Patent Application
20230045374
The present invention relates to an acoustic wave device including a support substrate, an intermediate layer, and a piezoelectric film that are laminated together.
Various types of acoustic wave devices in which an intermediate layer is provided between a support substrate and a piezoelectric film have been proposed. International Publication No. 2012/086639 describes an acoustic wave device in which a high-acoustic-velocity film, a low-acoustic-velocity film, and a piezoelectric film are laminated in that order on a support substrate. An IDT electrode is provided on the piezoelectric film.
In the acoustic wave device described in International Publication No. 2012/086639, a wave that travels from the piezoelectric film toward the support substrate is reflected by the support substrate, and a response in a higher-order mode tends to occur. Therefore, when the acoustic wave device is used as a band pass filter, a spurious response outside a pass band may occur. As a result, there is a risk of degradation of filter characteristics.
Preferred embodiments of the present invention provide acoustic wave devices in each of which degradation of characteristics due to a higher-order mode does not easily occur.
An acoustic wave device according to a preferred embodiment of the present invention includes a support substrate, an intermediate layer provided on the support substrate, a piezoelectric film laminated on the intermediate layer, and an interdigital transducer (IDT) electrode provided on the piezoelectric film. A plurality of cavities are provided at at least one of a location between the support substrate and the intermediate layer and a location in the intermediate layer. The plurality of cavities overlap the IDT electrode in plan view.
Preferred embodiments of the present invention provide acoustic wave devices in each of which degradation of characteristics due to a higher-order mode does not easily occur.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will be described with reference to the drawings to clarify the present invention.
Preferred embodiments described in this specification are illustrative and it is possible to partially replace or combine the structures in different preferred embodiments.
An acoustic wave device 1 includes a support substrate 2. An intermediate layer 3 and a piezoelectric film 6 are preferably laminated in that order on the support substrate 2. The intermediate layer 3 includes a high-acoustic-velocity film 4 laminated on the support substrate 2 and a low-acoustic-velocity film 5 provided between the high-acoustic-velocity film 4 and the piezoelectric film 6.
An IDT electrode 7 and reflectors 8 and 9 are provided on the piezoelectric film 6. As illustrated in
The support substrate 2 is preferably made of silicon, for example. The support substrate 2 may alternatively be made of various insulating materials and semiconductor materials. Such a material may be at least one material selected from a group including, for example, silicon, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, sapphire, lithium tantalate, lithium niobate, quartz crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, and diamond.
The piezoelectric film 6 is preferably made of, for example, a lithium tantalate film, more specifically a LiTaO3 film in this example. The piezoelectric film 6 may alternatively be made of other piezoelectric materials, such as lithium niobate (LiNbO3), for example.
The high-acoustic-velocity film 4 is made of a high-acoustic-velocity material. The high-acoustic-velocity material is a material through which a bulk wave propagates at an acoustic velocity higher than an acoustic velocity at which an acoustic wave propagates through the piezoelectric film 6. Examples of the high-acoustic-velocity material include various materials such as aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a diamond-like carbon (DLC) film, diamond, a medium having the above-mentioned materials as a main component, and a medium having a mixture of the above-described materials as a main component.
The low-acoustic-velocity film 5 is made of a low-acoustic-velocity material. The low-acoustic-velocity material is a material through which a bulk wave propagates at an acoustic velocity lower than an acoustic velocity at which a bulk wave propagates through the piezoelectric film 6. Examples of the low-acoustic-velocity material include various materials such as silicon oxide, glass, silicon oxynitride, tantalum oxide, a compound obtained by adding fluorine, carbon, boron, hydrogen, or a silanol group to silicon oxide, and a medium having the above-described materials as a main component.
In the present preferred embodiment, the high-acoustic-velocity film 4 is preferably made of, for example, silicon nitride, and the low-acoustic-velocity film 5 is preferably made of, for example, silicon oxide.
The IDT electrode 7 and the reflectors 8 and 9 may be made of various metals, such as, for example, Al, Cu, Au, W, and Mo, or alloys mainly including these metals. The IDT electrode 7 and the reflectors 8 and 9 may be defined by a multilayer body including a plurality of metal films.
The acoustic wave device 1 includes a plurality of cavities 10 provided between the support substrate 2 and the intermediate layer 3, and more specifically, between the support substrate 2 and the high-acoustic-velocity film 4 (at an interface between the support substrate 2 and the high-acoustic-velocity film 4). When the cavities are provided at the interface, in regions where the cavities are provided, the support substrate 2 and the high-acoustic-velocity film 4 have the cavities therebetween, and therefore no interface is present between the support substrate 2 and the high-acoustic-velocity film 4.
In the acoustic wave device 1, an alternating current voltage is applied to the IDT electrode 7 to excite an acoustic wave. The intermediate layer 3 defined by the high-acoustic-velocity film 4 and the low-acoustic-velocity film 5 is between the support substrate 2 and the piezoelectric film 6. Therefore, the acoustic wave is confined in the piezoelectric film 6. Accordingly, good resonance characteristics can be obtained.
When the IDT electrode 7 is excited, a wave in a mode other than a main mode that is used is also excited. The wave in the mode other than the main mode also propagates in a depth direction, that is, in a direction from the piezoelectric film 6 toward the support substrate 2.
In an acoustic wave device according to the related art, a wave that propagates is reflected by a support substrate, and a response in a higher-order mode tends to occur. Therefore, as described above, when the acoustic wave device is used as a resonator for a band pass filter, a spurious response outside a pass band may occur.
In contrast, in the acoustic wave device 1, the cavities 10 overlap the IDT electrode 7 with the intermediate layer 3 and the piezoelectric film 6 provided between the IDT electrode 7 and the cavities 10 in plan view. Therefore, portions (arrows A in
A method for forming the cavities 10 is not particularly limited. For example, the high-acoustic-velocity film 4 may be formed after forming recesses in an upper surface of the support substrate 2 by etching or mechanical grinding.
A plurality of cavities 10A to 10C have different shapes. According to a preferred embodiment of the present invention, when a plurality of cavities are provided, at least one of the cavities may have a shape that differs from that of other cavity or cavities. The cavity having a different shape may be various cavities including not only a cavity having a different cross-sectional shape but also a cavity having a different size.
In
In contrast, as in a second modification illustrated in
Alternatively, as illustrated in
Thus, the cavities provided between the support substrate and the intermediate layer may be provided such that the cavities are present in partial regions between the support substrate and the intermediate layer in sectional view, and that the cavities extend into at least one of the support substrate and the intermediate layer in a lamination direction from the boundary between the support substrate and the intermediate layer.
The cavities 22 in the acoustic wave device 21 are provided in an intermediate layer 3, more specifically, in the high-acoustic-velocity film 4 such that the cavities 22 extend through the high-acoustic-velocity film 4. As illustrated in
In the acoustic wave device 21, the cavities 22 extend to both the boundary between the high-acoustic-velocity film 4 and the low-acoustic-velocity film 5 and the boundary between the high-acoustic-velocity film 4 and the support substrate 2. The cavities 22 may instead extend to only one of the boundary between the support substrate 2 and the high-acoustic-velocity film 4 and the boundary between the high-acoustic-velocity film 4 and the low-acoustic-velocity film 5. Alternatively, the cavities 22 may be positioned in the high-acoustic-velocity film 4 or in the low-acoustic-velocity film 5 such that the cavities 22 do not extend to the above-described boundaries.
The cavities 22 are preferably partially filled with a filler 32. More specifically, among the cavities 22, the cavities that extend to the boundary between the high-acoustic-velocity film 4 and the low-acoustic-velocity film 5 and the boundary between the high-acoustic-velocity film 4 and the support substrate 2 are partially filled with the filler 32, and the cavity that extends only to the boundary between the high-acoustic-velocity film 4 and the low-acoustic-velocity film 5 is entirely filled with the filler 32. In the present preferred embodiment, the filler 32 is preferably formed by causing portions of the low-acoustic-velocity film 5 to enter the cavities 22 when the low-acoustic-velocity film 5 is formed. The filler 32 may instead be made of a material other than the material of the low-acoustic-velocity film 5.
Thus, in a preferred embodiment of the present invention, the cavities 22 may be partially or entirely filled with a filler. Also in such a case, a wave that propagates may be scattered upon reflection, and responses in higher-order modes may be reduced or prevented.
In the acoustic wave device 41, a filler 42 extends into the cavities 22. The filler 42 extends into the cavities 22 from the boundary between the support substrate 2 and the high-acoustic-velocity film 4. The filler 42 is preferably formed by causing the material of the support substrate 2 to enter the cavities 22. Thus, the filler 42 with which the cavities 22 are at least partially filled may be made of the material of the support substrate 2. Also in this case, since the cavities 22 are provided, a wave that propagates may be scattered upon reflection. Accordingly, responses in higher-order modes may be suppressed.
In the acoustic wave device 51, a main mode that is used is effectively confined in the piezoelectric film 6. Since the cavities 10 are provided, higher-order modes may be reduced or prevented. Therefore, also when the acoustic wave device 51 is used as a resonator of a band pass filter, spurious responses outside a pass band may be reduced or prevented.
In a preferred embodiment of the present invention, when a support substrate made of a high-acoustic-velocity material is used as in the acoustic wave device 51, the intermediate layer may be composed only of a low-acoustic-velocity film.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-093432 | May 2020 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2020-093432, filed on May 28, 2020, and is a Continuation Application of PCT Application No. PCT/JP2021/018965, filed on May 19, 2021. The entire contents of each application are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/018965 | May 2021 | US |
| Child | 17972605 | US |
