxide film, it is possible to improve adhesion, crystallinity, and further the properties of the functional film. A suitable example of the neutron absorber is hafnium (Hf). The epitaxial layer may be composed of one or more types of epitaxial films, and in the present invention, it is preferable that the epitaxial layer includes two or more types of the epitaxial films. More specifically, for example, it is preferable that a second epitaxial film having a composition different from that of the epitaxial film is laminated on the epitaxial film directly or via another layer. By stacking in this manner, the first epitaxial layer can be regularly transformed so that the lattice constant at the interface between the epitaxial layer (hereinafter also referred to as "first epitaxial layer") and the second epitaxial layer is approximately the same as that of the second epitaxial layer. As a preferred example of the regular transformation, for example, a transformation in which the shape is transformed into a mountain-valley structure is given. In the present invention, it is preferable that the angles formed by the adjacent vertices and bottom points of the mountain-valley structure are different from each other, and more preferably, each of the angles is within a range of 30° to 45°. Here, the epitaxial layer usually has a first crystal plane and a second crystal plane, but since the transformation can cause a lattice constant difference between the first crystal plane and the second crystal plane, it is preferable that the lattice constant difference between the first crystal plane and the second crystal plane is within a range of 0.1% to 20%. In the present invention, since the first crystal plane can be made substantially identical to the lattice constant of the second epitaxial film, it is easily possible to achieve a lattice constant difference between the first epitaxial layer and the second epitaxial layer within the range of 0.1% to 20%.

In the present invention, it is more preferable that the epitaxial film is a dielectric and the second epitaxial film is an electrode. By using the second epitaxial layer as an electrode, not only can the adhesion and crystallinity at the interface be further improved, but also, for example, the characteristics of the element can be made more excellent. In addition, according to the present invention, when the second epitaxial layer is made of a single crystal film of a conductive metal, a large-area defect-free film can be easily obtained, and not only the function as an electrode but also the characteristics of the element can be made more excellent. The conductive metal is not particularly limited as long as it does not hinder the object of the present invention, and examples thereof include gold, silver, platinum, palladium, silver-palladium, copper, nickel, and alloys thereof, but in the present invention, it is preferable to include platinum. Note that, in the present invention, according to the above-mentioned manufacturing method, a defect-free single crystal film can be obtained as an electrode preferably in an area of 100 ^nm2 or more, and more preferably, a defect-free single crystal film can be easily obtained in an area of 1000 ^nm2 or more. In addition, a single crystal film having a thickness of preferably 100 nm or more can be easily obtained as an electrode.

In the present invention, it is preferable that a third epitaxial film and/or a fourth epitaxial film having a composition different from that of the second epitaxial film is laminated on the second epitaxial film, directly or through another layer. Figure 2 shows a preferred example of a laminated structure in which the third epitaxial layer 5 and the fourth epitaxial layer 6 are laminated on the second epitaxial layer 4. The laminated structure of Figure 2 has a first epitaxial layer 3 laminated on a crystal substrate 1 using an oxide film, a second epitaxial layer 4 laminated on the first epitaxial layer 3, a third epitaxial layer 5 laminated on the second epitaxial layer 4, and a fourth epitaxial layer 6 laminated on the third epitaxial layer 5. The third epitaxial film in the third epitaxial layer is preferably a dielectric, a semiconductor, or a conductor, more preferably a dielectric, and most preferably a piezoelectric. The fourth epitaxial film in the fourth epitaxial layer is preferably a dielectric, a semiconductor, or a conductor, more preferably a dielectric, and most preferably a piezoelectric. The thickness of each of the epitaxial films is not particularly limited, but is preferably 10 nm to 1000 μm, and more preferably 10 nm to 100 μm.

The precursor can be easily obtained by laminating an epitaxial layer on a crystal substrate via at least an oxide film, by forming the epitaxial film using oxygen atoms in the oxide film at 350°C to 700°C. When the temperature is in the range of 350°C to 700°C, the oxygen atoms in the oxide film can be more easily incorporated into the epitaxial film to cause crystal growth.

In the present invention, it is preferable to form the epitaxial film using oxygen gas after using oxygen atoms in the oxide film, and by forming the epitaxial film in this manner, the film formation rate and the like are improved. Also, by forming the film in this manner, a laminated structure in which an epitaxial layer is laminated on a crystal substrate, and between the crystal substrate and the epitaxial layer, a laminated structure having an amorphous thin film containing a constituent metal of the epitaxial layer and/or the crystal substrate and/or a buried layer containing the constituent metal and embedded in one or more parts of the crystal substrate can be easily obtained. In the present invention, it is preferable that the laminated structure has both the amorphous layer and the buried layer, since the functionality of the epitaxial film can be further improved. Also, it is preferable that the amorphous layer and the buried layer each contain a constituent metal of the epitaxial layer, since the crystallinity of the epitaxial film and the like is further improved. In the present invention, it is preferable that the constituent metal contains Hf, since this further promotes stress relaxation and also makes it possible to realize stress relaxation in multiple stages. In the present invention, it is preferable that the amorphous thin film has a thickness of 1 nm to 10 nm, since this can further improve the crystallinity of the epitaxial film, and an amorphous thin film of such a preferable thickness can be easily obtained by the preferred manufacturing method of the present invention. In the present invention, it is preferable that the shape of the buried layer has a cross-sectional shape of an approximately inverted triangle, since this can further improve the functionality of the epitaxial film. These preferable laminated structures can be easily obtained by appropriately adjusting the thickness of the oxide film and the timing of introducing the oxygen gas.

As the lamination means used in laminating the epitaxial film, the deposition means of the epitaxial film is usually preferably used, and the deposition means may be a known deposition means. In the present invention, the deposition means is preferably vapor deposition or sputtering, and more preferably vapor deposition.

The lamination means used in laminating the third epitaxial film or the fourth epitaxial film is usually sputtering, and the sputtering may be non-high vacuum sputtering. By laminating in this manner, the center of the hysteresis of the polarization amount with respect to the applied voltage is shifted to the positive applied voltage side, and a piezoelectric body having a remanent polarization Pr ⁺ of 20 μC/cm ² or more at the applied voltage of 0 V can be more easily obtained. Note that the present invention also includes a laminated structure including at least the crystal substrate, the epitaxial film, the electrode, and the piezoelectric body, in which the epitaxial film is formed by incorporating oxygen atoms in an oxide film laminated on the crystal substrate into the crystalline oxide, and in the laminated structure of the present invention, the epitaxial film preferably constitutes a part or all of the buffer layer and is a substrate for crystal growth.

The laminated structure obtained as described above can be suitably used in electronic devices according to the usual method. For example, the laminated structure can be connected to a power source or an electric/electronic circuit as a piezoelectric element, and mounted on a circuit board or packaged to form various electronic devices. In the present invention, the electronic device is preferably a piezoelectric device, and can be used as a piezoelectric device in electronic devices such as inkjet printer heads, microactuators, gyroscopes, and motion sensors. In addition, for example, if an amplifier and a rectifier circuit are connected and packaged, it can be used as various sensors such as magnetic sensors. It can also be applied to constant voltage driven memories, and for example, if a storage element and a rectifier power management circuit are connected, it becomes an energy conversion device (energy harvester) that generates power from external magnetic fields and vibrations. The energy conversion device is incorporated and used in power supply systems and wearable terminals (earphones/hearable devices, smart watches, smart glasses (spectacles), smart contact lenses, cochlear implants, cardiac pacemakers, etc.). In the present invention, the laminated structure is preferably used in, for example, smart glasses, AR headsets, MEMS mirrors for LiDAR systems, piezoelectric MEMS ultrasonic transducers (PMUTs) for advanced medical applications, and piezo heads for commercial and industrial 3D printers.

The electronic device is suitable for use in electronic devices in the usual manner. The electronic devices can be applied to various electronic devices other than those mentioned above, and more specifically, suitable examples include liquid ejection heads, liquid ejection devices, vibration wave motors, optical devices, vibration devices, imaging devices, piezoelectric acoustic components, audio playback devices having the piezoelectric acoustic components, audio recording devices, mobile phones, various information terminals, etc.

The electronic devices may also be applied to systems in the usual manner, such as sensor systems.

Example 1
The crystal growth surface side of the Si substrate (100) was treated by RIE, and then heated in the presence of oxygen to form a thermal oxide film. Then, without using oxygen, a metal from the deposition source was thermally reacted with oxygen in the oxide film on the Si substrate by a deposition method to form a single crystal of a crystalline metal oxide on the Si substrate. Next, oxygen was introduced, the temperature was lowered, and the pressure was increased, and a single crystal film of a crystalline metal oxide was formed by a deposition method. The deposition conditions for this film formation were as follows:
Evaporation source: Hf, Zr
Voltage: 3.5 to 4.75 V
Pressure: 3× ^10-2 to 6× ^10-2 Pa
Substrate temperature: 450-700℃

Next, a platinum (Pt) metal film was formed as a conductive film on the single crystal film of the crystalline metal oxide by sputtering under the following conditions.
Equipment: ULVAC sputtering equipment QAM-4
Pressure: 1.20×10 ⁻¹ Pa
Target: Pt
Power: 100W (DC)
Thickness: 100 nm
Substrate temperature: 450-600℃

Next, an SRO film was formed on the conductive film by sputtering under the following conditions.
Equipment: ULVAC sputtering equipment QAM-4
Power: 150W (RF)
Gas: Ar
Pressure: 1.8 Pa
Substrate temperature: 600° C.
Thickness: 20 nm

Next, a Pb _{( Zr0.52Ti0.48} ) _O3 film was formed as a piezoelectric film on the SRO film by sputtering, adjusting the target, substrate temperature, pressure, and other conditions in accordance with the above. The relationship between the applied voltage and the remnant polarization of the formed piezoelectric film was measured, and a hysteresis curve of the polarization amount versus the applied voltage was obtained. The results are shown in FIG. 11. As is clear from the hysteresis curve in FIG. 11, good hysteresis without imprint was obtained, the obtained piezoelectric body shifted toward the positive applied voltage side, and the remnant polarization Pr ⁺ at the applied voltage of 0V was 20 μC/ ^cm2 or more.

In addition, cross-sectional STEM images of the obtained laminated structure are shown in Figs. 5 and 6. From Fig. 6, it can be seen that a very good laminated structure was obtained. In particular, in Fig. 5, it can be seen that a regular mountain-valley structure is provided at the interface between the single crystal film of the crystalline metal oxide and the conductive film, and the angles formed by the adjacent vertices and bottom points of the mountain-valley structure are different within the range of 30° to 45°. In addition, X-ray crystal lattice images of the conductive film are shown in Figs. 7 and 8. From Figs. 7 and 8, it can be seen that a defect-free large-area conductive film is obtained, and that these have a good effect on the electrode characteristics and the piezoelectric characteristics of the piezoelectric film laminated thereon. In addition, the crystals of the crystalline substrate of the laminated structure, the single crystal film of the crystalline metal oxide, and the conductive film were measured using an X-ray diffraction device. The results of the XPS measurement are shown in Fig. 11. As is clear from Fig. 12, a (Hf, Zr)O ₂ film and a Pt single crystal film having good crystallinity were formed on the Si crystal substrate.

Example 2
A platinum (Pt) metal film was formed as a conductive film on the single crystal film of the crystalline metal nitride in the same manner as in Example 1, except that nitrogen gas was used instead of oxygen gas. Then, the crystal substrate of the laminated structure, the single crystal film of the crystalline metal nitride, and the conductive film were measured using an X-ray diffraction device. FIG. 13 shows the XPS measurement results. As is clear from FIG. 13, a (Hf, Zr)N film and a Pt single crystal film having good crystallinity were formed on the Si crystal substrate. When measured by the four-terminal method, the obtained single crystal film of the crystalline metal nitride had good conductivity.

The deposition apparatus used in Example 1 is shown in Figure 14. The deposition apparatus in Figure 14 is equipped with at least metal sources 101a-101b, earths 102a-102h, ICP electrodes 103a-103b, cut filters 104a-104b, DC power sources 105a-105b, RF power sources 106a-106b, lamps 107a-107b, Ar source 108, reactive gas source 109, power source 110, substrate holder 111, substrate 112, cut filter 113, ICP ring 114, vacuum chamber 115, and rotating shaft 116 in a crucible. The ICP electrodes 103a-103b in Figure 14 have an approximately concave curved shape or parabolic shape curved toward the center of the substrate 112.

As shown in FIG. 14, the substrate 112 is secured on the substrate holder 111. Next, the rotating shaft 116 is rotated using the power supply 110 and a rotating mechanism (not shown) to rotate the substrate 112. The substrate 112 is heated by the lamps 107a-107b, and the vacuum chamber 115 is evacuated to a vacuum or reduced pressure using a vacuum pump (not shown). Then, Ar gas is introduced from the Ar source 108 into the vacuum chamber 115, and an argon plasma is formed on the substrate 112 using the DC power supplies 105a-105b, RF power supplies 106a-106b, ICP electrodes 103a-103b, cut filters 104a-104b, and earths 102a-102h, thereby cleaning the surface of the substrate 112.

Ar gas is introduced into the vacuum chamber 115, and reactive gas is introduced using the reactive gas source 109. At this time, the lamps 107a to 107b, which are lamp heaters, are turned on and off alternately, so that a better quality crystal growth film can be formed.

The laminated structure obtained in the same manner as in Example 1 was subjected to STEM analysis. The results are shown in Figures 15 to 17. From Figure 15, it can be seen that a buried layer 1004 is formed between the crystal substrate 1011 and the epitaxial layer 1001, and further, amorphous layers 1002 and 1003 are formed. Also, from Figure 16, it can be seen that the first amorphous layer 1002 on the crystal substrate 1011 contains Si of the crystal substrate and Zr, which is a constituent metal of the epitaxial layer 1001. Also, it can be seen that the second amorphous layer contains Si of the crystal substrate and Hf and Zr, which are constituent metals of the epitaxial layer 1001. Also, from Figure 17, it can be seen that the buried layer 1004 has a cross-sectional shape of an approximately inverted triangle, and is an oxide containing Hf and Si.

(Application example)
Examples of applications of the obtained laminated structure will be described in more detail below with reference to the drawings, but the present invention is not limited to these examples. In the present invention, unless otherwise specified, a piezoelectric device or the like can be manufactured from the laminated structure by using known means.

Figure 9 shows an embodiment of an acoustic MEMS transducer constituting a MEMS microphone in which the laminated structure of the present invention is preferably used. The MEMS transducer can constitute an acoustic emission device (e.g., a speaker, etc.).

The MEMS microphone constructed by the acoustic MEMS transducer in FIG. 9 shows a cantilever type MEMS microphone, and includes a Si substrate 21 having two cantilever beams 28A, 28B and a cavity 30. Each of the cantilever beams 28A, 28B is fixed to the substrate 21 at each end, and a gap 9 is provided between the cantilever beams 8A, 8B. The cantilever beams 8A, 8B are formed by a laminated structure including, for example, a plurality of piezoelectric layers (PZT films) 26a, 26b, which are alternated with a plurality of electrode layers, i.e., Pt films 24a, 24b, 24c and SRO films 25a, 25b, 25c, 25d. A dielectric layer (single crystal film of crystalline oxide) 23 electrically insulates the cantilever beams 8A, 8B from the crystal substrate 21. In FIG. 9, a neutron absorbing material (e.g., _HfO2 or its mixed crystal) is used for the dielectric layer (single crystal film of a crystalline oxide) 23, and compared with the case where _SiO2 , SiN, etc. are used, it has excellent adhesion to the Si substrate and crystallinity, and further has excellent piezoelectric properties and durability.

Fig. 10 shows an example of application to a printing application in which the laminated structure of the present invention is preferably used, particularly to a fluid ejection device that can be used in the form of an inkjet printhead, and specifically shows a cross-sectional view of a part of a wafer having a piezoelectric actuator including Pt films 34a, 34b and SRO films 35a, 35b as electrode layers and a PZT film 36 as a piezoelectric film. In addition to the piezoelectric actuator, the wafer of Fig. 10 has a chamber 41 for containing a fluid. The chamber 41 is configured to take in a fluid from a tank (not shown) through a flow path 40. The wafer of Fig. 10 also includes a Si substrate 31, on which a dielectric layer (single crystal film of a crystalline oxide) 33 is provided as a first epitaxial layer, facing the chamber 41. 10, a neutron absorbing material (e.g., _HfO2 or its mixed crystal) is used for the dielectric layer (single crystal film of crystalline oxide) 23, which has superior adhesion to the Si substrate and crystallinity as well as superior piezoelectric properties and durability compared to the case of using _SiO2 , SiN, etc. Note that the single crystal film 33 of the crystalline oxide has, for example, a quadrangular shape in a top view (not shown), and such a shape may be, for example, any of a square, a rectangle, a rectangle with rounded corners, a parallelogram, etc.

On the single crystal film 33 of the crystalline oxide, a Pt film 34a, an SRO film 35a, a piezoelectric film (PZT film) 36, an SRO film 35b, and a Pt film 34b are laminated in this order to form a piezoelectric actuator. The piezoelectric actuator further includes an insulating film 37 extending over the electrodes 34a and 35a, the piezoelectric film 36, and the electrodes 34b and 35b. The insulating film 37 includes a dielectric material used for electrical insulation, and such a dielectric material may be a known dielectric material, for example, a _SiO2 layer, a SiN layer, or _{an Al2O3} layer. The thickness of the insulating layer including the insulating film as a constituent material is not particularly limited, but is preferably between about 10 nm and about 10 μm. A conductive path 39 is provided on the insulating layer (insulating film) 37, and contacts the electrodes 34a and 35a and the electrodes 34b and 35b, respectively, to enable selective access during use. The conductive path may be made of a known conductive material, and a suitable example of such a conductive material is aluminum (Al). The passivation layer 42 is provided on the insulating layer 37, the electrodes 34b and 35b, and the conductive path 39. The passivation layer 42 may be made of a dielectric material used for passivation of the piezoelectric actuator, and the dielectric material is not particularly limited and may be a known dielectric material. Suitable examples of the dielectric material include SiN and SION (silicon oxynitrate). The thickness of the passivation layer is not particularly limited, but is preferably between about 0.1 μm and about 3 μm. The conductive pad 38 is also provided along the piezoelectric actuator and is electrically connected to the conductive path 39. The passivation layer 42 functions as a barrier layer that protects the piezoelectric body from moisture and the like.

The piezoelectric body and laminated structure of the present invention are suitable for use as electronic devices such as piezoelectric devices, and are suitable for use in electronic devices and sensor systems.

REFERENCE SIGNS LIST 1 Crystalline substrate 2 Oxide film 3 (First) epitaxial layer 4 Second epitaxial layer 5 Third epitaxial layer 6 Fourth epitaxial layer 11 Si substrate 13 Single crystal film of crystalline oxide 14 Conductive film 15 SRO film 16 PZT film 21 Crystalline substrate (Si substrate)
23 (First) Epitaxial Layer (Single Crystalline Film of Crystalline Oxide)
24a Second epitaxial layer (Pt film)
24b Sixth epitaxial layer (Pt film)
24c Tenth epitaxial layer (Pt film)
25a Third epitaxial layer (SRO film)
25b Fifth epitaxial layer (SRO film)
25c Seventh epitaxial layer (SRO film)
25d ninth epitaxial layer (SRO film)
26a Fourth epitaxial layer (PZT film)
26b Eighth epitaxial layer (PZT film)
28A Cantilever beam 28B Cantilever beam 29 Gap 30 Cavity 31 Crystal substrate (Si substrate)
33 (First) Epitaxial Layer (Single Crystal Film of Crystalline Oxide)
34a Second epitaxial layer (Pt film)
34b Sixth epitaxial layer (Pt film)
35a: third epitaxial layer (SRO film)
35b Fifth epitaxial layer (SRO film)
36 Fourth epitaxial layer (PZT film)
37 insulating film 38 conductive pad 39 conductive path 40 flow path 41 chamber 42 passivation layer 101a to 101b metal source 102a to 102j earth 103a to 103b ICP electrode 104a to 104b cut filter 105a to 105b DC power supply 106a to 106b RF power supply 107a to 107b lamp 108 Ar source 109 reactive gas source 110 power supply 111 substrate holder 112 substrate 113 cut filter 114 ICP ring 115 vacuum chamber 116 rotating shaft 1001 epitaxial layer 1002 first amorphous layer 1003 second amorphous layer 1004 buried layer 1011 substrate

Claims (8)

A laminated structure including at least a crystal substrate which is a Si substrate, an epitaxial film which is a metal oxide containing Hf and Zr, an electrode, and a piezoelectric body,
a first amorphous layer formed between the crystal substrate and the epitaxial film and containing Zr and Si;
a second amorphous layer formed between the first amorphous layer and the epitaxial film, the second amorphous layer including Hf, Zr and Si;
one or more buried layers embedded in a portion of the crystal substrate and containing Hf and Si;
having
The piezoelectric body has a hysteresis center of the polarization amount with respect to the applied voltage shifted toward a positive applied voltage side, and has a remanent polarization Pr ⁺ of 20 μC/ ^cm2 or more at an applied voltage of 0 V ;
The buried layer buried in a portion of the crystal substrate has a cross-sectional shape of a substantially inverted triangle. the electrode is formed on the epitaxial film,
a regular peak-valley structure is provided at an interface between the epitaxial film and the electrode;
2. The laminated structure according to claim 1, wherein the angles formed by adjacent vertices and bottoms of the peak-valley structure are different and fall within a range of 30° to 45°. 2. The laminated structure according to claim 1, wherein a peak-valley structure is provided at the interface between the second amorphous layer and the epitaxial film. 2. The laminated structure according to claim 1, wherein the center of hysteresis of the amount of polarization with respect to the applied voltage is shifted to a range of an applied voltage of 100 to 300 V. 2. The laminated structure according to claim 1 , wherein the remanent polarization Pr ⁺ at an applied voltage of 0 V is 75 μC/ ^cm2 or more. 2. The laminated structure according to claim 1 , wherein the remanent polarizations Pr ⁺ and ^Pr- at an applied voltage of 0 V have approximately the same absolute value. The laminated structure according to claim 1 , wherein the piezoelectric body is a PZT-based piezoelectric body. An electronic device, electronic equipment, or system including a laminate structure, characterized in that the laminate structure is the laminate structure according to any one of claims 1 to 7 .