Patent Application
20210194455
The present invention relates to an acoustic wave device, an acoustic wave filter, and a composite filter device including a lithium tantalate film that is laminated on a support substrate made of silicon.
A plurality of acoustic wave filters has been widely used in high frequency front end circuits of mobile phones and smartphones. For example, in a demultiplexer described in Japanese Unexamined Patent Application Publication No. 2014-68123, terminals of two or more band pass filters having different frequencies are connected in common. Each of the band pass filters is defined by a surface acoustic wave filter chip. Each surface acoustic wave filter chip includes a plurality of surface acoustic wave resonators.
An acoustic wave resonator described in Japanese Unexamined Patent Application Publication No. 2010-187373 discloses an acoustic wave device formed by laminating an insulation film made of silicon dioxide and a piezoelectric substrate made of lithium tantalate on a silicon support substrate. Bonding in the (111) plane of silicon enhances the heat resistance.
In an acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2014-68123, a plurality of acoustic wave filters having different frequencies are connected in common on antenna terminal side.
The inventors of preferred embodiments of the present application have discovered that a plurality of spurious responses appear on a higher frequency side relative to the main mode used in an acoustic wave resonator in which a lithium tantalate film is laminated directly on or indirectly above a silicon support substrate. When such an acoustic wave resonator is used for an acoustic wave filter having a lower pass band in an acoustic wave device, a spurious response appearing in the acoustic wave filter may appear in a pass band of another acoustic wave filter having a higher pass band in the acoustic wave device. Thus, the filter characteristic of another acoustic wave filter may deteriorate.
Preferred embodiments of the present invention provide acoustic wave devices, acoustic wave filters, and composite filter devices that are each less likely to generate a ripple in another acoustic wave filter.
An acoustic wave device according to a preferred embodiment of the present invention includes a silicon support substrate, a silicon oxide film laminated above the silicon support substrate, a lithium tantalate film laminated above the silicon oxide film, an IDT electrode including an electrode finger and being provided above the lithium tantalate film, and a protection film covering at least a portion of the IDT electrode. When a wavelength determined by an electrode finger pitch of the IDT electrode is denoted by λ, a wavelength normalized film thickness of the lithium tantalate film is denoted by TLT, θ of an Euler angle of the lithium tantalate film is denoted by θLT, a wavelength normalized film thickness of the silicon oxide film is denoted by TS, a wavelength normalized film thickness of the IDT electrode in terms of aluminum thickness being a product of a wavelength normalized film thickness of the IDT electrode and a value obtained when density of the IDT electrode is divided by density of aluminum is denoted by TE, a wavelength normalized film thickness of the protection film being a product of a value obtained when density of the protection film is divided by density of silicon oxide and a wavelength normalized film thickness which is a thickness of the protection film normalized by the wavelength λ is denoted by TP, a propagation direction in the silicon support substrate is denoted by ψSi, and a wavelength normalized film thickness which is a thickness of the silicon support substrate normalized by the wavelength λ is denoted by TSi, TLT, θLT, TS, TE, TP, and ψSi are set such that a value represented by Formula (1) below is larger than about −2.4:
Coefficients a, b, c, d, e, and f in Formula (1) are values described in Table 1 to Table 12 below that are determined in accordance with the crystal orientation of the silicon support substrate and the range of TS, TLT, and ψSi:
An acoustic wave device according to another preferred embodiment of the present invention includes a silicon support substrate, a silicon oxide film laminated above the silicon support substrate, a lithium tantalate film laminated above the silicon oxide film, an IDT electrode including an electrode finger and being provided above the lithium tantalate film, and a protection film covering at least a portion of the IDT electrode. When a wavelength determined by an electrode finger pitch of the IDT electrode is denoted by λ, a wavelength normalized film thickness of the lithium tantalate film is denoted by TLT, θ of an Euler angle of the lithium tantalate film is denoted by θLT, a wavelength normalized film thickness of the silicon oxide film is denoted by TS, a wavelength normalized film thickness of the IDT electrode in terms of aluminum thickness being a product of a wavelength normalized film thickness of the IDT electrode and a value obtained when density of the IDT electrode is divided by density of aluminum is denoted by TE, a wavelength normalized film thickness of the protection film being a product of a value obtained when density of the protection film is divided by density of silicon oxide and a wavelength normalized film thickness which is a thickness of the protection film normalized by the wavelength λ is denoted by TP, a propagation direction in the silicon support substrate is denoted by ψSi, and a wavelength normalized film thickness which is a thickness of the silicon support substrate normalized by the wavelength λ is denoted by TSi, TLT, θLT, TS, TE, TP, and ψSi are set such that a value represented by Formula (1) below is larger than about −2.4:
Coefficients a, b, c, d, e, and f in Formula (1) are values described in Table 13 to Table 24 below that are determined in accordance with the crystal orientation of the silicon support substrate and the range of TS, TLT, and ψSi:
An acoustic wave device according to another preferred embodiment of the present invention includes a silicon support substrate, a silicon oxide film laminated above the silicon support substrate, a lithium tantalate film laminated above the silicon oxide film, an IDT electrode including an electrode finger and being provided above the lithium tantalate film, and a protection film covering at least a portion of the IDT electrode. When a wavelength determined by an electrode finger pitch of the IDT electrode is denoted by λ, a wavelength normalized film thickness of the lithium tantalate film is denoted by TLT, θ of an Euler angle of the lithium tantalate film is denoted by θLT, a wavelength normalized film thickness of the silicon oxide film is denoted by TS, a wavelength normalized film thickness of the IDT electrode in terms of aluminum thickness being a product of a wavelength normalized film thickness of the IDT electrode and a value obtained when density of the IDT electrode is divided by density of aluminum is denoted by TE, a wavelength normalized film thickness of the protection film being a product of a value obtained when density of the protection film is divided by density of silicon oxide and a wavelength normalized film thickness which is a thickness of the protection film normalized by the wavelength λ is denoted by TP, a propagation direction in the silicon support substrate is denoted by ψSi, and a wavelength normalized film thickness which is a thickness of the silicon support substrate normalized by the wavelength λ is denoted by TSi, TLT, θLT, TS, TE, TP, and ψSi are set such that a value represented by Formula (1) below is larger than about −2.4:
Coefficients a, b, c, d, e, and f in Formula (1) are values described in Table 25 to Table 36 below that are determined in accordance with the crystal orientation of the silicon support substrate and the range of TS, TLT, and ψSi:
An acoustic wave filter according to a preferred embodiment of the present invention includes a plurality of resonators, and at least one of the plurality of resonators is defined by an acoustic wave device according to a preferred embodiment of the present invention.
A composite filter device according to a preferred embodiment of the present invention includes N band pass filters having different pass bands where N is two or more, and one terminal of each of the N band pass filters is connected in common on an antenna terminal side. At least one of the N band pass filters excluding a band pass filter having a highest pass band includes one or more acoustic wave resonators. At least one of the one or more acoustic wave resonators is defined by an acoustic wave device according to a preferred embodiment of the present invention.
According to preferred embodiments of the present invention, it is possible to provide acoustic wave devices that are each less likely to generate a ripple in another acoustic wave filter that is connected in common, and to provide acoustic wave filters and composite filter devices that each include an acoustic wave device according to a preferred embodiment of the present invention.
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 the description of preferred embodiments of the present invention with reference to drawings.
It should be noted that the preferred embodiments described in this description are merely exemplary, and that a partial replacement or a combination of configurations is possible between the different preferred embodiments.
An acoustic wave device 1 is a one-port acoustic wave resonator. The acoustic wave device 1 includes a single crystal Si layer 2 defining and functioning as a support substrate. A SiO2 film 3 as a silicon oxide film and a lithium tantalate film (LiTaO3 film) 4 are laminated above the single crystal Si layer 2. The lithium tantalate film 4 includes a first main surface 4a and a second main surface 4b opposite to each other. An IDT electrode 5 is provided above the first main surface 4a. Reflectors 6 and 7 are provided on both sides of the IDT electrode 5 in an acoustic wave propagation direction. The SiO2 film 3 as the silicon oxide film may include not only SiO2, but also silicon oxide, for example, in which SiO2 is doped with fluorine or the like. The silicon oxide film may be, for example, a multilayer structure including a plurality of layers made of silicon oxide. An intermediate layer made of, for example, titanium, nickel, or the like may be included between the plurality of layers. The thickness of the silicon oxide film in this case means the thickness of the entire multilayer structure.
A protection film 8 covers the IDT electrode 5 and the reflectors 6 and 7. The protection film 8 is preferably, for example, a silicon oxide film in the present preferred embodiment. However, the protection film 8 may be a film made of various dielectrics such as, for example, silicon oxynitride, silicon nitride, or the like. In addition, in the present preferred embodiment, the protection film 8 covers not only the upper side of an electrode finger of the IDT electrode 5, but also the upper surface of the lithium tantalate film 4 and the side surfaces of the electrode finger. However, the configuration of the protection film 8 is not limited thereto.
The inventors of preferred embodiments of the present application have discovered that responses are generated by spurious responses A, B, and C described below in the acoustic wave resonator in which a lithium tantalate film is laminated directly on or indirectly above the single crystal Si layer 2.
Euler angles (TSi, θSi, ψSi) of the single crystal Si layer are (0°, 0°, 45°). The film thickness of the SiO2 film is about 0.30λ, the film thickness of the lithium tantalate film is about 0.30λ, and the Euler angles (TLT, θLT, ψLT) of the lithium tantalate film are (0°, −40°, 0°). The wavelength λ determined by the electrode finger pitch of the IDT electrode is about 1 μm. The IDT electrode includes laminated metal films in which an Al film and a Ti film are laminated, and has a thickness of about 0.05λ in terms of aluminum.
As shown in
In the acoustic wave device 1 of the present preferred embodiment, at least one of the responses of the spurious response A, the response of the spurious response B, and the response of the spurious response C is reduced or prevented.
The wavelength determined by the electrode finger pitch of the IDT electrode 5 is denoted by λ. The wavelength normalized film thickness of the lithium tantalate film 4 is denoted by TLT, the Euler angle θ of the lithium tantalate film is denoted by θLT, the wavelength normalized film thickness of the SiO2 film 3 is denoted by TS, the wavelength normalized film thickness of the IDT electrode 5 in terms of aluminum thickness is denoted by TE. The wavelength normalized film thickness of the protection film 8 is denoted by TP, where TP is the product of a value obtained when density of the protection film 8 is divided by density of silicon oxide and the wavelength normalized film thickness of the protection film 8 normalized by the wavelength λ. The propagation direction in the single crystal Si layer 2 is denoted by ψSi, and the wavelength normalized film thickness of the single crystal Si layer 2 is denoted by TSi. TLT, θLT, TS, TE, TP, and ψSi are set such that the value Ih represented by Formula (1) below for at least one of the spurious responses A, B, and C is greater than about −2.4 and the inequality TSi>about 20 is satisfied at the same time. Thus, at least one of the responses of the spurious responses A, B and C is effectively reduced or prevented. This will be described in detail below.
Note that, in the present description, the wavelength normalized film thickness is the value obtained when a film thickness is normalized by the wavelength λ determined by the electrode finger pitch of the IDT electrode. That is, the wavelength normalized film thickness is the value obtained when an actual thickness is divided by λ. The wavelength λ determined by the electrode finger pitch of the IDT electrode may be determined by an average value of the electrode finger pitches.
The density of the IDT electrode 5 is the value obtained from the density of the metal material constituting the IDT electrode 5, rather than a measured value. The density of aluminum is about 2698.9 kg/m3. This value is described in page 26 of “Handbook of Chemistry: Pure Chemistry II, 4th edition, The Chemical Society of Japan, published by Maruzen Publishing Co., Ltd. (1993)”.
Here, the density of the protection film 8 is the value obtained based on the density of the material of the protection film 8, rather than a measured value. The density of silicon oxide is about 2200 kg/m3. This value is described in page 922 of “Handbook of Chemistry: Applied Chemistry II, Materials, 4th edition, The Chemical Society of Japan, published by Maruzen Publishing Co., Ltd. (1993)”.
Note that, in the present description, the thickness of the protection film 8 refers to a thickness of the protection film in a portion positioned on the upper side of the electrode finger of the IDT electrode.
The coefficients a, b, c, d, e, and f in Formula (1) are values in Table 37 to Table 72 below. The values are specified in accordance with the type of spurious responses, the orientation (100), (110), or (111) of the single crystal Si layer 2, and the range of the wavelength normalized film thicknesses of the SiO2 film 3 and the lithium tantalate film 4, and the like.
The inventors of preferred embodiments of the present application variously changed the design parameters TLT, θLT, TS, TE, TP, ψSi and TSi, and determined how the intensity of the response becoming the spurious response A, B, or C changed.
Note that the absolute value of S11 was calculated as the intensity of the response of the spurious response when the above parameters were changed. The smaller the value of the absolute value of S11 in decibel is, the greater the intensity of the response of the spurious response is. When calculating S11, the overlap width of the electrode fingers was 20λ and the number of pairs of the electrode fingers was 94 pairs, and S11 was obtained with the one pair electrode finger model of the two-dimensional finite element method.
Note that the IDT electrode has a structure in which the metal films were laminated in the order of Ti/Pt/Ti/Al from the lithium tantalate film side. The thickness of the IDT electrode was changed by varying the thickness of the Pt film. Further, the wavelength normalized film thickness TE of the IDT electrode was calculated as the wavelength normalized film thickness in terms of aluminum thickness, using the mass of the entire IDT electrode estimated from the density of each metal film.
The acoustic wave resonator having the admittance characteristic shown in
Similarly, as described in
Further, as described in
As described in
As described in
As described in
From
The inventors of preferred embodiments of the present application have discovered that Ih corresponding to the intensity of the response of the spurious response may be obtained by Formula (1) and the coefficients a, b, c, d, e, and f in Table 37 to Table 48, from the calculation results in
The coefficients in Formula (1) have been discovered to be values described in Table 37 to Table 48 in accordance with the crystal orientation of the single crystal Si layer, the respective ranges of the wavelength normalized film thickness TLT of the lithium tantalate film, the Euler angle θLT of the lithium tantalate film, the wavelength normalized film thickness TS of the SiO2 film, the wavelength normalized film thickness TE of the IDT electrode, and the wavelength normalized film thickness TP of the protection film, and the propagation direction ψSi in the single crystal Si layer. Thus, the conditions of TIT, θLT, TS, TE, TP, and ψSi, where Ih1 corresponding to the intensity of the response of the spurious response A is greater than about −2.4 are determined.
In the composite filter device in which the plurality of acoustic wave filters are connected at one end, the intensity of the response of the spurious response is required to be greater than about −2.4 dB in S11. This is to make the influence negligible on the bandpass characteristic of another acoustic wave filter other than one acoustic wave filter. Typically, the ripple appearing in the pass band is required to be equal to or greater than about −0.8 dB from the viewpoint of ensuring the reception sensitivity in a mobile phone or the like. Meanwhile, it has been known that when the spurious response is present in the pass band of another acoustic wave filter, a ripple of approximately ⅓ of the intensity of the response of the spurious response is generated in the pass band of another filter. Accordingly, in order to make the ripple in the pass band equal to or greater than about −0.8 dB, the intensity S11 of the response of the spurious response may be set to be greater than about −2.4 dB.
With Ih for the spurious response A, the inequality Ih>about −2.4 is satisfied, and thus it is possible to effectively reduce or prevent the influence by the response of the spurious response A on the pass band of another acoustic wave filter. This will be described with reference to
Note that, in the present invention, the circuit configuration of the acoustic wave filter including the acoustic wave device according to a preferred embodiment of the present invention is not limited thereto. For example, an acoustic wave filter including a longitudinally coupled resonator acoustic wave filter may be employed. In this case, the longitudinally coupled resonator acoustic wave filter may be an acoustic wave device according to a preferred embodiment of the present invention. Alternatively, the acoustic wave resonator connected to the longitudinally coupled resonator acoustic wave filter may be defined by an acoustic wave device according to a preferred embodiment of the present invention.
Note that the pass bands of the first acoustic wave filter 11 to the fourth acoustic wave filter 14 are referred to as a first pass band to a fourth pass band.
The first pass band is on the lowest frequency side, and the pass band is higher in the order of the second pass band, the third pass band, and the fourth pass band. That is, the pass bands satisfy the relation, first pass band<second pass band<third pass band<fourth pass band.
For a comparison, a composite filter device of a comparative example was prepared in which the first acoustic wave filter was configured in the same manner as in the preferred embodiment of the preferred embodiment described above, except that the acoustic wave resonator of the reference structure was used.
As described above, in the composite filter device according to the present preferred embodiment, the response of the spurious response A is reduced or prevented in the acoustic wave filter defined by the acoustic wave device according to the preferred embodiment of the present invention described above. Thus, it is possible to effectively reduce or prevent the deterioration of the filter characteristic of another acoustic wave filter having a higher pass band relative to the pass band of the one acoustic wave filter.
Still further, as described in
The coefficient values in Formula (1) for expressing Ih2 corresponding to the intensity of the response of the spurious response B were obtained from the calculation results in
Still further, as described in
The coefficient values in Formula (1) for expressing Ih3 corresponding to the intensity of the response of the spurious response C were obtained from
Preferably, the inequality Ih>about −2.4 is satisfied for all of the spurious responses A, B, and C. In this case, it is possible to effectively reduce or prevent the influence of the spurious responses A, B, and C on another acoustic wave filter. Alternatively, Ih for the spurious response A and the spurious response B, Ih for the spurious response A and the spurious response C, or Ih for the spurious response B and the spurious response C may satisfy the inequality Ih>about −2.4. In this case, it is possible to reduce or prevent the influence of two of the spurious responses A, B, and C.
With the structures of preferred embodiments of the present invention, as described above, the spurious response tends to be confined in a portion where the SiO2 film 3 and the lithium tantalate film 4 are laminated. However, the spurious response is less likely to be confined by making the thickness of the lithium tantalate film 4 equal to or less than about 3.5λ, for example, since the laminated portion of the SiO2 film 3 and the lithium tantalate film 4 becomes thin.
More preferably, the film thickness of the lithium tantalate film 4 is equal to or less than about 2.5λ, for example, and in this case, the absolute value of the frequency temperature coefficient TCF may be made small. Further, preferably, the film thickness of the lithium tantalate film 4 is equal to or less than about 1.5λ, for example. In this case, the electromechanical coupling coefficient may easily be adjusted. Further, more preferably, the film thickness of the lithium tantalate film 4 is equal to or less than about 0.5λ, for example. In this case, the electromechanical coupling coefficient may be easily adjusted in a wide range.
Note that in Formula (1) described above:
a) The range of ψSi is 0°≤ψSi≤45° when Si (100) having the Euler angles (φSi=0°±5°, θSi=0°±5°, ψSi) is preferably used. Meanwhile, due to the symmetricity of the crystal structure of Si (100), ψSi and ψSi±(n×90°) are synonymous with each other (note that n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi are synonymous with each other;
b) The range of ψSi is 0°≤ψSi≤90° when Si (110) having the Euler angles (φSi=−45°±5°, θSi=−90°±5°, ψSi) is used. Meanwhile, due to the symmetricity of the crystal structure of Si (110), ψSi and ψSi±(n×180°) are synonymous with each other (note that n=1, 2, 3 . . . ). Similarly, ψSi and ψSi are synonymous with each other; and
C) The range of ψSi is 0° about 60° when Si (111) having the Euler angles (φSi=−45°±5°, θSi=−54.73561°±5°, ψSi) is used. Meanwhile, due to the symmetricity of the crystal structure of Si (111), ψSi and ψSi±(n×120°) are synonymous with each other (note that n=1, 2, 3 . . . ).
Further, although the range of θLT is set to −180°<θLT about 0°, θLT and θLT+180° may be treated as synonymous with each other.
In the present description, for example, when the Euler angles (within the range of 0°±5°, θ, within the range of 0°±15°) is cited, “within the range of 0°±5°” means “within the range of equal to or greater than −5° and equal to or less than +5°”, and “within the range of 0°±15°” means “within the range of equal to or greater than −15° and equal to or less than +15°”. In the present description, for example, “within the range of 0°±5°” may simply be denoted by “0°+5°”.
From
From
Meanwhile, as described in
In the modification illustrated in
In the modification illustrated in
As illustrated in
As illustrated in
As illustrated in
The acoustic wave device of each of the above-described preferred embodiments may be used as a component for such as the composite filter device in a high frequency front end circuit. An example of such high frequency front end circuit according to a preferred embodiment of the present invention will be described below.
The output terminals of the amplifiers 221 to 223 are connected to the RF signal processing circuit 203. An input terminal of the amplifier 224 is connected to the RF signal processing circuit 203.
The composite filter device according to the present preferred embodiment may be suitably used as the composite filter device 210 in the communication apparatus 240 described above.
The acoustic wave device according to a preferred embodiment of the present invention is preferably the above-described acoustic wave resonator. The acoustic wave filter according to a preferred embodiment of the present invention includes a plurality of resonators and at least one of the plurality of resonators may be defined by an acoustic wave device according to a preferred embodiment of the present invention.
The composite filter device according to the present preferred embodiment includes N band pass filters (N is two or more) having different pass bands as in the composite filter device 210 described above, and one terminal of each of the N band pass filters is connected in common on the antenna terminal side. In this case, at least one of the N band pass filters excluding the band pass filter having the highest pass band includes one or more acoustic wave resonators, and at least one of the one or more acoustic wave resonators may be an acoustic wave device according to a preferred embodiment of the present invention. In addition, in the N band pass filters, at least one of the band pass filters other than the acoustic wave filters including the acoustic wave device according to a preferred embodiment of the present invention may not be an acoustic wave filter. That is, the band pass filters connected in common may include a band pass filter other than an acoustic wave filter, such as an LC filter, for example. Preferably, N is three or more, for example, and the three or more band pass filters define the composite filter device for simultaneously transmitting and receiving signals of a plurality of communication bands. Further, the acoustic wave filter may be a ladder filter, for example.
The acoustic wave devices according to preferred embodiments of the present invention may each be used in various communication bands, and preferably, the pass band in the acoustic wave filter is a pass band of a communication band defined by the 3GPP standard.
The composite filter devices according to preferred embodiments of the present invention may include only a plurality of transmission filters, or may include a plurality of reception filters.
Preferred embodiments of the present invention may widely be used in a communication device, such as a mobile phone, for example, as a filter or a composite filter device, a front end circuit, and a communication apparatus applicable to a multi-band system.
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 |
|---|---|---|---|
| 2018-168265 | Sep 2018 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2018-168265 filed on Sep. 7, 2018 and is a Continuation Application of PCT Application No. PCT/JP2019/035185 filed on Sep. 6, 2019. The entire contents of each application are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2019/035185 | Sep 2019 | US |
| Child | 17183431 | US |
