JP2020129727A - Filter and multiplexer - Google Patents

Abstract

To provide a filter and a multiplexer making the characteristics desirable.SOLUTION: In series resonators S1 through S4, an insertion film 28 is inserted into a piezoelectric film 14 between a lower electrode 12 and an upper electrode 16 along the outer boundary 51 of a resonance region 50 in at least a part surrounding a central region. Insertion widths of the insertion film are WL and WU in the direction orthogonal to the tangent line of the outer boundary 51 in the resonance region 50. From parallel resonators P1-P4, the insertion film is inserted into a piezoelectric film between the lower electrode and the upper electrode along the outer boundary 51 of the resonance region 50 in at least a part surrounding the central region. Insertion widths of the insertion film 28 are WL and WU in the direction orthogonal to the tangent line of the outer boundary 51 in the resonance region 50. Insertion widths WL and WU of parallel resonators P1-P4 are different from the insertion widths WL and WU of all the series resonators S1 through S4.SELECTED DRAWING: Figure 2

Description

The present invention relates to filters and multiplexers.

An acoustic wave device using a piezoelectric thin film resonator is used as a filter and a duplexer of a wireless device such as a mobile phone. The piezoelectric thin film resonator has a structure in which a lower electrode and an upper electrode face each other with a piezoelectric film interposed therebetween. A region where the lower electrode and the upper electrode face each other with the piezoelectric film sandwiched therebetween is a resonance region. It is known to provide an insertion film between the lower electrode and the upper electrode in the region along the outer circumference in the resonance region (for example, Patent Documents 1 to 3).

JP, 2005-95729, A JP, 2016-29766, A JP, 2008-101952, A

By providing the insertion film, the Q value of the piezoelectric thin film resonator is improved. Also, the electromechanical coupling coefficient can be changed by changing the insertion width of the insertion film in the resonance region. However, it is difficult to set the Q value and the electromechanical coupling coefficient of the series resonator and the parallel resonator of the ladder type filter to desired values and the filter characteristics to desired values.

The present invention has been made in view of the above problems, and an object thereof is to set a filter characteristic to a desired characteristic.

The present invention provides a substrate, a first lower electrode provided on the substrate and connected in series between an input terminal and an output terminal, and a first piezoelectric film provided on the first lower electrode, A first upper electrode provided on the first piezoelectric film and a first central region of a first resonance region where the first lower electrode and the first upper electrode face each other with the first piezoelectric film sandwiched therebetween. Not provided, the first outer periphery of the first resonance region is included in at least a portion surrounding the first central region, and the first outer region is provided along the first outer periphery between the first lower electrode and the first upper electrode. A first insertion film, a first piezoelectric thin film resonator having a first width of the first insertion film in a direction orthogonal to a tangent line of the first outer circumference in the first resonance region, and the first piezoelectric film resonator on the substrate. A second lower electrode, a second piezoelectric film provided on the second lower electrode, and a second piezoelectric film provided on the second piezoelectric film and connected in parallel between the input terminal and the output terminal. The second upper electrode is not provided in the second central region of the second resonance region where the second lower electrode and the second upper electrode face each other with the second piezoelectric film interposed therebetween, and the second central region is not provided. A second insertion film that includes a second outer circumference of the second resonance region in at least a part of the surrounding area and is provided along the second outer circumference between the second lower electrode and the second upper electrode; A second width of the second insertion film in a direction orthogonal to a tangent line of the second outer periphery in the second resonance region, the second width being different from the first width of the first piezoelectric thin film resonator; And a piezoelectric thin film resonator.

In the above configuration, a plurality of the first piezoelectric thin film resonators are provided, the first width in each of the first piezoelectric thin film resonators is substantially constant, and the first piezoelectric thin film resonators of the plurality of first piezoelectric thin film resonators are arranged in the first piezoelectric thin film resonators. The first piezoelectric thin film resonators have a plurality of second piezoelectric thin film resonators, and the second width in each of the second piezoelectric thin film resonators is substantially constant. The second widths may be substantially equal.

In the above structure, the first width is W1, the second width is W2, the total thickness of the first lower electrode, the first piezoelectric film, and the first upper electrode in the first resonance region, and When the sum of the total thickness of the second lower electrode, the second piezoelectric film, and the second upper electrode in the second resonance region is λ and an arbitrary natural number is N, N×λ/2−λ/ 8<|W1-W2|<N*[lambda]/2+[lambda]/8.

In the above configuration, 0.7λ+N×λ/2−λ/8<W1<0.7λ+N×λ/2+λ/8 and 0.7λ+N×λ/2−λ/8<W2<0.7λ+N×λ/2+λ/ 8 can be used.

In the above configuration, the first width in the first lower electrode lead-out region where the first lower electrode in the first piezoelectric thin film resonator is led out from the first resonance region, and the first upper electrode is the first resonance region. Different from the first width in the first upper electrode lead-out region drawn from the second upper electrode lead-out region in which the second lower electrode in the second piezoelectric thin film resonator is drawn from the second resonance region. The second width may be different from the second width in the second upper electrode lead-out region where the second upper electrode is pulled out from the second resonance region.

In the above structure, the first width in the first lower electrode lead-out region is WL1, the first width in the first upper electrode lead-out region is WU1, and the second width in the second lower electrode lead-out region is WL2. And the second width in the second upper electrode lead-out region is WU2, the total thickness of the first lower electrode, the first piezoelectric film and the first upper electrode in the first resonance region, and the second width. When the sum of the total thickness of the second lower electrode, the second piezoelectric film, and the second upper electrode in the resonance region is λ, and an arbitrary natural number is N, N×λ/2−λ/8 <|WL1-WL2|<N*[lambda]/2+[lambda]/8 and N*[lambda]/2-[lambda]/8<|WU1-WU2|<N*[lambda]/2+[lambda]/8.

In the above structure, the acoustic impedance of the first insertion film and the second insertion film may be smaller than the acoustic impedance of the first piezoelectric film and the second piezoelectric film.

In the above configuration, the first piezoelectric film and the second piezoelectric film are made of the same piezoelectric material, the thickness of the first piezoelectric film and the thickness of the second piezoelectric film are substantially equal, and the first insertion film and the second insertion film are the same. The second insertion film may be made of the same material, and the thickness of the first insertion film and the thickness of the second insertion film may be substantially equal.

The present invention is a multiplexer including the above filter.

According to the present invention, the filter characteristic can be set to a desired characteristic.

FIG. 1 is a circuit diagram of a filter according to the first embodiment. 2A is a plan view of the piezoelectric thin film resonator according to the first embodiment, FIG. 2B is a plan view of an insertion film, and FIGS. 2C and 2D are FIG. 2A. FIG. FIG. 3 is a diagram showing Q values for the insertion widths WU and WL in the simulation 1. FIGS. 4A and 4B are views showing Q values for the insertion widths WU and WL in the simulation 1, respectively. FIG. 5 is a diagram showing electromechanical coupling coefficients k ² with respect to the insertion widths WU and WL in the simulation 1. FIGS. 6A and 6B are diagrams showing electromechanical coupling coefficients k ² with respect to the insertion widths WU and WL in the simulation 1, respectively. 7A and 7B are plan views of the resonance region and the insertion film of the series resonator and the parallel resonator in the first embodiment. FIG. 8A is a diagram showing the pass characteristic of the filter in the simulation 2, and FIG. 8B is an enlarged view of the pass characteristic in the pass band. FIG. 9A and FIG. 9B are plan views of the resonance region and the insertion film of the series resonator and the parallel resonator in the first modification of the first embodiment. 10A to 10D are cross-sectional views showing the piezoelectric thin film resonators in Modifications 2 to 5 of the first embodiment. 11A to 11D are cross-sectional views showing the piezoelectric thin film resonators in Modifications 6 to 9 of the first embodiment. 12A and 12B are cross-sectional views of the piezoelectric thin film resonators in Modifications 10 and 11 of Example 1. FIG. 13 is a circuit diagram of the duplexer according to the second embodiment.

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

FIG. 1 is a circuit diagram of a filter according to the first embodiment. As shown in FIG. 1, in the filter according to the first embodiment, the series resonators S1 to S4 are connected in series between the input terminal T1 and the output terminal T2. Parallel resonators P1 to P4 are connected in parallel between the input terminal T1 and the output terminal T2. One ends of the parallel resonators P1 to P4 are connected to the ground terminal. The filter causes the output terminal T2 to output a signal in the pass band of the high frequency signal input from the input terminal T1, and suppresses a signal in another frequency band.

2A is a plan view of the piezoelectric thin film resonator according to the first embodiment, FIG. 2B is a plan view of an insertion film, and FIGS. 2C and 2D are FIG. 2A. FIG. FIG. 2C shows a series resonator, and FIG. 2D shows a parallel resonator.

The structure of the series resonators S1 to S4 will be described with reference to FIGS. 2(a) and 2(c). A lower electrode 12 is provided on a substrate 10, which is a silicon (Si) substrate. A void 30 having a dome-shaped bulge is formed between the flat main surface of the substrate 10 and the lower electrode 12. The dome-shaped bulge is, for example, a bulge in which the height of the void 30 is small around the void 30 and the height of the void 30 increases toward the inside of the void 30. The void 30 functions as an acoustic reflection layer that reflects the elastic wave excited by the piezoelectric film 14. The lower electrode 12 includes a lower layer 12a and an upper layer 12b. The lower layer 12a is, for example, a chromium (Cr) film, and the upper layer 12b is, for example, a ruthenium (Ru) film.

On the lower electrode 12, there is provided a piezoelectric film 14 mainly composed of aluminum nitride (AlN) having a (0001) direction as a main axis (that is, having C-axis orientation). The piezoelectric film 14 includes a lower piezoelectric film 14a and an upper piezoelectric film 14b. The lower piezoelectric film 14a is provided on the lower electrode 12, and the upper piezoelectric film 14b is provided between the lower piezoelectric film 14a and the upper electrode 16. An insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b.

The upper electrode 16 is provided on the piezoelectric film 14 so as to have a resonance region 50 that faces the lower electrode 12 with at least a portion of the piezoelectric film 14 interposed therebetween. The resonance region 50 has an elliptical shape and is a region in which elastic waves in the thickness extensional vibration mode resonate. The void 30 includes the resonance region 50 and is larger than the resonance region 50 in a plan view. As a result, the elastic wave excited in the piezoelectric film 14 is reflected by the air gap 30. The upper electrode 16 includes a lower layer 16a and an upper layer 16b. The lower layer 16a is, for example, a ruthenium film, and the upper layer 16b is, for example, a chromium film.

A silicon oxide film is formed as the frequency adjustment film 24 on the upper electrode 16. The laminated film 18 in the resonance region 50 includes the lower electrode 12, the piezoelectric film 14, the upper electrode 16, and the frequency adjustment film 24. The frequency adjustment film 24 may function as a passivation film.

As shown in FIG. 2B, the insertion film 28 is not provided in the central region 54 of the resonance region 50, but is provided in the outer peripheral region 52. That is, the insertion film 28 is provided along the outer periphery 51 including the outer periphery 51 of the resonance region 50 in at least a part surrounding the central region 54. The insertion film 28 has, for example, a ring shape or a shape obtained by cutting a part of the ring shape. The central region 54 is a region within the resonance region 50 and includes the center of the resonance region 50. The center does not have to be the geometric center.

The width of the insertion film 28 in the direction orthogonal to the tangent line of the outer periphery 51 in the resonance region 50 is the insertion width. A region of the resonance region 50 on the side where the lower electrode 12 is drawn out is referred to as a region 56L (lower electrode extraction region), and a region on the side where the upper electrode 16 is extracted is referred to as a region 56U (upper electrode extraction region). The lower electrode 12 is formed larger than the resonance region 50 except for the region 56U so that the area of the resonance region 50 does not change even if misalignment between the lower electrode 12 and the upper electrode 16 occurs. As a result, the area other than the area 56U becomes the area 56L. That is, the region surrounding the resonance region 50 is either the region 56U or 56L. The insertion width of the insertion film 28 in the region 56L is WL, and the insertion width of the insertion film 28 in the region 56U is WU. The insertion widths WL and WU may be the same or different.

In the lead-out region 56L of the lower electrode 12, the upper end of the end face of the upper piezoelectric film 14b substantially matches the contour of the resonance region 50, and the end face of the upper piezoelectric film 14b is inclined so that the lower end is located outside. The end surface of the lower piezoelectric film 14 a is located outside the contour of the resonance region 50. This improves the characteristics such as the Q value.

As shown in FIG. 2A, the introduction path 33 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 33 is not covered with the piezoelectric film 14, and the lower electrode 12 has a hole 35 at the tip of the introduction path 33.

The structure of the parallel resonators P1 to P4 will be described with reference to FIG. The parallel resonators P1 to P4 are different from the series resonators S1 to S4 in that a mass load film 20 made of a titanium (Ti) layer is provided between the lower layer 16a and the upper layer 16b of the upper electrode 16. Therefore, the laminated film 18 includes the laminated film of the series resonators S1 to S4 and the mass load film 20 formed on the entire surface in the resonance region 50. Other configurations are the same as those of the series resonators S1 to S4 shown in FIG.

The difference in resonance frequency between the series resonators S1 to S4 and the parallel resonators P1 to P4 is adjusted using the thickness of the mass load film 20. The resonance frequencies of both the series resonators S1 to S4 and the parallel resonators P1 to P4 are adjusted by adjusting the film thickness of the frequency adjusting film 24.

As the substrate 10, other than the silicon substrate, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a quartz substrate, a glass substrate, a ceramic substrate, a GaAs substrate, or the like can be used. As the lower electrode 12 and the upper electrode 16, in addition to ruthenium and chromium, aluminum (Al), titanium, copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium ( A single layer film such as Rh) or iridium (Ir) or a laminated film thereof can be used. For example, the lower layer 16a of the upper electrode 16 may be Ru and the upper layer 16b may be Mo.

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

The insertion film 28 is a material having a Young's modulus and/or acoustic impedance smaller than that of the piezoelectric film 14. As the insertion film 28, in addition to silicon oxide, a single layer film of aluminum (Al), gold (Au), copper, titanium, platinum, tantalum, chromium, or the like, or a laminated film thereof can be used.

As the frequency adjustment film 24, a silicon nitride film, an aluminum nitride film, or the like can be used instead of the silicon oxide film. As the mass load film 20, other than titanium, a metal film exemplified as the lower electrode 12 and the upper electrode 16 or an insulating film such as silicon nitride or silicon oxide can be used.

[Simulation 1]
The insertion width WL and WU of the insertion film 28 were changed, and the Q value and the electromechanical coupling coefficient were two-dimensionally simulated using the finite element method.
The simulation conditions are as follows.
Lower layer 12a of lower electrode 12: chromium film having a thickness of 99 nm Upper layer 12b of lower electrode 12: ruthenium film having a thickness of 198 nm Lower piezoelectric film 14a: aluminum nitride film having a thickness of 623 nm Upper piezoelectric film 14b: thickness of 623 nm Aluminum nitride film of lower electrode 16a of upper electrode 16: ruthenium film having a thickness of 238 nm Upper layer 16b of upper electrode 16 of chromium film having a thickness of 35 nm Insertion film 28: silicon oxide film having a thickness of 150 nm Resonance region 50: length Is 84 μm
The total thickness of the lower electrode 12, the piezoelectric film 14, and the upper electrode 16 is approximately half the wavelength of the elastic wave. Therefore, the wavelength λ of the elastic wave is about 3632 nm.

FIG. 3 is a diagram showing Q values for the insertion widths WU and WL in the simulation 1. FIGS. 4A and 4B are views showing Q values for the insertion widths WU and WL in the simulation 1, respectively. 4A is a Q value for WU when the insertion width WL in the straight line 59U in FIG. 3 is 2.2 μm, and FIG. 4B is when the insertion width WU in the straight line 59L in FIG. 3 is 2.8 μm. It is a figure which shows the Q value with respect to WL of. Qa is the Q value at the anti-resonance frequency.

As shown in FIGS. 3 to 4B, the Q value periodically changes with respect to the insertion widths WL and WU. The period of fluctuation is approximately λ/2, that is, about 1.816 μm. The peak of the Q value with the smallest insertion width WU is when the WU is about 2.7 μm (about 0.74λ). The peak of the Q value with the smallest insertion width WL is when WL is about 2.5 μm (about 0.69λ). Thus, when the insertion widths WL and WU are about 0.7λ, the Q value has the first peak.

FIG. 5 is a diagram showing electromechanical coupling coefficients k ² with respect to the insertion widths WU and WL in the simulation 1. FIGS. 6A and 6B are diagrams showing electromechanical coupling coefficients k ² with respect to the insertion widths WU and WL in the simulation 1, respectively. 6A shows an electromechanical coupling coefficient k ^{2 with} respect to WU when the insertion width WL on the straight line 59U in FIG. 5 is 2.2 μm, and FIG. 6B shows an insertion width WU on the straight line 59L in FIG. it is a diagram illustrating an electromechanical coupling coefficient ^{k 2} for WL when the .8Myuemu.

As shown in FIGS. 5 to 6B, the electromechanical coupling coefficient k ² becomes uniformly smaller as the insertion widths WL and WU become larger. Very little variation with the insertion width, such as the Q value, is observed.

If the insertion widths WL and WU are selected so that the Q value has a peak as in the simulation 1, the electromechanical coupling coefficient k ² can be set to a desired value without lowering the Q value.

7A and 7B are plan views of the resonance region and the insertion film of the series resonator and the parallel resonator in the first embodiment. As shown in FIG. 7A, the insertion widths WU1 and WL1 are substantially equal in the series resonators S1 to S4. As shown in FIG. 7B, the insertion widths WU2 and WL2 are substantially equal in the parallel resonators P1 to P4.

[Simulation 2]
The pass width of the filter was simulated by making the insertion widths WU1 and WL1 of the series resonators S1 to S4 different from the insertion widths WU2 and WL2 of the parallel resonators P1 to P4.
The simulation conditions are as follows.
Example 1
Insertion width WU1 and WL1 of series resonators S1 to S4: 2.8 μm
Insertion widths WU2 and WL2 of parallel resonators P1 to P4: 6.5 μm
Comparative Example 1
Insertion width WU1 and WL1 of series resonators S1 to S4: 2.8 μm
Insertion width WU2 and WL2 of parallel resonators P1 to P4: 2.8 μm
The other conditions are the same as in the simulation 1.

In the first embodiment, the difference in insertion width between the series resonators S1 to S4 and the parallel resonators P1 to P4 is 3.7 μm, which is approximately λ. In Comparative Example 1, the series resonators S1 to S4 and the parallel resonators P1 to P4 have the same insertion width.

⁶ is a diagram showing a Q value Qr at a resonant frequency, a Q value Qa at an antiresonant frequency, and an electromechanical coupling coefficient k ² of the series resonators S1 to S4 and the parallel resonators P1 to P4 in Example 1 and Comparative Example 1. FIG.

As shown in Table 1, in Example 1, the electromechanical coupling coefficient k ² of the parallel resonators P1 to P4 can be made lower than that in Comparative Example 1, and Qr and Qa can be made approximately the same as those in Comparative Example 1.

FIG. 8A is a diagram showing the pass characteristic of the filter in the simulation 2, and FIG. 8B is an enlarged view of the pass characteristic in the pass band. As shown in FIG. 8A, the pass characteristics and the attenuation characteristics of Example 1 and Comparative Example 1 are almost the same. As shown in FIG. 8B, the loss in the pass band is smaller in Example 1 than in Comparative Example 1. Further, the low frequency end of the pass band of Example 1 is lower than that of Comparative Example 1.

As in the simulation 2, by lowering the electromechanical coupling coefficient k ² of the parallel resonators P1 to P4, it is possible to lower the other frequency end of the pass band and widen the band.

The ladder-type filter, a larger electromechanical coupling coefficient k ² from the series resonators S1 S4, the higher the sharpness of the high-frequency end of the pass band, when reduced, so high frequency end is widened passband. Increasing the electromechanical coupling coefficient k ² of the parallel resonators P1 to P4, the higher the sharpness of the low frequency end of the pass band, when reduced, so the low frequency end bandwidth of the passband. When the electromechanical coefficient k ² from the series resonators S1 S4 to increase, the higher the sharpness of the high-frequency end of the pass band, when reduced, so high frequency end is widened passband.

According to the first embodiment, in the series resonators S1 to S4 (one or more first piezoelectric thin film resonators), the insertion film 28 (first insertion film) surrounds at least the central region 54 (first central region). A part of the piezoelectric film 14 between the lower electrode 12 (first lower electrode) and the upper electrode 16 (first upper electrode) along the outer periphery 51 (first outer periphery) of the resonance region 50 (first resonance region). The first piezoelectric film). The insertion width (first width) of the insertion film 28 in the direction orthogonal to the tangent line of the outer periphery 51 in the resonance region 50 is WL1 and WU1.

In the parallel resonators P1 to P4 (one or more second piezoelectric thin film resonators), the insertion film 28 (second insertion film) has the resonance region 50 (at least in part) surrounding the central region 54 (second central region). Inserted into the piezoelectric film 14 (second piezoelectric film) between the lower electrode 12 (second lower electrode) and the upper electrode 16 (second upper electrode) along the outer circumference 51 (second outer circumference) of the second resonance region). Has been done. The insertion width (second width) of the insertion film 28 in the direction orthogonal to the tangent line of the outer periphery 51 in the resonance region 50 is WL2 and WU2. The insertion widths WL2 and WU2 of the parallel resonators P1 to P4 are different from all the insertion widths WL1 and WU1 of the series resonators S1 to S4. Thereby, the filter characteristic can be set to a desired characteristic.

The insertion widths WU1 and WL1 of the series resonators S1 to S4 are substantially constant, and the insertion widths WU1 and WL1 of the series resonators S1 to S4 are substantially equal to each other. The insertion widths WU2 and WL2 of the parallel resonators P1 to P4 are substantially constant, and the insertion widths WU2 and WL2 of the parallel resonators P1 to P4 are substantially equal to each other. This allows the series resonators S1 to S4 to have substantially the same characteristics and the parallel resonators P1 to P4 to have substantially the same characteristics. It should be noted that the insertion widths being substantially constant and being substantially equal, for example, allow variations in the range of ±λ/16 and allow variations in the range of ±λ/32.

The insertion widths WU1 and WL1 of the series resonators S1 to S4 are W1, and the insertion widths WU2 and WL2 of the parallel resonators P1 to P4 are W2. When N is a natural number, N×λ/2−λ/8<|W1−W2|<N×λ/2+λ/8. As a result, W1 and W2 are approximately λ/2×N. Therefore, it is possible to make the Q values of the series resonators S1 to S4 and the parallel resonators P1 to P4 about the same and to make the electromechanical coupling coefficient k ² of the series resonators S1 to S4 and the parallel resonators P1 to P4 different. it can. Thereby, the filter characteristic can be set to a desired characteristic.

The wavelength of the elastic wave in the thickness extensional vibration mode that is mainly excited in the resonance region 50 is the thickness of the laminated film 18×2. The thickness of the laminated film 18 is almost the total thickness of the lower electrode 12, the piezoelectric film 14, and the upper electrode 16. The wavelength λ of the elastic wave is the average of the wavelengths of the elastic waves of the series resonators S1 to S4 and the parallel resonators P1 to P4. At this time, λ is the total thickness of the lower electrode 12, the piezoelectric film 14 and the upper electrode 16 in the resonance region 50 of the series resonators S1 to S4 and the lower electrode 12 and the piezoelectric film in the resonance region 50 of the parallel resonators P1 to P4. 14 and the total thickness of the upper electrode 16 are added.

As W1-W2, N*[lambda]/2-[lambda]/16<|W1-W2|<N*[lambda]/2+[lambda]/16 is more preferable.

As shown in FIGS. 3 to 4B, the peak of the first Q value is approximately 0.7λ, and therefore 0.7λ+N×λ/2−λ/8<W1<0.7λ+N×λ/2+λ/ 8 and 0.7λ+N×λ/2−λ/8<W2<0.7λ+N×λ/2+λ/8. As a result, the Q values of the series resonators S1 to S4 and the parallel resonators P1 to P4 can be increased. Therefore, the loss of the pass band can be suppressed. 0.7λ+N×λ/2−λ/16<W1<0.7λ+N×λ/2+λ/16 and 0.7λ+N×λ/2−λ/16<W2<0.7λ+N×λ/2+λ/16 are preferable.

[Modification 1 of Embodiment 1]
FIG. 9A and FIG. 9B are plan views of the resonance region and the insertion film of the series resonator and the parallel resonator in the first modification of the first embodiment. As shown in FIG. 9A, in the series resonators S1 to S4, the insertion width WU1 is wider than WL1. As shown in FIG. 9B, in the parallel resonators P1 to P4, the insertion width WU2 is wider than WL2. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted.

As an example, WU1=3.2 μm, WL1=2.6 μm, WU2=6.8 μm, and WL2=6.2 μm. WU2-WU1=WL2-WL1=3.6 μm, which is approximately λ. As shown in FIG. 3 to FIG. 4B, the introduction width at which the Q value reaches the peak may be slightly deviated between the regions 56U and 56L. This is because the structures of the outer periphery 51 of the resonance region 50 are different between the regions 56L and 56U. For example, in FIGS. 2A to 2D, the piezoelectric film 14 does not have an end face on the outer periphery of the resonance region 50 in the region 56U, but the piezoelectric film 14 has an end face near the outer periphery of the resonance region 50 in the region 56L. have.

In such a case, WU1 (first width in the first upper electrode lead-out region) and WL1 (first width in the first lower electrode lead-out region) in each of the series resonators S1 to S4 are made different, and the parallel resonator P1 is set. WU2 (second width in the second upper electrode lead-out region) and WL2 (second width in the second lower electrode lead-out region) in each of P1 to P4 are made different. The series resonators S1 to S4 preferably have substantially the same WU1 and WL1 which are substantially equal to each other, and the parallel resonators P1 to P4 preferably have the same WU2 and WL2 which are substantially equal to each other.

Further, N×λ/2−λ/8<|WL1-WL2|<N×λ/2+λ/8 and N×λ/2−λ/8<|WU1-WU2|<N×λ/2+λ/8 To do. The Q values of the series resonators S1 to S4 and the parallel resonators P1 to P4 can be set to be approximately the same, and the electromechanical coupling coefficient k ² of the series resonators S1 to S4 and the parallel resonators P1 to P4 can be made different. N*[lambda]/2-[lambda]/16<|WL1-WL2|<N*[lambda]/2+[lambda]/16 and N*[lambda]/2-[lambda]/16<|WU1-WU2|<N*[lambda]/2+[lambda]/16 are preferred.

When the series resonators S1 to S4 and the parallel resonators P1 to P4 are formed on the same substrate 10, the piezoelectric films 14 of the series resonators S1 to S4 and the parallel resonators P1 to P4 are made of the same piezoelectric material. The thickness is approximately equal to the manufacturing error. Further, the insertion films 28 of the series resonators S1 to S4 and the parallel resonators P1 to P4 are made of the same material, and the thickness of the insertion film 28 is approximately equal to the manufacturing error. As a result, the difference between WU1 and WU2 is set to approximately λ/2×N, and the difference between WL1 and WL2 is set to approximately λ/2×N, whereby series resonators S1 to S4 and parallel resonators P1 to P4 are connected. Can be made to have substantially the same Q value.

Further, the lower electrodes 12 of the series resonators S1 to S4 and the parallel resonators P1 to P4 are made of the same metal material, and the thickness of the lower electrode 12 is approximately equal to the manufacturing error. The upper electrodes 16 of the series resonators S1 to S4 and the parallel resonators P1 to P4 are made of the same metal material, and the thickness of the upper electrode 16 is approximately equal to the manufacturing error.

10A to 11D are cross-sectional views showing the piezoelectric thin film resonators according to Modifications 2 to 9 of the first embodiment. As shown in FIG. 10A, in the second modification of the first embodiment, the insertion film 28 is provided between the piezoelectric film 14 and the upper electrode 16. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted. As shown in FIG. 10B, in Modification 3 of Example 1, the insertion film 28 is provided in the region 56U and not provided in the region 56L. The rest of the configuration is the same as that of the second modification of the first embodiment, and a description thereof will be omitted.

As shown in FIG. 10C, in Modification 4 of Example 1, the insertion film 28 is provided between the lower electrode 12 and the piezoelectric film 14. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted. As shown in FIG. 10D, in the modified example 5 of the first embodiment, the insertion film 28 is provided in the region 56U and not provided in the region 56L. The other configurations are the same as those of the modified example 4 of the first embodiment, and the description thereof will be omitted.

As shown in FIG. 11A, in Modification 6 of Example 1, two insertion films 28 are provided between the lower piezoelectric film 14 a and the upper piezoelectric film 14 b and between the piezoelectric film 14 and the upper electrode 16. Has been. The other configuration is the same as that of the first embodiment, and the description is omitted. As shown in FIG. 11B, in Modification 7 of Example 1, the insertion film 28 is provided in the region 56U and not provided in the region 56L. The other configurations are the same as those in the modified example 6 of the first embodiment, and the description thereof will be omitted.

As shown in FIG. 11C, in Modification 8 of Example 1, two layers of the insertion film 28 are provided between the lower piezoelectric film 14 a and the upper piezoelectric film 14 b and between the lower electrode 12 and the piezoelectric film 14. Has been. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted. As shown in FIG. 11D, in the ninth modification of the first embodiment, the insertion film 28 is provided in the region 56U and not provided in the region 56L. The other configurations are the same as those of the modified example 8 of the first embodiment, and the description thereof will be omitted.

As in the modifications 2 and 5 of the first embodiment, one or a plurality of insertion films 28 may be provided between the lower electrode 12 and the upper electrode 16.

As in the modified examples 3, 5, 7, and 9 of the first embodiment, the insertion film 28 may be provided in at least a part surrounding the central region 54. When the insertion film 28 is not provided in the region 56L, the end surface of the piezoelectric film 14 is preferably located inside the end surface of the upper electrode 16. Thereby, the Q value can be improved.

As in the modified examples 6 to 9 of the first embodiment, the insertion film 28 may be provided in two or more layers in the thickness direction of the piezoelectric film 14. When two or more layers of the insertion film 28 are provided, it is preferable that all the insertion films 28 have the relationship of the insertion width shown in Example 1 and its modification 1, but at least one layer is formed in Example 1 and the same. It suffices to have the relationship of the insertion width shown in the first modification.

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

[Modification 11 of Embodiment 1]
FIG. 12B is a cross-sectional view of the piezoelectric thin film resonator in Modification 11 of Example 1. As shown in FIG. 12B, the acoustic reflection film 31 is formed below the lower electrode 12 in the resonance region 50. The acoustic reflection film 31 is formed by alternately providing a film 30a having a low acoustic impedance and a film 30b having a high acoustic impedance. The film thickness of each of the films 30a and 30b is, for example, approximately λ/4 (λ is the wavelength of the elastic wave). The number of stacked films 30a and 30b can be set arbitrarily. The acoustic reflection film 31 may be formed by laminating at least two types of layers having different acoustic characteristics with a gap. The substrate 10 may be one of at least two types of layers having different acoustic characteristics of the acoustic reflection film 31. For example, the acoustic reflection film 31 may have a structure in which one film having different acoustic impedances is provided in the substrate 10. The other configuration is the same as that of the first embodiment, and the description is omitted.

In the example 1 and its modified examples 1 to 9, the void 30 may be formed as in the modified example 10 of the example 1, and as in the modified example 11 of the example 1, the acoustic reflection film 31 is used instead of the void 30. May be formed.

As in the first embodiment and its modified examples 1 to 10, the piezoelectric thin film resonator may be an FBAR (Film Bulk Acoustic Resonator) in which the void 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. .. Further, as in the modified example 11 of the first embodiment, the piezoelectric thin film resonator includes an SMR (Solidly Mounted Resonator) including the acoustic reflection film 31 that reflects the acoustic wave propagating through the piezoelectric film 14 under the lower electrode 12 in the resonance region 50. ) Is OK. The acoustic reflection layer including the resonance region 50 may include the void 30 or the acoustic reflection film 31.

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

The second embodiment is an example of a duplexer using the filters of the first embodiment and its modification. FIG. 13 is a circuit diagram of the duplexer according to the second embodiment. As shown in FIG. 13, the transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. The reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes a signal in the transmission band of the signals input from the transmission terminal Tx as a transmission signal to the common terminal Ant and suppresses signals of other frequencies. The reception filter 42 passes a signal in the reception band out of 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 40 and the reception filter 42 can be the filter of the first embodiment and its modification.

A duplexer has been described as an example of the multiplexer, but 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 alterations are possible 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 24 frequency adjustment film 28 insertion film 30 void 31 acoustic reflection film 40 transmission filter 42 reception filter 50 resonance region 52 outer peripheral region 54 central region 56U, 56L region

Claims (9)

Board,
A first lower electrode provided on the substrate and connected in series between an input terminal and an output terminal, a first piezoelectric film provided on the first lower electrode, and a first piezoelectric film on the first piezoelectric film. The provided first upper electrode is not provided in the first central region of the first resonance region where the first lower electrode and the first upper electrode are opposed to each other with the first piezoelectric film interposed therebetween, and the first central region is not provided. A first insertion film provided between the first lower electrode and the first upper electrode along the first outer circumference, including a first outer circumference of the first resonance region in at least a part surrounding the region; A first piezoelectric thin film resonator having a first width of the first insertion film in a direction orthogonal to a tangent line of the first outer circumference in the first resonance region;
A second lower electrode provided on the substrate and connected in parallel between the input terminal and the output terminal; a second piezoelectric film provided on the second lower electrode; and a second piezoelectric film. The second upper electrode provided above is not provided in the second central region of the second resonance region where the second lower electrode and the second upper electrode face each other with the second piezoelectric film interposed therebetween, and the second central region is not provided. 2. A second insertion film provided at least in a part surrounding the central region, including a second outer periphery of the second resonance region, and provided along the second outer periphery between the second lower electrode and the second upper electrode. And having a second width of the second insertion film in a direction orthogonal to a tangent line of the second outer periphery in the second resonance region, the second width being the first width of the first piezoelectric thin film resonator. A second piezoelectric thin film resonator having a different width,
A filter with. A plurality of the first piezoelectric thin film resonators are provided, the first width in each of the first piezoelectric thin film resonators is substantially constant, and the first widths of the plurality of first piezoelectric thin film resonators are substantially the same. equally,
A plurality of the second piezoelectric thin film resonators are provided, the second width in each of the second piezoelectric thin film resonators is substantially constant, and the second widths of the plurality of second piezoelectric thin film resonators are substantially the same. A filter according to claim 1, which is equal. The first width is W1, the second width is W2, the total thickness of the first lower electrode, the first piezoelectric film, and the first upper electrode in the first resonance region, and the second resonance region. When the sum of the total thickness of the second lower electrode, the second piezoelectric film, and the second upper electrode at is λ and an arbitrary natural number is N,
N×λ/2−λ/8<|W1-W2|<N×λ/2+λ/8
The filter according to claim 2, wherein 0.7λ+N×λ/2−λ/8<W1<0.7λ+N×λ/2+λ/8 and 0.7λ+N×λ/2−λ/8<W2<0.7λ+N×λ/2+λ/8
The filter according to claim 3, wherein A first width in a first lower electrode lead-out region where the first lower electrode in the first piezoelectric thin film resonator is pulled out from the first resonance region, and a first upper electrode pulled out from the first resonance region. 1 Different from the first width in the upper electrode lead-out region,
A second width in a second lower electrode lead-out region where the second lower electrode of the second piezoelectric thin film resonator is pulled out of the second resonance region, and a second upper electrode which is pulled out of the second resonance region. The filter according to claim 1, wherein the second width is different from the second upper electrode lead-out region. The first width in the first lower electrode lead-out region is WL1, the first width in the first upper electrode lead-out region is WU1, the second width in the second lower electrode lead-out region is WL2, and 2 The second width in the upper electrode lead-out region is WU2, the total thickness of the first lower electrode, the first piezoelectric film and the first upper electrode in the first resonance region, and the second resonance region in the second resonance region. When the sum of the total thickness of the second lower electrode, the second piezoelectric film, and the second upper electrode is λ, and an arbitrary natural number is N,
N×λ/2−λ/8<|WL1-WL2|<N×λ/2+λ/8 and N×λ/2−λ/8<|WU1-WU2|<N×λ/2+λ/8
The filter according to claim 5, wherein The filter according to claim 1, wherein acoustic impedances of the first insertion film and the second insertion film are smaller than acoustic impedances of the first piezoelectric film and the second piezoelectric film. The first piezoelectric film and the second piezoelectric film are made of the same piezoelectric material, the thickness of the first piezoelectric film and the thickness of the second piezoelectric film are substantially equal to each other, and the first insertion film and the second insertion film are formed. 7. The filter according to claim 3, which is made of the same material, and the thickness of the first insertion film and the thickness of the second insertion film are substantially equal to each other. A multiplexer comprising the filter according to any one of claims 1-8.

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