JP5419488B2 - Piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric element used for a gyro sensor for a camera shake correction system, a navigation system, and a posture control system, as well as for a vibration shock detection of a device, a shock sensor for a security system, and the like.

  Piezoelectric materials have high electro-mechanical conversion efficiency, and can be used for various sensors because they can realize small and highly sensitive piezoelectric elements for sensors. In recent years, a technology to form a piezoelectric film with a thickness of several μm on a large-area substrate with good reproducibility and a technology to finely process the piezoelectric film have been established, and more and more small piezoelectric elements for sensors can be manufactured with high productivity. It has become like this.

  Under such circumstances, new technical issues have also arisen. One of them is capacitive coupling between electrodes. A plurality of electrodes are often formed on a piezoelectric element for a sensor. The distance between the electrodes is becoming extremely narrow, and a piezoelectric material such as lead zirconate titanate (PZT), which has particularly high piezoelectricity, is a dielectric. Since the rate is high, the capacitance between the electrodes increases, so-called capacitive coupling in which an electric signal handled by one electrode jumps to the other electrode becomes large, and the influence on the sensor performance cannot be ignored.

  The capacitive coupling will be described in a little more detail with reference to Patent Document 1. FIG. 8 is a diagram of a piezoelectric element according to Conventional Example 1. FIG. 8A is a perspective view, and FIG. 8B is a cross-sectional view. In order to make the explanation easy to understand, the structure of the piezoelectric element is a cantilever-like piezoelectric element in which one end side is free to vibrate and one end side is fixed. The perspective view is viewed from a direction in which one end side is free (the one end fixed side is not shown). A lower electrode 504, a piezoelectric film 506, and upper electrodes 501, 502, and 503 are formed on the substrate 509. The piezoelectric film 506 is previously polarized in the thickness direction as indicated by the arrow. With such a configuration, when an AC voltage is applied between the lower electrode 504 and the upper electrode 503, the piezoelectric element can be bent and oscillated in a direction perpendicular to the piezoelectric film forming surface, and the lower electrode 504 and the upper electrode 503 can be vibrated. It has been conventionally known that when an AC voltage having an opposite phase is applied between the electrode 501 and the upper electrode 502, bending vibration can be performed in a direction parallel to the piezoelectric film forming surface. For example, in order to use this piezoelectric element for a gyro piezoelectric element, several combinations are conceivable, but it can be realized by using the upper electrode 501 and the upper electrode 502 as drive electrodes and the upper electrode 503 as a detection electrode. Here, when considering miniaturization of the piezoelectric element, it is necessary not to increase the resonance frequency of the piezoelectric element in order to maintain the magnitude of the vibration amplitude. Since the resonance frequency is inversely proportional to the square of the length of the piezoelectric element and proportional to the width and thickness, the piezoelectric element becomes an elongated shape when it is downsized while maintaining the resonance frequency. On the other hand, since the capacitance between wirings is inversely proportional to the interval between adjacent electrodes and proportional to the length, the capacitance between wirings increases when the piezoelectric element is miniaturized. That is, the smaller the piezoelectric element is, the larger the capacitive coupling becomes, and the AC voltage applied to the upper electrode 501 and the upper electrode 502 flows into a large amount (strongly) into the upper electrode 503 disposed next to each other. This leads to a loss of stabilization of the detection output.

  As a countermeasure against the influence of capacitive coupling in Patent Document 1, for example, conventional techniques for reducing capacitive coupling described in Patent Documents 2 and 3 are known. This prior art mainly relates to a piezoelectric element for a gyro sensor, and is a technique that can reduce capacitive coupling by stabilizing the piezoelectric film in the piezoelectric element and stabilize the detection output with respect to the applied angular velocity.

  Patent Document 2 describes that the piezoelectric elements are spaced apart in the lateral direction as a measure for reducing capacitive coupling. FIG. 9 is a diagram of a piezoelectric element according to Conventional Example 2. FIG. 9A is a perspective view, and FIG. 9B is a cross-sectional view. A lower electrode 514, a piezoelectric film 516, and upper electrodes 511, 512, and 513 are formed on the substrate 519. The piezoelectric film 516 is previously polarized in the thickness direction as indicated by the arrow. The piezoelectric film 516 and the lower electrode 514 between the wirings of the upper electrodes 511, 512, and 513 are scraped, and the upper electrodes 511, 512, and 513 are spaced apart from each other in the width direction of the piezoelectric element. As a result, the space between the wires is widened, the capacitance between the wires is suppressed, that is, capacitive coupling is suppressed, and the detection output is stabilized.

  Further, Patent Document 3 describes that as a measure for reducing capacitive coupling, the piezoelectric element is spaced apart in the longitudinal direction and at the same time, the upper electrode is routed as an insulator. FIG. 10 shows a diagram of a piezoelectric element according to Conventional Example 3. FIG. 10A is a perspective view, and FIG. 10B is a cross-sectional view. A lower electrode 524, a piezoelectric film 526, and upper electrodes 521, 522, and 523 are formed on the substrate 529. The piezoelectric film 526 is previously polarized in the thickness direction as shown by the arrow. The upper electrode 523 is spaced apart from the upper electrodes 521 and 522 in the longitudinal direction of the piezoelectric element, and at the same time, the upper electrode 523 is routed on the insulator 528, thereby suppressing inter-wiring capacitance, that is, capacitive coupling. This leads to stabilization of the detection output.

JP 2005-227110 A JP 2005-249395 A JP 2003-227719 A

  However, the disposition of the upper electrode causes a decrease in the drive detection efficiency of the piezoelectric element. Specifically, in FIGS. 8 to 9, the upper electrode 503 and the upper electrode 513 are for driving or detecting bending vibration of the piezoelectric element generated in a direction perpendicular to the piezoelectric film forming surface. It is preferable in terms of efficiency to form the entire width of the. However, if the piezoelectric films are spaced apart in the width direction, the detection efficiency decreases accordingly. If the piezoelectric film 516 and the lower electrode 514 between the wirings of the upper electrodes 511, 512, and 513 are removed, the performance of the piezoelectric film 516 is deteriorated due to damage during processing, and the piezoelectric element drive detection efficiency is further reduced.

  Further, in FIG. 10, if the upper electrodes 521 and 522 are spaced apart in the longitudinal direction of the piezoelectric element, they cannot be properly placed at the location where the bending vibration of the piezoelectric element is generated, which also reduces the drive detection efficiency of the piezoelectric element. become. Although it is conceivable to place the electrodes apart from each other on the front and back of the substrate, the accuracy of alignment between the upper electrodes separated on the front and back of the substrate is deteriorated, although the drive detection efficiency and capacitive coupling of the piezoelectric element can be prevented. It does not lead to stabilization.

  As described above, there is a problem that the disposition of the upper electrode leads to a decrease in drive detection efficiency of the piezoelectric element. Therefore, the present invention has an object to provide a piezoelectric element for a sensor that has high sensitivity and stable output, that is, excellent S / N, without reducing the drive detection efficiency of the piezoelectric element and reducing capacitive coupling. To do.

  In order to solve the above-described problems, in the piezoelectric element of the present invention, at least one embedded electrode is provided in the piezoelectric film, and at least one of the embedded electrodes is connected to a reference potential that is an electrically stable potential. A reference electrode, an electrode for driving or detecting displacement in a direction parallel to the film-forming surface of the piezoelectric film, and an electrode for driving or detecting displacement in a direction perpendicular to the film-forming surface of the piezoelectric film Thus, the reference electrode is sandwiched in the thickness direction. With this configuration, the capacitive coupling between the electrodes sandwiching the embedded electrode connected to an electrically stable potential can be almost eliminated, and at the same time, the electrode can be ideally arranged at a location where displacement distortion of the piezoelectric element occurs, The output can be stabilized without reducing the drive detection efficiency of the piezoelectric element.

That is, according to the present invention, on a substrate, a lower electrode, a piezoelectric film, an upper electrode is formed, to enable the drive or detecting the displacement of the directions parallel and perpendicular to the deposition surface of the piezoelectric film A piezoelectric element, wherein at least one embedded electrode is provided on the piezoelectric film, and at least one of the embedded electrodes is a reference electrode connected to a reference potential which is an electrically stable potential, and the upper electrode and An alternating voltage is applied between the reference electrodes to drive or detect displacement in a direction parallel to the film formation surface of the piezoelectric film, and an alternating voltage is applied between the lower electrode and the reference electrode, Drive or detect a displacement in a direction perpendicular to the surface on which the piezoelectric film is formed , or apply an AC voltage between the upper electrode and the reference electrode so as to be perpendicular to the surface on which the piezoelectric film is formed. Drive or detect directional displacement , By applying an AC voltage between the lower electrode and the reference electrode, the piezoelectric element is obtained, characterized in that the driving or detecting a direction parallel displacement relative to the film formation surface of the piezoelectric film.

  The present invention provides an electrode for driving or detecting displacement in a direction parallel to the film formation surface of the piezoelectric film by providing at least one embedded electrode in the piezoelectric film and dividing the piezoelectric film into two or more in the thickness direction. And electrodes for driving or detecting displacement in the direction perpendicular to the film formation surface of the piezoelectric film can be formed in different layers, and the piezoelectric generated in the direction perpendicular to the film formation surface of the piezoelectric film. In the bending vibration of the element, it is not necessary to arrange the electrodes apart from each other, so that the electrodes can be formed in a wider area than before. That is, it is possible to provide a piezoelectric element for a sensor that can obtain high sensitivity efficiently.

  Further, at least one of the embedded electrodes is a reference electrode connected to a reference potential that is an electrically stable potential, and an electrode for driving or detecting a displacement in a direction parallel to the film formation surface of the piezoelectric film; By adopting a configuration in which the reference electrode is sandwiched in the thickness direction by an electrode for driving or detecting a displacement in a direction perpendicular to the film formation surface of the piezoelectric film, the displacement in a direction parallel to the film formation surface of the piezoelectric film is reduced. Capacitive coupling generated between the electrode for driving or detecting and the electrode for driving or detecting displacement in the direction perpendicular to the film formation surface of the piezoelectric film can be almost eliminated. Since the distance between the electrodes is determined by the thickness of the piezoelectric film, it is usually extremely narrow, and the capacitance between the wirings is increased. However, in order to place a stable reference potential between the electrodes, The electric field generated by the signal to be handled is interrupted by the reference electrode, and the influence on the other electrode can be extremely reduced. The relative dielectric constant of PZT and the like, which is a representative of highly piezoelectric materials, is several hundred to several thousand times higher than that of a substrate material such as air or silicon. Therefore, when PZT is used for the piezoelectric film, an electrode The effect of capacitive coupling between them appears greatly. Therefore, the effect of reducing the capacitive coupling of the present invention is particularly great when PZT is used for the piezoelectric film. That is, it is possible to provide a sensor piezoelectric element with a stable output.

  Furthermore, in processing and forming each electrode and each piezoelectric film layer, a method of arranging the upper electrode separately on the front and back sides of the substrate is conceivable, but this requires alignment processing from both sides of the substrate that is difficult to obtain accuracy. Come. However, the present invention eliminates the need for positioning from both sides, which is difficult to obtain accuracy, and can be processed and formed only by positioning from one side, so that the electrodes can be arranged with high accuracy with respect to the piezoelectric element, A piezoelectric element for a sensor having a stable output can be provided.

The figure of the piezoelectric element which concerns on Embodiment 1 of this invention is shown. 1A is a perspective view, and FIG. 1B is a cross-sectional view. The figure of the piezoelectric element which concerns on Embodiment 2 of this invention is shown. 2A is a perspective view, and FIG. 2B is a cross-sectional view. The figure of the piezoelectric element which concerns on Embodiment 3 of this invention is shown. 3A is a perspective view, and FIG. 3B is a cross-sectional view. The figure of the piezoelectric element which concerns on the Example of this invention is shown. 4A is a top view and circuit connection diagram, FIG. 4B is a cross-sectional view taken along the line AA in FIG. 4A, and FIG. 4C is a cross-sectional view taken along the line BB in FIG. . The figure after the piezoelectric element board | substrate processing which concerns on the Example of this invention is shown. 5A is a top view, and FIG. 5B is a cross-sectional view taken along the line CC in FIG. 5A. The sensitivity measurement result of a piezoelectric element is shown. The measurement result of the jump amount of the drive signal to the detection electrode is shown. The figure of the piezoelectric element which concerns on the prior art example 1 is shown. FIG. 8A is a perspective view, and FIG. 8B is a cross-sectional view. The figure of the piezoelectric element which concerns on the prior art example 2 is shown. FIG. 9A is a perspective view, and FIG. 9B is a cross-sectional view. The figure of the piezoelectric element which concerns on the prior art example 3 is shown. FIG. 10A is a perspective view, and FIG. 10B is a cross-sectional view.

  The piezoelectric element according to the present invention is characterized in that at least one embedded electrode is provided in the piezoelectric film, and at least one of the embedded electrodes is used as a reference electrode connected to a reference potential which is an electrically stable potential, The reference electrode is sandwiched in the thickness direction by the electrode for driving or detecting the displacement in the direction parallel to the film formation surface and the electrode for driving or detecting the displacement in the direction perpendicular to the film formation surface of the piezoelectric film. It is comprised so that.

  Hereinafter, embodiments of the present invention will be described in detail.

(Embodiment 1)
FIG. 1 shows a diagram of a piezoelectric element according to Embodiment 1 of the present invention. 1A is a perspective view, and FIG. 1B is a cross-sectional view. A lower electrode 3, a piezoelectric film 7, a buried electrode 4, a piezoelectric film 6, and upper electrodes 1 and 2 are formed on a substrate 9. The piezoelectric film 6 and the piezoelectric film 7 are previously polarized in the thickness direction as indicated by arrows. The embedded electrode 4 is a reference electrode connected to a reference potential that is an electrically stable potential.

  With such a configuration, the influence of capacitive coupling between the electrodes can be reduced. When an AC voltage is applied between the lower electrode 3 and the embedded electrode 4, the piezoelectric element can be bent and vibrated in a direction perpendicular to the piezoelectric film forming surface, and the embedded electrode 4, the upper electrode 1, and the upper electrode 2 When an alternating voltage having an opposite phase is applied between the two, a bending vibration can be generated in a direction parallel to the surface on which the piezoelectric film is formed.

(Embodiment 2)
FIG. 2 shows a diagram of a piezoelectric element according to Embodiment 2 of the present invention. 2A is a perspective view, and FIG. 2B is a cross-sectional view. A lower electrode 11 and a lower electrode 12, a piezoelectric film 17, a buried electrode 14, a piezoelectric film 16, and an upper electrode 13 are formed on a substrate 19. The piezoelectric film 16 and the piezoelectric film 17 are previously polarized in the thickness direction as indicated by arrows. The embedded electrode is a reference electrode connected to a reference potential that is an electrically stable potential.

  With such a configuration, the influence of capacitive coupling between the electrodes can be reduced. When an alternating voltage having an opposite phase is applied between the embedded electrode 14 and the lower electrode 11 and the lower electrode 12, bending vibration can be performed in a direction parallel to the piezoelectric film forming surface, and the upper electrode 13 and the embedded electrode can be vibrated. When an AC voltage is applied between the piezoelectric element 14 and the piezoelectric film forming surface, the piezoelectric element can be bent and vibrated in a direction perpendicular to the piezoelectric film forming surface.

  Although the second embodiment can be manufactured by almost the same method as the first embodiment, it is necessary to pattern the lower electrode before forming the piezoelectric film. become longer. However, when the piezoelectric element is bent and vibrated in the direction perpendicular to the surface on which the piezoelectric film is formed, the outermost layer portion of the piezoelectric element is most distorted, so that the piezoelectric at that location can be used. That is, the upper electrode can be used as an electrode for bending and vibrating the piezoelectric element in a direction perpendicular to the piezoelectric film forming surface. Further, when the piezoelectric element is bent and vibrated in a direction parallel to the surface on which the piezoelectric film is formed, since the piezoelectric element is most distorted at the side wall portion, the piezoelectric element at that location can be used. That is, although the cost is slightly higher, the sensitivity can be improved than in the first embodiment.

(Embodiment 3)
FIG. 3 shows a diagram of a piezoelectric element according to Embodiment 3 of the present invention. 3A is a perspective view, and FIG. 3B is a cross-sectional view. A lower electrode 25, a piezoelectric film 28, embedded electrodes 21 and 22, a piezoelectric film 27, an embedded electrode 24, a piezoelectric film 26, and an upper electrode 23 are formed on a substrate 29. The piezoelectric film 26, the piezoelectric film 27, and the piezoelectric film 28 are previously polarized in the thickness direction as indicated by arrows. The lower electrode 25 and the buried electrode 24 are reference electrodes connected to a reference potential that is an electrically stable potential.

  With such a configuration, the influence of capacitive coupling between the electrodes can be reduced. When an AC voltage having an opposite phase is applied between the lower electrode 25 and the embedded electrode 24 and the embedded electrode 21 and the embedded electrode 22, it can be bent and vibrated in a direction parallel to the piezoelectric film forming surface. When an AC voltage is applied between the electrode 23 and the embedded electrode 24, the piezoelectric element can be flexibly vibrated in a direction perpendicular to the surface on which the piezoelectric film is formed.

  The third embodiment can be manufactured by a method substantially equivalent to that of the second embodiment, but the process is slightly longer, such as an increase in the number of piezoelectric film layers. However, when the piezoelectric element is bent and vibrated in the horizontal direction with respect to the surface on which the piezoelectric film is formed, the piezoelectric film 27 and the piezoelectric film 28 can be used, and a larger driving amplitude can be obtained. That is, although the cost is high, the sensitivity can be further improved as compared with the second embodiment.

  Needless to say, the sensitivity can be improved by increasing the number of layers of the piezoelectric film as in the third embodiment, and thus the description of the multilayer film beyond this is omitted.

  The case where the piezoelectric element according to the first embodiment of the present invention is used as the gyro sensor piezoelectric element will be described. FIG. 4 shows a diagram of a piezoelectric element according to an embodiment of the present invention. 4A is a top view and circuit connection diagram, FIG. 4B is a cross-sectional view taken along the line AA in FIG. 4A, and FIG. 4C is a cross-sectional view taken along the line BB in FIG. . An input / output pad is formed on the piezoelectric element so that each electrode can be connected to a circuit, and the piezoelectric element is floated so that the end opposite to the input / output pad of the piezoelectric element can bend and vibrate freely. Support and fix. The embedded electrode 4 is exposed to the surface by removing the piezoelectric film 6, the upper electrode 1, and the upper electrode 2 on the embedded electrode 4 in the peripheral portion 10 of the input / output pad. Similarly, the lower electrode 3 is also exposed on the surface at the input / output pad peripheral portion 10.

  The self-excited oscillation circuit 101 is connected to the upper electrode 1 and the upper electrode 2 so that an alternating voltage substantially in phase with the resonance frequency of the bending vibration of the piezoelectric element can be applied to the upper electrode 1 and the upper electrode 2. The lower electrode 3 is connected to the current detection amplifier circuit 102, and after the charge generated in the lower electrode is amplified by the current detection amplifier circuit 102, the output terminal 105 is provided via the synchronous detection rectifier circuit 103. The synchronous detection rectifier circuit 103 detects the signal amplified by the current detection amplifier circuit 102 at the operating frequency of the self-excited transmission circuit 101 and removes noise in other frequency bands, and then considers the frequency band of the detected angular velocity. It is rectified by a low-pass filter with a cut-off frequency, and noise of high frequency components including the operating frequency is also removed and output. The embedded electrode 4 is connected to a reference voltage circuit 104 having an electrically stable potential.

  As described above, by connecting the piezoelectric element according to the embodiment of the present invention to the above-described circuit, the piezoelectric element can be bent and vibrated in advance in the direction parallel to the film formation surface of the piezoelectric film at the resonance frequency of the piezoelectric element. . At the same time, when an angular velocity centered on the longitudinal direction of the piezoelectric element is applied, the amplitude of the bending vibration in the direction perpendicular to the piezoelectric film newly generated by the action of the Coriolis force is also known as a change in the DC voltage obtained from the output terminal 105. That is, it functions as a gyro sensor.

  Although the structure of the piezoelectric element according to Embodiment 1 of the present invention is a cantilever shape that is a cantilever support burr, the structure of the piezoelectric element of the present invention is not limited to the above-described structure. The bending vibration mode may be one-wavelength resonance, any order of resonance, or torsional vibration. Furthermore, the piezoelectric element may have a sound shape in order to stabilize each vibration, or may have a shape in which a plurality of vibration parts are provided so as to detect multiaxial angular velocities.

  The important point of the structure of the present invention is that a piezoelectric film is provided with at least one buried electrode, and at least one of the buried electrodes is used as a reference electrode connected to a reference potential which is an electrically stable potential. The reference electrode is formed in the thickness direction by an electrode for driving or detecting a displacement in a direction parallel to the film formation surface of the piezoelectric film and an electrode for driving or detecting a displacement in a direction perpendicular to the film formation surface of the piezoelectric film. The point is that it is sandwiched between the two.

  That is, according to the configuration of the present invention, the electrode for driving or detecting the displacement in the direction perpendicular to the film formation surface of the piezoelectric film can be formed over a wide range with respect to the strain range caused by the bending vibration of the piezoelectric element. The drive signal generated by the self-excited oscillation circuit is that the electric field is blocked by the reference electrode so as not to jump into the detection electrode by capacitive coupling by returning the piezoelectric film having a high relative dielectric constant.

An example of the manufacturing process of the embodiment of the present invention will be described below. FIG. 5 shows a view after processing the piezoelectric element substrate according to the embodiment of the present invention. 5A is a top view, and FIG. 5B is a cross-sectional view taken along the line CC in FIG. 5A. First, an SOI (silicon on insulator) substrate 212 is prepared. The substrate size was 4 inches. The thicknesses of the active layer (substrate) 209 were Si of 100 μm, the buried oxide film layer SiO ₂ of 2 μm, and the support layer 211 of Si of 400 μm. Regarding the thickness, since the active layer 209 becomes a vibration part, it is necessary to make it a desired dimension. However, the buried oxide film layer 210 and the support layer 211 are damaged in the process in the process or deteriorated in processing accuracy due to warping. Any dimensions may be used in consideration of the etching processability described.

Next, the lower electrode 203, the piezoelectric film 207, the embedded electrode 204, the piezoelectric film 206, and the upper electrode 201 are formed in this order on the SOI substrate 212. In addition, in order to prevent diffusion of Si into the lower electrode layer, it is preferable to form a SiO ₂ layer having a thickness of about 1 μm on the surface of the SOI substrate 212 in advance by heat treatment. The lower electrode 203 was formed by sputtering 300 nm thick Pt on several tens of nm thick Ti. Subsequently, after PZT having a thickness of 2 μm was formed by sputtering as the first piezoelectric film 207, the buried electrode 204 was formed by sputtering with Pt having a thickness of 300 nm. The next piezoelectric film 206 was formed by sputtering the same 2 μm-thick PZT as the first piezoelectric film 207. Finally, the upper electrode 201 was formed by sputtering 400 nm thick Au on several tens nm thick Cr. The PZT film forming method is not particularly limited to the sputtering method, and a sol-gel method, an MOD method, an MOCVD method, an aerosol deposition method, or the like may be used. The electrode film forming method may be a vapor deposition method or the like.

  After the film formation, a resist was formed into a desired pattern using a general photolithography technique for resist application, exposure, and development. As a mask pattern used for exposure, it is necessary to arrange several hundreds of piezoelectric elements on a 4-inch substrate and prepare a mask that matches a desired resist pattern for each layer. After the resist pattern was formed, unnecessary portions were removed by etching, and then the process of removing and cleaning the resist was repeated for each layer to form a desired pattern. The etching method was wet etching for the upper electrode 201 and reactive ion etching for the piezoelectric films 206 and 207, the buried electrode 204, the lower electrode 203, and the SOI substrate 212. As for the SOI substrate 212, deep etching is performed perpendicularly to the substrate from the Si side of the active layer 209 using a Bosch process, and etching is stopped using the buried oxide film layer 210. Next, deep etching was similarly performed perpendicularly to the substrate from the back surface side of the SOI substrate 212, that is, the support layer 211 side.

  These methods are not limited to the methods of film formation, photolithography, and etching in that order. For example, the upper electrode is processed into a desired pattern in the order of photolithography, film formation, and lift-off. Alternatively, a method of processing the upper electrode by dry etching or a method of processing the piezoelectric film by wet etching or milling may be used.

  After pattern processing of each layer, it is separated into pieces by dicing, and then input / output pads are used to apply a voltage of 10 V between the lower electrode and the embedded electrode, and between the embedded electrode and the upper electrode. The membrane was polarized. The direction of polarization is not limited to the direction shown in FIG. 1A, and the lower electrode and the buried electrode, and the buried electrode and the upper electrode may be reversed. After the polarization treatment, the input / output pad and the drive detection circuit were connected by wire bonding as shown in FIG.

  In order to clarify the effect of the first embodiment of the present invention, the piezoelectric element having the conventional structure shown in FIGS. 8 and 9 is the same as the example in which the piezoelectric element according to the first embodiment of the present invention is manufactured. 4 inch SOI substrate, and after connecting to the circuit shown in FIG. 4A, the sensitivity of the gyro sensor and the amount of drive signal jumping into the detection electrode were measured. First, FIG. 6 shows the sensitivity measurement result of the piezoelectric element. The measured value 301 of Conventional Example 1 is that of the piezoelectric element of Conventional Example 1 shown in FIG. Further, the measurement value 302 of the conventional example 2 is that of the piezoelectric element of the conventional example 2 shown in FIG. 9, and includes an upper electrode 511 as a drive electrode, an upper electrode 512 as a drive electrode, and an upper electrode 513 as a detection electrode. This is a case in which a measure for separating the PZT piezoelectric film 516 is taken. The measured value 303 of the present invention is an example of the piezoelectric element according to the first embodiment of the present invention shown in FIG. 1, and the upper electrode 1 and the drive electrode using the embedded electrode 4 as a stable reference electrode as the drive electrode. Between the upper electrode 2 and the lower electrode 3 as a detection electrode. It can be seen that the voltage change of the output terminal 105 when the angular velocity of the piezoelectric element of the present invention is applied, that is, the sensitivity can be obtained nearly three times higher than the piezoelectric elements having the structures of the conventional examples 1 and 2 shown in FIGS. This result is considered that the sensitivity is increased by about 3 times because the area of the lower electrode 3 of the detection electrode of the present invention is about 3 times larger than the detection electrode of the conventional piezoelectric element.

  Next, FIG. 7 shows the measurement result of the amount of drive signal jumping into the detection electrode. The measured value 401 of Conventional Example 1 is that of the piezoelectric element of Conventional Example 1 shown in FIG. Further, the measured value 402 of Conventional Example 2 is that of the piezoelectric element of Conventional Example 2 shown in FIG. 9, and includes an upper electrode 511 as a drive electrode, an upper electrode 512 as a drive electrode, and an upper electrode 513 as a detection electrode. This is a case where a measure for separating the PZT piezoelectric film 516 is taken. The measured value 403 of the present invention is that of the piezoelectric element of the present invention shown in FIG. 1, and the upper electrode 1 as the drive electrode, the upper electrode 2 as the drive electrode, the upper electrode 2 as the drive electrode, and the detection electrode When sandwiched between the lower electrode 3 as described above. The dimensions of the piezoelectric element are all about 100 μm in thickness, 90 μm in width, 3 mm in length, and the width of the upper electrode is 20 μm. Regarding the measurement of the amount of drive signal jumping into the detection electrode, the upper electrode 1, the upper electrode 501, the upper electrode 511 as the drive electrode of each vibrator, the buried electrode 4 as the reference electrode, and the lower electrode 504 in the ambient air. A signal with an amplitude of 1 V is input from the outside to the lower electrode 514 in a variable manner from 0.1 kHz to 100 kHz, and a current generated by jumping is fed back to the lower electrode 3, the upper electrode 503, and the upper electrode 513 as detection electrodes. The voltage was measured by the current detection amplifier circuit 102 (FIG. 4A) configured with a charge amplifier having a capacitance of 5 pF. The horizontal axis of FIG. 7 shows the frequency of the input signal, and the vertical axis shows the level of the voltage measured by the charge amplifier with respect to the input signal as the capacitive coupling level. As shown by the measurement results, it was confirmed that the piezoelectric element of FIGS. 1 and 9 had a capacitive coupling level reduction of about 40 dB with respect to the measured value 401 of the conventional example 1 shown in FIG. Therefore, it can be said that the piezoelectric element of the present invention has higher sensitivity than the prior art and can greatly reduce the amount of drive signal jumping into the detection electrode.

  As described above, the piezoelectric element according to the present invention has been described using the embodiment and the examples. However, the present invention is not limited to these specific examples, and design changes can be made without departing from the gist of the present invention. Even if it exists, it is included in this invention. That is, various changes and modifications that can be naturally made by those skilled in the art are also included in the present invention.

  The present invention can be used for gyro sensors for camera shake correction systems, navigation systems, and attitude control systems, as well as for detecting vibration shocks in devices, impact sensors for crime prevention systems, and the like.

1, 2, 13, 23, 201, 501, 502, 503, 511, 512, 513,
521, 522, 523 Upper electrode
3, 11, 12, 25, 203, 504, 514, 524 Lower electrode 4, 14, 21, 22, 24, 204 Embedded electrode 6, 7, 16, 17, 26, 27, 28, 206, 207, 506, 516, 526 Piezoelectric films 9, 19, 29, 509, 519, 529 Substrate 10 Input / output pad peripheral portion 101 Self-excited oscillation circuit 102 Current detection amplifier circuit 103 Synchronous detection rectifier circuit 104 Reference voltage circuit 105 Output terminal 209 Active layer (substrate) )
210 Embedded oxide layer 211 Support layer 212 SOI substrates 301 and 401 Measurement values 302 and 402 of Conventional Example 1 Measurement values 303 and 403 of Conventional Example 2 Measurement value 528 of the present invention Insulator

Claims (1)

A piezoelectric element having a lower electrode, a piezoelectric film, and an upper electrode formed on a substrate and capable of driving or detecting displacement in a direction parallel to and perpendicular to a film formation surface of the piezoelectric film, An AC voltage is provided between the upper electrode and the reference electrode , wherein at least one embedded electrode is provided on the film, and at least one of the embedded electrodes is used as a reference electrode connected to a reference potential that is an electrically stable potential. To drive or detect displacement in a direction parallel to the film formation surface of the piezoelectric film , and apply an AC voltage between the lower electrode and the reference electrode to Drive or detect a displacement in a direction perpendicular to the upper surface or apply an AC voltage between the upper electrode and the reference electrode to drive or detect a displacement in a direction perpendicular to the film formation surface of the piezoelectric film. The lower electrode and the reference The piezoelectric element characterized by between electrode by applying an AC voltage to drive or detecting a displacement in a direction parallel to the deposition surface of the piezoelectric film.

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