Acoustic Wave Devices, Filters and Multiplexers

Abstract

To provide an acoustic wave device capable of suppressing deterioration of a piezoelectric film, etc.SOLUTION: An acoustic wave device includes a substrate 10, an acoustic reflection layer, a plurality of lower electrodes 12a, 12b, an insulating film 18, a piezoelectric film 14, and an upper electrode 16. The acoustic reflection layer includes a cavity 30 or an acoustic reflection film in which at least two types of layers having different acoustic properties are laminated. The lower electrodes are provided on the substrate 10, share one acoustic reflection layer including the cavity 30 between the lower electrodes and the substrate 10, and are arranged to be apart from each other via a groove 55. The insulating film 18 is provided in the groove 55 on the acoustic reflection layer. The piezoelectric film 14 is integrally provided on the plurality of lower electrodes 12a, 12b and the groove 55. The upper electrode 16 is integrally provided on the piezoelectric film 14, and the piezoelectric film 14 is interposed by the lower electrodes 12a and 12b to form a plurality of resonators 11a and 11b.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic wave device, a filter, and a multiplexer, for example, an acoustic wave device, a filter, and a multiplexer having a piezoelectric thin film resonator. [Background technology]

[0002] Acoustic wave devices using piezoelectric thin film resonators are used, for example, as filters and multiplexers in wireless devices such as mobile phones. A piezoelectric thin film resonator has a structure in which a lower electrode and an upper electrode face each other across a piezoelectric film. The region where the lower electrode and upper electrode face each other across the piezoelectric film is the resonance region. A gap or an acoustic reflection film is provided below the resonance region so as not to restrict vibration. The gap or the acoustic reflection film is provided so as to include the resonance region in a plan view.

[0003] A structure is known in which divided piezoelectric thin film resonators share a single gap or acoustic reflection film (e.g., Patent Document 1). In this structure, either the lower electrode or the upper electrode is divided on the gap or the acoustic reflection film. It is known to divide the resonator so that the polarization direction of the piezoelectric film suppresses secondary distortion (e.g., Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-6919 A [Patent Document 2] JP 2008-85989 A [Patent Document 3] JP 2009-10932 A Summary of the Invention [Problem to be solved by the invention]

[0005] For example, when dividing a resonator to suppress secondary distortion as in Patent Documents 2 and 3, it is conceivable that the divided resonators share a single gap or acoustic reflection film as in Patent Document 1. When the lower electrode is divided in a single gap or on an acoustic reflection film, and a piezoelectric film and an upper electrode are integrally formed on the divided lower electrode, damage such as cracks and regions with deteriorated crystallinity are likely to occur in the piezoelectric film.

[0006] The present invention has been made in consideration of the above problems, and has an object to suppress deterioration of a piezoelectric film, etc. [Means for solving the problem]

[0007] The present invention is an acoustic wave device comprising: a substrate; an acoustic reflection layer provided on the substrate, the acoustic reflection layer including an acoustic reflection film in which at least two types of layers having different acoustic properties are stacked, the acoustic reflection layer being provided on the substrate and sharing one of the acoustic reflection layers between the substrate and the lower electrodes being spaced apart from each other by grooves; an insulating film provided in the groove on the acoustic reflection layer; a piezoelectric film provided integrally on the lower electrodes and the grooves; and an upper electrode provided integrally on the piezoelectric film, forming a plurality of resonators by sandwiching the piezoelectric film between the lower electrodes, the surface of the insulating film facing the piezoelectric film and the surfaces of the lower electrodes facing the piezoelectric film being approximately coplanar.

[0008] In the above configuration, the upper electrode may be configured not to extend to the outside of the acoustic reflection layer in a plan view.

[0009] In the above configuration, the insulating film may be in contact with each of the plurality of lower electrodes.

[0012] In the above configuration, a side surface of the insulating film may be in contact with side surfaces of the plurality of lower electrodes.

[0013] In the above configuration, a surface of the insulating film facing the substrate may be substantially flat with a surface of the lower electrode facing the substrate.

[0014] In the above configuration, a part of the insulating film may be provided on at least a part of the surfaces of the lower electrodes facing the substrate.

[0015] In the above configuration, the insulating film may be configured to overlap the entire acoustic reflection layer in a plan view.

[0016] In the above configuration, the acoustic reflection layer may be a gap.

[0017] In the above configuration, the surface of the substrate facing the gap may be a substantially flat surface.

[0018] The above-mentioned configuration may further include an insertion film that is inserted between the upper electrode and the lower electrode and has a material different from that of the piezoelectric film.

[0019] The present invention is a filter including the above acoustic wave device.

[0020] The present invention is a multiplexer including the above filter. Effect of the Invention

[0021] According to the present invention, deterioration of the piezoelectric film and the like can be suppressed. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Diagram 2] 2(a) to 2(c) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Diagram 3] 3(a) to 3(c) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 4]4(a) and 4(b) are enlarged cross-sectional views of acoustic wave devices according to Comparative Example 1 and Example 1, respectively. [Diagram 5] 5(a) to 5(c) are cross-sectional views showing Modifications 1 to 3 of the first embodiment, respectively. [Figure 6] 6(a) to 6(d) are cross-sectional views showing Modifications 4 to 7 of the first embodiment, respectively. [Figure 7] 7(a) to 7(d) are cross-sectional views showing Modifications 8 to 11 of the first embodiment, respectively. [Figure 8] 8(a) to 8(d) are cross-sectional views showing Modifications 12 to 15 of the first embodiment, respectively. [Figure 9] 9(a) to 9(c) are cross-sectional views showing Modified Examples 16 to 18 of the first embodiment, respectively. [Figure 10] FIG. 10A is a plan view of an acoustic wave device in accordance with a nineteenth modification of the first embodiment, and FIG. 10B is a cross-sectional view taken along line AA of FIG. 10A. [Figure 11] 11(a) and 11(b) are cross-sectional views showing Modifications 20 and 21 of the first embodiment, respectively. [Figure 12] 12(a) and 12(b) are cross-sectional views showing Modifications 22 and 23 of the first embodiment, respectively. [Figure 13] FIG. 13 is a circuit diagram of a duplexer in accordance with the second embodiment. [Figure 14] FIG. 14(a) is a plan view of a transmission filter in the second embodiment, and FIG. 14(b) is a plan view of an air gap. [Figure 15] FIG. 15 is a plan view of the filter according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] An embodiment will be described with reference to the drawings. EXAMPLES

[0024] FIG. 1(a) is a plan view of an acoustic wave device according to a first embodiment, and FIG. 1(b) is a cross-sectional view taken along the line AA of FIG. 1(a). In FIG. 1(a), resonance regions 50a, 50b and an insulating film 18 are indicated by hatching. As shown in FIG. 1(a) and FIG. 1(b), a recess is formed on the upper surface of a substrate 10, and a gap 30 (air layer) is provided in the recess. Lower electrodes 12a and 12b are provided on the substrate 10 and the gap 30. The lower electrodes 12a and 12b are separated on the gap 30, and a groove 55 is formed between the lower electrodes 12a and 12b. An insulating film 18 is provided in the groove 55. The insulating film 18 extends in the groove 55 and is provided on the substrate 10 outside the gap 30 (see FIG. 1(a)). A piezoelectric film 14 is provided integrally on the lower electrodes 12a, 12b and the insulating film 18. An upper electrode 16 is provided integrally on the piezoelectric film 14. A frequency adjustment film or a protective film may be provided on the upper electrode 16. In the parallel resonator of the ladder type filter, a mass load film may be sandwiched between the upper electrode 16.

[0025] The regions where the lower electrodes 12a and 12b overlap with the upper electrode 16, sandwiching at least a portion of the piezoelectric film 14, are resonance regions 50a and 50b, respectively. In a plan view, a plurality of resonance regions 50a and 50b are provided within a single cavity 30. The resonance regions 50a and 50b have a semi-elliptical shape, and are regions where elastic waves in a thickness extensional vibration mode or a thickness shear vibration mode resonate. The lower electrode 12a, the piezoelectric film 14, and the upper electrode 16 form a piezoelectric thin film resonator 11a, and the lower electrode 12b, the piezoelectric film 14, and the upper electrode 16 form a piezoelectric thin film resonator 11b. The resonators 11a and 11b are connected in series between the lower electrodes 12a and 12b.

[0026] The planar shape of the gap 30 is an ellipse, and the center of the ellipse is a center 58. In a plan view, the region overlapping the upper electrode 16 and between the resonance regions 50a and 50b is a separation region 56. The separation region 56 includes a center 58. The resonance regions 50a and 50b are provided on both sides of the separation region 56, and the planar shape of the resonance regions 50a and 50b combined with the separation region 56 is a shape similar to that of the gap 30 (i.e., an ellipse), and is included in the gap 30. In a plan view, the planar shape of the resonance regions 50a and 50b combined with the separation region 56 is congruent with the gap 30, and may overlap. The areas of the resonance regions 50a and 50b are, for example, approximately the same. The planar shape of the gap 30 and the planar shape of the resonance regions 50a and 50b combined with the separation region 56 may be a polygonal shape such as a square shape or a pentagon shape other than an ellipse shape. The upper electrode 16 is not extended outside the cavity 30 and is not connected to any resonators other than the resonators 11a and 11b.

[0027] The substrate 10 is an insulating substrate or a semiconductor substrate, such as a silicon substrate, a sapphire substrate, a spinel substrate, an alumina substrate, a quartz substrate, a glass substrate, a crystal substrate, a ceramic substrate, a GaAs substrate, etc. The lower electrode 12 and the upper electrode 16 are a single layer film of a metal, such as ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), iridium (Ir), etc., or a laminate film of these metals.

[0028] The piezoelectric film 14 is made of aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO 3 ), single crystal lithium tantalate (LiTaO 3 ) or single crystal lithium niobate (LiNbO 3), etc. as the main component. For example, the piezoelectric film 14 may be mainly composed of aluminum nitride and may contain other elements to improve the resonance characteristics or the piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 is improved by using scandium (Sc), two elements of a group 2 element and a group 4 element, or two elements of a group 2 element and a group 5 element as the additive element. This improves the effective electromechanical coupling coefficient of the piezoelectric thin film resonator. The group 2 element is, for example, calcium (Ca), magnesium (Mg), strontium (Sr), or zinc (Zn). The group 4 element is, for example, titanium, zirconium (Zr), or hafnium (Hf). The group 5 element is, for example, tantalum, niobium (Nb), or vanadium (V). Furthermore, the piezoelectric film 14 may be mainly composed of aluminum nitride and may contain boron (B).

[0029] The insulating film is an inorganic insulating film, and may be, for example, a metal oxide film or a metal nitride film, such as a silicon oxide film, a silicon nitride film, a silicon nitride oxide film, or an aluminum oxide film. The frequency adjustment film or the protective film is, for example, an insulating film, such as a silicon oxide film, a silicon nitride film, or an aluminum oxide film. The mass load film is, for example, a metal film using the material exemplified for the lower electrodes 12a, 12b and the upper electrode 16, or an insulating film, such as a silicon oxide film, a silicon nitride film, or an aluminum oxide film.

[0030] In the case of a piezoelectric thin film resonator having a resonant frequency of 2 GHz, the lower electrodes 12a and 12b are, from the substrate 10 side, a chromium film having a thickness of 100 nm and a ruthenium film having a thickness of 250 nm. The piezoelectric film 14 is an aluminum nitride film having a thickness of 1100 nm. The upper electrode 16 is, from the piezoelectric film 14 side, a ruthenium film having a thickness of 250 nm and a chromium film having a thickness of 50 nm. The thickness of each layer can be appropriately set to obtain the desired resonant characteristics.

[0031] [Production method of Example 1] 2(a) to 3(c) are cross-sectional views showing a method for manufacturing the acoustic wave device according to the first embodiment. As shown in FIG. 2(a), a recess is formed on the upper surface of the substrate 10. A sacrificial layer 38 is formed in the recess by, for example, sputtering, vacuum deposition, or CVD (Chemical Vapor Deposition). The sacrificial layer 38 is made of, for example, magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), or silicon oxide (SiO 2 The upper surfaces of the substrate 10 and the sacrificial layer 38 are planarized using CMP (Chemical Mechanical Polishing).

[0032] As shown in Fig. 2(b), the lower electrode 12 is formed on the sacrificial layer 38 and the substrate 10 by, for example, sputtering, vacuum deposition, or CVD. As shown in Fig. 2(c), a mask layer 60 having an opening 61 is formed on the lower electrode 12. The mask layer 60 is, for example, a photoresist, and is formed by photolithography. The lower electrode 12 is removed using the mask layer 60 as a mask, and the lower electrodes 12a and 12b and the groove 55 are formed. The lower electrode 12 is removed by, for example, dry etching.

[0033] As shown in Fig. 3(a), insulating films 18 and 19 are formed in the groove 55 and on the mask layer 60. For example, a CVD method, a sputtering method, or a vacuum deposition method is used to form the insulating films 18 and 19. As shown in Fig. 3(b), the mask layer 60 is removed, and the insulating film 18 remains in the groove 55.

[0034] As shown in FIG. 3(c), the piezoelectric film 14 is formed on the lower electrodes 12a, 12b and the insulating film 18 by, for example, sputtering or vacuum deposition. The upper electrode 16 is formed on the piezoelectric film 14 by, for example, sputtering, vacuum deposition or CVD. The upper electrode 16 and the piezoelectric film 14 are patterned by, for example, photolithography and etching. This forms the resonance regions 50a, 50b and the separation region 56. Thereafter, the sacrificial layer 38 is removed by using an etching medium (etchant). It is preferable that the etching medium is a medium that does not etch the substrate 10, the lower electrodes 12a, 12b, the piezoelectric film 14, the upper electrode 16 and the insulating film 18 other than the sacrificial layer 38. For example, hydrofluoric acid or nitric acid is used as the etching medium. When the sacrificial layer 38 is removed, a gap 30 is formed between the lower electrode 12 and the substrate 10. In this manner, the acoustic wave device shown in FIG. 1(a) and FIG. 1(b) is manufactured.

[0035] 4(a) and 4(b) are enlarged cross-sectional views of acoustic wave devices according to Comparative Example 1 and Example 1, respectively. As shown in FIG. 4(a), in Comparative Example 1, an insulating film 18 is not provided. The lower surface of the piezoelectric film 14 and the lower surfaces of the lower electrodes 12a and 12b are substantially flat. The piezoelectric film 14 is formed on a step having thicknesses T1a and T1b of the lower electrodes 12a and 12b. For this reason, a crack 62 may be formed at the corner of the step. In addition, a region 63 in which the crystallinity of the piezoelectric film 14 is reduced may be formed near the ends of the lower electrodes 12a and 12b. In FIG. 3(c), when the sacrificial layer 38 is etched, the piezoelectric film 14 may be eroded by the etching solution as indicated by the arrow 64. In particular, when the crack 62 or the region 63 in which the crystallinity is reduced is formed in the piezoelectric film 14, the piezoelectric film 14 is easily eroded. Thus, in Comparative Example 1, the piezoelectric film 14 may be deteriorated.

[0036] As shown in FIG. 4(b), in Example 1, an insulating film 18 is formed in the groove 55. The thickness T2 of the insulating film 18 is set to be approximately the same as the thicknesses T1a and T1b of the lower electrodes 12a and 12b. The thicknesses T1a and T1b are approximately the same, and the upper surface of the insulating film 18 and the upper surfaces of the lower electrodes 12a and 12b are approximately flush with each other. This makes it possible to suppress the formation of cracks and regions 63 with reduced crystallinity near the ends of the lower electrodes 12a and 12b. In addition, the insulating film 18 protects the lower surface of the piezoelectric film 14 in the separation region 56. Therefore, it is possible to suppress the erosion of the piezoelectric film 14 when the sacrificial layer 38 is etched. In this way, in Example 1, it is possible to suppress the deterioration of the piezoelectric film 14.

[0037] [Modification 1 of Example 1] 5(a) to 9(c) are cross-sectional views showing modified examples 1 to 18 of the first embodiment. As shown in FIG. 5(a), in modified example 1 of the first embodiment, the thickness T2 of the insulating film 18 is thinner than the thicknesses T1a and T1b of the lower electrodes 12a and 12b. In modified example 1 of the first embodiment, the step D1 between the upper surfaces of the lower electrodes 12a and 12b and the upper surface of the insulating film 18 is smaller than the steps T1a and T1b of the lower electrodes 12a and 12b in the first comparative example. Thus, the formation of the cracks 62 and the region 63 can be suppressed. In addition, the insulating film 18 protects the lower surface of the piezoelectric film 14 in the division region 56, so that the erosion of the piezoelectric film 14 can be suppressed. The step D1 is preferably 3 / 4 or less of the thicknesses T1a and T1b, and more preferably 1 / 2 or less. The insulating film 18 may be thicker than the lower electrodes 12a and 12b. In this case as well, the step D1 is preferably 3 / 4 or less of the thicknesses T1a and T1b, and more preferably 1 / 2 or less. The other configurations are the same as those in the first embodiment, and therefore the description will be omitted.

[0038] [Modification 2 of Example 1] As shown in FIG. 5(b), in the second modification of the first embodiment, the insulating film 18 has a portion 18a provided in the groove 55 and a portion 18b provided under the lower electrodes 12a, 12b and the portion 18a. The thickness T2a of the portion 18a is substantially the same as the thicknesses T1a and T2b of the lower electrodes 12a and 12b. This suppresses the formation of the cracks 62 and the region 63, as in the first embodiment. Since the portion 18b is provided under the lower electrodes 12a and 12b throughout the entire gap 30, the resonance regions 50a and 50b can be reinforced. If the portion 18b is thick, the resonance characteristics of the resonators 11a and 11b are reduced. From this viewpoint, the thickness T2b of the portion 18b is preferably thinner than the thicknesses T1a and T1b of the lower electrodes 12a and 12b, and is preferably 1 / 2 or less, more preferably 1 / 4 or less, of T1a and T1b. If T2b is too thin, it does not provide reinforcement. From this viewpoint, it is preferable that the thickness T2b is 1 / 10 or more of the thicknesses T1a and T1b. The other configurations are the same as those in the first embodiment, and therefore the description thereof will be omitted.

[0039] [Modification 3 of Example 1] As shown in FIG. 5(c), in the third modification of the first embodiment, the thickness T2a of the portion 18a is thinner than the thicknesses T1a and T2b of the lower electrodes 12a and 12b. Thus, even if the portion 18a is thin, the step D1 between the upper surface of the portion 18a and the lower electrodes 12a and 12b is smaller than the thicknesses T1a and T1b. Therefore, similar to the second modification of the first embodiment, the formation of the crack 62 and the region 63 is suppressed. The preferable range of the step D1 is the same as the preferable range of the step D1 in the first modification of the first embodiment. The portion 18b is provided under the lower electrodes 12a and 12b throughout the entire gap 30. This makes it possible to reinforce the resonance regions 50a and 50b. The other configurations are the same as the second modification of the first embodiment, and therefore a description thereof will be omitted.

[0040] [Variation 4 of Example 1] As shown in FIG. 6(a), in the fourth modification of the first embodiment, the portion 18b is provided at a part of the outside of the separation region 56. The width of the portion 18b in the resonance regions 50a and 50b is D2. It is preferable that the width D2 is equal to or greater than the alignment accuracy with the lower electrodes 12a and 12b. From this viewpoint, the width D2 is preferably equal to or greater than 1 / 10 of the thicknesses T1a and T1b, and more preferably equal to or greater than 1 / 2. If the width D2 is large, the resonance characteristics of the resonators 11a and 11b deteriorate. From this viewpoint, it is preferable that the width D2 is equal to or less than twice the thicknesses T1a and T1b. The other configurations are the same as those of the second modification of the first embodiment, and therefore description thereof will be omitted.

[0041] [Modification 5 of Example 1] 6(b), in the fifth modification of the first embodiment, the thickness T2a of the portion 18a is smaller than the thicknesses T1a and T1b of the lower electrodes 12a and 12b. The other configurations are the same as those in the fourth modification of the first embodiment, and therefore the description thereof will be omitted.

[0042] [Modification 6 of Example 1] In the first embodiment, the side of the insulating film 18 is inclined with respect to the side of the insulating film 18. Therefore, at the lower end of the side of the insulating film 18, the insulating film 18 contacts the lower electrodes 12a and 12b, but near the upper surface of the insulating film 18, the insulating film 18 is separated from the lower electrodes 12a and 12b. Therefore, a recess is formed between the upper surfaces of the lower electrodes 12a and 12b and the upper surface of the insulating film 18. As shown in FIG. 6(c), in the sixth modification of the first embodiment, the side of the insulating film 18 contacts the side of the lower electrodes 12a and 12b. As a result, compared to the first embodiment, the upper surfaces of the lower electrodes 12a and 12b and the insulating film 18 are almost flat. Therefore, the formation of the cracks 62 and the regions 63 with reduced crystallinity in the piezoelectric film 14 can be further suppressed. The other configurations are the same as those of the first embodiment, and a description thereof will be omitted.

[0043] [Seventh Modification of the First Embodiment] As shown in FIG. 6(d), in the seventh modification of the first embodiment, the thickness T2 of the insulating film 18 is thinner than the thicknesses T1a and T1b of the lower electrodes 12a and 12b. The side surfaces of the insulating film 18 and the side surfaces of the lower electrodes 12a and 12b are in contact with each other. As a result, compared to FIG. 5(a) of the first modification of the first embodiment, the formation of recesses between the upper surfaces of the lower electrodes 12a and 12b and the upper surface of the insulating film 18 is suppressed. Therefore, the formation of cracks 62 and regions 63 with reduced crystallinity in the piezoelectric film 14 can be further suppressed. The other configurations are the same as those of the first modification of the first embodiment, and therefore a description thereof will be omitted.

[0044] [Variation 8 of Example 1] As shown in Fig. 7(a), in the eighth modification of the first embodiment, the side surfaces of the lower electrodes 12a and 12b are inclined with respect to the lower surfaces of the lower electrodes 12a and 12b. The angle (inner angle) between the lower surfaces and the side surfaces of the lower electrodes 12a and 12b is an acute angle, for example, 20° to 60°. The other configurations are the same as the first modification of the first embodiment, and therefore description thereof will be omitted.

[0045] [Modification 9 of Example 1] 7(b), in the 9th modification of the embodiment 1, the side surfaces of the lower electrodes 12a and 12b are inclined with respect to the lower surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those in the 1st modification of the embodiment 1, and therefore the description thereof will be omitted.

[0046] [Modification 10 of Example 1] 7(c), in the tenth modification of the first embodiment, the side surfaces of the lower electrodes 12a and 12b are inclined with respect to the lower surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those in the second modification of the first embodiment, and therefore the description thereof will be omitted.

[0047] [Modification 11 of Example 1] 7(d), in the eleventh modification of the first embodiment, the side surfaces of the lower electrodes 12a and 12b are inclined with respect to the lower surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those in the third modification of the first embodiment, and therefore the description thereof will be omitted.

[0048] [Modification 12 of Example 1] 8(a), in the modification 12 of the embodiment 1, the side surfaces of the lower electrodes 12a and 12b are inclined with respect to the lower surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those in the modification 4 of the embodiment 1, and therefore the description thereof will be omitted.

[0049] [Modification 13 of Example 1] As shown in FIG. 8(b), in the modification 13 of the embodiment 1, the side surfaces of the lower electrodes 12a and 12b are inclined with respect to the lower surfaces of the lower electrodes 12a and 12b. The other configurations are the same as the modification 5 of the embodiment 1, and the description will be omitted. As in the modifications 8 to 13 of the embodiment 1, the side surfaces of the lower electrodes 12a and 12b may be inclined with respect to the lower surfaces. When the angle between the lower surface and the side surface of the lower electrodes 12a and 12b is an acute angle, and the angle between the lower surface and the side surface of the insulating film 18 is an acute angle, the angle between the side surfaces of the lower electrodes 12a and 12b and the side surface of the insulating film 18 is larger than in the embodiment 1 and its modifications 1 to 5. Therefore, the formation of the cracks 62 and the regions 63 with reduced crystallinity in the piezoelectric film 14 can be further suppressed.

[0050] [Modification 14 of Example 1] 8(c), in the 14th modification of the first embodiment, the side surfaces of the insulating film 18 are in contact with the side surfaces of the lower electrodes 12a and 12b. As a result, the upper surfaces of the lower electrodes 12a and 12b and the upper surface of the insulating film 18 are substantially flat. The other configurations are the same as those in the 8th modification of the first embodiment, and therefore a description thereof will be omitted.

[0051] [Modification 15 of Example 1] 8(d), in the fifteenth modification of the first embodiment, the side surfaces of the insulating film 18 are in contact with the side surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those in the ninth modification of the first embodiment, and therefore the description thereof will be omitted.

[0052] [Modification 16 of Example 1] 9(a), in the sixteenth modification of the first embodiment, the side surfaces of the insulating film 18 are in contact with the side surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those in the tenth modification of the first embodiment, and therefore the description thereof will be omitted.

[0053] [Modification 17 of Example 1] 9(b), in Modification 17 of Example 1, the side surface of the insulating film 18 contacts the side surfaces of the lower electrodes 12a and 12b. The other configurations are the same as Modification 10 of Example 1, and the description will be omitted. As in Modifications 14 to 17 of Example 1, when the angle between the lower surfaces and the side surfaces of the lower electrodes 12a and 12b is an acute angle, the side surface of the insulating film 18 may contact the side surfaces of the lower electrodes 12a and 12b.

[0054] [Modification 18 of Example 1] As shown in FIG. 9(c), in the modification 18 of the embodiment 1, the angle between the bottom surfaces and the side surfaces of the lower electrodes 12a and 12b is an obtuse angle. The side surfaces of the insulating film 18 are in contact with the side surfaces of the lower electrodes 12a and 12b. The other configurations are the same as those of the modification 16 of the embodiment 1, and the description thereof is omitted. As in the modification 18 of the embodiment 1, when the angle between the bottom surfaces and the side surfaces of the lower electrodes 12a and 12b is an obtuse angle, the side surfaces of the insulating film 18 may be in contact with the side surfaces of the lower electrodes 12a and 12b.

[0055] [Modification 19 of Example 1] FIG. 10(a) is a plan view of an acoustic wave device according to a modification 19 of the first embodiment, and FIG. 10(b) is a cross-sectional view taken along the line AA of FIG. 10(a). In FIG. 10(a), the insertion film 28 is hatched. As shown in FIG. 10(a) and FIG. 10(b), the piezoelectric film 14 includes a lower piezoelectric film 14a and an upper piezoelectric film 14b. The insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The insertion film 28 is provided in the outer peripheral region 52 of the resonance regions 50a and 50b, but is not provided in the central region 54. The outer peripheral region 52 is a region within the resonance regions 50a and 50b, and is a region that includes and follows the outer periphery of the resonance regions 50a and 50b. The outer peripheral region 52 is, for example, strip-shaped. The central region 54 is a region within the resonance regions 50a and 50b, and is a region that includes the center of the resonance regions 50a and 50b. The center does not have to be the geometric center. The insertion film 28 is provided continuously from the outer peripheral region 52 to the outside of the resonance regions 50a and 50b, and is provided in the dividing region 56. The side surface of the lower piezoelectric film 14a is provided outward from the side surface of the upper piezoelectric film 14b, and the insertion film 28 is provided on the lower piezoelectric film 14a outside the upper piezoelectric film 14b.

[0056] The acoustic impedance of the insertion film 28 is preferably smaller than that of the piezoelectric film 14. When the piezoelectric film 14 is mainly composed of aluminum nitride, the insertion film 28 is, for example, a silicon oxide film, an aluminum film, a gold film, a copper film, a titanium film, a platinum film, or a tantalum film. By providing the insertion film 28 in the region where the resonance regions 50a and 50b are adjacent to each other, the interference of the elastic waves between the resonators 11a and 11b can be suppressed. In addition, the elastic waves can leak from the resonators 11a and 11b to the substrate 10, and the Q value can be improved. The other configurations are the same as those in the first embodiment, and therefore the description will be omitted.

[0057] [Modification 20 of Example 1] FIG. 11(a) is a cross-sectional view of an acoustic wave device according to a modification 20 of the first embodiment. As shown in FIG. 11(a), a temperature compensation film 26 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The temperature compensation film 26 is provided over the entire resonance regions 50a, 50b and the separation region 56. The sign of the temperature coefficient of the elastic constant of the temperature compensation film 26 is opposite to the sign of the temperature coefficient of the elastic constant of the piezoelectric film 14. This makes it possible to reduce the frequency temperature coefficient of the resonators 11a and 11b. The temperature compensation film 26 is, for example, a silicon oxide film to which no impurities are intentionally added or a silicon oxide film to which an impurity such as fluorine is added. The other configurations are the same as those of the first embodiment, and therefore a description thereof will be omitted.

[0058] [Modification 21 of Example 1] Fig. 11(b) is a cross-sectional view of an acoustic wave device according to Modification 21 of Example 1. As shown in Fig. 11(b), a temperature compensation film 26 and an insertion film 28 are provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The other configurations are the same as those of Modifications 19 and 20 of Example 1, and a description thereof will be omitted. As in Modifications 19 to 21 of Example 1, the insertion film 28 and / or the temperature compensation film 26 may be provided in Example 1 and its Modifications 1 to 18.

[0059] [Modification 22 of Example 1] Modifications 22 and 23 of Example 1 are examples in which the configuration of the gap is changed. FIG. 12(a) and FIG. 12(b) are cross-sectional views of the vicinity of the resonance region in Modifications 22 and 23 of Example 1. As shown in FIG. 12(a), the upper surface of the substrate 10 is flat. A dome-shaped gap 30 is formed between the upper surface of the substrate 10 and the lower surfaces of the lower electrodes 12a and 12b and the insulating film 18. The dome shape is such that the height of the gap 30 is small at the periphery of the gap 30 and the height of the gap 30 increases toward the inside of the gap 30. In order to form the dome-shaped gap 30, it is preferable that the total internal stress of the lower electrodes 12a and 12b, the piezoelectric film 14, and the upper electrode 16 is a compressive stress. The other configurations are the same as those of Example 1, and a description thereof will be omitted.

[0060] [Modification 23 of Example 1] As shown in FIG. 12(b), an acoustic reflection film 31 is formed in place of the gap 30 in Example 1. The acoustic reflection film 31 is formed by alternating films 31a with low acoustic impedance and films 31b with high acoustic impedance. The thickness of the films 31a and 31b is, for example, approximately λ / 4 (λ is the wavelength of the elastic wave). The number of layers of the films 31a and 31b can be set arbitrarily. For example, the acoustic reflection film 31 may be configured such that one film with a different acoustic impedance is provided in the substrate 10. The other configurations are the same as those in Example 1, and description thereof will be omitted.

[0061] In the first embodiment and its first to twenty-first modifications, a dome-shaped cavity 30 may be formed as in the twenty-second modification of the first embodiment, or an acoustic reflection film 31 may be formed instead of the cavity 30 as in the twenty-third modification of the first embodiment.

[0062] As in the first embodiment and its first to second modifications, the resonators 11a and 11b may be FBARs (Film Bulk Acoustic Resonators). As in the second modification of the first embodiment, the resonators 11a and 11b may be SMRs (Solidly Mounted Resonators). In this manner, the acoustic reflection layer provided in or on the substrate 10 may include the gap 30 or the acoustic reflection film 31 in which at least two types of layers having different acoustic characteristics are laminated.

[0063] According to the first embodiment and its modified example, an acoustic reflection layer including an air gap 30 or an acoustic reflection film 31 in which at least two types of layers having different acoustic properties are laminated is provided on a substrate 10. A plurality of lower electrodes 12a and 12b share one acoustic reflection layer with the substrate 10 and are arranged apart from each other via a groove 55. An insulating film 18 is provided in the groove 55 on the acoustic reflection layer. A piezoelectric film 14 is provided integrally on the plurality of lower electrodes 12a, 12b and the groove 55. An upper electrode 16 is provided integrally on the piezoelectric film 14, and a plurality of resonators 11a and 11b are formed by sandwiching the piezoelectric film 14 between the plurality of lower electrodes 12a and 12b.

[0064] As a result, as described with reference to Fig. 4(b), it is possible to suppress the formation of cracks 62 and regions 63 with reduced crystallinity in the piezoelectric film 14 formed in Comparative Example 1 in Fig. 4(a). Furthermore, when the sacrificial layer 38 is removed in Fig. 3(c), the insulating film 18 protects the piezoelectric film 14, so that it is possible to suppress erosion of the piezoelectric film 14. As a result, it is possible to suppress deterioration of the piezoelectric film 14, etc.

[0065] The upper electrode 16 is not drawn out to the outside of the acoustic reflection layer in plan view. That is, no other resonators are connected to the upper electrode 16. As a result, the resonators 11a and 11b are connected in series, and the polarization directions of the piezoelectric film 14 are opposite to each other, so that the secondary distortion can be suppressed as described in Patent Document 1. In addition, since the upper electrode 16 is above the atmosphere, the parasitic capacitance added to the upper electrode 16 in the separation region 56 can be reduced. As a result, the secondary distortion can be further suppressed as described in FIG. 4 of Patent Document 1. In order to suppress the secondary distortion, it is preferable that the areas of the resonance regions 50a and 50b are approximately the same to the extent of the manufacturing error. In addition, it is preferable that the planar shapes of the resonance regions 50a and 50b are symmetrical (for example, point symmetrical, line symmetrical, or mirror symmetrical). The planar shapes of the resonance regions 50a and 50b may be asymmetrical. This makes it possible to suppress interference between unnecessary waves of the resonators 11a and 11b.

[0066] Furthermore, when the upper electrode 16 is not extended to the outside of the acoustic reflection layer in plan view, the upper electrode 16 and the piezoelectric film 14 are included in the gap 30 in plan view. Therefore, the resonators 11a and 11b are supported on the substrate 10 mainly by the lower electrodes 12a and 12b, and the support strength is weak. Therefore, by providing the insulating film 18, the resonators 11a and 11b can be reinforced.

[0067] The insulating film 18 contacts each of the lower electrodes 12a and 12b. For example, the insulating film 18 contacts at least the lower ends of the lower electrodes 12a and 12b. The insulating film 18 can reinforce the lower electrodes 12a and 12b. In addition, the insulating film 18 can prevent the piezoelectric film 14 from being exposed to the etching solution of the sacrificial layer 38 as indicated by the arrow 64 in FIG. 4(a) of Comparative Example 1. Note that even if the insulating film 18 does not contact each of the lower electrodes 12a and 12b, the effect of preventing the formation of the cracks 62 and the regions 63 can be obtained.

[0068] As in Example 1 and its Modifications 2, 4, 6, 8, 10, 12, 14, 16, and 18, the surface of the insulating film 18 on the piezoelectric film 14 side and the surfaces of the lower electrodes 12a and 12b on the piezoelectric film 14 side are substantially flush with each other. This makes it possible to suppress the formation of cracks 62 and regions 63 in the piezoelectric film 14. Note that "substantially flush" refers to a plane within the range of manufacturing error. For example, as shown in FIG. 12(a) of Modification 22 of Example 1, when the void 30 is dome-shaped, the height of the void 30 is approximately 1 / 100 of the width of the void 30, and the upper surface of the void 30 can be regarded as being substantially flush with each other. A recess may be provided between the surface of the insulating film 18 on the piezoelectric film 14 side and the surfaces of the lower electrodes 12a and 12b on the piezoelectric film 14 side.

[0069] As in the first, third, fifth, seventh, ninth, eleventh, thirteenth, fifteenth and seventeenth variations of the first embodiment, the surface of the insulating film 18 on the piezoelectric film 14 side is located closer to the substrate 10 than the surfaces of the lower electrodes 12a and 12b on the piezoelectric film 14 side, and is located closer to the piezoelectric film 14 than the surfaces of the lower electrodes 12a and 12b on the substrate 10 side. This makes the step D1 smaller than the thicknesses T1a and T1b. This makes it possible to suppress the formation of cracks 62 and regions 63 in the piezoelectric film 14.

[0070] As in Modifications 6, 7, and 14 to 18 of Example 1, the side surface of the insulating film 18 is in contact with the side surfaces of the plurality of lower electrodes 12a and 12b so as to have a contacting surface. This prevents the formation of recesses between the upper surface of the insulating film 18 and the upper surfaces of the lower electrodes 12a and 12b, and therefore the formation of cracks 62 and regions 63 in the piezoelectric film 14 can be further suppressed.

[0071] As in the sixth, seventh, fourteenth, sixteenth and eighteenth variations of the first embodiment, the surface of the insulating film 18 on the piezoelectric film 14 side is substantially flat with the surfaces of the lower electrodes 12a and 12b on the piezoelectric film 14 side within the manufacturing tolerance. In other words, no recess is provided between the surface of the insulating film 18 on the piezoelectric film 14 side and the surfaces of the lower electrodes 12a and 12b on the piezoelectric film 14 side. This can further suppress the formation of cracks 62 and regions 63 in the piezoelectric film 14.

[0072] As in Example 1 and its Modifications 1, 6 to 9, 14, and 15, the surface of the insulating film 18 on the substrate 10 side is substantially flat to within a manufacturing error with the surfaces of the lower electrodes 12a and 12b on the substrate 10 side. This allows the insulating film 18 to be easily formed since it is sufficient to form the lower electrodes 12a, 12b and the insulating film 18 on the upper surface of the sacrificial layer 38 as shown in FIG.

[0073] As in Modifications 2 to 5, 10 to 13, and 16 to 18 of Example 1, a part of the insulating film 18 is provided on the surfaces of the lower electrodes 12a and 12b facing the substrate 10. This allows the insulating film 18 to reinforce the lower electrodes 12a and 12b.

[0074] As in the second, third, tenth, eleventh, and sixteenth to eighteenth variations of the first embodiment, the insulating film 18 overlaps the entire acoustic reflection layer in plan view, thereby enabling the insulating film 18 to reinforce the lower electrodes 12a and 12b.

[0075] When the acoustic reflection layer is the gap 30 as in the first to second modified examples of the first embodiment, the strength of the decoupling region 56 is weakened if the insulating film 18 is not provided. Therefore, by providing the insulating film 18 in the decoupling region 56, the lower electrodes 12a and 12b can be reinforced.

[0076] As in modification 22 of embodiment 1, when the surface of substrate 10 on the side of gap 30 is substantially flat within the limits of manufacturing error, lower electrodes 12a and 12b curve upward. If insulating film 18 is not provided, the strength of separation region 56 will be weakened. Therefore, by providing insulating film 18 in separation region 56, lower electrodes 12a and 12b can be reinforced.

[0077] As in the modified examples 19 to 21 of the first embodiment, an insertion film 28 and / or a temperature compensation film 26 made of a material different from that of the piezoelectric film 14 may be inserted between the upper electrode 16 and the lower electrodes 12a and 12b. EXAMPLES

[0078] The second embodiment is an example of a duplexer. FIG. 13 is a circuit diagram of the duplexer according to the second embodiment. As shown in FIG. 13, the common terminal Ant is connected to an antenna 44. A transmission filter 40 is connected between the common terminal Ant and a transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and a reception terminal Rx. An inductor L1 is connected as a matching circuit between the common terminal Ant and ground. The transmission filter 40 passes a signal in a transmission band among signals inputted from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in a reception band among signals inputted from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. The inductor L1 matches impedance so that the transmission signal that has passed through the transmission filter 40 is outputted from the common terminal Ant without leaking to the reception filter 42.

[0079] The transmit filter 40 is a ladder type filter. One or more series resonators S1 to S4 are connected in series between a common terminal Ant and a transmit terminal Tx. One or more parallel resonators P1 to P3 are connected in parallel between the common terminal Ant and the transmit terminal Tx. One end of the parallel resonators P1 to P3 is commonly grounded via an inductor L2. The parallel resonator P1 is divided into resonators P1a and P1b in series.

[0080] Fig. 14(a) is a plan view of the transmission filter in the second embodiment, and Fig. 14(b) is a plan view of the gap. As shown in Fig. 14(a), series resonators S1 to S4, parallel resonators P1 to P3, wiring 45, and terminals 46 are formed on a substrate 10. The series resonators S1 to S4 and the parallel resonators P1 to P3 have resonance regions 50. The wiring 45 connects the resonance regions 50 to each other and connects the resonance region 50 to the terminals 46. The terminals 46 include an input terminal Tin, an output terminal Tout, and a ground terminal Tg. The wiring 45 and the terminals 46 are formed by the lower electrode 12 or the upper electrode 16.

[0081] As shown in FIG. 14(a) and FIG. 14(b), the resonators other than the parallel resonator P1 have a single resonance region 50 in a single cavity 30. The resonators P1a and P1b are the resonators 11a and 11b according to the first embodiment and its modified example, and two resonance regions 50a and 50b and a separation region 56 are provided in a single cavity 30a. The cavity 30a in which the resonators P1a and P1b are provided and the other cavity 30 have an elliptical shape. In this way, since the cavity 30a and 30 have the same shape, the stress conditions for forming the piezoelectric film 14 and the like on the cavity 30a and 30 can be made almost the same. Therefore, the cavity 30a and 30 and the piezoelectric film 14 and the like can be easily formed.

[0082] As in the second embodiment, the transmission filter 40 includes a plurality of piezoelectric thin film resonators respectively corresponding to the plurality of resonance regions 50 provided in the single cavity 30 in the first embodiment and its modified examples. This makes it possible to reduce the parasitic capacitance of the wiring between the resonators P1a and P1b. As a result, it is possible to suppress the secondary distortion as in Patent Document 1. In addition, since the insulating film 18 is provided in the groove 55 between the lower electrodes 12a and 12b, it is possible to suppress the deterioration of the piezoelectric film and the like.

[0083] In the second embodiment, an example in which the first embodiment and its modified examples are used for the transmission filter 40 has been described, but the first embodiment and its modified examples may be used for the reception filter 42. In addition, an example in which the first embodiment and its modified examples are used for the ladder filter has been described, but the first embodiment and its modified examples may be used for the lattice filter or the multimode filter. A duplexer has been described as an example of a multiplexer. The multiplexer may be a triplexer or a quadplexer.

[0084] The parallel resonator P1 is divided into a plurality of resonators P1a and P1b (split resonators), and a plurality of resonance regions 50 corresponding to the resonators P1a and P1b are provided in common in the gap 30a. This makes it possible to suppress second-order distortion. The resonator to be divided may be at least one of one or more series resonators and one or more parallel resonators. From the viewpoint of suppressing second-order distortion, it is preferable that the series resonator S1 and / or the parallel resonator P1 closest to the output terminal is divided. The number of series resonators and parallel resonators can be set arbitrarily. EXAMPLES

[0085] The third embodiment is an example in which the first embodiment and its modified example are used in a ladder type filter. FIG. 15 is a plan view of the filter according to the third embodiment. The resonance regions 50a to 50c and the insulating film 18 are hatched. As shown in FIG. 15, three resonance regions 50a to 50c corresponding to the series resonators S1 and S2 and the parallel resonator P1 are provided in common in the gap 30. A separation region 56 is provided between the resonance regions 50a to 50c. A groove 55 is provided between the lower electrodes 12a to 12c. An insulating film 18 is provided in the groove 55. The upper electrode 16 is provided in common to the resonance regions 50a to 50c. The three resonators are electrically connected by the upper electrode 16. The lower electrodes 12a, 12b, and 12c are connected to the input terminal Tin, the output terminal Tout, and the ground terminal Tg, respectively. As a result, the series resonators S1 and S2 are connected in series and the parallel resonator P1 is connected in parallel between the input terminal Tin and the output terminal Tout.

[0086] According to the third embodiment, the resonance region 50 corresponding to at least one of the one or more series resonators and at least one of the one or more parallel resonators is provided in common in the gap 30. This makes it possible to suppress parasitic capacitance of the wiring between the series resonator and the parallel resonator.

[0087] Although the 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 gist of the present invention described in the claims. [Explanation of symbols]

[0088] 10 Substrate 12, 12a~12c lower electrode 11a, 11b resonator 14 Piezoelectric film 16 Upper electrode 18 Insulating film 18a, 18b part 26 Temperature compensation membrane 28 Insertion Membrane 30, 30a void 31 Acoustic reflective film 40 Transmission Filter 42 Receiving Filter 50, 50a~50c resonance area 55 Groove 56 Divided Areas

Claims

1. A substrate; an acoustic reflection layer provided on the substrate, the acoustic reflection layer including an acoustic reflection film having a gap or at least two layers having different acoustic characteristics laminated thereon; a plurality of lower electrodes provided on the substrate, sharing one of the acoustic reflection layers between the substrate and the plurality of lower electrodes and spaced apart from each other via grooves; an insulating film provided in the groove on the acoustic reflection layer; a piezoelectric film integrally provided on the plurality of lower electrodes and the grooves; an upper electrode provided integrally on the piezoelectric film, the upper electrode sandwiching the piezoelectric film between the lower electrodes to form a plurality of resonators; Equipped with An acoustic wave device in which a surface of the insulating film facing the piezoelectric film and surfaces of the plurality of lower electrodes facing the piezoelectric film are substantially flush with each other.

2. The acoustic wave device according to claim 1 , wherein the upper electrode is not extended to an outside of the acoustic reflection layer in a plan view.

3. The acoustic wave device according to claim 1 , wherein the insulating film is in contact with each of the plurality of lower electrodes.

4. The acoustic wave device according to claim 1 , wherein a side surface of the insulating film contacts side surfaces of the plurality of lower electrodes.

5. The acoustic wave device according to claim 1 , wherein a surface of the insulating film facing the substrate is substantially flat with a surface of the lower electrode facing the substrate.

6. The acoustic wave device according to claim 1 , wherein a part of the insulating film is provided on at least a part of the surfaces of the lower electrodes facing the substrate.

7. The acoustic wave device according to claim 6 , wherein the insulating film overlaps the entire acoustic reflection layer in a plan view.

8. The acoustic wave device according to claim 1 , wherein the acoustic reflection layer is an air gap.

9. The acoustic wave device according to claim 8 , wherein the surface of the substrate facing the gap is substantially flat.

10. The acoustic wave device according to claim 1 , further comprising an insertion film inserted between the upper electrode and the lower electrode, the insertion film having a material different from a material of the piezoelectric film.

11. A filter comprising an acoustic wave device according to any one of claims 1 to 10.

12. A multiplexer including a filter according to claim 11.

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