Vibratory angular velocity detector

Abstract

A vibration-type angular velocity detector 100 comprises a vibrator 10 including: a substrate 1 having a first silicon layer 11 having a crystal plane with a Miller index of (111) and a second silicon layer 13 having a crystal plane with a Miller index of (100); and a vibration excitation portion 2 having a piezoelectric layer 21 provided on the opposite side of the second silicon layer 13 of the substrate 1 from the first silicon layer 11. The piezoelectric layer 2 is made of a piezoelectric element material grown on the opposite side of the second silicon layer 13 from the first silicon layer 11 and having at least a crystal plane with a Miller index of (100) or a Miller index (001).

Description

Technical Field

[0001] The present invention relates to a vibrating angular velocity detector, and more particularly to a vibrating angular velocity detector including a substrate having a silicon layer.

Background Art

[0002] Conventionally, a vibrating angular velocity detector including a substrate having a silicon layer has been known. Such a vibrating angular velocity detector is disclosed, for example, in Japanese Patent Application Laid-Open No. 2003-302222.

[0003] Japanese Patent Application Laid-Open No. 2003-302222 discloses a thin film microelectromechanical resonator gyro (vibrating angular velocity detector) including a silicon wafer having a silicon layer. The thin film microelectromechanical resonator gyro includes a piezoelectric thin film. The piezoelectric thin film is formed on the surface of the silicon layer of the silicon wafer. The piezoelectric thin film is configured to vibrate on the surface of the silicon layer of the silicon wafer based on an electric field generated by an applied voltage. By this vibration, the angular velocity is detected in the thin film microelectromechanical resonator gyro. Such a piezoelectric thin film is a lead zirconate titanate film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in a conventional thin-film microelectromechanical resonator gyro as described in Japanese Patent Application Laid-Open No. 2003-302222, a general polycrystalline piezoelectric thin film may be used as the piezoelectric thin film. When the applied voltage is low, the vibration amplitude (driving amount) of this polycrystalline piezoelectric thin film is relatively small. Therefore, in order to ensure a sufficient driving amount, it is necessary to increase the applied voltage. In this case, since the resistance (insulation resistance) of the piezoelectric thin film to the voltage decreases due to the increase in the applied voltage, the deterioration of the piezoelectric thin film is accelerated. For this reason, in a conventional thin-film microelectromechanical resonator gyro as described in Japanese Patent Application Laid-Open No. 2003-302222, instead of a polycrystalline piezoelectric thin film, it is conceivable to form a piezoelectric thin film having at least a crystal plane with a Miller index of (100) or a Miller index of (001) on the surface of a silicon wafer, which can ensure a sufficient driving amount even when the applied voltage is low.

[0006] However, although not explicitly stated in Japanese Patent Application Laid-Open No. 2003-302222, in a conventional thin-film microelectromechanical resonator gyro as described in Japanese Patent Application Laid-Open No. 2003-302222, among silicon wafers having silicon layers with crystal planes of various Miller indices, it is considered that a silicon wafer having a silicon layer with a crystal plane of Miller index (111) may be used. Therefore, when a piezoelectric thin film having at least a crystal plane with a Miller index of (100) or a Miller index of (001) is formed on the surface of a diamond-structured silicon layer having a crystal plane of Miller index (111), in the crystal structure at the joint between the silicon layer of the silicon wafer and the piezoelectric thin film, due to the different shapes of the crystal planes, problems such as strain and non-junction of the crystal structures (misfit dislocations) are likely to occur. For this reason, in a conventional thin-film microelectromechanical resonator gyro as described in Japanese Patent Application Laid-Open No. 2003-302222, there is a problem that it is difficult to form a piezoelectric thin film (piezoelectric layer) having at least a crystal plane with a Miller index of (100) or a Miller index of (001) on the surface of a silicon layer having a crystal plane of Miller index (111) in a silicon wafer (substrate).

[0007] The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a vibration type angular velocity detector capable of forming a piezoelectric layer having at least a crystal plane with a Miller index of (100) or a Miller index of (001) on a substrate including a silicon layer having a crystal plane with a Miller index of (111).

Means for Solving the Problems

[0008] To achieve the above object, a vibration type angular velocity detector according to one aspect of the present invention includes a substrate having a first silicon layer having a crystal plane with a Miller index of (111) and a second silicon layer provided on one side in the thickness direction of the first silicon layer and having a crystal plane with a Miller index of (100), and a vibrator including a vibration excitation unit including a piezoelectric layer provided on the side of the substrate opposite to the first silicon layer side of the second silicon layer. The piezoelectric layer is composed of a piezoelectric element material having at least a crystal plane with a Miller index of (100) or a Miller index of (001) grown on the side of the second silicon layer opposite to the first silicon layer side.

[0009] In the vibrating angular velocity detector according to one aspect of the present invention, as described above, the piezoelectric layer is formed of a piezoelectric element material having at least a crystal plane with a mirror index (100) or a mirror index (001) grown on the side opposite to the first silicon layer of the second silicon layer. Here, the substrate is composed of not only the first silicon layer having a diamond structure with a crystal plane of mirror index (111) whose Young's modulus is isotropic, but also a second silicon layer having a crystal plane of mirror index (100). Thus, by forming the piezoelectric layer on the substrate via the second silicon layer, the shape of the crystal plane of the piezoelectric layer is substantially the same as the shape of the crystal plane of the second silicon layer. Therefore, in the crystal structure at the joint between the vibration excitation portion having the piezoelectric layer and the second silicon layer of the substrate, it is possible to suppress the occurrence of strain and non-junction of crystal structures (misfit dislocation) caused by the different shapes of the crystal planes. As a result, a piezoelectric layer having at least a crystal plane with a mirror index (100) or a mirror index (001) can be formed on a substrate including a first silicon layer having a crystal plane of mirror index (111). Further, since the piezoelectric layer is provided on a substrate including a first silicon layer having a crystal plane of mirror index (111), the Young's modulus of the first silicon layer having a diamond structure with a crystal plane of mirror index (111) is isotropic. Therefore, when the piezoelectric layer vibrates on the substrate, the piezoelectric layer can be vibrated appropriately. As a result, since the piezoelectric layer can be vibrated appropriately, the vibrating angular velocity detector can detect the angular velocity accurately.

[0010] In the vibration type angular rate detector according to the above-described one aspect, preferably, the vibrator has a shape that is rotationally symmetric with respect to the center of the vibrator when viewed from one side in the thickness direction, and is configured to perform a rotationally symmetric vibration with respect to the center of the vibrator. Here, in order for a vibrator having a rotationally symmetric shape to perform a rotationally symmetric vibration, a mechanical property is required in which the Young's modulus of the first silicon layer that dominantly affects the mechanical properties of the vibrator is isotropic in the in-plane direction of the substrate. Therefore, in the vibration type angular rate detector, a vibrator having a rotationally symmetric shape and performing a rotationally symmetric vibration is provided on a substrate including a first silicon layer having a diamond structure with a crystal plane of Miller index (111) whose Young's modulus is isotropic. Thus, a vibration type detector that effectively uses the property that the Young's modulus of the first silicon layer having a diamond structure with a crystal plane of Miller index (111) is isotropic can be realized.

[0011] In the vibration type angular rate detector according to the above-described one aspect, preferably, in the thickness direction, the thickness of the second silicon layer is smaller than the thickness of the first silicon layer. With this configuration, by making the thickness of the second silicon layer smaller than the thickness of the first silicon layer, the isotropic deformation of the first silicon layer has a greater influence compared to the anisotropic deformation of the second silicon layer due to the vibration of the piezoelectric layer. Thus, the substrate can undergo isotropic deformation. As a result, the vibrator can vibrate rotationally symmetrically.

[0012] In the vibration type angular rate detector according to the above-described one aspect, preferably, the piezoelectric layer is composed of lead zirconate titanate as a piezoelectric element material having at least a crystal plane of Miller index (100), Miller index (100), or Miller index (001). With this configuration, since lead zirconate titanate has excellent piezoelectric performance compared to other materials, it is possible to ensure a sufficient driving amount of the vibrator even when the applied voltage is lower, and thus it is possible to further suppress the acceleration of deterioration of the vibrator.

[0013] In the vibration type angular velocity detector including the vibrator having the rotationally symmetric shape, preferably, the vibrator has a ring shape when viewed from one side. With this configuration, the area to be vibrated can be made smaller than that of a disk-shaped vibrator having the same diameter, so that the power supplied to vibrate the vibrator can be made relatively small.

[0014] In the vibration type angular velocity detector according to the above aspect, preferably, the vibration excitation unit further includes a first electrode provided between the piezoelectric layer and the second silicon layer for applying a voltage to the piezoelectric layer, and a second electrode provided on one side of the piezoelectric layer for applying a voltage to the piezoelectric layer. The first electrode is composed of an electrode material having a crystal plane with a Miller index of (100) grown on the surface on one side of the second silicon layer. With this configuration, since the first electrode is composed of an electrode material having a crystal plane with a Miller index of (100), a piezoelectric layer having at least a crystal plane with a Miller index of (100) or a Miller index of (001) on one side of the first electrode can be formed. Therefore, a vibration type angular velocity detector including a vibrator capable of ensuring a sufficient driving amount even when the voltage applied by the first electrode and the second electrode is low can be obtained. Further, by forming the first electrode having a crystal plane with a Miller index of (100) on one side of the second silicon layer having a crystal plane with a Miller index of (100), the shape of the crystal plane of the first electrode is the same as the shape of the crystal plane of the second silicon layer. Therefore, in the crystal structure of the joint portion between the first electrode and the second silicon layer, the occurrence of strain and non-junction of crystal structures (misfit dislocation) due to different shapes of crystal planes can be suppressed.

[0015] In this case, preferably, each of the lattice misfit between the first electrode and the piezoelectric layer and the lattice misfit between the first electrode and the second silicon layer is 10% or less. With such a configuration, at each of the joint between the piezoelectric layer and the first electrode and the joint between the second silicon layer and the first electrode, it is possible to further suppress the occurrence of strain and non - joining of crystal structures (misfit dislocation) due to different lattice constants. Note that the lattice misfit indicates the lattice mismatch ratio based on the lattice constant of one layer and the lattice constant of the other layer. Also, the lattice misfit includes both cases where there is a difference between the lattice constant of one layer and the lattice constant of the other layer (when the lattice mismatch ratio is other than 0%) and cases where there is no difference between the lattice constant of one layer and the lattice constant of the other layer (when the lattice mismatch ratio is 0%).

[0016] In a vibration - type angular velocity detector in which each of the lattice misfit between the first electrode and the piezoelectric layer and the lattice misfit between the first electrode and the second silicon layer is 10% or less, preferably, the lattice constant of the crystal structure of the first electrode is substantially the same as each of the lattice constant of the crystal structure of the piezoelectric layer and the lattice constant of the crystal structure of the second silicon layer of the substrate. With such a configuration, at each of the crystal structures of the joint between the piezoelectric layer and the first electrode and the crystal structure of the joint between the second silicon layer and the first electrode, it is possible to further suppress the occurrence of strain and non - joining of crystal structures (misfit dislocation) due to different lattice constants of the crystal structures. As a result, a vibration excitation portion having a crystal plane with a Miller index (100) can be formed on a substrate having a crystal plane with a Miller index (111). Note that the lattice constant of the crystal structure of the first electrode being substantially the same means that the lattice constant of the crystal structure of the first electrode has the same lattice constant as, is slightly larger than, or is slightly smaller than each of the lattice constants of the crystal structure of the piezoelectric layer and the crystal structure of the second silicon layer.

[0017] In the vibrating angular velocity detector according to the above-described one aspect, preferably, the substrate further includes a silicon dioxide layer formed of amorphous silicon dioxide that is bonded to one surface of the first silicon layer and to the surface on the side opposite to the one side in the thickness direction of the second silicon layer. With this configuration, compared with the case of directly bonding the first silicon layer and the second silicon layer, the first silicon layer and the second silicon layer can be easily bonded via the silicon dioxide layer by a method of performing hydrogen bonding and then performing heat treatment at a high temperature.

[0018] In this case, preferably, the substrate is a SOI (Silicon on Insulator) substrate having a first silicon layer as a handle layer supported when moving the substrate, a silicon dioxide layer, and a second silicon layer as a device layer. With this configuration, a vibrating angular velocity detector can be easily manufactured using the SOI substrate.

Advantages of the Invention

[0019] According to the present invention, as described above, a piezoelectric layer having at least a crystal plane with a mirror index of (100) or a mirror index of (001) can be formed on a substrate having a silicon layer with a crystal plane having a mirror index of (111).

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0022] (Configuration of Ring Gyroscope) With reference to FIGS. 1 to 4, the configuration of a ring gyroscope 100 according to an embodiment of the present invention will be described. Here, the ring gyroscope 100 is also a ring resonator. Note that the ring gyroscope 100 is an example of the "vibratory angular velocity detector" in the claims.

[0023] As shown in FIG. 1, the ring gyroscope 100 is a sensor for detecting an angular velocity in a digital camera, a smartphone, a portable game machine, a robot, a car navigation system, a vehicle, and the like. The ring gyroscope 100 is, for example, a MEMS (Micro Electro Mechanical Systems) device.

[0024] The ring gyroscope 100 includes a vibrator 10 including a substrate 1 and a vibration excitation unit 2. The ring gyroscope 100 is configured to excite vibration of the vibration excitation unit 2 in a predetermined direction on the surface 13b of the substrate 1. Here, in the ring gyroscope 100, the vibration of the vibrator 10 changes due to the Coriolis force generated by applying a rotational motion to the vibrator 10 vibrating in a predetermined direction. The ring gyroscope 100 is configured to detect an angular velocity based on the change in the vibration of the vibrator 10. Here, the direction in which the substrate 1 and the vibration excitation unit 2 are aligned is defined as the Z direction, the side of the vibration excitation unit 2 in the Z direction is defined as the Z1 direction, and the side of the substrate 1 in the Z direction is defined as the Z2 direction. The Z direction is a direction parallel to the thickness direction of the substrate 1. One direction among the directions orthogonal to the Z direction is defined as the X direction, and the other direction orthogonal to the X direction is defined as the Y direction. Also, one direction in the X direction is defined as the X1 direction, and the other direction in the X direction is defined as the X2 direction. Also, one direction in the Y direction is defined as the Y1 direction, and the other direction in the Y direction is defined as the Y2 direction. The XY direction, which is the combination of the X direction and the Y direction, is a direction parallel to the surface 13b of the substrate 1 (see FIG. 4) (in-plane direction).

[0025] Specifically, as shown in FIG. 2, the vibrator 10 has a rotationally symmetric shape with respect to the center Ce of the vibrator 10 when viewed from the Z1 direction side. That is, the vibrator 10 has a ring shape when viewed from the Z1 direction side. Further, the ring-shaped vibrator 10 is configured to perform rotationally symmetric vibrations with respect to the center Ce of the vibrator 10. Specifically, the vibrator 10 alternately repeats vibrations in the Y direction and vibrations in the X direction orthogonal to the Y direction. Then, as shown in FIG. 3, when a rotational motion (for example, a rotational motion due to the turning of a vehicle) is applied to the vibrator 10, the vibrator 10 vibrates in a direction inclined with respect to the Y direction as a predetermined direction by the Coriolis force generated thereby. Thereby, the angular velocity is detected in the ring gyroscope 100.

[0026] Here, in other vibrators that do not have a rotationally symmetric shape such as a ring shape and do not perform rotationally symmetric vibrations, when vibrating other vibrators, it is not necessary to maintain a rotationally symmetric shape, so it is not necessary to vibrate other vibrators with a uniform load applied to the entire other vibrator. However, in the vibrator 10 of the present embodiment, as described above, since it has a rotationally symmetric shape such as a ring shape and needs to perform rotationally symmetric vibrations, it is necessary to maintain a rotationally symmetric shape when vibrating the vibrator 10. Therefore, when the vibrator 10 vibrates in the in-plane direction of the surface 13b of the substrate 1, in order to vibrate the rotationally symmetric vibrator in a rotationally symmetric shape, even if an equal load is applied in the rotationally symmetric direction, if the Young's modulus in each azimuth in the in-plane direction of the substrate 1 is different, the deformation in each azimuth in the in-plane direction of the substrate 1 will be different, and thus the rotationally symmetric shape of the vibrator 10 will collapse. For this reason, in the vibrator 10 of the present embodiment, it is required that the Young's modulus of the material of the vibrator 10 be isotropic.

[0027] Therefore, the ring gyroscope 100 of the present embodiment has a structure capable of appropriately vibrating the vibrator 10 and relatively lowering the voltage required for performing such appropriate vibrations. Specifically, as shown in FIG. 4, the vibrator 10 includes a substrate 1 and a vibration excitation unit 2 having a piezoelectric layer 21, a first electrode 22, and a second electrode 23.

[0028] (Substrate) Substrate 1 is a ring-shaped SOI (Silicon on Insulator) substrate. Substrate 1 includes a first silicon layer 11, a silicon dioxide layer 12, and a second silicon layer 13.

[0029] 〈First Silicon Layer〉 The first silicon layer 11 is a handle layer that is supported when moving substrate 1 in the SOI substrate. The first silicon layer 11 is the portion of substrate 1 on the most Z2-direction side. The first silicon layer 11 is composed of single-crystal silicon (Si). Here, the crystal structure of the silicon in the first silicon layer 11 is a so-called diamond structure. The first silicon layer 11 has a crystal plane with Miller indices (111). The first silicon layer 11 is composed of a silicon crystal structure having a crystal plane with Miller indices (111). The surface 11a on the Z1-direction side of the first silicon layer 11 is composed of a crystal plane with Miller indices (111) (an equilateral triangle-shaped plane). Here, in the crystal plane with Miller indices (111) of the first silicon layer 11 having a diamond-structure crystal structure, the Young's modulus is isotropic. The lattice constant of such a silicon crystal structure of the first silicon layer 11 is approximately 0.5431 nm. Note that a single crystal is a concept that includes not only a completely single-crystal state but also a substantially single-crystal state.

[0030] Here, the Miller index indicates an index that defines a crystal plane, which is a plane made of atoms in a unit lattice in a crystal, by three crystal axes of the crystal structure. Also, a crystal indicates a solid in which atoms, molecules, ions, etc. that constitute a substance are spatially arranged regularly. The crystal structure indicates the arrangement structure of atoms, molecules, and ions that constitute a substance. A lattice indicates the periodic arrangement of the crystal structure. Also, a unit lattice indicates the lattice that is the smallest unit of repetition of the periodic arrangement of the crystal structure. In a crystal, a plurality of crystal planes are arranged at equal intervals. The plurality of crystal planes are parallel to each other. The direction in which the plurality of crystal planes are arranged is the crystal orientation (the direction perpendicular to the crystal plane). Also, the lattice constant is the length of one side of the unit lattice.

[0031] <Silicon dioxide layer> The silicon dioxide layer 12 is provided for joining the first silicon layer 11 and the second silicon layer 13. That is, the silicon dioxide layer 12 is joined to the surface 11a on the Z1 direction side (one side) of the first silicon layer 11 and is composed of amorphous silicon dioxide (SiO2) joined to the surface 13a on the Z2 direction side (the other side) of the second silicon layer 13. Note that amorphous refers to a homogeneous solid material whose mechanical properties such as Young's modulus do not change depending on the direction.

[0032] Specifically, the silicon dioxide layer 12 is joined to the surface 11a on the Z1 direction side of the first silicon layer 11 by hydrogen bonding the surface 12a on the Z2 direction side of the silicon dioxide layer 12 and the surface 11a on the Z1 direction side of the first silicon layer 11 and then performing a high-temperature treatment. Also, the silicon dioxide layer 12 is joined to the surface 13a on the Z2 direction side of the second silicon layer 13 by hydrogen bonding the surface 12b on the Z1 direction side of the silicon dioxide layer 12 and the surface 13a on the Z2 direction side of the second silicon layer 13 and then performing a high-temperature treatment.

[0033] The silicon dioxide layer 12 is disposed between the first silicon layer 11 and the second silicon layer 13 in the Z direction.

[0034] Since the silicon dioxide layer 12 is amorphous, it is isotropic with respect to Young's modulus.

[0035] <Second silicon layer> The second silicon layer 13 is the device layer of the SOI substrate. The second silicon layer 13 is the portion on the most Z1 direction side in the substrate 1. The second silicon layer 13 is provided on the Z1 direction side of the first silicon layer 11. Specifically, the second silicon layer 13 is provided on the Z1 direction side of the first silicon layer 11 via the silicon dioxide layer 12.

[0036] The second silicon layer 13 is composed of single-crystalline silicon. The second silicon layer 13 has a crystal plane with Miller indices (100). The second silicon layer 13 is composed of a crystal structure of silicon having a crystal plane with Miller indices (100). The surface 13b on the Z1 direction side of the second silicon layer 13 is composed of a crystal plane with Miller indices (100) (a rectangular surface). The surface 13a on the Z2 direction side of the second silicon layer 13 is composed of a crystal plane with Miller indices (100) (a rectangular surface). Here, in the crystal plane with Miller indices (100) of the second silicon layer 13, the Young's modulus is anisotropic. The lattice constant of the crystal structure of silicon in such a second silicon layer 13 is approximately 0.5431 nm.

[0037] The second silicon layer 13 is a layer for converting the crystal plane with Miller indices (111) of the first silicon layer 11 into a crystal plane with Miller indices (100) on the substrate 1.

[0038] 〈Thickness of each of the first silicon layer and the second silicon layer〉 In the Z direction, the thickness Th2 of the second silicon layer 13 is smaller than the thickness Th1 of the first silicon layer 11. The thickness Th1 of the first silicon layer 11 is preferably 5.0 [μm] or more and 500 [μm] or less. Also, the second silicon layer 13 is a layer with a very small thickness thinner than the first silicon layer 11. The thickness Th2 of the second silicon layer 13 is preferably about 1% of the thickness Th1 of the first silicon layer 11. That is, the thickness Th2 of the second silicon layer 13 is preferably 0.05 [μm] or more and 5.0 [μm] or less.

[0039] Thus, since the thickness Th2 of the second silicon layer 13 is smaller than the thickness Th1 of the first silicon layer 11, the isotropic deformation of the first silicon layer 11 has a greater influence compared to the anisotropic deformation of the second silicon layer 13 due to the vibration of the oscillator 10, so the substrate 1 can undergo isotropic deformation. Thereby, the piezoelectric layer 21 can vibrate appropriately on the surface 13b on the Z1 direction side of the substrate 1.

[0040] (Vibration excitation unit) The vibration excitation unit 2 is a part that generates (excites) vibrations in the ring gyroscope 100. That is, in the vibration excitation unit 2, the piezoelectric layer 21 resonates at a high frequency of a predetermined wavelength due to the electric field generated by the voltage generated by the first electrode 22 and the second electrode 23. The vibration excitation unit 2 is provided on the side opposite to the first silicon layer 11 side (Z1 direction side) of the second silicon layer 13 of the substrate 1. In the vibration excitation unit 2, the first electrode 22 is configured by a crystal structure having a crystal plane with a Miller index (100) so as to match the crystal plane with a Miller index (100) of the second silicon layer 13. Further, in the vibration excitation unit 2, a piezoelectric layer 21 having at least a crystal plane with a Miller index (100) or a Miller index (001) is configured so as to match the crystal plane with a Miller index (100) of the second silicon layer 13. That is, the piezoelectric layer 21 has a crystal plane with a (100) - preferred orientation. Note that preferred orientation refers to a crystal in which a crystal plane with a specific Miller index (for example, (100), etc.) grows preferentially with respect to a crystal plane with another Miller index (for example, (001), etc.).

[0041] Specifically, the piezoelectric layer 21 is composed of a single - crystal piezoelectric element material having a crystal plane with a (100) - preferred orientation grown on the side opposite to the first silicon layer 11 side (Z1 direction side) of the second silicon layer 13 by epitaxial growth. That is, the piezoelectric layer 21 is joined by growing lead zirconate titanate (PZT) as a single - crystal piezoelectric element material having a crystal plane with a (100) - preferred orientation on the crystal plane with a Miller index (100) of the surface 22a on the Z1 direction side of the first electrode 22 by epitaxial growth. The piezoelectric layer 21 is provided on the Z1 direction side of the second silicon layer 13 via the first electrode 22.

[0042] Since the piezoelectric layer 21 is a thin film of a single crystal made of a material different from that of the first electrode 22, it is formed on the surface 22a on the Z1 direction side of the first electrode 22 by heteroepitaxial growth in epitaxial growth. As heteroepitaxial growth, vapor phase epitaxial growth in which components in the vapor phase are deposited on the surface 22a on the Z1 direction side of the first electrode 22, liquid phase epitaxial growth in which crystal components are precipitated from a supersaturated solution on the surface 22a on the Z1 direction side of the first electrode 22, solid phase epitaxial growth in which a material deposited on the surface 22a on the Z1 direction side of the first electrode 22 is heated by irradiating an electron beam or the like, and molecular beam epitaxial growth in which crystals are formed on the surface 22a on the Z1 direction side of the first electrode 22 in an ultrahigh vacuum are preferably used.

[0043] Here, the surface 21a on the Z2 direction side of the piezoelectric layer 21 formed by epitaxial growth is composed of a crystal plane (rectangular surface) with a (100) Miller index preferential orientation. Further, the surface 21b on the Z1 direction side of the piezoelectric layer 21 formed by epitaxial growth is composed of a crystal plane (rectangular surface) with a (100) Miller index preferential orientation.

[0044] In this way, since the piezoelectric layer 21 having a crystal plane with a (100) Miller index preferential orientation is formed on the surface 22a on the Z1 direction side of the first electrode 22 having a crystal plane with a (100) Miller index, the shape of the crystal plane of the surface 22a on the Z1 direction side of the first electrode 22 and the shape of the crystal plane of the surface 21a on the Z2 direction side of the piezoelectric layer 21 are substantially the same. Further, the lattice misfit between the first electrode 22 and the piezoelectric layer 21 is 10% or less. Here, the lattice constant of the crystal structure of the piezoelectric layer 21 has substantially the same lattice constant as the lattice constant of the crystal structure of the first electrode 22. That is, the lattice constant of the crystal structure of the piezoelectric layer 21 has the same lattice constant as, slightly larger than, or slightly smaller than the lattice constant of the crystal structure of the first electrode 22.

[0045] As a result, in the crystal structure of the joint between the piezoelectric layer 21 and the first electrode 22, it becomes difficult for strain and misfit dislocation (where crystal structures are not joined) to occur due to differences in the shapes and lattice constants of crystal planes. Therefore, in the piezoelectric layer 21, in the crystal structure of the joint between the piezoelectric layer 21 and the first electrode 22, it becomes difficult for strain and misfit dislocation to occur, and lead zirconate titanate having high temperature resistance and the like is used.

[0046] The piezoelectric layer 21 has a ring shape (see FIG. 1) when viewed from the Z1 direction side. The ring-shaped piezoelectric layer 21 is joined to the substrate 1 via the first electrode 22.

[0047] (First Electrode) The first electrode 22 is provided between the piezoelectric layer 21 and the second silicon layer 13 in order to apply a voltage to the piezoelectric layer 21. That is, the first electrode 22 is provided on the Z2 direction side of the piezoelectric layer 21 and on the Z1 direction side of the second silicon layer 13. The first electrode 22 is a multi-layer film electrode including an insulating layer, an electrode layer, and a buffer layer. The first electrode 22 is formed of a single crystal electrode material with a Miller index of (100) grown on the surface 12b on the Z1 direction side of the second silicon layer 13 by epitaxial growth (heteroepitaxial growth). Note that the first electrode 22 may be a single-layer electrode. As the heteroepitaxial growth, the above-described vapor phase epitaxial growth, liquid phase epitaxial growth, solid phase epitaxial growth, and molecular beam epitaxial growth are preferably used.

[0048] That is, the electrode material of the insulating layer may have zirconium oxide (ZrO2) having a crystal plane with a Miller index of (100) (a rectangular surface), or yttria-stabilized zirconia (YSZ), etc. The electrode material of the electrode layer may have platinum (Pt), iridium (Ir), cerium oxide (CeO2), cuprate high-temperature superconductor (LSCO), lanthanum (La), or strontium (Sr), etc., having a crystal plane with a Miller index of (100) (a rectangular surface). The electrode material of the buffer layer may have strontium ruthenate (SrRuO3) having a crystal plane with a Miller index of (100) (a rectangular surface), or lanthanum nickelate (LaNiO3), etc. Note that the electrode material of the first electrode 22 is not limited to the above-described electrode materials.

[0049] Thus, since the first electrode 22 having a crystal plane with a Miller index of (100) is formed on the surface 13b on the Z1 direction side of the second silicon layer 13 having a crystal plane with a Miller index of (100), the shape of the crystal plane of the surface 13b on the Z1 direction side of the second silicon layer 13 is the same as the shape of the crystal plane of the surface 22b on the Z2 direction side of the first electrode 22.

[0050] Also, similar to the lattice misfit between the first electrode 22 and the piezoelectric layer 21, the lattice misfit between the first electrode 22 and the second silicon layer 13 is 10% or less. Here, the lattice constant of the crystal structure of the first electrode 22 has a lattice constant that is substantially the same as each of the lattice constants of the crystal structures of the piezoelectric layer 21 and the second silicon layer 13. That is, the lattice constant of the crystal structure of the first electrode 22 has a lattice constant that is the same as, slightly larger than, or slightly smaller than each of the lattice constants of the crystal structures of the piezoelectric layer 21 and the second silicon layer 13.

[0051] As a result, in the crystal structure of the junction between the first electrode 22 and the second silicon layer 13, it becomes difficult for strain and misfit dislocation (where crystal structures do not join) to occur due to differences in the shapes and lattice constants of crystal planes. In the first electrode 22, in the crystal structure of the junction between the piezoelectric layer 21 and the first electrode 22, strain and misfit dislocation are less likely to occur, and the above electrode material having high-temperature resistance and the like is used.

[0052] (Second Electrode) The second electrode 23 is provided on the Z1 direction side of the piezoelectric layer 21 in order to apply a voltage to the piezoelectric layer 21. The second electrode 23 is formed on the Z1 direction side of the piezoelectric layer 21 by a known method. Unlike the crystalline piezoelectric layer 21, the second electrode 23 may be amorphous or may be crystalline like the crystalline piezoelectric layer 21. The second electrode 23 is an electrode of a multilayer film including an electrode layer and a buffer layer. That is, the second electrode 23 may have titanium (Ti), gold (Au), platinum (Pt), iridium dioxide (IrO2), or the like as the electrode layer. Also, the second electrode 23 may have strontium ruthenate (SrRuO3), lanthanum nickelate (LaNiO3), or the like as the buffer layer. Note that the second electrode 23 may be a single-layer electrode. Also, the electrode material of the second electrode 23 is not limited to the above-described electrode materials.

[0053] (Manufacturing Method of Ring Gyroscope) A method for manufacturing the ring gyroscope 100 will be described.

[0054] First, a substrate 1 including a first silicon layer 11, a silicon dioxide layer 12, and a second silicon layer 13 is prepared. After the substrate 1 is prepared, a first electrode 22 is formed on a surface 13b of the second silicon layer 13 of the substrate 1 by epitaxial growth. After the first electrode 22 is formed, a piezoelectric layer 21 is formed on a surface 22a of the first electrode 22 by epitaxial growth. After the piezoelectric layer 21 is formed, a second electrode 23 is formed on a surface 21b of the piezoelectric layer 21 by a known method. After the second electrode 23 is formed, the substrate 1, the piezoelectric layer 21, the first electrode 22, and the second electrode 23 are processed for use in a device. Then, for example, by dividing the substrate 1 into individual pieces with a blade or the like, a ring gyroscope 100 is manufactured.

[0055] (Effect of this embodiment) In this embodiment, the following effects can be obtained.

[0056] In this embodiment, as described above, the piezoelectric layer 21 is formed of a piezoelectric element material having at least a crystal plane with a Miller index of (100) grown on the side opposite to the first silicon layer 11 side of the second silicon layer 13. Here, the substrate 1 is composed of not only the first silicon layer 11 having a diamond structure with a crystal plane of Miller index (111) whose Young's modulus is isotropic, but also the second silicon layer 13 having a crystal plane of Miller index (100). Thus, by forming the piezoelectric layer 21 on the side opposite to the first silicon layer 11 side of the second silicon layer 13, the shape of the crystal plane of the piezoelectric layer 21 and the shape of the crystal plane of the second silicon layer 13 are substantially the same. Therefore, in the crystal structure at the joint between the vibration excitation part 2 including the piezoelectric layer 21 and the second silicon layer 13 of the substrate 1, the occurrence of strain and non - joining of crystal structures (misfit dislocations) due to different shapes of crystal planes can be suppressed. As a result, the piezoelectric layer 21 having at least a crystal plane with a Miller index of (100) can be formed on the substrate 1 including the first silicon layer 11 having a crystal plane with a Miller index of (111). Here, for other oscillators that do not have a rotation - symmetric shape and do not cause rotation - symmetric vibration, when vibrating other oscillators, it is not necessary to maintain a rotation - symmetric shape, so it is not necessary to vibrate other oscillators with a uniform load applied to the whole of other oscillators. However, when vibrating the oscillator 10 that has a rotation - symmetric shape and needs to cause rotation - symmetric vibration, it is necessary to maintain a rotation - symmetric shape. Therefore, when the oscillator 10 vibrates in the in - plane direction of the surface 13b of the substrate 1, in order to vibrate the rotation - symmetric oscillator 10 in a rotation - symmetric shape, even if an equal load is applied in the rotation - symmetric direction, if the Young's modulus in each azimuth in the in - plane direction of the substrate 1 is different, the deformation in each azimuth in the in - plane direction of the substrate 1 will be different, and thus the rotation - symmetric shape of the oscillator 10 will be disrupted. For this reason, in the oscillator 10, it is required that the Young's modulus of the material of the oscillator 10 is isotropic.That is, since the piezoelectric layer 21 is provided on the substrate 1 including the first silicon layer 11 having a crystal plane with Miller index (111), the Young's modulus of the first silicon layer 11 having a diamond structure with a crystal plane of Miller index (111) is isotropic. Therefore, when the piezoelectric layer 21 vibrates on the substrate 1, the piezoelectric layer 21 can be vibrated appropriately. As a result, since the piezoelectric layer 21 can be vibrated appropriately, the ring gyroscope 100 can detect the angular velocity accurately.

[0057] Further, in the present embodiment, as described above, the vibrator 10 has a shape that is rotationally symmetric with respect to the center Ce of the piezoelectric layer 21 when viewed from the Z1 direction side. Further, the vibrator 10 is configured to perform a rotationally symmetric vibration with respect to the center Ce of the piezoelectric layer 21. Here, in order for the vibrator 10 having a rotationally symmetric shape to perform a rotationally symmetric vibration, a mechanical property is required in which the Young's modulus of the first silicon layer 11 that dominantly affects the mechanical properties of the vibrator 10 is isotropic in the in-plane direction of the substrate 1. Therefore, in the ring gyroscope 100, the vibrator 10 having a rotationally symmetric shape and performing a rotationally symmetric vibration is provided on the substrate 1 including the first silicon layer 11 having a diamond structure with a crystal plane of Miller index (111) whose Young's modulus is isotropic. Thus, a ring gyroscope 100 that effectively uses the property that the Young's modulus of the first silicon layer 11 having a diamond structure with a crystal plane of Miller index (111) is isotropic can be realized.

[0058] Further, in the present embodiment, as described above, in the Z direction, the thickness Th2 of the second silicon layer 13 is smaller than the thickness Th1 of the first silicon layer 11. Thereby, by making the thickness Th2 of the second silicon layer 13 smaller than the thickness Th1 of the first silicon layer 11, the isotropic deformation of the first silicon layer 11 has a greater influence than the anisotropic deformation of the second silicon layer 13 due to the vibration of the piezoelectric layer 21. Therefore, the substrate 1 can be deformed isotropically. As a result, the vibrator 10 can vibrate rotationally symmetrically on the surface of the substrate 1.

[0059] In addition, in the present embodiment, as described above, the piezoelectric layer 21 is made of lead zirconate titanate as a piezoelectric element material having at least a crystal plane with a Miller index of (100). As a result, since lead zirconate titanate has excellent piezoelectric performance compared to other materials, it is possible to ensure a sufficient driving amount of the piezoelectric layer 21 even when the applied voltage is relatively low, so that it is possible to suppress the acceleration of deterioration of the piezoelectric layer 21.

[0060] In addition, in the present embodiment, as described above, the piezoelectric layer 21 has a ring shape when viewed from the Z1 direction side (one side). As a result, since the area to be vibrated can be made smaller than that of the piezoelectric layer 21 having a disc shape with the same diameter, the power supplied to vibrate the piezoelectric layer 21 can be made relatively small.

[0061] In addition, in the present embodiment, as described above, the vibration excitation unit 2 includes a first electrode 22 provided between the piezoelectric layer 21 and the second silicon layer 13 for applying a voltage to the piezoelectric layer 21, and a second electrode 23 provided on the Z1 direction side of the piezoelectric layer 21 for applying a voltage to the piezoelectric layer 21. The first electrode 22 is made of an electrode material having a crystal plane with a Miller index of (100) grown on the surface 13b on the Z1 direction side of the second silicon layer 13. As a result, since the first electrode 22 is made of an electrode material having a crystal plane with a Miller index of (100), it is possible to form a piezoelectric layer 21 having at least a crystal plane with a Miller index of (100) on the Z1 direction side of the first electrode 22. Therefore, it is possible to obtain a ring gyroscope 100 including a piezoelectric layer 21 capable of ensuring a sufficient driving amount even when the voltage applied by the first electrode 22 and the second electrode 23 is low. Further, by forming the first electrode 22 having a crystal plane with a Miller index of (100) on the Z1 direction side of the second silicon layer 13 having a crystal plane with a Miller index of (100), the shape of the crystal plane of the first electrode 22 and the shape of the crystal plane of the second silicon layer 13 are the same. Therefore, in the crystal structure of the joint portion between the first electrode 22 and the second silicon layer 13, it is possible to suppress the occurrence of strain and non-bonding of crystal structures (misfit dislocations) caused by different shapes of crystal planes.

[0062] Also, in the present embodiment, as described above, each of the lattice misfit between the first electrode 22 and the piezoelectric layer 21 and the lattice misfit between the first electrode 22 and the second silicon layer 13 is 10% or less. Thereby, at each of the joint portions between the piezoelectric layer 21 and the first electrode 22 and between the second silicon layer 13 and the first electrode 22, the occurrence of strain and non-junction of crystal structures (misfit dislocation) due to different lattice constants can be more suppressed.

[0063] Also, in the present embodiment, as described above, the lattice constant of the crystal structure of the first electrode 22 is substantially the same as each of the lattice constant of the crystal structure of the piezoelectric layer 21 and the lattice constant of the crystal structure of the second silicon layer 13 of the substrate 1. Thereby, at each of the crystal structures of the joint portion between the piezoelectric layer 21 and the first electrode 22 and the crystal structure of the joint portion between the second silicon layer 13 and the first electrode 22, the occurrence of strain and non-junction of crystal structures (misfit dislocation) due to different lattice constants of the crystal structures can be further suppressed. As a result, the piezoelectric layer 21 having a crystal plane with a mirror index (100) preferential orientation can be formed on the substrate 1 having a crystal plane with a mirror index (111).

[0064] Also, in the present embodiment, as described above, the substrate 1 includes a silicon dioxide layer 12 formed of amorphous silicon dioxide that is joined to the surface 11a on one side of the first silicon layer 11 and is joined to the surface 13a on the Z2 direction side (the side opposite to the one side) of the second silicon layer 13. Thereby, compared with the case of directly joining the first silicon layer 11 and the second silicon layer 13, the first silicon layer 11 and the second silicon layer 13 can be easily joined via the silicon dioxide layer 12 by a method of performing high-temperature treatment after hydrogen bonding through the silicon dioxide layer 12.

[0065] Also, in the present embodiment, as described above, the substrate 1 is an SOI substrate having a first silicon layer 11 as a handle layer supported when moving the substrate 1, a silicon dioxide layer 12, and a second silicon layer 13 as a device layer. Thereby, the ring gyroscope 100 can be easily manufactured using the SOI substrate.

[0066] Also, in the present embodiment, as described above, the piezoelectric layer 21 is composed of a single-crystal piezoelectric element material having a crystal plane with a mirror index (100) preferential orientation grown on the side opposite to the first silicon layer 11 side of the second silicon layer 13. Thereby, the piezoelectric layer 21 of the single-crystal piezoelectric element material having a crystal plane with a mirror index (100) preferential orientation can generate a sufficient vibration magnitude (driving amount) of the piezoelectric layer 21 at a low voltage as compared with a polycrystalline piezoelectric layer. As a result, since the piezoelectric layer 21 can be vibrated at a low voltage in the ring gyroscope 100, it is possible to suppress the acceleration of deterioration of the piezoelectric layer 21.

[0067] (Modification example) It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the description of the above-described embodiments, and further includes all changes (modification examples) within the meaning and scope equivalent to the scope of claims.

[0068] For example, in the above embodiment, an example in which the substrate 1 is an SOI substrate including the first silicon layer 11, the silicon dioxide layer 12, and the second silicon layer 13 is shown, but the present invention is not limited thereto. In the present invention, the substrate only needs to include the first silicon layer and the second silicon layer. In this case, the first silicon layer and the second silicon layer are joined by pressing the flat surfaces against each other at a high pressure in a high vacuum state.

[0069] In the above-described embodiment, an example is shown in which the piezoelectric layer 21 has a ring shape when viewed from the Z1 direction side. However, the present invention is not limited to this. In the present invention, the vibrator may have a disk shape, a polygonal plate shape, a polygonal ring shape, or a polygonal shape when viewed from the Z1 direction side.

[0070] In the above-described embodiment, an example is shown in which the piezoelectric layer 21 is composed of lead zirconate titanate as a single-crystal piezoelectric element material having a crystal plane with a Miller index (100) preferential orientation. However, the present invention is not limited to this. In the present invention, the vibrator may be formed of a ferroelectric film as a single-crystal piezoelectric element material having a crystal plane with a Miller index (100) preferential orientation.

[0071] In the above-described embodiment, an example is shown in which the piezoelectric layer 21 is composed of a single-crystal piezoelectric element material having a crystal plane with a Miller index (100) preferential orientation. However, the present invention is not limited to this. In the present invention, the piezoelectric layer may be composed of a single-crystal piezoelectric element material having a crystal plane with a Miller index (001) preferential orientation.

[0072] In the above-described embodiment, an example is shown in which the lattice constant of the crystal structure of the piezoelectric layer 21 has substantially the same lattice constant as the lattice constant of the crystal structure of the first electrode 22. However, the present invention is not limited to this. In the present invention, the lattice misfit between the first electrode and the piezoelectric layer may be 10% or less. That is, instead of matching the lattice constant of one unit of the crystal structure of the piezoelectric layer to the lattice constant of one unit of the crystal structure of the first electrode, as an example only, for example, the lattice constant of four units of the crystal structure of the piezoelectric layer may be matched to the lattice constant of three units of the crystal structure of the first electrode.

[0073] In the above embodiment, an example was shown in which the lattice constant of the crystal structure of the first electrode 22 has substantially the same lattice constant as each of the lattice constants of the crystal structures of the second silicon layers 13. However, the present invention is not limited to this. In the present invention, the lattice misfit between the first electrode and the second silicon layer may be 10% or less. That is, instead of matching the lattice constant of one crystal structure of the second silicon layer to the lattice constant of one crystal structure of the first electrode, although this is merely an example, for example, the lattice constant of four crystal structures of the second silicon layer may be matched to the lattice constant of three crystal structures of the first electrode.

Explanation of Signs

[0074] 1 Substrate 2 Vibration excitation unit 10 Vibrator 11 First silicon layer 11a Surface 12 Silicon dioxide layer 13 Second silicon layer 13a Surface 13b Surface 21 Piezoelectric layer 22 First electrode 23 Second electrode 100 Ring gyroscope (vibratory angular rate detector) Ce Center Th1 Thickness Th2 Thickness

Claims

1. A substrate having a first silicon layer with a crystal plane of Miller index (111) and a second silicon layer provided on one side in the thickness direction of the first silicon layer and having a crystal plane of Miller index (100), and a vibration excitation unit including a piezoelectric layer provided on the side opposite to the first silicon layer side of the second silicon layer of the substrate, a vibrator comprising: The piezoelectric layer is composed of a piezoelectric element material having at least a crystal plane of Miller index (100) or Miller index (001) grown on the side opposite to the first silicon layer side of the second silicon layer, a vibration type angular velocity detector.

2. The vibrator has a shape that is rotationally symmetric with respect to the center of the vibrator when viewed from the one side in the thickness direction, and is configured to perform a vibration that is rotationally symmetric with respect to the center of the vibrator, the vibration type angular velocity detector according to claim 1.

3. In the thickness direction, the thickness of the second silicon layer is smaller than the thickness of the first silicon layer, the vibration type angular velocity detector according to claim 1.

4. The piezoelectric layer is composed of lead zirconate titanate as the piezoelectric element material having at least a crystal plane of Miller index (100) or Miller index (001), the vibration type angular velocity detector according to claim 1.

5. The vibrator has a ring shape when viewed from the one side, the vibration type angular velocity detector according to claim 2.

6. The vibration excitation unit is A first electrode provided between the piezoelectric layer and the second silicon layer for applying a voltage to the piezoelectric layer, Further includes a second electrode provided on the one side of the piezoelectric layer for applying a voltage to the piezoelectric layer, The first electrode is composed of an electrode material having a crystal plane of Miller index (100) grown on the surface of the one side of the second silicon layer, the vibration type angular velocity detector according to claim 1.

7. Each of the lattice misfit between the first electrode and the piezoelectric layer and the lattice misfit between the first electrode and the second silicon layer is 10% or less, the vibration type angular velocity detector according to claim 6.

8. The lattice constant of the crystal structure of the first electrode is substantially the same as each of the lattice constant of the crystal structure of the piezoelectric layer and the lattice constant of the crystal structure of the second silicon layer of the substrate, the vibration type angular velocity detector according to claim 7.

9. The vibration type angular velocity detector according to claim 1, wherein the substrate further includes a silicon dioxide layer composed of amorphous silicon dioxide that is joined to the surface on one side of the first silicon layer and to the surface on the side opposite to the one side in the thickness direction of the second silicon layer.

10. The vibration type angular velocity detector according to claim 9, wherein the substrate is an SOI (Silicon on Insulator) substrate having the first silicon layer as a handle layer supported when moving the substrate, the silicon dioxide layer, and the second silicon layer as a device layer.

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