JP2010145121A - Piezoelectric vibrator and vibrating gyroscope device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric vibrator whose electromechanical coupling coefficient has been improved, and which uses flexural vibration, and to provide a vibrating gyroscope device for acquiring stable sensitivity. <P>SOLUTION: The vibrating gyroscope device 1 includes a piezoelectric substrate 3, and an upper surface electrode 2 and an underside electrode 4, and vibrates according to the potential difference between the upper surface electrode 2 and the undersurface electrode 4 in the normal line direction of a major face. The undersurface electrode 4 includes an electrode thickness different from a thickness value at which the electromechanical coupling coefficient becomes a lower limit extreme value. Here, a frequency signal is applied to the upper surface electrode 2, and the undersurface electrode 4 is connected to a reference potential. The electromechanical coupling coefficient of this vibrating gyroscope device changes by changing the thickness of the undersurface electrode 4 and displays the lower limit extreme value of the electromechanical coupling coefficient. The vibrating gyroscope device includes a characteristic wherein if the thickness of the undersurface driving electrode deviates from the value at which the electromechanical coupling coefficient becomes the lower limit extreme value, the electromechanical coupling coefficient steeply rises up to a value to be clipped. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a piezoelectric vibrator that excites vibration in the normal direction of the principal surface by applying a frequency signal to the electrodes provided on both principal surfaces of the plate-like piezoelectric substrate, and applies Coriolis force to the piezoelectric vibrator. It is related with the vibration gyro apparatus which detects the rotational angular velocity of a piezoelectric vibrator from the detection signal excited by electromechanical vibration by doing.

  In a filter or gyro, a piezoelectric body that vibrates electromechanically may be used. In a piezoelectric vibrator using flexural vibration having a displacement in a direction perpendicular to the main surface of the piezoelectric body, a frequency signal is applied to the electrodes provided on both main surfaces of the plate-like piezoelectric substrate so that the main surface normal direction is obtained. Bending vibration is excited. In particular, in the case of a piezoelectric vibrator used in a gyroscope, the rotation of the piezoelectric vibrator is detected from a detection signal excited by the Coriolis force acting in a direction perpendicular to the vibration direction.

In the case of a gyro, the detection accuracy of rotation depends on the mechanical amplitude and voltage conversion efficiency of the piezoelectric vibrator. For this reason, there is a demand to increase the electromechanical coupling coefficient, which is the main characteristic of the piezoelectric vibrator, to increase the mechanical amplitude and the voltage conversion efficiency. Conventionally, in a piezoelectric body that uses the vibration of a bulk wave that is totally reflected at the interface between the electrode and air without using bending vibration, the lower surface driving electrode of the piezoelectric substrate is made thicker than the upper surface driving electrode. In some cases, the electromechanical coupling coefficient of the piezoelectric body is increased (for example, see Patent Document 1).
JP 2006-319479 A

  On the other hand, a piezoelectric vibrator using flexural vibration has a vibration form different from that of the bulk wave of the above-mentioned patent document. Therefore, a measure for improving the electromechanical coupling coefficient of the piezoelectric vibrator is described in the bulk of the above-mentioned patent document. It does not always coincide with the case of waves.

  Therefore, the inventors have conducted intensive research and found that in a piezoelectric vibrator using flexural vibration, the change in electromechanical coupling coefficient with respect to the change in the electrode thickness of the lower surface drive electrode has a specific extreme value. Invented the technical idea of the invention.

  An object of the present invention is to provide a piezoelectric vibrator using flexural vibration with improved electromechanical coupling coefficient, and a vibration gyro apparatus capable of obtaining stable sensitivity.

  The present invention is a piezoelectric vibrator that includes a piezoelectric substrate, an upper surface driving electrode, and a lower surface driving electrode, and vibrates in the normal direction of the main surface in accordance with a potential difference between the upper surface driving electrode and the lower surface driving electrode. The electrode thickness excluding the value at which the electromechanical coupling coefficient becomes the lower limit extreme value. Here, a frequency signal is applied to the upper surface driving electrode, and the lower surface driving electrode is connected to a reference potential. The electromechanical coupling coefficient changes by changing the electrode thickness of the lower surface driving electrode. When the electrode thickness of the lower surface driving electrode deviates from the value at which the electromechanical coupling coefficient becomes the lower limit extreme value, the electromechanical coupling coefficient reaches the value at which clipping occurs. It has the characteristic of rising sharply.

  Since this piezoelectric vibrator has the above characteristics, the electromechanical coupling coefficient decreases only in the vicinity of the lower limit extreme value of the resonance frequency that changes according to the electrode thickness of the lower surface driving electrode. Therefore, the electromechanical coupling coefficient can be improved by setting the lower surface driving electrode to an electrode thickness that excludes the electromechanical coupling coefficient from the lower limit value.

  The electromechanical coupling coefficient is changed by changing the electrode thickness of the lower surface driving electrode, and has an upper limit extreme value of the electromechanical coupling coefficient. The lower surface driving electrode has an electrode thickness at which the electromechanical coupling coefficient becomes the upper limit extreme value. Is preferable. Thus, the electromechanical coupling coefficient can be maximized by setting the lower surface driving electrode to an electrode thickness at which the electromechanical coupling coefficient becomes the upper limit extreme value.

  It is preferable that the piezoelectric substrate is a single crystal of lithium niobate and the lower surface driving electrode is a tungsten electrode. A single crystal of lithium niobate has a large electromechanical coupling coefficient. Since the tungsten electrode has a high melting point, it is possible to suppress diffusion of the electrode due to heat load, and since the specific gravity is large and the specific acoustic impedance is large, damping of the elastic wave mechanical vibration excited by the piezoelectric vibrator can be suppressed. Since the aluminum electrode has a small specific resistance, the series equivalent resistance of the piezoelectric vibrator can be suppressed.

  The vibration gyro apparatus according to the present invention preferably includes the above-described piezoelectric vibrator, a drive unit that applies a frequency signal to the piezoelectric vibrator, and a detection unit that detects Coriolis force acting on the piezoelectric vibrator. . The sensitivity of the gyro can be stabilized by using the above-described piezoelectric vibrator having a large electromechanical coupling coefficient.

  According to this invention, the electromechanical coupling coefficient can be improved by setting the lower surface driving electrode of the piezoelectric vibrator using the bending vibration to an electrode thickness that is excluded from the value at which the electromechanical coupling coefficient becomes the lower limit extreme value.

  A vibration gyro apparatus according to a first embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a configuration example of a vibration gyro device. 1A is a top view, FIG. 1B is a central sectional view, FIG. 1C is an A-A ′ sectional view, and FIG. 1D is a B-B ′ sectional view.

  The vibrating gyroscope device 1 is line-symmetric with respect to the X-axis as a symmetric axis and line-symmetrical with respect to the Y-axis as a symmetric axis so that rotation about two orthogonal axes (X-axis and Y-axis) can be detected. It is configured. Further, the support substrate 5, the lower surface electrode 4, the piezoelectric substrate 3, and the upper surface electrode 2 are laminated in order from the bottom along the Z axis perpendicular to the XY plane.

The support substrate 5 and the piezoelectric substrate 3 are right-handed Euler angles (0 °, 50 °, 0 °) lithium niobate (LiNbO ₃ ) substrates, the support substrate 5 is 0.34 mm thick, and the piezoelectric substrate 3 is 1 μm. It is thick. By employing lithium niobate, the electromechanical coupling coefficient and the Q value of the vibrator can be increased, and good sensitivity characteristics can be obtained. If lithium tantalate is used instead of lithium niobate, the balance between sensitivity and temperature characteristics can be improved, and temperature stability can be improved if quartz is used. The lower surface electrode 4 is a tungsten (W) electrode, and the upper surface electrode 2 is an aluminum (Al) electrode. Since the tungsten electrode has a high melting point, it is possible to suppress diffusion of the electrode due to heat load, and since the specific gravity is large and the specific acoustic impedance is large, damping of the elastic wave mechanical vibration excited by the piezoelectric vibrator can be suppressed. Since the aluminum electrode has a small specific resistance, the series equivalent resistance of the piezoelectric vibrator can be suppressed.

  The piezoelectric substrate 3 is divided into an inner region 3A, a frame-like region 3B, and an outer region 3C when viewed from the piezoelectric main surface (XY plane). The frame-shaped region 3B has a circular inner shape / circular outer shape with an inner diameter of 400 μm and an outer diameter of 500 μm. The inner region 3 </ b> A is a circle having a diameter of 300 μm and is bonded to the support substrate 5 via the lower surface electrode 4. The outer region 3 </ b> C has a circular inner shape and a rectangular outer shape with an inner diameter of 600 μm, and is bonded to the support substrate 5 via the lower surface electrode 4. Four inner open holes 31 and four inner beam portions 32 are provided between the inner region 3A and the frame-like region 3B, and four outer open holes are provided between the outer region 3C and the frame-like region 3B. 33 and four inner beam portions 32 are provided. The inner beam portion 32 and the outer beam portion 34 are beam-like regions having a width of 20 μm along the 45 °, 135 °, 225 °, and 315 ° directions, where the X-axis positive direction in the XY plane is 0 °. . The inner beam portion 32 and the outer beam portion 34 support the frame-shaped region 3 </ b> B in a state where it floats from the support substrate 5. The inner opening hole 31 and the outer opening hole 33 expose the inner surface and the outer surface of the frame-shaped region 3B, respectively. The support substrate 5 includes an inner region 5A, a vibration region 5B, and an outer region 5C on the XY plane. The vibration region 5B is a region in which a vibration space is provided by digging the support substrate 5 at a depth of 3 μm from the upper main surface into a circular inner shape / circular outer shape frame having an inner shape of 300 μm and an outer shape of 600 μm. The region 3B, the inner opening hole 31, the inner beam portion 32, the outer opening hole 33, and the inner beam portion 32 are provided at positions facing each other. The vibration space communicates with the inner opening hole 31 and the outer opening hole 33, and prevents interference between the frame-shaped region 3B and the support substrate 5. The inner region 5A is a region having a diameter of 300 μm, and the inner region 3A of the piezoelectric substrate 3 is bonded to the upper main surface thereof. The outer region 5C is a region having an inner diameter of 600 μm, and the outer region 3C of the piezoelectric substrate 3 is bonded to the upper main surface thereof. In addition to using the same piezoelectric material as that of the piezoelectric substrate 3, the support substrate 5 may be made of Si or glass, which has a different thermal expansion coefficient from the piezoelectric substrate 3 but has excellent heat resistance and is easily available and inexpensive.

  The upper surface electrode 2 includes eight drive detection electrodes 2A, eight circuit connection electrodes 2B, four reference potential connection electrodes 2C, and eight wirings 2D. The drive detection electrode 2A is the upper surface drive electrode of the present invention, and is patterned on the upper surface of the frame-like region 3B. The circuit connection electrode 2B and the reference potential connection electrode 2C are patterned on the upper surface of the outer region 3C. The wiring 2D is provided from the frame-like region 3B to the outer region 3C via the outer beam portion. Two drive detection electrodes 2A are disposed on both sides of the positive X axis, both sides of the negative X axis, both sides of the positive Y axis, and both sides of the negative Y axis. Specifically, each drive detection electrode 2A is about 0 ° to 30 °, 60 ° to 90 °, 90 ° to 120 °, 150 ° to 180 °, with the Y-axis positive direction on the XY plane being 0 °. It occupies ranges of 180 ° to 210 °, 240 ° to 270 °, 270 ° to 300 °, 330 ° to 360 °. The adjacent drive detection electrodes 2A are spaced at an interval of about 5 μm. The circuit connection electrode 2B is connected to a drive detection circuit that will be described in detail later. The reference potential connection electrode 2C is connected to the lower surface electrode 4 through a through hole. The wiring 2D connects between the drive detection electrode 2A and the circuit connection electrode 2B, and is joined to the piezoelectric substrate 3 via the insulating layer 2E. Since the insulating layer 2E is provided, no voltage is excited in the wiring 2D due to the displacement of the beam portion. The lower electrode 4 has a region facing the drive detection electrode 2A which is the lower drive electrode of the present invention and is provided on the entire lower main surface of the piezoelectric substrate 3 and is connected to the reference potential via the reference potential connection electrode 2C. . Each drive detection electrode 2A faces the lower surface electrode 4 and is electromechanically coupled to the displacement in the Y-axis direction and the displacement in the X-axis direction and the Y-axis direction of the frame-like region 3B.

  In the vibration gyro apparatus 1 described above, the frame-like region 3B of the piezoelectric substrate 3 constitutes eight piezoelectric vibrating bodies in which the drive detection electrode 2A and the lower surface electrode 4 are provided.

  FIG. 2 is a circuit diagram illustrating a drive detection circuit connected to the vibration gyro device 1. The drive detection circuit of the vibration gyro apparatus 1 includes a frequency signal generation circuit 6, differential circuits 7A and 7B, and smoothing circuits 8A and 8B. A ground is connected to the reference potential connection electrode 2C.

  The frequency signal generation circuit 6 is connected to the eight circuit connection electrodes 2B via the drive resistor R, and gives a frequency signal to each of the eight drive detection electrodes 2A. The frequency signals given to each drive detection electrode 2A have the same phase and the same amplitude. The frequency is such that the vibration in the Z-axis direction of the frame-like region 3B forms a vibration antinode at positions on the X-axis and Y-axis (0 °, 90 °, 180 °, 270 °) on the XY plane. The resonance frequency forms a vibration node at a position (45 °, 135 °, 225 °, 315 °) supported by the beam portion.

  Of the four drive detection electrodes 2A arranged on both sides of the Y axis, the two drive detection electrodes 2A arranged in the negative direction of the X axis (left side in the figure) are connected to the first input terminal of the differential circuit 7A. The In addition, the two drive detection electrodes 2A arranged in the positive X-axis direction (right side in the figure) are connected to the second input terminal of the differential circuit 7A. Of the four drive detection electrodes 2A arranged on both sides of the X axis, the two drive detection electrodes 2A arranged in the negative Y-axis direction (lower side) are connected to the first input terminal of the differential circuit 7B. The two drive detection electrodes 2A arranged in the positive Y-axis direction (upper side) are connected to the second input terminal of the differential circuit 7B.

  The output terminals of the differential circuits 7A and 7B are connected to the smoothing circuits 8A and 8B, and the differential circuits 7A and 7B output the voltage difference between the first input terminal and the second input terminal. Smoothing circuits 8A and 8B smooth the output voltages of the differential circuits 7A and 7B.

  FIG. 3 is a diagram for explaining the operation of the vibrating gyroscope device 1. 3A shows an example of rotating around the X axis, and FIG. 3B shows an example of rotating around the Y axis.

  When bending vibration is performed at the resonance frequency, a Coriolis force is applied in the X-axis direction when an angular velocity around the Y-axis is applied to the vibration gyro device. Then, the phases of the frequency signals applied to the four drive detection electrodes 2A arranged on both sides of the Y axis are the same as the drive detection electrode 2A arranged in the X axis positive direction and the drive arranged in the X axis negative direction. The detection electrode 2A changes in the opposite direction. For this reason, the differential output by the differential circuit 7A becomes a voltage corresponding to the magnitude of the Coriolis force.

  Further, when an angular velocity around the X axis is applied to the vibration gyro device, a Coriolis force is applied in the Y axis direction. Then, the phases of the frequency signals applied to the four drive detection electrodes 2A arranged on both sides of the X axis are the drive detection electrode 2A arranged in the Y axis positive direction and the drive arranged in the Y axis negative direction. The detection electrode 2A changes in the opposite direction. For this reason, those differential outputs by the differential circuit 7B become voltages according to the magnitude of the Coriolis force.

  In the state where the vibration gyro apparatus 1 is not rotating, the frequency signals are removed by the differential circuits 7A and 7B because they have the same phase and the same amplitude. In addition, a signal that excites each drive detection electrode when an impact is applied to the vibration gyro device, a signal that excites the drive detection electrode arranged along the Y axis when rotating around the X axis, Since the signals excited in the drive detection electrodes arranged along the X axis during the rotation of the rotation are still in phase and amplitude, they are removed by the differential circuits 7A and 7B.

  FIG. 4 is a diagram for explaining the relationship between the electrode thickness of the bottom electrode 4 and the electromechanical coupling coefficient. Here, for the three patterns in which the electrode thickness of the upper surface electrode 2 is (0.5 μm, 1.0 μm, 1.5 μm), the above relationship is examined based on the result of resonance analysis using the finite element method.

In any of the three patterns, the electromechanical coupling coefficient changes as the electrode thickness of the lower surface electrode 4 changes within the range of 0.1 × 10 ^{−3 to} 3.0 × 10 ⁻³ mm. When the upper electrode 2 has an electrode thickness of 0.5 μm, the lower electrode has an electrode thickness of 0.1 × 10 ⁻³ mm. When the upper electrode 2 has an electrode thickness of 1.0 μm, the lower electrode has an electrode thickness of 0.3 × 10 ⁻³ mm. When the electrode thickness of the upper electrode 2 is 1.5 μm, the electrode thickness of the lower electrode is 0.5 × 10 ⁻³ mm, and the electromechanical coupling coefficient shows the lower limit extreme value. Further, when the electrode thickness deviates therefrom, the electromechanical coupling coefficient rises steeply to a specific value and shows a clipped state. Therefore, a sufficient electromechanical coupling coefficient can be obtained if the electromechanical coupling coefficient is an electrode thickness of the bottom electrode that is excluded from the value indicating the lower limit extreme value. The extreme value of the resonance frequency is similarly generated even if the plate thickness of the piezoelectric substrate 3 and the electrode thickness of the upper surface electrode 2 are changed in the vibration gyro device 1. A sufficient electromechanical coupling coefficient can be obtained by appropriately setting the electrode thickness of the lower surface electrode.

When the upper electrode 2 has an electrode thickness of 0.5 μm, the lower electrode has an electrode thickness of 2.0 × 10 ⁻³ mm. When the upper electrode 2 has an electrode thickness of 1.0 μm, the lower electrode has an electrode thickness of 2.5 × 10 ⁻³ mm. The mechanical coupling coefficient showed the upper limit extreme value. Therefore, the maximum electromechanical coupling coefficient can be obtained if the electromechanical coupling coefficient has the electrode thickness of the lower surface electrode that indicates the upper limit extreme value.

  Next, a method for manufacturing the vibration gyro device 1 will be described. FIG. 5 is a diagram for explaining a manufacturing flow of the vibrating gyroscope device 1. Here, a case where a thin film of a piezoelectric substrate is formed by ion implantation is shown.

  First, a recess is provided in the support substrate 5 by reactive ion etching or the like, a copper film is formed as a sacrificial layer in this recess, and the surface is planarized by CMP or the like (S101).

  Next, a piezoelectric single crystal having a predetermined thickness is prepared, and hydrogen ions are implanted from the main surface (S102). The piezoelectric single crystal is a lithium niobate substrate, and hydrogen ions are implanted at a depth of about 1 μm from the ion implantation surface by implanting hydrogen ions with an acceleration energy of 150 KeV and a dose of 1.0 × 10 17 atoms / cm 2. Form a layer.

  Next, an electrode film to be the lower surface electrode 4 is formed on the sacrificial layer forming surface of the support substrate 5, and the surface is polished and flattened by CMP treatment or the like, and bonded to the ion implantation surface of the piezoelectric single crystal (S103). .

  Next, the piezoelectric single crystal to which the support substrate 5 is bonded is placed in a reduced-pressure atmosphere, heated to 500 ° C., and peeled off by a hydrogen ion implantation layer (S104). As a result, a piezoelectric single crystal thin film supported by the support substrate 5 is formed as the piezoelectric substrate 3. Thereby, since the piezoelectric substrate 3 can be made into an extremely thin film, the amount of piezoelectric single crystal used can be suppressed.

  Next, mirror finishing is performed by CMP or the like on the upper main surface of the piezoelectric substrate 3 which is a peeling surface (S105).

  Next, the upper surface electrode 2 is formed by patterning with aluminum on the upper main surface of the piezoelectric substrate 3 by electron beam vapor deposition and photolithography (S106).

  Next, a resist film is formed on the upper main surface of the piezoelectric substrate 3 (S107). Then, an etching window is formed in the resist film using a photolithography technique (S108).

  Next, the inner opening hole 31 and the outer opening hole 33 are formed by introducing an etching solution or etching gas into the etching window. Then, the sacrificial layer, which is a copper film, is removed by introducing a copper etchant into the sacrificial layer from the inner open hole 31 and the outer open hole 33. Thereby, a vibration space is formed below the frame-shaped region 3B (S109).

  After the sacrificial layer is removed, the resist film is removed to form a through hole that connects the reference potential connection electrode 2C and the lower electrode 4 and packaging (S110). Thereafter, aluminum is thickened on the other electrodes excluding the drive detection electrode 2A on the upper main surface of the piezoelectric substrate 3, and the wiring electrical resistance at these electrodes is lowered (S111).

  The vibration gyro apparatus is manufactured by adopting the above process.

It is a figure explaining the structure of the vibration gyro apparatus which concerns on 1st Embodiment. It is a figure explaining the circuit structure of the drive detection circuit of the vibration gyro apparatus shown in FIG. It is a figure explaining operation | movement of the vibration gyro apparatus shown in FIG. It is a figure explaining the relationship between the electromechanical coupling coefficient by vibration analysis, and a lower surface electrode. It is a figure explaining the manufacturing flow of the vibration gyro apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vibration gyro apparatus 2 ... Upper surface electrode 2A ... Drive detection electrode 2B ... Circuit connection electrode 2C ... Reference electric potential connection electrode 2D ... Wiring 2E ... Insulating layer 3 ... Piezoelectric substrate 31 ... Inner opening hole 32 ... Inner beam part 33 ... Outer opening Hole 34 ... Outer beam portion 3A ... Inner region 3B ... Frame-like region 3C ... Outer region 4 ... Bottom electrode 5 ... Support substrate 5A ... Inner region 5B ... Vibration region 5C ... Outer region 6 ... Frequency signal generating circuit 7A, 7B ... Difference Dynamic circuit 8A, 8B ... Smoothing circuit

Claims (4)

A plate-like piezoelectric substrate; an upper surface driving electrode provided on the upper main surface of the piezoelectric substrate to which a frequency signal is applied; and a lower surface driving electrode provided on the lower main surface of the piezoelectric substrate and connected to a reference potential. A piezoelectric vibrator that vibrates in a principal surface normal direction based on a potential difference between the upper surface driving electrode and the lower surface driving electrode,
The electromechanical coupling coefficient of the piezoelectric vibrator is changed by changing the electrode thickness of the lower surface driving electrode to indicate the lower limit extreme value of the electromechanical coupling coefficient, and the electromechanical coupling coefficient becomes the lower limit extreme value When the electrode thickness of the lower surface driving electrode is deviated from, the electromechanical coupling coefficient has a characteristic of rising steeply to the value to clip,
The piezoelectric vibrator according to claim 1, wherein the lower surface drive electrode has an electrode thickness excluding the value at which the electromechanical coupling coefficient becomes the lower limit extreme value. The electromechanical coupling coefficient of the piezoelectric vibrator is changed by changing the electrode thickness of the lower surface driving electrode, and has an upper limit extreme value of the electromechanical coupling coefficient,
2. The piezoelectric vibrator according to claim 1, wherein the lower surface driving electrode has an electrode thickness at which the electromechanical coupling coefficient becomes the upper limit extreme value. The piezoelectric substrate is a single crystal of lithium niobate,
The lower surface drive electrode is a tungsten electrode,
The piezoelectric vibrator according to claim 1, wherein the upper surface drive electrode is an aluminum electrode. The piezoelectric vibrator according to any one of claims 1 to 3,
A drive unit for applying the frequency signal to the piezoelectric vibrator;
A vibration gyro apparatus comprising: a detection unit that detects Coriolis force acting on the piezoelectric vibrator.

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