Patent Grant
12113509
The present invention relates to an acoustic wave device.
Existing acoustic wave devices have been widely used for a filter of a cellular phone or the like. International Publication No. 2012/086639, which will be described below, discloses an example of the acoustic wave device. In this acoustic wave device, a support substrate, a high-acoustic-velocity film, a low-acoustic-velocity film, and a piezoelectric film are laminated in this order, and an IDT (Inter Digital Transducer) electrode is provided on the piezoelectric film. A Q value is increased by providing the above-described laminated structure.
When a generally known Al electrode is applied as the IDT electrode of the acoustic wave device described above, an effect of increasing the Q value can be obtained. However, since the Young's modulus of Al is relatively small, there is a limit to the Q value that can be obtained, and such a Q value is sometimes insufficient for the desired Q value.
Preferred embodiments of the present invention provide acoustic wave devices each having an improved Q characteristic.
An acoustic wave device according to a preferred embodiment of the present invention includes an energy confinement layer, a piezoelectric layer on the energy confinement layer and made of Y-cut X-propagation lithium tantalate having a cut angle of equal to or more than about −10° and equal to or less than about 65°, and an IDT electrode on the piezoelectric layer, wherein the IDT electrode includes a plurality of electrode fingers, the plurality of electrode fingers including a multilayer body including an Al metal layer defined by an Al layer or an alloy layer including Al, and a high acoustic impedance metal layer that has a Young's modulus equal to or more than about 200 GPa and a higher acoustic impedance than Al, the high acoustic impedance metal layer is located closer to the piezoelectric layer than the Al metal layer, when a wavelength defined by an electrode finger pitch of the IDT electrode is denoted by λ and a wavelength specific film thickness of the piezoelectric layer is denoted by tLT, tLT≤1λ is satisfied, and a total of normalized film thicknesses obtained by normalizing a film thickness of each layer of the electrode finger by a density and a Young's modulus of the Al metal layer is denoted by T, the following Expression 1 is satisfied.
T≤0.1125tLT+0.0574 Expression 1
An acoustic wave device according to a preferred embodiment of the present invention includes an energy confinement layer, a piezoelectric layer on the energy confinement layer and made of Y-cut X-propagation lithium tantalate having a cut angle of equal to or more than about −10° and equal to or less than about 65°, and an IDT electrode on the piezoelectric layer, wherein the IDT electrode includes a plurality of electrode fingers, the plurality of electrode fingers including a multilayer body including an Al metal layer defined by an Al layer or an alloy layer including Al, and a high acoustic impedance metal layer that has a Young's modulus equal to or more than about 200 GPa and a higher acoustic impedance than Al, the high acoustic impedance metal layer is located closer to the piezoelectric layer than the Al metal layer, the high acoustic impedance metal layer is an Mo layer, a W layer, or an Ru layer, the following Expression 2 is satisfied, and a combination of each coefficient of Expression 2 and a metal of the high acoustic impedance metal layer is a combination shown in Table 1 below.
a0(2)(tLT−c0)2+a0(1)(tLT−c0)+b0≤aLT(2)(tLT−cLT)2+aLT(1)(tLT−cLT)+aM(2)(T−cM)2+aM(1)(T−cM)+dLT-M(tLT−cLT)(T−cM)+b Expression 2
With acoustic wave devices according to preferred embodiments of the present invention, Q characteristics are able to be improved.
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.
Hereinafter, the present invention will be clarified by describing preferred embodiments of the present invention with reference to the drawings.
The preferred embodiments described in the present specification are exemplary, and partial replacement or combination of components between different preferred embodiments is possible.
An acoustic wave device 1 includes a piezoelectric substrate 2. The piezoelectric substrate 2 of the present preferred embodiment includes an energy confinement layer 3 and a piezoelectric layer 7 provided on the energy confinement layer 3. The energy confinement layer 3 of the present preferred embodiment is a multilayer body including a high-acoustic-velocity support substrate 5 as a high-acoustic-velocity material layer and a low-acoustic-velocity film 6 provided on the high-acoustic-velocity support substrate 5. The piezoelectric layer 7 is a piezoelectric layer using Y-cut X-propagation lithium tantalate having a cut angle of equal to or more than about −10° and equal to or less than about 65°, for example.
An IDT electrode 8 is provided on the piezoelectric layer 7 of the piezoelectric substrate 2. An acoustic wave is excited by applying an AC voltage to the IDT electrode 8. A pair of reflectors 9A and 9B are provided on both sides of the IDT electrode 8 in an acoustic wave propagation direction on the piezoelectric substrate 2. The acoustic wave device 1 of the present preferred embodiment is an acoustic wave resonator, for example. However, the acoustic wave device 1 according to the present invention is not limited to an acoustic wave resonator, and may be, for example, a filter device or the like having a plurality of acoustic wave resonators.
The low-acoustic-velocity film 6 is a film having a relatively low acoustic velocity. More specifically, an acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film 6 is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer 7. In the present preferred embodiment, the low-acoustic-velocity film 6 is, for example, a silicon oxide film. Silicon oxide is represented by SiOx. x is an arbitrary positive number. In the acoustic wave device 1, for example, silicon oxide of the low-acoustic-velocity film 6 is SiO2. Note that the material of the low-acoustic-velocity film 6 is not limited to the above, and for example, a material including glass, silicon oxynitride, tantalum oxide, or a compound obtained by adding fluorine, carbon, boron, hydrogen, or a silanol group to silicon oxide as a main component can be used.
The high-acoustic-velocity material layer is a layer made of a material having a relatively high acoustic velocity. More specifically, an acoustic velocity of a bulk wave propagating through the high-acoustic-velocity material layer is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer 7. As the material of the high-acoustic-velocity support substrate 5 that is the high-acoustic-velocity material layer, for example, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a DLC (diamond-like carbon) film, diamond, or the like, and media containing these materials as a main component can be used.
Since the acoustic wave device 1 of the present preferred embodiment has a configuration in which the piezoelectric layer 7 is laminated on the energy confinement layer 3 that is a multilayer body including the high-acoustic-velocity support substrate 5 and the low-acoustic-velocity film 6, the energy of the acoustic wave can be effectively confined to the piezoelectric layer 7 side. The low-acoustic-velocity film 6 may not be provided. In the present preferred embodiment, the piezoelectric layer 7 is indirectly provided on the high-acoustic-velocity material layer via the low-acoustic-velocity film 6, but the piezoelectric layer 7 may be directly provided on the high-acoustic-velocity material layer.
The IDT electrode 8 includes a first bus bar 16 and a second busbar 17 facing each other. The IDT electrode 8 includes a plurality of first electrode fingers 18 each including one end connected to the first busbar 16. Further, the IDT electrode 8 includes a plurality of second electrode fingers 19 each including one end connected to the second busbar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interdigitated with each other.
As illustrated in
When a wavelength defined by an electrode finger pitch of the IDT electrode 8 is λ and a wavelength specific film thickness of the piezoelectric layer 7 is tLT, tLT≤1λ is satisfied. The electrode finger pitch refers to a distance between the centers of the electrode fingers of the IDT electrode 8.
The total of normalized film thicknesses obtained by normalizing the film thickness of each layer of the electrode finger of the IDT electrode 8 by the density and the Young's modulus of the Al metal layer 15 is denoted by T. T is the total of the above-described normalized film thicknesses of an arbitrary electrode finger among the plurality of electrode fingers included in the IDT electrode 8. In the present preferred embodiment, T of any of the first electrode fingers 18 and T of any of the second electrode fingers 19 are the same or substantially the same. Here, it is assumed that the wavelength specific film thickness of an arbitrary metal type i is ti, the density is ρi, and the Young's modulus is Yi. i is a positive number of 0 or more, and i=0 means a metal type of the Al metal layer 15. The wavelength specific film thickness of the Al metal layer 15 is to, the density is ρ0, and the Young's modulus is Y0. The inventors of preferred embodiments of the present invention discovered that, by being defined as described above, the total film thickness T of each layer of the plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 of the IDT electrode 8 normalized by the density ρ0 and the Young's modulus Y0 of the Al metal layer 15 can be expressed as follows.
Hereinafter, the film thickness normalized by the density ρ0 and the Young's modulus Y0 of the Al metal layer 15 may be simply referred to as a normalized film thickness. Here, in the acoustic wave device 1, the relationship between the total T of the normalized film thicknesses of each layer of the electrode finger of the IDT electrode 8 and the wavelength specific film thickness tLT of the piezoelectric layer 7 satisfies the following Expression 1.
T≤0.1125tLT+0.0574 Expression 1
Further, the acoustic wave device 1 satisfies the following Expression 2. In the case where the high acoustic impedance metal layer 14 is an Mo layer, in the case of a W layer, and in the case of an Ru layer, each coefficient of Expression 2 takes a value as shown in Table 2 below.
a0(2)(tLT−c0)2+a0(1)(tLT−c0)+b0≤aLT(2)(tLT−cLT)2+aLT(1)(tLT−cLT)+aM(2)(T−cM)2+aM(1)(T−cM)+dLT-M(tLT−cLT)(T−cM)+b Expression 2
However, as long as Expression 1 is satisfied, Expression 2 does not necessarily need to be satisfied.
The present preferred embodiment has the following configuration. 1) The first electrode finger 18 and the second electrode finger 19 of the IDT electrode 8 include a multilayer body including the Al metal layer 15 and the high acoustic impedance metal layer 14, and the high acoustic impedance metal layer 14 is located closer to the piezoelectric layer 7 than the Al metal layer 15. 2) The Young's modulus of the high acoustic impedance metal layer 14 is equal to or more than about 200 GPa. 3) tLT≤1λ and the above-described Expression 1 is satisfied. 4) The above-described Expression 2 is satisfied and a combination of each coefficient of Expression 2 and the metal of the high acoustic impedance metal layer 14 is a combination shown in Table 2. As a result, the Q characteristic can be improved and the energy loss can be effectively reduced. This will be described below.
Note that in the present specification, the Q characteristic is a characteristic represented by f×Q that is a product of a frequency f and a Q value. Hereinafter, the film thickness may be expressed as t/λ×100(%), where t is the film thickness.
With reference to
Here, a metal layer corresponding to the high acoustic impedance metal layer in the first preferred embodiment is referred to as an M layer. In order to obtain the relationship between the Young's modulus of the M layer and the Q value, a simulation by the finite element method was performed by changing the density and the Young's modulus of the M layer. Note that the above-described simulation was performed under the condition that the acoustic wave device did not include the low-acoustic-velocity film and the piezoelectric layer was directly provided on the high-acoustic-velocity support substrate. More specifically, the conditions are as follows.
As shown in
As shown in
As shown in
T0≈0.1125tLT+0.0574
As shown in
Here, in the relationship of T≤T0, Expression 1 can be derived by applying the above-described approximate expression of T0.
T≤0.1125tLT+0.0574 Expression 1
By satisfying Expression 1, the Q characteristic can be improved, and the energy loss can be reduced. Further, in the following description, it is shown that the Q characteristic can be improved by satisfying Expression 1 even in a case where the high acoustic impedance metal layer is other than the Mo layer.
The Q characteristics of the acoustic wave device under the same or substantially the same conditions as the conditions under which the Q characteristics shown in
As shown in
As shown in
Furthermore, the Q characteristic may be improved not only in the case where the total film thickness T of each layer of the electrode finger of the IDT electrode is equal to or less than the normalized film thickness T0, but also in the case where the total film thickness T of each layer of the electrode finger of the IDT electrode is larger than the normalized film thickness T0. The inventors of preferred embodiments of the present invention have discovered conditions under which the Q characteristic can be improved both in the case of T≤T0 and in the case of T>T0. T0 be more specific, the following Expression 2 is satisfied and the respective coefficients in Expression 2 and the metal of the high acoustic impedance metal layer are combinations as shown in Table 2, wherein it is possible to improve the Q characteristic both in the case of T≤T0 and in the case of T>T0. That is, when T has any value, the Q characteristic can be improved. Therefore, the energy loss can be further reliably reduced.
a0(2)(tLT−c0)2+a0(1)(tLT−c0)+b0≤aLT(2)(tLT−cLT)2+aLT(1)(tLT−cLT)+aM(2)(T−cM)2+aM(1)(T−cM)+dLT-M(tLT−cLT)(T−cM)+b Expression 2
In the case where Expression 2 is satisfied and the respective coefficients in Expression 2 and the metal of the high acoustic impedance metal layer are the combinations shown in Table 2, Expression 1 may not be satisfied. However, it is preferable to satisfy Expression 1.
The Al metal layer 15 in the IDT electrode 8 illustrated in
As shown in
Note that the relationship between the film thickness of the Al layer and the normalized conductivity shown in
κ(hi)=κsat{0.36 ln(hi)−0.6} Expression 3
Expression 3 is an expression in the case where the film thickness hi is smaller than a critical film thickness hi-sat at which the conductivity κ becomes the saturation conductivity κsat. When the film thickness hi exceeds the critical film thickness hi-sat, the relationship of κ(hi)=κsat is maintained for the conductivity κ. The critical film thickness hi-sat is a film thickness hi when {0.36 ln (hi)−0.6} in Expression 3 is 1 and κ(hi)=κsat is established. More particularly, the critical film thickness hi-sat is about 85.15 nm. As is clear from this, by setting the film thickness of the Al layer to be equal to or more than about 85 nm, the conductivity can be stabilized, and the electric resistance value can be stabilized.
As shown in
As shown in
As illustrated in
In the first modification illustrated in
In the second modification illustrated in
As the material of the high-acoustic-velocity film 25, for example, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a diamond-like carbon (DLC) film, diamond, or the like, and media containing these materials as a main component can be used.
Examples of the material of the support substrate 24 include, for example, piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as sapphire, diamond, and glass; semiconductors such as silicon and gallium nitride; and resins.
In the third modification illustrated in
The acoustic reflection film 26 is a multilayer body including a plurality of acoustic impedance layers. T0 be more specific, the acoustic reflection film 26 includes a low acoustic impedance layer 27A and a low acoustic impedance layer 27B that have a relatively low acoustic impedance, and a high acoustic impedance layer 28A and a high acoustic impedance layer 28B that have a relatively high acoustic impedance. In this modification, low acoustic impedance layers and high acoustic impedance layers are alternately laminated in the acoustic reflection film 26. Note that the low acoustic impedance layer 27A is located closest to the piezoelectric layer 7 in the acoustic reflection film 26.
The acoustic reflection film 26 includes two low acoustic impedance layers and two high acoustic impedance layers. However, the acoustic reflection film 26 may include at least one low acoustic impedance layer and at least one high acoustic impedance layer.
As a material of the low acoustic impedance layer, for example, silicon oxide, aluminum, or the like can be used.
As a material of the high acoustic impedance layer, for example, a metal such as platinum or tungsten, or a dielectric such as aluminum nitride or silicon nitride can be used.
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 |
|---|---|---|---|
| 2019-071735 | Apr 2019 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2019-071735 filed on Apr. 4, 2019 and is a Continuation Application of PCT Application No. PCT/JP2020/014839 filed on Mar. 31, 2020. The entire contents of each application are hereby incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 9319023 | Tanaka | Apr 2016 | B2 |
| 10425060 | Nakamura | Sep 2019 | B2 |
| 10700662 | Miura | Jun 2020 | B2 |
| 20130285768 | Watanabe et al. | Oct 2013 | A1 |
| 20140152146 | Kimura et al. | Jun 2014 | A1 |
| 20140203893 | Kando et al. | Jul 2014 | A1 |
| Number | Date | Country |
|---|---|---|
| 2001-094382 | Apr 2001 | JP |
| 2012-222458 | Nov 2012 | JP |
| 2012086441 | Jun 2012 | WO |
| 2012086639 | Jun 2012 | WO |
| 2013047433 | Apr 2013 | WO |
| Entry |
|---|
| Official Communication issued in International Patent Application No. PCT/JP2020/014839, mailed on Jun. 23, 2020. |
| Number | Date | Country | |
|---|---|---|---|
| 20220014175 A1 | Jan 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2020/014839 | Mar 2020 | WO |
| Child | 17482660 | US |
