JP7383404B2 - Piezoelectric thin film resonators, filters and multiplexers - Google Patents

Description

The present invention relates to piezoelectric thin film resonators, filters and multiplexers, for example piezoelectric thin film resonators, filters and multiplexers with additional membranes or grooves.

Filters and multiplexers having piezoelectric thin film resonators are used for high frequency circuits in wireless terminals such as mobile phones. A piezoelectric thin film resonator has a laminated film in which a lower electrode, a piezoelectric film, and an upper electrode are laminated. A region where the lower electrode and the upper electrode face each other with at least a portion of the piezoelectric film in between is a resonant region where elastic waves vibrate. It is known to insert an insertion film into a piezoelectric film within a resonance region (for example, Patent Document 1).

Japanese Patent Application Publication No. 2015-95729

Characteristics such as the Q value can be improved by inserting an insertion film in the outer peripheral region of the resonance region. However, characteristics such as the Q value change depending on the position of the end face of the piezoelectric film.

The present invention has been made in view of the above problems, and aims to obtain stable characteristics.

The present invention includes a substrate, a lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode, and a piezoelectric film provided on the piezoelectric film with at least a portion of the piezoelectric film sandwiched between the lower electrodes. an upper electrode provided to form a resonant region defined by an area that overlaps with the piezoelectric film in plan view; A laminated film including the lower electrode and the piezoelectric film in the inner region of the end face is provided so as to be apart from the resonant region and extend along the outer periphery of the resonant region so as to surround the resonant region. This piezoelectric thin film resonator includes a plurality of additional films or a plurality of grooves provided apart from each other in the direction connecting the end faces of the piezoelectric film.

In the above configuration, the width of the plurality of additional films or the plurality of grooves , the width between adjacent additional films or grooves among the plurality of additional films or the plurality of grooves, and the width of the plurality of additional films or the plurality of grooves. The width between the additional film or the groove closest to the resonant region among the grooves and the resonant region is 0.2 times or more the total thickness of the lower electrode, the piezoelectric film, and the upper electrode in the resonant region. In addition, it is possible to have a configuration in which the ratio is 1.5 times or less.

In the above configuration, the width between the additional film or groove closest to the resonance region among the plurality of additional films or the plurality of grooves and the resonance region is the width between the additional film or the groove closest to the resonance region among the plurality of additional films or the plurality of grooves. 0.2 times or more and 0.8 times or less the wavelength of an elastic wave propagating in the plane direction in a region between the additional film or groove closest to the resonant region and the resonant region, and the wavelength of the plurality of additional films or the The width between adjacent additional films or grooves among the plurality of grooves is 0.2 times or more and 0.8 times or less the wavelength of an elastic wave propagating in the plane direction in the area between adjacent additional films or grooves. The width of the plurality of additional films or the plurality of grooves is 0.2 times or more the wavelength of the elastic wave propagating in the plane direction in the region where the plurality of additional films or the plurality of grooves are provided, and It is possible to have a configuration in which the number is 8 times or less.

In the above structure, the thickness of the plurality of additional films or the depth of the plurality of grooves may be 0.05 times or more the total thickness of the lower electrode and the piezoelectric film.

In the above configuration, the plurality of additional films may include a plurality of additional films provided between the substrate and the laminated film, within the laminated film, or on the laminated film.

In the above structure, the plurality of grooves may include a plurality of grooves provided in a surface of the substrate on the laminated film side or in a plurality of layers included in the laminated film.

In the above structure, the widths of the plurality of additional films or the plurality of grooves are the same, and the width between adjacent additional films or grooves among the plurality of additional films or the plurality of grooves is the same as the width of the plurality of additional films or the plurality of grooves. The width between the resonant region and the additional film or groove closest to the resonant region among the films or the plurality of grooves may be the same.

In the above structure, three or more of the plurality of additional films or the plurality of grooves may be provided apart from each other in a direction connecting the resonance region and the end surface of the piezoelectric film.

In the above configuration, the lower electrode and the upper electrode are not provided in the central region of the resonant region, and are arranged in the resonant region so as to surround at least a part of the central region along the outer periphery of the resonant region. The configuration may include an insertion membrane inserted between the two.

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

The present invention is a multiplexer including the above filter.

According to the present invention, it is an object to obtain stable characteristics.

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). FIG. 2 is a cross-sectional view of the piezoelectric thin film resonator according to the first embodiment. 3(a) to 3(c) are cross-sectional views showing a method of manufacturing a piezoelectric thin film resonator according to Example 1. FIG. FIG. 4 is a cross-sectional view of a piezoelectric thin film resonator according to Comparative Example 1. FIG. 5 is a diagram showing Qa with respect to the width D5 in simulation 1. FIG. 6 is a diagram showing Qa for widths D1 and D3 in simulation 2. FIGS. 7(a) and 7(b) are diagrams showing Qa for D4 in simulation 3. FIG. 8 is a diagram showing the average and standard deviation of Qa with respect to the number of additional films in simulation 3. FIGS. 9A to 9C are cross-sectional views of piezoelectric thin film resonators according to Modifications 1 to 3 of Example 1, respectively. FIGS. 10A to 10C are cross-sectional views of piezoelectric thin film resonators according to Modifications 4 to 6 of Example 1, respectively. FIGS. 11A to 11C are cross-sectional views of piezoelectric thin film resonators according to Modifications 7 to 9 of Example 1, respectively. FIGS. 12A to 12C are cross-sectional views of piezoelectric thin film resonators according to Modifications 10 to 12 of Example 1, respectively. FIGS. 13A to 13C are cross-sectional views of piezoelectric thin film resonators according to Modifications 13 to 15 of Example 1, respectively. FIGS. 14A to 14C are cross-sectional views of piezoelectric thin film resonators according to Modifications 16 to 18 of Example 1, respectively. FIGS. 15A and 15B are cross-sectional views of piezoelectric thin film resonators according to Modifications 19 and 20 of Example 1, respectively. 16(a) is a circuit diagram of a filter according to a second embodiment, and FIG. 16(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment.

Examples will be described below with reference to the drawings.

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). FIG. 1A mainly shows the lower electrode 12, the piezoelectric film 14, the upper electrode 16, and the additional film 17.

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

A piezoelectric film 14 is provided on the lower electrode 12. The piezoelectric film 14 has, for example, aluminum nitride as a main component having C-axis orientation. The piezoelectric film 14 includes a lower piezoelectric film 14a provided on the lower electrode 12 and an upper piezoelectric film 14b provided on the lower piezoelectric film 14a.

An upper electrode 16 is provided on the piezoelectric film 14 so as to face the lower electrode 12 with the piezoelectric film 14 in between. Upper electrode 16 includes a lower layer 16a and an upper layer 16b. The lower layer 16a and the upper layer 16b are, for example, a ruthenium film and a chromium film, respectively. The resonance region 50 is defined by a region where the lower electrode 12 and the upper electrode 16 overlap in plan view with at least a portion of the piezoelectric film 14 sandwiched therebetween. The resonance region 50 has an elliptical shape, and is a region where elastic waves in the thickness longitudinal vibration mode resonate. In a plan view, the resonance region 50 overlaps the air gap 30, and the air gap 30 is the same as or larger than the resonance area 50. That is, all of the resonance region 50 overlaps with the air gap 30 in plan view.

An insertion film 28 is provided between the lower piezoelectric film 14a and the upper piezoelectric film 14b. The insertion film 28 is, for example, a silicon oxide film. The insertion film 28 is not provided in the central region 54 within the resonant region 50 but is provided in the outer peripheral region 52 surrounding the central region 54 and along the outer periphery of the resonant region 50 within the resonant region 50 . The insertion film 28 only needs to be provided in at least a part of the area surrounding the central area 54.

Extraction regions 58 and 60 are regions where lower electrode 12 and upper electrode 16 are extracted from resonance region 50, respectively. In the extraction region 58 , the outer periphery of the resonant region 50 is defined by the outer periphery of the upper electrode 16 , and the outer periphery of the lower electrode 12 is located outside the outer periphery of the resonant region 50 . In the extraction region 60 , the outer periphery of the resonant region 50 is defined by the outer periphery of the lower electrode 12 , and the outer periphery of the upper electrode 16 is located outside the outer periphery of the resonant region 50 . Thereby, even if the lower electrode 12 and the upper electrode 16 are misaligned, the change in the area of the resonance region 50 can be reduced.

In the extraction region 58, the end surface 62 of the upper piezoelectric film 14b is located outside the outer periphery of the resonance region 50. The end surface 64 of the lower piezoelectric film 14a is located outside the end surface 62 of the upper piezoelectric film 14b. The end surface 64 of the lower piezoelectric film 14a may substantially match the end surface 62 of the upper piezoelectric film 14b. The region 56 is a region between the end surface of the upper piezoelectric film 14b and the outer periphery of the resonance region 50.

In region 56, a plurality of additional films 17 are provided on piezoelectric film 14. The plurality of additional films 17 are arranged in a direction away from the resonance region 50 and are provided so as to surround the resonance region 50.

A silicon oxide film is formed as a frequency adjustment film 24 so as to cover the upper electrode 16 and additional film 17 . The frequency adjustment film 24 may function as a passivation film.

As shown in FIG. 1A, an introduction path 33 for etching the sacrificial layer is formed in the lower electrode 12. The sacrificial layer is a layer for forming voids 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.

FIG. 2 is a cross-sectional view of the piezoelectric thin film resonator according to the first embodiment. FIG. 2 is a laterally enlarged view of region 56 compared to resonance region 50. In FIG. As shown in FIG. 2, in the region 56, the additional film 17 is provided on the laminated film 18 including the lower electrode 12, the insertion film 28, and the piezoelectric film 14. The additional film 17 includes a lower layer 16a and an upper layer 16b. The plurality of additional films 17 are provided periodically.

Additional film 17 is provided in region 56a. The width of the additional film 17 in the direction of the resonance region 50 and the end face 62 is D1. No additional film 17 is provided in the region 56b between adjacent additional films 17. The width of the region 56b is D2. No additional film 17 is provided in a region 56c between the innermost additional film 17 and the resonance region 50. The width of the region 56c is D3. No additional film is provided in a region 56d between the outermost additional film 17 and the end surface 62. The width of the region 56d is D4. The widths D1 of the plurality of additional films 17 are approximately equal to each other to the extent of manufacturing error, the widths D2 between the additional films 17 are approximately equal to each other to the extent of manufacturing error, and the widths D2 and D3 are approximately equal to each other to the extent of manufacturing error. The width D4 varies as described below. The width of the region 56 is D5.

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, upper electrode 16, and additional film 17 may include aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), A single layer film of platinum (Pt), rhodium (Rh), or iridium (Ir), or a laminated film of these films can be used. For example, the lower layer 16a of the upper electrode 16 may be made of ruthenium, and the upper layer 16b may be made of molybdenum. The additional film 17 may be an insulating film made of silicon oxide, silicon nitride, aluminum oxide, or the like.

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

The insertion film 28 is made of a material having a smaller Young's modulus and/or acoustic impedance than the piezoelectric film 14 . In addition to silicon oxide, the insertion film 28 can be a single layer film or a laminated film of aluminum (Al), gold (Au), copper, titanium, platinum, tantalum, chromium, or the like. As the frequency adjustment film 24, in addition to the silicon oxide film, a metal nitride film such as a silicon nitride film or an aluminum nitride film, or a metal oxide film can be used.

[Production method of Example 1]
3(a) to 3(c) are cross-sectional views showing a method of manufacturing a piezoelectric thin film resonator according to Example 1. FIG. As shown in FIG. 3A, a sacrificial layer 38 is formed on the substrate 10 using, for example, a sputtering method, a vacuum evaporation method, or a CVD (Chemical Vapor Deposition) method. The sacrificial layer 38 is made of magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), silicon oxide (SiO ₂ ), etc., and has a thickness of 10 nm to 100 nm, for example. Thereafter, the sacrificial layer 38 is patterned into a desired shape using photolithography and etching. The shape of the sacrificial layer 38 corresponds to the planar shape of the void 30, and includes a region that will become the resonance region 50, for example. A lower layer 12a and an upper layer 12b are formed as the lower electrode 12 on the sacrificial layer 38 and the substrate 10 using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. Thereafter, the lower electrode 12 is patterned into a desired shape using photolithography and etching. The lower electrode 12 may be formed by a lift-off method.

As shown in FIG. 3B, a lower piezoelectric film 14a is formed on the lower electrode 12 and the substrate 10 using, for example, a sputtering method or a vacuum evaporation method. The insertion film 28 is formed on the lower piezoelectric film 14a 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. The insertion film 28 may be formed by a lift-off method.

As shown in FIG. 3C, the upper piezoelectric film 14b is formed on the insertion film 28 and the lower piezoelectric film 14a using, for example, a sputtering method or a vacuum evaporation method. The piezoelectric film 14 is formed by the lower piezoelectric film 14a and the upper piezoelectric film 14b. A lower layer 16a and an upper layer 16b are formed as the upper electrode 16 on the piezoelectric film 14 using, for example, a sputtering method, a vacuum evaporation method, or a CVD method. Thereafter, the upper electrode 16 and additional film 17 are patterned into a desired shape using photolithography and etching. The upper electrode 16 and additional film 17 may be formed by a lift-off method. The upper piezoelectric film 14b is patterned into a desired shape using photolithography and etching. The lower piezoelectric film 14a is etched using the insertion film 28 as a mask.

The frequency adjustment film 24 is formed using, for example, a sputtering method or a CVD method. The frequency adjustment film 24 is patterned into a desired shape using a photolithography method and an etching method. Thereafter, an etching solution for the sacrificial layer 38 is introduced into the sacrificial layer 38 under the lower electrode 12 through the hole 35 and the introduction path 33 (see FIG. 1(a)). As a result, the sacrificial layer 38 is removed. As a result, a gap 30 having a dome-shaped bulge is formed between the lower electrode 12 and the substrate 10. Through the above steps, the piezoelectric thin film resonance shown in FIGS. 1(a) and 1(b) is manufactured.

[Comparative example 1]
FIG. 4 is a cross-sectional view of a piezoelectric thin film resonator according to Comparative Example 1. As shown in FIG. 4, in Comparative Example 1, the additional film 17 was not formed in the region 56. The other configurations are the same as in the first embodiment.

[Simulation 1]
The Q value (Qa) at the antiresonant frequency in Comparative Example 1 was simulated by changing the width D5 of the region 56. The simulation conditions are as follows.
Frequency adjustment film 24: Silicon oxide film with a thickness of 52 nm Upper layer 16b: Chromium film with a thickness of 22 nm Lower layer 16a: Ruthenium film with a thickness of 219 nm Insertion film 28: Silicon oxide film with a thickness of 150 nm Piezoelectric film 14: Thickness Magnesium and hafnium added aluminum nitride film with a diameter of 1163 nm Upper layer 12b: Ruthenium film with a thickness of 278 nm Lower layer 12a: Chromium film with a thickness of 96 nm Substrate 10: Silicon substrate Width of resonance region 50: 84 μm
In the simulation, an AC voltage of 1800 MHz to 2100 MHz was applied between the lower electrode 12 and the upper electrode 16, and the frequency dependence of admittance was calculated. The calculation results were fitted with the mBVD model to calculate Qa.

FIG. 5 is a diagram showing Qa with respect to the width D5 in simulation 1. As shown in FIG. 5, when the width D5 of the region 56 changes, the Q value Qa at the anti-resonant frequency changes. In order to electrically connect to the lower electrode 12, the piezoelectric film 14 on the lower electrode 12 is removed using, for example, an etching method. The amount of side etching when etching the piezoelectric film 14 varies within a wafer and between wafers. In particular, when the piezoelectric film 14 is thicker than the additional film 17 and/or when the piezoelectric film 14 is etched using a wet etching method, the amount of side etching of the piezoelectric film 14 tends to fluctuate. For this reason, D5 fluctuates, and fluctuations in characteristics such as the Q value become large.

[Simulation 2]
Next, a piezoelectric thin film resonator provided with one additional film 17 was simulated. The simulation conditions are as follows.
Number of additional films 17: 1 Width D5 of region 56: 50 μm
The width D1 of the additional film 17 and the width D3 of the region 56c between the resonance region 50 and the additional film 17 were changed. Other simulation conditions are the same as simulation 1.

FIG. 6 is a diagram showing Qa for widths D1 and D3 in simulation 2. As shown in FIG. 6, Qa roughly varies with respect to the sum of width D1 and width D3. Qa reaches its maximum when D1=1.8 μm and D3=2.2 μm.

[Simulation 3]
A piezoelectric thin film resonator was simulated by changing the number of additional films 17 at regular intervals. The simulation conditions are as follows.
Width D1 of additional film 17: 1.8 μm
Widths D2 and D3 of regions 56b and 56c: 2.2 μm
The number of additional films 17 and the width D4 of the region 56d were varied. Other simulation conditions are the same as simulation 1.

FIGS. 7(a) and 7(b) are diagrams showing Qa for D4 in simulation 3. FIG. 7A shows cases where the number of additional films 17 is 0, 1, 2, and 3, and FIG. 7B shows cases where the number of additional films 17 is 0, 4, 5, and 6. When the number of additional films 17 is 0, the horizontal axis is D5. Each dot indicates a simulation point, and each line is a line connecting the dots.

As shown in FIGS. 7(a) and 7(b), Qa increases as the number of additional films 17 increases compared to when the number of additional films 17 is zero. Further, the fluctuation of Qa with respect to D4 or D5 is reduced.

FIG. 8 is a diagram showing the average and standard deviation of Qa with respect to the number of additional films in simulation 3. Error bars added to the Qa average dots indicate maximum and minimum values. As shown in FIG. 8, as the number of additional films 17 increases, the average value of Qa increases. Furthermore, as the number of additional films 17 increases, the standard deviation of Qa and the size of the error bar become smaller.

When elastic waves (transverse mode elastic waves) propagating in the lateral direction (in the plane direction of the piezoelectric film 14) leak from the resonance region 50, the Q value and the like decrease. By reflecting transverse mode acoustic waves at the inner periphery of the insertion film 28, the Q value etc. can be improved. When the additional film 17 is provided, transverse mode acoustic waves are reflected at the outer periphery of the resonance region 50 and at both ends of the additional film 17. Furthermore, it is thought that increasing the number of additional films 17 increases the number of locations where transverse mode acoustic waves are reflected, thereby improving the Q value and the like.

In simulation 1, the reason why the variation in Qa with respect to D5 becomes large is considered to be that the phase of the transverse mode acoustic wave reflected by the end face 62 of the piezoelectric film 14 changes depending on the width D5. If the number of additional films 17 is increased, the number of transverse mode acoustic waves reaching the end face 62 is reduced, so it is considered that the variation in Qa is small even if D4 is changed. It is considered that as the number of additional films 17 increases, the number of transverse mode acoustic waves that reach the end face 62 decreases, so that the fluctuation in Qa becomes smaller.

The wave numbers of the transverse mode elastic waves in the resonance region 50, the regions 56b to 56d where the additional film 17 is not provided, and the region 56a where the additional film 17 is provided were calculated from the dispersion characteristics of the plate wave. The wavelength of the transverse mode elastic wave was calculated from the wave number by setting the antiresonance frequency to 1906 MHz.

Table 1 is a table showing the wave number and wavelength of transverse mode elastic waves in each region.

As shown in Table 1, in the regions 56b to 56d, the wavelength of the transverse mode elastic wave is longer than that in the resonant region 50, and in the region 56a, the wavelength of the transverse mode acoustic wave is shorter than that in the resonant region 50. In FIG. 6, D3 = 2.2 μm, where Qa is maximum, is close to 1/2 of the wavelength of the transverse mode elastic wave in the region 56a in Table 1, and D1 = 1.8 μm is the transverse mode in regions 56b to 56d in Table 1. It is close to 1/2 of the wavelength of an elastic wave. In this way, when the widths D1 to D3 are close to 1/2 of the wavelength of the transverse mode elastic wave, the Q value etc. are improved.

From the above viewpoint, the width D1 is preferably 0.2 times or more and 0.8 times or less, more preferably 0.3 times or more and 0.7 times or less, and 0. More preferably, it is 4 times or more and 0.6 times or less. The widths D2 and D3 are preferably 0.2 times or more and 0.8 times or less, more preferably 0.3 times or more and 0.7 times or less, and 0.4 times the wavelength of the transverse mode elastic waves in the regions 56b and 56c. More preferably, it is at least twice that amount and no more than 0.6 times.

The wavelength of the longitudinal mode elastic wave in the resonance region 50 is approximately twice the total thickness of the lower electrode 12, piezoelectric film 14, and upper electrode 16, which is 1.78 μm. The frequency adjustment film 24 was ignored because it was thinner than other layers. In order to set the widths D1 to D3 to be 0.2 times or more and 0.8 times or less the wavelength of the transverse mode acoustic wave, the widths D1 to D3 must be set to 0.0 times the thickness of the lower electrode 12, the piezoelectric film 14, and the upper electrode 16. .2 times or more and 1.2 times or less, more preferably 0.3 times or more and 1.1 times or less, and even more preferably 0.6 times or more and 1.0 times or less. preferable.

The thickness of the lower layer 16a in the additional film 17 was changed, and the wave number and wavelength of the transverse mode acoustic wave in the region 56a were calculated. Table 2 shows the thickness T16a of the lower layer 16a of the additional film 17 and the ratio T17/ It is a table showing T, wave number, wavelength, and the wave number difference between the wave numbers in regions 56b and 56c. The thickness of the frequency adjustment film 24 was ignored.

As shown in Table 2, as the additional film 17 becomes thicker, the wave number increases and the wavelength decreases. As the wave number difference between the region 56a and the regions 56b to d56d increases, the acoustic impedance difference of transverse mode elastic waves increases. Therefore, the reflectance of transverse mode elastic waves at the boundaries between the region 56a and the regions 56b to 56d increases. This further improves the Q value and the like. Furthermore, as the wave number increases, the width D1 can be reduced, which allows for miniaturization.

From the above viewpoint, the thickness T17 of the additional film 17 is preferably 0.05 times or more, more preferably 0.1 times or more, the thickness T of the laminated film 18. As the additional film 17 becomes thicker, the processing accuracy of the additional film 17 deteriorates. Therefore, T17/T is preferably 1 or less, more preferably 0.5 or less.

9A to 15B are cross-sectional views of piezoelectric thin film resonators according to Modifications 1 to 20 of Example 1, respectively.

[Modification 1 of Example 1]
As shown in FIG. 9A, in the first modification of the first embodiment, the additional film 15 is provided on the piezoelectric film 14 in the region 56a, and is made of the same material as the piezoelectric film 14. The additional film 15 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 2 of Example 1]
As shown in FIG. 9(b), in the second modification of the first embodiment, the additional film 27 is provided between the insertion film 28 and the upper piezoelectric film 14b in the region 56a, and is made of the same material as the insertion film 28. . The additional film 27 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Variation 3 of Example 1]
As shown in FIG. 9(c), in the third modification of the first embodiment, the additional film 13 is provided between the lower electrode 12 and the piezoelectric film 14 in the region 56a, and is made of the same material as the upper layer 12b of the lower electrode 12. Consisting of The additional film 13 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 4 of Example 1]
As shown in FIG. 10A, in the fourth modification of the first embodiment, the additional film 13 is provided between the lower layer 12a and the upper layer 12b of the lower electrode 12 in the region 56a, and the additional film 13 is provided between the lower layer 12a and the upper layer 12b of the lower electrode 12. Made of the same material. The additional film 13 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

In Example 1 and Modifications 1 to 4 thereof, the region in contact with the resonance region 50 within the region 56 is a region 56c in which the additional film 13, 15, 17, or 27 is not provided. The materials and thicknesses of the lower electrode 12, insertion film 28, and piezoelectric film 14 in regions 56b to 56d are substantially the same as those of the lower electrode 12, insertion film 28, and piezoelectric film 14, respectively, in the resonant region 50. . In region 56a, additional films 13, 15, 17, or 27 are provided in addition to the laminated films 18 in regions 56b to 56d. The additional films 13, 15, 17, or 27 may be provided within or on the laminated film 18. The material of the additional film may be the same as that of the layer in contact with it, or may be a different material. In FIGS. 9(b) to 10(a), the top surface of the layer above the additional films 27 and 13 is flat in the region 56, but the top surface of the layer above the additional films 27 and 13 is Concave and convex portions corresponding to 13 may be formed.

[Variation 5 of Example 1]
As shown in FIG. 10(b), in the fifth modification of the first embodiment, a groove 15a is provided in the upper surface of the piezoelectric film 14 in the region 56a. The grooves 15a are not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 6 of Example 1]
As shown in FIG. 10(c), in the sixth modification of the first embodiment, a groove 27a is provided in the insertion film 28 in the region 56a. The groove 27a is not provided in the regions 56b to 56d. The groove 27a passes through the insertion membrane 28. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 7 of Example 1]
As shown in FIG. 11A, in the seventh modification of the first embodiment, a groove 13a is provided in the upper surface of the upper layer 12b of the lower electrode 12 in the region 56a. The groove 13a is not provided in the regions 56b to 56d. Groove 13a does not penetrate upper layer 12b. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 8 of Example 1]
As shown in FIG. 11(b), in the eighth modification of the first embodiment, a groove 11a is provided on the upper surface of the substrate 10 in the region 56a. No groove 11a is provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

In Modifications 5 to 8 of Example 1, the region in contact with the resonance region 50 within the region 56 is a region 56c in which the grooves 11a, 13a, 15a, or 27a are not provided. The materials and thicknesses of the lower electrode 12, insertion film 28, and piezoelectric film 14 in regions 56b to 56d are substantially the same as those of the lower electrode 12, insertion film 28, and piezoelectric film 14, respectively, in the resonant region 50. . In the region 56a, a groove 11a, 13a, 15a, or 27a is provided in at least one layer of the laminated film 18 in the regions 56b to 56d. In FIGS. 10(c) to 11(b), the upper surface of the layer above grooves 11a, 13a, and 27a is flat in region 56, but the upper surface of the layer above grooves 11a, 13a, and 27a has grooves. Concave and convex portions corresponding to 11a, 13a, and 27a may be formed.

[Modification 9 of Example 1]
As shown in FIG. 11(c), in the ninth modification of the first embodiment, the insertion membrane 28 is not provided. An additional film 17 is provided on the piezoelectric film 14 in the region 56a. The additional film 17 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 10 of Example 1]
As shown in FIG. 12(a), in the tenth modification of the first embodiment, the insertion membrane 28 is not provided. In region 56a, additional film 15 is provided on piezoelectric film 14 and is made of the same material as piezoelectric film 14. The additional film 15 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 11 of Example 1]
As shown in FIG. 12(b), in Modification 11 of Example 1, the insertion membrane 28 is not provided. In the region 56a, the additional film 13 is provided between the lower electrode 12 and the piezoelectric film 14, and is made of the same material as the upper layer 12b of the lower electrode 12. The additional film 13 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 12 of Example 1]
As shown in FIG. 12(c), in the twelfth modification of the first embodiment, the insertion membrane 28 is not provided. In the region 56a, the additional film 13 is provided between the lower layer 12a and the upper layer 12b of the lower electrode 12, and is made of the same material as the lower layer 12a of the lower electrode 12. The additional film 13 is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 13 of Example 1]
As shown in FIG. 13(a), in the thirteenth modification of the first embodiment, the insertion membrane 28 is not provided. A groove 15a is provided in the upper surface of the piezoelectric film 14 in the region 56a. The grooves 15a are not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 14 of Example 1]
As shown in FIG. 13(b), in the 14th modification of the first embodiment, the insertion membrane 28 is not provided. In the region 56a, a groove 13a is provided on the upper surface of the upper layer 12b of the lower electrode 12. The groove 13a is not provided in the regions 56b to 56d. Groove 13a does not penetrate upper layer 12b. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 15 of Example 1]
As shown in FIG. 13(c), in modification example 15 of example 1, the insertion membrane 28 is not provided. A groove 11a is provided in the upper surface of the substrate 10 in the region 56a. No groove 11a is provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

As in Modifications 9 to 15 of the first embodiment, the insertion film 28 may not be provided in the resonance region 50 and the region 56.

[Modification 16 of Example 1]
As shown in FIG. 14(a), in the sixteenth modification of the first embodiment, the additional film 17d is provided in regions 56a and 56b, but not in regions 56c and 56d. The additional film 17c is provided in the region 56a, and is not provided in the regions 56b to 56d. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 17 of Example 1]
As shown in FIG. 14B, in Modification 17 of Example 1, the thickness of the additional film 17 decreases from the resonance region 50 side to the end face 64 side. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 18 of Example 1]
As shown in FIG. 14C, in Modification 18 of Example 1, the thickness of the additional film 17 increases from the resonance region 50 side to the end face 64 side. The other configurations are the same as those in Example 1, and their explanation will be omitted.

As in Modifications 16 to 18 of Example 1, the thickness of the additional film may not be uniform. Also in Example 1 and Modifications 1 to 15 thereof, the thickness of the additional film or the depth of the grooves may not be uniform.

[Modification 19 of Example 1]
FIG. 15A is a cross-sectional view of a piezoelectric thin film resonator according to Modification Example 19 of Example 1. As shown in FIG. 15(a), a depression is formed on the upper surface of the substrate 10. The lower electrode 12 is formed flat on the substrate 10. As a result, a void 30 is formed in the depression of the substrate 10. The air gap 30 is formed to include a resonance region 50. The other configurations are the same as in Example 1, and the explanation will be omitted. The void 30 may be formed to penetrate the substrate 10.

[Modification 20 of Example 1]
FIG. 15(b) is a cross-sectional view of a piezoelectric thin film resonator according to Modification Example 20 of Example 1. As shown in FIG. 15(b), an acoustic reflection film 31 is formed under the lower electrode 12 in the resonance region 50. The acoustic reflection film 31 includes films 31a with high acoustic impedance and films 31b with low acoustic impedance alternately provided. The thicknesses of the films 31a and 31b are, for example, approximately λ/4 (λ is the wavelength of the elastic wave). The number of laminated films 31a and 31b 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 an interval between them. Further, the substrate 10 may be one of at least two types of layers of the acoustic reflection film 31 having different acoustic characteristics. For example, the acoustic reflection film 31 may have a structure in which two films with different acoustic impedances are provided in the substrate 10. The other configurations are the same as in Example 1, and the explanation will be omitted.

As in Example 1 and Modifications 1 to 19 thereof, the piezoelectric thin film resonator may be an FBAR (Film Bulk Acoustic Resonator) in which a gap 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. . Further, as in the modification 20 of the first embodiment, the piezoelectric thin film resonator is an SMR (Solidly Mounted Resonator) that includes an acoustic reflection film 31 that reflects elastic waves propagating through the piezoelectric film 14 under the lower electrode 12 in the resonance region 50. ) is also fine. The acoustic reflection layer may include the void 30 or the acoustic reflection film 31.

In the first embodiment and its modifications 1 to 8 and 16 to 20, the insertion film 28 is provided in the outer peripheral region 52 of the resonance region 50, but the insertion film 28 is provided in the outer peripheral region 54 of the resonance region 50. It is sufficient if it is provided in at least a portion of the region 52. The insertion film 28 does not need to be provided outside the resonance region 50. The insertion film 28 only needs to be provided in at least a portion of the resonance region 50. In the first embodiment and its modified examples, the planar shape of the resonance region 50 has been explained using an elliptical shape as an example, but it may also be a polygonal shape such as a quadrangular shape or a pentagonal shape.

According to the first embodiment and its modifications, the additional films 13, 15, 17, and 27 or the grooves 11a, 13a, and 15a are formed in the region 56 (i.e., the outer periphery of the resonant region 50 defined by the outer periphery of the upper electrode 16). and the end surface 62 of the piezoelectric film 14), the layered film 18 is provided apart from the resonance region 50, and is not provided between the resonance region 50. As a result, transverse mode elastic waves propagating in the plane direction from the resonance region 50 are transmitted to at least the outer periphery of the resonance region 50, the end of the additional film or groove on the resonance region 50 side, and the end of the additional film or groove on the end surface 62 side. It is reflected in three places. As a result, leakage of transverse mode elastic waves to the outside of the resonance region 50 is suppressed, and characteristics such as the Q value are improved. Further, since the number of elastic waves propagating to the end face 62 is reduced, fluctuations in the characteristics due to fluctuations in the position of the end face 62 are suppressed, and the characteristics are stabilized.

The width D1 of the additional film or groove and the width D3 between the resonance region 50 and the additional film or groove are at least 0.2 times the total thickness of the lower electrode 12, piezoelectric film 14, and upper electrode 16 in the resonance region 50. and 1.5 times or less. As a result, the phases of the elastic waves reflected at at least three locations are different. Therefore, the characteristics such as the Q value are further improved and the characteristics are further stabilized. D1 and D3 are more preferably 0.3 times or more and 1.1 times or less, respectively, 0.6 times or more and 1.0 times the total thickness of the lower electrode 12, piezoelectric film 14, and upper electrode 16, respectively. It is more preferable to make it less than double.

The width D3 is at least 0.2 times and at most 0.8 times the wavelength of the elastic wave propagating in the plane direction in the region 56c between the resonance region 50 and the additional film or groove. The width D1 is at least 0.2 times and at most 0.8 times the wavelength of the elastic wave propagating in the plane direction in the region 56a where the additional film or groove is provided. As a result, the phases of the elastic waves reflected at at least three locations are different. Therefore, the characteristics such as the Q value are further improved and the characteristics are further stabilized. D1 and D3 are each more preferably 0.3 times or more and 0.7 times or less, and even more preferably 0.4 times or more and 0.6 times or less, respectively, than the wavelength of the elastic wave propagating in the plane direction.

The thickness of the additional film or the depth of the groove is 0.05 times or more the total thickness of the lower electrode 12 and the piezoelectric film 14. This increases the reflectance of elastic waves at both ends of the additional film or groove. Therefore, the characteristics such as the Q value are further improved and the characteristics are further stabilized. The thickness of the additional film or the depth of the groove is more preferably 0.1 times or more the total thickness of the lower electrode 12 and the piezoelectric film 14. The thickness of the additional film or the depth of the groove is preferably 1 or less, more preferably 0.5 or less of the total thickness of the lower electrode 12 and piezoelectric film 14.

The additional film or groove may include additional films 13 , 15 , 17 and 27 provided between the substrate 10 and the laminated film 18 , within the laminated film 18 , or on the laminated film 18 , or may include additional films 13 , 15 , 17 and 27 provided between the substrate 10 and the laminated film 18 , or may include additional films 13 , 15 , 17 and 27 provided between the substrate 10 and the laminated film 18 It may also include grooves 11a, 13a, and 15a provided in the side surface or in the layers included in the laminated film 18.

A plurality of additional films or grooves are provided apart from each other in the direction connecting the resonance region 50 and the end surface 62 of the piezoelectric film 14 . This further improves the characteristics such as the Q value and makes the characteristics more stable. It is preferable that three or more additional films or grooves are provided, and it is preferable that four or more additional films or grooves are provided. The number of additional films or grooves is preferably 10 or less, since the larger the number, the larger the size.

An insertion film is not provided in the central region 54 and is inserted between the lower electrode 12 and the upper electrode 16 so as to surround at least a portion of the central region 54 along the outer periphery of the resonant region 50 within the resonant region 50. 28 may be provided. Thereby, the Q value can be further improved.

Example 2 is an example of a filter and a duplexer using the piezoelectric thin film resonator of Example 1 and its modification. FIG. 16(a) is a circuit diagram of a filter according to the second embodiment. As shown in FIG. 16(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The piezoelectric thin film resonator of Example 1 and its modifications can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The number of resonators of the ladder filter can be set as appropriate.

FIG. 16(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 16(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes signals in the transmission band among the signals input from the transmission terminal Tx to the common terminal Ant as transmission signals, and suppresses signals at other frequencies. The reception filter 42 passes signals in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as reception signals, and suppresses signals at other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second 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 these specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 Substrate 11a, 13a, 15a groove 12 Lower electrode 13, 15, 17, 27 Additional film 14 Piezoelectric film 14a Lower piezoelectric film 14b Upper piezoelectric film 16 Upper electrode 18 Laminated film 28 Insert film 40 Transmission filter 42 Reception filter 50 Resonance region 52 Outer area 54 Central area 56, 56a-56d area

Claims (11)

A substrate and
a lower electrode provided on the substrate;
a piezoelectric film provided on the lower electrode;
an upper electrode provided on the piezoelectric film so as to form a resonance region defined by a region that overlaps the lower electrode in a plan view with at least a portion of the piezoelectric film sandwiched therebetween;
a laminated film including the lower electrode and the piezoelectric film in a region outside the outer periphery defined by the outer periphery of the upper electrode and inside the end surface of the piezoelectric film out of the outer periphery of the resonant region, away from the resonant region; a plurality of additional films or a plurality of grooves extending along the outer periphery of the resonant region so as to surround the resonant region and separated from each other in a direction connecting the resonant region and the end surface of the piezoelectric film; ,
A piezoelectric thin film resonator comprising: The width of the plurality of additional films or the plurality of grooves, the width between adjacent additional films or grooves among the plurality of additional films or the plurality of grooves, and the width of the plurality of additional films or the plurality of grooves. The width between the additional film or groove closest to the resonant region and the resonant region is 0.2 times or more and 1.5 times the total thickness of the lower electrode, the piezoelectric film, and the upper electrode in the resonant region. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is less than twice as large. The width between the additional film or groove that is closest to the resonance region among the plurality of additional films or the plurality of grooves and the resonance region is the width between the additional film or groove that is closest to the resonance region among the plurality of additional films or the plurality of grooves. 0.2 times or more and 0.8 times or less the wavelength of an elastic wave propagating in the plane direction in a region between a nearby additional film or groove and the resonant region,
The width between adjacent additional films or grooves among the plurality of additional films or the plurality of grooves is 0.2 times or more the wavelength of an elastic wave propagating in a plane direction in a region between adjacent additional films or grooves. and is 0.8 times or less,
The width of the plurality of additional films or the plurality of grooves is 0.2 times or more and 0.8 times the wavelength of the elastic wave propagating in the plane direction in the region where the plurality of additional films or the plurality of grooves are provided. The piezoelectric thin film resonator according to claim 1, which is: The piezoelectric thin film resonator according to claim 2 or 3, wherein the thickness of the plurality of additional films or the depth of the plurality of grooves is 0.05 times or more the total thickness of the lower electrode and the piezoelectric film. . The piezoelectric device according to any one of claims 1 to 4, wherein the plurality of additional films include a plurality of additional films provided between the substrate and the laminated film, within the laminated film, or on the laminated film. Thin film resonator. The piezoelectric thin film resonator according to any one of claims 1 to 4, wherein the plurality of grooves include a plurality of grooves provided in a surface of the substrate on the laminated film side or in a plurality of layers included in the laminated film. . The widths of the plurality of additional films or the plurality of grooves are the same,
The width between adjacent additional films or grooves among the plurality of additional films or the plurality of grooves, and the additional film or groove closest to the resonance region among the plurality of additional films or the plurality of grooves and the resonance region. The piezoelectric thin film resonator according to any one of claims 1 to 6, wherein the width between and is the same as each other. The piezoelectric device according to any one of claims 1 to 7, wherein the plurality of additional films or the plurality of grooves are provided in three or more spaces apart from each other in a direction connecting the resonance region and the end surface of the piezoelectric film. Thin film resonator. The electrode is not provided in the central region of the resonant region, and is inserted between the lower electrode and the upper electrode so as to surround at least a portion of the central region along the outer periphery of the resonant region within the resonant region. 9. A piezoelectric thin film resonator according to any one of claims 1 to 8, comprising an inserted membrane. A filter comprising a piezoelectric thin film resonator according to any one of claims 1 to 9. A multiplexer comprising a filter according to claim 10.

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