JP7068011B2 - Piezoelectric thin film resonators, filters and multiplexers - Google Patents

Description

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

Elastic wave devices using piezoelectric thin film resonators are used as filters and duplexers for wireless devices such as mobile phones. The piezoelectric thin film resonator has a structure in which the lower electrode and the upper electrode face each other with the piezoelectric film interposed therebetween. The region where the lower electrode and the upper electrode face each other across the piezoelectric film is the resonance region.

It is known to add elements other than nitrogen and aluminum to a piezoelectric membrane containing aluminum nitride as a main component in order to increase the electromechanical coupling coefficient of the piezoelectric thin film resonator (for example, Patent Documents 1-3). It is known to provide an AlN film on the upper electrode (for example, Patent Document 4). It is known that a film of tensile stress is provided on the upper electrode from the end of the resonance region to the outside (for example, Patent Document 5).

Japanese Unexamined Patent Publication No. 2013-46111 Japanese Unexamined Patent Publication No. 2013-219743 International Publication No. 2013/175985 Japanese Unexamined Patent Publication No. 2009-11623 US Patent Application Publication No. 2018/0019726

The piezoelectric membrane may be used as a compressive stress to improve the characteristics of the piezoelectric thin film resonator. For example, as in Patent Documents 1 to 3, by adding an element other than nitrogen and aluminum to a piezoelectric film containing aluminum nitride as a main component, the piezoelectricity of the piezoelectric film is improved and the piezoelectric thin film resonance such as the electromechanical coupling coefficient is improved. The characteristics of the vessel are improved. As described in Patent Document 1, at this time, the residual stress of the piezoelectric film becomes a compressive stress. When the residual stress of the piezoelectric film becomes a compressive stress, there is a possibility that the piezoelectric film may be cracked or the piezoelectric film or the like may be peeled off.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress stress applied to a piezoelectric film or the like.

In the present invention, a substrate, a lower electrode provided on the substrate, and aluminum nitride as a main component provided on the lower electrode, scandium or boron, or a group 2 or group 12 element and a group 4 element Alternatively, an element such as a group 5 element is added , and an upper portion provided so as to form a piezoelectric film whose residual stress is compressive stress and a resonance region which is a region facing the lower electrode with the piezoelectric film sandwiched between them. An electrode, an additional film provided on the piezoelectric film in the resonance region, having an argon concentration higher than that of the piezoelectric film, containing aluminum nitride as a main component, and having a residual stress of tensile stress, the substrate and the above. An acoustic reflective layer provided between the lower electrode and reflecting the excited elastic wave in the piezoelectric film is provided, and the concentration of the element in the additional film is lower than the concentration of the element in the piezoelectric film. Alternatively, it is a piezoelectric thin film resonator in which the element is not substantially added to the additional film.

In the above configuration, the additional film may be configured such that the element is not substantially added.

In the above configuration, the additional film may be configured to be provided on the upper electrode.

In the above configuration, the additional film may be provided between the piezoelectric film and the upper electrode.

In the above configuration, an insulating film made of a material different from the material of the additional film provided on the upper electrode is further provided, and the additional film is provided between the upper electrode and the insulating film. can do.

In the above configuration, the additional film may be configured to be provided on the piezoelectric film in at least the central region of the resonance region.

In the above configuration, the Young's modulus of the additional film can be larger than the Young's modulus of at least one layer in the lower electrode and the upper electrode.

In the above configuration, the film thickness of the additional film may be 8% or more of the film thickness of the piezoelectric film.

In the above configuration, the acoustic reflection layer is a void, and the end of the lower electrode in the region where the upper electrode is drawn out from the resonance region can be configured to be located between the void and the piezoelectric film. ..

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

The present invention is a multiplexer including the above filter.

According to the present invention, the stress applied to the piezoelectric film or the like can be suppressed.

1 (a) is a plan view of the piezoelectric thin film resonator according to the first embodiment, FIG. 1 (b) is a plan view of an insertion membrane and a gap, and FIGS. 1 (c) and 1 (d) are FIGS. 1 (A) is a sectional view taken along the line AA. FIG. 2 is an enlarged cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 1. FIG. 3 is a diagram showing the residual stress of the piezoelectric film and the breakage of the piezoelectric film in the experiment. FIG. 4 is a diagram showing the stress ratio in the simulation. FIG. 5 is a diagram showing residual stress with respect to Ar flow rate. 6 (a) and 6 (b) are cross-sectional views of the piezoelectric thin film resonator according to the first and second modifications of the first embodiment, respectively. 7 (a) and 7 (b) are cross-sectional views of the piezoelectric thin film resonator according to the modified examples 3 and 4, respectively, of the first embodiment. 8 (a) and 8 (b) are circuit diagrams of the filter and the duplexer according to the second embodiment and the first modification thereof, respectively.

Hereinafter, examples of the present invention will be described with reference to the drawings.

1 (a) is a plan view of the piezoelectric thin film resonator according to the first embodiment, FIG. 1 (b) is a plan view of an insertion membrane and a gap, and FIGS. 1 (c) and 1 (d) are FIGS. 1 (A) is a sectional view taken along the line AA. FIG. 1C shows, for example, a series resonator of a ladder type filter, and FIG. 1D shows, for example, a parallel resonator of a ladder type filter.

The structure of the series resonator S will be described with reference to FIGS. 1 (a) and 1 (c). The lower electrode 12 is provided on the substrate 10 which is a silicon (Si) substrate. 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 in which the height of the void 30 is small around the void 30 and the height of the void 30 is increased toward the inside of the void 30. The void 30 functions as an acoustic reflection layer that reflects elastic waves 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 Cr (chromium) film, and the upper layer 12b is, for example, a Ru (ruthenium) film.

A piezoelectric film 14 containing aluminum nitride (AlN) as a main component having the main axis in the (002) direction is provided on the lower electrode 12. The piezoelectric film 14 includes a lower piezoelectric film 14a and an upper piezoelectric film 14b. The lower piezoelectric film 14a 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.

As shown in FIG. 1 (b), the insertion film 28 is provided in the outer peripheral region 52 in the resonance region 50 and not in the central region 54. The outer peripheral region 52 is a region within the resonance region 50, and is a region along the outer circumference including the outer circumference of the resonance region 50. The outer peripheral region 52 is, for example, ring-shaped. 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 a geometric center.

The upper electrode 16 is provided on the piezoelectric film 14 so as to have a region (resonance region 50) facing the lower electrode 12 with 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 longitudinal vibration mode resonate. The gap 30 is provided so as to include the resonance region 50 in a plan view. As a result, the elastic wave excited by the piezoelectric film 14 is reflected by the void 30. The upper electrode 16 includes a lower layer 16a and an upper layer 16b. The lower layer 16a is, for example, a Ru film, and the upper layer 16b is, for example, a Cr film.

An additional film 26 containing aluminum nitride as a main component is provided on the upper electrode 16 in the resonance region 50. A silicon oxide film is formed on the additional film 26 as a frequency adjusting film 24. The laminated film 18 in the resonance region 50 includes a lower electrode 12, a piezoelectric film 14, an upper electrode 16, and a frequency adjusting film 24. The frequency adjusting film 24 may function as a passivation film.

As shown in FIG. 1A, the lower electrode 12 is formed with an introduction path 33 for etching the sacrificial layer. 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. Further, as shown in FIG. 1 (b), the insertion membrane 28 has a hole portion 34 communicating with the hole portion 35.

The structure of the parallel resonator P will be described with reference to FIG. 1 (d). Compared with the series resonator S, the parallel resonator P is provided with a mass load film 20 made of a Ti (titanium) layer between the lower layer 16a and the upper layer 16b of the upper electrode 16. Therefore, in addition to the laminated film of the series resonator S, the laminated film 18 includes the mass load film 20 formed on the entire surface in the resonance region 50. Other configurations are the same as those in FIG. 1 (c) of the series resonator S, and the description thereof will be omitted.

The difference in resonance frequency between the series resonator S and the parallel resonator P is adjusted by using the film thickness of the mass load film 20. The resonance frequencies of both the series resonator S and the parallel resonator P are adjusted by adjusting the film thickness of the frequency adjusting film 24.

As the substrate 10, a quartz substrate, a glass substrate, a ceramic substrate, a sapphire substrate, a spinel substrate, a crystal substrate, a GaAs substrate, or the like can be used in addition to the Si substrate. In addition to Ru and Cr, the lower electrode 12 and the upper electrode 16 include Al (aluminum), Ti, Cu (copper), Mo (molybdenum), W (tungsten), Ta (tantalum), Pt (platinum), and Rh ( A monolayer film such as rhodium) or Ir (iridium) 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.

As the piezoelectric film 14, ZnO (zinc oxide), PZT (lead zirconate titanate), PbTiO ₃ (lead titanate) and the like can be used in addition to 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. The residual stress of the piezoelectric film 14 is, for example, a compressive stress.

The Young's modulus of the insertion membrane 28 is preferably smaller than that of the piezoelectric membrane 14. If the densities are substantially the same, Young's modulus correlates with the acoustic impedance, so that the acoustic impedance of the insertion membrane 28 is preferably smaller than that of the piezoelectric membrane 14. Thereby, the Q value can be improved. Further, in order to make the acoustic impedance of the insertion film 28 smaller than that of the piezoelectric film 14, when the piezoelectric film 14 contains aluminum nitride as a main component, the insertion film 28 may be an Al film, an Au film, a Cu film, a Ti film, or a Pt film. It is preferably a Ta film, a Cr film or a silicon oxide film.

As the additional film 26, an insulating film such as a silicon oxide film, a silicon nitride film, or an aluminum oxide film can be used in addition to the aluminum nitride film. The additional film 26 may be a metal film. The residual stress of the additional film 26 is, for example, a tensile stress.

As the frequency adjusting film 24, a silicon nitride film, aluminum nitride, or the like can be used in addition to the silicon oxide film. As the mass loading film 20, a single-layer film such as Ru, Cr, Al, Cu, Mo, W, Ta, Pt, Rh or Ir can be used in addition to Ti. Further, an insulating film made of a metal nitride or a metal oxide such as silicon nitride or silicon oxide can also be used. The mass loading film 20 includes not only the layers of the upper electrode 16 (between the lower layer 16a and the upper layer 16b), but also the layers below the lower electrode 12, between the lower electrodes 12, above the upper electrode 16, the lower electrode 12 and the piezoelectric film 14. It can be formed between and between the piezoelectric film 14 and the upper electrode 16. The mass load film 20 may be larger than the resonance region 50 as long as it is formed so as to include the resonance region 50.

[Comparative Example 1]
FIG. 2 is an enlarged cross-sectional view of the piezoelectric thin film resonator according to Comparative Example 1. FIG. 2 is a cross-sectional view of the vicinity of the region where the upper electrode is pulled out from the resonance region. As shown in FIG. 2, the end of the gap 30 and the end of the lower electrode 12 substantially coincide with each other, and the end of the lower electrode 12 is located between the gap 30 and the piezoelectric film 14. When the compressive stress of the piezoelectric film 14 is large, the stress is concentrated on the end portion 56 of the lower electrode 12. Therefore, the piezoelectric film 14 is cracked and / or the piezoelectric film 14 is peeled off.

[Experiment in Comparative Example 1]
Therefore, a piezoelectric thin film resonator having a structure B without an additional film 26 was manufactured. The stress of the piezoelectric film 14 was changed, and the presence or absence of breakage such as cracks and / or peeling of the piezoelectric film 14 was investigated. The production conditions of the structure B are as follows.
Lower layer 12a of lower electrode 12: Cr film with a film thickness of 98 nm Upper layer 12b of lower electrode 12: Cr film with a film thickness of 192 nm Piezoelectric film 14: AlN film with a film thickness of 1250 nm Insert film 28: Silicon oxide with a film thickness of 150 nm The membrane insertion membrane 28 was provided at the center of the piezoelectric membrane 14 in the thickness direction.
Lower layer 16a of the upper electrode 16: Ru film having a film thickness of 232 nm Upper layer 16b of the upper electrode 16: Cr layer having a film thickness of 35 nm Frequency adjusting film 24: Silicon oxide film having a film thickness of 50 nm Shape of resonance region 50: Long axis Elliptical shape with 211 μm and 151 μm minor axis

The film forming method of the piezoelectric film 14 is as follows. Sputtering was performed in a mixed gas atmosphere of Ar (argon) gas and N ₂ (nitrogen gas) at a pressure of 0.3 Pa. The residual stress of the piezoelectric film 14 was changed by changing the ratio of the flow rate of Ar to the flow rate of Ar + N ₂ (Ar flow rate ratio) in the Ar / N ₂ mixed gas. Elements other than nitrogen and aluminum are not intentionally added to the piezoelectric film 14.

The piezoelectric film was formed on the silicon substrate under the same conditions as the conditions for forming the piezoelectric film 14 of the piezoelectric thin film resonator. Residual stress was measured from the warp of the silicon substrate at room temperature. When the residual stress of the piezoelectric film 14 is tensile stress, the silicon substrate warps so that the surface on which the piezoelectric film 14 is provided is recessed. When the residual stress of the piezoelectric film 14 is compressive stress, the silicon substrate warps so that the surface on which the piezoelectric film 14 is provided swells. The sign of residual stress is positive for tensile stress and negative for compressive stress. The residual stress is also referred to as internal stress.

In the prepared sample of the piezoelectric thin film resonator, the fracture of the piezoelectric film 14 was observed using an SEM (Scanning Electron Microscope). A sample in which the piezoelectric film 14 is cracked and / or peeled is regarded as “presence” in the destruction of the piezoelectric film 14, and a sample in which neither crack or peeling is generated in the piezoelectric film 14 is “absent” in the destruction of the piezoelectric film 14. And said.

FIG. 3 is a diagram showing the residual stress of the piezoelectric film and the breakage of the piezoelectric film in the experiment. As shown in FIG. 3, when the residual stress of the piezoelectric film 14 is −200 MPa or less, the piezoelectric film 14 is destroyed, and when the residual stress is −150 MPa or more, the piezoelectric film 14 is not destroyed.

[simulation]
For the structure A provided with the AlN film as the additional film 26 and the structure B without the additional film 26, the stress applied to the end portion 56 (see FIG. 2) of the lower electrode 12 was calculated by using the two-dimensional finite element method. The simulation conditions were the same as the experimental conditions. From the experimental results of FIG. 3, in the structure B, when the residual stress of the piezoelectric film 14 is −150 MPa, the critical value of the presence or absence of breakage of the piezoelectric film 14 is obtained. Therefore, the stress applied to the end portion 56 of the lower electrode 12 is standardized by the stress applied to the end portion 56 when the residual stress in the structure B is −150 MPa. The normalized stress was taken as the stress ratio and expressed in parts per hundred. It is considered that the piezoelectric film 14 is broken when the stress ratio is 100% or more, and the piezoelectric film 14 is not broken when the stress ratio is less than 100%.

FIG. 4 is a diagram showing the stress ratio in the simulation. As shown in FIG. 4, in the structure B, the residual stress of the piezoelectric film 14 is −200 MPa or less and the stress ratio is 100% or more, and the residual stress of the piezoelectric film 14 is −100 MPa or less and the stress ratio is less than 100%. This is in agreement with the result in FIG. In this way, the presence or absence of damage to the piezoelectric film 14 can be predicted by simulation.

In the structure A, the stress ratio can be made less than 100% by providing the additional film 26 for tensile stress. That is, the damage of the piezoelectric film 14 can be suppressed. The larger the film thickness of the additional film 26, the smaller the stress ratio, and the larger the residual stress of the additional film 26, the smaller the stress ratio. When the absolute value of the residual stress of the piezoelectric film 14 becomes large (that is, the compressive stress becomes large), the stress ratio does not become less than 100% unless the film thickness of the additional film 26 is increased and the residual stress is increased.

As shown in FIG. 4, since the stress ratio is less than 100%, the film thickness of the additional film 26 is preferably 100 nm or more. This corresponds to 8% or more of the film thickness of the piezoelectric film 14. As described above, the film thickness of the additional film 26 is preferably 8% or more, more preferably 10% or more, and further preferably 15% or more of the film thickness of the piezoelectric film 14. If the additional film 26 is too thick, it may peel off from the additional film 26 or the piezoelectric film 14. Therefore, the film thickness of the additional film 26 is preferably 50% or less, more preferably 40% or less, still more preferably 30% or less of the film thickness of the piezoelectric film 14.

Further, since the stress ratio is less than 100%, the absolute value of the residual stress of the additional film 26 is preferably 50% or more, more preferably 75% or more, and 100% or more of the absolute value of the residual stress of the piezoelectric film 14. More preferred. If the tensile stress of the additional film 26 is too large, peeling from the additional film 26 or the piezoelectric film 14 or the like occurs. Therefore, the absolute value of the residual stress of the additional film 26 is preferably 500% or less, more preferably 300% or less, still more preferably 200% or less of the absolute value of the residual stress of the piezoelectric film 14.

A method for forming an AlN film for setting the residual stress of the additional film 26 was examined. AlN was targeted, and the sputtering gas was an Ar / N ₂ mixed gas. N ₂ is a gas for reacting with Al to obtain Al N. Ar mainly contributes to the sputtering of the target. The pressure was 0.3 Pa, the N ₂ flow rate was a constant value of 80 sccm, and the Ar flow rate was changed to form an AlN film. No element other than nitrogen and aluminum was intentionally added to the AlN film.

FIG. 5 is a diagram showing residual stress with respect to Ar flow rate. As shown in FIG. 5, when the Ar flow rate is small, the residual stress is a compressive stress. When the Ar flow rate becomes large, the residual stress becomes large and becomes a tensile stress. In this way, the residual stress of the additional film 26 can be controlled by changing the Ar flow rate. It is considered that the Ar concentration of the addition film 26 having a large Ar flow rate (that is, a large residual stress) is higher than the Ar concentration of the addition film 26 having a small Ar flow rate (that is, a small residual stress).

The cause of the piezoelectric film 14 becoming a compressive stress is, for example, the addition of an element that improves the piezoelectricity of the piezoelectric film 14 to the piezoelectric film 14. As described in Patent Document 2, a group 2 element or a group 12 element and a group 4 element are added to the piezoelectric film 14, or a group 2 element and a group 5 element are added. The name of the group of elements is based on the notation of IUPAC (International Union of Pure and Applied Chemistry). Group 2 elements are, for example, calcium (Ca), magnesium (Mg) or strontium (Sr). The Group 12 element is, for example, zinc (Zn). Group 4 elements are, for example, titanium (Ti), zirconium (Zr) or hafnium (Hf). Group 5 elements are, for example, tantalum (Ta), niobium (Nb) or vanadium (V). As described in Patent Document 3, the piezoelectric film 14 contains an aluminum nitride film as a main component, and scandium (Sc) may be added. Further, the piezoelectric film 14 contains aluminum nitride as a main component, and boron (B) may be added.

Assuming that the group 2 element or group 12 element, the group 4 element or group 5 element, scandium and boron are the element M, the element M is replaced with Al of AlN. That is, the element M is located at the Al site. As a result, the piezoelectricity of the piezoelectric film 14 is improved, and the characteristics such as the electromechanical coupling coefficient of the piezoelectric thin film resonator are improved. At this time, the piezoelectric film 14 becomes a compressive stress.

In order to structure the electromechanical coupling coefficient of the piezoelectric thin film resonator, the concentration of the element M (concentration of M with respect to M + Al) is preferably 5 atomic% or more, more preferably 10 atomic% or more, still more preferably 20 atomic% or more. Further, since the piezoelectric film 14 is an AlN film, the concentration of the element M is preferably 50 atomic% or less, more preferably 40 atomic% or less. The fact that the piezoelectric film 14 contains an aluminum nitride film as a main component means that the piezoelectric film 14 contains aluminum nitride to the extent that the effects of the present specification can be obtained. For example, 50 atomic% or more of the piezoelectric film 14 is Al and N. Is.

As described above, in Comparative Example 1 in which the additional film 26 is not provided, when the piezoelectric film 14 is used as a compressive stress, the stress applied to the piezoelectric film 14 becomes large.

According to the first embodiment, the piezoelectric film 14 is mainly composed of aluminum nitride, and an element selected from other than nitrogen, aluminum and argon is intentionally added. This improves the piezoelectricity of the piezoelectric film 14. However, the residual stress of the piezoelectric film 14 becomes the compressive stress. Therefore, the additional film 26 is provided on the piezoelectric film 14 in the resonance region 50. The additional film 26 is a film having an argon concentration lower than that of the piezoelectric film 14 and containing aluminum nitride as a main component. As a result, the additional film 26 becomes a tensile stress, and the stress applied to the piezoelectric film 14 at the end of the lower electrode 12 or the like can be suppressed. Therefore, the destruction of the piezoelectric film 14 can be suppressed.

The additional film 26 is substantially (ie, intentionally) free of elements selected from other than nitrogen, aluminum and argon. As a result, the additional film 26 can be made more tensile stress.

Elements selected from other than nitrogen, aluminum and argon are scandium or boron, or Group 2 or Group 12 elements and Group 4 or Group 5 elements. As a result, the piezoelectricity of the piezoelectric film 14 is further improved. However, the piezoelectric film 14 tends to be compressive stress, and the stress tends to concentrate on the end of the lower electrode 12. Therefore, it is preferable to provide the additional film 26.

When the piezoelectric film 14 contains aluminum nitride as a main component and boron is added, the piezoelectric film 14 becomes hard. Therefore, when stress is applied to the piezoelectric film 14, damage such as cracks is likely to occur. Therefore, it is preferable to provide the additional film 26.

Further, according to the first embodiment, the residual stress of the piezoelectric film 14 is set as the compressive stress in order to improve the characteristics of the piezoelectric thin film resonator. At this time, an additional film 26 whose residual stress is tensile stress is provided on the piezoelectric film 14 in the resonance region 50. As a result, the stress applied to the piezoelectric film 14 at the end of the lower electrode 12 or the like can be suppressed. Therefore, the destruction of the piezoelectric film 14 can be suppressed.

The additional film 26 may be provided outside the resonance region 50, but is provided so as to overlap at least the entire resonance region 50. As a result, the stress applied to the piezoelectric film 14 at the end of the lower electrode 12 can be suppressed. The additional film 26 overlaps a part of the resonance region 50 and does not have to overlap the other part of the resonance region 50. In order to suppress the concentration of stress on the end of the lower electrode 12, the additional film 26 is preferably provided on the piezoelectric film 14 in at least the central region 54 in the resonance region 50.

If the Young's modulus of the additional film 26 is small, the additional film 26 is distorted. This makes it difficult to relieve the stress of the piezoelectric film 14. Therefore, the Young's modulus of the additional film 26 is preferably larger than the Young's modulus of at least one layer in the lower electrode 12 and the upper electrode 16. For example, the Young's modulus of ruthenium and chromium used as the lower electrode 12 and the upper electrode 16 is 447 GPa and 279 GPa, respectively. Young's modulus of silicon dioxide and aluminum nitride is 79 GPa and 395 GPa, respectively. Therefore, as the additional film 26, an aluminum nitride film is preferable to a silicon oxide film.

As shown in FIG. 2, the end of the lower electrode 12 in the region where the upper electrode 16 is drawn out from the resonance region 50 is located between the gap 30 and the piezoelectric film 14. In such a structure, stress is concentrated on the end of the lower electrode 12. Therefore, the piezoelectric film 14 is easily destroyed. Therefore, the additional film 26 is provided. This makes it possible to suppress the concentration of stress on the end of the lower electrode 12. Even if the end of the lower electrode 12 is not located between the gap 30 and the piezoelectric film 14, stress is concentrated on the end of the lower electrode 12, so it is preferable to provide the additional film 26.

[Modification 1 of Example 1]
FIG. 6A is a cross-sectional view of the piezoelectric thin film resonator according to the first modification of the first embodiment. As shown in FIG. 6A, the additional film 26 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 in the first embodiment, the additional film 26 may be provided on the upper electrode 16. As in the modified example 1 of the first embodiment, the additional film 26 may be provided between the piezoelectric film 14 and the upper electrode 16. Further, as in the first embodiment, the additional film 26 is provided in the resonance region 50 and may not be provided in other than the resonance region 50. As in the modified example 1 of the first embodiment, the additional film 26 may be provided in a region other than the resonance region 50.

For example, when the main component of the additional film 26 is different from the main component of the piezoelectric film 14, if the additional film 26 is provided between the piezoelectric film 14 and the upper electrode 16 as in the modified example 1 of the first embodiment, the piezoelectric thin film resonance occurs. The characteristics of the vessel deteriorate. Therefore, it is preferable to provide the additional film 26 on the upper electrode 16 as in the first embodiment. When a frequency adjusting film 24 (insulating film) made of a material different from the material of the additional film 26 provided on the upper electrode 16 is provided, the additional film 26 is placed between the upper electrode 16 and the frequency adjusting film 24. It is preferable to provide it. As a result, the additional film 26 is located near the piezoelectric film 14, so that the stress can be further relaxed.

When the main component of the additional film 26 is the same as the main component of the piezoelectric film 14, for example, when the main component of the additional film 26 and the piezoelectric film 14 is aluminum nitride, the additional film 26 is made into a piezoelectric film as in the modified example 1 of the first embodiment. It may be provided between 14 and the upper electrode 16. As a result, since the additional film 26 is located closer to the piezoelectric film 14 than in the first embodiment, the stress can be further relaxed.

[Modification 2 of Example 1]
FIG. 6B is a cross-sectional view of the piezoelectric thin film resonator according to the second modification of the first embodiment. As shown in FIG. 6B, in the extraction region of the lower electrode 12, the end face of the upper piezoelectric film 14b substantially coincides with the contour of the resonance region 50. The end face of the lower piezoelectric film 14a is located outside the contour of the resonance region 50. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted.

As in the second modification of the first embodiment, in the first embodiment and the first modification thereof, the piezoelectric film 14 may be provided in a stepped shape.

[Modification 3 of Example 1]
FIG. 7A is a cross-sectional view of the piezoelectric thin film resonator according to the third modification of the first embodiment. As shown in FIG. 7A, 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 recess of the substrate 10. The void 30 is formed so as to include the resonance region 50. Other configurations are the same as those in the first embodiment, and the description thereof will be 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.

[Modified Example 4 of Example 1]
FIG. 7B is a cross-sectional view of the piezoelectric thin film resonator according to the modified example 4 of the first embodiment. As shown in FIG. 7B, the acoustic reflection film 31 is formed under the lower electrode 12 in the resonance region 50. The acoustic reflection film 31 is provided with a film 30a having a low acoustic impedance and a film 30b having a high acoustic impedance alternately. The film thicknesses of the films 30a and 30b are, for example, approximately λ / 4 (λ is the wavelength of the elastic wave), respectively. The number of layers of the film 30a and the film 30b can be arbitrarily set. The acoustic reflection film 31 may be formed by laminating at least two types of layers having different acoustic characteristics 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 reflective film 31 may be configured such that a film having different acoustic impedances is further provided in the substrate 10. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted.

In Example 1 and the modified examples 1 and 2, the void 30 may be formed in the same manner as in the modified example 3 of the first embodiment, and the acoustic reflective film 31 may be formed instead of the void 30 as in the modified example 4 of the first embodiment. May be formed.

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 a gap 30 is formed between the substrate 10 and the lower electrode 12 in the resonance region 50. .. Further, as in the modified example 4 of the first embodiment, the piezoelectric thin film resonator includes an SMR (Solidly Mounted Resonator) including an acoustic reflecting film 31 that reflects an elastic wave propagating in the piezoelectric film 14 under the lower electrode 12 in the resonance region 50. ) May be. 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.

Example 2 is an example of a filter and a duplexer using a piezoelectric thin film resonator of Example 1 and its modifications. FIG. 8A is a circuit diagram of the filter according to the second embodiment. As shown in FIG. 8A, one or a plurality of series resonators S1 to S4 are connected in series between the input terminal T1 and the output terminal T2. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal T1 and the output terminal T2. The piezoelectric thin film resonators of Example 1 and its modifications can be used for at least one resonator of one or more series resonators S1 to S4 and one or more parallel resonators P1 to P4. The number of resonators of the ladder type filter can be set as appropriate.

FIG. 8B is a circuit diagram of the duplexer according to the first modification of the second embodiment. As shown in FIG. 8B, 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 a signal in the transmission band among the signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

Although the duplexer has been described as an example as the multiplexer, a triplexer or a quadplexer may be used.

Although the examples of the present invention have been described in detail above, the present invention is not limited to such specific examples, and various modifications and variations are made within the scope of the gist of the present invention described in the claims. It can be changed.

10 Substrate 12 Lower electrode 14 Pietrical film 14a Lower piezoelectric film 14b Upper piezoelectric film 16 Upper electrode 24 Frequency adjustment film 26 Additional film 28 Insertion film 30 Void 31 Acoustic reflection film 40 Transmission filter 42 Resonance filter 50 Resonance region

Claims (11)

With the board
The lower electrode provided on the substrate and
It is provided on the lower electrode and contains aluminum nitride as a main component, and scandium or boron, or an element which is a group 2 or group 12 element and a group 4 or group 5 element is added, and the residual stress is a compressive stress. With a piezoelectric film that is
An upper electrode provided so as to form a resonance region which is a region facing the lower electrode and sandwiching the piezoelectric film,
An additional film provided on the piezoelectric film in the resonance region, having an argon concentration higher than that of the piezoelectric film, having aluminum nitride as a main component, and having a residual stress of tensile stress .
An acoustic reflection layer provided between the substrate and the lower electrode and reflecting elastic waves excited in the piezoelectric film,
Equipped with
A piezoelectric thin film resonator in which the concentration of the element in the additional film is lower than the concentration of the element in the piezoelectric film, or the element is not substantially added to the additional film. The piezoelectric thin film resonator according to claim 1, wherein the element is not substantially added to the additional film. The piezoelectric thin film resonator according to claim 1 or 2 , wherein the additional film is provided on the upper electrode. The piezoelectric thin film resonator according to claim 1 or 2 , wherein the additional film is provided between the piezoelectric film and the upper electrode. Further, an insulating film made of a material different from the material of the additional film provided on the upper electrode is provided.
The piezoelectric thin film resonator according to claim 1 or 2 , wherein the additional film is provided between the upper electrode and the insulating film. The piezoelectric thin film resonator according to any one of claims 1 to 5 , wherein the additional film is provided on the piezoelectric film in at least the central region of the resonance region. The piezoelectric thin film resonator according to any one of claims 1 to 6 , wherein the Young's modulus of the additional film is larger than the Young's modulus of the lower electrode and at least one layer in the upper electrode. The piezoelectric thin film resonator according to any one of claims 1 to 7 , wherein the film thickness of the additional film is 8% or more of the film thickness of the piezoelectric film. The acoustic reflection layer is a void and
The piezoelectric thin film resonator according to any one of claims 1 to 8 , wherein the end of the lower electrode in the region where the upper electrode is drawn out from the resonance region is located between the gap and the piezoelectric membrane. The filter including the piezoelectric thin film resonator according to any one of claims 1 to 9 . A multiplexer including the filter according to claim 10 .

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