Patent Grant
11463067
The present invention relates to a multiplexer including two or more acoustic wave filters, a radio-frequency front end circuit including the multiplexer, and a communication device.
Heretofore, multiplexers have been widely used in radio-frequency front end circuits of mobile phones and smartphones. For example, a multiplexer serving as a splitter disclosed in Japanese Unexamined Patent Application Publication No. 2014-68123 includes two or more band pass filters having different frequencies. Each band pass filter is formed of a surface acoustic wave filter chip. Each surface acoustic wave filter chip includes a plurality of surface acoustic wave resonators.
Japanese Unexamined Patent Application Publication No. 2010-187373 discloses an acoustic wave device in which an insulating film composed of silicon dioxide and a piezoelectric substrate composed of lithium tantalate are stacked on a silicon support substrate. In addition, the acoustic wave device has improved heat resistance due to the support substrate being bonded to the piezoelectric substrate at the (111) plane of silicon.
In the multiplexer disclosed in Japanese Unexamined Patent Application Publication No. 2014-68123, a plurality of acoustic wave filters having different frequencies are connected so as to form a common connection on the antenna terminal side.
The inventors of preferred embodiments of the present application discovered that, in the case of a structure in which a piezoelectric substrate made of lithium tantalate is directly or indirectly stacked on a support substrate made of silicon, a plurality of higher-order modes appear on the high-frequency side of the utilized main mode. In the case where such an acoustic wave resonator is used in an acoustic wave filter of a multiplexer having a lower frequency, there is a risk that a ripple generated by a higher-order mode of that acoustic wave filter will appear in the pass band of another acoustic wave filter of the multiplexer having a higher frequency than that acoustic wave filter. In other words, if a higher-order mode of the acoustic wave filter of the multiplexer having the lower frequency is located inside the pass band of the acoustic wave filter of the multiplexer having the higher frequency, a ripple will be generated in the pass band of the acoustic wave filter having the higher frequency. Therefore, there is a risk of the filter characteristics of the other acoustic wave filter being degraded.
Preferred embodiments of the present invention provide multiplexers in which a ripple due to a higher-order mode is unlikely to be generated in another band pass filter, radio-frequency front end circuits including the multiplexers, and communication devices.
As described later, the inventors of preferred embodiments of the present application discovered that in an acoustic wave resonator in which a piezoelectric body made of lithium tantalate is directly or indirectly stacked on a support substrate made of silicon, first to third higher-order modes, which are described later, appear on the high-frequency side of a main mode.
Multiplexers according to preferred embodiments of the present invention avoid a situation in which at least one higher-order mode among first, second, and third higher-order modes of one filter is generated in the pass band of another filter.
A multiplexer according to a preferred embodiment of the present invention includes N acoustic wave filters (N is an integer greater than or equal to 2) including first ends connected to define a common connection and having different pass bands from each other. At least one acoustic wave filter among the N acoustic wave filters except for the acoustic wave filter having the highest pass band includes a piezoelectric body made of lithium tantalate having Euler angles (φLT=0°±5°, θLT, ψLT=0°±15°), a support substrate made of silicon having Euler angles (φSi, θSi, ψSi), a silicon oxide film stacked between the piezoelectric body and the support substrate, and a plurality of acoustic wave resonators including interdigital transducer (IDT) electrodes provided on one surface of the piezoelectric body. When a thickness normalized using a wavelength λ determined by an electrode finger pitch of the IDT electrode is referred to as a wavelength-normalized thickness, at least one out of first, second, and third higher-order mode frequencies fhs_t(n) (s is 1, 2, or 3, and the at least one higher-order mode is the first, second, or third higher-order mode when s is 1, 2, or 3) determined by Formula (1) and Formula (2) below using a wavelength-normalized thickness TLT of the piezoelectric body, Euler angles θLT of the piezoelectric body, a wavelength-normalized thickness TS of the silicon oxide film, a wavelength-normalized thickness TE of the IDT electrode converted into a thickness of aluminum, a propagation direction ψSi inside the support substrate, and a wavelength-normalized thickness TSi of the support substrate has a value that satisfies Formula (3) or Formula (4) below in at least one acoustic wave resonator among the plurality of acoustic wave resonators for all values of m where m>n.
The h in Formulas (1) to (4) indicates a higher-order mode, t indicates the t-th element (resonator) in a filter n, m indicates the m-th (m>n) filter, n indicates the n-th filter, fu(m) is the frequency of the high-frequency end of the pass band of the m-th filter, and fl(m) is the frequency of the low-frequency end of the pass band of the m-th filter.
The coefficients in Formula (1) respectively have values illustrated in Table 1, Table 2, or Table 3 below for the various crystal orientations of the support substrate when s=1, 2, or 3.
A multiplexer according to a preferred embodiment of the present invention includes N acoustic wave filters (N is an integer greater than or equal to 2) having first ends connected to define a common connection and having different pass bands from each other. When the N acoustic wave filters are regarded as being an acoustic wave filter (1), an acoustic wave filter (2), . . . an acoustic wave filter (N) in order of increasing pass band, at least one acoustic wave filter (n) (1≤n<N) except for the acoustic wave filter having the highest pass band among the N acoustic wave filters includes at least one acoustic wave resonator. The acoustic wave resonator includes a piezoelectric body made of lithium tantalate having Euler angles (φLT=0°±5°, θLT, ψLT=0°±15°), a support substrate made of silicon having Euler angles (φSi, θSi, ψSi), and an IDT electrode provided on one surface of the piezoelectric body. In the acoustic wave resonator, when a thickness normalized using a wavelength λ determined by an electrode finger pitch of the IDT electrode is referred to as a wavelength-normalized thickness, TLT is a wavelength-normalized thickness of the piezoelectric body, θLT is Euler angles of the piezoelectric body, TS is a wavelength-normalized thickness of the silicon oxide film, TE is a wavelength-normalized thickness of the IDT electrode converted into a thickness of aluminum, ψSi is a propagation direction inside the support substrate, and TSi is a wavelength-normalized thickness of the support substrate, at least one out of first, second, and third higher-order mode frequencies fhs_t(n) (s is 1, 2, or 3, and the at least one higher-order mode is the first, second, or third higher-order mode when s is 1, 2, or 3) determined by Formula (5) and Formula (2) below determined using TLT, θLT, TS, TE, ψSi, and TSi has a value that satisfies below Formula (3) or Formula (4) in all acoustic wave filters (m) (n<m≤N) having a higher pass band than the at least one acoustic wave filter (n).
The h in Formulas (2) to (4) and Formula (5) indicates a higher-order mode, fu(m) is the frequency of the high-frequency end of the pass band of the acoustic wave filter (m), and fl(m) is the frequency of the low-frequency end of the pass band of the acoustic wave filter (m).
The coefficients in Formula (5) respectively have values illustrated in below Table 4, Table 5, or Table 6 for the various crystal orientations of the support substrate when s=1, 2, or 3.
Using Formula (5), in the multiplexer of the present preferred embodiment, θLT, which is not considered in Formula (1), is also taken into consideration, and therefore the at least one higher-order mode among the plurality of higher-order modes of one acoustic wave filter is even less likely to be generated inside the pass band of another acoustic wave filter having a higher pass band.
In a multiplexer according to a preferred embodiment of the present invention, the values of TLT, θLT, TS, TE, ψSi, and TSi are selected so that the first and second higher-order mode frequencies fhs_t(n) satisfy Formula (3) or Formula (4).
In a multiplexer according to a preferred embodiment of the present invention, the values of TLT, θLT, TS, TE, ψSi, and TSi are selected so that the first and third higher-order mode frequencies fhs_t(n) satisfy Formula (3) or Formula (4).
In a multiplexer according to a preferred embodiment of the present invention, the values of TLT, θLT, TS, TE, ψSi, and TSi are selected so that the second and third higher-order mode frequencies fhs_t(n) satisfy Formula (3) or Formula (4).
In a multiplexer according to a preferred embodiment of the present invention, the values of TLT, θLT, TS, TE, ψSi, and TSi are selected so that the first, second, and third higher-order mode frequencies fhs_t(n) all satisfy Formula (3) or Formula (4). In this case, ripples caused by responses of the first higher-order mode, the second higher-order mode, and the third higher-order mode do not appear in the pass band of the other acoustic wave filter.
In a multiplexer according to a preferred embodiment of the present invention, TSi>4 for the wavelength-normalized thickness TSi of the support substrate.
In a multiplexer according to a preferred embodiment of the present invention, TSi>10.
In a multiplexer according to a preferred embodiment of the present invention, TSi>20.
In a multiplexer according to a preferred embodiment of the present invention, the wavelength-normalized thickness of the piezoelectric body is less than or equal to about 3.5λ.
In a multiplexer according to a preferred embodiment of the present invention, the wavelength-normalized thickness of the piezoelectric body is less than or equal to about 2.5λ.
In a multiplexer according to a preferred embodiment of the present invention, the wavelength-normalized thickness of the piezoelectric body is less than or equal to about 1.5λ.
In a multiplexer according to a preferred embodiment of the present invention, the wavelength-normalized thickness of the piezoelectric body is less than or equal to about 0.5λ.
In a multiplexer according to a preferred embodiment of the present invention, the multiplexer further includes an antenna terminal to which first ends of a plurality of acoustic wave filters are connected to define a common connection, the acoustic wave resonator that satisfies Formula (3) and Formula (4) being an acoustic wave resonator that is closest to the antenna terminal. In this case, ripples due to the first, second, and third higher-order modes are even less likely to be generated in the pass band of the other acoustic wave filter.
In a multiplexer according to a preferred embodiment of the present invention, the plurality of acoustic wave resonators are all acoustic wave resonators that satisfy Formula (3) and Formula (4). In this case, ripples due to at least one higher-order mode among the first, second, and third higher-order modes can be more effectively suppressed in other acoustic wave filter.
A multiplexer according to a preferred embodiment of the present invention may be a duplexer.
In addition, a multiplexer according to a preferred embodiment the present invention may be a composite filter in which three or more acoustic wave filters are connected to define a common connection on the antenna terminal side.
In a multiplexer according to a preferred embodiment of the present invention, the multiplexer is a composite filter device used in carrier aggregation.
In a multiplexer according to a preferred embodiment of the present invention, the acoustic wave filter including a plurality of acoustic wave resonators is preferably a ladder filter that includes a plurality of series arm resonators and a plurality of parallel arm resonators. In this case, the effect of higher-order modes can be more effectively reduced or prevented.
A radio-frequency front end circuit according to a preferred embodiment of the present invention includes a multiplexer according to a preferred embodiment of the present invention and a power amplifier.
A communication device according to a preferred embodiment of the present invention includes a radio-frequency front end circuit including a multiplexer according to a preferred embodiment of the present invention and a power amplifier, and an RF signal processing circuit.
According to a multiplexers of preferred embodiments of the present invention, at least one higher-order mode among a plurality of higher-order modes generated by at least one acoustic wave resonator of an acoustic wave filter having a lower pass band is unlikely to be generated inside the pass band of another acoustic wave filter having a higher pass band. Therefore, degradation of the filter characteristics of the other acoustic wave filter is unlikely to occur. Therefore, radio-frequency front end circuits and communication devices that each include a multiplexer having excellent filter characteristics are able to be provided.
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.
Hereafter, the present invention will be made clearer by describing specific preferred embodiments of the present invention with reference to the drawings.
The preferred embodiments described in the present specification are illustrative examples and portions of the configurations illustrated in different preferred embodiments can be substituted for one another or combined with one another.
In the multiplexer 1, a first acoustic wave filter 3, a second acoustic wave filter 4, a third acoustic wave filter 5, and a fourth acoustic wave filter 6 are connected to the antenna terminal 2 via a common connection. The first to fourth acoustic wave filters 3 to 6 are preferably band pass filters.
The frequency positions of the pass bands are preferably as follows: first pass band<second pass band<third pass band<fourth pass band. In the second to fourth pass bands, a low-frequency end is denoted as fl(m) and a high-frequency end is denoted as fu(m). The low-frequency end is the low-frequency end of the pass band. In addition, the high-frequency end is the high-frequency end of the pass band. For example, the ends of the frequency bands of the bands standardized in 3GPP or the like can be used as the low-frequency ends and high-frequency ends of the pass bands.
Here, (m) is 2, 3, or 4 in accordance with the second to fourth pass bands.
The first to fourth acoustic wave filters 3 to 6 each preferably include a plurality of acoustic wave resonators.
Furthermore, the second to fourth filters 4 to 6 are similarly each preferably a ladder filter and include a plurality of series arm resonators and a plurality of parallel arm resonators.
Provided that the first to fourth acoustic wave filters 3 to 6 include a plurality of acoustic wave resonators, the first to fourth acoustic wave filters 3 to 6 may have a configuration other than a ladder filter configuration. For example, the first to fourth acoustic wave filters 3 to 6 may each be an acoustic wave filter in which an acoustic wave resonator is serially electrically connected to a longitudinally coupled resonator acoustic wave filter. In addition, the first to fourth acoustic wave filters 3 to 6 may each be an acoustic wave filter in which a ladder filter is connected to a longitudinally coupled resonator acoustic wave filter.
An acoustic wave resonator 11 preferably includes a support substrate 12, a silicon oxide film 13 stacked on the support substrate 12, and a piezoelectric body 14 stacked on the silicon oxide film 13. It is sufficient that a silicon oxide film 13 may be stacked indirectly on (or above) the support substrate 12, and the piezoelectric body 14 may be stacked indirectly on (or above) the silicon oxide film 13.
The support substrate 12 is preferably made of silicon, for example. Specifically, the support substrate 12 is preferably made of single crystal silicon, but it is sufficient that the support substrate 12 have a crystal orientation and does not need to be a perfect single crystal. The silicon oxide film 13 is preferably a silicon oxide film. Specifically, the silicon oxide film 13 may preferably contain silicon oxide doped with fluorine or the like as long as the silicon oxide film 13 contains silicon oxide. The piezoelectric body 14 is preferably made of lithium tantalate, for example. Specifically, the piezoelectric body 14 is preferably single crystal lithium tantalate, but it is sufficient that the piezoelectric body 14 have a crystal orientation and does not have to be a perfect single crystal. In addition, the piezoelectric body 14 is preferably made of lithium tantalate but may instead be material other than LiTaO3.
The thickness of the silicon oxide film 13 may be 0 μm if so desired. In other words, the silicon oxide film 13 does not necessarily have to be provided.
An interdigital transducer (IDT) electrode 15 is preferably provided on an upper surface of the piezoelectric body 14. More specifically, reflectors 16 and 17 are provided on both sides of the IDT electrode 15 in the acoustic wave propagation direction, and a one-port surface acoustic wave resonator is thus defined. The IDT electrode 15 may be provided indirectly on (or above) the piezoelectric body 14.
The inventors of preferred embodiments of the present invention discovered that, in addition to the response of the main mode that is to be utilized, a plurality of higher-order mode responses appear on the high-frequency side of the main mode when an acoustic wave is excited in the acoustic wave filter device in which the piezoelectric body 14 made of lithium tantalate is directly or indirectly stacked on the support substrate 12. The plurality of higher-order modes will be described with reference to
As described above, in a multiplexer in which a plurality of acoustic wave filters having different frequencies are connected on an antenna terminal side to define a common connection, when a higher-order mode generated by an acoustic wave filter of the multiplexer having a lower frequency appears in the pass band of another acoustic wave filter of the multiplexer having a higher frequency, a ripple is generated. Therefore, it is preferable that at least one higher-order mode out of the first higher-order mode, the second higher-order mode, and the third higher-order mode does not appear in the pass bands of the second to fourth acoustic wave filters 4 to 6. Preferably, two higher-order modes out of the first higher-order mode, the second higher-order mode, and the third higher-order mode do not appear in the pass bands of the second to fourth acoustic wave filters 4 to 6. For example, it is preferable that the first higher-order mode and second higher-order mode responses, the first higher-order mode and third higher-order mode responses, or the second higher-order mode and third higher-order mode responses do not appear in the pass bands of the second to fourth acoustic wave filters 4 to 6. Furthermore, preferably, none of the first higher-order mode, the second higher-order mode, and the third higher-order mode appear in the pass bands of the second to fourth acoustic wave filters 4 to 6.
A feature of the multiplexer 1 of the present preferred embodiment is that the first higher-order mode response of at least one acoustic wave resonator of the first acoustic wave filter 3 does not appear in the second to fourth pass bands illustrated in
i) Formula (1) and Formula (2) below are determined from the values of the wavelength-normalized thickness TLT of the piezoelectric body 14 made of lithium tantalate, Euler angles θLT of the piezoelectric body 14 made of lithium tantalate, the wavelength-normalized thickness TS of the silicon oxide film 13, the wavelength-normalized thickness TE of the IDT electrode 15 converted into an aluminum thickness, the propagation direction ψSi in the support substrate 12, and a wavelength-normalized thickness TSi of the support substrate 12, and a frequency fh1_t(n), that is, a first higher-order mode frequency fh1_t(n) has a value that satisfies Formula (3) or Formula (4) below for all values of m where m>n; and ii) TSi>20.
Consequently, the response due to the first higher-order mode is located outside the pass bands of the second to fourth acoustic wave filters 4 to 6. Therefore, degradation of the filter characteristics of the second to fourth acoustic wave filters 4 to 6 due to the first higher-order mode is unlikely to occur. Positioning of the first higher-order mode frequency outside of the second to fourth pass bands by satisfying the above conditions will be described in more detail below.
It is further preferable that an acoustic velocity Vh expressed by Formula (5) below is used instead of the acoustic velocity Vh expressed by Formula (1). In this case, a ripple due to a higher-order mode is even less likely to occur in the other band pass filters.
Vh=aT
In this case as well, at least one of the first, second, and third higher-order mode frequencies fhs_t(n) determined by Formula (5) and Formula (2) (s is 1, 2, or 3, and the at least one higher-order mode is the first, second, third higher-order mode when s is 1, 2, or 3) has a value that satisfies Formula (3) or Formula (4) for all acoustic wave filters (m) (n<m≤N) having a pass band that is higher than that of the at least one acoustic wave filter (n).
fhs_t(n)>fu(m) Formula (3)
fhs_t(n)<fl(m) Formula (4)
The h represents a higher-order mode in Formulas (1) to (4) and Formula (5). Furthermore, in this specification, “wavelength-normalized thickness” refers to a thickness obtained by normalizing a thickness using the wavelength of the IDT electrode. Here, “wavelength” refers to a wavelength λ determined by the electrode finger pitch of the IDT electrode. Therefore, a “wavelength-normalized thickness” is a thickness obtained by normalizing the actual thickness by treating λ as 1 and is a value obtained by dividing the actual thickness by λ. The wavelength λ determined by the electrode finger pitch of the IDT electrode may be determined as the average value of the electrode finger pitch. In this specification, a wavelength-normalized thickness may be simply referred to as a “film thickness”.
The inventors of preferred embodiments of the present application discovered that the frequency position of the first higher-order mode is affected by the various parameters described above.
As illustrated in
When Vh1_t represents the acoustic velocity of the first higher-order mode, the frequency of the first higher-order mode is expressed as fh1_t(n)=Vh1_t/λt(n) according to Formula (2). Here, fh1 is the frequency of the first higher-order mode, t is the number of an element, such as a resonator forming the n-th filter.
In the present preferred embodiment, as illustrated in Formula (3) and Formula (4), fh1_t is higher than fu(m) or lower than fl(m). In other words, fh1_t is lower than the low-frequency ends or higher than the high-frequency ends of the second pass band, the third pass band, and the fourth pass band illustrated in
In Formula (1), (a) In the case where Si(100) (Euler angles (φSi=0±5°, θSi=0±5°, ψSi)) is used, the range of ψSi is 0°≤ψSi≤45°. Here, ψSi is the angle between the acoustic wave propagation direction and a Miller index, which is crystal orientation [100], of silicon in a plan view seen from the main surface side of the piezoelectric body where the IDT electrode is provided. However, due to the symmetry of the crystal structure of Si(100) ψSi and ψSi±(n×90°) have the same meaning (n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi have the same meaning. (b) In the case where Si(110) (Euler angles (φSi=−45±5°, θSi=−90±5°, ψSi)) is used, the range of ψSi is 0°≤ψSi≤90°. Here, ψSi is the angle between the acoustic wave propagation direction and a Miller index, which is crystal orientation [1-10], of silicon in a plan view seen from the main surface side of the piezoelectric body where the IDT electrode is provided. Due to the symmetry of the crystal structure of Si(110), ψSi and ψSi±(n×180°) are identical (n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi have the same meaning.
(c) In the case where Si(111) (Euler angles (φSi=−45±5°, θSi=−54.73561±5°, ψSi)) is used, the range of ψSi is 0°≤ψSi≤60°. Here, ψSi is the angle between the acoustic wave propagation direction and a Miller index, which is crystal orientation [1-10], of silicon in a plan view seen from the main surface side of the piezoelectric body where the IDT electrode is provided. However, due to the symmetry of the crystal structure of Si(111), ψSi and ψSi±(n×120°) have the same meaning (n=1, 2, 3 . . . ). Similarly, ψSi and −ψSi have the same meaning.
In addition, although the range of θLT is −180°<θLT≤0°, θLT and θLT+180° may be treated as having the same meaning.
In this specification, in Euler angles (0°±5°, θ, 0°±15°), “0°±5°” means within a range greater than or equal to about −5° and less than or equal to about +5° and “0°±15°” means within a range greater than or equal to about −15° and less than or equal to about +15°.
The wavelength-normalized thickness TE of the IDT electrode 15 is a thickness converted into a film thickness of an IDT electrode which is preferably made of aluminum, for example. However, the electrode material is not limited to Al. Various metals such as Ti, NiCr, Cu, Pt, Au, Mo, and W can be used. In addition, alloys having these metals as main components may be used. Furthermore, a multilayer metal film obtained by stacking a plurality of metal films made of such metals or alloys may be used.
In
In the present preferred embodiment, the frequency of the first higher-order mode in at least one acoustic wave resonator among the plurality of acoustic wave resonators of the first acoustic wave filter 3 satisfies Formula (3) or Formula (4). More preferably, the frequency of a higher-order mode response in an acoustic wave resonator that is closest to the antenna terminal satisfy Formula (3) or Formula (4). This is because the effect of a higher-order mode of the acoustic wave resonator that is closest to the antenna terminal tends to appear more significantly in the pass bands of the other second to fourth acoustic wave filters 4 to 6 compared with the other acoustic wave resonators.
More preferably, the frequency position of the first higher-order mode satisfy Formula (3) or Formula (4) in all of the acoustic wave resonators. As a result, it is even more unlikely that a ripple caused by a first higher-order mode response will appear in the pass bands of the second to fourth acoustic wave filters 4 to 6.
When the structure according to preferred embodiments of the present invention is used, as described above, there is a tendency for a higher-order mode to be trapped in a portion of the structure where the silicon oxide film 13 and the piezoelectric body 14 are stacked, but by making the portion where the silicon oxide film 13 and the piezoelectric body 14 are stacked thin by making the thickness of the piezoelectric body 14 less than or equal to about 3.5λ, for example, it becomes less likely that a higher-order mode will be trapped.
More preferably, the film thickness of the piezoelectric body 14 made of lithium tantalate is less than or equal to about 2.5λ, for example, and in this case, the absolute value of the temperature coefficient of frequency TCF can be reduced. Still more preferably, the film thickness of the piezoelectric body 14 made of lithium tantalate is less than or equal to about 1.5λ, for example. In this case, the electromechanical coupling coefficient can be easily adjusted. Still more preferably, the film thickness of the piezoelectric body 14 made of lithium tantalate is less than or equal to about 0.5λ, for example. In this case, the electromechanical coupling coefficient can be easily adjusted over a wide range.
In a second preferred embodiment of the present invention, a ripple of a second higher-order mode rather than a first higher-order mode is not located in the pass bands of the second to fourth filters 4 to 6. This will be explained with reference to
As illustrated in
As described above, a frequency position fh2_t(n)=Vh2_t/λt(n) of the second higher-order mode response is obtained using Formula (2) from the obtained second higher-order mode acoustic velocity Vh2_t. In the second preferred embodiment, the frequency position fh2_t(n) of the second higher-order mode is set so as to satisfy Formula (3A) or (4A) below. Therefore, in the second preferred embodiment, the second higher-order mode response is located outside the second to fourth pass bands of the second to fourth acoustic wave filters 4 to 6. Therefore, a ripple due to the second higher-order mode response is unlikely to be generated in the filter characteristics of the second to fourth acoustic wave filters 4 to 6.
fh2_t(n)>fu(m) Formula (3A)
fh2_t(n)<fl(m) Formula (4A)
More preferably, the frequency position of the second higher-order mode response satisfy Formula (3A) or Formula (4A) in all of the acoustic wave resonators. As a result, it is even more unlikely that a ripple caused by a second higher-order mode response will appear in the pass bands of the second to fourth acoustic wave filters 4 to 6.
In a third preferred embodiment of the present invention, a ripple of a third higher-order mode rather than a first higher-order mode is not located in the pass bands of the second to fourth filters 4 to 6. This will be explained while referring to
As illustrated in
The frequency position of the third higher-order mode response is obtained from the frequency position fh3_t(n)=Vh3_t/λt(n) of the third higher-order mode using Formula (2) from the obtained third higher-order mode acoustic velocity Vh3_t. In the third preferred embodiment, the frequency position of the third higher-order mode is set so as to satisfy Formula (3B) or (4B) below. Therefore, in the third preferred embodiment, the third higher-order mode response is located outside the second to fourth pass bands of the second to fourth acoustic wave filters 4 to 6. Therefore, a ripple due to the third higher-order mode response is unlikely to occur in the filter characteristics of the second to fourth acoustic wave filters 4 to 6.
fh3_t(n)>fu(m) Formula (3B)
fh3_t(n)<fl(m) Formula (4B)
More preferably, the frequency position of the third higher-order mode response satisfy Formula (3B) or Formula (4B) in all of the acoustic wave resonators. As a result, it is even more unlikely that a ripple caused by the third higher-order mode response will appear in the pass bands of the second to fourth acoustic wave filters 4 to 6.
A fourth preferred embodiment of the present invention satisfies all of the content of the first preferred embodiment, the second preferred embodiment, and the third preferred embodiment. The specific structure of a multiplexer of the fourth preferred embodiment is the same or substantially the same as that of the first to third preferred embodiments.
In the fourth preferred embodiment, when Vh1_t, Vh2_t, and Vh3_t respectively represent the acoustic velocities of the first, second, and third higher-order modes, the frequency positions of the responses of the first to third higher-order modes represented by Formula (2) are expressed by fhs_t(n)=Vhs_t/λt(n). Here, s is 1, 2, or 3. In the fourth preferred embodiment, the frequency fh1_t(n) of the response of the first higher-order mode, the frequency fh2_t(n) of the response of the second higher-order mode, and the frequency fh3_t(n) of the response of the third higher-order mode are all higher than fu(m) or lower than fl(m). Therefore, the responses of the first to third higher-order modes are located outside the second to fourth pass bands of the second to fourth acoustic wave filters 4 to 6. Therefore, degradation of the filter characteristics of the second to fourth acoustic wave filters is less likely to occur.
Therefore, summarizing the conditions of the fourth preferred embodiment, fhs_t(n) (s is 1, 2, or 3) satisfies fhs_t(n)>fu(m) or fhs_t(n)<fl(m) when s is 1, 2, or 3. In the fourth preferred embodiment as well, preferably, TSi>20, and as a result, the sizes of the responses of the first to third higher-order modes can be reduced.
In the fourth preferred embodiment, the responses of the first higher-order mode, the second higher-order mode, and the third higher-order mode are not located in the pass bands of the second to fourth acoustic wave filters, which are the other acoustic wave filters, but alternatively two higher-order modes among the first to third higher-order modes may be located outside the pass bands of the second to fourth acoustic wave filters such as the first higher-order mode and the second higher-order mode, the first higher-order mode and third higher-order mode, or the second higher-order mode and the third higher-order mode. In other words, the values of TLT, θLT, TS, TE, ψSi, and TSi may be selected so that the frequencies fhs_t(n) of the first and second higher-order modes satisfy the above Formulas (3) or (4), the values of TLT, θLT, TS, TE, ψSi, and TSi may be selected so that the frequencies fhs_t(n) of the first and third higher-order modes satisfy the above Formulas (3) or (4), or the values of TLT, θLT, TS, TE, ψSi, and TSi may be selected so that the frequencies fhs_t(n) of the second and third higher-order modes satisfy the above Formulas (3) or (4). In this case, the effects of the higher-order modes can be further reduced compared with the first to third preferred embodiments.
Furthermore, from
From
However, as illustrated in
The acoustic wave devices of the above-described preferred embodiments can be used as a duplexer of a radio-frequency front end circuit, for example. An example of such a radio-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 multiplexers according to preferred embodiments of the present invention can be suitably used as the multiplexer 210 in the communication device 240.
The multiplexers according to preferred embodiments of the present invention may include only a plurality of transmission filter or may include only a plurality of reception filters. The multiplexers preferably includes n band pass filters, where n is greater than or equal to 2. Therefore, the multiplexers according to preferred embodiments of the present invention may be implemented as a duplexer.
Preferred embodiments of the present invention are widely applicable to communication devices such as mobile phones, for example, in the form of filters, multiplexers applicable to multi-band systems, front end circuits, and communication devices.
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 |
|---|---|---|---|
| JP2017-044688 | Mar 2017 | JP | national |
This application claims the benefit of priority to Japanese Patent Application No. 2017-044688 filed on Mar. 9, 2017 and is a Continuation Application of PCT Application No. PCT/JP2018/008914 filed on Mar. 8, 2018. The entire contents of each application are hereby incorporated herein by reference.
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| 20210184654 | Nakagawa | Jun 2021 | A1 |
| Number | Date | Country |
|---|---|---|
| 2010-187373 | Aug 2010 | JP |
| 2014-068123 | Apr 2014 | JP |
| 2012086639 | Jun 2012 | WO |
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| Entry |
|---|
| Official Communication issued in International Patent Application No. PCT/JP2018/008914, dated May 22, 2018. |
| Number | Date | Country | |
|---|---|---|---|
| 20190393855 A1 | Dec 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/008914 | Mar 2018 | US |
| Child | 16561198 | US |
