Patent Grant
10680577
The present invention relates to an acoustic wave device, a multiplexer, a high-frequency front-end circuit, and a communication apparatus including a piezoelectric body made of lithium tantalate that is stacked on or above a supporting substrate made of silicon.
Multiplexers have been widely used in high-frequency front-end circuits of cellular phones and smartphones. For example, a multiplexer defining and functioning as a splitter described in Japanese Unexamined Patent Application Publication No. 2014-68123 includes two or more band pass filters for different frequencies. Each of the band pass filters is formed of a surface acoustic wave filter chip. The surface acoustic wave filter chip includes multiple surface acoustic wave resonators.
Japanese Unexamined Patent Application Publication No. 2010-187373 discloses an acoustic wave device in which an insulating film made of silicon dioxide and a piezoelectric substrate made of lithium tantalate are stacked on a supporting substrate made of silicon. The heat resistance is increased by bonding the support substrate and the insulating film on a silicon (111) surface.
In the multiplexer as described in Japanese Unexamined Patent Application Publication No. 2014-68123, multiple acoustic wave filters for different frequencies are commonly connected on an antenna terminal side.
The inventors of preferred embodiments of the present invention have discovered that in the case where a structure in which a piezoelectric body made of lithium tantalate is stacked directly or indirectly on a supporting substrate made of silicon is included, multiple higher-order modes appear at higher frequencies than a main mode used. In the case where such an acoustic wave resonator is used for an acoustic wave filter associated with a lower frequency in a multiplexer, ripples due to the higher-order modes of the acoustic wave filter may appear in the pass band of another acoustic wave filter associated with a higher frequency in the multiplexer. That is, when a higher-order mode of the acoustic wave filter associated with a lower frequency in the multiplexer is located in the pass band of another acoustic wave filter associated with a higher frequency in the multiplexer, ripples occur in the pass band. This deteriorates the filter characteristics of another acoustic wave filter.
Preferred embodiments of the present invention provide acoustic wave devices, multiplexers, high-frequency front-end circuits including multiplexers, and communication apparatus in which ripples due to a higher-order mode are less likely to occur in another acoustic wave filter.
The inventors of preferred embodiments of the present invention have discovered that, as described below, in an acoustic wave device including a piezoelectric body made of lithium tantalate stacked directly or indirectly on a supporting substrate made of silicon, first to third higher-order modes described below appear at higher frequencies than the main mode.
The acoustic wave devices according to preferred embodiments of the present invention reduce or prevent at least one higher-order mode among the first, second, and third higher-order modes.
An acoustic wave device according to a preferred embodiment of the present invention includes a supporting substrate made of silicon, a silicon oxide film stacked on the supporting substrate, a piezoelectric body stacked on the silicon oxide film, the piezoelectric body being made of lithium tantalate, and interdigital transducer electrodes disposed on a main surface of the piezoelectric body, in which a wave length determined by the pitch of electrode fingers of the interdigital transducer electrodes is denoted by λ, the wave length-normalized film thickness of the piezoelectric body is denoted by TLT, the Euler angle θ of the piezoelectric body is denoted by θLT, the wave length-normalized film thickness of the silicon oxide film is denoted by TS, the wave length-normalized film thickness of the interdigital transducer electrodes of the interdigital transducer electrodes in terms of aluminum thickness is denoted by TE, a propagation direction in the supporting substrate is denoted by ψSi, and the wave length-normalized film thickness of the supporting substrate is denoted by TSi, TLT, θLT, TS, TE, and ψSi are set such that Ih represented by Formula (1) for at least one of responses of a first higher-order mode, a second higher-order mode, and a third higher-order mode is more than about −2.4, and TSi>about 20.
Coefficients a, b, c, d, and e in Formula (1) are values presented in Tables 1 to 36 below in accordance with ranges of orientation of the supporting substrate either of (100), (110), or (111), the type of higher-order mode, the wave length-normalized film thickness of the silicon oxide film, the wave length-normalized film thickness of the piezoelectric body, and the propagation direction in the supporting substrate. In the case where the orientation of the supporting substrate is (100), ψSi is the angle between the propagation direction of an acoustic wave when viewed from the main surface side of the piezoelectric body on which the interdigital transducer electrodes are disposed and the Miller indices of silicon represented by a crystal direction of [100] when viewed from the above-written main surface side. In the case where the orientation of the supporting substrate is (110), ψSi is the angle between the propagation direction of an acoustic wave when viewed from the main surface side of the piezoelectric body on which the interdigital transducer electrodes are disposed and Miller indices of the silicon represented by crystal direction of [1-10] when viewed from the above-written main surface side. In the case where the orientation of the supporting substrate is (111), ψSi is the angle between the propagation direction of an acoustic wave when viewed from the main surface side of the piezoelectric body on which the interdigital transducer electrodes are disposed and Miller indices of the silicon represented by crystal direction of [1-10] when viewed from the above-written main surface side.
In an acoustic wave device according to a preferred embodiment of the present invention, Ih for each of the first and second higher-order modes is more than about −2.4.
In an acoustic wave device according to a preferred embodiment of the present invention, Ih for each of the first and third higher-order modes is more than about −2.4.
In an acoustic wave device according to a preferred embodiment of the present invention, Ih for each of the second and third higher-order modes is more than about −2.4.
In an acoustic wave device according to a preferred embodiment of the present invention, preferably, Ih for each of the first, second, and third higher-order modes is more than about −2.4. In this case, all of the responses of the first higher-order mode, the second higher-order mode, and the third higher-order mode are able to be effectively reduced or prevented.
In an acoustic wave device according to a preferred embodiment of the present invention, the piezoelectric body has a thickness of about 3.5λ or less.
In an acoustic wave device according to a preferred embodiment of the present invention, the piezoelectric body has a thickness of about 2.5λ or less.
In an acoustic wave device according to a preferred embodiment of the present invention, the piezoelectric body has a thickness of about 1.5λ or less.
In an acoustic wave device according to a preferred embodiment of the present invention, the piezoelectric body has a thickness of about 0.5λ or less.
In an acoustic wave device according to a preferred embodiment of the present invention, an acoustic wave resonator is provided as the acoustic wave device.
An acoustic wave filter according to a preferred embodiment of the present invention includes multiple resonators, in which at least one of the multiple resonators is defined by an acoustic wave device according to a preferred embodiment of the present invention. Thus, the acoustic wave filter in which at least one of the responses of the first, second, and third higher-order modes is reduced or prevented is provided.
A multiplexer according to a preferred embodiment of the present invention includes N acoustic wave filters (where N is 2 or more) having different pass bands, one terminal of each of the N acoustic wave filters being commonly connected on an antenna terminal side, in which at least one acoustic wave filter among the N acoustic wave filters excluding an acoustic wave filter having a highest-frequency pass band includes multiple acoustic wave resonators, and at least one acoustic wave resonator among the multiple acoustic wave resonators is defined by an acoustic wave device according to a preferred embodiment of the present invention.
Preferably, the multiplexers according to preferred embodiments of the present invention are each used as a composite filter device for carrier aggregation.
A high-frequency front-end circuit according to a preferred embodiment of the present invention includes an acoustic wave filter including an acoustic wave device according to a preferred embodiment of the present invention and a power amplifier connected to the acoustic wave filter.
A communication apparatus according to a preferred embodiment of the present invention includes a high-frequency front-end circuit including an acoustic wave filter that includes an acoustic wave device according to a preferred embodiment of the present invention and a power amplifier connected to the acoustic wave filter, and an RF signal processing circuit.
In the acoustic wave devices, the multiplexers, the high-frequency front-end circuits, and the communication apparatuses according to preferred embodiments of the present invention, at least one of the response of the first higher-order mode, the response of the second higher-order mode, and the response of the third higher-order mode located at higher frequencies than the main mode is able to be effectively reduced or prevented. Thus, in the multiplexers, the high-frequency front-end circuits, and the communication apparatuses including the acoustic wave devices according to preferred embodiments of the present invention, ripples due to the higher-order mode are less likely to occur in another band pass filter having a pass band with a higher frequency than the acoustic wave device.
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 according to the present invention will be described in detail below with reference to the attached drawings so as to clarify the present invention.
Preferred embodiments described in this specification are illustrative. It should be noted that partial replacement and combination of configurations in different preferred embodiments may be made.
An acoustic wave device 1 is preferably a one-port acoustic wave resonator, for example. The acoustic wave device 1 includes a single-crystal Si layer 2 defining and functioning as a supporting substrate made of silicon. The term “supporting substrate made of silicon” includes a supporting substrate including only of silicon; and a supporting substrate made of a material including silicon as a main component and impurities. A SiO2 film 3 defining and functioning as a silicon oxide film and a piezoelectric body 4 made of lithium tantalate (LiTaO3) are stacked on the single-crystal Si layer 2. The piezoelectric body 4 includes first and second main surfaces 4a and 4b opposed to each other. Interdigital transducer electrodes 5 are disposed on the first main surface 4a. Reflectors 6 and 7 are disposed on both sides of the interdigital transducer electrodes 5 in the propagation direction of an acoustic wave. The SiO2 film 3 defining and functioning as a silicon oxide film may include not only SiO2 but also, for example, silicon oxide in which SiO2 is doped with fluorine or the like. In
The inventors of preferred embodiments of the present invention have discovered that in an acoustic wave resonator having such a structure in which a piezoelectric body made of lithium tantalate is stacked directly or indirectly on the single-crystal Si layer 2, responses due to first, second, and third higher-order modes are generated.
The single-crystal Si layer has Euler angles ( Si, θSi, ψSi)=(0°, 0°, 45°). The SiO2 film has a film thickness of about 0.30λ. The piezoelectric body made of lithium tantalate has a film thickness of about 0.30λ. The piezoelectric body made of lithium tantalate has Euler angles (φLT, θLT, ψLT)=(0°, −40°, 0°) The wave length λ determined by the pitch of electrode fingers of the interdigital transducer electrodes is about 1 μm. Each of the interdigital transducer electrodes is defined by a stacked metal film in which an Al film and a Ti film are stacked, and each interdigital transducer electrode has a thickness of about 0.05λ in terms of aluminum.
As is apparent from
A feature of the acoustic wave device 1 according to the present preferred embodiment is the fact that at least one of the response of the first higher-order mode, the response of the second higher-order mode, and the response of the third higher-order mode is reduced or prevented.
The wave length determined by the pitch of the electrode fingers of the interdigital transducer electrodes 5 is denoted by λ. The wave length-normalized film thickness of the piezoelectric body 4 made of lithium tantalate is denoted by TLT. The Euler angle θ of the piezoelectric body made of lithium tantalate is denoted by θLT. The wave length-normalized film thickness of the SiO2 film 3 is denoted by TS. The wave length-normalized film thickness of the interdigital transducer electrodes 5 in terms of aluminum thickness is denoted by TE. The propagation direction in the single-crystal Si layer 2 is denoted by ψSi. The wave length-normalized film thickness of the single-crystal Si layer 2 is denoted by TSi. TLT, θLT, TS, TE, and ψSi are set such that Ih represented by Formula (1) for at least one of the responses of the first higher-order mode, the second higher-order mode, and the third higher-order mode is preferably more than about −2.4, and TSi>about 20, for example. Thus, the at least one of the responses of the first, second, and third higher-order modes is effectively reduced or prevented. This will be described in detail below.
In this specification, the wave length-normalized film thickness is a value obtained by normalizing the thickness of the film to the wave length λ determined by the pitch of the electrode fingers of the interdigital transducer electrodes. Thus, a value obtained by dividing actual thickness of the film by λ is the wave length-normalized film thickness. The wave length λ determined by the pitch of the electrode fingers of the interdigital transducer electrodes may be determined by the average pitch of the electrode fingers.
In Formula (1), coefficients a, b, c, d, and e are values presented in Tables 37 to 72 below in accordance with ranges of, for example, the type of higher-order mode, the orientation of the single-crystal Si layer 2 either of (100), (110), or (111), the wave length-normalized film thickness of the SiO2 film 3, the wave length-normalized film thickness of the piezoelectric body made of lithium tantalate, and the propagation direction in the single-crystal Si layer 2.
The inventors of preferred embodiments of the present invention have examined how the strength of the responses of the first higher-order mode, the second higher-order mode, and the third higher-order mode change by variously changing the design parameters of TLT, θLT, TS, TE, ψSi, and TSi.
As the strength of response of the higher-order mode when the parameters are changed, the absolute value of S11 was determined. A smaller decibel value of the absolute value of S11 indicates a higher strength of the response of the higher-order mode. In the case of calculating S11, the intersecting width of the electrode fingers was 20λ, the number of pairs of the electrode fingers was 94, and S11 was determined by a two-dimensional finite element method using an electrode single-pair model.
The interdigital transducer electrodes had a structure in which metal films were stacked in order of Ti/Pt/Ti/Al from the piezoelectric body side. The thickness of the interdigital transducer electrodes was changed by changing the thickness of the Pt film. As the wave length-normalized film thickness TE of the interdigital transducer electrodes, a wave length-normalized film thickness in terms of aluminum thickness was determined using the total mass of the interdigital transducer electrodes estimated from the density of each of the metal films.
First Higher-Order Mode
An acoustic wave resonator having the admittance characteristics illustrated in
Similarly,
As illustrated in
As illustrated in
As illustrated in
From the calculation results of
The inventors of preferred embodiments of the present invention have discovered that the coefficients in Formula (1) are values presented in Table 37 to 40, Tables 49 to 52, or Tables 61 to 64 in accordance with the ranges of the crystal orientation of the single-crystal Si layer, the wave length-normalized film thickness TLT of the piezoelectric body made of lithium tantalate, the wave length-normalized film thickness TS of the SiO2 film, the wave length-normalized film thickness TE of the interdigital transducer electrodes, and the propagation direction ψSi in the single-crystal Si layer. Thus, the conditions of TLT, θLT, TS, TE, and ψSi when Ih1 corresponding to the strength of the response of the first higher-order mode is more than about −2.4 are determined.
In a multiplexer in which multiple acoustic wave filters are connected at one terminal of each filter, the response of a higher-order mode in any one of the multiple acoustic wave filters is required to have a strength S11 of more than about −2.4 dB. This is because the influence on transmission characteristics of acoustic wave filters other than the one of the multiple acoustic wave filters is negligible. In cellular phones and the like, for example, usually, ripples appearing in a pass band of a filter are required to be about −0.8 dB or more from the viewpoint of ensuring the receiver sensitivity. It has been discovered that in the case where a higher-order mode of one acoustic wave filter is in the pass band of another acoustic wave filter, ripples having a strength of about ⅓ of the strength of the response of the higher-order mode occur in the pass band of another filter. Thus, in order to achieve ripples having a magnitude of about −0.8 dB or more in the pass band of another filter, the strength S11 of the response of the higher-order mode of one filter may be more than about −2.4 dB.
Additionally, in the acoustic wave device 1 according to the first preferred embodiment, TSi>20.
Regarding the first higher-order mode, Ih is larger than about −2.4 (Ih>−2.4), and TSi is larger than about 20 (TSi>20). It is thus possible to effectively reduce or prevent the influence of the response of the first higher-order mode on the pass band of another acoustic wave filter. This will be described with reference to
In preferred embodiments of the present invention, the circuit configuration of the acoustic wave filter including the acoustic wave device is not limited thereto. For example, an acoustic wave filter including a longitudinally coupled resonator acoustic wave filter may be used. In this case, the longitudinally coupled resonator acoustic wave filter may be the acoustic wave device. An acoustic wave resonator coupled to the longitudinally coupled resonator acoustic wave filter may be defined by the acoustic wave device according to preferred embodiments of the present invention.
Pass bands of the first to fourth acoustic wave filters 11 to 14 are referred to as a first pass band to a fourth pass band. Regarding the frequency positions, preferably, first pass band<second pass band<third pass band<fourth pass band.
For comparison, a multiplexer including a first acoustic wave filter according to a comparative example was provided as in the foregoing preferred embodiment, except that the acoustic wave resonator having the reference structure described above was used. That is, in the multiplexer of the comparative example, the acoustic wave resonator having the reference structure and having the admittance characteristics illustrated in
As described above, in the multiplexer according to a preferred embodiment of the present invention, the response of the first higher-order mode is reduced or prevented in the acoustic wave filter including the acoustic wave device according to a preferred embodiment of the present invention. It is thus possible to effectively reduce or prevent the deterioration of the filter characteristics of another acoustic wave filter having a higher-frequency pass band than the acoustic wave filter.
Second Higher-Order Mode
From the calculation results of
Third Higher-Order Mode
From
Regarding Ih for all of the first higher-order mode, the second higher-order mode, and the third higher-order mode, Ih>−about 2.4 is preferable. In this case, it is possible to effectively reduce or prevent the influence of the first to third higher-order modes on another acoustic wave filter. Regarding Ih for the first higher-order mode and the second higher-order mode, Ih for the first higher-order mode and the third higher-order mode, or Ih for the second higher-order mode and the third higher-order mode, Ih>about −2.4 may preferably be used. In this case, it is possible to reduce or prevent the influence of two higher-order modes selected from the first to third higher-order modes.
In the case of using the structure of preferred embodiments of the present invention, as described above, a higher-order mode tends to be confined in a portion where the SiO2 film 3 and the piezoelectric body 4 are stacked. However, in the case where the piezoelectric body 4 has a thickness of about 3.5λ or less, the stacked portion of the SiO2 film 3 and the piezoelectric body 4 has a small thickness. Thus, the higher-order mode is not easily confined therein.
More preferably, the piezoelectric body 4 made of lithium tantalate has a thickness of about 2.5λ or less, for example. In this case, the absolute value of the temperature coefficient of frequency TCF is able to be reduced. Even more preferably, the piezoelectric body 4 made of lithium tantalate has a thickness of about 1.5λ or less, for example. In this case, the electromechanical coupling coefficient is able to be easily adjusted. Still even more preferably, the piezoelectric body 4 made of lithium tantalate has a thickness of about 0.5λ or less, for example. In this case, the electromechanical coupling coefficient is able to be easily adjusted in a wide range.
In Formula (1),
a) In the case of using Si(100) (Euler angles (φSi=0±5°, θSi=0±5°, ψSi)), the range of ψSi is preferably 0°≤ψSi≤45°, for example. However, from the symmetry of the crystal structure of Si(100), ψSi and ψSi±(n×90°) have the same meaning (where n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi have the same meaning.
b) In the case of using Si(110) (Euler angles (φSi=−45±5°, θSi=−90±5°, ψSi)), the range of ψSi is preferably 0°≤ψSi≤90°, for example. However, from the symmetry of the crystal structure of Si(110), ψSi and ψSi±(n×180°) have the same meaning (where n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi have the same meaning.
c) In the case of using Si(111) (Euler angles (φSi=−45±5°, θSi=−54.73561±5°, ψSi)), the range of ψSi is preferably 0°≤ψSi≤60° for example. However, from the symmetry of the crystal structure of Si(111), ψSi and ψSi±(n×120°) have the same meaning (where n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi have the same meaning.
The range of θLT is −180°<θLT≤0°. θLT and θLT+180° may be treated as having the same meaning.
In this specification, for example, the range of “0°±5°” in the Euler angles (0°±5°, θ, 0°±15°) means within the range about −5° or more and about +5° or less. The range of 0°±15° means within the range of about −15° or more and about +15° or less.
From
From
As illustrated in
The acoustic wave device of each preferred embodiment may be used as a component, such as a multiplexer, used in a high-frequency front-end circuit. An example of such a high-frequency front-end circuit will be described below.
The output terminals of the amplifiers 221 to 223 are connected to the RF signal processing circuit 203. The input terminal of the amplifier 224 is connected to the RF signal processing circuit 203.
The multiplexer according to the present preferred embodiment may be appropriately used as the multiplexer 210 in the communication apparatus 240.
Multiplexer according to preferred embodiments of the present invention may include multiple transmission filters and multiple reception filters. The multiplexer includes n band-pass filters where n is 2 or more. Thus, a duplexer is also included in a multiplexer in the present invention.
Filters, multiplexers that can be used for a multiband system, front-end circuits, and communication apparatuses according to preferred embodiments of the present invention can be widely used for communication equipment such as mobile phones, for example.
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 |
|---|---|---|---|
| 2017-044689 | Mar 2017 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2017-044689 filed on Mar. 9, 2017 and is a Continuation Application of PCT Application No. PCT/JP2018/008913 filed on Mar. 8, 2018. The entire contents of each application are hereby incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4449107 | Asai et al. | May 1984 | A |
| 7213314 | Abbott | May 2007 | B2 |
| 7589452 | Hauser | Sep 2009 | B2 |
| 8436510 | Yamane | May 2013 | B2 |
| 20040226162 | Miura et al. | Nov 2004 | A1 |
| 20100182101 | Suzuki | Jul 2010 | A1 |
| 20130285768 | Watanabe et al. | Oct 2013 | A1 |
| 20130300519 | Tamasaki et al. | Nov 2013 | A1 |
| 20150280689 | Nakamura et al. | Oct 2015 | A1 |
| 20180102755 | Takamine | Apr 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 58-56513 | Apr 1983 | JP |
| 2004-343359 | Dec 2004 | JP |
| 2010-187373 | Aug 2010 | JP |
| 2014-068123 | Apr 2014 | JP |
| 2015-073331 | Apr 2015 | JP |
| 2015-111845 | Jun 2015 | JP |
| 2015-188123 | Oct 2015 | JP |
| 2016208236 | Dec 2016 | WO |
| Entry |
|---|
| Official Communication issued in International Patent Application No. PCT/JP2018/008913 dated Apr. 10, 2018. |
| Number | Date | Country | |
|---|---|---|---|
| 20200007109 A1 | Jan 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/008913 | Mar 2018 | US |
| Child | 16561244 | US |
