MEMS element and piezoelectric acoustic device

Abstract

A MEMS element (1) is provided with: a piezoelectric element (100) that includes a piezoelectric film (40) that includes a ferroelectric and that vibrates when a voltage is applied; and a diode unit (200) electrically connected in parallel to the piezoelectric element (100) and including at least one diode (200A, 210, 220).

Description

Technical Field

[0001] This technology relates to MEMS components and piezoelectric acoustic devices. Background Art

[0002] A MEMS (Micro Electro Mechanical Systems) element using a piezoelectric body is currently known. Japanese Patent Application Laid-Open No. 2021-52305 (Patent Document 1) discloses a MEMS element having a membrane having a structure in which a piezoelectric membrane is sandwiched between a pair of electrodes. Prior Art Literature Patent Literature

[0003] Patent Document 1: Japanese Patent Application Publication No. 2021-52305 Summary of the invention Problems to be solved by the invention

[0004] It is sought to protect piezoelectric elements when ESD (Electro-Static Discharge) etc. From the above point of view, it cannot be said that existing MEMS elements are necessarily sufficient.

[0005] The present technology provides a MEMS element that realizes protection of a piezoelectric element against ESD or the like, and a piezoelectric acoustic device including the MEMS element. Means for solving problems

[0006] A MEMS element according to one embodiment of the present technology includes: a piezoelectric element including a piezoelectric film including a ferroelectric and vibrating when a voltage is applied; and a diode unit electrically connected in parallel to the piezoelectric element and including at least one diode. A piezoelectric acoustic device according to one embodiment of the present technology includes the above-mentioned MEMS element. Effects of the Invention

[0007] According to the present technology, it is possible to provide a MEMS element and a piezoelectric acoustic device that can protect a piezoelectric element from ESD or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a cross-sectional view showing a manufacturing process of the MEMS element according to the first embodiment (part 1). Figure 2 This is a cross-sectional view (part 2) showing the manufacturing process of the MEMS element according to the first embodiment. Figure 3 This is a cross-sectional view (part 3) showing the manufacturing process of the MEMS element involved in the first embodiment. Figure 4This is a cross-sectional view (part 4) showing the manufacturing process of the MEMS element involved in the first embodiment. Figure 5 This is a cross-sectional view (part 5) showing the manufacturing process of the MEMS element involved in the first embodiment. Figure 6 This is a cross-sectional view (part 6) showing the manufacturing process of the MEMS element involved in the first embodiment. Figure 7 Yes means Figure 6 A diagram showing a modified example of the process shown. Figure 8 This is a top view of the MEMS element according to the first embodiment. Fig. 9 yes Figure 8 Section IX-IX in. Fig.10 yes Figure 8 XX cross-section diagram in. Fig.11 This is a circuit diagram of the MEMS element according to the first embodiment. Fig.12 This is a cross-sectional view of a MEMS element according to the second embodiment. Fig.13 This is a circuit diagram of a MEMS element according to the second embodiment. Fig.14 This is a top view of the MEMS element according to the third embodiment. Fig.15 yes Fig.14 Section XV-XV in FIG. Fig.16 This is a circuit diagram of a MEMS element according to the third embodiment. Fig.17 This is a top view of a MEMS element according to a fourth embodiment. Fig.18 yes Fig.17 Section XVIII-XVIII in . Fig.19 yes Fig.17 Section XIX-XIX in. Fig. 20 This is a cross-sectional view of a MEMS element according to the fifth embodiment. Fig.21 This is a cross-sectional view of a MEMS element according to the sixth embodiment. Fig. 22 This is a top view of the MEMS element involved in the seventh embodiment. Fig.23 yes Fig. 22 Section XXIII-XXIII in FIG. Fig.24 This is a top view of the MEMS element involved in the eighth embodiment. Fig.25 yes Fig.24 Section XXV-XXV in FIG. Fig.26 This is a diagram for explaining the polarization direction of the piezoelectric film 40 . DETAILED DESCRIPTION

[0009] Hereinafter, embodiments of the present technology will be described. In addition, the same reference numerals may be given to the same or corresponding parts, and the description thereof may not be repeated.

[0010] In addition, in the embodiments described below, when the number, amount, etc. are mentioned, the scope of the present technology is not limited to the number, amount, etc., unless there is a special record. In addition, in the following embodiments, except for the case where there is a special record, each component is not essential to the present technology. In addition, the present technology is not limited to the case where all the effects mentioned in the present embodiment must be achieved.

[0011] In addition, in this specification, the descriptions of "comprise", "include", and "have" are open-ended. That is, when a certain configuration is included, other configurations other than the configuration may be included, or other configurations may not be included.

[0012] (Implementation Method 1) Figure 1 to Figure 7 The steps in the manufacturing process of the MEMS element according to the first embodiment are shown in FIG. Figure 7 yes Figure 6 A cross-sectional view of a modified example of the process shown). Figure 8 is a top view of a MEMS element according to this embodiment. Fig. 9 , Fig.10 They are Figure 8 IX-IX cross-sectional view and XX cross-sectional view. In addition, Fig.11 This is a circuit diagram of a MEMS element according to this embodiment.

[0013] like Fig.11 As shown, the MEMS element 1 involved in this embodiment has a structure in which a piezoelectric element 100 and a diode unit 200 are electrically connected in parallel. The diode unit 200 is composed of a diode 200A. The piezoelectric element 100 includes a piezoelectric film that vibrates by applying a voltage. The piezoelectric element 100 has a membrane structure in which a piezoelectric film is sandwiched by a pair of electrode bodies (upper and lower electrodes). When the MEMS element 1 is driven, a voltage is applied to the piezoelectric film, so that the film vibrates. Fig.11In the example, the MEMS element 1 is driven by a unipolar AC power source 300A.

[0014] The MEMS element 1 can be applied to, for example, a pMUT (Piezoelectric Micromachined Ultrasonic Transducer), but is not limited thereto. The MEMS element 1 can also be applied to other piezoelectric acoustic devices such as a MEMS speaker and a MEMS pickup. In addition, the MEMS element 1 can also be applied to devices other than piezoelectric acoustic devices.

[0015] Below, use Figures 1 to 10 The manufacturing process of the MEMS element 1 and the cross-sectional structure of the MEMS element 1 are described.

[0016] like Figure 1 As shown, an SOI wafer having an oxide film layer 20 (BOX layer) and an active layer silicon 30 (semiconductor film) formed on a silicon substrate 10 (semiconductor substrate) is prepared. The active layer silicon 30 is required to have a low resistance because it constitutes the lower electrode of the piezoelectric element 100. The conductivity type of the active layer silicon 30 can be either p-type or n-type. The resistivity of the active layer silicon 30 is adjusted by a commonly used dopant (boron, phosphorus, antimony, arsenic, etc.). In the following description, the conductivity type of the active layer silicon 30 is described as p-type.

[0017] The stacked structure of the silicon substrate 10 , the oxide film layer 20 , and the active silicon layer 30 described above is an example, and the present technology is not limited thereto. The present technology can also be applied to semiconductor materials other than silicon.

[0018] like Figure 2 As shown, a piezoelectric film 40 (piezoelectric film) having ferroelectricity is formed on the active layer silicon 30. The active layer silicon 30 is adjacent to the piezoelectric film 40. The piezoelectric film 40 is composed of a ferroelectric formed by, for example, lithium niobate (LN: LiNbO3) and lithium tantalate (LT: LiTaO3). A single crystal substrate composed of these materials is bonded to the active layer silicon 30 by surface activation bonding and atomic diffusion bonding. Then, by grinding using a grinder, the single crystal substrate is thinned to form the piezoelectric film 40. As a method for thinning the single crystal substrate, in addition to grinding and polishing, it can also be a method such as the following: a damaged layer is preliminarily provided on the bonding surface side of the piezoelectric single crystal substrate by an ion implantation method, and the damaged layer is used to peel off the single crystal substrate after bonding. In addition, it is also conceivable to combine the method using peeling with polishing. Alternatively, the piezoelectric thin film 40 having ferroelectricity can be formed by forming a thin film of lead zirconate titanate (PZT: Pb(Zr,Ti)O 3 ) or the like using a sol-gel method, a sputtering method, or the like.

[0019] like Figure 3 As shown, the piezoelectric film 40 is patterned into a desired shape. The patterning can be performed by dry etching such as reactive ion etching (RIE) or wet etching using fluorine nitric acid or the like.

[0020] In the region where the diode portion 200 is formed, as shown in FIG. Figure 4 As shown, an n-type impurity region 50 is formed in the p-type active silicon layer 30. The impurity region 50 is formed by ion implantation and diffusion used in a common semiconductor process. As dopants, for example, phosphorus, arsenic, etc. are used. The dopants are implanted into the active silicon layer 30 through the opening 40A of the piezoelectric film 40.

[0021] In this embodiment, if Fig.11 As shown, an electric field in the same direction as the polarization direction of the piezoelectric film 40 (the direction of the arrow DR40) is applied to the piezoelectric element 100. In this case, when the voltage (V) acting on the piezoelectric film 40 reaches the dielectric breakdown voltage (first voltage) of the piezoelectric film 40, the piezoelectric film 40 is destroyed. The diode 200A is formed so that the direction opposite to the direction corresponding to the polarization direction of the piezoelectric film 40 is the forward direction. In order to suppress the destruction of the piezoelectric element 100, the concentration and depth of the impurity region 50 are adjusted to a voltage that makes the breakdown voltage (second voltage) of the diode 200A less than the dielectric breakdown voltage of the piezoelectric film 40 (preferably about 0.7 times or more and about 1.0 times or less, more preferably about 0.8 times or more and about 0.9 times or less). The detailed description of the polarization direction of the piezoelectric film 40 will be described later.

[0022] In the region where the piezoelectric element 100 is formed, as shown in FIG. Figure 5 As shown, openings 30B, 40B are formed in the active layer silicon 30 and the piezoelectric film 40. The openings 30B, 40B are formed by dry etching or the like.

[0023] like Figure 6 As shown, an upper electrode 60 is formed on the surface of the piezoelectric film 40 and the impurity region 50. The upper electrode 60 can be formed of, for example, Pt, but the present technology is not limited thereto, and the upper electrode 60 can be formed of other materials such as Al.

[0024] An adhesion layer (not shown) for the upper electrode 60 may be formed before forming the upper electrode 60. The adhesion layer can be formed of, for example, Ti, but the present technology is not limited thereto, and the adhesion layer may be formed of other materials such as NiCr.

[0025] As an example, the thickness of the upper electrode 60 is about 0.05 μm or more and 0.2 μm or less, and as an example, the thickness of the adhesive layer is about 0.005 μm or more and 0.05 μm or less.

[0026] The upper electrode 60 and the adhesion layer can be formed into a desired pattern by, for example, vapor deposition and peeling, but the present technology is not limited to this. For example, a film may be formed on the entire surface by sputtering and then etched to form the pattern of the upper electrode 60 and the adhesion layer.

[0027] The pattern of the upper electrode 60 is not limited to Figure 6 The pattern shown, for example, can also be Figure 7 As shown, the upper electrode 60 on the piezoelectric film 40 and the upper electrode 60 on the impurity region 50 are formed integrally.

[0028] like Figure 6 , Figure 7 As shown, a PAD electrode 70 is formed on the upper electrode 60, and a PAD electrode 80 is formed on the active layer silicon 30 exposed from the opening 40A of the piezoelectric film 40. The PAD electrodes 70 and 80 can be formed of Au, for example, but the present technology is not limited thereto, and the PAD electrodes 70 and 80 can also be formed of other materials such as Al.

[0029] An adhesion layer (not shown) for the PAD electrodes 70 and 80 may be formed before forming the PAD electrodes 70 and 80. The adhesion layer can be formed of Ti, for example, but the present technology is not limited thereto, and the adhesion layer may be formed of other materials such as NiCr.

[0030] As an example, the thickness of the PAD electrodes 70 and 80 is about 0.1 μm or more and 1.0 μm or less, and as an example, the thickness of the adhesive layer is about 0.005 μm or more and 0.1 μm or less.

[0031] The PAD electrodes 70, 80 and the adhesion layer can be formed into a desired pattern by, for example, vapor deposition and peeling, but the present technology is not limited to this. For example, a film can be formed on the entire surface by sputtering and then the pattern of the PAD electrodes 70, 80 and the adhesion layer can be formed by etching.

[0032] like Figure 8 As shown in the top view, the piezoelectric element 100 and the diode unit 200 are arranged separately from each other on the main surface of the silicon substrate 10 constituting the MEMS element 1. However, the positional relationship between the piezoelectric element 100 and the diode unit 200 is not limited to Figure 8 Configuration shown.

[0033] like Fig. 9As shown in FIG. 2 (Cross-sectional view of diode unit 200 ), lead wires 70A and 80A having opposite polarities are connected to PAD electrodes 70 and 80 .

[0034] like Fig.10 As shown in (a cross-sectional view of a piezoelectric element 100), in the region where the piezoelectric element 100 is formed, openings 10B and 20B are formed in the silicon substrate 10 and the oxide film layer 20. The opening 10A can be formed by removing a portion of the silicon substrate 10 using deep RIE (Deep Reactive Ion Etching). The opening 20A can be formed by removing the oxide film layer 20 using RIE (Reactive Ion Etching). The openings 30B and 40B formed in the active layer silicon 30 and the piezoelectric film 40 constitute the slit 110 of the piezoelectric element 100.

[0035] In the MEMS element 1 according to the present embodiment, since the piezoelectric element 100 and the diode unit 200 are electrically connected in parallel, when ESD or the like occurs, current can escape to the diode unit 200 side, thereby suppressing destruction of the piezoelectric element 100 .

[0036] In addition, since the diode portion 200 is formed by using the impurity region 50 formed in the active layer silicon 30, the piezoelectric element 100 and the diode portion 200 can be provided on a single silicon substrate 10 (semiconductor substrate). As a result, the piezoelectric element 100 can be suppressed from being damaged while miniaturizing the MEMS element 1.

[0037] like Fig.11 As shown in the example of FIG. 1 , the diode 200A constituting the diode unit 200 is preferably formed so that the forward direction is opposite to the direction corresponding to the polarization direction (arrow DR40 direction) of the piezoelectric film 40. Since the dielectric breakdown electric field of the piezoelectric film 40 is relatively large relative to the coercive electric field, it is usually as shown in FIG. Fig.11 As shown, a unipolar AC power source 300A is connected in a direction corresponding to the polarization direction of the piezoelectric film 40. Fig.11 In the example of FIG. 1 , the diode 200A is connected in such a manner that the forward direction of the diode 200A becomes the opposite direction to the direction corresponding to the polarization direction of the piezoelectric film 40, so that when the unipolar AC power source 300A is connected in the wrong direction (the direction opposite to the above direction), the diode 200A becomes the forward direction, and no voltage is applied to the piezoelectric element 100. As a result, the destruction of the piezoelectric element 100 due to polarization reversal can be suppressed.

[0038] (Implementation Method 2) Fig.12 This is a cross-sectional view of the MEMS element 1 according to the second embodiment. Fig.13 yes Fig.12 A circuit diagram of the MEMS element 1 is shown.

[0039] In the MEMS element 1 according to the present embodiment, Fig.13 As shown, the diode unit 200 includes a first diode 210 having a first direction as a forward direction, and a second diode 220 connected in series with the first diode 210 and having a second direction opposite to the first direction as a forward direction.

[0040] like Fig.12 As shown, an n-type (first conductivity type) impurity region 50A (first impurity region) is formed inside the p-type active layer silicon 30, and a p-type (second conductivity type) impurity region 50B (second impurity region) is formed inside the impurity region 50A. Thus, a diode unit 200 can be formed in which a first diode 210 and a second diode 220 facing opposite directions are connected in series.

[0041] The breakdown voltages of the first diode 210 and the second diode 220 may be substantially the same or different from each other. Fig.13 As shown, a bipolar AC power source 300B is used. Therefore, an electric field in the same direction as the polarization direction (arrow DR40 direction) of the piezoelectric film 40 and an electric field in the opposite direction are alternately applied to the piezoelectric element 100.

[0042] When an electric field in the opposite direction to the polarization direction (arrow DR40 direction) of the piezoelectric film 40 is applied to the piezoelectric element 100, when a coercive electric field (V / m) acts on the piezoelectric film 40, polarization reversal occurs in the piezoelectric film 40 and the piezoelectric element 100 is destroyed. The first diode 210 is formed so that the direction corresponding to the polarization direction of the piezoelectric film 40 is the forward direction. In order to suppress the destruction of the piezoelectric element 100, the first diode 210 is formed so that it breaks down at least when a coercive electric field acts on the piezoelectric film 40 (preferably when an electric field of about 0.7 times or more and about 1.0 times or less of the coercive electric field acts, and more preferably when an electric field of about 0.8 times or more and about 0.9 times or less of the coercive electric field acts). That is, the concentration and depth of the impurity region 50 are adjusted so that the breakdown voltage (second voltage) of the first diode 210 becomes a voltage lower than the voltage (first voltage) at which the polarization reversal of the piezoelectric film 40 occurs.

[0043] When an electric field having the same direction as the polarization direction of the piezoelectric film 40 (the direction of the arrow DR40) is applied to the piezoelectric element 100, the piezoelectric film 40 is destroyed when the voltage (V) applied to the piezoelectric film 40 reaches the dielectric breakdown voltage (first voltage) of the piezoelectric film 40. The second diode 220 is formed so that the forward direction is the opposite direction to the direction corresponding to the polarization direction of the piezoelectric film 40. In order to suppress the destruction of the piezoelectric element 100, the concentration and depth of the impurity region 50 are adjusted so that the breakdown voltage (second voltage) of the second diode 220 becomes a voltage lower than the dielectric breakdown voltage of the piezoelectric film 40 (preferably about 0.7 times or more and about 1.0 times or less, more preferably about 0.8 times or more and about 0.9 times or less).

[0044] Of course, the conductivity types of the active silicon layer 30 and the impurity regions 50A and 50B may be opposite to the above-mentioned types.

[0045] In the MEMS element 1 involved in this embodiment, since the diode part 200 formed by connecting the first diode 210 and the second diode 220 facing opposite directions in series is connected in parallel with the piezoelectric element 100, even when the MEMS element 1 is driven by the bipolar AC power supply 300B and an electric field exceeding the coercive electric field or the dielectric breakdown electric field is applied, the destruction of the piezoelectric element 100 due to polarization reversal or dielectric breakdown can be suppressed.

[0046] As described above, by driving the MEMS element 1 using the bipolar AC power source 300B, the voltage range that can be applied to the piezoelectric film 40 is increased compared to the case of using the unipolar AC power source 300A (Embodiment 1). As a result, the radiated sound pressure can be increased in a piezoelectric acoustic device using the MEMS element 1, for example.

[0047] In the MEMS element 1 according to this embodiment, it is also possible to protect the piezoelectric element 100 while miniaturizing the entire MEMS element 1. The rest of the contents are the same as those of the first embodiment, and thus detailed descriptions thereof will not be repeated.

[0048] (Implementation 3) Fig.14 is a top view of the MEMS element 1 according to the third embodiment. Fig.15 yes Fig.14 Section XV-XV in FIG. Fig.16 yes Fig.14 , Fig.15 A circuit diagram of the MEMS element 1 is shown.

[0049] In the MEMS element 1 according to the present embodiment, Fig.15As shown, the diode unit 200 includes a first diode 210 having a first direction as a forward direction, and a second diode 220 connected in series with the first diode 210 and having a second direction opposite to the first direction as a forward direction.

[0050] like Fig.14 , Fig.15 As shown, the active silicon layer 30 includes a first portion 31 constituting an electrode (lower electrode) of the piezoelectric film 40 , and a second portion 32 separated from the first portion 31 .

[0051] The impurity region 50 formed at the second portion 32 of the p-type (second conductivity type) active layer silicon 30 includes an n-type (first conductivity type) impurity region 50C (first impurity region) and an n-type (first conductivity type) impurity region 50D (second impurity region). The impurity regions 50C and 50D are formed separately from each other. The impurity region 50C is connected to the PAD electrode 70, and the impurity region 50D is connected to the PAD electrode 80. Thus, the diode portion 200 in which the first diode 210 and the second diode 220 facing opposite directions are connected in series can be formed.

[0052] Of course, the conductivity types of the active silicon layer 30 and the impurity regions 50C and 50D may be opposite to the above-mentioned types.

[0053] In the MEMS element 1 according to this embodiment, it is also possible to protect the piezoelectric element 100 while miniaturizing the entire MEMS element 1. The rest of the contents are the same as those of the first and second embodiments, and thus detailed descriptions thereof will not be repeated.

[0054] (Implementation 4) Fig.17 is a top view of a MEMS element 1 according to a fourth embodiment. Fig.18 , Fig.19 They are Fig.17 XVIII-XVIII cross-sectional view and XIX-XIX cross-sectional view in FIG.

[0055] like Figure 17 to Figure 19 As shown, in the MEMS element 1 according to the present embodiment, a lower electrode 90 is provided below the piezoelectric film 40 . The lower electrode 90 can be formed of a metal material. The lower electrode 90 is formed to have a lower resistance than the active layer silicon 30 .

[0056] like Fig.18As shown, a p-type (second conductivity type) impurity region 50E (first impurity region) is formed inside the p-type active layer silicon 30, and an n-type (first conductivity type) impurity region 50F (second impurity region) is formed inside the impurity region 50E. The impurity region 50F is connected to the upper electrode 60 (first electrode) and the PAD electrode 70, and the impurity region 50E is connected to the lower electrode 90 (second electrode) and the PAD electrode 80. Thus, the same embodiment as the first embodiment ( Fig.11 )Same circuit.

[0057] Of course, the conductivity types of the active silicon layer 30 and the impurity regions 50E and 50F may be opposite to the above-mentioned types.

[0058] In the MEMS element 1 involved in this embodiment, by providing a lower electrode 90 with a lower resistance than the active layer silicon 30, it is easy to meet the performance (lower resistance of the electrode) required when the MEMS element 1 is used at a high frequency and the piezoelectric film 40 has a high dielectric constant.

[0059] exist Fig.18 In the example shown in FIG. 1 , the impurity region 50 is formed in the active layer silicon 30 , but the impurity region 50 may be formed so as to extend to the oxide film layer 20 and the silicon substrate 10 .

[0060] In the MEMS element 1 according to the present embodiment, it is also possible to protect the piezoelectric element 100 while miniaturizing the entire MEMS element 1. The rest of the contents are the same as those of the above-mentioned embodiments, and thus detailed descriptions thereof will not be repeated.

[0061] (Implementation method 5) Fig. 20 is a cross-sectional view of the MEMS element 1 according to the fifth embodiment. Fig. 20 As shown, in the MEMS element 1 according to the present embodiment, similarly to the fourth embodiment, a lower electrode 90 made of metal and having a low resistance is provided.

[0062] A p-type (second conductivity type) impurity region 50G (first impurity region) is formed inside the p-type active layer silicon 30, an n-type (first conductivity type) impurity region 50H (second impurity region) is formed inside the impurity region 50G, and a p-type (second conductivity type) impurity region 50I (third impurity region) is formed inside the impurity region 50H. The impurity region 50I is connected to the upper electrode 60 (first electrode) and the PAD electrode 70, and the impurity region 50G is connected to the lower electrode 90 (second electrode) and the PAD electrode 80. Thus, the same structure as in the above-mentioned embodiment 2 ( Fig.13 )Same circuit.

[0063] Of course, the conductivity types of the active layer silicon 30 and the impurity regions 50G to 50I may be opposite to the above-mentioned types. Fig.19 )same.

[0064] In the MEMS element 1 according to the present embodiment, it is also possible to protect the piezoelectric element 100 while miniaturizing the entire MEMS element 1. The rest of the contents are the same as those of the above-mentioned embodiments, and thus detailed descriptions thereof will not be repeated.

[0065] (Implementation 6) Fig.21 is a cross-sectional view of the MEMS element 1 according to the sixth embodiment. Fig.21 As shown, in the MEMS element 1 according to the present embodiment, similarly to the fourth and fifth embodiments, a lower electrode 90 made of metal and having a low resistance is provided.

[0066] A p-type (second conductivity type) impurity region 50J (first impurity region) is formed inside the p-type active layer silicon 30, and an n-type (first conductivity type) impurity region 50K (second impurity region) and an impurity region 50L (third impurity region) are formed inside the impurity region 50J. The impurity region 50K is connected to the upper electrode 60 (first electrode) and the PAD electrode 70, and the impurity region 50L is connected to the lower electrode 90 (second electrode) and the PAD electrode 80. Thus, the same embodiment as the third embodiment ( Fig.16 )Same circuit.

[0067] Of course, the conductivity types of the active layer silicon 30 and the impurity regions 50J to 50L may be opposite to the above-mentioned types. Fig.19 )same.

[0068] In the MEMS element 1 according to the present embodiment, it is also possible to protect the piezoelectric element 100 while miniaturizing the entire MEMS element 1. The rest of the contents are the same as those of the above-mentioned embodiments, and thus detailed descriptions thereof will not be repeated.

[0069] (Implementation 7) Fig. 22 is a top view of the MEMS element 1 according to the seventh embodiment. Fig.23 yes Fig. 22 Section XXIII-XXIII in FIG.

[0070] In the MEMS element 1 according to the present embodiment, the diode portion 200 is constituted by a Schottky diode formed by bringing a metal Schottky electrode 55 into contact with an active silicon layer 30. The active silicon layer 30 includes a first portion 31 constituting an electrode (lower electrode) of the piezoelectric film 40 and a second portion 32 separated from the first portion 31.

[0071] In this embodiment, when the p-type (second conductivity type) active layer silicon 30 is used, the same as in the above-mentioned embodiment 2 ( Fig.13 On the other hand, when the active layer silicon 30 of n-type (first conductivity type) is used, the same circuit as in the above-mentioned embodiment 3 ( Fig.16 In either case, the MEMS element 1 can be obtained in which the diode part 200 formed by connecting the first diode 210 and the second diode 220 in opposite directions in series and the piezoelectric element 100 are connected in parallel.

[0072] The metal constituting the Schottky electrode 55 is not particularly limited. When the active layer silicon 30 of the n-type (first conductivity type) is used, for example, Au, Pt, Mo, Co, W, Al, Pd, Ni, Mo, Ta, Nb, Ti, etc. can be used as the material constituting the Schottky electrode 55, among which Au and Pt can be cited as preferred materials. On the other hand, when the active layer silicon 30 of the p-type (second conductivity type) is used, for example, Sn, In, Cs, Fr, Mg, etc. can be used as the material constituting the Schottky electrode 55, among which Sn can be cited as a preferred material.

[0073] In the MEMS element 1 involved in this embodiment, similarly to the first to sixth embodiments, since the piezoelectric element 100 and the diode unit 200 are electrically connected in parallel, when ESD or the like occurs, current can escape to the diode unit 200 side, thereby suppressing destruction of the piezoelectric element 100.

[0074] In addition, since the diode portion 200 is formed by using the Schottky electrode 55 formed on the silicon substrate 10 and the oxide film layer 20, the piezoelectric element 100 and the diode portion 200 can be provided on a single silicon substrate 10 (semiconductor substrate). As a result, the damage of the piezoelectric element 100 can be suppressed while miniaturizing the MEMS element 1.

[0075] In addition, in the MEMS element 1 according to the present embodiment, the diode portion 200 is formed by using the active layer silicon 30 and the Schottky electrode 55, so that it is not necessary to form the impurity regions 50, 50A to 50L. Therefore, ion implantation and diffusion for forming the impurity regions 50, 50A to 50L are not necessary. As a result, the destruction of the piezoelectric element 100 can be stably suppressed through a simple process.

[0076] Furthermore, the diode portion 200 including the Schottky diode using the Schottky electrode 55 can perform a high-speed switching operation compared to the diode portion 200 using the impurity regions 50 and 50A to 50L, and the film-structured piezoelectric element 100 can be driven at a higher speed.

[0077] As other contents are the same as those in the above-mentioned Embodiments 1 to 6, detailed descriptions thereof will not be repeated.

[0078] (Implementation 8) Fig.24 is a top view of the MEMS element 1 according to the eighth embodiment. Fig.25 yes Fig.24 Section XXV-XXV in FIG.

[0079] like Fig.24 , Fig.25 As shown, in the MEMS element 1 according to the present embodiment, similarly to the seventh embodiment, the diode portion 200 is constituted by a Schottky diode formed by bringing a Schottky electrode 55 made of metal into contact with an active layer silicon 30 .

[0080] In the MEMS element 1 according to the present embodiment, a lower electrode 90 is further provided below the piezoelectric film 40 . The lower electrode 90 can be formed of a metal material. The lower electrode 90 is formed to have a lower resistance than the active layer silicon 30 .

[0081] In the MEMS element 1 involved in this embodiment, by providing the lower electrode 90 having a lower resistance than the active layer silicon 30, it is possible to easily meet the performance (lower resistance of the electrode) required when the MEMS element 1 is used at a high frequency and the piezoelectric film 40 has a high dielectric constant. As the other contents are the same as those in the above-mentioned embodiment 7, detailed description will not be repeated.

[0082] In the MEMS element 1 according to the present embodiment, it is also possible to protect the piezoelectric element 100 while miniaturizing the entire MEMS element 1 .

[0083] (Polarization Direction of Piezoelectric Film 40) Below, refer to Fig.26 The polarization direction of the piezoelectric film 40 is described as follows ( Fig.11 , Fig.13 , Fig.16 in the direction of arrow DR40 shown).

[0084] exist Fig.26In the example, (A) represents a piezoelectric film 40 composed of a ferroelectric such as PZT. In the state of (A), the direction of the charge bias (spontaneous polarization) of each crystal constituting the piezoelectric film 40 is formed randomly (arrow A in the figure), and there is no charge bias when observing the piezoelectric film 40 as a whole. From the state of (A), as shown in (B), after a specified voltage (for example, about 3kV / mm) is applied to the piezoelectric film 40, the direction of the spontaneous polarization is uniform as a whole (in Fig.26 In the example, the spontaneous polarization is aligned upward. ). Starting from the state (B), when the voltage applied to the piezoelectric film 40 is removed as shown in (C), the direction of the spontaneous polarization does not return to the state (A), and the polarization facing upward remains when the piezoelectric film 40 is observed as a whole. That is, the direction of the arrow DR40 becomes the polarization direction of the piezoelectric film 40. The situation in which the direction of the spontaneous polarization is arranged in an orderly manner as described above is called polarization treatment. In addition, in the case where the piezoelectric film 40 is formed by a single crystal substrate such as LN, LT, etc., the single crystal substrate has been polarized. In either case, the polarization direction of the piezoelectric film 40 (the direction of the arrow DR40) becomes the same as that of the piezoelectric film 40. Fig.26 (B) The voltage application direction during the polarization treatment is the same as that shown in the example.

[0085] (Summarize) The contents of the above-mentioned Embodiments 1 to 8 are summarized as follows. <1> A MEMS element comprises: a piezoelectric element including a piezoelectric film including a ferroelectric and vibrating when a voltage is applied; and a diode unit electrically connected in parallel to the piezoelectric element and including at least one diode.

[0086] <2> according to <1> In the MEMS element, the piezoelectric element and the diode portion are formed on a single semiconductor substrate.

[0087] <3> according to <1> or <2> In the above-mentioned MEMS element, the piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film, and the diode portion includes an impurity region formed in the semiconductor film.

[0088] <4> according to <1> to <3> A MEMS element as described in any one of the above, wherein when a first voltage is applied to the above-mentioned piezoelectric film, the above-mentioned piezoelectric film undergoes dielectric breakdown, and the above-mentioned diode included in the above-mentioned diode part is formed to have a forward direction opposite to a direction corresponding to a polarization direction of the above-mentioned piezoelectric film, and to undergo breakdown when a second voltage lower than the above-mentioned first voltage is applied.

[0089] <5> according to <1> or <2> In the above-mentioned MEMS element, the piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film, and the diode portion is a Schottky diode formed by bringing metal into contact with the semiconductor film.

[0090] <6> according to <5> In the above-mentioned MEMS element, the semiconductor film includes a first portion constituting the electrode and a second portion separated from the first portion.

[0091] <7> according to <1> to <3> , <5> and <6> The MEMS element as described in any one of the above, wherein the above-mentioned diode part includes a first diode and a second diode, the first diode has a first direction corresponding to the polarization direction of the above-mentioned piezoelectric film as a forward direction, the second diode is connected in series with the above-mentioned first diode, and has a second direction opposite to the above-mentioned first direction as a forward direction, the breakdown voltage of the above-mentioned first diode is a voltage lower than the voltage at which the polarization reversal of the above-mentioned piezoelectric film occurs, and the breakdown voltage of the above-mentioned second diode is a voltage lower than the voltage at which the above-mentioned piezoelectric film undergoes dielectric breakdown.

[0092] <8> according to <1> or <2> The MEMS element described above, wherein the piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film, the diode portion includes a first diode and a second diode, the first diode has a first direction corresponding to the polarization direction of the piezoelectric film as a forward direction, the second diode is connected in series with the first diode, and has a second direction opposite to the first direction as a forward direction, the breakdown voltage of the first diode is a voltage below the voltage at which the piezoelectric film undergoes polarization reversal, the breakdown voltage of the second diode is a voltage below the voltage at which the piezoelectric film undergoes dielectric breakdown, the first diode includes a first impurity region of a first conductivity type formed in the semiconductor film, and the second diode includes a second impurity region of a second conductivity type formed in the first impurity region.

[0093] <9> according to <1> or <2> The MEMS element described above, wherein the piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film, the semiconductor film includes a first part constituting the electrode and a second part separated from the first part, the diode part includes a first diode and a second diode, the first diode has a first direction corresponding to the polarization direction of the piezoelectric film as a forward direction, the second diode is connected in series with the first diode, and has a second direction opposite to the first direction as a forward direction, the breakdown voltage of the first diode is a voltage below the voltage at which the piezoelectric film undergoes polarization reversal, the breakdown voltage of the second diode is a voltage below the voltage at which the piezoelectric film undergoes dielectric breakdown, the first diode includes a first impurity region formed in the semiconductor film, and the second diode includes a second impurity region formed in the semiconductor film and separated from the first impurity region.

[0094] <10> according to <1> to <9> The MEMS element described in any one of the above, wherein the piezoelectric element includes: a first electrode adjacent to the piezoelectric film; and a second electrode made of a metal material, the second electrode being provided on the opposite side of the first electrode across the piezoelectric film.

[0095] <11> A piezoelectric acoustic device, using <1> to <10> The MEMS element as described in any one of the above.

[0096] The embodiments of the present technology have been described above, but it should be understood that the embodiments disclosed this time are merely illustrative in all aspects and are not restrictive. The scope of the present technology is indicated by the claims, and it is intended to include all changes within the meaning and scope equivalent to the claims. Description of the label

[0097] 1MEMS element, 10 silicon substrate, 10B, 20B, 30B, 40A, 40B opening, 20 oxide film layer, 30 active layer silicon, 31 first part, 32 second part, 40 piezoelectric film, 50, 50A to 50L impurity regions, 55 Schottky electrode, 60 upper electrode, 70, 80 PAD electrode, 70A, 80A wire wiring, 90 lower electrode, 100 piezoelectric element, 110 slit, 200 diode part, 200A diode, 210 first diode, 220 second diode, 300A unipolar AC power supply, 300B bipolar AC power supply.

Claims

1. A MEMS element, comprising: a piezoelectric element including a piezoelectric film including a ferroelectric and vibrating by application of a voltage; and The diode unit is electrically connected in parallel with the piezoelectric element and includes at least one diode.

2. The MEMS element according to claim 1, wherein: The piezoelectric element and the diode portion are formed on a single semiconductor substrate.

3. The MEMS element according to claim 1 or 2, wherein: The piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film. The diode portion includes an impurity region formed in the semiconductor film.

4. The MEMS element according to any one of claims 1 to 3, wherein: When a first voltage is applied to the piezoelectric film, the piezoelectric film undergoes dielectric breakdown. The diode included in the diode unit is formed so as to break down when a second voltage less than the first voltage is applied with a forward direction opposite to a direction corresponding to the polarization direction of the piezoelectric film.

5. The MEMS element according to claim 1 or 2, wherein: The piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film. The diode portion is a Schottky diode formed by bringing metal into contact with the semiconductor film.

6. The MEMS element according to claim 5, wherein: The semiconductor film includes a first portion constituting the electrode and a second portion separated from the first portion.

7. The MEMS element according to any one of claims 1 to 3, 5 and 6, wherein: The diode unit includes a first diode and a second diode, wherein the first diode has a first direction corresponding to the polarization direction of the piezoelectric film as a forward direction, and the second diode is connected in series with the first diode and has a second direction opposite to the first direction as a forward direction. The breakdown voltage of the first diode is a voltage lower than the voltage at which the polarization reversal of the piezoelectric film occurs. The breakdown voltage of the second diode is a voltage lower than or equal to a voltage at which the piezoelectric film undergoes dielectric breakdown.

8. The MEMS element according to claim 1 or 2, wherein: The piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film. The diode unit includes a first diode and a second diode, wherein the first diode has a first direction corresponding to the polarization direction of the piezoelectric film as a forward direction, and the second diode is connected in series with the first diode and has a second direction opposite to the first direction as a forward direction. The breakdown voltage of the first diode is a voltage lower than the voltage at which the polarization reversal of the piezoelectric film occurs. The breakdown voltage of the second diode is a voltage below the voltage at which the piezoelectric film undergoes dielectric breakdown. The first diode includes a first impurity region of a first conductivity type formed in the semiconductor film, The second diode includes a second impurity region of a second conductivity type formed in the first impurity region.

9. The MEMS element according to claim 1 or 2, wherein: The piezoelectric element includes an electrode composed of a semiconductor film adjacent to the piezoelectric film. The semiconductor film includes a first portion constituting the electrode and a second portion separated from the first portion, The diode unit includes a first diode and a second diode, wherein the first diode has a first direction corresponding to the polarization direction of the piezoelectric film as a forward direction, and the second diode is connected in series with the first diode and has a second direction opposite to the first direction as a forward direction. The breakdown voltage of the first diode is a voltage lower than the voltage at which the polarization reversal of the piezoelectric film occurs. The breakdown voltage of the second diode is a voltage below the voltage at which the piezoelectric film undergoes dielectric breakdown. The first diode includes a first impurity region formed in the semiconductor film, The second diode includes a second impurity region formed in the semiconductor film and separated from the first impurity region.

10. The MEMS element according to any one of claims 1 to 9, wherein: The piezoelectric element includes: a first electrode adjacent to the piezoelectric film; and a second electrode made of a metal material, the second electrode being provided on the opposite side of the first electrode across the piezoelectric film.

11. A piezoelectric acoustic device, The device uses the MEMS element according to any one of claims 1 to 10.

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