Thin-film piezoelectric resonator device and its manufacturing method

Abstract

To provide a thin-film piezoelectric resonance device capable of having a single resonance characteristic at high frequencies and a manufacturing method for the same.SOLUTION: A thin-film piezoelectric resonance device 10 includes a substrate 11 with an aperture 11a formed through the top and bottom and a laminated body 33 with peripheral parts supported by the substrate. The laminated body includes a resonant portion 20 including a front surface electrode 16, a back surface electrode 15, and a piezoelectric thin film 14 sandwiched between the front surface electrode and the back surface electrode. The resonant portion is smaller than the aperture in the substrate in plan view, and is arranged within the aperture separated from the end portion of the aperture. The resonant frequency of the resonant portion is higher than that of the surroundings of the resonant portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thin film piezoelectric resonator device and a method for manufacturing the same. [Background technology]

[0002] The fifth-generation mobile communication system (5G) will use the Sub6 region below 6 GHz and the high-band region of approximately 24 GHz or higher as radio frequency bands. A large market has already been formed for resonators used in acoustic wave filters in the Sub6 band. The market for millimeter-wave band resonators is also expected to expand significantly.

[0003] Chip-sized piezoelectric thin film resonators using aluminum nitride (AlN) piezoelectric thin films are known (see, for example, Non-Patent Document 1). In a piezoelectric thin film resonator, electrodes are provided above and below the piezoelectric thin film, and an air gap is formed below them, and electrical signals are transmitted between the upper and lower electrodes by thickness vibration of these electrodes. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] S. Ruby et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 59, pp.334-345 (2012) Summary of the Invention [Problem to be solved by the invention]

[0005] In the piezoelectric thin film resonator of Non-Patent Document 1, the upper and lower electrodes sandwiching the piezoelectric thin film are formed wider than the entire surface of the air gap, and therefore vibrations of the piezoelectric thin film leak around the electrodes at the end faces where the upper and lower electrodes face each other, resulting in an undesirable characteristic of increased loss and a reduced Q factor of the resonance characteristics.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film piezoelectric resonator device that can have a single resonance characteristic in the frequency range used by the device, and a method for manufacturing the same. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, there is provided a thin-film piezoelectric resonator device comprising: a substrate having an opening formed therethrough in the vertical direction; and a laminate having a peripheral portion supported by the substrate, the laminate including a resonator portion consisting of a surface electrode, a back electrode, and a piezoelectric thin film sandwiched between the surface electrode and the back electrode, the resonator portion being smaller than the opening of the substrate in a plan view and being positioned within the opening at a distance from the edge of the opening, and the resonator portion having a higher resonant frequency than the surrounding area of ​​the resonator portion.

[0008] According to the above aspect, the resonator element is smaller than the opening in the substrate in plan view, and is disposed within the opening at a distance from the edge of the opening, and the resonant frequency of the resonator element is set higher than the resonant frequency of the surrounding area. This aspect makes it possible to confine the vibration energy of the thickness vibration by preventing it from diffusing to the surrounding area of ​​the resonator element. This makes it possible to provide a thin-film piezoelectric resonator device with a high Q value that exhibits single resonance characteristics in the frequency range of use.

[0009] According to another aspect of the present disclosure, there is provided a method for manufacturing a thin-film piezoelectric resonator device, the method including the steps of: forming a laminate on an insulating layer of a substrate having an insulating layer formed on its surface, the laminate including a resonator portion consisting of a front electrode, a back electrode, and a piezoelectric thin film sandwiched between the front electrode and the back electrode; and removing a portion of the substrate and the insulating layer to form an opening, the opening being formed below the resonator portion, wherein the resonator portion is smaller than the opening in a planar view and is positioned within the opening at a distance from an edge of the opening, and the resonator portion has a higher resonant frequency than the surrounding area of ​​the resonator portion.

[0010] According to the above-described other aspect, the resonant frequency of the resonant portion is set higher than that of the surrounding area of ​​the resonant portion, and an opening is formed by etching the substrate and the insulating layer on the back side of the resonant portion, thereby forming a structure for confining thickness vibration of the resonant portion and facilitating the manufacture of a diaphragm-type thin film piezoelectric resonator device.

[0011] The thin film piezoelectric resonator device according to the present invention, as described in the claims, specification, and drawings, includes a piezoelectric thin film resonator whose peripheral edge is supported by a substrate and which includes a piezoelectric thin film sandwiched between a front electrode and a back electrode, and also includes a filter form in which a signal line and a ground line are connected to the piezoelectric thin film resonator. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating a configuration of a thin film piezoelectric resonator device according to a first embodiment of the present invention. [Figure 2] FIG. 10 is a cross-sectional view showing a modified example of the thin film piezoelectric resonator device. [Figure 3] 3A to 3C are process diagrams (part 1) of the thin film piezoelectric resonator device according to the first embodiment. [Figure 4] 5A to 5C are process diagrams (part 2) of the thin film piezoelectric resonator device according to the first embodiment. [Figure 5] FIG. 4 is a schematic diagram illustrating the configuration of a thin film piezoelectric resonator device according to a second embodiment of the present invention. [Figure 6] 10A to 10C are process diagrams (part 1) for manufacturing the thin film piezoelectric resonator device according to the second embodiment. [Figure 7] 10A to 10C are process diagrams (part 2) of the thin film piezoelectric resonator device according to the second embodiment. [Figure 8] FIG. 10 is a schematic diagram illustrating the configuration of a thin film piezoelectric resonator device according to a third embodiment of the present invention. [Figure 9] 10A to 10C are process diagrams (part 1) of the thin film piezoelectric resonator device according to the third embodiment. [Figure 10] 10A to 10C are process diagrams (part 2) of the thin film piezoelectric resonator device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Elements common to multiple drawings are designated by the same reference numerals, and detailed descriptions of those elements will not be repeated.

[0014] [First embodiment] FIG. 1 is a schematic diagram showing the configuration of a thin-film piezoelectric resonator device according to a first embodiment of the present invention. FIG. 1(a) is a cross-sectional view of the thin-film piezoelectric resonator device, and FIG. 1(b) is a plan view of the thin-film piezoelectric resonator device. Referring to FIGS. 1(a) and 1(b), a thin-film piezoelectric resonator device 10 includes a silicon substrate 11, a silicon oxide film 12 on the silicon substrate 11, and a laminate 13 on the silicon oxide film 12. The laminate 13 includes a piezoelectric thin film 14 whose peripheral edge is supported by the silicon substrate 11 and the silicon oxide film 12, a back electrode 15 on the back surface of the piezoelectric thin film 14, a front electrode 16 formed on the front surface of the piezoelectric thin film 14, a signal line 17 that is in electrical contact with the back electrode 15 at one end, a signal line 18 that is in electrical contact with the front electrode 16 at one end, and ground lines 19 on the surface of the silicon oxide film 12 on both sides of the signal lines 17 and 18 in a plan view.

[0015] A recess 14a is provided in the center of the surface of the piezoelectric thin film 14, and a surface electrode 16 extends from one end to the bottom surface 14b of the recess 14a. A back surface electrode 15 extends from the other end to a position facing the bottom surface 14b of the recess 14a on the back surface of the piezoelectric thin film 14. An electric field is applied from signal lines 17 and 18 to a portion of the piezoelectric thin film 14 sandwiched between the tip of the surface electrode 16 on the bottom surface 14b of the recess 14a and the tip of the back surface electrode 15, generating thickness vibration. Hereinafter, the surface electrode 16, the back surface electrode 15, and the portion of the piezoelectric thin film 14 sandwiched between the surface electrode 16 and the back surface electrode 15 will be referred to as a resonator portion 20.

[0016] On the other hand, in the portion of the piezoelectric thin film 14 where the front electrode 16 and the back electrode 15 do not face each other, that is, in the peripheral portion of the resonator portion 20, no electric field is applied to the piezoelectric thin film 14, and no thickness vibration occurs.

[0017] The recess 14a is formed so that its inner wall surface 14c is at an angle of 90 degrees with respect to the surface (upper surface) of the piezoelectric thin film 14. This angle is not particularly limited and can be any angle. Furthermore, as shown in FIG. 1(b), the recess 14a is formed in a rectangular shape when viewed from above, but it may also be formed in a square, circular, elliptical, or other shape.

[0018] 1(a) and 1(b), the surface electrode 16 is formed on a part of the bottom surface 14b of the recess 14a in the resonator unit 20, but may be formed on the entire bottom surface 14b. Accordingly, the back electrode 15 may be formed to face the surface electrode 16.

[0019] The silicon substrate 11 and the silicon oxide film 12 support the peripheral portion of the laminate 13, more specifically the peripheral portion of the piezoelectric thin film 14. An opening 11a is formed in the center of the silicon substrate 11 and the silicon oxide film 12, penetrating vertically. The lower surface of the back electrode 15 and the lower surface of the piezoelectric thin film 14 are exposed in the opening 11a. The lower surface of the back electrode 15 and the lower surface of the piezoelectric thin film 14 are supported by the silicon substrate 11 and the silicon oxide film 12 in the opening 11a. The resonating portion 20 can vibrate in the vertical direction, that is, in the thickness direction. When viewed from above, one or more resonating portions 20 may be provided within the opening 11a.

[0020] 1, opening edge 11c is rectangular (e.g., 2 μm × 1 μm) in plan view, but is not limited thereto and may be elliptical, polygonal, or the like. Resonator portion 20 is smaller than opening 11a in plan view and is disposed at a position separated from opening edge 11c, preferably at a position sufficiently separated therefrom. More specifically, in plan view, the distance from opening edge 11c to the edge of bottom surface 14b of recess 14a is set to be equal to or greater than the shorter of the width and depth when opening edge 11c is rectangular, and is set to be equal to or greater than the minor axis when opening edge 11c is elliptical.

[0021] The silicon substrate 11 may be replaced with other insulating substrates such as sapphire or quartz, and the silicon oxide film 12 may be replaced with other insulating layers such as silicon nitride, zirconium oxide, or aluminum oxide.

[0022] An inner wall surface 11b of the silicon substrate 11 and the silicon oxide film 12 that form the opening 11a is formed at a right angle to the lower surface of the stacked body 13. The inner wall surface 11b is not limited to this and may have any angle.

[0023] Fig. 2 is a cross-sectional view showing a modified example of a thin film piezoelectric resonator device. Referring to Figs. 2(a) to 2(d), the opening 11a of the thin film piezoelectric resonator device 10 may have opposing inner wall surfaces 11b1 that gradually widen downward as shown in Fig. 2(a), or may have opposing inner wall surfaces 11b2 that gradually narrow as shown in Fig. 2(b). Furthermore, the opening 11a may have inner wall surfaces 11b that are flat or curved, inner wall surface 11b3 that is concave as shown in Fig. 2(c), or inner wall surface 11b4 that is convex as shown in Fig. 2(d), or a combination of these.

[0024] Returning to FIG. 1 , in the resonator unit 20, the thickness of the piezoelectric thin film 14 is determined according to the desired resonance frequency, taking into account the thicknesses of the front electrode 16 and the back electrode 15. Furthermore, in the resonator unit 20, the total thickness of the piezoelectric thin film 14, front electrode 16, and back electrode 15 is configured to be thinner than the thickness of the piezoelectric thin film 14 around the resonator unit 20 or the total thickness of the piezoelectric thin film 14 and back electrode 15. In other words, the step of the recess 14a is configured to be thicker than the thickness of the front electrode 16. Since the resonance frequency of thickness vibration is inversely proportional to the total thickness of the piezoelectric thin film 14, front electrode 16, and back electrode 15, the resonance frequency of thickness vibration in the resonator unit 20 is higher than the resonance frequency if thickness vibration were generated around the resonator unit 20. When viewed from above, the recess 14a is a rectangle measuring, for example, 2 μm × 1 μm, and the step is, for example, 0.05 μm.

[0025] Since the resonating portion 20 is formed in the recess 14a, it is possible to confine the vibration energy of the thickness vibration, and to transmit signals efficiently.

[0026] The piezoelectric thin film 14 is made of a material whose main component is aluminum nitride (AlN). The piezoelectric thin film 14 may be ScAlN, preferably ScAlN in which Sc is dissolved in AlN at a concentration of 0.1 at% to 30 at% and more preferably ScAlN in which Sc is dissolved at a concentration of 2 at% to 30 at%. By using ScAlN for the piezoelectric thin film 14, which has higher piezoelectricity than AlN, the thin film piezoelectric resonator device 10 can have a wider bandwidth. The thickness of the piezoelectric thin film 14 is selected depending on the resonant frequency, and is, for example, approximately 600 nm for 10 GHz and approximately 200 nm for 30 GHz. In these cases, the thicknesses of the front electrode 16 and the back electrode 15 are each, for example, 30 nm.

[0027] The crystallinity of the piezoelectric thin film 14 in the resonator portion 20 may be configured to be higher than the crystallinity of the piezoelectric thin film 14 around the resonator portion 20. As will be described later, when the piezoelectric thin film 14 is formed by sputtering or the like so as to cover the back electrode 15 and the silicon oxide film 12, the morphology (i.e., morphological characteristics including the crystal state, etc.) of the piezoelectric thin film 14 in the portion underlying the back electrode 15 changes compared to the portion underlying the silicon oxide film 12. This improves the Young's modulus of the piezoelectric thin film 14 in the resonator portion 20, and as a result, the resonant frequency of the thin film piezoelectric resonator device 10 can be set high and vibration energy can be effectively trapped in the resonator portion 20.

[0028] The surface electrode 16 and the back electrode 15 are preferably formed of a conductive material with a high Young's modulus. The surface electrode 16 and the back electrode 15 are preferably made of molybdenum (Mo) and tungsten (W) or an alloy containing at least one of these. This allows the resonant frequency of the thin-film piezoelectric resonator 10 to be set high. The thicknesses of the surface electrode 16 and the back electrode 15 in the resonator unit 20 are selected according to the resonant frequency. The surface electrode 16 and the back electrode 15 in the resonator unit 20 may have different thicknesses from those in other portions. From the perspective of improving the degree of freedom in resonant frequency design and achieving good transmission, it is preferable that the thicknesses of the surface electrode 16 and the back electrode 15 in the resonator unit 20 be thinner than those of the surface electrode 16 and the back electrode 15 in the other portions. The thicknesses of the surface electrode 16 and the back electrode 15 in the resonator unit 20 are, for example, in the range of 0.01 μm to 0.1 μm, and the thicknesses of the surface electrode 16 and the back electrode 15 in the other portions are, for example, in the range of 1 μm to 2 μm.

[0029] The thickness of the silicon substrate 11 is set in the range of, for example, 200 μm to 800 μm, the thickness of the silicon oxide film 12 is set in the range of, for example, 0.1 μm to 2.0 μm, and the height of the opening 11a is set in the range of, for example, 200 nm to 800 nm.

[0030] The signal lines 17 and 18 and the ground line 19 are preferably made of a conductive material such as gold (Au), platinum (Pt), aluminum (Al), copper (Cu), or an alloy containing at least one of these, and a base layer of chromium (Cr) or tantalum (Ta) may be formed thereon.

[0031] According to this embodiment, the resonator portion 20 is smaller than the opening 11a in the silicon substrate 11 and the silicon oxide film 12 in plan view, and is disposed in a recess 14a substantially at the center of the opening 11a. The resonator portion 20 is formed thinner than its surroundings. Thickness vibrations generated in the resonator portion 20 occur in a portion thinner than the surroundings. This configuration makes it possible to confine the vibration energy of the thickness vibrations by suppressing diffusion to the surroundings of the resonator portion 20. This allows for the realization of a thin-film piezoelectric resonator device 10 exhibiting single resonance characteristics. The piezoelectric thin film 14 of the resonator portion 20 is formed thinner than the surroundings and has a higher Young's modulus, so that the resonant frequency of the thickness vibrations is higher than the surroundings, and the vibration energy of the thickness vibrations can be further confined.

[0032] 3 and 4 are process diagrams (parts 1 and 2) of the thin film piezoelectric resonator device according to the first embodiment. A method for manufacturing the thin film piezoelectric resonator device 10 using MEMS (Micro Electro Mechanical Systems) technology will be described with reference to Figs. 3(a) to 3(d) and 4(a) to 4(c) in addition to Fig. 1.

[0033] In the step of FIG. 3(a), a silicon oxide film 12A is formed on the surface of a silicon substrate 11A to a thickness of, for example, 1 μm. The method for forming the silicon oxide film 12A is not particularly limited, but may be, for example, a chemical vapor deposition (CVD) method, a sputtering method, or the like. Next, a metal film that will serve as a back electrode is formed on the surface of the silicon oxide film 12A to a thickness of 30 nm by, for example, a sputtering method. The metal film is, for example, molybdenum (Mo) and tungsten (W) or an alloy containing at least one of these. Next, the metal film is shaped by photolithography and dry etching to form a back electrode 15.

[0034] 3(b), a piezoelectric thin film 14A is formed by sputtering, for example, reactive sputtering, to cover the silicon oxide film 12A and the back electrode 15. The piezoelectric thin film 14A can be made of a material containing aluminum nitride (AlN) as its main component. The piezoelectric thin film 14A is formed to a thickness of, for example, 200 nm.

[0035] 3(c), a recess 14a is formed by photolithography and dry etching on the surface of the piezoelectric thin film 14A above the tip of the back electrode 15. The depth of the recess 14a is, for example, 50 nm.

[0036] Next, in the step of FIG. 3(d), the entire piezoelectric thin film 14A is etched by photolithography and dry etching to expose the base of the back electrode 15 and the silicon oxide film 12A, and then shaped to form the piezoelectric thin film 14.

[0037] 4(a), a surface electrode 16 is formed by sputtering and dry etching on the bottom surface 14b and side surfaces of the recessed portion 14a and on the surface of the piezoelectric thin film 14. The surface electrode 16 is formed to a thickness of 30 nm, for example. In order to set the resonant frequency of the resonating portion to a desired frequency, the surface electrode 16 may be formed thinner than other portions of the surface electrode 16 by dry etching the portion of the bottom surface 14b of the recessed portion 14a.

[0038] 4(b), signal lines 17, 18 and ground lines 19 are formed on the surface of silicon oxide film 12A by sputtering and dry etching. Signal lines 17, 18 are formed so as to contact the bases of back electrode 15 and front electrode 16, respectively. For the signal lines 17, 18 and ground line 19, for example, a chromium (Cr) film is formed as an underlayer, and a highly conductive metal or alloy film such as a gold (Au) film is formed thereon. This completes the laminate 13 having the resonator unit 20.

[0039] 4(c), the silicon substrate 11A and the silicon oxide film 12A are removed from the back surface of the silicon substrate 11A by, for example, deep reactive ion etching (DRIE), to form an opening 11a that exposes part of the back surface electrode 15 and part of the back surface of the piezoelectric thin film 14, while leaving its peripheral edge. The opening 11a is formed so that it is larger than the resonator unit 20 in plan view and so that the resonator unit 20 is substantially at the center. This forms the silicon substrate 11 and silicon oxide film 12 that support the peripheral edge of the laminate 13, and the diaphragm-type thin film piezoelectric resonator device 10.

[0040] According to the manufacturing method of this embodiment, the recess 14a is formed by etching the surface of the piezoelectric thin film 14, and the opening 11a is formed by etching the silicon substrate 11A and the silicon oxide film 12A on the back surface side of the resonator portion 20. This makes the resonator portion 20 thinner than its surroundings, thereby increasing the resonant frequency of the resonator portion 20 compared to its surroundings, forming a structure for confining thickness vibration of the resonator portion 20, and also facilitating the manufacturing of the diaphragm-type thin film piezoelectric resonator device 10.

[0041] [Second embodiment] 5A and 5B are schematic diagrams showing the configuration of a thin film piezoelectric resonator device according to a second embodiment of the present invention. Fig. 5A is a cross-sectional view of the thin film piezoelectric resonator device, and Fig. 5B is a plan view of the thin film piezoelectric resonator device. Referring to Figs. 5A and 5B, a thin film piezoelectric resonator device 30 has a silicon substrate 11, a silicon oxide film 12 on the silicon substrate 11, and a laminate 33 on the silicon oxide film 12. The laminate 33 includes a piezoelectric thin film 34 whose peripheral edge is supported by a silicon substrate 11 and a silicon oxide film 12, a back electrode 15 formed on the back surface of the piezoelectric thin film 34, a front electrode 36 formed on the surface of the piezoelectric thin film 34, an insulating layer 38 having an opening 38a penetrating vertically on the surface of part of the piezoelectric thin film 34 and the front electrode 36, a signal line 17 whose one end is in contact with and electrically conductive to the back electrode 15, a signal line 18 whose one end is in contact with and electrically conductive to the front electrode 36, and ground lines 19 on the surface of the silicon oxide film 12 on both sides of the signal lines 17 and 18 when viewed in plan.

[0042] The thin film piezoelectric resonator device 30 includes a resonator section 40 consisting of a surface electrode 36, a back electrode 15, and a portion of the piezoelectric thin film 34 sandwiched between the surface electrode 36 and the back electrode 15. In the resonator section 40, an electric field is applied from the signal lines 17 and 18 to the portion of the piezoelectric thin film 34 sandwiched between the tip of the surface electrode 36 and the tip of the back electrode 15, generating thickness vibration.

[0043] The surface electrode 36 of the resonator part 40 is disposed on the surface of the piezoelectric thin film 34 within the opening 38a of the insulating layer 38. That is, in plan view, the resonator part 40 is disposed within a recess formed on the surface of the thin film piezoelectric resonator device 30. This allows the resonator part 40 to trap the energy of thickness vibration and transmit signals efficiently.

[0044] The materials and thicknesses of the piezoelectric thin film 34, the front electrode 36, and the back electrode 15 are the same as those of the thin-film piezoelectric resonator device 10 according to the first embodiment. As in the first embodiment, the piezoelectric thin film 34 of the resonator portion 40 is formed on the back electrode 15 as an underlying layer. Therefore, its morphology is different from that of the portion formed on the silicon oxide film 12, improving the Young's modulus of the piezoelectric thin film 34 of the resonator portion 40. As a result, the resonant frequency of the thin-film piezoelectric resonator device 10 can be set high and vibration energy can be effectively concentrated in the resonator portion 40. The insulating layer 38 may be made of any material, including, but not limited to, silicon oxide, silicon nitride, zirconium oxide, and titanium oxide. The insulating layer 38 may be made of a material primarily composed of the piezoelectric thin film 34, but may be a film that does not exhibit piezoelectricity, such as a polycrystalline film with random crystal orientation. The thickness of the insulating layer 38 is set to the same thickness as the step of the recess 14a in the first embodiment, e.g., 300 nm.

[0045] According to this embodiment, the resonator unit 40 is smaller than the opening 11a in the silicon substrate 11 and the silicon oxide film 12 in plan view. The resonator unit 40 is located in the opening 38a of the insulating layer 38, substantially at the center of the opening 11a. The resonator unit 40 is thinner than its surroundings. Thickness vibrations generated in the resonator unit 40 occur in a portion of the resonator unit 40 that is thinner than its surroundings. This configuration prevents the vibrational energy of the thickness vibrations from diffusing to the surroundings of the resonator unit 40 and confines it within the resonator unit 40. This allows the thin-film piezoelectric resonator device 30 to exhibit single-resonance characteristics in the frequency range of interest. Furthermore, the piezoelectric thin film 34 of the resonator unit 40 has a higher Young's modulus than the surrounding piezoelectric thin films. Therefore, the resonant frequency of the thickness vibrations is higher than the surroundings, further confining the vibrational energy of the thickness vibrations.

[0046] 6 and 7 are process diagrams (parts 1 and 2) of the thin film piezoelectric resonator device according to the second embodiment. A method for manufacturing the thin film piezoelectric resonator device 30 will be described with reference to Figs. 6(a) to 6(d) and 7(a) to 7(b) in addition to Fig. 5. Detailed descriptions of steps that are the same as those in the manufacturing method according to the first embodiment will be omitted.

[0047] In the step of FIG. 6(a), a silicon oxide film 12A, a back electrode 15, and a piezoelectric thin film 34A are formed on the surface of a silicon substrate 11A in the same manner as in the steps of FIGS. 3(a) and 3(b).

[0048] 6(b), the entire piezoelectric thin film 34A is etched by photolithography and dry etching to expose the base of the back electrode 15 and the silicon oxide film 12A and to shape the piezoelectric thin film 34. Next, a front surface electrode 36 is formed on the surface of the piezoelectric thin film 34 by sputtering and dry etching in a position where its tip faces the tip of the back surface electrode 15. The tip of the front surface electrode 36 (the portion included in the resonator portion 40) may be formed thinner than other portions of the front surface electrode 36 by dry etching.

[0049] Next, in the step of FIG. 6(c), an insulating layer 38A is formed by CVD, sputtering, or the like so as to cover the surface of the piezoelectric thin film 34 and the surface electrode 36.

[0050] 6(d), the insulating layer 38A is etched by photolithography and dry etching to expose the base of the surface electrode 36, form an opening 38a, and expose the tip of the surface electrode 36. As a result, the insulating layer 38 has an opening 38a that penetrates the insulating layer 38 from top to bottom above the portion that will become the resonator 40.

[0051] 7(a), signal lines 17, 18 and a ground line 19 are formed on the surface of the silicon oxide film 12A by sputtering and dry etching. The signal lines 17, 18 are formed so as to contact the bases of the back electrode 15 and the front electrode 36, respectively. In this manner, a laminate 33 having a resonator unit 40 is formed.

[0052] 7(b), the silicon substrate 11A and the silicon oxide film 12A are removed from the back surface of the silicon substrate 11A, for example by DRIE, to form an opening 11a that exposes part of the back surface electrode 15 and part of the back surface of the piezoelectric thin film 34, while leaving its peripheral edge. The opening 11a is formed so that it is larger than the resonator unit 40 in plan view and so that the resonator unit 40 is substantially at the center. This forms the silicon substrate 11 and silicon oxide film 12 that support the peripheral edge of the laminate 33, and the diaphragm-type thin film piezoelectric resonator device 30.

[0053] According to the manufacturing method of this embodiment, the insulating layer 38 is formed to cover the piezoelectric thin film 34, and the opening 38a is formed in the insulating layer 38 by etching, and the opening 11a is also formed by etching the silicon substrate 11A and the silicon oxide film 12A on the back surface side of the resonator portion 40. This makes it possible to form the resonator portion 40 thinner than its surroundings, thereby forming a structure for confining thickness vibration of the resonator portion 40, and also makes it possible to easily manufacture the diaphragm-type thin film piezoelectric resonator device 30.

[0054] [Third embodiment] FIG. 8 is a schematic diagram showing the configuration of a thin-film piezoelectric resonator device according to a third embodiment of the present invention. FIG. 8(a) is a cross-sectional view of the thin-film piezoelectric resonator device, and FIG. 8(b) is a plan view of the thin-film piezoelectric resonator device. Referring to FIGS. 8(a) and 8(b), a thin-film piezoelectric resonator device 50 includes a silicon substrate 11, a silicon oxide film 12 on the silicon substrate 11, and a laminate 53 on the silicon oxide film 12. The laminate 53 is supported at its periphery by the silicon substrate 11 and the silicon oxide film 12. The laminate 53 includes an insulating layer 58 having an opening 58a penetrating vertically, and a resonator unit 60 disposed within the opening 58a. The resonator unit 60 includes a piezoelectric thin film 54 disposed within the opening 58a, a tip of a front electrode 56 disposed on a front surface 54b of the piezoelectric thin film 54, and a tip of a back electrode 15 disposed on the back surface of the piezoelectric thin film 54. The piezoelectric thin film 54 is sandwiched between the tip of the front electrode 56 and the tip of the back electrode 15. The back electrode 15 extends over the back surfaces of the piezoelectric thin film 54 and the insulating layer 58, with its base contacting the signal line 17 for electrical conduction. The front electrode 56 extends over the surface 54b of the piezoelectric thin film 54 and the surface of the insulating layer 58, with its base contacting the signal line 18 for electrical conduction. The thin film piezoelectric resonator 50 has ground lines 19 on the surface of the silicon oxide film 12 on both sides of the signal lines 17 and 18 in a plan view.

[0055] In the resonator 60, an electric field is applied from the signal lines 17 and 18 to the portion of the piezoelectric thin film 54 sandwiched between the tip of the front electrode 56 and the tip of the back electrode 15, generating thickness vibration.

[0056] The resonator part 60 is disposed in an opening 58a in the insulating layer 58. The surface electrode 56 is disposed stepwise downward from the surface of the insulating layer 58. In other words, the resonator part 60 is disposed in a recess in the surface of the thin film piezoelectric resonator device 50. This allows the thin film piezoelectric resonator device 50 to trap the energy of thickness vibration of the resonator part 60, enabling efficient signal transmission.

[0057] The materials and thicknesses of the piezoelectric thin film 54, the front electrode 56, and the back electrode 15 are the same as those of the thin film piezoelectric resonator device 10 according to the first embodiment. As in the first embodiment, the piezoelectric thin film 54 of the resonator unit 60 is formed on the back electrode 15 as an underlying layer. Therefore, the crystallinity is improved compared to the portion of the first embodiment that is formed on the silicon oxide film 12 as an underlying layer. This improves the Young's modulus of the piezoelectric thin film 54 of the resonator unit 60. As a result, the resonant frequency of the thin film piezoelectric resonator device 50 can be set high, and vibration energy can be effectively concentrated in the resonator unit 60. The insulating layer 58 is made of a material having a lower Young's modulus than the piezoelectric thin film 54, such as a silicon oxide film, titanium oxide film, zirconium oxide film, or zinc oxide film. The thickness of the insulating layer 58 may be thicker than the combined thickness of the piezoelectric thin film 54 and the front electrode 56. The thickness of the insulating layer 58 is preferably set in the range of 100 nm to 1000 nm. The thickness of the insulating layer 58 may be the same as the total thickness of the piezoelectric thin film 54 and the surface electrode 56, or may be thinner, as long as the design allows the resonant frequency to be lower than that of the resonating portion.

[0058] According to this embodiment, the resonator unit 60 is smaller than the opening 11a in the silicon substrate 11 and the silicon oxide film 12 in plan view, and is disposed substantially in the center of the opening 11a within the opening 58a in the insulating layer 58. The resonator unit 60 is thinner than the insulating layer 58 surrounding it. Thickness vibrations generated in the resonator unit 60 occur in a portion of the resonator unit 60 that is thinner than the surrounding area. This configuration prevents the vibrational energy of the thickness vibrations from diffusing to the surrounding area of ​​the resonator unit 60 and confines it within the resonator unit 60. This allows the thin-film piezoelectric resonator device 60 to exhibit single-resonance characteristics. Furthermore, the piezoelectric thin film 54 of the resonator unit 60 has a higher Young's modulus than the surrounding insulating layer 58. This increases the resonant frequency of the thickness vibrations relative to the surrounding area, further confining the vibrational energy of the thickness vibrations.

[0059] 9 and 10 are process diagrams (parts 1 and 2) of the thin film piezoelectric resonator device according to the second embodiment. A method for manufacturing the thin film piezoelectric resonator device 30 will be described with reference to Figs. 9(a) to 9(d) and 10(a) to 10(c) in addition to Fig. 8. Detailed descriptions of steps similar to those in the manufacturing methods of the first and second embodiments will be omitted.

[0060] In the step of FIG. 9(a), a silicon oxide film 12A and a back electrode 15 are formed on the surface of a silicon substrate 11A in the same manner as in the step of FIG. 3(a).

[0061] 9(b), an insulating layer 58A is formed by a CVD method, a sputtering method, or the like so as to cover the silicon oxide film 12A and the back surface electrode 15. The insulating layer 58A is preferably formed to a thickness in the range of 100 nm to 1000 nm.

[0062] 9(c), a photoresist mask 59 is formed on the surface of the insulating layer 58A by photolithography, and openings 59a in the photoresist mask 59 are formed above the tips of the back electrodes 15. Next, the insulating layer 58A is etched through the openings 59a in the photoresist mask 59 by dry etching, to form openings 58a that expose the tips of the back electrodes 15. At this time, the silicon oxide film 12A may or may not be exposed in the front and rear directions of the page.

[0063] 9(d), a piezoelectric thin film 54A is formed on the back surface electrode 15 in the opening 58a by sputtering, for example, reactive sputtering. The piezoelectric thin film 54A is also formed on the surface of the photoresist mask 59.

[0064] 10(a), the photoresist mask 59 and the piezoelectric thin film 54A on the photoresist mask 59 are removed by wet etching. Next, the insulating layer 58A is entirely etched by photolithography and dry etching to expose the base of the back electrode 15 and the silicon oxide film 12A and to form a shaped insulating layer 58.

[0065] 10(b), a surface electrode 56 is formed on the surface of the piezoelectric thin film 54, the side surfaces of the openings 58a, and the surface of the insulating layer 58 by sputtering and dry etching. In order to set the resonance frequency of the resonator 60 to a desired frequency, the portion of the surface electrode 56 on the surface of the piezoelectric thin film 54 may be dry etched to be thinner than the other portions of the surface electrode 56. Next, signal lines 17 and 18 and a ground line 19 are formed on the surface of the silicon oxide film 12A by sputtering and dry etching. The signal lines 17 and 18 are formed so as to contact the bases of the back electrode 15 and the surface electrode 56, respectively. In this manner, a laminate 53 having a resonator 60 is formed.

[0066] 10(c), the silicon substrate 11A and the silicon oxide film 12A are removed from the back surface side of the silicon substrate 11A by, for example, DRIE, to form an opening 11a that exposes part of the back surface electrode 15 and part of the back surface of the piezoelectric thin film 54, while leaving its peripheral edge. The opening 11a is formed so that it is larger than the resonator unit 60 in plan view and so that the resonator unit 60 is substantially at the center. This forms the silicon substrate 11 and the silicon oxide film 12 that support the peripheral edge of the laminate 53, and the diaphragm-type thin film piezoelectric resonator device 50.

[0067] According to the manufacturing method of this embodiment, an insulating layer 58 thicker than the piezoelectric thin film 54 is formed, and the resonator unit 60 including the piezoelectric thin film 54 sandwiched between the back electrode 15 and the front electrode 56 is formed in the opening 58a, and the silicon substrate 11A and the silicon oxide film 12A on the back surface side of the resonator unit 60 are etched to form the opening 11a. This makes the resonator unit 60 thinner than its surroundings, forming a structure for confining thickness vibration of the resonator unit 60, and also makes it possible to easily manufacture the diaphragm-type thin film piezoelectric resonator device 50.

[0068] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the present invention as defined in the claims. [Explanation of symbols]

[0069] 10,30,50 Thin film piezoelectric resonator 11 Silicon substrate 11a opening 12 Silicon oxide film 13,33,53 laminate 14,34,54 Piezoelectric thin film 14a Recess 15 Back electrode 16,36,56 surface electrode 17,18 signal lines 20,40,60 Resonant part 38a,58a opening

Claims

1. a substrate having an opening formed therethrough in the vertical direction; a laminate having a peripheral portion supported by the substrate, and having a back electrode, a piezoelectric thin film, and a front electrode laminated in this order; the laminate includes a resonator portion formed of a piezoelectric thin film sandwiched between a portion of the front electrode and a portion of the back electrode, the resonator portion is smaller than the opening of the substrate in a plan view and is disposed within the opening at a distance from an edge of the opening; A thin film piezoelectric resonator device, wherein the piezoelectric thin film of the resonator portion has a higher Young's modulus than the piezoelectric thin film surrounding the resonator portion.

2. a substrate having an opening formed therethrough in the vertical direction; a laminate having a peripheral portion supported by the substrate, and having a back electrode, a piezoelectric thin film, and a front electrode laminated in this order; the laminate includes a resonator portion formed of a piezoelectric thin film sandwiched between a portion of the front electrode and a portion of the back electrode, the resonator portion is smaller than the opening of the substrate in a plan view and is disposed within the opening at a distance from an edge of the opening; The front electrode and the rear electrode are formed so that the thickness of the resonating portion is thinner than the thickness of the other portions.

3. 3. The thin film piezoelectric resonator device according to claim 1, wherein the piezoelectric thin film of the resonator portion is formed thinner than the piezoelectric thin film surrounding the resonator portion.

4. 4. The thin film piezoelectric resonator device according to claim 3, wherein the piezoelectric thin film of the resonator portion is formed to be 1% or more thinner than the piezoelectric thin film surrounding the resonator portion.

5. 5. The thin film piezoelectric resonator device according to claim 1, wherein the surface electrode of the resonator portion is disposed on a bottom surface of a recess formed in the surface of the laminate.

6. 6. The thin film piezoelectric resonator device according to claim 5, wherein the recess is formed on the surface of the piezoelectric thin film.

7. 6. The thin film piezoelectric resonator device according to claim 5, wherein the recess is an opening in an insulating layer formed on the surface of the piezoelectric thin film.

8. 8. The thin film piezoelectric resonator device according to claim 5, wherein the surface electrode is formed on a part of the bottom surface of the recess.

9. 9. The thin film piezoelectric resonator device according to claim 1, wherein the side and top surfaces of the rear electrode are covered with the piezoelectric thin film.

10. the stack includes another insulating layer disposed on the substrate; 2. The thin film piezoelectric resonator device according to claim 1, wherein the resonator portion is disposed in an opening in the other insulating layer.

11. a substrate and another insulating layer disposed thereon, the substrate having a first opening formed therethrough in the vertical direction; a laminate including an insulating layer having a second opening penetrating vertically, the peripheral edge of which is supported by the other insulating layer, and a resonator portion disposed within the second opening, the resonator portion comprising a piezoelectric thin film sandwiched between a portion of a front electrode and a portion of a back electrode; the resonator portion is smaller than the first opening in plan view and is disposed within the first opening at a distance from an end of the first opening; In the resonator portion, a portion of the surface electrode is disposed below the surface of the insulating layer with a step.

12. A method for manufacturing a thin film piezoelectric resonator device, comprising: forming a laminate on an insulating layer formed on a surface of a substrate, the laminate including a resonator portion made of a front electrode, a back electrode, and a piezoelectric thin film sandwiched between the front electrode and the back electrode; removing a portion of the substrate and the insulating layer to form an opening, the opening being formed below the resonator; the resonator portion is smaller than the opening portion in a plan view and is disposed within the opening portion at a distance from an edge of the opening portion; The step of forming the laminate includes: forming another insulating layer so as to cover the insulating layer and the back electrode formed on the insulating layer; opening the other insulating layer at the position of the resonator portion to expose the rear electrode; forming the piezoelectric thin film so as to cover the other insulating layer and the exposed back electrode; removing the piezoelectric thin film on the other insulating layer and forming the surface electrode on the surface of the piezoelectric thin film of the resonator portion.

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