Elastic wave resonator and integrated circuit

Abstract

To provide an elastic wave resonator having a monocrystalline piezoelectric thin film, and an integrated circuit including the elastic wave resonator.SOLUTION: An elastic wave resonator 1 comprises: a first electrode 11 including a laminated film 110 that generates two-dimensional electron gas; a piezoelectric thin film 20 that is arranged on the laminated film 110; and a second electrode 12 that faces the first electrode 11 across the piezoelectric thin film 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic wave resonator and an integrated circuit. [Background technology]

[0002] In wireless communication systems, devices that use high frequencies such as the GHz band (hereinafter referred to as "high frequency devices") are being developed. In high frequency devices, acoustic wave filters are used as radio frequency (RF) filters that extract signals of specific frequencies from a wide frequency band. The acoustic wave filters used include SAW filters that use surface acoustic waves (SAW) and BAW filters that use acoustic waves (Bulk Acoustic Wave: BAW) that propagate through a piezoelectric section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-51000

[0004] [overview] BAW filters use elastic wave resonators with a structure in which a piezoelectric thin film is sandwiched between two electrodes. Single-crystal piezoelectric thin films have a large amount of displacement due to the inverse piezoelectric effect (the ratio of displacement due to voltage). Therefore, by using single-crystal piezoelectric thin films, it is possible to increase the bandwidth of RF filters and improve their Q values.

[0005] An object of the present disclosure is to provide an acoustic wave resonator having a single crystal piezoelectric thin film and an integrated circuit including the acoustic wave resonator.

[0006] In order to solve the above-mentioned problems, one aspect of the present disclosure is an acoustic wave resonator including a first electrode including a laminated film that generates two-dimensional electron gas, a piezoelectric thin film disposed on the laminated film, and a second electrode facing the first electrode with the piezoelectric thin film sandwiched therebetween. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a configuration of an acoustic wave resonator according to a first preferred embodiment of the present invention. [Figure 2A] FIG. 2A is a schematic plan view showing a configuration in which wiring is connected to the acoustic wave resonator according to the first preferred embodiment. [Figure 2B] FIG. 2B is a cross-sectional view taken along the direction II-II of FIG. 2A. [Figure 3A] FIG. 3A is a schematic plan view illustrating a configuration of a filter including an acoustic wave resonator according to a first preferred embodiment of the present invention. [Figure 3B] FIG. 3B is a cross-sectional view taken along the line III-III of FIG. 3A. [Figure 4] FIG. 4 is a circuit diagram showing an example of a filter formed by an acoustic wave resonator. [Diagram 5] 5A to 5C are cross-sectional views (part 1) illustrating steps in a manufacturing method for the acoustic wave resonator according to the first embodiment. [Figure 6] 6A to 6C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 2). [Figure 7] 7A to 7C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 3). [Figure 8] 8A to 8C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 4). [Figure 9] 9A to 9C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 5). [Figure 10] 10A to 10C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 6). [Figure 11] 11A to 11C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 7). [Figure 12]12A to 12C are cross-sectional views illustrating steps in a manufacturing method of the acoustic wave resonator according to the first embodiment (part 8). [Figure 13] FIG. 13 is a schematic cross-sectional view illustrating a configuration of an acoustic wave resonator according to a second embodiment. [Figure 14] FIG. 14 is a schematic cross-sectional view illustrating a configuration of an acoustic wave resonator according to a modification of the second embodiment. [Figure 15] 15A to 15C are cross-sectional views illustrating steps in a manufacturing method of an acoustic wave resonator according to a modification of the second embodiment (part 1). [Figure 16] 16A to 16C are cross-sectional views illustrating steps in a manufacturing method of an acoustic wave resonator according to a modification of the second embodiment (part 2). [Figure 17] FIG. 17 is a schematic cross-sectional view illustrating a configuration of an acoustic wave resonator according to a third embodiment. [Figure 18] FIG. 18 is a schematic cross-sectional view illustrating a configuration of an acoustic wave resonator according to a fourth embodiment. [Figure 19] FIG. 19 is a schematic cross-sectional view showing a configuration in which wiring is connected to an acoustic wave resonator according to a fourth embodiment. [Figure 20] FIG. 20 is a schematic cross-sectional view illustrating another configuration of the acoustic wave resonator according to the fourth embodiment. [Figure 21] FIG. 21 is a schematic cross-sectional view illustrating a configuration of an acoustic wave resonator according to another embodiment.

[0008] [Detailed Description] Hereinafter, the embodiments will be described with reference to the drawings. The embodiments described below are comprehensive or specific examples. The numerical values, shapes, materials, components, installation positions and connection forms of the components shown in the following embodiments are examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept are described as optional components. Furthermore, the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios. In addition, the following embodiments and their modified examples may include similar components, and similar components are given common symbols and overlapping explanations are omitted.

[0009] (First embodiment) 1, an acoustic wave resonator 1 according to the first embodiment includes a first electrode 11 including a laminated film 110, a piezoelectric thin film 20 disposed on the laminated film 110, and a second electrode 12 facing the first electrode 11 with the piezoelectric thin film 20 interposed therebetween. The laminated film 110 generates a two-dimensional electron gas (2DEG). In the following description, the first electrode 11 and the second electrode 12 will be referred to as "electrode 10" unless otherwise specified.

[0010] The acoustic wave resonator 1 is a BAR (Bulk Acoustic Resonator) type acoustic wave resonator (hereinafter also referred to as a "BAR type resonator") that utilizes acoustic waves propagating inside a piezoelectric thin film 20. In the acoustic wave resonator 1, an electrical signal is applied by the electrode 10 to excite an acoustic wave in the piezoelectric thin film 20. The excited acoustic wave travels back and forth between the electrode 10 and the piezoelectric thin film 20. In the BAR type resonator, the acoustic wave propagates in the thickness direction of the piezoelectric thin film 20. The thickness direction is the direction toward the space between the first electrode 11 and the second electrode 12.

[0011] When an input signal input to acoustic wave resonator 1 has a specific frequency, the impedance between first electrode 11 and second electrode 12 decreases. For this reason, an RF filter that passes only an input signal of a specific frequency can be configured using acoustic wave resonator 1. For example, of an input signal including signals of various frequencies input to second electrode 12, only a signal of a predetermined frequency is output from first electrode 11.

[0012] As shown in FIG. 1, the acoustic wave resonator 1 further includes a substrate 30 on which a first electrode 11 is disposed. The substrate 30 may be, for example, a silicon substrate. A cavity 31 is formed between the substrate 30 and the first electrode 11. That is, the acoustic wave resonator 1 shown in FIG. 1 is a film bulk acoustic resonator (FBAR) type BAW filter. For example, the cavity 31 may be formed by removing a part of the surface of the substrate 30 facing the first electrode 11. Since the cavity 31 is formed between the substrate 30 and the first electrode 11, the acoustic wave propagating through the piezoelectric thin film 20 is reflected by the first electrode 11 without propagating inside the substrate 30. Therefore, in the acoustic wave resonator 1, the acoustic wave propagating from the piezoelectric thin film 20 to the substrate 30 can be suppressed, and an electromechanical coupling coefficient corresponding to the conversion efficiency between electrical energy and mechanical energy can be improved.

[0013] The first electrode 11 may be formed on the substrate 30 by epitaxial growth that inherits the atomic arrangement of the substrate 30. The laminated film 110 may have a laminated structure of, for example, a first semiconductor film 111 of a gallium nitride (GaN) film and a second semiconductor film 112 of an aluminum gallium nitride (AlGaN) film. The first semiconductor film 111 may be an n-type GaN layer doped with donor-type impurities, or an undoped GaN layer. The second semiconductor film 112 has a larger band gap than the first semiconductor film 111. The higher the Al composition ratio, the larger the band gap of the second semiconductor film 112 of an AlGaN film. In the following, a case where the first electrode 11 is a laminated film 110 of the first semiconductor film 111 of a GaN film and the second semiconductor film 112 of an AlGaN film will be described as an example.

[0014] The first semiconductor film 111 and the second semiconductor film 112 are composed of nitride semiconductors having different lattice constants. Therefore, the nitride semiconductor (e.g., GaN) constituting the first semiconductor film 111 and the nitride semiconductor (e.g., AlGaN) constituting the second semiconductor film 112 form a lattice-mismatched heterojunction. Due to spontaneous polarization of the first semiconductor film 111 and the second semiconductor film 112 and piezoelectric polarization caused by crystal distortion near the heterojunction interface, the energy level of the conduction band of the first semiconductor film 111 near the heterojunction interface becomes lower than the Fermi level. As a result, two-dimensional electron gas is generated in the first semiconductor film 111 at a position close to the heterojunction interface between the first semiconductor film 111 and the second semiconductor film 112 (for example, within a range of about several nm from the interface).

[0015] Although the laminated film 110 has a laminated structure of a GaN film and an AlGaN film in the above example, the laminated film 110 may be a laminated film of another configuration that generates two-dimensional electron gas. Hereinafter, a laminated film that generates two-dimensional electron gas is also referred to as a "2DEG laminated film."

[0016] The piezoelectric thin film 20 is a single crystal thin film epitaxially grown while inheriting the atomic arrangement of the laminated film 110. For example, an aluminum nitride (AlN) film or an AlN film doped with scandium (Sc) (hereinafter referred to as an "ScAlN film") may be used for the piezoelectric thin film 20. Alternatively, a zinc oxide (ZnO) film or a ZnO film doped with magnesium (Mg) (hereinafter referred to as an "MgZnO film") may be used for the piezoelectric thin film 20. In the following, the AlN film and the ScAlN film are referred to as AlN-based films, and the ZnO film and the MgZoN film are referred to as ZnO-based films. The AlN-based film and the ZnO-based film have a wurtzite crystal structure.

[0017] An AlN-based film or a ZnO-based film having a wurtzite crystal structure is used for the piezoelectric thin film used in the BAR resonator. As described above, the acoustic wave resonator 1 according to the first embodiment uses a single crystal piezoelectric thin film 20 epitaxially grown on the laminated film 110. Alternatively, an AlN-based film or a ZnO-based film can be formed by a sputtering method. A piezoelectric thin film having a wurtzite crystal structure formed by a sputtering method is a polycrystalline structure with the C-axis oriented, and has a crystallinity with a half-width of about 1 to 3 degrees in a rocking curve using X-rays.

[0018] Increasing the crystallinity of a polycrystalline piezoelectric thin film makes the structure closer to that of a single crystal. This increases the amount of displacement due to the inverse piezoelectric effect of the piezoelectric thin film (the ratio of the amount of displacement due to voltage), enabling an increase in the bandwidth of the RF filter and an improvement in the Q value. However, it is difficult to manufacture a single crystal piezoelectric thin film using the sputtering method, which is suitable for mass production with low manufacturing costs.

[0019] As a method for forming a single crystal piezoelectric thin film other than the sputtering method, a method using a base substrate (also called a "template") that indicates the positions of atoms in advance has also been considered. For example, a silicon substrate, sapphire substrate, or silicon carbide (SiC) substrate with a (111) growth surface is used as a template for growing an AlN film.

[0020] However, BAR-type resonators have a structure in which a piezoelectric thin film is sandwiched between a pair of electrodes. If the piezoelectric thin film is grown as a single crystal directly on a template, it is not possible to sandwich the piezoelectric thin film between the electrodes. For this reason, a peeling and bonding technique (also called a "transfer technique") was required in which the template is separated by some method (etching or polishing, etc.) after the piezoelectric thin film is formed, and then the electrodes are formed. Since the transfer technique involves cutting and pasting multiple substrates, it is necessary to overcome issues such as manufacturing costs and the cleanliness of the bonding interface.

[0021] In contrast, in the acoustic wave resonator 1 according to the first embodiment, by growing the piezoelectric thin film 20 on the laminated film 110 that generates two-dimensional electron gas of the first electrode 11, it is possible to realize a resonator structure in which the single-crystal piezoelectric thin film 20 is integrated with the first electrode 11. The piezoelectric effect of the laminated film 110 and the piezoelectric effect of the piezoelectric thin film 20 laminated on the laminated film 110 can cause the acoustic wave resonator 1 to generate resonance characteristics.

[0022] The use of acoustic wave resonator 1 including a 2DEG laminated film allows a single crystal thin film with high piezoelectric performance to be used for the piezo portion of the resonator, making it possible to provide a resonator with a high electromechanical coupling coefficient and a high Q value at low cost. By increasing the electromechanical coupling coefficient, acoustic wave resonator 1 can realize an RF filter with a wide passband.

[0023] As described above, in the acoustic wave resonator 1 according to the first embodiment, the piezoelectric thin film 20 is grown on the first electrode 11 that generates two-dimensional electron gas. Therefore, there is no need for a transfer technique for peeling the substrate on which the piezoelectric thin film 20 is grown from the piezoelectric thin film 20. Therefore, according to the acoustic wave resonator 1, a resonator structure having a single crystal piezoelectric thin film 20 can be easily realized.

[0024] The RF filter can be realized, for example, as shown in FIG. 2A and FIG. 2B, by using an acoustic wave resonator 1 having a first wiring 41 electrically connected to the first electrode 11 and a second wiring 42 electrically connected to the second electrode 12. FIG. 2B is a cross-sectional view taken along the II-II direction in FIG. 2A. The first wiring 41 and the second wiring 42 are, for example, metal wiring. In the acoustic wave resonator 1 shown in FIG. 2A and FIG. 2B, above the region where the resonator is formed by stacking the first electrode 11, the piezoelectric thin film 20, and the second electrode 12, the piezoelectric thin film 20 and the second electrode 12 are covered with an insulating film 60 in the region where the wiring is arranged. The first wiring 41 is electrically connected to the first electrode 11 through a first contact hole 51 penetrating the insulating film 60 and the piezoelectric thin film 20 in the remaining region except the region where the second electrode 12 is arranged. The second wiring 42 is electrically connected to the second electrode 12 through a second contact hole 52 penetrating the insulating film 60. In order to facilitate understanding of the structure of acoustic wave resonator 1, insulating film 60 is omitted from the plan view (the same applies below).

[0025] 2A and 2B, signals are input and output via a first wiring 41 and a second wiring 42. For example, an input signal is input to the second electrode 12 via the second wiring 42. Then, a signal of a predetermined frequency is output from the acoustic wave resonator 1 via the first electrode 11 and the first wiring 41.

[0026] 3A and 3B show an example of an RF filter 100 configured using the acoustic wave resonator 1 shown in Fig. 2A and 2B. Fig. 3B is a cross-sectional view taken along the III-III direction in Fig. 3A. The RF filter 100 shown in Fig. 3A and 3B is an integrated circuit having a circuit board 300 on a main surface of which a first region 301 and a second region 302 spaced apart from the first region 301 are defined.

[0027] A first acoustic wave resonator 1A is disposed in a first region 301 of a circuit board 300, and a second acoustic wave resonator 1B is disposed in a second region 302. The first acoustic wave resonator 1A and the second acoustic wave resonator 1B have the same configuration as the acoustic wave resonator 1. Each of the first region 301 and the second region 302 corresponds to the substrate 30 of the acoustic wave resonator 1. Each of the first acoustic wave resonator 1A and the second acoustic wave resonator 1B is formed by epitaxial growth that inherits the atomic arrangement of the substrate 30. The first electrode 11 of the first acoustic wave resonator 1A and the second electrode 12 of the second acoustic wave resonator 1B are electrically connected by a connection wiring 45. That is, the connection wiring 45 serves both as the first wiring 41 of the first acoustic wave resonator 1A and the second wiring 42 of the second acoustic wave resonator 1B. As described above, RF filter 100 shown in FIGS. 3A and 3B has a configuration in which two acoustic wave resonators 1 are connected in series.

[0028] For example, an input signal is input to RF filter 100 via second wiring 42 of first acoustic wave resonator 1A. Then, a signal of a predetermined frequency is output from RF filter 100 via first wiring 41 of second acoustic wave resonator 1B. RF filter 100 in which two acoustic wave resonators 1 are connected in series can realize a filter with a high Q value and high selectivity.

[0029] An RF filter may be configured using a ladder circuit in which multiple elastic wave resonators 1 with slightly different resonant frequencies are connected in series and in parallel. Figure 4 shows an example of the basic configuration of a ladder circuit. Bandpass filter characteristics can be obtained by matching the resonant frequency of the elastic wave resonators 1 connected in series with the anti-resonant frequency of the elastic wave resonators 1 connected in parallel.

[0030] Hereinafter, a method for manufacturing the acoustic wave resonator 1 according to the first embodiment will be described with reference to the drawings. Note that the method for manufacturing the acoustic wave resonator 1 described below is just an example, and it goes without saying that various other manufacturing methods, including modifications thereof, can be used.

[0031] First, as shown in Fig. 5, a substrate 30 is prepared. The substrate 30 is, for example, a silicon substrate. As shown in Fig. 6, a first semiconductor film 111 and a second semiconductor film 112 are formed on the main surface of the substrate 30 by epitaxial growth to form a first electrode 11. The first semiconductor film 111 is, for example, a GaN film having a thickness of about 50 nm. The second semiconductor film 112 is, for example, an AlGaN film having a thickness of about 20 nm.

[0032] 7, the piezoelectric thin film 20 is formed by epitaxial growth on the upper surface of the second semiconductor film 112. The piezoelectric thin film 20 is, for example, an AlN film. The thickness of the piezoelectric thin film 20 is set arbitrarily depending on the frequency of the signal to be passed through the RF filter.

[0033] Next, the second electrode 12 is formed on the upper surface of the piezoelectric thin film 20. Then, after forming a first resist film 501 covering the second electrode 12, the first resist film 501 is formed into a predetermined pattern by a photolithography technique or the like. Thereafter, as shown in FIG. 8, using the first resist film 501 as an etching mask, a part of the second electrode 12 is etched away, and the second electrode 12 is formed into a predetermined shape.

[0034] After removing the first resist film 501, an insulating film 60 is formed to cover the second electrode 12 and the piezoelectric thin film 20 in the region where the wiring is to be arranged. Furthermore, a second resist film 502 is formed on the upper surface of the insulating film 60. Then, after a part of the second resist film 502 is removed by a photolithography technique or the like, as shown in FIG. 9, a first contact hole 51 is formed in the insulating film 60 and a part of the piezoelectric thin film 20, penetrating to the first electrode 11, using the second resist film 502 as an etching mask. Similarly, a second contact hole 52 is formed in a part of the insulating film 60, penetrating to the second electrode 12, and the upper part of the second electrode 12 is opened.

[0035] 10, after removing the second resist film 502, the first contact hole 51 is filled to form a first wiring 41 that is electrically connected to the first electrode 11. Furthermore, the second contact hole 52 is filled to form a second wiring 42 that is electrically connected to the second electrode 12.

[0036] Thereafter, as shown in Fig. 11, through-holes 210 are formed so as to continuously penetrate portions of the piezoelectric thin film 20 and the first electrode 11 and reach the main surface of the substrate 30. Then, portions of the surface of the substrate 30 facing the first electrode 11 are removed using a wet etching method in which an etchant is injected from the through-holes 210, to form cavities 31 in the substrate 30, as shown in Fig. 12. In this manner, the acoustic wave resonator 1 according to the first embodiment is completed.

[0037] Second Embodiment The acoustic wave resonator 1 according to the second embodiment is an SMR (Solid Mounted Resonator) type BAW filter including an acoustic multilayer film 70, as shown in Fig. 13. In the acoustic wave resonator 1 shown in Fig. 13, the acoustic multilayer film 70 is disposed on a surface (hereinafter also referred to as a "reflection surface") facing in the opposite direction to the surface of the second electrode 12 facing the piezoelectric thin film 20. The acoustic multilayer film 70 reflects acoustic waves propagating through the piezoelectric thin film 20 at the interface between the acoustic multilayer film 70 and the second electrode 12.

[0038] The acoustic wave resonator 1 according to the second embodiment differs from the first embodiment in that an acoustic wave propagated to the second electrode 12 is reflected by an acoustic multilayer film 70. The rest of the configuration of the second embodiment is similar to that of the first embodiment shown in FIG.

[0039] 13 shows a configuration in which the acoustic multilayer film 70 is disposed on the reflecting surface of the second electrode 12, but the acoustic multilayer film 70 may be disposed on a reflecting surface of the first electrode 11 facing the piezoelectric thin film 20 in the opposite direction. In other words, the acoustic multilayer film 70 may be disposed on at least one of the reflecting surface of the first electrode 11 and the reflecting surface of the second electrode 12.

[0040] The acoustic multilayer film 70 has a structure in which high-impedance films 71, which have a relatively high acoustic impedance through which elastic waves pass, and low-impedance films 72, which have a relatively low acoustic impedance, are alternately laminated. For example, a tungsten (W) film may be used as the high-impedance film 71, and a silicon oxide film may be used as the low-impedance film 72.

[0041] 13, an elastic wave is reflected by cavity 31 at first electrode 11, and an elastic wave is reflected by acoustic multilayer film 70 at second electrode 12. Therefore, the elastic wave resonator 1 including acoustic multilayer film 70 can have a high electromechanical coupling coefficient. Otherwise, the elastic wave resonator 1 according to the second embodiment is substantially similar to the first embodiment, and therefore a duplicated description will be omitted.

[0042] <Modification> In the acoustic wave resonator 1 according to the modified example of the second embodiment shown in Fig. 14, an acoustic multilayer film 70 is disposed on the second electrode 12, and a support substrate 35 is disposed on the surface of the acoustic multilayer film 70 facing the opposite direction to the surface facing the second electrode 12. However, unlike the acoustic wave resonator 1 shown in Fig. 13, the substrate 30 is removed from the first electrode 11. Therefore, the reflecting surface of the first electrode 11 faces the space.

[0043] 14, acoustic waves can be more reliably reflected at first electrode 11. This makes it possible to increase the electromechanical coupling coefficient.

[0044] The acoustic wave resonator 1 including the acoustic multilayer film 70 is manufactured, for example, as follows. First, a structure is formed by laminating the first electrode 11 and the piezoelectric thin film 20 on the substrate 30 in the same manner as in the method shown in Figs. 5 to 7. Next, the second electrode 12 and the acoustic multilayer film 70 are formed in this order on the upper surface of the piezoelectric thin film 20 as shown in Fig. 15. Then, a support substrate 35 is formed on the acoustic multilayer film 70 as shown in Fig. 16. Thereafter, the substrate 30 is removed from the first electrode 11 to complete the acoustic wave resonator 1 shown in Fig. 14.

[0045] (Third embodiment) As shown in Fig. 17, an acoustic wave resonator 1 according to the third embodiment includes a substrate 30 and a crystal growth inhibiting film 80 disposed in a certain region of the main surface of the substrate 30. In the acoustic wave resonator 1 shown in Fig. 17, a first electrode 11 is formed by epitaxial growth inheriting the atomic arrangement of the substrate 30 in the remaining region of the main surface of the substrate 30 excluding the region where the crystal growth inhibiting film 80 is disposed. For example, a silicon oxide film or the like may be used as the crystal growth inhibiting film 80.

[0046] The acoustic wave resonator 1 according to the third embodiment differs from the first embodiment in that a crystal growth inhibition film 80 is disposed on the main surface of the substrate 30 except for the region where the first electrode 11 is disposed. The other configurations of the third embodiment are similar to those of the first embodiment shown in FIG.

[0047] 17, it is possible to prevent acoustic waves from propagating from the periphery of first electrode 11 to substrate 30. This makes it possible to increase the electromechanical coupling coefficient.

[0048] Furthermore, according to the acoustic wave resonator 1 in which the crystal growth inhibition film 80 is disposed on a portion of the main surface of the substrate 30, it is possible to suppress distortion occurring between the substrate 30 and the laminated film 110 of the first electrode 11. This distortion occurs due to differences in crystal structure and lattice constant between the substrate 30 and the laminated film 110. By disposing the crystal growth inhibition film 80 on a portion of the main surface of the substrate 30, the range of the area on the main surface of the substrate 30 in which the first electrode 11 is formed is limited. As a result, distortion occurring between the substrate 30 and the laminated film 110 of the first electrode 11 is suppressed.

[0049] The acoustic wave resonator 1 according to the third embodiment is substantially similar to the first and second embodiments, and therefore the description will not be repeated. For example, an acoustic multilayer film 70 may be disposed on at least one of the reflecting surface of the first electrode 11 and the reflecting surface of the second electrode 12.

[0050] (Fourth embodiment) 18, the acoustic wave resonator 1 according to the fourth embodiment has a structure 200 in which a plurality of unit structures 201 are stacked, with each unit structure 201 being a stacked structure of a first electrode 11 and a piezoelectric thin film 20. A second electrode 12 is disposed on the piezoelectric thin film 20 of the uppermost unit structure 201 of the structure 200 that is the furthest from the substrate 30. Although FIG. 18 exemplarily illustrates a case in which the structure 200 includes two unit structures 201, the number of unit structures 201 included in the structure 200 may be three or more.

[0051] The acoustic wave resonator 1 according to the fourth embodiment differs from the first embodiment in that it has alternately stacked first electrodes 11 and piezoelectric thin films 20. The rest of the configuration of the fourth embodiment is similar to that of the first embodiment shown in FIG.

[0052] 18 has a structure in which resonators, each having a piezoelectric thin film 20 sandwiched between electrodes 10, are stacked. In other words, a plurality of resonators are connected in series. This makes it possible to reduce the area of ​​the substrate 30 on which the acoustic wave resonators 1 are arranged, compared to when a plurality of resonators are arranged on the main surface of the substrate 30.

[0053] In high-frequency devices, a large number of RF filters are used as the frequency band that must be processed inside increases. For example, in a mobile communication system that uses a high frequency of 5 GHz, more than 50 RF filters are used. For this reason, there is a demand for miniaturization and high-density mounting of RF filters in order to mount the required number of RF filters in the limited space inside the device. According to the acoustic wave resonator 1 having a configuration in which multiple resonators are stacked, the chip size of the RF filter can be reduced. By forming the first electrode 11 from a 2DEG stacked film, it is easy to stack many unit structures 201 each having a stack of the first electrode 11 and the piezoelectric thin film 20.

[0054] The acoustic wave resonator 1 may include a wiring electrically connected to the first electrode 11 of at least one of the unit structures 201. For example, as shown in Fig. 19, a wiring 40 may be connected to the first electrodes 11 of each of the two unit structures 201 constituting the acoustic wave resonator 1. In other words, the first electrodes 11 of the series-connected resonators may be used as electrode terminals, and a wiring may be connected to any of the electrode terminals. This can increase the degree of freedom in the circuit design of the RF filter.

[0055] In the above, the elastic wave resonator 1 includes two unit structures 201. However, as shown in FIG. 20, the elastic wave resonator 1 may include three or more unit structures 201. FIG. 20 shows an elastic wave resonator 1 including six unit structures 201. FIG. 20 also shows an example in which the wiring 40 is connected to the first electrode 11 of the unit structure 201 in the bottom layer that is closest to the substrate 30. However, it is possible to arbitrarily set which first electrode 11 of the multiple unit structures 201 the wiring is connected to. By connecting the wiring to any first electrode 11 of the resonators connected in series, the degree of freedom in the circuit design of the RF filter can be increased.

[0056] Otherwise, the acoustic wave resonator 1 according to the fourth embodiment is substantially similar to the first to third embodiments, and therefore the duplicated description will be omitted. For example, an acoustic multilayer film 70 may be disposed on at least one of the reflecting surface of the first electrode 11 and the reflecting surface of the second electrode 12. Also, a crystal growth inhibition film 80 may be selectively disposed on the main surface of the substrate 30.

[0057] (Other embodiments) Although the embodiment has been described above, the description and drawings forming a part of this disclosure should not be understood as limiting the embodiment. Various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art from this disclosure.

[0058] For example, the above describes an example in which the first electrode 11 has a structure in which the first semiconductor film 111 and the second semiconductor film 112 are laminated, but the first electrode 11 may further include another conductive film. For example, as shown in FIG. 21, a third semiconductor film 113 may be disposed between the first semiconductor film 111 and the substrate 30. The third semiconductor film 113 may be, for example, an AlN film. The AlN film functions as a buffer film that stabilizes epitaxial growth on the surface of the substrate 30.

[0059] The above-described embodiment is merely an example of the present invention, and the present invention is not limited to the above-described embodiment, and various modifications can be made to the design and other aspects of the present invention without departing from the technical concept of the present invention.

[0060] [Note] The technical ideas that can be understood from the present disclosure are described below. Note that, for the purpose of aiding understanding, not for the purpose of limitation, the components described in the appendices are given the reference symbols of the corresponding components in the embodiments. The reference symbols are shown as examples for the purpose of aiding understanding, and the components described in each appendix should not be limited to the components indicated by the reference symbols.

[0061] (Appendix 1) The acoustic wave resonator 1 includes a first electrode 11 including a laminated film 110 that generates two-dimensional electron gas, a piezoelectric thin film 20 disposed on the laminated film 110, and a second electrode 12 facing the first electrode 11 with the piezoelectric thin film 20 sandwiched between them. According to the acoustic wave resonator 1 described in Appendix 1, a single crystal thin film with high piezoelectric performance can be used for the piezoelectric part of the resonator, so that a resonator with a high electromechanical coupling coefficient and a high Q value can be provided at low cost.

[0062] (Appendix 2) In the acoustic wave resonator 1 described in Appendix 1, the piezoelectric thin film 20 is a single crystal thin film that is epitaxially grown so as to inherit the atomic arrangement of the laminated film 110. According to the acoustic wave resonator 1 described in Appendix 2, a single crystal piezoelectric thin film having high piezoelectric performance can be formed.

[0063] (Appendix 3) In the acoustic wave resonator 1 according to claim 1 or 2, the laminated film 110 has a laminated structure of a gallium nitride film and an aluminum gallium nitride film. According to the acoustic wave resonator 1 according to claim 3, the laminated structure of the gallium nitride film and the aluminum gallium nitride film can generate two-dimensional electron gas.

[0064] (Appendix 4) The acoustic wave resonator 1 according to any one of Supplementary Note 1 to 3 further includes a substrate 30 on which a first electrode 11 is disposed. The first electrode 11 is formed by epitaxial growth inheriting the atomic arrangement of the substrate 30. According to the acoustic wave resonator 1 according to Supplementary Note 4, the first electrode 11 that generates a two-dimensional electron gas can be formed on the substrate 30.

[0065] (Appendix 5) In the acoustic wave resonator 1 according to any one of Supplementary Note 1 to 4, a cavity 31 is formed between the substrate 30 and the first electrode 11. According to the acoustic wave resonator 1 according to Supplementary Note 5, an FBAR-type BAW filter can be provided.

[0066] (Appendix 6) The acoustic wave resonator 1 according to any one of Supplementary Note 1 to 5 further includes an acoustic multilayer film 70. The acoustic multilayer film 70 is disposed on at least one of a surface of the first electrode 11 facing in the opposite direction to a surface facing the piezoelectric thin film 20 and a surface of the second electrode 12 facing in the opposite direction to a surface facing the piezoelectric thin film 20. According to the acoustic wave resonator 1 according to Supplementary Note 6, an SMR type BAW filter can be provided.

[0067] (Appendix 7) The acoustic wave resonator 1 described in Appendix 6 further includes an acoustic multilayer film 70 disposed on the second electrode 12, and a support substrate 35 disposed on a surface of the acoustic multilayer film 70 facing in the opposite direction to the surface facing the second electrode 12. The surface of the first electrode 11 facing in the opposite direction to the surface facing the piezoelectric thin film 20 faces space. According to the acoustic wave resonator 1 described in Appendix 7, the first electrode 11 can more reliably reflect acoustic waves.

[0068] (Appendix 8) The acoustic wave resonator 1 according to any one of Supplementary Note 1 to 7 further includes a substrate 30 and a crystal growth inhibiting film 80 disposed in a certain region of the main surface of the substrate 30. The first electrode 11 is formed by epitaxial growth inheriting the atomic arrangement of the substrate 30 in a remaining region of the main surface excluding the region where the crystal growth inhibiting film 80 is disposed. The acoustic wave resonator 1 according to Supplementary Note 8 can prevent acoustic waves from propagating from the periphery of the first electrode 11 to the substrate 30. In addition, distortion occurring between the substrate 30 and the laminated film 110 of the first electrode 11 can be suppressed.

[0069] (Appendix 9) The acoustic wave resonator 1 according to any one of Supplementary Note 1 to 8 has a structure 200 in which a laminated structure of a first electrode 11 and a piezoelectric thin film 20 is defined as a unit structure 201 and a plurality of unit structures 201 are laminated. A second electrode 12 is disposed on the piezoelectric thin film 20 of the unit structure 201 in the uppermost layer of the structure 200. According to the acoustic wave resonator 1 according to Supplementary Note 9, the area of ​​the substrate 30 on which the acoustic wave resonator 1 is disposed can be reduced.

[0070] (Appendix 10) The acoustic wave resonator 1 according to Supplementary Note 9 further includes a wiring electrically connected to at least any first electrode 11 of the plurality of unit structures 201. According to the acoustic wave resonator 1 according to Supplementary Note 10, the first electrodes 11 of the plurality of resonators connected in series are used as electrode terminals, and a wiring can be connected to any of the electrode terminals.

[0071] (Appendix 11) The acoustic wave resonator 1 according to any one of Supplementary Note 1 to 10 further includes an insulating film 60 covering the piezoelectric thin film 20 and the second electrode 12, a first wiring 41, and a second wiring 42. The first wiring 41 is electrically connected to the first electrode 11 through a first contact hole 51 penetrating the insulating film 60 and the piezoelectric thin film 20 in a remaining region of the region where the second electrode 12 is disposed. The second wiring 42 is electrically connected to the second electrode 12 through a second contact hole 52 penetrating the insulating film 60. According to the acoustic wave resonator 1 according to Supplementary Note 11, signals can be input and output to and from the acoustic wave resonator 1 through the wiring.

[0072] (Appendix 12) The integrated circuit includes a circuit board 300 in which a first region 301 and a second region 302 spaced apart from the first region 301 are defined, a first acoustic wave resonator 1A disposed in the first region 301, and a second acoustic wave resonator 1B disposed in the second region 302. The first acoustic wave resonator 1A and the second acoustic wave resonator 1B are the acoustic wave resonators 1 described in any one of Supplementary Notes 1 to 11, and each includes a first electrode 11 formed by epitaxial growth that inherits the atomic arrangement of the circuit board 300. The first electrode 11 of the first acoustic wave resonator 1A and the second electrode 12 of the second acoustic wave resonator 1B are electrically connected by a connection wiring 45. According to the integrated circuit described in Supplementary Note 12, an RF filter configured by electrically connecting a plurality of acoustic wave resonators 1 can be realized. [Explanation of symbols]

[0073] 1. Elastic wave resonator 11 1st electrode 12 2nd electrode 20 Piezo thin film 30 Substrate 31 Cavity 35 Support substrate 40 Wiring 41 1st wiring 42 2nd wiring 45 Connection Wiring 51 Contact Hall No. 1 52 Second Contact Hole 60 Insulating film 70 Acoustic multilayer film 80 Crystal Growth Inhibitor Film 100 RF Filters 110 Laminated Film 111 First semiconductor film 112 Second semiconductor film 200 structures 201 Unit Structure 300 Circuit Board 301 1st area 302 Second area

Claims

1. A first electrode including a laminated film that generates a two-dimensional electron gas; a piezoelectric thin film disposed on the laminated film; a second electrode facing the first electrode with the piezoelectric thin film interposed therebetween; An acoustic wave resonator comprising:

2. 2. The elastic wave resonator according to claim 1, wherein the piezoelectric thin film is a single crystal thin film epitaxially grown so as to inherit the atomic arrangement of the laminated film.

3. 2. The acoustic wave resonator according to claim 1, wherein the laminated film has a laminated structure of a gallium nitride film and an aluminum gallium nitride film.

4. Further comprising a substrate on which the first electrode is disposed, The acoustic wave resonator according to claim 1 , wherein the first electrode is formed by epitaxial growth so as to inherit an atomic arrangement of the substrate.

5. The acoustic wave resonator according to claim 4 , wherein a cavity is formed between the substrate and the first electrode.

6. 2. The elastic wave resonator according to claim 1, further comprising an acoustic multilayer film disposed on at least one of a surface of the first electrode facing in an opposite direction to a surface facing the piezoelectric thin film and a surface of the second electrode facing in an opposite direction to a surface facing the piezoelectric thin film.

7. The acoustic multilayer is disposed on the second electrode, The acoustic multilayer further includes a support substrate disposed on a surface facing in a direction opposite to a surface facing the second electrode of the acoustic multilayer, A surface of the first electrode facing in a direction opposite to a surface facing the piezoelectric thin film faces a space. The acoustic wave resonator according to claim 6 .

8. A substrate; a crystal growth inhibiting film disposed on a certain region of the main surface of the substrate; Further comprising: the first electrode is formed by epitaxial growth inheriting the atomic arrangement of the substrate in a remaining region of the main surface excluding a region in which the crystal growth inhibiting film is disposed; The acoustic wave resonator according to claim 1 .

9. a laminated structure of the first electrode and the piezoelectric thin film is a unit structure, and a structure is formed by laminating a plurality of the unit structures, The second electrode is disposed on the piezoelectric thin film of the unit structure of the uppermost layer of the structure. The acoustic wave resonator according to claim 1 .

10. The acoustic wave resonator according to claim 9 , further comprising a wiring electrically connected to the first electrode of at least any of the plurality of unit structures.

11. an insulating film covering the piezoelectric thin film and the second electrode; a first wiring electrically connected to the first electrode through a first contact hole penetrating the insulating film and the piezoelectric thin film in a remaining region of the region where the second electrode is disposed; a second wiring electrically connected to the second electrode via a second contact hole penetrating the insulating film; The acoustic wave resonator according to claim 1 , further comprising:

12. a circuit board defining a first region and a second region spaced apart from the first region; a first elastic wave resonator disposed in the first region and a second elastic wave resonator disposed in the second region, each of which is an elastic wave resonator according to any one of claims 1 to 10, and each of the first elastic wave resonator and the second elastic wave resonator includes the first electrode formed by epitaxial growth inheriting an atomic arrangement of the circuit board; a connection wiring that electrically connects the first electrode of the first acoustic wave resonator and the second electrode of the second acoustic wave resonator; 1. An integrated circuit comprising:

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