JP2023133978A - Piezoelectric thin film resonator, filter, and multiplexer - Google Patents

Abstract

To provide a piezoelectric thin film resonator capable of suppressing an ESD destroy between a lower electrode and an upper electrode.SOLUTION: A piezoelectric thin film resonator comprises: a substrate 10; a piezoelectric film 14 that is provided on the substrate 10; an upper electrode 16 that is provided on the piezoelectric film 14; a lower electrode 12 which is provided between the substrate 10 and the piezoelectric film 14, forms a resonance region 50 that is overlapped with the upper electrode 16 across the piezoelectric film 14 on a gap 30 formed in a space between itself and the substrate 10, and in which an end surface 11 on a leading region 52 side where the upper electrode 16 is led from the resonance region 50 is positioned on the gap 30 separated from a peripheral edge 31 of the gap 30; and an insulation film 18 which is provided between the gap 30 and the piezoelectric film 14, and in which a lower end 19 of an end surface 17 on the side where the upper electrode 16 is led from the resonance region 50 in the leading region 52 is in contact with the peripheral edge 31 of the gap 30 and the piezoelectric film 14 is in contact with the end surface 17 in a manner to cover it.SELECTED DRAWING: Figure 2

Description

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

Acoustic wave devices using piezoelectric thin film resonators are used, for example, as filters and duplexers for wireless devices such as mobile phones. A piezoelectric thin film resonator has a laminated film in which a lower electrode and an upper electrode face each other with a piezoelectric film in between. It is known to form a dome-shaped gap between the substrate and the lower electrode by applying compressive stress to the laminated film (for example, Patent Documents 1 to 3). Furthermore, it is known that changes in film quality can be suppressed by covering the lower surface of the lower electrode and the upper surface of the upper electrode with a protective film (for example, Patent Document 4). Further, in order to suppress deterioration of the piezoelectric film due to concentration of stress on the piezoelectric film, it is known to provide an additional film from the inside to the outside of the gap (for example, Patent Document 5).

Japanese Patent Application Publication No. 2005-347898 Japanese Patent Application Publication No. 2018-182463 JP2017-108288A Japanese Patent Application Publication No. 2010-154233 JP2020-57991A

If stress is concentrated at the edge of the gap, cracks may occur from the edge of the gap toward the inside of the piezoelectric film. When a crack occurs in the piezoelectric film, ESD (Electro-Static Discharge) destruction may occur between the lower electrode and the upper electrode at the location where the crack occurs.

The present invention was made in view of the above problems, and an object of the present invention is to suppress ESD damage between the lower electrode and the upper electrode.

The present invention provides a substrate, a piezoelectric film provided on the substrate, an upper electrode provided on the piezoelectric film, and an upper electrode provided between the substrate and the piezoelectric film, and formed between the substrate and the piezoelectric film. A resonance region is formed overlapping the upper electrode with the piezoelectric film sandwiched therebetween, and a first end surface on the extraction region side where the upper electrode is drawn out from the resonance region is separated from the periphery of the void and forms a resonance region overlapping the upper electrode with the piezoelectric film sandwiched therebetween. a lower electrode located above, the gap and the piezoelectric film, and a lower end of a second end surface on the side where the upper electrode is drawn out from the resonance area in the lead-out area is in contact with a periphery of the gap; or a piezoelectric thin film comprising: an insulating film in which the second end face is located on the gap closer to the periphery of the gap than the first end face of the lower electrode, and the piezoelectric film is in contact with the second end face so as to cover it; It is a resonator.

In the above structure, the angle between the first end surface of the lower electrode and the surface of the lower electrode on the void side is the angle between the second end surface of the insulating film and the surface of the insulating film on the void side. A smaller configuration is possible.

In the above structure, the insulating film may not be provided in a central region of the resonance region.

In the above structure, the insulating film is arranged in the lower electrode so that the third end surface opposite to the second end surface is located between the first end surface of the lower electrode and the periphery of the gap. The structure may be such that the gap is provided between one end face and the periphery of the gap.

In the above structure, the third end surface of the insulating film may be in contact with the first end surface of the lower electrode.

In the above structure, the void may have a dome shape.

In the above structure, the thickness of the insulating film may be 1/2 or more of the thickness of the lower electrode.

In the above structure, the insulating film may be formed of a material having a larger Young's modulus than the piezoelectric film.

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

The invention is a multiplexer including the filter described above.

According to the present invention, ESD damage between the lower electrode and the upper electrode can be suppressed.

FIG. 1(a) is a plan view of the piezoelectric thin film resonator according to Example 1, and FIG. 1(b) is a sectional view taken along line AA in FIG. 1(a). 2(a) is a cross-sectional view near the boundary between the resonance region and the extraction region in Example 1, and FIG. 2(b) is a sectional view near the end of the lower electrode and the end of the insulating film in FIG. 2(a). FIG. 3(a) to 3(c) are cross-sectional views (part 1) showing the method for manufacturing the piezoelectric thin film resonator according to the first embodiment. FIGS. 4A to 4C are cross-sectional views (part 2) showing the method for manufacturing the piezoelectric thin film resonator according to the first embodiment. FIGS. 5A and 5B are cross-sectional views for explaining problems that occur in a piezoelectric thin film resonator according to a comparative example. FIG. 6 is a cross-sectional view for explaining the effect of the piezoelectric thin film resonator according to the first embodiment. FIG. 7 is a cross-sectional view of a piezoelectric thin film resonator according to Modification 1 of Example 1. FIG. 8(a) is a cross-sectional view near the boundary between the resonance region and the extraction region of the piezoelectric thin film resonator according to Modification Example 2 of Example 1, and FIG. 8(b) is an end face of the insulating film in FIG. 8(a). FIG. 3 is an enlarged cross-sectional view of the vicinity. FIG. 9A is a plan view of a piezoelectric thin film resonator according to Example 2, and FIG. 9B is a cross-sectional view near the boundary between the resonance region and the extraction region in Example 2. 10(a) is a plan view of the piezoelectric thin film resonator according to the third embodiment, and FIG. 10(b) is a cross-sectional view near the boundary between the resonance region and the extraction region in the third embodiment. FIG. 11 is a circuit diagram of a filter according to the fourth embodiment. FIG. 12 is a block diagram of a duplexer according to the fifth embodiment.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a plan view of a piezoelectric thin film resonator 100 according to Example 1, and FIG. 1(b) is a cross-sectional view taken along line AA in FIG. 1(a). In FIG. 1A, the lower electrode 12, the upper electrode 16, the insulating film 18, and the void 30 are mainly illustrated. Further, in FIG. 1A, the outline of the insulating film 18 is shown by a thick line, and the region where the insulating film 18 is provided is hatched. Moreover, the outline of the void 30 is shown by a broken line. The plane directions of the substrate 10 are the X direction and the Y direction, and the stacking direction of the laminated film 20 is the Z direction.

As shown in FIGS. 1(a) and 1(b), an insulating film 18 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 insulating film 18. The dome-shaped bulge is a bulge that has a shape in which the height of the void 30 is small around the void 30 and the height of the void 30 is larger toward the inside of the void 30. The substrate 10 is, for example, a silicon substrate. The insulating film 18 is, for example, silicon nitride (Si ₃ N ₄ ).

A lower electrode 12 is provided on the insulating film 18. The lower electrode 12 is, for example, a metal film in which a chromium (Cr) film and a ruthenium (Ru) film are laminated from the substrate 10 side. A piezoelectric film 14 is provided on the lower electrode 12. The piezoelectric film 14 is, for example, an aluminum nitride film whose main component is aluminum nitride (AlN) whose main axis is in the (0001) direction (that is, has C-axis orientation).

An upper electrode 16 is provided on the piezoelectric film 14 . The upper electrode 16 is, for example, a metal film in which a ruthenium film and a chromium film are laminated from the piezoelectric film 14 side. A region above the gap 30 where the lower electrode 12 and the upper electrode 16 face each other with at least a portion of the piezoelectric film 14 in between is a resonance region 50 . The resonance region 50 is a region where elastic waves in the thickness longitudinal vibration mode resonate. The planar shape of the resonance region 50 is, for example, approximately elliptical. In plan view, the size of the air gap 30 is larger than the resonance region 50. Note that the planar shape of the resonance region 50 may be other shapes such as a polygon such as a quadrangle or a pentagon.

An insertion membrane 28 is provided within the piezoelectric membrane 14 . The insertion film 28 is provided in the outer peripheral region of the resonant region 50 and is not provided in the central region. The outer peripheral region is a region within the resonance region 50, including the outer periphery of the resonance region 50 and along the outer periphery. The central region is a region within the resonant region 50 and includes the center of the resonant region 50. The central region does not have to be the geometric center. For example, the insertion film 28 is provided continuously to the region surrounding the resonance region 50 in addition to the outer peripheral region, but may be provided only within the resonance region 50. The insertion film 28 is, for example, a silicon oxide film. The insertion film 28 is provided to suppress leakage of elastic wave energy from the resonance region 50 to the outside.

A cover film 24 is provided on the upper electrode 16 and the piezoelectric film 14. Cover film 24 may function as a frequency adjustment film and/or a protective film. The cover film 24 is, for example, an insulating film such as a silicon oxide film. The laminated film 20 includes an insulating film 18 , a lower electrode 12 , a piezoelectric film 14 , an insertion film 28 , an upper electrode 16 , and a cover film 24 .

A region where the upper electrode 16 is drawn out from the resonance region 50 is a lead-out region 52 . The extraction region 52 is provided in the -X direction of the resonance region 50. The planar shape of the piezoelectric film 14 is larger than that of the upper electrode 16. The piezoelectric film 14 is provided at least in the resonance region 50 and the extraction region 52. Note that in FIGS. 1(a) and 1(b), illustration of wiring is omitted.

2(a) is a cross-sectional view near the boundary between the resonance region 50 and the extraction region 52 in Example 1, and FIG. 2(b) is a sectional view of the end of the lower electrode 12 and the insulating film 18 in FIG. 2(a). FIG. 2 is an enlarged cross-sectional view of the vicinity of the end. As shown in FIGS. 2(a) and 2(b), the end surface 11 of the lower electrode 12 between the resonance region 50 and the extraction region 52 is separated from the periphery 31 of the void 30 to the inside of the void 30 and is located above the void 30. It is located in The end surface 11 of the lower electrode 12 is inclined in a tapered shape, and the angle θ1 between the end surface 11 and the surface 25 of the lower electrode 12 on the gap 30 side is, for example, 60° or less, may be 45° or less, or 30° or less. It may be less than °.

The insulating film 18 is provided between the void 30 and the piezoelectric film 14. The insulating film 18 is provided between the void 30 and the piezoelectric film 14, for example, so as to cover the entire void 30. In the extraction region 52 , the lower end 19 of the end surface 17 of the insulating film 18 on the side where the upper electrode 16 is extracted from the resonance region 50 is in contact with the peripheral edge 31 of the gap 30 . The distance X between the end surface 11 of the lower electrode 12 and the end surface 17 of the insulating film 18 is, for example, 1 μm or more. For example, the distance It may be more than double. An end surface 17 of the insulating film 18 is covered with the piezoelectric film 14 and is in contact with the piezoelectric film 14 . Therefore, the end portion of the insulating film 18 is recessed into the piezoelectric film 14. The angle θ2 between the end surface 17 of the insulating film 18 and the surface 27 of the insulating film 18 on the void 30 side is larger than the angle θ1, for example, 70° or more and 90° or less, and may be 75° or more and 90° or less. , 80° or more and 90° or less. The thickness of the insulating film 18 is, for example, 1/2 or more of the thickness of the lower electrode 12.

In the lead-out region 52, a metal wiring 26 is provided on the upper electrode 16. The metal wiring 26 is made of gold, for example.

As the substrate 10, in addition to a silicon substrate, 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 ruthenium and chromium, the lower electrode 12 and the upper electrode 16 include aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), and platinum (Pt). A single layer film of , rhodium (Rh), or iridium (Ir) or a laminated film of these can be used.

As the piezoelectric film 14, other than aluminum nitride, zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), or the like can be used. Furthermore, the piezoelectric film 14 mainly contains aluminum nitride, and may contain other elements to improve resonance characteristics or piezoelectricity. The piezoelectricity of the piezoelectric film 14 is improved by using, for example, scandium (Sc), two elements, a group 2 element and a group 4 element, or two elements, a group 2 element and a group 5 element, as additive elements. This improves the effective electromechanical coupling coefficient of the piezoelectric thin film resonator. Group 2 elements are, for example, calcium (Ca), magnesium (Mg), strontium (Sr), or zinc (Zn). The Group 4 element is, for example, titanium (Ti), zirconium (Zr), or hafnium (Hf). Group 5 elements are, for example, tantalum (Ta), niobium (Nb), or vanadium (V). Furthermore, the piezoelectric film 14 mainly contains aluminum nitride and may also contain fluorine (F) or boron (B).

The insulating film 18 is preferably formed of a material having a larger Young's modulus than the piezoelectric film 14. As the insulating film 18, other than silicon nitride, aluminum oxide (Al ₂ O ₃ ), beryllium oxide (BeO), or the like can be used.

The insertion film 28 is preferably formed of a material having a smaller Young's modulus and/or acoustic impedance than the piezoelectric film 14 . Thereby, the Q value can be improved. In addition to silicon oxide, the insertion film 28 is a single layer film of aluminum (Al), gold (Au), copper (Cu), titanium (Ti), platinum (Pt), tantalum (Ta), or chromium (Cr). Alternatively, a laminated film of these can be used.

[Production method]
FIGS. 3A to 4C are cross-sectional views showing a method of manufacturing the piezoelectric thin film resonator 100 according to the first embodiment. As shown in FIG. 3A, a sacrificial layer 38 for forming a void 30 is formed on a substrate 10 having a flat principal surface. The thickness of the sacrificial layer 38 is, for example, 10 nm to 100 nm. The sacrificial layer 38 is selected from materials that are easily dissolved in the etching solution or gas, such as magnesium oxide (MgO), zinc oxide, germanium (Ge), or silicon oxide. The sacrificial layer 38 is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD (Chemical Vapor Deposition) method. The sacrificial layer 38 is patterned into a desired shape using photolithography and etching. The sacrificial layer 38 may be formed by a lift-off method. The shape of the sacrificial layer 38 corresponds to the planar shape of the void 30. Next, the insulating film 18 is formed on the sacrificial layer 38 and the substrate 10. The insulating film 18 is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. The insulating film 18 is patterned into a desired shape using photolithography and etching techniques. At this time, patterning is performed so that the end surface 17 of the insulating film 18 located in the lead-out region 52 (see FIGS. 1(a) to 2(a)) substantially coincides with the end surface of the sacrificial layer 38. The insulating film 18 may be formed by a lift-off method.

As shown in FIG. 3(b), the lower electrode 12 is formed on the insulating film 18. The lower electrode 12 is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. The lower electrode 12 is patterned into a desired shape using photolithography and etching techniques. At this time, patterning is performed so that the end surface 11 of the lower electrode 12, which will be located on the side of the extraction region 52 (see FIGS. 1(a) to 2(a)), is located away from the end surface of the sacrificial layer 38 inward. do. Further, by adjusting the etching conditions, the end surface 11 of the lower electrode 12 is patterned to have a tapered shape. The lower electrode 12 may be formed by a lift-off method.

As shown in FIG. 3C, the lower piezoelectric film 14a and the insertion film 28 are formed on the lower electrode 12 and the substrate 10 using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. The insertion film 28 is patterned into a desired shape using photolithography and etching techniques. The insertion film 28 may be formed by a lift-off method.

As shown in FIG. 4A, an upper piezoelectric film 14b and an upper electrode 16 are formed on the lower piezoelectric film 14a using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. The piezoelectric film 14 is formed from the lower piezoelectric film 14a and the upper piezoelectric film 14b. The upper electrode 16 is patterned into a desired shape using photolithography and etching techniques. The upper electrode 16 may be formed by a lift-off method.

As shown in FIG. 4(b), the piezoelectric film 14 is patterned into a desired shape using photolithography and etching techniques. Next, the cover film 24 is formed using, for example, a sputtering method, a vacuum evaporation method, or a CVD method, and then patterned into a desired shape using a photolithography technique and an etching technique. A laminated film 20 is formed by the insulating film 18, the lower electrode 12, the piezoelectric film 14, the insertion film 28, the upper electrode 16, and the cover film 24.

As shown in FIG. 4C, the etching solution for the sacrificial layer 38 is introduced into the sacrificial layer 38 under the insulating film 18 through an introduction path (not shown) that has been formed in advance so as to connect to the sacrificial layer 38. . As a result, the sacrificial layer 38 is removed. The stress of the laminated film 20 is set to be compressive stress. As a result, when the sacrificial layer 38 is removed, the laminated film 20 bulges away from the substrate 10 to the opposite side of the substrate 10. A gap 30 having a dome-shaped bulge is formed between the substrate 10 and the insulating film 18. The end surface 11 of the lower electrode 12 is located above the void 30, away from the peripheral edge 31 of the void 30, and the lower end 19 of the end surface 17 of the insulating film 18 comes into contact with the peripheral edge 31 of the void 30. Through the above steps, the piezoelectric thin film resonator 100 according to the first embodiment is formed.

[Comparative example]
FIGS. 5A and 5B are cross-sectional views for explaining problems that occur in a piezoelectric thin film resonator according to a comparative example. FIG. 5(a) is a cross-sectional view showing the state during the manufacturing process corresponding to FIG. 4(b) in the comparative example, and FIG. 5(b) is a sectional view showing the state during the manufacturing process corresponding to FIG. 4(c). FIG. As shown in FIG. 5A, in the comparative example, the insulating film 18 is not provided between the substrate 10 and the lower electrode 12. Further, the lower end of the end surface 11 of the lower electrode 12 is formed to substantially coincide with the end of the sacrificial layer 38.

As shown in FIG. 5B, by removing the sacrificial layer 38, a gap 30 having a dome-shaped bulge is formed between the substrate 10 and the lower electrode 12. The peripheral edge 31 of the gap 30 and the substrate 10 come into contact at a location 40 . Furthermore, the lower electrode 12 and the piezoelectric film 14 are also in contact with the location 40 . For this reason, stress tends to concentrate at the location 40. For example, when the laminated film 20 is subjected to compressive stress in order to form the dome-shaped void 30, the stress is concentrated at the location 40. Furthermore, when the temperature changes, stress due to the difference in thermal expansion coefficients is concentrated at the location 40. The piezoelectric film 14 is fragile because it is formed by a sputtering method, a vacuum evaporation method, or a CVD method. For example, when an aluminum nitride film is formed on the substrate 10 using a sputtering method, the aluminum nitride film has a columnar crystal structure extending perpendicularly to the surface of the substrate 10. Therefore, the aluminum nitride film is easily cleaved and cracked. Therefore, cracks 42 starting from the vicinity of the end surface 11 of the lower electrode 12 may occur in the piezoelectric film 14 . Note that since the substrate 10 is made of a strong material to support the laminated film 20, cracks are less likely to occur. Since the lower electrode 12 is a metal film, it has high ductility and malleability, so cracks are less likely to occur.

When a crack 42 occurs in the piezoelectric film 14 starting from the vicinity of the end surface 11 of the lower electrode 12, ESD (Electro-Static Discharge) destruction occurs between the lower electrode 12 and the upper electrode 16, resulting in poor characteristics. Put it away.

[Effects of Example 1]
FIG. 6 is a cross-sectional view for explaining the effect of the piezoelectric thin film resonator 100 according to the first embodiment. As shown in FIG. 6, in Example 1, the end surface 11 of the lower electrode 12 is located above the gap 30, away from the periphery 31 of the gap 30. As shown in FIG. The end surface 17 of the insulating film 18 is located closer to the periphery 31 of the gap 30 than the end surface 11 of the lower electrode 12 . As a result, cracks 42 tend to occur in the piezoelectric film 14 starting from the vicinity of the end surface 17 of the insulating film 18 . Therefore, a crack 42 is formed between the insulating film 18 and the upper electrode 16. Therefore, ESD damage between the lower electrode 12 and the upper electrode 16 is suppressed.

[Modified example]
FIG. 7 is a cross-sectional view of a piezoelectric thin film resonator 110 according to a first modification of the first embodiment. As shown in FIG. 7, in the first modification of the first embodiment, a depression is formed on the upper surface of the substrate 10. As shown in FIG. The insulating film 18 is formed flat on the substrate 10. As a result, a cavity 30 is formed by the depression formed on the upper surface of the substrate 10. The other configurations are the same as those in the first embodiment, so their explanation will be omitted.

8(a) is a cross-sectional view of the piezoelectric thin film resonator 120 according to the second modification of the first embodiment near the boundary between the resonance region 50 and the extraction region 52, and FIG. 8(b) is the insulating FIG. 3 is an enlarged cross-sectional view of the vicinity of the end surface 17 of the membrane 18a. As shown in FIGS. 8(a) and 8(b), in the second modification of the first embodiment, the end surface 17 of the insulating film 18a is further away from the periphery 31 of the void 30, and the end surface 17 of the insulating film 18a is further away from the edge 31 of the void 30 than the end surface 11 of the lower electrode 12. It is located above the air gap 30 near the periphery 31 of 30 . The distance X1 between the peripheral edge 31 of the void 30 and the end surface 17 of the insulating film 18a is, for example, 0.1 μm or more and 2 μm or less. The distance X2 between the end surface 17 of the insulating film 18a and the end surface 11 of the lower electrode 12 is, for example, 1 μm or more and 5 μm or less. The distance X2 is, for example, larger than the thickness of the lower electrode 12 and the insulating film 18, and may be, for example, twice or more, five times or more, or ten times the thickness of the thicker one of the lower electrode 12 and the insulating film 18. The above is fine. The distance X1 may be shorter than the distance X2, for example, 1/2 or less of the distance X2, or 1/3 or less of the distance X2. The distance X1 may be smaller than the thickness of the thicker one of the lower electrode 12 and the insulating film 18, or may be less than or equal to 1/2 of the thickness, or may be less than or equal to 1/3 of the thickness. The other configurations are the same as those in the first embodiment, so their explanation will be omitted.

In Modification 1 and Modification 2 of Embodiment 1, cracks 42 tend to occur in the piezoelectric film 14 starting near the end surfaces 17 of the insulating films 18 and 18a, similarly to FIG. 6 of Embodiment 1. Therefore, since the crack 42 is formed between the insulating films 18, 18a and the upper electrode 16, ESD breakdown between the lower electrode 12 and the upper electrode 16 is suppressed.

According to the first embodiment and its modifications, the end surface 11 (first end surface) of the lower electrode 12 on the extraction region 52 side is located on the void 30 away from the periphery 31 of the void 30 . The insulating films 18 and 18a are such that the lower end 19 of the end surface 17 (second end surface) on the side where the upper electrode 16 is drawn out from the resonance region 50 in the extraction region 52 is in contact with the periphery 31 of the gap 30 or the end surface 17 is in contact with the periphery 31 of the lower electrode 12. It is located above the gap 30 closer to the periphery 31 of the gap 30 than the end face 11 . End surfaces 17 of the insulating films 18 and 18a are covered with and in contact with the piezoelectric film 14. As a result, cracks 42 that occur in the piezoelectric film 14 tend to occur starting near the end surfaces 17 of the insulating films 18 and 18a. Therefore, the crack 42 is formed between the insulating films 18 and 18a and the upper electrode 16, and it is possible to suppress ESD breakdown between the lower electrode 12 and the upper electrode 16.

Further, according to the first embodiment and its modifications, as shown in FIG. 2B, the angle θ1 between the end surface 11 of the lower electrode 12 and the surface 25 on the gap 30 side is It is smaller than the angle θ2 between the surface 27 and the surface 27 on the void 30 side. Since the end surface 11 of the lower electrode 12 is tapered and inclined in this way, cracks starting from the vicinity of the end surface 11 of the lower electrode 12 are less likely to occur in the piezoelectric film 14. Therefore, ESD damage between the lower electrode 12 and the upper electrode 16 can be suppressed.

Further, according to the first embodiment and its modifications, the void 30 has a dome-like shape. In this case, the laminated film 20 becomes under compressive stress, stress tends to concentrate at a location 40 in FIG. 6, and cracks 42 tend to occur in the piezoelectric film 14 from the vicinity of the location 40. Therefore, it is preferable to separate the end surface 11 of the lower electrode 12 from the periphery 31 of the gap 30 and to provide the end surfaces 17 of the insulating films 18 and 18a closer to the periphery 31 of the gap 30 than the end surface 11 of the lower electrode 12.

Further, according to the first embodiment and its modifications, the thickness of the insulating films 18 and 18a is 1/2 or more of the thickness of the lower electrode 12. As a result, cracks 42 that occur in the piezoelectric film 14 tend to occur near the end surfaces 17 of the insulating films 18 and 18a, and are less likely to occur near the end surfaces 11 of the lower electrode 12. Therefore, ESD damage between the lower electrode 12 and the upper electrode 16 can be suppressed. The thickness of the insulating films 18, 18a is preferably 2/3 or more of the thickness of the lower electrode 12, and more preferably 3/4 or more of the thickness of the lower electrode 12, in order to cause the cracks 42 to occur near the end surfaces 17 of the insulating films 18, 18a. Preferably, 4/5 or more is more preferable. If the insulating films 18 and 18a are too thick, there is a concern that the piezoelectric thin film resonator 100 will become larger and its characteristics will deteriorate. It is preferably 1.5 times or less, more preferably 1 time or less, and even more preferably 1 time or less.

Further, according to the first embodiment and its modifications, the insulating films 18 and 18a are formed of a material having a larger Young's modulus than the piezoelectric film 14. As a result, cracks 42 that occur in the piezoelectric film 14 tend to occur starting from the vicinity of the end surfaces 17 of the insulating films 18 and 18a.

9(a) is a plan view of the piezoelectric thin film resonator 200 according to the second embodiment, and FIG. 9(b) is a cross-sectional view near the boundary between the resonance region 50 and the extraction region 52 in the second embodiment. In FIG. 9A, similarly to FIG. 1A, the outline of the insulating film 18b is shown by a thick line, and the region where the insulating film 18b is provided is hatched. Moreover, the outline of the void 30 is shown by a broken line. As shown in FIGS. 9(a) and 9(b), in the piezoelectric thin film resonator 200 of Example 2, the insulating film 18b extends between the periphery 31 of the void 30 and the end surface 11 of the lower electrode 12. It is not provided in the resonant region 50. Therefore, the end surface 23 of the insulating film 18b on the lower electrode 12 side is located closer to the peripheral edge 31 of the gap 30 than the end surface 11 of the lower electrode 12. For example, at least a portion of the end surface 23 of the insulating film 18 a is in contact with the end surface 11 of the lower electrode 12 , for example, more than half or all of the end surface 23 is in contact with the end surface 11 of the lower electrode 12 . Note that the piezoelectric film 14 may be provided between the end surface 23 of the insulating film 18b and the end surface 11 of the lower electrode 12, and the end surface 23 of the insulating film 18b and the end surface 11 of the lower electrode 12 may not be in contact with each other. The other configurations are the same as those in the first embodiment, so their explanation will be omitted.

In the second embodiment as well, the end surface 11 of the lower electrode 12 is located above the gap 30, away from the periphery 31 of the gap 30. The end surface 17 of the insulating film 18b is located closer to the periphery 31 of the gap 30 than the end surface 11 of the lower electrode 12, and the lower end 19 is in contact with the periphery 31 of the gap 30. The end surface 17 of the insulating film 18b is covered with the piezoelectric film 14 and is in contact with the piezoelectric film 14. As a result, as in Example 1, cracks 42 occurring in the piezoelectric film 14 tend to occur starting from the vicinity of the end surface 17 of the insulating film 18b, and ESD breakdown occurs between the lower electrode 12 and the upper electrode 16. can be suppressed.

Further, according to the second embodiment, the insulating film 18b is arranged such that the end surface 23 (third end surface) opposite to the end surface 17 is located between the end surface 11 of the lower electrode 12 and the periphery 31 of the gap 30. It is provided between the end surface 11 of the lower electrode 12 and the peripheral edge 31 of the gap 30 . Therefore, the insulating film 18b is not provided in the resonance region 50. Thereby, deterioration of the characteristics of the piezoelectric thin film resonator 200 can be suppressed.

Further, according to the second embodiment, the end surface 23 of the insulating film 18b is in contact with the end surface 11 of the lower electrode 12. Thereby, it is possible to suppress the occurrence of cracks in the piezoelectric film 14 near the end surface 11 of the lower electrode 12.

10(a) is a plan view of a piezoelectric thin film resonator 300 according to the third embodiment, and FIG. 10(b) is a cross-sectional view near the boundary between the resonance region 50 and the extraction region 52 in the third embodiment. In FIG. 10A, as in FIG. 1A, the outline of the insulating film 18c is shown by a thick line, and the region where the insulating film 18c is provided is hatched. Moreover, the outline of the void 30 is shown by a broken line. As shown in FIGS. 10(a) and 10(b), in the piezoelectric thin film resonator 300 of Example 3, the insulating film 18c extends from between the periphery 31 of the gap 30 and the end surface 11 of the lower electrode 12 to the lower electrode 12. 12. That is, the insulating film 18c covers the end surface 11 of the lower electrode 12 from above. The insulating film 18c is provided in the outer peripheral region 54 of the resonance region 50, but not in the central region 56. The outer peripheral region 54 is a region within the resonant region 50, including the outer periphery of the resonant region 50 and along the outer periphery. The central region 56 is a region within the resonant region 50 and includes the center of the resonant region 50. The central region does not have to be the geometric center. The distance X between the end surface 11 of the lower electrode 12 and the end surface 23 of the insulating film 18c is, for example, 1 μm or more and 5 μm or less. For example, the distance The above is fine. The other configurations are the same as those in the first embodiment, so the explanation will be omitted.

In the third embodiment as well, the end surface 11 of the lower electrode 12 is provided on the gap 30 apart from the periphery 31 of the gap 30. The end surface 17 of the insulating film 18c is located closer to the periphery 31 of the gap 30 than the end surface 11 of the lower electrode 12, and the lower end 19 is in contact with the periphery 31 of the gap 30. The end surface 17 of the insulating film 18c is covered with the piezoelectric film 14 and is in contact with the piezoelectric film 14. As a result, as in Example 1, cracks 42 occurring in the piezoelectric film 14 tend to occur starting from the vicinity of the end surface 17 of the insulating film 18c, and ESD breakdown occurs between the lower electrode 12 and the upper electrode 16. can be suppressed.

Further, according to the third embodiment, the insulating film 18c is not provided in the central region 56 of the resonance region 50. Thereby, deterioration of the characteristics of the piezoelectric thin film resonator 200 can be suppressed.

Further, according to the third embodiment, the insulating film 18c is provided between the periphery 31 of the gap 30 and the end surface 11 of the lower electrode 12 and over the lower electrode 12 so as to cover the end surface 11 of the lower electrode 12. This suppresses the occurrence of cracks in the piezoelectric film 14 near the end surface 11 of the lower electrode 12.

FIG. 11 is a circuit diagram of a filter 400 according to the fourth embodiment. As shown in FIG. 11, the filter 400 includes one or more series resonators S1 to S3 connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The parallel resonators P1 and P2 are connected between the path between the input terminal Tin and the output terminal Tout and the ground terminal. The piezoelectric thin film resonator according to Examples 1 to 3 can be used for at least one of one or more series resonators S1 to S3 and one or more parallel resonators P1 and P2. The number of resonators in the ladder filter can be set as appropriate.

FIG. 12 is a block diagram of a duplexer 500 according to the fifth embodiment. As shown in FIG. 12, in the duplexer 500, a transmission filter 60 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 62 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 60 passes a signal in the transmission band among the high-frequency signals inputted from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 62 passes a signal in the reception band among the high-frequency signals inputted from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals at other frequencies. At least one of the transmission filter 60 and the reception filter 62 can be the filter of the fourth embodiment. Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also 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 changes can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 Substrate 11 End face of lower electrode 12 Lower electrode 14 Piezoelectric film 16 Upper electrode 17 End face of insulating film 18, 18a, 18b, 18c Insulating film 19 Lower end of end face of insulating film 20 Laminated film 23 End face of insulating film 24 Cover film 25 Lower part Gap side surface of the electrode 26 Metal wiring 27 Gap side surface of the insulating film 28 Insert film 30 Gap 31 Periphery of the gap 38 Sacrificial layer 40 locations 42 Cracks 50 Resonance region 52 Leading region 54 Outer region 56 Central region 60 Transmission filter 62 Reception Filter 100, 110, 120, 200, 300 Piezoelectric thin film resonator 400 Filter 500 Duplexer S1, S2, S3 Series resonator P1, P2 Parallel resonator

Claims (10)

A substrate and
a piezoelectric film provided on the substrate;
an upper electrode provided on the piezoelectric film;
A resonant region is provided between the substrate and the piezoelectric film, and overlaps with the upper electrode across the piezoelectric film over a gap formed between the substrate, and the upper electrode is separated from the resonant region. a lower electrode whose first end face on the pulled-out region side is located on the void apart from the periphery of the void;
The lower end of the second end surface is provided between the gap and the piezoelectric film, and the lower end of the second end surface on the side where the upper electrode is drawn out from the resonance area in the extraction region is in contact with the periphery of the gap, or the second end surface is in contact with the periphery of the gap. A piezoelectric thin film resonator comprising: an insulating film located on the gap closer to the periphery of the gap than the first end face of the electrode, and in contact with the piezoelectric film so as to cover the second end face. An angle between the first end surface of the lower electrode and a surface of the lower electrode on the void side is smaller than an angle between the second end surface of the insulating film and the surface of the insulating film on the void side. The piezoelectric thin film resonator according to item 1. 3. The piezoelectric thin film resonator according to claim 1, wherein the insulating film is not provided in a central region of the resonant region. The insulating film is arranged between the first end surface of the lower electrode and the periphery of the gap such that a third end surface opposite to the second end surface is located between the first end surface of the lower electrode and the periphery of the gap. The piezoelectric thin film resonator according to any one of claims 1 to 3, wherein the piezoelectric thin film resonator is provided between the piezoelectric thin film resonator and the peripheral edge of the gap. The piezoelectric thin film resonator according to claim 4, wherein the third end surface of the insulating film is in contact with the first end surface of the lower electrode. The piezoelectric thin film resonator according to any one of claims 1 to 5, wherein the void has a dome-like shape. The piezoelectric thin film resonator according to any one of claims 1 to 6, wherein the thickness of the insulating film is 1/2 or more of the thickness of the lower electrode. The piezoelectric thin film resonator according to any one of claims 1 to 7, wherein the insulating film is formed of a material having a larger Young's modulus than the piezoelectric film. A filter comprising the piezoelectric thin film resonator according to any one of claims 1 to 8. A multiplexer comprising a filter according to claim 9.

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