JP7075232B2 - Piezoelectric thin film resonators, filters and duplexers - Google Patents

Description

The present invention relates to piezoelectric thin film resonators, filters and duplexers.

Elastic wave devices using piezoelectric thin film resonators are used as filters and duplexers for wireless devices such as mobile phones. The piezoelectric thin film resonator has a structure in which the lower electrode and the upper electrode face each other with the piezoelectric film interposed therebetween. The region where the lower electrode and the upper electrode face each other across the piezoelectric film is the resonance region. It is known to remove the piezoelectric film on the outside of the upper electrode (for example, Patent Document 1).

An insertion membrane is inserted between the lower piezoelectric membrane and the upper piezoelectric membrane, a piezoelectric membrane is provided so that the contour of the lower piezoelectric membrane is located outside the contour of the upper piezoelectric membrane, and the lower part is placed on the lower piezoelectric membrane via the insertion membrane. It is known to provide a metal layer connected to an electrode (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2007-300430 Japanese Unexamined Patent Publication No. 2017-158161

By removing the piezoelectric film on the outside of the upper electrode as in Patent Document 1, it is possible to suppress leakage of elastic wave energy from the resonance region. Thereby, the Q value and the like can be improved. By providing a metal layer on the lower piezoelectric membrane via the insertion membrane as in Patent Document 2, it is possible to prevent the insertion membrane from peeling off from the lower piezoelectric membrane.

However, in Patent Document 2, an insulating film such as an insertion film or a protective film is provided between the piezoelectric film and the metal layer. This hinders heat dissipation from the piezoelectric film to the metal layer.

The present invention has been made in view of the above problems, and an object of the present invention is to improve heat dissipation from a piezoelectric film.

The present invention comprises a substrate, a lower electrode provided on the substrate, a thick film portion provided on the lower electrode, and a thin film portion thinner than the thick film portion and having a substantially constant thickness . A piezoelectric film having a piezoelectric film, an upper electrode provided so as to form a resonance region which is a region facing the lower electrode across the thick film portion, and a thin film portion located outside the resonance region from above to the lower portion. It is a piezoelectric thin film resonator provided over an electrode and having a metal layer in contact with at least a part of the surface of the thin film portion.

In the above configuration, the metal layer may be configured to be in contact with at least a part directly above the thin film portion.

In the above configuration, the metal layer may be configured to be in contact with at least a part of the side surface of the thin film portion.

In the above configuration, the metal layer may be configured to be in contact with at least a part of the surface of the thin film portion in the region where the lower electrode is provided from the resonance region to the outside.

In the above configuration, a gap is formed under the lower electrode, and the outer circumference of the thin film portion may be located outside the outer circumference of the gap in a plan view.

The present invention comprises a substrate, a lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode and having a thick film portion and a thin film portion thinner than the thick film portion, and the thick film portion. An upper electrode provided so as to form a resonance region which is a region facing the lower electrode, and a thin film portion located outside the resonance region from the thin film portion to the lower electrode portion of the thin film portion. A metal layer in contact with at least a part of the surface and an insertion film inserted into the piezoelectric film are provided, and the piezoelectric film has a lower piezoelectric film and an upper piezoelectric film provided on the lower piezoelectric film. The insertion film is provided between the lower piezoelectric film and the upper piezoelectric film, the thick film portion is formed of the lower piezoelectric film and the upper piezoelectric film, and the thin film portion is formed of the lower piezoelectric film. It is a piezoelectric thin film resonator that does not include the upper piezoelectric film.

In the above configuration, an insulating film covering the piezoelectric film can be provided.

In the above configuration, the insulating film may be configured not to be provided between the metal layer and the thin film portion.

The present invention is a filter including the above-mentioned piezoelectric thin film resonator.

The present invention is a duplexer comprising the above filter.

According to the present invention, the heat dissipation from the piezoelectric film can be improved.

1 (a) is a plan view of the piezoelectric thin film resonator according to the first embodiment, and FIGS. 1 (b) and 1 (c) are sectional views taken along the line AA of FIG. 1 (a). FIG. 2 is a plan view showing the positional relationship of each layer of the piezoelectric thin film resonator according to the first embodiment. 3 (a) to 3 (c) are cross-sectional views (No. 1) showing Example 1 of the manufacturing method of the piezoelectric thin film resonator according to the first embodiment. 4 (a) to 4 (c) are cross-sectional views (No. 2) showing Example 1 of the manufacturing method of the piezoelectric thin film resonator according to the first embodiment. 5 (a) to 5 (c) are cross-sectional views (No. 1) showing Example 2 of the manufacturing method of the piezoelectric thin film resonator according to the first embodiment. 6 (a) to 6 (c) are cross-sectional views (No. 2) showing Example 2 of the manufacturing method of the piezoelectric thin film resonator according to the first embodiment. 7 (a) and 7 (b) are diagrams showing the cross-sectional shapes of Comparative Example 1 and Example 1 in which simulation was performed, and FIG. 7 (c) is a diagram showing the simulation results. 8 (a) and 8 (b) are cross-sectional views of the piezoelectric thin film resonator according to Comparative Example 2 and Example 1, respectively. 9 (a) and 9 (b) are cross-sectional views showing the piezoelectric thin film resonators according to the first and second modifications of the first embodiment, respectively. 10 (a) and 10 (b) are cross-sectional views showing the piezoelectric thin film resonators according to the modified examples 3 and 4, respectively, of the first embodiment. 11 (a) and 11 (b) are cross-sectional views showing the piezoelectric thin film resonators according to the modified examples 5 and 6, respectively, of the first embodiment. 12 (a) is a cross-sectional view of the piezoelectric thin film resonator of Example 2, and FIG. 12 (b) is a cross-sectional view of the piezoelectric thin film resonator of Modification 1 of Example 2. FIG. 13 is a circuit diagram of the duplexer according to the third embodiment. 14 (a) is a plan view and a cross-sectional view of the transmission filter in the third embodiment, and FIG. 14 (b) is a sectional view taken along the line AA of FIG. 14 (a).

Hereinafter, examples of the present invention will be described with reference to the drawings.

1 (a) is a plan view of the piezoelectric thin film resonator according to the first embodiment, and FIGS. 1 (b) and 1 (c) are sectional views taken along the line AA of FIG. 1 (a). FIG. 1B shows, for example, a series resonator of a ladder type filter, and FIG. 1C shows a cross-sectional view of, for example, a parallel resonator of a ladder type filter.

As shown in FIGS. 1A and 1B, in the series resonator S, the lower electrode 12 is provided on the substrate 10. A gap 30 having a dome-shaped bulge is formed between the flat main surface of the substrate 10 and the lower electrode 12. The dome-shaped bulge is, for example, a bulge having a shape in which the height of the void 30 is small around the void 30 and the height of the void 30 is increased toward the inside of the void 30. The substrate 10 is, for example, a Si (silicon) substrate. The lower electrode 12 includes a lower layer 12a and an upper layer 12b. The lower layer 12a and the upper layer 12b are, for example, a Cr (chromium) film and a Ru (ruthenium) film, respectively.

A piezoelectric film 14 is provided on the lower electrode 12. The piezoelectric film 14 is, for example, an aluminum nitride film containing aluminum nitride as a main component having the main axis in the (002) direction. The upper electrode 16 is provided on the piezoelectric film 14 so as to form a resonance region 50 facing the lower electrode 12 with the piezoelectric film 14 interposed therebetween. The resonance region 50 has an elliptical shape and is a region in which elastic waves in the thickness longitudinal vibration mode resonate. The upper electrode 16 includes a lower layer 16a and an upper layer 16b. The lower layer 16a and the upper layer 16b are, for example, a Ru film and a Cr film, respectively.

The piezoelectric film 14 has a thick film portion 15a and a thin film portion 15b thinner than the thick film portion 15a. The piezoelectric film 14 in the resonance region 50 is a thick film portion 15a. The piezoelectric film 14 in the region where the lower electrode is pulled out from the resonance region 50 is the thin film portion 15b.

A protective film 24 is formed on the upper electrode 16, a part of the side surface of the thick film portion 15a, and a part of the upper surface of the thin film portion 15b. The protective film 24 is, for example, a silicon oxide film. The laminated film 18 in the resonance region 50 includes a lower electrode 12, a piezoelectric film 14, an upper electrode 16, and a protective film 24. The protective film 24 may function as a frequency adjusting film.

Metal layers 22 and 22a are provided on the lower electrode 12 and the upper electrode 16. The metal layers 22 and 22a are in contact with the lower electrode 12 and the upper electrode 16 and function as wiring and / or a pad. The metal layers 22 and 22a are, for example, Au (gold) layers. An underlayer such as a Ti layer or a W layer may be provided under the Au layer. The metal layer 22 is provided from the upper surface of the thin film portion 15b to the lower electrode 12. The metal layer 22 is in contact with the upper surface and the side surface of the thin film portion 15b.

As shown in FIG. 1A, the lower electrode 12 is formed with an introduction path 33 for etching the sacrificial layer. The sacrificial layer is a layer for forming the void 30. The vicinity of the tip of the introduction path 33 is not covered with the piezoelectric film 14, and the lower electrode 12 has a hole 35 at the tip of the introduction path 33.

The structure of the parallel resonator P will be described with reference to FIGS. 1 (a) and 1 (c). Compared with the series resonator S, the parallel resonator P is provided with a mass load film 20 made of a Ti (titanium) layer between the lower layer 16a and the upper layer 16b of the upper electrode 16. Other configurations are the same as those in FIG. 1 (b) of the series resonator S, and the description thereof will be omitted.

The difference in resonance frequency between the series resonator S and the parallel resonator P is adjusted by using the film thickness of the mass load film 20. The resonance frequencies of both the series resonator S and the parallel resonator P are adjusted by adjusting the film thickness of the protective film 24.

In the case of a piezoelectric thin film resonator having a resonance frequency of 2 GHz, the thickness of the lower layer 12a made of the Cr film of the lower electrode 12 is 100 nm, and the thickness of the upper layer 12b made of the Ru film is 230 nm. The film thickness of the piezoelectric film 14 made of the AlN film is 1200 nm. The film thickness of the lower layer 16a made of the Ru film of the upper electrode 16 is 230 nm, and the film thickness of the upper layer 16b made of the Cr film is 50 nm. The film thickness of the protective film 24 made of the silicon oxide film is 50 nm. The film thickness of the mass loading film 20 made of the Ti film is 100 nm. The film thickness of each layer can be appropriately set in order to obtain desired resonance characteristics.

As the substrate 10, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a glass substrate, a ceramic substrate, a GaAs substrate, or the like can be used in addition to the Si substrate. In addition to Ru and Cr, the lower electrode 12 and the upper electrode 16 include Al (aluminum), Ti, Cu (copper), Mo (molybdenum), W (tungsten), Ta (tantal), Pt (platinum), and Rh ( A monolayer film such as rhodium) or Ir (iridium) or a laminated film thereof can be used. For example, the lower layer 16a of the upper electrode 16 may be Ru and the upper layer 16b may be Mo.

As the piezoelectric film 14, ZnO (zinc oxide), PZT (lead zirconate titanate), PbTiO ₃ (lead titanate) and the like can be used in addition to aluminum nitride. Further, the piezoelectric film 14 contains aluminum nitride as a main component and may contain other elements for improving resonance characteristics or piezoelectricity. For example, by using Sc (scandium), two elements of a group 2 element or a group 12 element and a group 4 element, or two elements of a group 2 element or a group 12 element and a group 5 element, as an additive element, The piezoelectricity of the piezoelectric film 14 is improved. Therefore, the effective electromechanical coupling coefficient of the piezoelectric thin film resonator can be improved. Group 2 elements are, for example, Ca (calcium), Mg (magnesium) or Sr (strontium). The Group 12 element is, for example, Zn (zinc). Group 4 elements are, for example, Ti, Zr (zirconium) or Hf (hafnium). Group 5 elements are, for example, Ta, Nb (niobium) or V (vanadium). Further, the piezoelectric film 14 contains aluminum nitride as a main component and may contain B (boron).

As the protective film 24, a silicon nitride film, aluminum nitride, or the like can be used in addition to the silicon oxide film. As the mass loading film 20, a single-layer film such as Ru, Cr, Al, Cu, Mo, W, Ta, Pt, Rh or Ir can be used in addition to Ti. Further, an insulating film made of a metal nitride or a metal oxide such as silicon nitride or silicon oxide can also be used. The mass loading film 20 includes not only the layers of the upper electrode 16 (between the lower layer 16a and the upper layer 16b), but also the layers below the lower electrode 12, between the lower electrodes 12, above the upper electrode 16, the lower electrode 12 and the piezoelectric film 14. It can be formed between and between the piezoelectric film 14 and the upper electrode 16. The mass load film 20 may be larger than the resonance region 50 as long as it is formed so as to include the resonance region 50.

FIG. 2 is a plan view showing the positional relationship of each layer of the piezoelectric thin film resonator according to the first embodiment. As shown in FIG. 2, in the extraction region 52 from which the upper electrode 16 is pulled out from the resonance region 50, the outer circumference 60 of the resonance region 50 is defined by the outer circumference of the lower electrode 12. In the extraction region 54 from which the lower electrode 12 is pulled out from the resonance region 50, the outer circumference 60 of the resonance region 50 is defined by the outer circumference of the upper electrode 16. A thin film portion 15b is provided so as to surround the resonance region 50 in the drawer region 54. The outer circumference 64 of the lower electrode 12 is located outside the outer circumference 65 of the thin film portion 15b. The metal layer 22 is provided so as to overlap the thin film portion 15b and the lower electrode 12. The inner circumference 62 of the metal layer 22 is located between the outer circumference 60 of the resonance region 50 and the outer circumference 65 of the thin film portion 15b. The outer circumference 66 of the metal layer 22 is located outside the outer circumference 64 of the lower electrode 12. The outer circumference 66 of the metal layer 22 may be provided between the outer circumference 65 of the thin film portion 15b and the outer circumference 64 of the lower electrode 12.

As shown in FIGS. 1 (b) and 1 (c), the outer circumference of the upper portion of the thick film portion 15a of the piezoelectric film 14 is located inside the outer circumference of the upper electrode 16. Thereby, the Q value can be improved. The outer circumference of the upper portion of the thick film portion 15a may coincide with the outer circumference of the upper electrode 16, or may be located outside the outer circumference of the upper electrode 16. The protective film 24 does not cover the upper side surface of the thick film portion 15a of the piezoelectric film 14. This is because the upper electrode 16 overhangs the side surface of the piezoelectric film 14. From the viewpoint of protecting the piezoelectric film 14, it is preferable that the piezoelectric film 14 is not exposed from the protective film 24.

[Manufacturing Method Example 1 of Example 1]
3A to 4C are cross-sectional views showing Example 1 of a method for manufacturing a piezoelectric thin film resonator according to the first embodiment. As shown in FIG. 3A, a sacrificial layer 38 for forming a void is formed on the substrate 10 having a flat main surface. The film thickness of the sacrificial layer 38 is, for example, 10 to 100 nm, and is selected from materials that can be easily dissolved in an etching solution or an etching gas such as MgO, ZnO, Ge, or SiO ₂ . Then, the sacrificial layer 38 is patterned into a desired shape by using a photolithography method and an etching method. The shape of the sacrificial layer 38 is a shape corresponding to the planar shape of the gap 30, and includes, for example, a region that becomes a resonance region 50. Next, the lower layer 12a and the upper layer 12b are formed as the lower electrode 12 on the sacrificial layer 38 and the substrate 10. The sacrificial layer 38 and the lower electrode 12 are formed by, for example, a sputtering method, a vacuum vapor deposition method, or a CVD (Chemical Vapor Deposition) method. Then, the lower electrode 12 is patterned into a desired shape by using a photolithography method and an etching method. The lower electrode 12 may be formed by a lift-off method.

As shown in FIG. 3B, a piezoelectric film 14 is formed on the lower electrode 12 and the substrate 10 by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method. The upper electrode 16 is patterned on the piezoelectric film 14 into a desired shape by using, for example, a photolithography method and an etching method. The upper electrode 16 may be formed by a lift-off method.

In the parallel resonator P shown in FIG. 1 (c), after the lower layer 16a is formed, the mass-loaded film 20 is formed into a film by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method. The mass-loaded film 20 is patterned into a desired shape by using, for example, a photolithography method and an etching method. After that, the upper layer 16b is formed.

As shown in FIG. 3C, a mask layer 44 having a desired shape is formed on the upper electrode 16 and the piezoelectric film 14. The mask layer 44 is, for example, a photoresist, and is formed by using a photolithography method. A part of the piezoelectric film 14 is removed by using an etching method with the mask layer 44 as a mask. As a result, the thick film portion 15a and the thin film portion 15b are formed on the piezoelectric film 14. When the piezoelectric film 14 is side-etched, the outer circumference of the thick film portion 15a is located inside the outer circumference of the upper electrode 16.

As shown in FIG. 4A, the mask layer 44 is removed by, for example, an organic cleaning method or an ashing method. A mask layer 46 having a desired shape is formed on the upper electrode 16 and the piezoelectric film 14. The mask layer 46 is, for example, a photoresist, and is formed by using a photolithography method. A part of the piezoelectric film 14 is removed by using an etching method with the mask layer 46 as a mask. As a result, the lower electrode 12 is exposed.

As shown in FIG. 4B, the mask layer 46 is removed using, for example, an organic cleaning method or an ashing method. The protective film 24 is formed into a film by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method. Since the upper electrode 16 is overhanging, the protective film 24 is not formed on the upper side surface of the thick film portion 15a.

As shown in FIG. 4 (c), the protective film 24 is patterned into a desired shape by using, for example, a photolithography method and an etching method. The metal layers 22 and 22a are formed into a film by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method, respectively, so as to be in contact with the exposed lower electrode 12 and the upper electrode 16. Then, the metal layers 22 and 22a are patterned into a desired shape by using, for example, a photolithography method and an etching method. The metal layers 22 and 22a may be formed by a lift-off method.

After that, the etching solution of the sacrificial layer 38 is introduced into the sacrificial layer 38 under the lower electrode 12 via the hole 35 and the introduction path 33 (see FIG. 1A). As a result, the sacrificial layer 38 is removed. The medium for etching the sacrificial layer 38 is preferably a medium that does not etch the material constituting the resonator other than the sacrificial layer 38. In particular, the etching medium is preferably a medium in which the lower electrode 12 with which the etching medium is in contact is not etched. The stress of the laminated film 18 of the lower electrode 12, the piezoelectric film 14, and the upper electrode 16 is set to be a compressive stress. As a result, when the sacrificial layer 38 is removed, the laminated film 18 swells on the opposite side of the substrate 10 so as to be separated from the substrate 10. A gap 30 having a dome-shaped bulge is formed between the lower electrode 12 and the substrate 10. As described above, the piezoelectric thin film resonator according to the first embodiment is manufactured.

[Manufacturing Method Example 2 of Example 1]
5 (a) to 6 (c) are cross-sectional views showing a manufacturing method example 2 of the piezoelectric thin film resonator according to the first embodiment. As shown in FIG. 5A, the sacrificial layer 38 and the lower electrode 12 are formed on the substrate 10 in the same manner as in FIG. 3A.

As shown in FIG. 5B, a lower piezoelectric film 14a is formed on the lower electrode 12 and the substrate 10. The film forming method of the lower piezoelectric film 14a is the same as the film forming method of the piezoelectric film 14 of FIG. 3 (b). A processing film 26 is formed on the lower piezoelectric film 14a by using, for example, a sputtering method, a vacuum vapor deposition method, or a CVD method. The processing film 26 is patterned into a desired shape by using, for example, a photolithography method and an etching method. The processing film 26 may be formed by using a lift-off method. The processing film 26 is made of a material that is difficult to be etched when the piezoelectric film 14 is etched, and is, for example, a silicon oxide film.

As shown in FIG. 5 (c), the upper piezoelectric film 14b is formed on the processing film 26 and the lower piezoelectric film 14a. The piezoelectric film 14 is formed from the lower piezoelectric film 14a and the upper piezoelectric film 14b. The upper electrode 16 is formed on the piezoelectric film 14 in the same manner as in FIG. 3 (b). The upper electrode 16 is patterned into a desired shape by using, for example, a photolithography method and an etching method.

As shown in FIG. 6A, the piezoelectric film 14 is patterned into a desired shape by using, for example, a photolithography method and an etching method. At this time, the processing film 26 serves as a mask, the piezoelectric film 14 under the processing film 26 remains, and the thin film portion 15b is formed. For example, when the piezoelectric film 14 is an aluminum nitride film and the processing film 26 is a silicon oxide film, the piezoelectric film 14 can be selectively etched with respect to the processing film 26 by using a phosphoric acid-based etching solution.

As shown in FIG. 6B, the processing film 26 is removed by using, for example, an etching method. The protective film 24 is formed in the same manner as in FIG. 4 (b). As shown in FIG. 6 (c), the protective film 24 is patterned into a desired shape in the same manner as in FIG. 4 (c). The metal layers 22 and 22a in contact with the lower electrode 12 and the upper electrode 16 are formed. Then, by removing the sacrificial layer 38, the piezoelectric thin film resonator according to the first embodiment is produced.

In the manufacturing method Example 2 of the first embodiment, by providing the processing film 26, it is possible to suppress the manufacturing variation of the film thickness of the thin film portion 15b.

[simulation]
A simulation using the two-dimensional finite element method was performed. 7 (a) and 7 (b) are diagrams showing the cross-sectional shapes of Comparative Example 1 and Example 1 in which simulation was performed, and FIG. 7 (c) is a diagram showing the simulation results. As shown in FIG. 7A, in Comparative Example 1, the lower electrode 12 is provided on the substrate 10 and the gap 30. A piezoelectric film 14 is provided on the lower electrode 12 on the gap 30. The piezoelectric film 14 is supported by the substrate 10 only by the lower electrode 12. The upper electrode 16 is provided on the piezoelectric film 14. The end of the piezoelectric film 14 is located inside the end of the upper electrode 16. A metal layer 22 is provided on the lower electrode 12 on the substrate 10. The end of the metal layer 22 is located inside the end of the void 30.

The center 68 of the resonance region 50 is the mirror interface condition. The width of the resonance region 50 is W1, the width of the void 30 is W2, the offset width of the upper electrode 16 and the piezoelectric film 14 is W3, and the offset width of the metal layer 22 and the substrate 10 is W4. The thickness of the piezoelectric film 14 is T1.

As shown in FIG. 7B, in the first embodiment, the thin film portion 15b of the piezoelectric film 14 extends from the resonance region 50 to the top of the substrate 10. The inner end of the metal layer 22 is located on the upper surface of the thin film portion 15b. The offset width between the thin film portion 15b and the void 30 is W5. Let the thickness of the thin film portion b be T2. Other configurations are the same as those in FIG. 7 (a).

The materials and dimensions used in the simulation are as follows.
Lower electrode 12: Cr film having a film thickness of 100 nm and Ru film film portion 15a having a film thickness of 190 nm: AlN film film portion 15b having a film thickness T1 of 1260 nm: AlN film film portion having a film thickness T2 of 630 nm Upper electrode 16: Film thickness Ru film with a thickness of 230 nm and Cr film with a film thickness of 30 nm Width W1: 40 μm
Width W2: 47 μm
Width W3: 0.2 μm
Width W4: 2 μm
Width W5: 3 μm

As shown in FIG. 7 (c), as a result of the simulation, the electromechanical coupling coefficient k ² is 7.12, which is the same in Comparative Example 1 and Example 1. The Q value Qa at the antiresonance frequency of Example 1 is larger than the Qa of Comparative Example 1. As in the first embodiment, the thin film portion 15b is provided on the lower electrode 12 on the void 30 outside the resonance region 50. A metal layer 22 is provided from the upper surface of the thin film portion 15b to the lower electrode 12. Thereby, the Q value can be improved. Further, since the metal layer 22 is provided on the thin film portion 15b, it is possible to suppress the peeling of the piezoelectric film 14 from the lower electrode 12.

[Comparison of Comparative Example 2 and Example 1]
8 (a) and 8 (b) are cross-sectional views of the piezoelectric thin film resonator according to Comparative Example 2 and Example 1, respectively. As shown in FIG. 8A, in Comparative Example 2, the upper surface and the side surface of the thin film portion 15b of the piezoelectric film 14 are covered with the protective film 24. As a result, the protective film 24 is provided between the metal layer 22 and the thin film portion 15b. As shown by the arrow 55, the heat generated in the resonance region 50 is conducted through the thin film portion 15b of the piezoelectric film 14. The protective film 24 is, for example, an insulating film such as a silicon oxide film, and has a thermal conductivity lower than that of the piezoelectric film 14 and the metal layer 22. Therefore, heat conduction from the piezoelectric film 14 to the metal layer 22 is hindered. As a result, when a high-frequency signal with high power is applied between the lower electrode 12 and the upper electrode 16, the temperature of the resonance region 50 rises. Therefore, the power resistance of the piezoelectric thin film resonator is lowered.

Further, in Comparative Example 2, there is an interface between the metal layer 22 and the protective film 24, an interface between the protective film 24 and the piezoelectric film 14, and an interface between the protective film 24 and the lower electrode 12. The piezoelectric film 14, the protective film 24, the metal layer 22, and the lower electrode 12 are made of different materials, and as the number of types of interfaces increases, the risk of peeling at an interface having weak adhesion increases.

As shown in FIG. 8B, in the first embodiment, the upper surface and the side surface of the thin film portion 15b are in contact with the metal layer 22. As a result, as shown by the arrow 56, the heat generated in the resonance region 50 is efficiently conducted from the thin film portion 15b to the metal layer 22, and reaches the substrate 10 from the metal layer 22. As a result, even if a high-frequency signal of high power is applied between the lower electrode 12 and the upper electrode 16, the temperature rise in the resonance region 50 is suppressed. Therefore, the power resistance of the piezoelectric thin film resonator can be improved.

Further, in Example 1, the interface corresponding to the three interfaces in Comparative Example 2 is the interface between the metal layer 22 and the piezoelectric film 14. In this way, the number of types of interfaces can be reduced as compared with Comparative Example 2. Thereby, the adhesion of the interface between the metal layer 22 and the piezoelectric film 14 may be improved, and the risk of peeling from the interface can be suppressed.

[Modified Examples 1 and 2 of Example 1]
9 (a) and 9 (b) are cross-sectional views showing the piezoelectric thin film resonators according to the first and second modifications of the first embodiment, respectively. In FIGS. 1 (b) and 8 (b), the protective film 24 and the metal layer 22 do not overlap on the thin film portion 15b, and there is no gap between the protective film 24 and the metal layer 22.

As shown in FIG. 9A, in the modified example 1 of the first embodiment, the protective film 24 and the metal layer 22 overlap each other in a part of the thin film portion 15b as in the region 74, and the other thin film portion 15b. The metal layer 22 is in contact with the thin film portion 15b in a part thereof. By partially overlapping the protective film 24 and the metal layer 22, it is possible to prevent the thin film portion 15b from being exposed even when the protective film 24 and the metal layer 22 are misaligned.

As shown in FIG. 9B, in the modified example 2 of the first embodiment, there is a gap between the protective film 24 and the metal layer 22 on the thin film portion 15b as in the region 75. By separating the protective film 24 and the metal layer 22, even if the protective film 24 and the metal layer 22 are misaligned, the protective film 24 is not located between the metal layer 22 and the thin film portion 15b. Therefore, as described in FIG. 8B, the thermal conductivity can be improved and the types of interfaces can be reduced.

[Modified Examples 3 and 4 of Example 1]
10 (a) and 10 (b) are cross-sectional views of the piezoelectric thin film resonator according to the modified examples 3 and 4, respectively, of the first embodiment. As shown in FIG. 10A, in the modification 3 of the first embodiment, the piezoelectric film 14 has a lower piezoelectric film 14a and an upper piezoelectric film 14b provided on the lower piezoelectric film 14a. The thick film portion 15a is formed from the lower piezoelectric film 14a and the upper piezoelectric film 14b, and the thin film portion 15b is formed from the lower piezoelectric film 14a. The insertion film 28 is inserted between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The insertion film 28 is not provided in the central region of the resonance region 50, but is provided in a ring shape in the outer peripheral region along the outer circumference. The insertion film 28 is provided from the inside to the outside of the resonance region 50 in the extraction region 52 of the upper electrode 16 and the extraction region 54 of the lower electrode 12. The insertion film 28 is provided on the upper surface of the thin film portion 15b so as not to overlap the metal layer 22. A protective film 24 is provided on the insertion film 28. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted.

As shown in FIG. 10B, in the modified example 4 of the first embodiment, the insertion film 28 is provided in the resonance region 50 in the extraction region 52 of the upper electrode 16. In the extraction region 54 of the lower electrode 12, the insertion film 28 is not provided in the resonance region 50, but is provided on the upper surface of the thin film portion 15b outside the resonance region 50. Other configurations are the same as those of the third modification of the first embodiment, and the description thereof will be omitted.

[Modified Examples 5 and 6 of Example 1]
11 (a) and 11 (b) are cross-sectional views of the piezoelectric thin film resonator according to the modified examples 5 and 6 of the first embodiment, respectively. As shown in FIG. 11A, in the modified example 5 of the first embodiment, the insertion film 28 is provided in the resonance region 50 in the extraction region 52 of the upper electrode 16. The insertion membrane 28 is not provided in the drawer region 54 of the lower electrode 12. Other configurations are the same as those of the third modification of the first embodiment, and the description thereof will be omitted.

As shown in FIG. 11B, in the modified example 6 of the first embodiment, the insertion film 28 is not provided in the extraction region 52 of the upper electrode 16. An insertion film 28 is provided on the upper surface of the thin film portion 15b outside the resonance region 50 in the extraction region 54 of the lower electrode 12. Other configurations are the same as those of the third modification of the first embodiment, and the description thereof will be omitted.

An insertion membrane 28 may be provided between the lower electrode 12 and the upper electrode 16 as in the modifications 3 to 6 of the first embodiment. The insertion membrane 28 is not provided in the central region of the resonance region 50. The insertion film 28 is, for example, an insulating film such as a silicon oxide film or a metal film such as an Al film, and has a smaller acoustic impedance than the piezoelectric film 14. Thereby, the Q value can be improved.

According to the first embodiment and its modifications, the region where the lower electrode 12 and the upper electrode 16 face each other across the thick film portion 15a is the resonance region 50, and the thin film portion 15b is located outside the resonance region 50. The metal layer 22 is provided from the thin film portion 15b located outside the resonance region 50 to the lower electrode 12. Thereby, the Q value can be improved. Further, it is possible to prevent the piezoelectric film 14 from peeling off from the lower electrode 12. Further, the metal layer 22 is in contact with at least a part of the surface of the thin film portion 15b. As a result, the heat dissipation from the resonance region 50 is improved and the power resistance can be improved.

The metal layer 22 may be in contact with at least a part of the upper surface (immediately above) of the thin film portion 15b. Further, the metal layer 22 may be in contact with at least a part of the side surface of the thin film portion 15b.

As shown in FIG. 2, in the region 54 where the lower electrode 12 is provided from the resonance region 50 to the outside, the metal layer 22 is in contact with at least a part of the surface of the thin film portion 15b. This makes it possible to further improve the heat dissipation.

A gap 30 is formed under the lower electrode 12, and the outer circumference of the thin film portion 15b is located outside the outer circumference of the gap 30 in a plan view. Thereby, the mechanical strength of the lower electrode 12 can be improved.

A protective film 24 (insulating film) that covers the piezoelectric film 14 is provided. Thereby, the piezoelectric film 14 can be protected. The protective film 24 is not provided between the metal layer 22 and the thin film portion 15b. As a result, the heat dissipation from the resonance region 50 is improved. Further, since the types of the interface between the protective film 24 and other materials are reduced, the film peeling can be suppressed.

As in the modifications 3 to 6 of the first embodiment, the insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The thick film portion 15a is formed of a lower piezoelectric film 14a and an upper piezoelectric film 14b. The thin film portion 15b is formed from the lower piezoelectric film 14a and does not include the upper piezoelectric film 14b. Thereby, the thick film portion 15a and the thin film portion 15b can be easily formed. The insertion film 28 is a temperature compensation film, and may be provided on the entire surface including the central region of the resonance region 50. As described above, it is preferable that the insertion film 28 is provided in at least a part of the resonance region 50.

Example 2 and the modified example 1 thereof are examples in which the configuration of the void is changed. 12 (a) is a cross-sectional view of the piezoelectric thin film resonator of Example 2, and FIG. 12 (b) is a cross-sectional view of the piezoelectric thin film resonator of Modification 1 of Example 2. As shown in FIG. 12A, in the second embodiment, a recess is formed on the upper surface of the substrate 10. The lower electrode 12 is formed flat on the substrate 10. As a result, the void 30 is formed in the recess of the substrate 10. The void 30 is formed so as to include the resonance region 50. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted. The void 30 may be formed so as to penetrate the substrate 10. An insulating film may be formed in contact with the lower surface of the lower electrode 12. That is, the void 30 may be formed between the substrate 10 and the insulating film in contact with the lower electrode 12. As the insulating film, for example, an aluminum nitride film can be used.

As shown in FIG. 12B, in the modified example 1 of the second embodiment, the acoustic reflection film 31 is formed under the lower electrode 12 of the resonance region 50. The acoustic reflection film 31 is provided with a film 31a having a high acoustic impedance and a film 31b having a low acoustic impedance alternately. The film thicknesses of the films 31a and 31b are, for example, approximately λ / 4 (λ is the wavelength of the elastic wave), respectively. The number of layers of the film 31a and the film 31b can be arbitrarily set. The acoustic reflection film 31 may be formed by laminating at least two types of layers having different acoustic characteristics at intervals. Further, the substrate 10 may be one of at least two types of layers having different acoustic characteristics of the acoustic reflection film 31. For example, the acoustic reflective film 31 may be configured such that a film having different acoustic impedances is further provided in the substrate 10. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted.

In Example 1 and the modified example thereof, the void 30 may be formed as in the second embodiment, or the acoustic reflection film 31 may be formed instead of the void 30 as in the modified example 1 of the second embodiment.

As in the first embodiment, its modifications, and the second embodiment, the piezoelectric thin film resonator may also 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. good. Further, as in the first modification of the second embodiment, the piezoelectric thin film resonator includes an SMR (Solidly Mounted Resonator) including an acoustic reflecting film 31 that reflects an elastic wave propagating in the piezoelectric film 14 under the lower electrode 12 in the resonance region 50. ) May be.

Although the example in which the resonance region 50 has an elliptical shape has been described, other shapes may be used. For example, the resonance region 50 may be a polygon such as a quadrangle or a pentagon.

Example 3 is an example of a duplexer. FIG. 13 is a circuit diagram of the duplexer according to the third embodiment. As shown in FIG. 13, the duplexer includes a transmit filter 40 and a receive filter 42. The transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. The reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. An inductor L1 is provided as a matching circuit between the common terminal Ant and the ground. The transmission filter 40 passes a signal in the transmission band among the signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. The inductor L1 matches the impedance so that the transmission signal that has passed through the transmission filter 40 does not leak to the reception filter 42 and is output from the common terminal Ant.

The transmission filter 40 is a ladder type filter. One or more series resonators S1 to S4 are connected in series between the transmission terminal Tx (input terminal) and the common terminal Ant (output terminal). One or a plurality of parallel resonators P1 to P3 are connected in parallel between the transmission terminal Tx and the common terminal Ant. The ground side of the parallel resonators P1 to P3 is commonly grounded via the inductor L2. The number and connections of the series resonator, parallel resonator, inductor and the like can be appropriately changed in order to obtain the desired transmission filter characteristics. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 can be the piezoelectric thin film resonators of Examples 1 to 2 and its modifications.

14 (a) is a plan view and a cross-sectional view of the transmission filter in the third embodiment, and FIG. 14 (b) is a sectional view taken along the line AA of FIG. 14 (a). As shown in FIGS. 14 (a) and 14 (b), the piezoelectric thin film resonator according to the first embodiment can be formed on the same substrate 10 to form a ladder type filter. An opening 36 is formed in the piezoelectric film 14. It can be electrically connected to the lower electrode 12 through the opening 36. Other configurations are the same as those of the second modification of the second embodiment, and the description thereof will be omitted. The size and shape of the resonance region 50 of each resonator S1 to S4 and P1 to P3 can be appropriately changed.

The reception filter 42 may be a ladder type filter or a multiple mode filter. At least one of the transmission filter 40 and the reception filter 42 can be a ladder type filter or a lattice type filter. Further, at least one resonator of at least one of the transmission filter 40 and the reception filter 42 can be used as a piezoelectric thin film resonator of Examples 1 and 2 and a modification thereof.

Although the duplexer has been described as an example as the multiplexer, a triplexer or a quadplexer may be used.

Although the examples of the present invention have been described in detail above, the present invention is not limited to such specific examples, and various modifications and variations are made within the scope of the gist of the present invention described in the claims. It can be changed.

10 Substrate 12 Lower electrode 14 Pietrical film 14a Lower piezoelectric film 14b Upper piezoelectric film 15a Thick film part 15b Thin film part 16 Upper electrode 22, 22a Metal layer 24 Protective film 28 Insertion film 30 Void 31 Acoustic reflection film 50 Resonance region 52, 54

Claims (10)

With the board
The lower electrode provided on the substrate and
A piezoelectric film provided on the lower electrode and having a thick film portion and a thin film portion thinner than the thick film portion and having a substantially constant thickness .
An upper electrode provided so as to form a resonance region which is a region facing the lower electrode and sandwiching the thick film portion,
A metal layer provided from the thin film portion located outside the resonance region to the lower electrode and in contact with at least a part of the surface of the thin film portion.
Piezoelectric thin film resonator. With the board
The lower electrode provided on the substrate and
A piezoelectric film provided on the lower electrode and having a thick film portion and a thin film portion thinner than the thick film portion,
An upper electrode provided so as to form a resonance region which is a region facing the lower electrode and sandwiching the thick film portion,
A metal layer provided from the thin film portion located outside the resonance region to the lower electrode and in contact with at least a part of the surface of the thin film portion.
The insertion membrane inserted into the piezoelectric membrane and
Equipped with
The piezoelectric film has a lower piezoelectric film and an upper piezoelectric film provided on the lower piezoelectric film.
The insertion membrane is provided between the lower piezoelectric membrane and the upper piezoelectric membrane.
A piezoelectric thin film resonator in which the thick film portion is formed of the lower piezoelectric film and the upper piezoelectric film, and the thin film portion is formed of the lower piezoelectric film and does not include the upper piezoelectric film. The piezoelectric thin film resonator according to claim 1 or 2 , wherein the metal layer is in contact with at least a part directly above the thin film portion. The piezoelectric thin film resonator according to claim 1 or 2 , wherein the metal layer is in contact with at least a part of a side surface of the thin film portion. The piezoelectric thin film resonator according to any one of claims 1 to 4 , wherein in a region where the lower electrode is provided from the resonance region to the outside, the metal layer is in contact with at least a part of the surface of the thin film portion. The piezoelectric thin film resonator according to any one of claims 1 to 5 , wherein a gap is formed under the lower electrode, and the outer periphery of the thin film portion is located outside the outer circumference of the gap in a plan view. The piezoelectric thin film resonator according to any one of claims 1 to 6, further comprising an insulating film covering the piezoelectric film. The piezoelectric thin film resonator according to claim 7, wherein the insulating film is not provided between the metal layer and the thin film portion. A filter including the piezoelectric thin film resonator according to any one of claims 1 to 8. A duplexer comprising the filter of claim 9.

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