JP2021158511A - Piezoelectric thin film resonator, filter, and multiplexer - Google Patents

Abstract

To provide a piezoelectric thin-film resonator capable of suppressing Q-value reduction and suppressing piezoelectric film damage.SOLUTION: A piezoelectric thin-film resonator 100 has a substrate 10, a lower electrode 12, an upper electrode 16, a piezoelectric film 14, and an insertion film 28. The lower electrode 12 is provided on the substrate with an air gap 30 between the same and the substrate. The upper electrode 16 is provided on the lower electrode 12. The piezoelectric film 14 has a lower piezoelectric film 14a and an upper piezoelectric film 14b. The lower piezoelectric film 14a has its end face farther from the air gap than the upper piezoelectric film 14b. The insertion film 28 is inserted between the lower piezoelectric film 14a and the upper piezoelectric film 14b.SELECTED DRAWING: Figure 1

Description

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

Filters and multiplexers using piezoelectric thin film resonators are used as filters and multiplexers for high-frequency circuits of wireless terminals 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.

As the frequency of wireless communication increases, there is concern that the Q value of the piezoelectric thin film resonator will decrease. It is known that an insertion membrane is inserted into a piezoelectric membrane in order to suppress a decrease in Q value (for example, Patent Document 1). Further, in addition to inserting the insertion film into the piezoelectric film, it is known to reduce the thickness of the outer peripheral portion of the piezoelectric film (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2015-95729 Japanese Unexamined Patent Publication No. 2017-158161

As described in Patent Document 2, when the contour of the upper piezoelectric film is positioned inside the contour of the lower piezoelectric film, stress is concentrated on the end portion of the upper piezoelectric film when the elastic wave is excited, and the piezoelectric film is damaged. May occur.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress damage to the piezoelectric film while suppressing a decrease in Q value.

The present invention comprises a lower electrode provided on the substrate so as to have a gap between the substrate and the substrate, an upper electrode provided on the lower electrode, and the lower electrode and the upper electrode. The lower electrode is sandwiched between them and has a lower piezoelectric film and an upper piezoelectric film, and the lower electrode is pulled out from a first region in which the lower electrode, the lower piezoelectric film, the upper piezoelectric film, and the upper electrode overlap in a plan view. In one extraction region, the contour of the first region is located on the opposite side of the contour of the void from the contour of the void, and in the first extraction region, the end face of the lower piezoelectric film is more than the end face of the upper piezoelectric film. The piezoelectric film provided so as to be located away from the center region is not provided in the central region of the second region where the void, the lower electrode, the piezoelectric film, and the upper electrode overlap in a plan view. Among the surrounding regions, at least in the region located in the first drawer region, the central region is surrounded along the contour of the second region, the inner end face is located on the gap side of the contour of the gap, and the outer end face is located. Is a piezoelectric thin film resonator comprising an insertion film inserted between the lower piezoelectric film and the upper piezoelectric film so that is located on the side opposite to the void from the contour of the void.

In the above configuration, in the second drawing region where the upper electrode is pulled out from the first region, the contour of the first region may be located on the opposite side of the void from the contour of the void.

In the above configuration, the insertion membrane surrounds the central region along the contour of the second region in the region located in the second drawer region among the regions surrounding the central region, and the inner end face is the contour of the void. The configuration may be such that the outer end face is located on the side opposite to the gap with respect to the contour of the gap.

In the above configuration, a support layer provided between the substrate and the lower electrode and formed of a material different from the substrate is provided, the void is formed in the support layer, and the lower electrode is placed on the support layer. It can be configured to be formed substantially flat.

In the above configuration, a support layer provided between the substrate and the lower electrode and formed of a material different from the substrate is provided, the void is formed in the support layer, and the lower electrode is placed on the support layer. The end surface of the lower electrode, which is formed substantially flat and defines the first region, may be in contact with the side surface of the support layer on the void side.

In the above configuration, the support layer may be configured such that the thickness in the first drawing region is thinner than the thickness in the second drawing region in which the upper electrode is pulled out from the first region.

In the above configuration, the acoustic impedance of the support layer may be larger than the acoustic impedance of the substrate.

In the above configuration, the volume resistivity of the support layer can be larger than the volume resistivity of the substrate.

In the above configuration, the void may be formed by recesses provided in the substrate, and the lower electrode may be formed substantially flat on the substrate.

In the above configuration, the acoustic impedance of the insertion film can be smaller than the acoustic impedance of the piezoelectric film.

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

The present invention is a multiplexer containing the filters described above.

According to the present invention, it is possible to suppress the breakage of the piezoelectric film while suppressing the decrease in the Q value.

1 (a) is a plan view of the piezoelectric thin film resonator according to the first embodiment, and FIG. 1 (b) is a cross-sectional view taken along the line AA of FIG. 1 (a). FIG. 2 is a plan view showing the positional relationship between the lower electrode, the upper electrode, and the insertion membrane of the piezoelectric thin film resonator in Example 1. FIG. 3A is a plan view showing the positional relationship of each layer of the piezoelectric thin film resonator according to the first embodiment, and FIG. 3B is a cross-sectional view taken along the line AA of FIG. 3A. 4 (a) to 4 (d) are cross-sectional views (No. 1) showing a method of manufacturing the piezoelectric thin film resonator according to the first embodiment. 5 (a) to 5 (c) are cross-sectional views (No. 2) showing a method of manufacturing the piezoelectric thin film resonator according to the first embodiment. FIG. 6 is a cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 1. FIG. 7 is a cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 2. FIG. 8 is a cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 3. 9 (a) is a cross-sectional view of the piezoelectric thin film resonator according to the second embodiment, and FIG. 9 (b) is a cross-sectional view of the piezoelectric thin film resonator according to the first modification of the second embodiment. 10 (a) is a cross-sectional view of the piezoelectric thin film resonator according to the third embodiment, and FIG. 10 (b) is a cross-sectional view of the piezoelectric thin film resonator according to the first modification of the third embodiment. 11 (a) and 11 (b) are cross-sectional views showing a method of manufacturing the piezoelectric thin film resonator according to the third embodiment. 12 (a) is a plan view of the piezoelectric thin film resonator according to the fourth embodiment, and FIG. 12 (b) is a cross-sectional view taken along the line AA of FIG. 12 (a). FIG. 13 is a plan view showing the positional relationship between the lower electrode, the upper electrode, the insertion membrane, and the void of the piezoelectric thin film resonator in Example 4. FIG. 14 is a circuit diagram of the filter according to the fifth embodiment. FIG. 15 is a circuit diagram of the duplexer according to the sixth embodiment.

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 FIG. 1 (b) is a cross-sectional view taken along the line AA of FIG. 1 (a). With reference to FIGS. 1 (a) and 1 (b), the piezoelectric thin film resonator 100 of the first embodiment is provided with a lower electrode 12 on a substrate 10. The lower electrode 12 covers the recess formed on the upper surface of the substrate 10 and is formed flat on the substrate 10. A gap 30 is formed between the substrate 10 and the lower electrode 12 by the recess formed on the upper surface of the substrate 10. The substrate 10 is, for example, a silicon (Si) substrate, and the thickness thereof is, for example, 100 μm to 1000 μm. The lower electrode 12 is, for example, a ruthenium (Ru) film having a thickness of, for example, 30 nm to 400 nm.

A piezoelectric film 14 is provided on the substrate 10 and on the lower electrode 12. The piezoelectric film 14 includes a lower piezoelectric film 14a and an upper piezoelectric film 14b. The lower piezoelectric film 14a and the upper piezoelectric film 14b each contain, for example, aluminum nitride (AlN) having c-axis orientation as a main component, and the thickness thereof is 30 nm to 700 nm. An insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The insertion film 28 is, for example, a silicon oxide (SiO ₂ ) film, and its thickness is 10 nm to 200 nm.

The upper electrode 16 is provided on the piezoelectric film 14 so as to sandwich the piezoelectric film 14 and face the lower electrode 12. The region where the lower electrode 12, the piezoelectric film 14 (lower piezoelectric film 14a and upper piezoelectric film 14b) and the upper electrode 16 overlap in a plan view is defined as a region 50. Further, the region where the gap 30, the lower electrode 12, the piezoelectric film 14 (lower piezoelectric film 14a and upper piezoelectric film 14b) and the upper electrode 16 overlap in a plan view is defined as a region 51. The region 51 has, for example, an elliptical shape in a plan view, and is a region in which elastic waves in the thickness longitudinal vibration mode are excited by the piezoelectric film 14. Area of the region 51 is, for example, 200μm ² ~40000μm ^2. The region 51 is not limited to having an elliptical shape, and may have a polygonal shape such as a quadrangle or a pentagon. The upper electrode 16 is, for example, a ruthenium film having a thickness of 30 nm to 400 nm. A protective film 24 is provided on the upper electrode 16 and the insertion film 28. The protective film 24 is, for example, a silicon oxide film having a thickness of 10 nm to 100 nm.

The lower electrode 12 is drawn from the region 50 to the extraction region 70. The upper electrode 16 is pulled out from the area 50 to the drawing area 72. In the extraction region 70, the contour of the upper electrode 16 becomes the contour of the region 50. In the extraction region 72, the contour of the lower electrode 12 becomes the contour of the region 50. In the drawer region 70, a wiring 20 in contact with the lower electrode 12 is provided on the lower electrode 12. In the extraction region 72, a wiring 22 in contact with the upper electrode 16 is provided on the upper electrode 16.

An introduction path 32 for etching the sacrificial layer is formed in the lower electrode 12. The sacrificial layer is a layer for forming the void 30. The vicinity of the tip of the introduction path 32 is not covered with the piezoelectric film 14, and the lower electrode 12 has a hole 34 at the tip of the introduction path 32.

FIG. 2 is a plan view showing the positional relationship between the lower electrode, the upper electrode, and the insertion membrane of the piezoelectric thin film resonator in Example 1. In FIG. 2, the insertion membrane 28 is cross-hatched for clarity. With reference to FIG. 2, the insertion membrane 28 is provided in the outer peripheral region 52 in the region 51 and not in the central region 54. The outer peripheral region 52 is a region within the region 51 and is a region along the contour 64 of the region 51. The central region 54 is a region within the region 51 and includes the center of the region 51. The center does not have to be the geometric center. The insertion film 28 is continuously provided from the outer peripheral region 52 in the region 51 to the peripheral region 56 outside the region 51. As described above, in the insertion film 28, the inner end surface 60 is located inside the contour 62 of the gap 30 (on the side of the gap 30), and the outer end surface 61 is outside the contour 62 of the gap 30 (opposite to the gap 30). Located on the side).

In the region 51, the energy of the elastic wave excited in the central region 54 inside the insertion membrane 28 is large, and the energy of the elastic wave excited in the outer peripheral region 52 provided with the insertion membrane 28 is small.

A piezoelectric thin film resonator having a resonance frequency of 6 GHz will be described as an example. A silicon substrate is used as the substrate 10. The lower electrode 12 is a ruthenium film having a film thickness of 100 nm. The piezoelectric film 14 is an aluminum nitride film having a film thickness of 400 nm. The film thickness of the lower piezoelectric film 14a and the upper piezoelectric film 14b is 200 nm, respectively. The insertion film 28 is a silicon oxide film having a film thickness of 50 nm. The upper electrode 16 is a ruthenium film having a film thickness of 200 nm. The protective film 24 is a silicon oxide film having a film thickness of 70 nm.

As the substrate 10, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, a glass substrate, a ceramic substrate, a GaAs substrate, or the like can be used in addition to the silicon substrate. In addition to ruthenium, the lower electrode 12 and the upper electrode 16 include aluminum (Al), titanium (Ti), chromium (Cr), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), and the like. Single-layer films such as platinum (Pt), rhodium (Rh), or iridium (Ir), laminated films thereof, or alloys thereof can be used.

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

The insertion film 28 preferably has a Young's modulus smaller than that of the piezoelectric film 14. If the densities are substantially the same, Young's modulus correlates with the acoustic impedance. Therefore, it is preferable that the insertion film 28 has a smaller acoustic impedance than the piezoelectric film 14. Thereby, the Q value can be improved. For example, when the piezoelectric film 14 contains aluminum nitride as a main component, the insertion film 28 is an aluminum film, a gold (Au) film, a copper film, a titanium film, a platinum film, a tantalum film, a chromium film, or a silicon oxide film. Is preferable. In particular, from the viewpoint of Young's modulus, the insertion film 28 is preferably an aluminum film or a silicon oxide film. Silicon oxide may contain additives such as fluorine.

As the protective film 24, a silicon nitride film, an aluminum nitride film, or the like can be used in addition to the silicon oxide film. As the wirings 20 and 22, metals having low electrical resistance such as copper and gold are used. An adhesion layer such as a titanium layer may be provided under the metal layer having low electrical resistance.

FIG. 3A is a plan view showing the positional relationship of each layer of the piezoelectric thin film resonator according to the first embodiment, and FIG. 3B is a cross-sectional view taken along the line AA of FIG. 3A. In FIGS. 3A and 3B, the inner end surface 60 of the insertion film 28, the outer end surface 61 of the insertion film 28, the contour 62 of the gap 30, the contour 63 of the region 50, the contour 64 of the region 51, and the lower portion. The end face 65 of the piezoelectric film 14a, the end face 66 of the upper piezoelectric film 14b, the end face 67 of the lower electrode 12, and the end face 68 of the upper electrode 16 are shown. The contour 62 of the gap 30 is the contour at the upper end of the gap 30.

With reference to FIGS. 3 (a) and 3 (b), the contour 63 of the region 50 in the drawer region 70 is located on the side opposite to the contour 62 of the gap 30. That is, in the extraction region 70, the end face 65 of the lower piezoelectric film 14a, the end face 66 of the upper piezoelectric film 14b, and the end face 68 of the upper electrode 16 are located on the opposite side of the contour 62 of the gap 30 from the contour 62. Further, in the extraction region 70, the contour 63 of the region 50 substantially coincides with the end surface 66 of the upper piezoelectric film 14b and the end surface 68 of the upper electrode 16. Approximately matching means, for example, that it matches the variation in the manufacturing process and the degree of matching accuracy in the manufacturing process (the same applies hereinafter). The end face 66 of the upper piezoelectric film 14b and the end face 68 of the upper electrode 16 are not limited to substantially coincide with each other, and the end face 66 of the upper piezoelectric film 14b may be recessed inward with respect to the end face 68 of the upper electrode 16. However, it may protrude outward. Further, the end surface 66 of the upper piezoelectric film 14b and the end surface 68 of the upper electrode 16 may be inclined or curved in the film thickness direction.

In the extraction region 70, the end face 65 of the lower piezoelectric film 14a is located farther from the gap 30 than the end face 66 of the upper piezoelectric film 14b. In the extraction region 70, the outer end surface 61 of the insertion film 28 and the end surface 65 of the lower piezoelectric film 14a substantially coincide with each other. The outer end face 61 of the insertion film 28 and the end face 65 of the lower piezoelectric film 14a are not limited to substantially coincide with each other, and the outer end face 61 of the insertion film 28 is recessed inward with respect to the end face 65 of the lower piezoelectric film 14a. You may be. Further, the outer end surface 61 of the insertion film 28 and the end surface 65 of the lower piezoelectric film 14a may be inclined or curved in the film thickness direction.

In the drawer region 72, the contour 63 of the region 50 is located on the side opposite to the contour 62 of the gap 30 with respect to the contour 62 of the gap 30. That is, in the extraction region 72, the end surface 67 of the lower electrode 12 is located on the side opposite to the gap 30 with respect to the contour 62 of the gap 30. The end face 67 of the lower electrode 12 may be inclined or curved in the film thickness direction. The lower electrode 12, the lower piezoelectric film 14a, the upper piezoelectric film 14b, and the upper electrode 16 overlap, for example, the entire void 30 and cover the entire void 30.

[Production method]
4 (a) to 5 (c) are cross-sectional views showing a method of manufacturing the piezoelectric thin film resonator according to the first embodiment. With reference to FIG. 4A, a recess 80 is formed on the flat main surface of the substrate 10 by a photolithography method and an etching method. The depth of the recess 80 is, for example, 10 nm to 5000 nm. The sacrificial layer 82 in which the recess 80 is embedded is formed into a film by a sputtering method, a vacuum deposition method, or a CVD (Chemical Vapor Deposition) method. After embedding the sacrificial layer 82 in the recess 80, the upper surface of the substrate 10 is flattened by a CMP (Chemical Mechanical Polishing) method. The sacrificial layer 82 is formed of, for example, magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), or silicon oxide (SiO ₂ ). The shape of the recess 80 is a shape corresponding to the planar shape of the void 30. The lower electrode 12 is formed on the sacrificial layer 82 and the substrate 10 by a sputtering method, a vacuum vapor deposition method, or a CVD 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.

With reference to FIG. 4B, a lower piezoelectric film 14a is formed on the lower electrode 12 and the substrate 10 by a sputtering method or a vacuum vapor deposition method. The insertion film 28 is formed on the lower piezoelectric film 14a by a sputtering method, a vacuum deposition method, or a CVD method. Then, the insertion film 28 is patterned into a desired shape by using a photolithography method and an etching method. The insertion membrane 28 may be formed by a lift-off method.

With reference to FIG. 4C, an upper piezoelectric film 14b is formed on the lower piezoelectric film 14a by a sputtering method or a vacuum deposition method. The piezoelectric film 14 is formed by the lower piezoelectric film 14a and the upper piezoelectric film 14b.

With reference to FIG. 4D, the upper electrode 16 is formed on the piezoelectric film 14 by a sputtering method, a vacuum deposition method, or a CVD method. Then, the upper electrode 16 is patterned into a desired shape by using a photolithography method and an etching method. The upper electrode 16 may be formed by a lift-off method.

With reference to FIG. 5A, the upper piezoelectric film 14b is patterned into a desired shape using a photolithography method and an etching method. Next, the lower piezoelectric film 14a is patterned into a desired shape by using a photolithography method and an etching method.

With reference to FIG. 5B, the protective film 24 is formed by a sputtering method, a vacuum vapor deposition method, or a CVD method. Then, the protective film 24 is patterned into a desired shape by using a photolithography method and an etching method. Next, the wirings 20 and 22 are formed into a film by using a sputtering method, a vacuum vapor deposition method, or a CVD method, and are patterned into a desired shape by using a photolithography method and an etching method. Wiring 20 and 22 may be formed using a plating method.

With reference to FIG. 5C, the etching solution of the sacrificial layer 82 is introduced into the sacrificial layer 82 under the lower electrode 12 via the hole 34 and the introduction path 32 (see FIG. 1A). As a result, the sacrificial layer 82 is removed. By removing the sacrificial layer 82, a gap 30 is formed between the lower electrode 12 and the substrate 10 due to the recess formed on the upper surface of the substrate 10.

[Comparison example]
FIG. 6 is a cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 1. With reference to FIG. 6, in the piezoelectric thin film resonator 1000 of Comparative Example 1, the end face 65 of the lower piezoelectric film 14a and the end face 66 of the upper piezoelectric film 14b are located closer to the gap 30 than the contour 62 of the gap 30 in the extraction region 70. doing. In the extraction region 72, the end surface 67 of the lower electrode 12 is located closer to the gap 30 than the contour 62 of the gap 30. Since other configurations are the same as those of the piezoelectric thin film resonator 100 of the first embodiment, the description thereof will be omitted.

FIG. 7 is a cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 2. With reference to FIG. 7, in the piezoelectric thin film resonator 1100 of Comparative Example 2, the end surface 65 of the lower piezoelectric film 14a is located on the side opposite to the contour 62 of the gap 30 in the extraction region 70 and is opposite to the gap 30. The end surface 66 of 14b is located closer to the gap 30 than the contour 62 of the gap 30. In the extraction region 72, the end surface 67 of the lower electrode 12 is located closer to the gap 30 than the contour 62 of the gap 30. Since other configurations are the same as those of the piezoelectric thin film resonator 100 of the first embodiment, the description thereof will be omitted.

In Comparative Example 1 and Comparative Example 2, the end surface 66 of the upper piezoelectric film 14b is located on the gap 30 side of the contour 62 of the gap 30 in the drawer region 70. When an elastic wave is excited in the region 50, stress tends to be concentrated on the end portion of the upper piezoelectric film 14b. When the end surface 66 of the upper piezoelectric film 14b is located closer to the void 30 than the contour 62 of the void 30, stress is concentrated on the end of the upper piezoelectric film 14b due to the excitation of elastic waves, so that cracks or the like occur in the upper piezoelectric film 14b. Damage may occur. In addition, peeling may occur at the interface between the end portion of the upper piezoelectric film 14b and the insertion film 28.

Further, when an elastic wave is excited in the region 50, the stress of the laminated film on the substrate 10 tends to increase at a position located on the contour 62 of the void 30. In Comparative Example 1 and Comparative Example 2, since the end surface 67 of the lower electrode 12 is located closer to the gap 30 than the contour 62 of the gap 30 in the extraction region 72, the lower electrode 12 exists on the contour 62 of the gap 30. do not. Therefore, the piezoelectric film 14 may be damaged such as cracks at a position located on the contour 62 of the gap 30.

FIG. 8 is a cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 3. With reference to FIG. 8, in the piezoelectric thin film resonator 1200 of Comparative Example 3, the inner end surface 60 of the insertion membrane 28 is located on the side opposite to the void 30 from the contour 62 of the void 30. Since other configurations are the same as those of the piezoelectric thin film resonator 100 of the first embodiment, the description thereof will be omitted.

In Comparative Example 3, since the inner end surface 60 of the insertion membrane 28 is located on the side opposite to the void 30 with respect to the contour 62 of the void 30, the energy of the elastic wave excited in the region 51 is large. However, when the inner end surface 60 of the insertion membrane 28 is located on the side opposite to the void 30 from the contour 62 of the void 30, an elastic wave that excites with a large energy in the region 51 as shown by the thick arrow in FIG. Is likely to leak to the substrate 10. If the elastic wave leaks to the substrate 10, the Q value will decrease.

According to the first embodiment, as shown in FIGS. 3 (a) and 3 (b), the contour 63 of the region 50 is located on the side opposite to the contour 62 of the gap 30 in the drawer region 70. Further, in the extraction region 70, the end surface 65 of the lower piezoelectric film 14a is located farther from the gap 30 than the end surface 66 of the upper piezoelectric film 14b. As shown in FIG. 2, the insertion membrane 28 is not provided in the central region 54 of the region 51, and is centered along the contour of the region 51 in the region located at least in the drawer region 70 of the outer peripheral region 52 surrounding the central region 54. It is provided so as to surround the area 54. The inner end surface 60 of the insertion membrane 28 is located on the gap 30 side of the contour 62 of the gap 30, and the outer end face 61 is located on the opposite side of the gap 30 from the contour 62 of the gap 30. The decrease in the Q value can be suppressed by inserting the insertion film 28 into the piezoelectric film 14 and forming a step in the piezoelectric film 14. The contour 63 of the region 50 is located outside the contour 62 of the gap 30, and the end face 65 of the lower piezoelectric film 14a and the end face 66 of the upper piezoelectric film 14b are located outside the contour 62 of the gap 30. The end portion of the film 14b is fixed to the substrate 10. Therefore, even when an elastic wave is excited by the piezoelectric film 14, it is possible to prevent the upper piezoelectric film 14b from being damaged. Further, the laminated film at the position located on the contour 62 of the void 30 in the extraction region 70 includes the lower electrode 12, the piezoelectric film 14, the insertion film 28, and the upper electrode 16 and is thick, so that the laminated film is damaged. Can be suppressed. Further, since the energy of the elastic wave excited in the outer peripheral region 52 provided with the insertion membrane 28 of the region 51 is small, the inner end surface 60 of the insertion membrane 28 is located inside the contour 62 of the gap 30 and is outside. Since the end face 61 of the is located outside the contour 62 of the gap 30, it is possible to suppress leakage of elastic waves to the substrate 10. Therefore, according to the piezoelectric thin film resonator 100 of Example 1, damage to the piezoelectric film 14 can be suppressed while suppressing a decrease in the Q value.

Further, since the end face 65 of the lower piezoelectric film 14a is located farther from the gap 30 than the end face 66 of the upper piezoelectric film 14b, the heat generated by the excitation of the elastic wave in the region 51 is easily transferred to the substrate 10. , Improves heat dissipation.

As shown in FIGS. 3 (a) and 3 (b), the contour 63 of the region 50 in the drawer region 72 is located on the side opposite to the contour 62 of the gap 30 with respect to the contour 62 of the gap 30. As a result, the laminated film at the portion located on the contour 62 of the void 30 in the extraction region 72 becomes thicker and stronger, so that damage to the laminated film can be suppressed. Further, since the end portion of the lower electrode 12 is fixed to the substrate 10, the load generated on the lower electrode 12 when the elastic wave is excited is reduced, and the damage of the lower electrode 12 is suppressed.

As shown in FIG. 2, the insertion membrane 28 surrounds the central region 54 along the contour of the region 51 in the region located in the drawer region 72 of the outer peripheral region 52 surrounding the central region 54, and the inner end surface 60 has a gap 30. The outer end surface 61 is located on the side of the gap 30 with respect to the contour 62, and the outer end surface 61 is located on the side opposite to the gap 30 with respect to the contour 62 of the gap 30. As a result, the thickness of the laminated film at the portion located on the contour 62 of the void 30 in the drawing region 72 is increased, so that damage to the laminated film can be suppressed. Further, it is possible to suppress leakage of elastic waves excited in the region 51 to the substrate 10.

The gap 30 may be formed by bulging in a dome shape on the flat main surface of the substrate 10. However, in this case, since the laminated film including the lower electrode 12, the piezoelectric film 14, and the upper electrode 16 has a curved shape due to compressive stress, the laminated film may be damaged as the thinning of the laminated film progresses. Therefore, as shown in FIG. 1B, it is preferable that the gap 30 is formed by the recesses provided in the substrate 10 and the lower electrode 12 is formed substantially flat on the substrate 10. As a result, the stress applied to the laminated film is reduced, so that the laminated film is suppressed from being damaged. The term “substantially flat” includes, for example, the case where the product deviates from the flat surface to the extent of variation in the manufacturing process.

FIG. 9A is a cross-sectional view of the piezoelectric thin film resonator according to the second embodiment. With reference to FIG. 9A, in the piezoelectric thin film resonator 200 of the second embodiment, the upper electrode 16 includes a lower layer 16a and an upper layer 16b, and an insulating layer 42 is provided between the lower layer 16a and the upper layer 16b. For example, the lower layer 16a and the upper layer 16b are laminated films of chromium and ruthenium. The insulating layer 42 may be in the upper layer 16b. The code of the temperature coefficient of the elastic constant of the insulating layer 42 is opposite to the code of the temperature coefficient of the elastic constant of the piezoelectric film 14. For example, when the piezoelectric film 14 contains aluminum nitride as a main component, the insulating layer 42 is a silicon oxide film containing impurities such as fluorine and nitrogen or intentionally not containing impurities. Since other configurations are the same as those of the piezoelectric thin film resonator 100 of the first embodiment, the description thereof will be omitted.

FIG. 9B is a cross-sectional view of the piezoelectric thin film resonator according to the first modification of the second embodiment. With reference to FIG. 9B, in the piezoelectric thin film resonator 210 of the first modification of the second embodiment, the lower electrode 12 includes a lower layer 12a and an upper layer 12b, and an insulating layer 42 is provided between the lower layer 12a and the upper layer 12b. Has been done. For example, the lower layer 12a and the upper layer 12b are laminated films of chromium and ruthenium. The insulating layer 42 may be in the upper layer 12b. As described above, the code of the temperature coefficient of the elastic constant of the insulating layer 42 is opposite to the code of the temperature coefficient of the elastic constant of the piezoelectric film 14. Since other configurations are the same as those of the piezoelectric thin film resonator 100 of the first embodiment, the description thereof will be omitted.

According to the second embodiment and the first modification of the second embodiment, the insulating layer 42 is provided on the upper electrode 16 or the lower electrode 12. The code of the temperature coefficient of the elastic constant of the insulating layer 42 is opposite to the code of the temperature coefficient of the elastic constant of the piezoelectric film 14. As a result, the temperature coefficient of frequency (TCF) of the piezoelectric thin film resonator can be reduced.

In the second embodiment, the insulating layer 42 is provided between the lower layer 16a and the upper layer 16b of the upper electrode 16, but the present invention is not limited to this case, and the insulating layer 42 may be provided on the upper surface or the lower surface of the upper electrode 16. .. Similarly, in the first modification of the second embodiment, the insulating layer 42 is provided between the lower layer 12a and the upper layer 12b of the lower electrode 12, but the insulating layer 42 is not limited to this case, and the insulating layer 42 is the upper surface or the lower surface of the lower electrode 12. It may be provided in. Further, in the second embodiment and the first modification of the second embodiment, the insulating layer 42 is provided on the upper electrode 16 or the lower electrode 12, but may be provided on both the upper electrode 16 and the lower electrode 12.

FIG. 10A is a cross-sectional view of the piezoelectric thin film resonator according to the third embodiment. With reference to FIG. 10A, in the piezoelectric thin film resonator 300 of the third embodiment, a support layer 40 formed of a material different from that of the substrate 10 is formed between the substrate 10 and the lower electrode 12 and the piezoelectric film 14. It is provided. The upper surface of the substrate 10 is flat, and the gap 30 is formed in the support layer 40. The void 30 may or may not penetrate the support layer 40. The support layer 40 is, for example, a film having a higher acoustic impedance than the substrate 10. As an example, when the substrate 10 is a silicon substrate, the support layer 40 is a silicon nitride (SiN) film. The thickness of the support layer 40 is, for example, 10 nm to 5000 nm, and in a piezoelectric thin film resonator having a resonance frequency of 6 GHz, the thickness of the support layer 40 is, for example, 1000 nm. Since other configurations are the same as those of the piezoelectric thin film resonator 100 of the first embodiment, the description thereof will be omitted.

11 (a) and 11 (b) are cross-sectional views showing a method of manufacturing the piezoelectric thin film resonator according to the third embodiment. With reference to FIG. 11A, a support layer 40 is formed on the substrate 10 by a sputtering method, a vacuum vapor deposition method, or a CVD method. Then, a recess 84 is formed in the support layer 40 by using a photolithography method and an etching method. With reference to FIG. 11B, the sacrificial layer 82 in which the recess 84 is embedded is formed into a film by a sputtering method, a vacuum vapor deposition method, or a CVD method. After embedding the sacrificial layer 82 in the recess 84, the upper surface of the support layer 40 is flattened by the CMP method. The lower electrode 12 is formed on the sacrificial layer 82 and the support layer 40 by a sputtering method, a vacuum vapor deposition method, or a CVD method. Then, the lower electrode 12 is patterned into a desired shape by using a photolithography method and an etching method. After FIG. 11 (b), the same steps as in FIGS. 4 (b) to 5 (c) of Example 1 are performed.

FIG. 10B is a cross-sectional view of the piezoelectric thin film resonator according to the first modification of the third embodiment. With reference to FIG. 10B, in the piezoelectric thin film resonator 310 of the first modification of the third embodiment, a protective film 44 is provided between the substrate 10 and the support layer 40. The protective film 44 may be made of the same material as the support layer 40, or may be made of a different material. Since other configurations are the same as those of the piezoelectric thin film resonator 300 of the third embodiment, the description thereof will be omitted.

According to the third embodiment and the first modification of the third embodiment, a support layer 40 made of a material different from that of the substrate 10 is provided between the substrate 10 and the lower electrode 12. The void 30 is formed in the support layer 40, and the lower electrode 12 is formed substantially flat on the support layer 40. The material of the substrate 10 is limited in terms of the strength of the resonator and the like. By providing the support layer 40 formed of a material different from that of the substrate 10 between the substrate 10 and the lower electrode 12, it is possible to improve the characteristics and / or the manufacturability.

For example, the acoustic impedance of the support layer 40 is made larger than the acoustic impedance of the substrate 10. As a result, elastic waves excited in the region 51 are less likely to leak to the substrate 10. For example, the volume resistivity (electric resistivity) of the support layer 40 is made larger than the volume resistivity of the substrate 10. As an example, the support layer 40 is a silicon oxide film or a silicon nitride film. As a result, the current flowing through the lower electrode 12 is less likely to leak to the substrate 10. For example, the support layer 40 is a film formed of a material having better workability than the substrate 10. As an example, the support layer 40 is a polysilicon film. Thereby, the void 30 can be easily formed in the support layer 40.

According to the first modification of the third embodiment, the protective film 44 is provided between the substrate 10 and the support layer 40. Since the protective film 44 exists under the gap 30 provided in the support layer 40, it is possible to suppress etching of the substrate 10 during etching when the gap 30 is formed. Further, by forming the protective film 44 with a material having an etching rate slower than that of the support layer 40, the protective film 44 can be used as an etching stopper layer when forming voids in the support layer 40.

12 (a) is a plan view of the piezoelectric thin film resonator according to the fourth embodiment, and FIG. 12 (b) is a cross-sectional view taken along the line AA of FIG. 12 (a). FIG. 13 is a plan view showing the positional relationship between the lower electrode, the upper electrode, the insertion membrane, and the void of the piezoelectric thin film resonator in Example 4. In FIG. 13, for clarity of the figure, the insertion membrane 28 is cross-hatched, and the region 50 is shown by a thick line. With reference to FIGS. 12 (a), 12 (b), and 13, in the piezoelectric thin film resonator 400 of the fourth embodiment, the substrate 10 is located between the substrate 10 and the lower electrode 12 and the piezoelectric film 14. A support layer 40 made of a different material is provided. The upper surface of the substrate 10 is flat, and the gap 30 is formed in the support layer 40. The support layer 40 is, for example, a film having a higher acoustic impedance than the substrate 10.

The thickness of the support layer 40 in the drawer region 72 is thicker than the thickness of the support layer 40 in the drawer region 70. The lower electrode 12 is formed substantially flat on the support layer 40 in the drawer region 70, and the end surface of the lower electrode 12 on the drawer region 72 side is in contact with the side surface of the support layer 40 on the void 30 side. In other words, the end surface of the lower electrode 12 that defines the region 50 is in contact with the side surface of the support layer 40 on the void 30 side. The upper surface of the support layer 40 and the upper surface of the lower electrode 12 in the extraction region 72 are substantially the same surface. That is, the total thickness of the support layer 40 in the drawer region 70 and the thickness of the lower electrode 12 and the thickness of the support layer 40 in the drawer region 72 are substantially the same size. Approximately the same surface and substantially the same size correspond to, for example, variations in the manufacturing process and the degree of alignment accuracy in the manufacturing process. The piezoelectric film 14 is provided on the support layer 40 and the lower electrode 12. Since other configurations are the same as those of the piezoelectric thin film resonator of the first embodiment, the description thereof will be omitted.

According to the fourth embodiment, the support layer 40 is provided between the substrate 10 and the lower electrode 12. The void 30 is formed in the support layer 40, and the lower electrode 12 is formed substantially flat on the support layer 40. The end surface of the lower electrode 12 that defines the region 50 is in contact with the side surface of the support layer 40 on the void 30 side. Since the end face of the lower electrode 12 is in contact with the side surface of the support layer 40, damage to the lower electrode 12 can be suppressed as compared with the case where the end face of the lower electrode 12 is not in contact with the substrate 10 as in Comparative Example 1 of FIG. .. Further, when the end portion of the lower electrode 12 is located on the support layer 40 as in the third embodiment of FIG. 10A, a step is formed in the piezoelectric film 14, whereas in the fourth embodiment, the piezoelectric film 14 is formed. Since it is difficult to form a step on the piezoelectric film 14, damage to the piezoelectric film 14 can be suppressed. Further, since the contact area between the lower electrode 12 and the support layer 40 is smaller than that in the third embodiment of FIG. 10A, elastic waves excited in the region 51 are less likely to leak to the substrate 10.

The support layer 40 is preferably thinner in the drawer region 70 than in the drawer region 72. As a result, it is possible to easily obtain a structure in which the lower electrode 12 is formed substantially flat on the support layer 40 and the end surface of the lower electrode 12 is in contact with the side surface of the support layer 40 on the void 30 side.

Also in the third embodiment, the first modification of the third embodiment, and the fourth embodiment, the insulating layer 42 is provided on the lower electrode 12 and / or the upper electrode 16 as in the modification 1 of the second and second embodiments. May be good.

FIG. 14 is a circuit diagram of the filter according to the fifth embodiment. With reference to FIG. 14, in the filter 500 of the fifth embodiment, one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout, and one or more parallel resonators are connected. P1 to P4 are connected in parallel. The number of resonators can be set as appropriate.

In Example 5, the piezoelectric thin film resonators of Examples 1 to 4 can be used for at least one resonator of the series resonators S1 to S4 and the parallel resonators P1 to P4. For example, at least two of the series resonators S1 to S4 and the parallel resonators P1 to P4 are the piezoelectric thin film resonators of Examples 1 to 4, and the thicknesses of the insertion films 28 are different from each other. You may. For example, at least two of the series resonators S1 to S4 and the parallel resonators P1 to P4 are the piezoelectric thin film resonators of Examples 1 to 4, and the end faces of the upper electrodes 16 in the extraction region 70 of each other. The distance between the 68 and the inner end face 60 of the insertion thin film 28 (L1 in FIG. 3B) may be different. For example, at least two of the series resonators S1 to S4 and the parallel resonators P1 to P4 are the piezoelectric thin film resonators of Examples 1 to 4, and the end faces of the lower electrodes 12 in the extraction region 72 of each other. The distance between the 67 and the inner end face 60 of the insertion thin film 28 (L2 in FIG. 3B) may be different.

For example, the piezoelectric thin film resonators of Examples 1 to 4 are used for at least one resonator of the series resonators S1 to S4 and at least one resonator of the parallel resonators P1 to P4, and the upper electrode 16 is used in the extraction region 70. The distance between the end face 68 and the inner end face 60 of the insertion membrane 28 (L1 in FIG. 3B) may be shorter in the series resonator than in the parallel resonator. As a result, steep skirt characteristics and low ripple characteristics can be obtained. The distance L1 is, for example, 0.5 μm to 5.5 μm. Further, in the extraction region 72, the distance between the end surface 67 of the lower electrode 12 and the end surface 60 inside the insertion membrane 28 (L2 in FIG. 3B) is shortened in the series resonator as compared with the parallel resonator. May be good. This also provides steep skirt characteristics and low ripple characteristics. The distance L2 is, for example, 1.0 μm to 6.0 μm.

FIG. 15 is a circuit diagram of the duplexer according to the sixth embodiment. With reference to FIG. 15, in the duplexer 600 of the sixth embodiment, a transmission filter 90 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 92 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 90 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 92 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. At least one of the transmission filter 90 and the reception filter 92 can be the filter 500 of the fifth embodiment.

Although a duplexer is shown as an example as a multiplexer, a triplexer or a quadplexer may be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and modifications 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 piezoelectric film 14a Lower piezoelectric film 14b Upper piezoelectric film 16 Upper electrode 20, 22 Wiring 24 Protective film 28 Insertion film 30 Void 32 Introductory path 34 Hole 40 Support layer 42 Insulation layer 44 Protective film 50, 51 Area 52 Outer region 54 Central region 56 Peripheral region 60 Inner end face of insertion membrane 61 Outer end face of insertion membrane 62 Void contour 63 Region contour 64 Region contour 65 Lower piezoelectric membrane end face 66 Upper piezoelectric membrane end face 67 Lower electrode End face 68 Top electrode end face 70, 72 Drawer area 90 Transmission filter 92 Reception filter 100, 200, 210, 300, 310, 400, 1000, 1100, 1200 piezoelectric thin film resonator 500 filter 600 Duplexer

Claims (12)

With the board
A lower electrode provided on the substrate so as to have a gap between the substrate and the substrate.
The upper electrode provided on the lower electrode and the upper electrode
A first unit that is sandwiched between the lower electrode and the upper electrode, has a lower piezoelectric film and an upper piezoelectric film, and the lower electrode, the lower piezoelectric film, the upper piezoelectric film, and the upper electrode overlap in a plan view. In the first extraction region where the lower electrode is pulled out from the region, the contour of the first region is located on the side opposite to the void of the contour of the void, and in the first extraction region, the end face of the lower piezoelectric film is said. A piezoelectric film provided so as to be located away from the voids from the end face of the upper piezoelectric film,
In a plan view, the gap, the lower electrode, the piezoelectric film, and the upper electrode are not provided in the central region of the second region where they overlap, and the region surrounding the central region is located at least in the first extraction region. In, the central region is surrounded along the contour of the second region, the inner end face is located on the gap side of the contour of the gap, and the outer end face is on the opposite side of the gap from the contour of the gap. A piezoelectric thin film resonator comprising an insertion membrane inserted between the lower piezoelectric membrane and the upper piezoelectric membrane so as to be located. The piezoelectric thin film resonator according to claim 1, wherein in the second drawing region where the upper electrode is pulled out from the first region, the contour of the first region is located on the side opposite to the contour of the gap. The insertion membrane surrounds the central region along the contour of the second region in a region located in the second extraction region among the regions surrounding the central region, and the inner end surface of the gap is larger than the contour of the gap. The piezoelectric thin film resonator according to claim 2, wherein the piezoelectric thin film resonator is located on the side and the outer end surface is located on the side opposite to the void from the contour of the void. A support layer provided between the substrate and the lower electrode and formed of a material different from that of the substrate is provided.
The voids are formed in the support layer
The piezoelectric thin film resonator according to any one of claims 1 to 3, wherein the lower electrode is formed substantially flat on the support layer. A support layer provided between the substrate and the lower electrode and formed of a material different from that of the substrate is provided.
The voids are formed in the support layer
The lower electrode is formed substantially flat on the support layer.
The piezoelectric thin film resonator according to claim 1, wherein the end surface of the lower electrode defining the first region is in contact with the side surface of the support layer on the void side. The piezoelectric thin film resonator according to claim 5, wherein the support layer has a thickness in the first extraction region thinner than a thickness in a second extraction region in which the upper electrode is drawn from the first region. The piezoelectric thin film resonator according to any one of claims 4 to 6, wherein the acoustic impedance of the support layer is larger than the acoustic impedance of the substrate. The piezoelectric thin film resonator according to any one of claims 4 to 7, wherein the volume resistivity of the support layer is larger than the volume resistivity of the substrate. The gap is formed by a recess provided in the substrate.
The piezoelectric thin film resonator according to any one of claims 1 to 3, wherein the lower electrode is formed substantially flat on the substrate. The piezoelectric thin film resonator according to any one of claims 1 to 9, wherein the acoustic impedance of the insertion membrane is smaller than the acoustic impedance of the piezoelectric membrane. A filter including the piezoelectric thin film resonator according to any one of claims 1 to 10. A multiplexer containing the filter according to claim 11.

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