JP2020027987A - Piezoelectric thin film resonator, filter, and multiplexer - Google Patents

Abstract

To miniaturize a piezoelectric thin film resonator.SOLUTION: A piezoelectric thin film resonator includes: a substrate; a lower electrode provided on the substrate; an upper electrode provided on the lower electrode: and a piezoelectric film provided on the lower electrode, and having a first region and a second region in a resonance region where the lower electrode and the upper electrode faces each other, the first region having a first thickness different from a second thickness of the second region, the second thickness being 2/3 times or more and 4/3 times or less of the first thickness, and an area of the second region in plan view being 1/3 times or less of an area of the resonance region in plan view.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a piezoelectric thin film resonator, a filter, and a multiplexer.

  2. Description of the Related Art Filters and multiplexers using a piezoelectric thin-film resonator are widely 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 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 across the piezoelectric film is a resonance region. It is known that spurious is suppressed by increasing the thickness of the piezoelectric layer at the periphery of the resonance region (for example, Patent Document 1). It is known that the thickness of the temperature compensation film in the resonance region is made different, and the thickness of the piezoelectric layer is made different in order to reduce the deviation of the resonance frequency in the resonance region (for example, Patent Document 2).

JP 2005-159402 A JP 2008-219237 A

  A capacitor may be connected in parallel with the piezoelectric thin-film resonator to reduce the anti-resonance frequency. However, providing a capacitor in the piezoelectric thin-film resonator increases the size.

  The present invention has been made in view of the above problems, and has as its object to reduce the size.

  According to the present invention, a substrate, a lower electrode provided on the substrate, an upper electrode provided on the lower electrode, and an upper electrode provided on the lower electrode, wherein the lower electrode and the upper electrode face each other. A first region and a second region within the resonance region, wherein a first thickness of the first region is different from a second thickness of the second region, and the second thickness is two times the first thickness. And a piezoelectric film, wherein the area of the second region in plan view is not more than 1/3 times the area of the resonance region in plan view. is there.

  In the above configuration, the second thickness may be smaller than the first thickness.

  In the above configuration, the second thickness may be larger than the first thickness.

  In the above configuration, a lower reflective surface located below the lower electrode that reflects the elastic wave propagating through the piezoelectric film, and an upper reflective surface located above the upper electrode that reflects the elastic wave, comprising: The difference between a first distance between the lower reflecting surface and the upper reflecting surface in one region and a second distance between the lower reflecting surface and the upper reflecting surface in the second region is the third distance. The configuration may be substantially equal to the difference between the first thickness and the second thickness.

  The present invention relates to a resonance region in which a first terminal, a second terminal, and a pair of electrodes are connected in series to a path between the first terminal and the second terminal, and a pair of electrodes face each other with at least a part of the piezoelectric film interposed therebetween. One or more first series resonators having a substantially uniform thickness of the piezoelectric film therein, and the one or more first series resonators connected to the path in series with the one or more first series resonators. Alternatively, the filter includes a plurality of second series resonators and one or more parallel resonators connected between the path and the ground.

  In the above configuration, at least one anti-resonance frequency of the one or more second series resonators is one of the anti-resonance frequencies of the one or more first series resonators and the one or more second series resonators. It can be the lowest configuration.

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

  The present invention is a multiplexer including the above filter.

  According to the present invention, size reduction can be achieved.

FIGS. 1A to 1C are circuit diagrams of filters according to Comparative Examples 1 to 3. FIG. FIG. 2 is a diagram illustrating examples of the pass characteristics of Comparative Examples 1 to 3. FIG. 3A and FIG. 3B are a plan view and a cross-sectional view of the piezoelectric thin-film resonator according to the first embodiment. FIGS. 4A and 4B are cross-sectional views of piezoelectric thin-film resonators according to Modification Example 1 of Example 1 and Comparative Example 4. FIG. FIG. 5 is a diagram illustrating pass characteristics of the piezoelectric thin-film resonators according to Example 1, Modification Example 1 of Example 1, and Comparative Example 4. FIG. 6 is a diagram showing an equivalent circuit of the piezoelectric thin-film resonator. FIGS. 7A and 7B are diagrams showing ΔC with respect to ΔS and ΔT, respectively. FIGS. 8A and 8B are cross-sectional views of piezoelectric thin-film resonators according to Modifications 2 and 3 of the first embodiment. FIG. 9 is a sectional view of a piezoelectric thin-film resonator according to Modification 4 of Example 1. FIGS. 10A to 10C are plan views illustrating examples of the resonance region according to the first embodiment and its modification. FIG. 11 is a plan view of the ladder-type filter according to the second embodiment. FIG. 12 is a diagram illustrating pass characteristics of the ladder-type filter according to the second embodiment. FIG. 13 is a circuit diagram of a duplexer according to a first modification of the second embodiment.

  FIGS. 1A to 1C are circuit diagrams of filters according to Comparative Examples 1 to 3. FIG. As shown in FIG. 1A, in Comparative Example 1, series resonators S1 to S4 are connected in series between an input terminal Tin and an output terminal Tout, and parallel resonators P1 to P3 are connected in parallel.

  As shown in FIG. 1B, in Comparative Example 2, a capacitor C is connected in parallel with the series resonator S2. As shown in FIG. 1C, in Comparative Example 3, a resonator R is connected in parallel with the series resonator S2. The resonator R has a different resonance frequency from the series resonators S1 to S4 and the parallel resonators P1 to P3, and functions as a capacitor.

  FIG. 2 is a diagram illustrating examples of the pass characteristics of Comparative Examples 1 to 3. As shown in FIG. 2, Comparative Examples 1 to 3 function as bandpass filters. As shown in FIG. 2, in Comparative Examples 2 and 3, the skirt characteristic on the high frequency side of the pass band is steeper than in Comparative Example 1. This is because, in a resonance circuit including the series resonator S2 and the capacitor C or the resonator R, the resonance frequency is almost the same as the series resonator S2, and the antiresonance frequency is lower than the series resonator S2.

  By connecting a capacitor or a resonator in parallel to the resonator as in Comparative Examples 2 and 3, the characteristics of the resonance circuit can be changed. However, when the capacitor C or the resonator R is connected, the size of the resonance circuit increases.

  FIG. 3A and FIG. 3B are a plan view and a cross-sectional view of the piezoelectric thin-film resonator according to the first embodiment. FIG. 3B is a sectional view taken along line AA of FIG.

  As shown in FIGS. 3A and 3B, a lower electrode 12 is provided on a substrate 10. A gap 30 is formed between the substrate 10 and the lower electrode 12. A piezoelectric film 14 is provided on the lower electrode 12. An upper electrode 16 is provided on the piezoelectric film 14. The frequency adjustment film 20 is provided on the upper electrode 16. A protection film 24 is provided so as to cover upper electrode 16 and lower electrode 12.

  A region where the lower electrode 12 and the upper electrode 16 face each other with at least a part of the piezoelectric film 14 interposed therebetween is a resonance region 50. The resonance region 50 is a region where elastic waves in the thickness longitudinal vibration mode resonate. The air gap 30 is provided so as to include the resonance region 50 in a plan view. The protective film 24 from the lower electrode 12 in the resonance region 50 is the laminated film 18 in which elastic waves resonate. The elastic waves are reflected on the upper surface and the lower surface of the laminated film 18.

  Regions 52 and 54 are provided in the resonance region 50. The area of the region 54 is smaller than the area of the region 52. For example, the area of the region 54 is equal to or less than １ ／ of the area of the resonance region 50. A projection is provided on the upper surface of the piezoelectric film 14. The thickness T1 of the piezoelectric film 14 in the region 52 is larger than the thickness T2 of the piezoelectric film 14 in the region 54. The thickness T3 of the laminated film 18 in the region 52 is larger than the thickness T4 of the laminated film 18 in the region 54. T3-T4 is approximately T1-T2. It is preferable that the thickness T1 of the piezoelectric film 14 in the region 52 is substantially uniform, and the thickness T2 of the piezoelectric film 14 in the region 54 is substantially uniform.

  The substrate 10 is, for example, a silicon substrate, a sapphire substrate, a spinel substrate, a glass substrate, or a quartz substrate. The piezoelectric film 14 is, for example, an aluminum nitride substrate, a lithium tantalate substrate, a lithium niobate substrate, or a quartz substrate. When an aluminum nitride layer is used as the piezoelectric film 14, an element that enhances piezoelectricity may be added.

  The lower electrode 12 and the upper electrode 16 are made of, for example, Ru (ruthenium), Cr (chromium), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), It is a single layer film of platinum (Pt), rhodium (Rh), iridium (Ir), or the like, or a laminated film of these.

  The frequency adjustment film 20 is a film for adjusting the resonance frequency, and is, for example, a metal film exemplified as the lower electrode 12 and the upper electrode 16, or an insulating film such as a silicon oxide film or a silicon nitride film. The protective film 24 is an insulating film such as a silicon oxide film, a silicon nitride film, or an aluminum oxide film.

  In the case of a piezoelectric thin-film resonator having a resonance frequency of 2 GHz, the lower electrode 12 is, for example, a Cr film having a thickness of 100 nm and a Ru film having a thickness of 210 nm. The piezoelectric film 14 is, for example, an aluminum nitride film having a thickness of 1100 nm. The upper electrode 16 is, for example, a Ru film having a thickness of 230 nm and a Cr film having a thickness of 50 nm. The frequency adjusting film 20 is, for example, a Ti film having a thickness of 120 nm. The protective film 24 is, for example, a silicon oxide film having a thickness of 50 nm.

[Modification 1 of Embodiment 1]
FIG. 4A is a cross-sectional view of a piezoelectric thin-film resonator according to a first modification of the first embodiment. As shown in FIG. 4A, in the first modification of the first embodiment, the thickness T2 of the piezoelectric film 14 in the region 54 is larger than the thickness T1 of the piezoelectric film 14 in the region 52. Thus, the thickness T4 of the laminated film 18 in the region 54 is larger than the thickness T3 of the laminated film 18 in the region 52. Other configurations are the same as those of the first embodiment, and a description thereof will be omitted.

[Comparative Example 4]
FIG. 4B is a cross-sectional view of the piezoelectric thin-film resonator according to Comparative Example 4. As shown in FIG. 4B, in Comparative Example 4, the thickness T1 of the piezoelectric film 14 in the resonance region 50 is substantially uniform, and the thickness T3 of the laminated film 18 is substantially uniform. Other configurations are the same as those of the first embodiment, and a description thereof will be omitted.

[Simulation 1]
Passage characteristics were simulated for Example 1, Modification 1 of Example 1, and Comparative Example 4.
Area of resonance region 50: 14000 μm ²
Area of region 52: 3200 μm ²
Thickness T1: 1 μm
Thickness T2: 0.667 μm (Example 1)
1.333 μm (Modification 1 of Example 1)

  FIG. 5 is a diagram illustrating pass characteristics of the piezoelectric thin-film resonators according to Example 1, Modification Example 1 of Example 1, and Comparative Example 4. As shown in FIG. 5, the resonance frequency fr of the first embodiment, the first modification of the first embodiment, and the comparative example 4 are almost the same. The anti-resonance frequency fa1 of Example 1 is lower than the anti-resonance frequency fa0 of Comparative Example 4. The anti-resonance frequency fa2 of the first modification of the first embodiment is higher than the anti-resonance frequency fa0 of the fourth comparative example.

  FIG. 6 is a diagram showing an equivalent circuit of the piezoelectric thin-film resonator. When the piezoelectric thin film resonator is a one-port resonator, an equivalent circuit uses an mBVD (modified Butterworth Van Dyke) model. As shown in FIG. 6, a path in which the inductor L1, the capacitor C1, and the resistor R1 are connected in series and a path in which the capacitor Co and the resistor Ro are connected in series are connected in parallel between the terminals T01 and T02. Have been. A resistor Rs is connected in series with the two paths. The capacitor Co is the capacitance of the one-port resonator. The resistance Ro is a leakage resistance. The inductor L1 and the capacitor C1 exhibit mechanical resonance. The resistance R1 is a mechanical resonance resistance. The resistance Rs is the resistance of the electrode.

  The capacitor Co is mainly a capacitance between the lower electrode 12 and the upper electrode 16. In the first embodiment, the capacitor Co in the region 54 is larger than that in the comparative example 4. In the simulation of FIG. 5, the increase of the capacitor Co from Comparative Example 4 is 0.2 pF. As a result, the electromechanical coupling coefficient decreases and the anti-resonance frequency fa1 becomes lower than fa0. In the first modification of the first embodiment, the capacitor Co in the region 54 is smaller than that in the fourth comparative example. In the simulation of FIG. 5, the reduction of the capacitor Co from Comparative Example 4 is 0.2 pF. Thereby, the electromechanical coupling coefficient increases and the anti-resonance frequency fa2 becomes higher than fa0.

  Simulations were performed in the case where the thickness T2 in the first embodiment and its modification 1 was constant and the area of the region 54 was changed, and in the case where the thickness of the region 54 was constant and the thickness T2 was changed. S54 / S50 × 100 [%], which is the area S54 of the region 54 with respect to the area S50 of the resonance region 50, was defined as ΔS [%]. The amount of change | T2−T1 | / T1 × 100 [%] of the thickness T2 of the region 54 with respect to the thickness T1 of the piezoelectric film 14 in the region 52 was defined as ΔT [%]. The amount of change | Co1-Co0 | of Co (Co1) of Example 1 or Modification 1 of Example 1 with respect to Co (Co0) of Comparative Example 4 in which the region 54 was not provided was defined as ΔC [pF].

  FIGS. 7A and 7B are diagrams showing ΔC with respect to ΔS and ΔT, respectively. Co0 of Comparative Example 4 in which the region 54 is not provided is 1.15 pF. As shown in FIG. 7A, as ΔS increases, ΔC increases. As shown in FIG. 7B, as ΔT increases, ΔC increases. When ΔS and ΔT are 33% or less, ΔC is 0.2 pF or less, which is about 20% or less of 1.15 pF which is Co0 of Comparative Example 4.

  If ΔS and ΔT are too large, it also affects the inductor L1 and the capacitor C1 in the equivalent circuit of FIG. As a result, for example, the resonance frequency is changed and / or spurious is generated. If ΔC is about 20% or less of Co0, it is considered that the influence on other than Co is small.

  Therefore, in the first embodiment and its modification 1, the resonance region 50 includes the region 52 (first region) and the region 54 (second region), and the thickness T1 (first thickness) of the piezoelectric film 14 in the region 52 is provided. Is different from the thickness T2 (second thickness) of the piezoelectric film 14 in the region 54, and the thickness T2 is not less than 2/3 times and not more than 4/3 times the thickness T1. The area of the region 54 in plan view is equal to or less than 1/3 the area of the resonance region 50 in plan view. Thereby, it is possible to suppress a change in the resonator characteristics other than the anti-resonance frequency and change the anti-resonance frequency. Further, as in Comparative Examples 2 and 3, no capacitor or resonator is connected in parallel with the resonator, so that downsizing is possible.

  In order to suppress changes in characteristics other than the anti-resonance frequency, T2 is preferably 3/4 or more and 5/4 or less of T1, more preferably 4/5 or more and 6/5 or less. It is more preferably 9/10 times or more and 11/10 times or less. In order to change the anti-resonance frequency, T2 is preferably 99/100 times or less and 101/100 times or more, more preferably 19/20 times or less and 21/20 times or more, more preferably 9/10 times or less and 11 / times of T1. 10 times or more is more preferable. T2 may be smaller than T1 as in the first embodiment, or T2 may be larger than T1 as in the first modification of the first embodiment.

  In order to suppress a change in characteristics other than the anti-resonance frequency, the area S54 of the region 54 is more preferably １ ／ or less, more preferably １ ／ or less, of the area S50 of the resonance region 50. In order to substantially change Co, the area S54 is preferably 1/100 or more of the area S50, more preferably 1/50 or more.

  If the thickness of each layer of the laminated film 18 other than the thickness of the piezoelectric film 14 is different between the regions 52 and 54, the resonator characteristics other than the anti-resonance frequency characteristics change. Therefore, the lower surface of the laminated film 18 is located below the lower electrode 12, is exposed to the gap 30, and functions as a lower reflecting surface that reflects an elastic wave propagating through the piezoelectric film 14. The upper surface of the laminated film 18 is located above the upper electrode 16, is exposed to the atmosphere, and functions as an upper reflecting surface that reflects elastic waves. A first distance between the lower reflecting surface and the upper reflecting surface in the region 52 (that is, the thickness T3 of the laminated film 18) and a second distance between the lower reflecting surface and the upper reflecting surface in the region 54 (that is, the thickness T4) ) Is substantially equal to the difference between the thicknesses T1 and T2. Thereby, it is possible to suppress a change in the resonator characteristics other than the anti-resonance frequency.

[Modification 2 of Embodiment 1]
FIG. 8A is a cross-sectional view of a piezoelectric thin-film resonator according to a second modification of the first embodiment. As shown in FIG. 8A, in the second modification of the first embodiment, a concave portion is provided on the lower surface of the piezoelectric film 14. Accordingly, the thickness T2 of the piezoelectric film 14 in the region 54 is smaller than the thickness T1 of the piezoelectric film 14 in the region 52. Other configurations are the same as those of the first embodiment, and a description thereof will be omitted. T2 may be made larger than T1 by providing a projection on the lower surface of the piezoelectric film 14.

[Modification 3 of Embodiment 1]
FIG. 8B is a cross-sectional view of a piezoelectric thin-film resonator according to a third modification of the first embodiment. As shown in FIG. 8B, in a third modification of the first embodiment, an insertion film 28 is provided in the piezoelectric film 14. The insertion film 28 is not provided in the central region of the resonance region 50. It is provided along the outer periphery of the resonance region 50 so as to surround the central region. The Young's modulus and / or acoustic impedance of the insertion film 28 is preferably smaller than that of the piezoelectric film 14. For example, when the piezoelectric film 14 is an aluminum nitride film, the insertion film 28 is a silicon oxide film. Accordingly, leakage of elastic wave energy from the resonance region 50 to the outside can be suppressed. Therefore, the Q value of the piezoelectric thin film resonator is improved. The other configuration is the same as that of the first embodiment, and the description is omitted. The insertion film 28 may be provided in the first embodiment and its modifications 1 and 2.

[Modification 4 of Embodiment 1]
FIG. 9 is a sectional view of a piezoelectric thin-film resonator according to Modification 4 of Example 1. As shown in FIG. 9, in the fourth modification of the first embodiment, the acoustic reflection film 31 is formed below the lower electrode 12 in the resonance region 50. In the acoustic reflection film 31, films 31a having a low acoustic impedance and films 31b having a high acoustic impedance are provided alternately. The thickness of each of the films 31a and 31b is, for example, approximately λ / 4 (λ is the wavelength of the elastic wave). The number of layers of the films 31a and 31b can be set arbitrarily. The acoustic reflection film 31 may have at least two types of layers having different acoustic characteristics laminated at intervals. Further, the substrate 10 may be one of at least two types of layers having different acoustic characteristics of the acoustic reflection film 31. For example, the acoustic reflection film 31 may have a configuration in which one film having a different acoustic impedance is provided in the substrate 10. Other configurations are the same as those in the first embodiment, and a description thereof will be omitted.

  In the first embodiment and the first to third modifications thereof, an acoustic reflection film 31 may be formed instead of the gap 30 as in the fourth modification of the first embodiment. Further, the gap 30 may have a dome shape. A depression may be formed on the upper surface of the substrate 10, and the void 30 may be formed by the depression.

  As in the first embodiment and the first to third modifications thereof, the piezoelectric thin-film resonator may be an FBAR (Film Bulk Acoustic Resonator) in which the cavity 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. . Further, as in Modification Example 4 of Embodiment 1, the piezoelectric thin-film resonator has an SMR (Solidly Mounted Resonator) including an acoustic reflection film 31 that reflects an elastic wave propagating through the piezoelectric film 14 below the lower electrode 12 in the resonance region 50. ). The acoustic reflection layer including the resonance region 50 may include the gap 30 or the acoustic reflection film 31.

  FIGS. 10A to 10C are plan views illustrating examples of the resonance region according to the first embodiment and its modification. As shown in FIG. 10A, the planar shape of the resonance region 50 is an elliptical shape, and the planar shape of the region 54 is a pentagonal shape. The region 54 includes the center 56 (for example, the center of gravity) of the resonance region 50. As shown in FIG. 10B, the planar shape of the resonance region 50 is a square shape, and the planar shape of the region 54 is an elliptical shape. Region 54 does not include center 56 of resonance region 50. As shown in FIG. 10C, the planar shape of the resonance region 50 is a pentagonal shape, and the planar shape of the region 54 is a rectangular shape. Region 54 does not include center 56 of resonance region 50.

  The planar shape of the resonance region 50 and the region 54 may be elliptical or polygonal. The region 54 may or may not include the center 56 of the resonance region 50 in plan view.

  FIG. 11 is a plan view of the ladder-type filter according to the second embodiment. As shown in FIG. 11, a piezoelectric thin film resonator and a wiring 22 are provided on a substrate 10. The piezoelectric thin film resonator includes series resonators S1 to S6 and parallel resonators P1 to P3. The wiring 22 connects the piezoelectric thin film resonator. The wiring 22 includes an input pad Pin, an output pad Pout, and a ground pad Pgnd. The input pad Pin, the output pad Pout, and the ground pad Pgnd are electrically connected to an input terminal, an output terminal, and a ground terminal, respectively. The series resonators S1 to S6 are connected in series to a path between the input pad Pin and the output pad Pout. One end of each of the parallel resonators P1 to P3 is electrically connected to a path between the input pad Pin and the output pad Pout via the wiring 22, and the other end is electrically connected to the ground pad Pgnd via the wiring 22. I have.

  The region 54 is not provided in the resonance region 50 of the resonator other than the series resonator S4, and is a piezoelectric thin film resonator of Comparative Example 4. This is a piezoelectric thin-film resonator according to the first embodiment or the first modification of the first embodiment in which a region 54 is provided in the resonance region 50 of the series resonator S4. The number of series resonators and parallel resonators can be set as appropriate.

[Simulation 2]
The pass characteristics of the ladder filter of the second embodiment were simulated under the same conditions as in the first simulation. FIG. 12 is a diagram illustrating pass characteristics of the ladder-type filter according to the second embodiment. The thick solid line indicates the pass characteristic of the filter of the second embodiment. The thin solid line shows the pass characteristics of the series resonator S4, and the other lines show the pass characteristics of the series resonators S1 to S3, S5, and S6 other than S4. As shown in FIG. 12, the anti-resonance frequency of the series resonator S4 is the lowest among the series resonators S1 to S6. The skirt on the high frequency side of the pass band of the filter mainly depends on the pass characteristic between the resonance frequency and the anti-resonance frequency of the series resonator S4. Therefore, by providing the region 54 in the series resonator S4, the skirt characteristic on the high frequency side can be made a desired characteristic. Resonators other than the series resonator S4 do not contribute to the skirt characteristics. Therefore, the region 54 is not provided in the resonators other than the series resonator S4. Thus, the area of the resonance region 50 is reduced, and the size of the filter can be reduced.

  According to the second embodiment, one or a plurality of series resonators S1 to S3, S5, and S6 (first series resonators) are connected to a path between an input terminal (first terminal) and an output terminal (second terminal). The thickness T1 of the piezoelectric film 14 in the resonance region 50 in which the lower electrode 12 and the upper electrode 16 (a pair of electrodes) face each other with at least a part of the piezoelectric film 14 interposed therebetween is substantially uniform. One or a plurality of series resonators S4 (second series resonators) are connected in series with the series resonators S1 to S3, S5 and S6, and are the piezoelectric thin-film resonators of the first embodiment and its modifications. Thus, by appropriately selecting the area of the region 54 and / or the thickness of the piezoelectric film 14, the filter characteristics can be set to desired characteristics.

  At least one anti-resonance frequency of the one or more series resonators S4 is the lowest among the anti-resonance frequencies of the series resonators S1 to S6. Thereby, the steepness of the skirt on the high frequency side of the pass band can be set to a desired characteristic.

  In the second embodiment, the ladder-type filter has been described as an example. However, the filters using the first embodiment and its modifications may be other types of filters.

[Modification 1 of Embodiment 2]
FIG. 13 is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 13, a 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 allows a signal in a transmission band among high-frequency signals input from the transmission terminal Tx to pass through the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 allows a signal in the reception band among the high-frequency signals input from the common terminal Ant to pass through 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 second embodiment.

  It is preferable to use the filter of the second embodiment as a filter having a lower pass band among the transmission filter 40 and the reception filter 42. Thereby, the skirt characteristic on the guard band side can be made steep. Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may be used.

  As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the specific embodiments, and various modifications and changes may be made within the scope of the present invention described in the appended claims. Changes are possible.

DESCRIPTION OF SYMBOLS 10 Substrate 12 Lower electrode 14 Piezoelectric film 16 Upper electrode 18 Laminated film 20 Frequency adjustment film 22 Wiring 24 Protective film 28 Insertion film 30 Void 40 Transmission filter 42 Reception filter 50 Resonance area 52, 54 area

Claims (8)

Board and
A lower electrode provided on the substrate,
An upper electrode provided on the lower electrode,
A first region and a second region are provided on the lower electrode and in a resonance region where the lower electrode and the upper electrode face each other, and a first thickness of the first region is equal to a first thickness of the second region. Unlike the second thickness, the second thickness is not less than 2/3 times and not more than 4/3 times the first thickness, and the area of the second region in plan view is equal to the area of the resonance region in plan view. A piezoelectric film that is 1/3 or less,
A piezoelectric thin film resonator comprising:   The piezoelectric thin film resonator according to claim 1, wherein the second thickness is smaller than the first thickness.   The piezoelectric thin-film resonator according to claim 1, wherein the second thickness is larger than the first thickness. A lower reflective surface positioned below the lower electrode, reflecting an elastic wave propagating through the piezoelectric film,
An upper reflecting surface that reflects the elastic wave and is located above the upper electrode,
A difference between a first distance between the lower reflection surface and the upper reflection surface in the first region and a second distance between the lower reflection surface and the upper reflection surface in the second region is: The piezoelectric thin-film resonator according to claim 1, wherein a difference between the first thickness and the second thickness is substantially equal. A first terminal;
A second terminal;
1 or which is connected in series to a path between the first terminal and the second terminal and has a substantially uniform thickness of the piezoelectric film in a resonance region in which at least a part of the piezoelectric film is sandwiched and a pair of electrodes face each other. A plurality of first series resonators;
5. One or more second series resonators connected to the path in series with the one or more first series resonators and being the piezoelectric thin-film resonator according to any one of claims 1 to 4,
One or more parallel resonators connected between the path and ground;
A filter comprising:   The anti-resonance frequency of at least one of the one or more second series resonators is the lowest among the anti-resonance frequencies of the one or more first series resonators and the one or more second series resonators. 5. The filter according to 5.   A filter comprising the piezoelectric thin-film resonator according to claim 1. A multiplexer comprising the filter according to any one of claims 5 to 7.

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