Elastic wave device and method for manufacturing the same, filter, and multiplexer

Abstract

To provide an elastic wave device capable of improving the characteristics.SOLUTION: An elastic wave device comprises a piezoelectric film 14 having a single-crystal region 56 within a resonance region 50 and a polycrystalline region 58 that is provided outside the resonance region 50 and surrounds the resonance region 50, and first and second electrodes sandwiching the piezoelectric film 14 so as to form the resonance region 50 overlapping at least a portion of the piezoelectric film 14, viewed from the thickness direction of the piezoelectric film 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an elastic wave device, a method for manufacturing the same, a filter, and a multiplexer.

Background Art

[0002] Filters and multiplexers having a piezoelectric thin film resonator are used for high-frequency circuits of wireless terminals such as mobile phones. It is known to use a single crystal piezoelectric film for the piezoelectric film of the piezoelectric thin film resonator (for example, Patent Document 1). It is known to grow a single crystal nitride semiconductor film such as single crystal aluminum nitride on a support substrate such as a sapphire substrate (for example, Patent Document 2). It is known to insert an insertion film into the piezoelectric film in the outer peripheral region of the resonance region where the lower electrode and the upper electrode overlap with the piezoelectric film interposed therebetween (for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] As in Patent Document 1, by using a single crystal for the piezoelectric film, the quality of the piezoelectric film is improved and the characteristics are improved. In Patent Document 3, by inserting an insertion film into the piezoelectric film, it is possible to suppress the leakage of elastic waves outside the resonance region and the deterioration of the Q value. However, when the piezoelectric film is a single crystal, an insertion film cannot be inserted into the piezoelectric film. Therefore, by making the thickness of the lower electrode or the upper electrode different, it is possible to suppress the leakage of elastic waves outside the resonance region and the deterioration of the Q value. However, the suppression of the deterioration of the Q value is insufficient.

[0005] The present invention has been made in view of the above problems, and aims to improve characteristics.

Means for Solving the Problems

[0006] The present invention includes a piezoelectric film having a single crystal region provided within a resonance region and a polycrystalline region outside the resonance region that surrounds the resonance region, and a first electrode and a second electrode that sandwich the piezoelectric film so as to form the resonance region that overlaps with at least a part of the piezoelectric film when viewed from the thickness direction of the piezoelectric film, and is an elastic wave device.

[0007] In the above configuration, in the polycrystalline region outside the resonance region, at least one grain boundary can be configured to penetrate the piezoelectric film in the thickness direction of the piezoelectric film.

[0008] In the above configuration, the piezoelectric film can be configured to have a polycrystalline region within the resonance region provided around the single crystal region within the resonance region.

[0009] In the above configuration, in the polycrystalline region outside the resonance region, at least one grain boundary penetrates the piezoelectric film in the thickness direction of the piezoelectric film, and in the polycrystalline region within the resonance region, the grain boundary does not penetrate the piezoelectric film in the thickness direction, or the density of the grain boundaries that penetrate the piezoelectric film in the thickness direction in the polycrystalline region within the resonance region is smaller than the density of the grain boundaries that penetrate the piezoelectric film in the thickness direction in the polycrystalline region outside the resonance region.

[0010] In the above configuration, the crystallinity of the piezoelectric film in the polycrystalline region within the resonance region can be configured to be lower than the crystallinity of the piezoelectric film in the polycrystalline region outside the resonance region.

[0011] In the above configuration, a single-crystal piezoelectric layer provided between the piezoelectric film and the second electrode and in contact with the single-crystal region, and a main component of the single-crystal piezoelectric layer as a main component, provided between the single-crystal piezoelectric layer and a polycrystalline region outside the resonance region, and an amorphous region in contact with the polycrystalline region outside the resonance region can be provided.

[0012] In the above configuration, the piezoelectric film can be configured to have aluminum nitride as a main component.

[0013] The present invention includes a step of forming an amorphous region outside the region on the surface of the single-crystal piezoelectric layer around a region where a resonance region of the single-crystal piezoelectric layer is formed, a step of forming a single-crystal region in the resonance region and forming a polycrystalline region outside the resonance region on the amorphous region outside the region, and forming a piezoelectric film on the single-crystal piezoelectric layer, and a step of forming a first electrode and a second electrode sandwiching the piezoelectric film so that the resonance region overlapping with at least a part of the piezoelectric film is formed as viewed from the thickness direction of the piezoelectric film. It is a method for manufacturing an elastic wave device.

[0014] In the above configuration, it may include a step of forming an amorphous region within the region around the central portion of the region on the surface of the single-crystal piezoelectric layer within the region, and the step of forming the piezoelectric film includes forming the piezoelectric film on the single-crystal piezoelectric layer so that a polycrystalline region within the resonance region is formed on the amorphous region within the region.

[0015] In the above configuration, the amorphous region outside the region can be configured to be thicker than the amorphous region within the region.

[0016] The present invention is a filter including the elastic wave device described above.

[0017] The present invention is a multiplexer including the filter described above.

Advantages of the Invention

[0018] According to the present invention, the characteristics can be improved.

Brief Description of the Drawings

[0019]

Figure 1

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Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments will be described with reference to the drawings.

Embodiment

[0021] Embodiment 1 is an example of a piezoelectric thin film resonator as an elastic wave device. FIG. 1(a) is a plan view of the piezoelectric thin film resonator according to Embodiment 1, and FIG. 1(b) is a cross-sectional view taken along line A-A of FIG. 1(a). The thickness direction of the substrate 10 is defined as the Z direction, the direction in which the lower electrode 12 is drawn out from the resonance region 50 is defined as the X direction, and the direction orthogonal to the X direction in the plane direction of the substrate 10 is defined as the Y direction.

[0022] As shown in FIGS. 1(a) and 1(b), in the piezoelectric thin film resonator 100, an insulating layer 11 is provided on the substrate 10, a lower electrode 12 (first electrode) is provided in the insulating layer 11, and the upper surface of the lower electrode 12 is exposed from the upper surface of the insulating layer 11. The upper surface of the insulating layer 11 and the upper surface of the lower electrode 12 are substantially flat. A gap 30 is provided in the insulating layer 11 below the lower electrode 12. A piezoelectric film 14 is provided on the insulating layer 11 and the lower electrode 12. An upper electrode 16 (second electrode) is provided on the piezoelectric film 14.

[0023] The resonance region 50 is defined by a region that sandwiches at least a part of the piezoelectric film 14 when viewed from the Z direction and where the lower electrode 12 and the upper electrode 16 overlap. The lower electrode 12, the piezoelectric film 14, and the upper electrode 16 in the resonance region 50 form a laminated film. Elastic waves such as thickness longitudinal vibration mode or thickness shear vibration resonate in the laminated film in the resonance region 50. In plan view, the gap 30 includes the resonance region 50. In plan view, the size of the gap 30 is the same as or larger than the resonance region 50. The planar shape of the resonance region 50 is, for example, an elliptical shape.

[0024] The piezoelectric film 14 has a single crystal region 56 and a polycrystalline region 58. The single crystal region 56 is provided so as to include the resonance region 50. In plan view, the size of the single crystal region 56 is the same as or larger than the resonance region 50. The polycrystalline region 58 is provided so as to surround the resonance region 50 and the single crystal region 56. In the single crystal region 56, the piezoelectric film 14 is a single crystal 15a, and in the polycrystalline region 58, the piezoelectric film 14 is a polycrystal 15b and has, for example, a columnar structure.

[0025] The substrate 10 is an insulating substrate or a semiconductor substrate such as, for example, a silicon substrate, a sapphire substrate, a spinel substrate, an alumina substrate, a quartz substrate, a glass substrate, a ceramic substrate, or a GaAs substrate. The insulating layer 11 is an inorganic insulating layer such as, for example, a silicon oxide layer, a silicon nitride layer, or an aluminum oxide layer. The insulating layer 11 may be an organic insulating layer. The lower electrode 12 and the upper electrode 16 are, for example, a single layer film mainly composed of ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), silver (Ag), gold (Au), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), or iridium (Ir), or a laminated film thereof.

[0026] The piezoelectric film 14 is aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO3), lithium tantalate (TaLiO3), lithium niobate (NbLiO3), or quartz. The piezoelectric film 14 may contain, for example, aluminum nitride as a main component and other elements for improving resonance characteristics or piezoelectricity. For example, 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 additive elements, the piezoelectricity of the piezoelectric film 14 is improved. Therefore, the effective electromechanical coupling coefficient of the piezoelectric thin film resonator can be improved. 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). Further, the piezoelectric film 14 may contain boron (B) with aluminum nitride as a main component.

[0027] In the case of a piezoelectric thin film resonator having a resonance frequency of 5 GHz, the lower electrode 12 is, for example, a chromium film with a thickness of 60 nm and a ruthenium film with a thickness of 60 nm from the insulating layer 11 side. The piezoelectric film 14 is, for example, aluminum nitride with a thickness of 600 nm. The upper electrode 16 is a ruthenium film with a thickness of 60 nm and a chromium film with a thickness of 60 nm from the piezoelectric film 14 side. The film thickness of each layer can be appropriately set to obtain desired resonance characteristics.

[0028] [Manufacturing Method of Example 1] Figs. 2(a) to 5(b) are cross-sectional views showing a manufacturing method of a piezoelectric thin film resonator according to Example 1. As shown in Fig. 2(a), a single crystal piezoelectric layer 36 is grown on the upper surface of a support substrate 34 such as a sapphire substrate. The sapphire substrate has, for example, a c-plane as a main surface. For forming the single crystal piezoelectric layer 36, for example, the vapor phase growth method described in Patent Document 2 is used. As the single crystal piezoelectric layer 36, a single crystal piezoelectric substrate (for example, a single crystal aluminum nitride substrate) may be used without using the support substrate 34.

[0029] As shown in Fig. 2(b), a mask layer 60 is formed on the single-crystal piezoelectric layer 36 in the single-crystal region 56. The mask layer 60 is not formed on the single-crystal piezoelectric layer 36 in the polycrystalline region 58. The mask layer 60 is, for example, a photoresist.

[0030] As shown in Fig. 2(c), an amorphous region 35 is formed on the surface of the single-crystal piezoelectric layer 36 using the mask layer 60 as a mask. The formation of the amorphous region 35 is performed, for example, by irradiating ions of an inert element such as argon onto the surface of the single-crystal piezoelectric layer 36 using the mask layer 60 as a mask. The inert element is, in addition to argon, a Group 18 element (noble gas element) such as helium, neon, or xenon. For the ion irradiation, an inverse sputtering method or the like is used. The main component of the amorphous region 35 is the same as the main component of the single-crystal piezoelectric layer 36, and the concentration of the Group 18 element such as argon in the amorphous region 35 is higher than the concentration of the Group 18 element in the single-crystal piezoelectric layer 36. The thickness T1 of the amorphous region 35 is, for example, 1 nm or more. Thereafter, the mask layer 60 is removed.

[0031] As shown in Fig. 3(a), a piezoelectric film 14 is formed on the single-crystal piezoelectric layer 36 and the amorphous region 35. The piezoelectric film 14 is formed by, for example, a sputtering method. When the piezoelectric film 14 is a nitride layer such as aluminum nitride, a reactive sputtering method using nitrogen gas may be used. As a result, the piezoelectric film 14 in the single-crystal region 56 is directly formed on the single-crystal piezoelectric layer 36 and thus becomes a single crystal 15a. The piezoelectric film 14 in the polycrystalline region 58 is directly formed on the amorphous region 35 and thus becomes polycrystalline 15b.

[0032] As shown in Fig. 3(b), a lower electrode 12 is formed on the piezoelectric film 14. The lower electrode 12 is formed using, for example, a sputtering method and an etching method. The lower electrode 12 may be formed using a vacuum evaporation method and a lift-off method.

[0033] As shown in Fig. 4(a), a sacrificial layer 38 is formed on the lower electrode 12. The sacrificial layer 38 is, for example, magnesium oxide. An insulating layer 11 is formed so as to cover the sacrificial layer 38 and the lower electrode 12 on the piezoelectric film 14. The insulating layer 11 is formed using, for example, the CVD (Chemical Vaper Deposition) method. The upper surface of the insulating layer 11 is planarized using, for example, the CMP (Chemical Mechanical Polishing) method.

[0034] As shown in Fig. 4(b), it is turned upside down and the lower surface of the insulating layer 11 is bonded to the upper surface of the substrate 10. For the bonding between the substrate 10 and the insulating layer 11, for example, the surface activation method is used.

[0035] As shown in Fig. 5(a), the support substrate 34, the single crystal piezoelectric layer 36, and the amorphous region 35 are removed using, for example, the CMP (Chemical Mechanical Polishing) method.

[0036] As shown in Fig. 5(b), an upper electrode 16 is formed on the piezoelectric film 14. For the formation of the upper electrode 16, for example, the sputtering method and the etching method are used. The upper electrode 16 may be formed using the vacuum evaporation method and the lift-off method. Thereby, a resonance region 50 is formed in which the lower electrode 12 and the upper electrode 16 overlap with the piezoelectric film 14 interposed therebetween. Thereafter, the sacrificial layer 38 is removed with an etching solution to form a void 30. Thus, the piezoelectric thin film resonator 100 shown in Fig. 1(b) is manufactured.

[0037] Figs. 6(a) and 6(b) are cross-sectional schematic views showing the single crystal piezoelectric layer and the piezoelectric film in Fig. 3(a). Figs. 6(a) and 6(b) are diagrams obtained by schematizing cross-sectional TEM (Transmission Electron Microscopy) images. The single crystal piezoelectric layer 36 and the piezoelectric film 14 are aluminum nitride to which no impurities are added. Fig. 6(a) shows the piezoelectric film 14 in the single crystal region 56, and Fig. 6(b) shows the piezoelectric film 14 in the polycrystalline region 58.

[0038] As shown in Fig. 6(a), according to the findings of the inventors, when a piezoelectric film 14 made of aluminum nitride is formed on a single-crystal piezoelectric layer 36 made of aluminum nitride using a sputtering method, the piezoelectric film 14 becomes a single crystal 15a. The interface between the single-crystal piezoelectric layer 36 and the single crystal 15a is difficult to distinguish.

[0039] As shown in Fig. 6(b), the upper part of the single-crystal piezoelectric layer 36 is an amorphous region 35. According to the findings of the inventors, when a piezoelectric film 14 made of aluminum nitride is formed on the amorphous region 35 made of aluminum nitride using a sputtering method, the piezoelectric film 14 becomes a polycrystal 15b. In one example, when the thickness T1 of the amorphous region 35 is 5 nm or more, the polycrystal 15b has a columnar structure. In the columnar structure, a plurality of crystal grains 62 penetrating the piezoelectric film 14 are provided, and at least a part of the grain boundaries 64 between the crystal grains 62 penetrates the piezoelectric film 14. In the piezoelectric film 14 having a columnar structure, a gap is generated between the crystal grains 62 at the grain boundary 64, so that the grain boundary 64 penetrating the piezoelectric film 14 can be clearly observed by cross-sectional TEM. The crystallinity of the polycrystal 15b is poor, and the sound velocity of the elastic wave propagating through the polycrystal 15b is slower than the sound velocity of the elastic wave propagating through the single crystal 15a. The average grain size of the crystal grains 62 is, for example, 20 nm or more and 50 nm or less on the upper surface of the piezoelectric film 14 (the lower surface of the piezoelectric film 14 in contact with the lower electrode 12 in Fig. 1(b)). When the piezoelectric film 14 is aluminum nitride, the piezoelectric film 14 is oriented in the c-axis direction.

[0040] According to Example 1, the single-crystal region 56 of the piezoelectric film 14 is provided within the resonance region 50, and the polycrystalline region 58 (the polycrystalline region outside the resonance region) is provided outside the resonance region 50 and surrounds the resonance region 50. The sound velocity of the elastic wave of the polycrystal 15b is slower than the sound velocity of the elastic wave of the single crystal 15a. Thereby, the elastic wave is confined in the resonance region 50. Therefore, leakage of the elastic wave outside the resonance region 50 can be suppressed. Therefore, deterioration of characteristics such as deterioration of the Q value can be suppressed. The single crystal 15a and the polycrystal 15b can be evaluated using an electron beam diffraction method using TEM. For example, in the single crystal 15a, distinct diffraction spots according to the symmetry of the crystal are observed in the electron beam diffraction image. In the polycrystal 15b, a pattern concentric with the diffraction spots is observed.

[0041] To manufacture the piezoelectric thin film resonator 100 of Example 1, as shown in Fig. 2(c), an amorphous region 35 (an amorphous region outside the region) is formed on the surface of the single crystal piezoelectric layer 36 so as to surround the region where the resonance region of the single crystal piezoelectric layer 36 is formed. As shown in Fig. 3(a), a piezoelectric film 14 is formed on the single crystal piezoelectric layer 36 such that a single crystal region 56 is formed in the resonance region 50 and a polycrystalline region 58 is formed on the amorphous region 35. As shown in Figs. 3(b) and 5(b), a lower electrode 12 and an upper electrode 16 sandwiching the piezoelectric film 14 are formed so that the resonance region 50 is formed. In this way, by manufacturing the piezoelectric thin film resonator 100, the single crystal region 56 and the polycrystalline region 58 can be easily formed in the piezoelectric film 14.

[0042] As shown in Fig. 6(b), in the polycrystalline region 58, at least one grain boundary 64 penetrates the piezoelectric film 14 in the Z direction. Thus, when the piezoelectric film 14 has a columnar structure, since a gap is generated at the grain boundary 64, the sound velocity of the piezoelectric film 14 becomes slow. Thereby, deterioration of characteristics can be further suppressed. Whether the grain boundary 64 penetrates the piezoelectric film 14 or not is observed, for example, by a cross-sectional TEM image at 50,000 times magnification. In the observed TEM image, it is sufficient that at least one of the grain boundaries 64 penetrates the piezoelectric film 14. In the observed TEM image, it is preferable that 25% or more or 50% or more of the observable grain boundaries 64 penetrate the piezoelectric film 14.

[0043] In order for the polycrystal 15b to have a columnar structure, the thickness T1 of the amorphous region 35 is preferably 5 nm or more, more preferably 10 nm or more. If the amorphous region 35 is too thick, it becomes difficult to form the piezoelectric film 14. From this viewpoint, the thickness T1 is preferably 50 nm or less.

[0044] When the single crystal region 56 is located outside the resonance region 50, elastic waves are likely to leak to the insulating layer 11 and the substrate 10, and the loss increases. From this viewpoint, the distance D1 between the resonance region 50 and the polycrystalline region 58 (see Figs. 1(a) and 1(b)) is preferably 0.5 times or less, more preferably 0.2 times or less, and even more preferably 0.1 times or less of the thickness of the piezoelectric film 14.

[0045] [Modification Example 1 of Example 1] FIG. 7 is a cross-sectional view of a piezoelectric thin-film resonator according to Modification Example 1 of Example 1. As shown in FIG. 7, in the piezoelectric thin-film resonator 102 according to Modification Example 1 of Example 1, a single-crystal piezoelectric layer 36 that contacts the piezoelectric film 14 within the single-crystal region 56 is provided between the piezoelectric film 14 and the upper electrode 16. The amorphous region 35 is provided between the single-crystal piezoelectric layer 36 and the polycrystalline region 58 and contacts the piezoelectric film 14 within the polycrystalline region 58. Other configurations are the same as those in Example 1.

[0046] In Modification Example 1 of Example 1, in the manufacturing process, in FIG. 5(a), the support substrate 34 is removed, and the single-crystal piezoelectric layer 36 and the amorphous region 35 are not removed. In FIG. 5(b), the upper electrode 16 is formed on the single-crystal piezoelectric layer 36. Other manufacturing methods are the same as those in Example 1.

[0047] According to Modification Example 1 of Example 1, since the single-crystal piezoelectric layer 36 having better thermal conductivity than the polycrystal 15b is provided, the heat dissipation can be improved. In addition, the process of removing the single-crystal piezoelectric layer 36 and the amorphous region 35 can be simplified. The amorphous region 35 has the main component of the single-crystal piezoelectric layer 36 as its main component. Also, in order to form the single-crystal region 56 on the single-crystal piezoelectric layer 36, the single-crystal piezoelectric layer 36 has the main component of the piezoelectric film 14 as its main component. For example, the main components of the piezoelectric film 14, the single-crystal piezoelectric layer 36, and the amorphous region 35 are aluminum nitride. In this case, the total of the aluminum concentration and the nitrogen concentration in the piezoelectric film 14, the single-crystal piezoelectric layer 36, and the amorphous region 35 is 50 atomic% or more, 80 atomic% or more, and 90 atomic% or more.

[0048] [Modification Example 2 of Example 1] FIG. 8(a) is a plan view of the piezoelectric thin film resonator according to Modification Example 2 of Example 1, and FIG. 8(b) is a cross-sectional view taken along line A-A of FIG. 8(a). As shown in FIGS. 8(a) and 8(b), in the piezoelectric thin film resonator 104 according to Modification Example 2 of Example 1, a polycrystalline region 57 is provided between the single crystal region 56 and the polycrystalline region 58. The single crystal region 56 is provided at the central portion 54 of the resonance region 50. The polycrystalline region 57 is provided at the peripheral portion 52 surrounding the central portion 54 within the resonance region 50 and at a portion surrounding the resonance region 50. The polycrystalline region 58 is provided so as to surround the polycrystalline region 57. The piezoelectric film 14 in the polycrystalline region 57 is polycrystal 15c. The polycrystal 15c has better crystallinity than the polycrystal 15b. For example, when the piezoelectric film 14 is an oriented material, the orientation of the polycrystal 15c is higher than that of the polycrystal 15b.

[0049] [Manufacturing Method of Modification Example 2 of Example 1] FIGS. 9(a) to 9(c) are cross-sectional views showing a manufacturing method of the piezoelectric thin film resonator according to Modification Example 2 of Example 1. As shown in FIG. 9(a), after the step of FIG. 2(a) of Example 1, a mask layer 61 is formed on the single crystal piezoelectric layer 36 in the single crystal region 56. The mask layer 61 is not formed on the single crystal piezoelectric layer 36 in the polycrystalline regions 57 and 58. Using the mask layer 61 as a mask, an amorphous region 35b is formed on the surface of the single crystal piezoelectric layer 36. The method of forming the amorphous region 35b is the same as that in FIG. 2(c).

[0050] As shown in FIG. 9(b), after removing the mask layer 61, a mask layer 60 is formed on the single crystal piezoelectric layer 36 in the single crystal region 56 and the polycrystalline region 57. The mask layer 60 is not formed on the single crystal piezoelectric layer 36 in the polycrystalline region 58. Using the mask layer 60 as a mask, an amorphous region 35a is formed on the surface of the single crystal piezoelectric layer 36. As a result, the thickness T1 of the amorphous region 35a in the polycrystalline region 58 becomes larger than the thickness T2 of the amorphous region 35b in the polycrystalline region 57.

[0051] As shown in Fig. 9(c), after removing the mask layer 60, a piezoelectric film 14 is formed on the single-crystal piezoelectric layer 36 and the amorphous regions 35a and 35b. The method of forming the piezoelectric film 14 is the same as that in Fig. 3(a) of Example 1. The piezoelectric film 14 in the single-crystal region 56 becomes a single crystal 15a. The piezoelectric films 14 in the polycrystalline regions 57 and 58 become polycrystals 15c and 15b, respectively. The polycrystal 15c formed on the thin amorphous region 35b has better crystallinity than the polycrystal 15b formed on the thick amorphous region 35a. Thereafter, by performing the steps from Fig. 3(b) to Fig. 5(b) of Example 1, the piezoelectric thin-film resonator 104 according to the second modification of Example 1 is manufactured.

[0052] Fig. 10 is a cross-sectional schematic view showing the single-crystal piezoelectric layer and the piezoelectric film in Fig. 9(c). Fig. 10 is a diagram schematically showing a cross-sectional TEM image. The single-crystal piezoelectric layer and the piezoelectric film are aluminum nitride without added impurities. The cross-sectional schematic views of the piezoelectric film 14 in the single-crystal region 56 and the polycrystalline region 58 are the same as those in Fig. 6(a) and Fig. 6(b), respectively.

[0053] As shown in Fig. 10, the upper part of the single-crystal piezoelectric layer 36 is the amorphous region 35b. The thickness T2 of the amorphous region 35b is smaller than the thickness T1 of the amorphous region 35 (corresponding to the amorphous region 35a in Fig. 9(c)) in Fig. 6(b). A piezoelectric film 14 of polycrystal 15c is provided on the amorphous region 35b. No columnar structure is observed in the polycrystal 15c, and the grain boundary 64 does not penetrate the piezoelectric film 14. Since there is almost no gap at the grain boundary 64, although a part of the grain boundary 64 is observed, a distinct grain boundary 64 as shown in Fig. 6(b) is not observed. In one example, when the thickness T2 of the amorphous region 35 is 1 nm or more and less than 5 nm, the polycrystal 15c does not become a columnar structure. Since the crystallinity of the polycrystal 15c is better than that of the polycrystal 15b, the sound velocity of the elastic wave propagating through the polycrystal 15c is slower than the sound velocity of the elastic wave propagating through the single crystal 15a and faster than the sound velocity of the elastic wave propagating through the polycrystal 15b.

[0054] According to Modification Example 2 of Embodiment 1, the piezoelectric film 14 has a polycrystalline region 57 (including the polycrystalline region within the resonance region) provided so as to surround a single crystal region 56 within the resonance region 50. The sound velocity of the polycrystal 15c is slower than that of the single crystal 15a. Thereby, leakage of elastic waves outside the resonance region 50 can be suppressed as in Patent Document 3. Therefore, deterioration of characteristics such as the Q value can be suppressed.

[0055] As shown in FIG. 6(b), in the polycrystalline region 58, at least one grain boundary penetrates the piezoelectric film 14 in the Z direction. Thereby, leakage of elastic waves within the resonance region 50 outside the resonance region 50 can be suppressed. Since the polycrystal 15b has poor crystallinity, if the polycrystal 15b exists within the resonance region 50, in the polycrystal 15b, the elastic waves do not resonate and the resonance characteristics deteriorate. Therefore, the polycrystalline region 57 is provided at the peripheral portion 52 within the resonance region 50. As shown in FIG. 10, in the polycrystalline region 57, the grain boundary 64 does not penetrate the piezoelectric film 14 in the Z direction. Thus, since the polycrystal 15c in the polycrystalline region 57 has better crystallinity than the polycrystal 15b, deterioration of the resonance characteristics can be suppressed. Furthermore, the sound velocity of the polycrystal 15c is slower than the sound velocity of the single crystal 15a. For this reason, leakage of elastic waves outside the resonance region 50 can be suppressed.

[0056] Even when the grain boundary 64 penetrates the piezoelectric film 14 in the polycrystalline region 57, the density of the grain boundary 64 that penetrates the piezoelectric film 14 in the Z direction in the polycrystalline region 57 may be smaller than the density of the grain boundary 64 that penetrates the piezoelectric film 14 in the Z direction in the polycrystalline region 58. The density of the grain boundary 64 that penetrates the piezoelectric film 14 is observed, for example, by a cross-sectional TEM image at a magnification of 50,000 times. In cross-sectional TEM images at the same magnification in the polycrystalline regions 57 and 58, the number of grain boundaries 64 that penetrate the piezoelectric film 14 in the Z direction is counted, and when the number is small, it is determined that the density of the grain boundary 64 that penetrates the piezoelectric film 14 in the Z direction is small. The number of grain boundaries 64 that penetrate the piezoelectric film 14 in the Z direction in the polycrystalline region 57 is, for example, 1 / 2 or less, and 1 / 10 or less of the number of grain boundaries 64 that penetrate the piezoelectric film 14 in the Z direction in the polycrystalline region 58.

[0057] The crystallinity of the polycrystal 15b of the piezoelectric film 14 in the polycrystalline region 58 is lower than that of the polycrystal 15c of the piezoelectric film 14 in the polycrystalline region 57. For example, the crystallinity of the polycrystals 15b and 15c can be evaluated using the electron beam diffraction method with TEM. For example, compared with 15b, the diffraction spots in the electron beam diffraction image of the polycrystal 15c are unclear, and a concentric pattern is observed darkly.

[0058] In order to manufacture the piezoelectric thin film resonator 104 of Modification 2 of Example 1, as shown in Fig. 9(a), an amorphous region 35b (the amorphous region within the region) surrounding the central portion 54 of the resonance region 50 is formed on the surface of the single crystal piezoelectric layer 36 within the resonance region 50. As shown in Fig. 9(b), an amorphous region 35a (the amorphous region outside the region) surrounding the resonance region 50 is formed on the surface of the single crystal piezoelectric layer 36. As shown in Fig. 9(c), the piezoelectric film 14 is formed such that a polycrystalline region 57 is formed on the amorphous region 35b and a polycrystalline region 58 is formed on the amorphous region 35a.

[0059] The amorphous region 35a is thicker than the amorphous region 35b. Thereby, the crystallinity of the polycrystal 15c becomes better than that of the polycrystal 15b. The thickness T1 of the amorphous region 35a is, for example, 1.5 times or more, and 2 times or more, the thickness T2 of the amorphous region 35b. The thickness T1 is, for example, 10 times or less the thickness T2. The thickness T1 is, for example, 5 nm or more, and the thickness T2 is, for example, less than 5 nm and 3 nm or less. The thickness T2 is 0.1 nm or more. The thicknesses of the amorphous regions 35a and 35b may gradually increase from the inside to the outside of the resonance region 50. In this case, the crystallinity of the polycrystals 15b and 15c gradually deteriorates from the inside to the outside of the resonance region 50.

[0060] Similar to Example 1, the distance D1 (see Figs. 8(a) and 8(b)) between the resonance region 50 and the polycrystalline region 58 is preferably 0.5 times or less, more preferably 0.2 times or less, and even more preferably 0.1 times or less the thickness of the piezoelectric film 14.

[0061] In order to suppress the leakage of elastic waves outside the resonance region 50, the overlapping distance D2 (see FIGS. 8(a) and 8(b)) between the resonance region 50 and the polycrystalline region 57 is preferably 2.5 times or less, more preferably 1.5 times or less, the wavelength of the elastic wave. Also, the distance D2 is preferably 0.3 times or more the wavelength of the elastic wave. The wavelength of the elastic wave is twice the total thickness of the lower electrode 12, the piezoelectric film 14, and the upper electrode 16.

[0062] [Modification Example 3 of Example 1] FIG. 11(a) is a cross-sectional view of a piezoelectric thin-film resonator according to Modification Example 3 of Example 1. As shown in FIG. 11(a), in the piezoelectric thin-film resonator 106 according to Modification Example 3 of Example 1, a single-crystal piezoelectric layer 36 that contacts the single-crystal region 56 is provided between the piezoelectric film 14 and the upper electrode 16. The amorphous regions 35a and 35b are provided between the single-crystal piezoelectric layer 36 and the polycrystalline regions 58 and 57, respectively. The amorphous regions 35a and 35b are in contact with the polycrystalline regions 58 and 57, respectively. Other configurations are the same as those of Modification Example 2 of Example 1.

[0063] In Modification Example 3 of Example 1, the heat dissipation can be improved compared to Modification Example 2 of Example 1. Also, the process of removing the single-crystal piezoelectric layer 36 and the amorphous region 35 can be simplified.

[0064] [Modification Example 4 of Example 1] FIG. 11(b) is a cross-sectional view of a piezoelectric thin-film resonator according to Modification Example 4 of Example 1. As shown in FIG. 11(b), in the piezoelectric thin-film resonator 108 according to Modification Example 4 of Example 1, an acoustic reflection film 31 is formed under the lower electrode 12 of the resonance region 50. The acoustic reflection film 31 has a low acoustic impedance film 31a and a high acoustic impedance film 31b provided alternately. The film thicknesses of the films 31a and 31b are, for example, approximately λ / 4 (λ is the wavelength of the elastic wave) each. The number of stacked layers of the films 31a and 31b can be set arbitrarily. The acoustic reflection film 31 only needs to have at least two types of layers with different acoustic characteristics stacked with a gap therebetween. Other configurations are the same as those of Example 1 and the description thereof is omitted.

[0065] In Modifications 1 to 3 of Example 1, an acoustic reflection film 31 may be formed instead of the void 30, similar to Modification 4 of Example 1. Similar to Example 1 and its Modifications 1 to 3, the piezoelectric thin film resonator may be an FBAR (Film Bulk Acoustic Resonator) in which a void 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. Also, similar to Modification 4 of Example 1, the piezoelectric thin film resonator may be an SMR (Solidly Mounted Resonator) provided with an acoustic reflection film 31 that reflects an elastic wave propagating through the piezoelectric film 14 under the lower electrode 12 in the resonance region 50.

[0066] Although the planar shape of the resonance region 50 has been described by taking an elliptical shape as an example, the planar shape of the resonance region 50 may be any shape such as a polygonal shape like a rectangular shape or a pentagonal shape.

[0067] In Example 1 and its modifications, the piezoelectric film 14 is mainly composed of aluminum nitride. Thereby, the piezoelectricity of the single crystal 15a can be enhanced. The piezoelectric film 14 may be gallium nitride or the like. Aluminum nitride or gallium nitride can grow a single crystal on a c-plane sapphire substrate in FIG. 2(a).

Example

[0068] Example 2 is an example of a filter and a duplexer using the piezoelectric thin film resonator of Example 1 and its modifications. FIG. 12(a) is a circuit diagram of the filter according to Example 2. As shown in FIG. 12(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. The piezoelectric thin film resonator of Example 1 and its modifications can be used for at least one resonator among one or more series resonators S1 to S4 and one or more parallel resonators P1 to P4. The number of resonators of the ladder-type filter and the like can be set as appropriate.

[0069] [Modification 1 of Example 2] FIG. 12(b) is a circuit diagram of a duplexer according to Modification 1 of Example 2. As shown in FIG. 12(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 allows a signal in the transmission band among the signals input from the transmission terminal Tx to pass through to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 allows a signal in the reception band among the signals input from the common terminal Ant to pass through to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of Example 2.

[0070] Although the duplexer has been described as an example of the multiplexer, a triplexer or a quadplexer may also be used.

[0071] 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 changes can be made within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0072] 10 Substrate 11 Insulating layer 12 Lower electrode 14 Piezoelectric film 15a Single crystal 15b, 15c Polycrystal 16 Upper electrode 30 Gap 31 Acoustic reflection film 40 Transmission filter 42 Reception filter 50 Resonance region 52 Peripheral portion 54 Central portion 56 Single crystal region 57, 58 Polycrystal regions 62 Crystal grains 64 Grain boundaries

Claims

1. A piezoelectric film having a single crystal region provided within a resonance region and a polycrystalline region outside the resonance region that is provided outside the resonance region and surrounds the resonance region, a first electrode and a second electrode sandwiching the piezoelectric film so as to form the resonance region that overlaps with at least a part of the piezoelectric film when viewed from the thickness direction of the piezoelectric film, and an elastic wave device including the same.

2. The elastic wave device according to claim 1, wherein in the polycrystalline region outside the resonance region, at least one grain boundary penetrates the piezoelectric film in the thickness direction of the piezoelectric film.

3. The elastic wave device according to claim 1, wherein the piezoelectric film has a polycrystalline region within the resonance region provided around the single crystal region within the resonance region.

4. In the polycrystalline region outside the resonance region, at least one grain boundary penetrates the piezoelectric film in the thickness direction of the piezoelectric film, in the polycrystalline region within the resonance region, the grain boundary does not penetrate the piezoelectric film in the thickness direction, or the density of the grain boundaries that penetrate the piezoelectric film in the thickness direction in the polycrystalline region within the resonance region is smaller than the density of the grain boundaries that penetrate the piezoelectric film in the thickness direction in the polycrystalline region outside the resonance region. The elastic wave device according to claim 3.

5. The elastic wave device according to claim 3, wherein the crystallinity of the piezoelectric film in the polycrystalline region within the resonance region is lower than the crystallinity of the piezoelectric film in the polycrystalline region outside the resonance region.

6. a single crystal piezoelectric layer provided between the piezoelectric film and the second electrode and in contact with the single crystal region, an amorphous region provided between the single crystal piezoelectric layer and the polycrystalline region outside the resonance region, having the main component of the single crystal piezoelectric layer as the main component and in contact with the polycrystalline region outside the resonance region, and the elastic wave device according to any one of claims 1 to 5 including the same.

7. The elastic wave device according to any one of claims 1 to 5, wherein the piezoelectric film is mainly composed of aluminum nitride.

8. a step of forming an amorphous region outside the region on the surface of the single crystal piezoelectric layer around the region where the resonance region of the single crystal piezoelectric layer is formed, a step of forming a piezoelectric film on the single crystal piezoelectric layer such that a single crystal region is formed within the resonance region and a polycrystalline region outside the resonance region is formed on the amorphous region outside the region, a step of forming a first electrode and a second electrode sandwiching the piezoelectric film so as to form the resonance region that overlaps with at least a part of the piezoelectric film when viewed from the thickness direction of the piezoelectric film, A method for manufacturing an elastic wave device including the same. **Claim 9** The method includes a step of forming an amorphous region within the region around the central portion of the region on the surface of the single crystal piezoelectric layer within the region, The method for manufacturing an elastic wave device according to claim 8, wherein the step of forming the piezoelectric film includes a step of forming the piezoelectric film on the single crystal piezoelectric layer so that a polycrystalline region within the resonance region is formed on the amorphous region within the region. **Claim 10** The method for manufacturing an elastic wave device according to claim 9, wherein the amorphous region outside the region is thicker than the amorphous region within the region. **Claim 11** A filter including the elastic wave device according to any one of claims 1 to 5. **Claim 12** A multiplexer including the filter according to claim 11.

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