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

Abstract

To provide an acoustic wave device that reduces a manufacturing process.SOLUTION: A piezoelectric thin film resonator comprises: a substrate 10; an upper electrode 16 provided on the substrate; a piezoelectric film 14 provided between the substrate and the upper electrode; a first conductive film 12a that forms a resonance region 50 overlapped with the upper electrode while nipping the piezoelectric film, and contains a first element as a main component; a second conductive film 12b that contains a second element as a main component, and is provided between the first conductive film and the piezoelectric film; and an intermediate film 13 provided between the first conductive film and the second conductive film. The intermediate film 13 comprises a lower electrode that is provided in a first region 54 containing a center of the resonance region, and is not provided in a second region 56 containing an outer periphery of the resonance region while surrounding the outer periphery of the first region, in which a concentration of the second element in the first conductive film in the second region is higher than the concentration of the second element in the first conductive film in the first region and / or the concentration of the first element in the second conductive film in the second region is higher the concentration of the first element in the second conductive film in the first region.SELECTED DRAWING: Figure 2

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. The piezoelectric thin film resonator has a laminated film in which a lower electrode, a piezoelectric film, and an upper electrode are laminated. A region where the lower electrode and the upper electrode face each other with at least a part of the piezoelectric film interposed therebetween is a resonance region where elastic waves are excited. It is known that an insertion film is provided in the piezoelectric film in the outer peripheral region within the resonance region, and no insertion film is provided in the central region of the resonance region (for example, Patent Documents 1 and 2). It is known that the crystallinity of the piezoelectric film is reduced by providing the piezoelectric film on a base layer having a large surface roughness on the upper surface (for example, Patent Documents 3 to 5).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent documents 1 and 2 describe how characteristics such as the Q value can be improved. However, after forming the lower piezoelectric film, an insert film is formed on the lower piezoelectric film, the insert film is patterned, and then the upper piezoelectric film is formed on the lower piezoelectric film and the insert film. This increases the manufacturing time.

[0005] This invention has been made in view of the above problems and aims to reduce the number of manufacturing steps. [Means for solving the problem]

[0006] The present invention relates to an elastic wave device comprising: a substrate; an upper electrode provided on the substrate; a piezoelectric film provided between the substrate and the upper electrode; a first conductive film provided between the substrate and the piezoelectric film, forming a resonant region defined by a region that sandwiches at least a portion of the piezoelectric film and overlaps with the upper electrode, and mainly composed of a first element; a second conductive film provided between the first conductive film and the piezoelectric film, mainly composed of a second element different from the first element; and an interlayer provided between the first conductive film and the second conductive film, wherein the interlayer is provided in a first region including the center of the resonant region, and is not provided in a second region surrounding at least a portion of the outer periphery of the first region and including at least a portion of the outer periphery of the resonant region, and the concentration of the second element in the first conductive film in the second region is higher than the concentration of the second element in the first conductive film in the first region, and / or the concentration of the first element in the second conductive film in the second region is higher than the concentration of the first element in the second conductive film in the first region.

[0007] In the above configuration, the first conductive film and the second conductive film can be in contact in the second region.

[0008] In the above configuration, the lower electrode may be provided between the second conductive film and the piezoelectric film and may include a third conductive film whose main component is a third element different from the second element.

[0009] In the above configuration, the acoustic impedance of the third conductive film can be set to be higher than the acoustic impedance of the second conductive film.

[0010] In the above configuration, the surface roughness of the upper surface of the piezoelectric film in the second region can be greater than the surface roughness of the upper surface of the piezoelectric film in the first region.

[0011] In the above configuration, the orientation of the crystal orientation of the piezoelectric film in the second region can be lower than the orientation of the crystal orientation of the piezoelectric film in the first region.

[0012] In the above configuration, the resistivity of the first element, which is the main component of the first conductive film, can be set to be lower than the resistivity of the second element, which is the main component of the second conductive film.

[0013] In the above configuration, the concentration of the second element in the first conductive film in the second region is at least twice the concentration of the second element in the first conductive film in the first region, and / or the concentration of the first element in the second conductive film in the second region is at least twice the concentration of the first element in the second conductive film in the first region.

[0014] In the above configuration, the thickness of the interlayer can be smaller than either the thickness of the first conductive film or the thickness of the second conductive film.

[0015] In the above configuration, the first element may be aluminum, the second element may be chromium, and the main component of the interlayer may be titanium or titanium nitride.

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

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

[0018] The present invention relates to a method for manufacturing an elastic wave device, comprising: forming a lower electrode on a substrate, the lower electrode including a first conductive film containing a first element as a main component, a second conductive film containing a second element different from the first element as a main component and provided on the first conductive film, and an intermediate film provided in a first region including the center of a resonance region and not provided in a second region that surrounds at least a part of the outer periphery of the first region and includes at least a part of the outer periphery of the resonance region; heat-treating the lower electrode to make the concentration of the second element in the first conductive film in the second region higher than the concentration of the second element in the first conductive film in the first region, and / or make the concentration of the first element in the second conductive film in the second region higher than the concentration of the first element in the second conductive film in the first region; forming a piezoelectric film on the lower electrode; and forming the upper electrode on the piezoelectric film such that a resonance region defined by a region where the upper electrode and the lower electrode overlap with each other sandwiching at least a part of the piezoelectric film is formed.

Advantages of the Invention

[0019] According to the present invention, the manufacturing process can be reduced.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a plan view of a piezoelectric thin film resonator according to Example 1. [Figure 2] FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1. [Figure 3] FIGS. 3(a) to 3(d) are cross-sectional views showing a method for manufacturing a piezoelectric thin film resonator according to Example 1. [Figure 4] FIGS. 4(a) and 4(b) are cross-sectional views showing a method for manufacturing a piezoelectric thin film resonator according to Example 1. [Figure 5] FIGS. 5(a) and 5(b) are cross-sectional views showing a method for manufacturing a piezoelectric thin film resonator according to Example 1. [Figure 6] FIG. 6 is a cross-sectional view of a piezoelectric thin film resonator according to Comparative Example 1. [Figure 7]Figure 7 is a cross-sectional view of a piezoelectric thin-film resonator according to Modification 1 of Example 1. [Figure 8] Figures 8(a) to 8(c) are cross-sectional views of samples A to C, respectively, from the experiment. [Figure 9] Figures 9(a) and 9(b) show the EDX spectra of sample B. [Figure 10] Figures 10(a) and 10(b) show the EDX spectra of sample C. [Figure 11] Figures 11(a) and 11(b) are cross-sectional views of piezoelectric thin-film resonators according to modified examples 2 and 3 of Example 1. [Figure 12] Figure 12 is a cross-sectional view of a piezoelectric thin-film resonator according to a modified example 4 of Example 1. [Figure 13] Figure 13(a) is a circuit diagram of the filter according to Example 2, and Figure 13(b) is a circuit diagram of the duplexer according to Modification 1 of Example 2. [Modes for carrying out the invention]

[0021] The following describes an embodiment with reference to the drawings. [Examples]

[0022] Example 1 is an example of a piezoelectric thin-film resonator as an elastic wave device. Figure 1 is a plan view of the piezoelectric thin-film resonator according to Example 1. Figure 2 is a cross-sectional view AA of Figure 1. For ease of understanding, the dimensions of each component are changed in Figure 2 compared to Figure 1. The Z-axis is the normal direction of the substrate 10, the X-direction is the direction in which the lower electrode 12 is drawn out from the resonance region 50, and the Y-direction is the direction perpendicular to the X-direction in the planar direction of the substrate 10.

[0023] As shown in Figures 1 and 2, a lower electrode 12 is provided on a substrate 10. A recess is provided on the upper surface of the substrate 10, and a gap 30 is provided within the recess. The lower electrode 12 is provided on the substrate 10 and the gap 30. The lower electrode 12 comprises conductive films 12a, 12b and an interlayer 13. Conductive film 12a is provided on the substrate 10, and conductive film 12b is provided on conductive film 12a. The interlayer 13 is provided between conductive films 12a and 12b. A piezoelectric film 14 is provided on the lower electrode 12. An upper electrode 16 is provided on the piezoelectric film 14.

[0024] The resonant region 50 is defined by the region in a plan view where the lower electrode 12 and the upper electrode 16 overlap, with at least a portion of the piezoelectric film 14 in between. The lower electrode 12, piezoelectric film 14, and upper electrode 16 within the resonant region 50 form a laminated film 18. Elastic waves, such as thickness longitudinal vibration modes or thickness shear vibrations, resonate in the laminated film 18 within the resonant region 50. In a plan view, the air gap 30 includes the resonant region 50. In a plan view, the size of the air gap 30 is the same as or larger than the resonant region 50. The planar shape of the resonant region 50 is, for example, elliptical.

[0025] The interlayer 13 is provided in the first region 54 but not in the second region 52. The first region 54 is the region that includes the center of the resonance region 50. The second region 52 is the region that surrounds at least a part of the outer periphery of the first region 54 and includes at least a part of the outer periphery of the resonance region 50. As shown in Figure 1, the second region 52 may surround the entire outer periphery of the first region 54, or it may surround a part of the outer periphery of the first region 54 and not surround the other part of the outer periphery of the first region 54. The second region 52 may include the entire outer periphery of the resonance region 50, or it may include a part of the outer periphery of the resonance region 50 and not include the other part of the outer periphery of the resonance region 50.

[0026] Region 55 is the region on the lower electrode 12 where the piezoelectric film 14 is provided, excluding the first region 54. Region 56 is the region where the lower electrode 12 is not provided but the piezoelectric film 14 is provided. The second region 52 is included in region 55. The portion 15a of the piezoelectric film 14 in the first region 54 and region 56 has good crystallinity. On the other hand, the crystallinity of the portion 15b of the piezoelectric film 14 in region 55, which includes the second region 52, is worse than that of portion 15a. Also, the surface roughness of the upper surface of portion 15b is greater than that of the upper surface of portion 15a. Furthermore, in the first region 54, the main component elements of the conductive film 12b are hardly diffused into the conductive film 12a, and the main component elements of the conductive film 12a are hardly diffused into the conductive film 12b. In the second region 52, the main component elements of the conductive film 12b are diffused into the conductive film 12a, and / or the main component elements of the conductive film 12a are diffused into the conductive film 12b.

[0027] The substrate 10 is an insulating or semiconductor substrate such as a silicon substrate, sapphire substrate, spinel substrate, alumina substrate, quartz substrate, glass substrate, ceramic substrate, or GaAs substrate. The conductive films 12a, 12b and the upper electrode 16 are single-layer films or multilayer films thereof, mainly composed of elements such as 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). In particular, the conductive film 12a is mainly composed of elements with low resistivity such as copper, aluminum, or silver. The conductive film 12b is mainly composed of elements with high acoustic impedance such as ruthenium, chromium, tungsten, or tantalum. The interlayer 13 is a diffusion-blocking film for suppressing the diffusion of elements between the conductive films 12a and 12b, and is mainly composed of, for example, titanium or titanium nitride. The main component of the interlayer 13 is appropriately selected considering the main components of the conductive films 12a and 12b.

[0028] The piezoelectric film 14 is made of aluminum nitride (AlN), zinc oxide (ZnO), zirconium titanate (PZT), lead titanate (PbTiO3), lithium tantalate (TaLiO3), lithium niobate (NbLiO3), or quartz. The piezoelectric film 14 may be polycrystalline or single-crystal. The piezoelectric film 14 mainly consists of aluminum nitride and may contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 can be improved by using scandium (Sc), two elements from group 2 and group 4, or two elements from group 2 and group 5 as additive elements. This improves the effective electromechanical coupling coefficient of the piezoelectric thin-film resonator. Examples of group 2 elements are calcium (Ca), magnesium (Mg), strontium (Sr), or zinc (Zn). Examples of group 4 elements are titanium, zirconium (Zr), or hafnium (Hf). Group 5 elements include, for example, tantalum, niobium (Nb), or vanadium (V). Furthermore, the piezoelectric film 14 may mainly consist of aluminum nitride and may also contain boron (B).

[0029] [Manufacturing method of Example 1] Figures 3(a) to 5(b) are cross-sectional views showing a method for manufacturing a piezoelectric thin-film resonator according to Example 1. As shown in Figure 3(a), a recess is formed on the upper surface of the substrate 10. A sacrificial layer 38 is deposited on the substrate 10 using, for example, sputtering, vacuum deposition, or CVD (Chemical Vapor Deposition). The sacrificial layer 38 is, for example, magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), or silicon oxide (SiO2). Subsequently, the sacrificial layer 38 outside the recess is removed using, for example, CMP (Chemical Mechanical Polishing), thereby embedding the sacrificial layer 38 in the recess.

[0030] As shown in Figure 3(b), a conductive film 12a and an interlayer 13 are deposited on the sacrificial layer 38 and the substrate 10 using, for example, sputtering, vacuum deposition, or CVD. As shown in Figure 3(c), the interlayer 13 is patterned into a desired shape using photolithography and etching. The interlayer 13 may also be formed by the lift-off method. As a result, the interlayer 13 is formed in the first region 54. As shown in Figure 3(d), a conductive film 12b is deposited on the conductive film 12a and the interlayer 13 using, for example, sputtering, vacuum deposition, or CVD.

[0031] As shown in Figure 4(a), the conductive films 12a and 12b are patterned into the desired shape using photolithography and etching. This forms the lower electrode 12 with the conductive films 12a, 12b and the interlayer 13.

[0032] As shown in Figure 4(b), a piezoelectric film 14 is formed on the substrate 10 and the lower electrode 12, for example, using a sputtering method. At this time, the sputtering process is carried out by heating the substrate 10. The lower electrode 12 may be heated before forming the piezoelectric film 14. When the lower electrode 12 is heated, in region 55, the first element in the conductive film 12a diffuses into the conductive film 12b, and / or the second element in the conductive film 12b diffuses into the conductive film 12a. If the conductive film 12a is an aluminum film and the conductive film 12b is a chromium film, the substrate 10 is heated to, for example, 300°C or higher, preferably 400°C or higher.

[0033] In the first region 54, since an interlayer 13 is provided between the conductive films 12a and 12b, the diffusion of elements between the conductive films 12a and 12b is suppressed. The crystallinity of the piezoelectric film 14 in region 55 is worse than that of the piezoelectric film 14 in the first region 54 and region 56. The reason why the crystallinity of the piezoelectric film 14 in region 55 is worse can be considered as follows: When elements diffuse between the conductive films 12a and 12b, the upper surface of the conductive film 12b is thought to become rougher. As a result, the upper surface of the lower electrode 12 in region 55 is rougher than the upper surface of the lower electrode 12 in the first region 54. As described in Patent Documents 3 to 5, when a piezoelectric film is deposited on a rough substrate, the crystallinity of the piezoelectric film decreases.

[0034] As shown in Figure 5(a), the upper electrode 16 is formed on the piezoelectric film 14 using, for example, sputtering, vacuum deposition, or CVD. The upper electrode 16 is patterned into a desired shape using, for example, photolithography and etching. The upper electrode 16 may also be formed using a lift-off method. This forms a resonance region 50. Region 55 in the resonance region 50 becomes a second region 52.

[0035] As shown in Figure 5(b), the piezoelectric film 14 is patterned into a desired shape using, for example, photolithography and etching. This forms a laminated film 18 having a lower electrode 12, a piezoelectric film 14, and an upper electrode 16 in the resonant region 50. Subsequently, the sacrificial layer 38 is removed using an etching medium (etching solution). Through these steps, the piezoelectric thin-film resonator shown in Figure 2 is manufactured.

[0036] Figure 6 is a cross-sectional view of a piezoelectric thin-film resonator according to Comparative Example 1. As shown in Figure 6, in Comparative Example 1, the piezoelectric film 14 comprises a piezoelectric film 14a provided on the substrate 10 and the lower electrode 12, and a piezoelectric film 14b provided on the piezoelectric film 14a. An insertion film 28 is provided between the piezoelectric films 14a and 14b. The insertion film 28 is provided in the second region 52, but not in the first region 54. The lower electrode 12 does not have conductive films 12a and 12b, which allow elements to easily diffuse with each other, as in Example 1. Therefore, the piezoelectric film 14a is a portion 15a with good crystallinity. Because the upper surface of the insertion film 28 is rough, the crystallinity of the portion 15b of the piezoelectric film 14b on the insertion film 28 is poor. The piezoelectric film 14b on the piezoelectric film 14a where the insertion film 28 is not provided is a portion 15a with good crystallinity.

[0037] In the second region 52, an insertion film 28 is provided compared to the first region 54. As a result, the laminated film 18 in the second region 52 has an additional mass equal to that of the insertion film 28 compared to the laminated film 18 in the first region 54. Furthermore, the velocity of sound in the bulk material in the poorly crystalline portion 15b is different from the velocity of sound in the well-crystalline portion 15a. For example, the velocity of sound in the bulk material in portion 15b is slower than the velocity of sound in portion 15a. Due to these factors, the velocity of sound of elastic waves propagating within the laminated film 18 in the second region 52 is different from the velocity of sound of elastic waves propagating within the laminated film 18 in the first region 54. Therefore, elastic waves propagating in the X direction within the laminated film 18 from the first region 54 are reflected in the second region 52. This suppresses the leakage of elastic waves from the first region 54 outside the resonance region 50. As a result, losses are suppressed and the Q factor is improved.

[0038] However, in Comparative Example 1, a piezoelectric film 14a is formed on the substrate 10 and the lower electrode 12, an inset film 28 is formed on the piezoelectric film 14a, the inset film 28 is patterned, and a piezoelectric film 14b is formed on top of the piezoelectric film 14a and the inset film 28. This increases the manufacturing process and raises costs. In addition, the crystallinity of the piezoelectric films 14a and 14b differs in the second region 52. Furthermore, cracks may occur in the piezoelectric film 14b due to the step in the inset film 28.

[0039] In Example 1, an interlayer 13 is provided between the conductive films 12a and 12b in the first region 54, while the interlayer 13 is not provided in the second region 52. As a result, the crystallinity of portion 15b of the piezoelectric film 14 in the second region 52 is worse than that of portion 15a of the piezoelectric film 14 in the first region 54. Therefore, the sound velocity of elastic waves propagating within the laminated film 18 in the second region 52 is different from the sound velocity of elastic waves propagating within the laminated film 18 in the first region 54. As a result, similar to Comparative Example 1, elastic waves propagating in the X direction from the first region 54 within the laminated film 18 are reflected in the second region 52. This suppresses elastic waves leaking from the first region 54 outside the resonance region 50. Therefore, losses are suppressed and the Q value is improved. Furthermore, as with Comparative Example 1, complex manufacturing processes are unnecessary, thus reducing the manufacturing process and costs. In addition, the crystallinity of the piezoelectric film 14 in the second region 52 is more uniform than in Comparative Example 1.

[0040] [Example 1 Modification 1] Figure 7 is a cross-sectional view of a piezoelectric thin-film resonator according to Modification 1 of Example 1. As shown in Figure 7, the lower electrode 12 has a conductive film 12c between the conductive film 12b and the piezoelectric film 14. To improve the characteristics of the piezoelectric thin-film resonator, it is preferable that the conductive film 12c in contact with the piezoelectric film 14 has a high acoustic impedance. It is preferable that the conductive film 12b is made of a material that allows elements to diffuse between it and the conductive film 12a. It is preferable that the conductive film 12a is made of a material with low resistivity. As such conductive films 12a to 12c, conductive film 12a is an aluminum film, conductive film 12b is a chromium film, and conductive film 12c is a ruthenium film. The interlayer film 13 is a titanium nitride film.

[0041] [experiment] Experiments were conducted using a structure that assumed a modified example 1 of Example 1. Figures 8(a) to 8(c) are cross-sectional views of samples A to C in the experiment. As shown in Figure 8(a), in sample A, the lower electrode 12 has conductive films 12b and 12c, but does not have conductive film 12a and interlayer 13. As shown in Figure 8(b), in sample B, the lower electrode 12 has conductive films 12a to 12c, but does not have interlayer 13. As shown in Figure 8(c), in sample C, the lower electrode 12 has conductive films 12a to 12c, and an interlayer 13 is provided over the entire surface between conductive films 12a and 12b.

[0042] The preparation conditions for samples A to C are as follows: Substrate 10: Silicon substrate Conductive film 12a: Aluminum film with a thickness of 80 nm Conductive film 12b: Chromium film with a thickness of 60 nm Conductive film 12c: A ruthenium film with a thickness of 60 nm. Interlayer 13: Titanium nitride film with a thickness of 15 nm Piezoelectric film 14: Aluminum nitride film with a thickness of 600 nm A piezoelectric film 14 was deposited on the lower electrode 12 using the sputtering method. The temperature of the substrate 10 during film deposition was approximately 400°C.

[0043] Table 1 shows the arithmetic mean roughness Ra of the upper surface of the piezoelectric film 14 for samples A to C in the experiment, and the orientation of the piezoelectric film 14. [Table 1]

[0044] The piezoelectric film 14 is a polycrystalline aluminum nitride with the (002) direction as its principal axis. The orientation is indicated by the full width at half maximum of the rocking curve peak of the (002) plane in the X-ray diffraction evaluation. Piezoelectric films 14 with low orientation (full width at half maximum of the rocking curve peak) have high crystal orientation and good crystallinity. As shown in Table 1, samples A and C have a smaller arithmetic mean roughness Ra on the upper surface of the piezoelectric film 14 and higher crystal orientation compared to sample B.

[0045] Figures 9(a) and 9(b) show the EDX (Energy dispersive X-ray spectroscopy) spectra of sample B. Figures 10(a) and 10(b) show the EDX spectra of sample C. Figures 9(a) and 10(a) show the EDX spectra of conductive film 12b, and Figures 9(b) and 10(b) show the EDX spectra of conductive film 12a. The vertical lines indicate the peak positions, with Cr, Al, Si, and Cu representing the peaks of chromium, aluminum, silicon, and copper, respectively. The silicon originates from substrate 10, and the copper originates from the copper mesh on which the sample is placed during EDX analysis. At least copper is not an element present in conductive films 12a and 12b.

[0046] As shown in Figure 9(a), chromium peaks (CrKa, CrKb, CrLa, and CrL1) are observed in conductive film 12b of sample B. The aluminum peak (AlKa), as shown in range 43, is very small compared to the CrKa peak. This indicates that the element in conductive film 12b is almost entirely chromium. As shown in Figure 9(b), in conductive film 12a of sample B, the aluminum peak (AlKa) is the largest, but chromium peaks (CrKa and CrKb) are also observed, as shown in range 44. The height of the CrKa peak is 1 / 3 the height of the AlKa peak. This suggests that conductive film 12a contains chromium in addition to aluminum.

[0047] As shown in Figure 10(a), in the conductive film 12b of sample C, chromium peaks (CrKa, CrKb, CrLa, and CrL1) are observed, and, similar to Figure 9(a), the aluminum peak (AlKa) is very small, as shown in range 43. This indicates that the element in conductive film 12b is almost entirely chromium. As shown in Figure 10(b), in the conductive film 12a of sample C, the aluminum peak (AlKa) is the largest, and no chromium peak is observed. This indicates that the element in conductive film 12a is almost entirely aluminum, with chromium below the detection limit.

[0048] The above experimental results are summarized. In sample A, the chromium in conductive film 12b and the ruthenium in conductive film 12c do not diffuse at approximately 400°C, which is the deposition temperature of the piezoelectric film 14. As shown in Table 1, the arithmetic mean roughness Ra of the upper surface of the piezoelectric film 14 is 2.1 nm. When the piezoelectric film 14 is deposited on the lower electrode 12, the orientation of the piezoelectric film 14 is good at 3.0°.

[0049] In sample B, a conductive film 12a is provided between the conductive film 12b and the substrate 10. As shown in Figure 9(b), the chromium of conductive film 12b diffuses into conductive film 12a due to the deposition temperature of 400°C for the piezoelectric film 14. As shown in Table 1, the arithmetic mean roughness Ra of the upper surface of the piezoelectric film 14 is 4.2 nm, which is larger than that of sample A. The orientation of the piezoelectric film 14 is 5.5°, which is also larger than that of sample A. Thus, the crystallinity of the piezoelectric film 14 deteriorates due to the diffusion of elements from conductive film 12b into conductive film 12a. In sample B, the reason for the deterioration of the crystallinity of the piezoelectric film 14 is thought to be, for example, that the upper surface of the lower electrode 12 became rougher due to the diffusion of chromium from conductive film 12b into conductive film 12a.

[0050] In sample C, an interlayer 13 is provided between the conductive films 12a and 12b. As shown in Figures 10(a) and 10(b), the interlayer 13 suppresses the diffusion of chromium into the conductive film 12a and the diffusion of aluminum into the conductive film 12b. As shown in Table 1, the arithmetic mean roughness Ra of the upper surface of the piezoelectric film 14 is smaller than that of sample B and is about the same as that of sample A. In addition, the orientation of the piezoelectric film 14 is higher than that of sample B and is about the same as that of sample A. Furthermore, in samples B and C, the resistivity of the conductive film 12a is low, which helps to suppress losses.

[0051] According to Example 1 and Modification 1, in the lower electrode 12, the conductive film 12a (first conductive film) is mainly composed of a first element (e.g., aluminum), and the conductive film 12b (second conductive film) is mainly composed of a second element different from the first element (e.g., chromium). The interlayer film 13 is provided between the conductive films 12a and 12b in the first region 54, which includes the center of the resonance region 50, and is not provided in the second region 52, which surrounds the outer periphery of the first region 54 and includes the outer periphery of the resonance region 50. As shown in Figure 4(b), the lower electrode 12 is heat-treated when the piezoelectric film 14 is formed. As a result, the concentration of the second element in the conductive film 12a in the second region 52 becomes higher than the concentration of the second element in the conductive film 12a in the first region 54. The crystallinity of the piezoelectric film 14 in the second region 52 becomes lower than the crystallinity of the piezoelectric film 14 in the first region 54. Therefore, the sound velocity of elastic waves propagating through the laminated film 18 in the second region 52 is different from the sound velocity of elastic waves propagating through the laminated film 18 in the first region 54. As a result, elastic waves propagating in the X and Y directions within the laminated film 18 are reflected in the second region 52. Thus, leakage of elastic wave energy outside the resonance region 50 can be suppressed, reducing losses and improving the Q factor.

[0052] In the experiment, the second element, the main component of conductive film 12b, diffused into conductive film 12a. However, the first element, the main component of conductive film 12a, may diffuse into conductive film 12b, or the second element, the main component of conductive film 12b, may diffuse into conductive film 12a, and the first element, the main component of conductive film 12a, may diffuse into conductive film 12b. That is, the concentration of the second element in conductive film 12a in the second region 52 should be higher than the concentration of the second element in conductive film 12a in the first region 54, and / or the concentration of the first element in conductive film 12b in the second region 52 should be higher than the concentration of the first element in conductive film 12b in the first region 54.

[0053] In Figure 1, the second region 52 surrounds the outer periphery of the first region 54 and includes the outer periphery of the resonance region 50, but the second region 52 only needs to surround at least a part of the outer periphery of the first region 54 and include at least a part of the outer periphery of the resonance region 50. Preferably, the second region 52 surrounds 1 / 2 or more of the outer periphery of the first region 54, and more preferably 2 / 3 or more. Preferably, the second region 52 includes 1 / 2 or more of the outer periphery of the resonance region 50, and more preferably 2 / 3 or more. The lower electrode 12 other than the resonance region 50 may or may not have an interlayer film 13.

[0054] The concentration of the second element in the conductive film 12a in the second region 52 is preferably twice or more, more preferably five times or more, and more preferably ten times or more, than the concentration of the second element in the conductive film 12a in the first region 54. Alternatively, the concentration of the first element in the conductive film 12b in the second region 52 is preferably twice or more, more preferably five times or more, and more preferably ten times or more, than the concentration of the first element in the conductive film 12b in the first region 54. The concentration of the second element in the conductive film 12a in the second region 52 is preferably 0.1 atomic percent or more, and more preferably 1 atomic percent or more. Alternatively, the concentration of the first element in the conductive film 12b in the second region 52 is preferably 0.1 atomic percent or more, and more preferably 1 atomic percent or more.

[0055] The lower electrode 12 may be heat-treated before forming the piezoelectric film 14, and then the piezoelectric film 14 may be formed. In the second region 52, the conductive films 12a and 12b are in contact. This causes the diffusion of elements between the conductive films 12a and 12b.

[0056] As shown in Modification 1 of Example 1, the lower electrode 12 is provided between the conductive film 12b and the piezoelectric film 14 and includes a conductive film 12c (third conductive film) whose main component is a third element different from the first and second elements. This allows for the use of a material that improves the characteristics of the piezoelectric thin-film resonator for the conductive film 12c in contact with the piezoelectric film 14, and for the conductive film 12b, a material that allows elements to diffuse between it and the conductive film 12a.

[0057] The acoustic impedance of the conductive film 12c is higher than that of the conductive film 12b. This improves the characteristics of the piezoelectric thin film resonator. For example, if the piezoelectric film 14 is aluminum nitride, the acoustic impedances normalized by the acoustic impedance of aluminum nitride are 5.47, 1.97, 3.35, and 7.83 for ruthenium, chromium, molybdenum, and tungsten, respectively. The conductive film 12c mainly consists of ruthenium, molybdenum, or tungsten. The conductive film 12b mainly consists of chromium. This improves the characteristics of the piezoelectric thin film resonator. The acoustic impedance of the conductive film 12c is preferably 1.5 times or more, and more preferably 2.0 times or more, than that of the acoustic impedance of the conductive film 12b. The conductive film 12b is made of a material that allows elements to easily diffuse between it and the conductive film 12a.

[0058] As shown in Table 1, the surface roughness of the upper surface of the piezoelectric film 14 in the second region 52 is greater than the surface roughness of the upper surface of the piezoelectric film 14 in the first region 54. Furthermore, the crystal orientation of the piezoelectric film 14 in the second region 52 is lower than that of the piezoelectric film 14 in the first region 54. As a result, the crystallinity of the piezoelectric film 14 in the second region 52 is worse than that of the piezoelectric film 14 in the first region 54, and elastic waves attempting to propagate from the first region 54 to the outside of the resonant region 50 are reflected in the second region 52. Therefore, losses can be suppressed. The surface roughness of the upper surface of the piezoelectric film 14 in the second region 52 is preferably 1.1 times or more, and more preferably 1.2 times or more, than the surface roughness of the upper surface of the piezoelectric film 14 in the first region 54. The orientation of the crystal orientation of the piezoelectric film 14 in the second region 52 (full width at half maximum of the rocking curve peak) is preferably 1.1 times or more, and more preferably 1.2 times or more, than the orientation of the crystal orientation of the piezoelectric film 14 in the first region 54.

[0059] The resistivity of the first element, the main component of conductive film 12a, is lower than that of the second element, the main component of conductive film 12b. Note that the resistivity of the first and second elements refers to the resistivity of the bulk material where the first and second elements constitute 100% of each element. This allows for a lower resistance of the lower electrode 12, thereby suppressing losses. For example, the resistivity of ruthenium, chromium, molybdenum, and tungsten is 7.1 × 10⁻⁶, respectively.-8 Ωm, 12.9 × 10 -8 Ωm, 5.0 × 10 -8 Ωm and 5.29 × 10⁻⁶ -8 The resistivity is Ωm, and the resistivity of silver, copper, gold, and aluminum is 1.59 × 10⁻⁶ each. -8 Ωm, 1.68 × 10⁻⁶ -8 Ωm, 2.44 × 10⁻⁶ -8 Ωm and 2.65 × 10⁻⁶ -8 The resistivity is Ωm. The resistivity of the conductive film 12a is preferably 1 / 2 or less of the resistivity of the conductive film 12b, and more preferably 1 / 4 or less. Furthermore, the acoustic impedance of the conductive film 12a is lower than the acoustic impedance of the conductive film 12b, for example, 1 / 2 or less of the acoustic impedance of the conductive film 12b, and 1 / 5 or less.

[0060] If the interlayer 13 is too thick, the conductive film 12b will have difficulty covering the interlayer 13. From this viewpoint, the thickness of the interlayer 13 is preferably less than the thickness of the conductive film 12a and the conductive film 12b, preferably 1 / 2 times or less the thickness of the conductive film 12a and the conductive film 12b, and more preferably 1 / 5 times or less. The interlayer 13 is a film that suppresses the diffusion of elements between the conductive films 12a and 12b, and is, for example, a titanium film or a titanium nitride film.

[0061] By analogy with the preferred range of width for the insertion film in Patent Document 1, the width of the second region 52 in the XY plane is preferably 2.5 times or less, more preferably 1.5 times or less, and even more preferably 0.8 times or less, of the wavelength λ of the elastic wave in the first region 54. The width of the second region 52 in the XY plane is preferably 0.3 times or more, more preferably 0.5 times or more, and even more preferably 0.6 times or more, of the wavelength λ of the elastic wave in the first region 54. The wavelength λ of the elastic wave in the first region 54 is approximately twice the thickness of the laminated film 18 in the first region 54 (i.e., the total thickness of the lower electrode 12, piezoelectric film 14, and upper electrode 16).

[0062] The first element, which is the main component of conductive film 12a, is aluminum; the second element, which is the main component of conductive film 12b, is chromium; and the main component of the interlayer 13 is titanium or titanium nitride. This makes the crystallinity of the piezoelectric film 14 in the second region 52 worse than that of the piezoelectric film 14 in the first region 54. The main component of the piezoelectric film 14 is aluminum nitride. This makes the crystallinity of the piezoelectric film 14 in the second region 52 worse than that of the piezoelectric film 14 in the first region 54. The main component of conductive film 12c is ruthenium.

[0063] For a film to be primarily composed of a certain element, it is sufficient that the film contains that element to the extent that it has the desired function, and it is permissible for the film to contain elements other than the primary element, either unintentionally or intentionally. For example, the concentration of a certain element in a film is 50 atomic% or more, 80 atomic% or more, and 90 atomic% or more. If a film is primarily composed of multiple elements, the total concentration of the multiple elements is 50 atomic% or more, 80 atomic% or more, and 90 atomic% or more. If a film is a metal nitride, the concentration of nitrogen in the film is 10 atomic% or more or 20 atomic% or more, and the concentration of the metal in the film is 10 atomic% or more or 20 atomic% or more.

[0064] [Modification 2 of Example 1] Figure 11(a) is a cross-sectional view of a piezoelectric thin-film resonator according to a modification 2 of Example 1. As shown in Figure 11(a), a recess is provided on the upper surface of the conductive film 12a, and the interlayer film 13 is embedded in the recess. As a result, the upper surfaces of the conductive film 12a and the interlayer film 13 become flat, and the upper surface of the lower electrode 12 also becomes flat. This makes it possible to suppress the occurrence of cracks in the piezoelectric film 14 due to the step on the upper surface of the lower electrode 12 when the piezoelectric film 14 becomes thin.

[0065] [Modification 3 of Example 1] Modification 3 of Example 1 is an example in which the configuration of the void is changed. Figure 11(b) is a cross-sectional view of the piezoelectric thin-film resonator according to Modification 3 of Example 1. As shown in Figure 11(b), the upper surface of the substrate 10 is flat, and a dome-shaped void 30 is provided between the substrate 10 and the lower electrode 12. The other configurations are the same as in Example 1 and will not be described. The void 30 may be formed to penetrate the substrate 10.

[0066] [Modification 4 of Example 1] Figure 12 is a cross-sectional view of a piezoelectric thin-film resonator according to a modification 4 of Example 1. As shown in Figure 12, an acoustic reflective film 32 is formed below the lower electrode 12 of the resonance region 50. The acoustic reflective film 32 is made up of alternating layers of films 34 with low acoustic impedance and films 36 with high acoustic impedance. The thickness of films 34 and 36 is, for example, approximately λ / 4 (where λ is the wavelength of an elastic wave). The number of layers of films 34 and 36 can be arbitrarily set. The acoustic reflective film 32 only needs to consist of at least two layers with different acoustic properties stacked at intervals. Alternatively, the substrate 10 may be one of the at least two layers with different acoustic properties of the acoustic reflective film 32. For example, the acoustic reflective film 32 may be configured in which a layer of films with different acoustic impedances is provided in the substrate 10. The other configurations are the same as in Example 1 and will not be described.

[0067] In Modifications 1 and 2 of Example 1, a void 30 similar to that in Modification 3 of Example 1 may be formed, or an acoustic reflective film 32 may be formed instead of the void 30, similar to Modification 4 of Example 1.

[0068] As shown in Example 1 and its modifications 1 to 3, the piezoelectric thin-film resonator may be an FBAR (Film Bulk Acoustic Resonator) in which a gap 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. Alternatively, as shown in Modification 4 of Example 1, the piezoelectric thin-film resonator may be an SMR (Solidly Mounted Resonator) equipped with an acoustic reflective film 32 that reflects elastic waves propagating through the piezoelectric film 14 below the lower electrode 12 in the resonance region 50. The acoustic reflective layer including the resonance region 50 may include either a gap 30 or an acoustic reflective film 32.

[0069] Although an elliptical shape was used as an example for the planar shape of the resonance region 50, the planar shape of the resonance region 50 may be any shape, such as a square or a polygon such as a pentagon. [Examples]

[0070] Example 2 is an example of a filter and duplexer using piezoelectric thin-film resonators of Example 1 and its modified counterparts. Figure 13(a) is a circuit diagram of the filter according to Example 2. As shown in Figure 13(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. Piezoelectric thin-film resonators of Example 1 and its modified counterparts can be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P4. The number of resonators in the ladder-type filter can be set as appropriate.

[0071] [Modification 1 of Example 2] Figure 13(b) is a circuit diagram of a duplexer according to Modification 1 of Example 2. As shown in Figure 13(b), a transmit filter 40 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 42 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 40 allows signals in the transmit band from the signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 42 allows signals in the receive band from the signal input from the common terminal Ant to pass to the receive terminal Rx as the received signal, and suppresses signals of other frequencies. At least one of the transmit filter 40 and the receive filter 42 can be the filter of Example 2.

[0072] I used Duplexa as an example of a multiplexer, but Triplexa or Quadplexa would also work.

[0073] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0074] 10 circuit boards 12 Lower electrode 12a~12c Conductive film 13 Interlayer 14 Piezoelectric film 15a, 15b part 16 Upper electrode 18. Multilayer film 28 Insertion membrane 30 void 32 Acoustic reflective film 40 Transmission Filters 42 Receiving Filter 50 resonance area 52 Second area 54 1st area

Claims

1. circuit board and The upper electrode provided on the substrate, A piezoelectric film is provided between the substrate and the upper electrode, A resonant region is provided between the substrate and the piezoelectric film, and is defined by a region that sandwiches at least a portion of the piezoelectric film and overlaps with the upper electrode. A first conductive film mainly composed of the first element, A second conductive film is provided between the first conductive film and the piezoelectric film, and the second conductive film is mainly composed of a second element different from the first element. An interlayer provided between the first conductive film and the second conductive film, A third conductive film is provided between the second conductive film and the piezoelectric film, and the third conductive film mainly consists of a third element different from the second element, Equipped with, The interlayer is provided in a first region including the center of the resonance region, and is not provided in a second region that surrounds at least a part of the outer periphery of the first region and includes at least a part of the outer periphery of the resonance region. The lower electrode, wherein the concentration of the second element in the first conductive film in the second region is higher than the concentration of the second element in the first conductive film in the first region, and / or the concentration of the first element in the second conductive film in the second region is higher than the concentration of the first element in the second conductive film in the first region. A wave-based elastic device equipped with the following features.

2. The elastic wave device according to claim 1, wherein the first conductive film and the second conductive film are in contact in the second region.

3. The elastic wave device according to claim 1, wherein the acoustic impedance of the third conductive film is higher than the acoustic impedance of the second conductive film.

4. The acoustic wave device according to any one of claims 1 to 3, wherein the surface roughness of the upper surface of the piezoelectric film in the second region is greater than the surface roughness of the upper surface of the piezoelectric film in the first region.

5. The elastic wave device according to any one of claims 1 to 3, wherein the orientation of the crystal orientation of the piezoelectric film in the second region is lower than the orientation of the crystal orientation of the piezoelectric film in the first region.

6. The elastic wave device according to any one of claims 1 to 3, wherein the resistivity of the first element that is the main component of the first conductive film is lower than the resistivity of the second element that is the main component of the second conductive film.

7. The elastic wave device according to any one of claims 1 to 3, wherein the concentration of the second element in the first conductive film in the second region is at least twice the concentration of the second element in the first conductive film in the first region, and / or the concentration of the first element in the second conductive film in the second region is at least twice the concentration of the first element in the second conductive film in the first region.

8. The elastic wave device according to any one of claims 1 to 3, wherein the thickness of the interlayer is smaller than the thickness of the first conductive film and the thickness of the second conductive film.

9. The elastic wave device according to any one of claims 1 to 3, wherein the first element is aluminum, the second element is chromium, and the main component of the interlayer is titanium or titanium nitride.

10. A filter comprising an elastic wave device according to any one of claims 1 to 3.

11. A multiplexer comprising the filter described in claim 10.

12. A step of forming a lower electrode comprising: a first conductive film mainly composed of a first element on a substrate; a second conductive film mainly composed of a second element different from the first element and provided on the first conductive film; an intermediate film provided between the first conductive film and the second conductive film in a first region including the center of the resonance region, surrounding at least a part of the outer periphery of the first region and not provided in a second region including at least a part of the outer periphery of the resonance region; and a third conductive film provided between the second conductive film and the piezoelectric film and mainly composed of a third element different from the second element; A step of heat-treating the lower electrode to make the concentration of the second element in the first conductive film in the second region higher than the concentration of the second element in the first conductive film in the first region, and / or making the concentration of the first element in the second conductive film in the second region higher than the concentration of the first element in the second conductive film in the first region, The steps include forming the piezoelectric film on the lower electrode, A step of forming the upper electrode on the piezoelectric film such that the resonance region is formed by the region in which the upper electrode and the lower electrode overlap, with at least a portion of the piezoelectric film sandwiched between them; A method for manufacturing elastic wave devices, including

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