This application is a U.S. national phase application of PCT international application PCT/JP2010/003459, filed May 24, 2010.
The present invention relates to an acoustic wave resonator and a duplexer using the resonator.
Conventionally, a piezoelectric body has been used with a large electromechanical coupling factor such as a lithium niobate (LiNbO3) substrate to achieve an acoustic wave filter with wide-band characteristics.
However, an acoustic wave filter using this type of piezoelectric body typically has a disadvantage of poor temperature characteristics. To improve temperature characteristics, a way is devised in which a dielectric thin film made of SiO2 is formed on a piezoelectric body made of lithium niobate.
In
Acoustic wave resonator 101 further has opening 109 in dielectric thin film 105 above bus bar electrode region 106 and dummy electrode region 107 to expose IDT electrode 103 in the regions.
This structure enables the sound velocity of an acoustic wave in bus bar electrode region 106 and dummy electrode region 107 of acoustic wave resonator 101 to be faster than that in IDT cross region 108. This condition, prevents leakage of an acoustic wave from IDT cross region 108 to dummy electrode region 107, which reduces insertion degradation loss of the acoustic wave.
As shown in
There is known patent literature 1 as a prior art document related to the patent application.
An acoustic wave resonator includes a piezoelectric body, an IDT electrode provided on the piezoelectric body, for exciting an acoustic wave with wavelength λ; and a dielectric thin film provided on the piezoelectric body so as to cover the IDT electrode. The IDT electrode includes a bus bar electrode region, a dummy electrode region, and an IDT cross region, in order from outside. The film thickness of the dielectric thin film above at least one of the bus bar electrode region and the dummy electrode region is smaller than that above the IDT cross region by 0.1λ to 0.25λ.
Such a configuration of an acoustic wave resonator reduces transverse-mode waves in the IDT cross region to prevent transverse-mode spurious emission.
Hereinafter, a description is made of the first exemplary embodiment of the present invention using the related drawings.
In
Piezoelectric body 2 is a substrate based on lithium niobate (LiNbO3); however, body 2 may be another piezoelectric single-crystal medium such as a substrate or thin film based on crystal, lithium tantalate (LiTaO3), or potassium niobate (KNbO3).
IDT electrode 3 is made of metal primarily containing aluminum; however, electrode 3 may be formed of one of the following three types of materials: a single metal such as copper, silver, gold, titanium, tungsten, platinum, chromium, or molybdenum; an alloy primarily containing at least one of these metals; or a lamination of at least one of these metals. When IDT electrode 3 is made of a metal primarily containing aluminum for example, the normalized film thickness of IDT electrode 3 needs to be between 0.045λ and 0.12λ, where λ is twice the electrode pitch in
IDT electrode 3 is a normal-type, comb-shaped electrode with a roughly constant cross width. In
IDT cross region 8 is a region where electrode fingers of IDT electrodes 3 at the input and output sides cross each other and main acoustic waves (e.g. SH (shear horizontal) waves) are excited. Bus bar electrode region 6 is a region where bus bar electrodes that input an electric signal to the electrode fingers of IDT electrode 3 are placed. Dummy electrode region 7 is a region where dummy electrodes provided in parts where the electrode fingers of IDT electrodes 3 at the input and output sides do not cross each other are placed. The sound velocity in dummy electrode region 7 can be made different from that in the IDT cross region by adjusting the film thickness of the dummy electrodes and that of SiO2 on the electrodes. Adjusting the difference in sound velocity enables transverse-mode waves to be dispersed into dummy electrode region 7 to reduce transverse-mode spurious emission.
Dielectric thin film 5 is made of silicon oxide for example; however any medium may be used as long as it has a propagation velocity of a side wave lower than the velocity of the slowest side wave propagating through piezoelectric body 2. Here, silicon oxide is a medium having frequency-temperature characteristics inverse to those of piezoelectric body 2, thereby improving the frequency-temperature characteristics of acoustic wave resonator 1.
The film thickness of dielectric thin film 5 above IDT cross region 8 is set so that the sound velocity of an acoustic wave excited by IDT electrode 3 is lower than the velocity of the slowest side wave propagating through piezoelectric body 2. This setting hopefully reduces leakage of main acoustic waves toward piezoelectric body 2.
Further, for dielectric thin film 5 made of silicon oxide, the film thickness of dielectric thin film 5 above IDT cross region 8 is set so that the frequency-temperature characteristic of a main acoustic wave excited by IDT electrode 3 is less than 10 ppm/° C.
Normalized film thickness 9 of dielectric thin film 5 above IDT cross region 8 satisfying the above conditions is between 0.2λ and 0.5λ. Desirably, it is between 0.25λ and 0.5λ, and more desirably between 0.3λ and 0.45λ, which especially balances preventing leakage of an acoustic wave with improving the frequency-temperature characteristics.
Here, the film thickness of dielectric thin film 5 refers to the distance from the boundary surface between piezoelectric body 2 at a part where piezoelectric body 2 contacts dielectric thin film 5 (IDT electrode 3 is not formed) and dielectric thin film 5; to the top surface of dielectric thin film 5.
Here, when IDT electrodes 3 in bus bar electrode region 6 and dummy electrode region 7 are completely exposed in order to reduce leakage of a main acoustic wave from IDT cross region 8 to dummy electrode region 7, then transverse-mode waves have a stronger effect. This is because even transverse-mode waves (as well as main acoustic waves) are confined in IDT cross region 8 of acoustic wave resonator 1.
Thus in the first embodiment, normalized film thickness 10 of dielectric thin film 5 above at least one of bus bar electrode region 6 and dummy electrode region 7 is made smaller than normalized film thickness 9 of dielectric thin film 5 above IDT cross region 8 by 0.1λ to 0.25λ.
This condition suppresses transverse-mode waves in IDT cross region 8 to reduce transverse-mode spurious emission. This is because the difference in sound velocity in IDT cross region 8 and dummy electrode region 7 is decreased to cause acoustic coupling between transverse-mode waves excited in IDT cross region 8 and those excited in dummy electrode region 7. The coupling possibly disperses energy of transverse-mode waves resonated in IDT cross region 8 toward dummy electrode region 7. Although the difference in sound velocity has been decreased, the sound velocity in dummy electrode region 7 is higher than that in IDT cross region 8 in the configuration.
Hereinafter, a description is made of the frequency characteristics of acoustic wave resonator 1 according to the first embodiment using the related drawings.
For piezoelectric body 2 of acoustic wave resonator 1, a rotating Y plate (cut angle: 5 degrees) of a lithium niobate substrate is used. For IDT electrode 3, a normal-type, comb-shaped electrode is used made of aluminum with a normalized film thickness of 0.08λ. For dielectric thin film 5, a dielectric thin film is used made of silicon oxide with a normalized film thickness of 0.37λ. For normalized film thickness difference 11 between normalized film thickness 9 of dielectric thin film 5 above IDT cross region 8; and normalized film thickness 10 of dielectric thin film 5 above bus bar electrode region 6 and dummy electrode region 7,
As shown in
To provide normalized film thickness difference 11 in dielectric thin film 5 between above IDT cross region 8 and above dummy electrode region 7, dielectric thin film 5 may be etched after film-formed. Alternatively, by masking dummy electrode region 7 and bus bar electrode region 6 of IDT electrode 3 halfway of film-forming dielectric thin film 5, film 5 may be made enter a non-formed state from halfway of film-forming.
To further reduce transverse-mode spurious emission, IDT electrode 3 may be apodized weighted (the cross width becomes gradually narrower from the center of the IDT electrode toward grating reflector 4). At this moment, dummy electrode region 7 becomes a region with the minimum length of the dummy electrodes of IDT electrode 3, and IDT cross region 8 becomes a region with the maximum length where IDT electrodes 3 cross each other. As described above, however, it is advantageous if normal-type, comb-shaped electrode 3, not apodized-weighted, can reduce transverse-mode spurious emission. That is, the configuration can prevent degration of the resonator characteristics (e.g. the Q value) due to apodized weighting on IDT electrode 3, which is advantageous in characteristics in implementing acoustic wave resonator 1.
Hereinbefore, the description is made of the configuration in which normalized film thickness 10 of dielectric thin film 5 above all the regions in bus bar electrode region 6 and dummy electrode region 7 is smaller than normalized film thickness 9 of dielectric thin film 5 above IDT cross region 8. However, normalized film thickness 10 of dielectric thin film 5 above part of bus bar electrode region 6 and dummy electrode region 7 may be smaller than normalized film thickness 9 of dielectric thin film 5 above IDT cross region 8 by 0.1λ to 0.25λ. For example, the film thickness of dielectric thin film 5 above only dummy electrode region 7 may be smaller than normalized film thickness 9 of dielectric thin film 5 above IDT cross region 8 by 0.1λ to 0.25λ. However, the configuration shown in
The step between dielectric thin film 5 above IDT cross region 8 and dielectric thin film 5 above dummy electrode region 7 is desirably formed roughly perpendicular to the top surface of dielectric thin film 5; however, the step may be tapered. The end of dielectric thin film 5 at this step is desirably positioned the same as the end of dummy electrode region 7; however, the end of film 5 may be formed in gap region 12 between dummy electrode region 7 and IDT cross region 8. This condition prevents this step from adversely affecting the frequency characteristics of acoustic wave resonator 1, which reduces unnecessary spurious emission.
As shown in
In the first embodiment, the dielectric thin film layer on IDT electrode 3 and dummy electrode is one-layered; however, the layer may be two-layered or more.
In the first embodiment, the description is made for a case where acoustic wave resonator 1 is provided with grating reflector 4; however, the same advantage is obtained in a case where grating reflector 4 is not provided because the present invention is applied to IDT electrode 3.
As shown in
At this moment, angle ∠E formed by straight line C connecting the front ends of the electrode fingers from the center of IDT cross region 8 toward its end; and direction D of the acoustic wave propagatation is desirably between 4 and 10 degrees. This condition reduces transverse-mode spurious emission as shown in
Next, a description is made of acoustic wave resonator 1 of the second exemplary embodiment using the related drawings. The configuration is the same as that of the first embodiment unless particularly described.
As shown in
This condition suppresses transverse-mode waves in IDT cross region 8 to reduce transverse-mode spurious emission. This is because the difference in sound velocity in IDT cross region 8 and gap region 12 is decreased to cause acoustic coupling between transverse-mode waves excited in IDT cross region 8 and those excited in gap region 12. In other words, this is possibly because the coupling disperses energy of transverse-mode waves resonating in IDT cross region 8 toward gap region 12.
In this case, the step on the top surface of dielectric thin film 5 is desirably formed above gap region 12. This condition prevents this step from adversely affecting the frequency characteristics of acoustic wave resonator 1, which reduces unnecessary spurious emission.
Next, a description is made of acoustic wave resonator 1 of the third exemplary embodiment using the related drawings. The configuration is the same as that of the first embodiment unless particularly described.
In acoustic wave resonator 1 of
Here, piezoelectric body 2 based on lithium niobate is a trigonal crystal, and thus the Euler angle has the next relationship.
Dielectric thin film 5 is made of a silicon oxide (SiO2) film. Film 5 has temperature characteristics inverse to those of piezoelectric body 2, thereby improving the frequency-temperature characteristics of acoustic wave resonator 1 by making the film thickness thicker than a given one.
In this way, for the film thickness of dielectric thin film 5 made thicker than a given one in order to improve the frequency-temperature characteristics of acoustic wave resonator 1, when Euler angle (φ, θ, ψ) of piezoelectric body 2 made of lithium niobate is changed from φ=ψ=0° while keeping φ and ψ larger than a given angle and ψ=1.193φ to some extent, unnecessary spurious emission near a frequency band where a fast side wave occurs can be prevented while unnecessary spurious emission due to a Rayleigh wave is reduced.
Next, a detailed description is made of effects and advantages that unnecessary spurious emission is reduced for the Euler angle of piezoelectric body 2 made of lithium niobate in a specific range.
In
The above-described fast side wave undesirably degrades the characteristics quality of a filter or duplexer with this acoustic wave resonator applied thereto. To reduce this unnecessary spurious emission, φ and ψ of Euler angle (φ, θ, ψ) of piezoelectric body 2 are changed. The case of changing φ is shown in
In
When the film thickness of dielectric thin film 5 above IDT cross region 8 of acoustic wave resonator 1 is larger than 0.27λ, unnecessary spurious emission due to a Rayleigh wave, as well as due to a fast side wave, is reduced. For this purpose, acoustic wave resonator 1 includes piezoelectric body 2 having Euler angle (φ, θ, ψ), based on lithium niobate; IDT electrode 3 provided on this piezoelectric body 2, for exciting a main acoustic wave with wavelength λ; and dielectric thin film 5 provided on piezoelectric body 2 so as to cover this IDT electrode 3, thicker than 0.27λ above IDT cross region 8. Further, the Euler angle of piezoelectric body 2 satisfies −100°≦θ≦−60°, 1.193φ−2°≦ψ≦1.193φ+2°, ψ≦−2φ−3°, and −2φ+3°≦ψ.
As described above, when Euler angle (φ, θ, ψ) of piezoelectric body 2 is changed from φ=ψ=0° while keeping φ and ψ larger than a given angle and ψ=1.193φ to some extent, unnecessary spurious emission near a frequency band where a fast side wave occurs can be prevented while unnecessary spurious emission due to a Rayleigh wave is reduced.
Here, as shown in
The line of ψ=−2φ in
The main acoustic wave described above is applicable to both of a surface acoustic wave propagating on the surface of piezoelectric body 23 and a boundary acoustic wave. For example, for a film thickness of protective film 24 of λ or greater, the above main acoustic wave is a boundary acoustic wave.
Hereinafter, a description is made of acoustic wave resonator 1 of the fourth exemplary embodiment using the related drawings. The configuration is the same as that of the other embodiments unless particularly described.
Acoustic wave resonator 1 according to the fourth embodiment includes piezoelectric body 2 based on lithium niobate having Euler angle (φ, θ, ψ); and IDT electrode 3 provided on piezoelectric body 2, for exciting a main acoustic wave with wavelength λ. Resonator 1 further includes dielectric thin film 5 provided on piezoelectric body 2 so as to cover this IDT electrode 3, with a film thickness above IDT cross region 8 thicker than 0.2λ. This film 5 has projection 50 on a cross section orthogonal to the direction in which the electrode fingers of IDT electrode 3 extend, above the electrode fingers of IDT electrode 3. The width of top 29 of this projection 50 is smaller than that of the electrode fingers of IDT electrode 3.
The Euler angle of above-described piezoelectric body 2 satisfies −100°≦θ≦−60°, 1.193φ−2°≦ψ≦1.193φ+2°, ψ≦−2φ−3°, and −2φ+3°≦ψ.
When dielectric thin film 5 has projection 50 as in the above configuration, unnecessary spurious emission due to a fast side wave is particularly problematic. Then, for the film thickness of dielectric thin film 5 made of silicon oxide for example that is made thicker than 0.2λ above IDT cross region 8 in order to improve the frequency-temperature characteristics of acoustic wave resonator 1, when φ and ψ of Euler angle (φ, θ, ψ) of piezoelectric body 2 are changed from φ=ψ=0° while keeping φ and ψ larger than a given angle and ψ=1.193φ to some extent, unnecessary spurious emission near a frequency band where a fast side wave occurs can be prevented while unnecessary spurious emission due to a Rayleigh wave is reduced.
Projection 50 of dielectric thin film 5 above IDT cross region 8 desirably has a side line gradually curved outward from top 29 of projection 50 toward bottom 30. In this case, width L of top 29 is smaller than the width of the electrode fingers of IDT electrode 3, where width L is defined by the distance between the points at which the curved line (or its extension) intersects with a line parallel to the top surface of piezoelectric body 2 including top 29. This shape allows the mass addition of dielectric thin film 5 at projection 50 to be changed continuously and gradually. Consequently, the electrical characteristics of acoustic wave resonator 1 can be improved while unnecessary reflection resulting from the shape of dielectric thin film 5 is reduced.
Here, the width of top 29 of projection 50 is desirably smaller than ½ of the width of an electrode finger of IDT electrode 3. The center position of top 29 desirably coincides substantially with a point above the center position of the electrode finger. This structure further increases the reflectivity at the electrode finger owing to the mass addition effect, thereby improving the electrical characteristics of acoustic wave resonator 1.
Further, assuming that the height of projection 50 is T and the film thickness of IDT electrode 3 is h, satisfying 0.03λ<T≦h is desirable. This is because, when a relationship between height T (from bottom 30 of projection 50 of dielectric thin film 5 to top 29) and the electrical characteristics, the reflectivity of dielectric thin film 5 is found improved to a large degree for T higher than 0.03λ and the surface of film 5 made flat. Meanwhile, for T higher than film thickness h of IDT electrode 3, the manufacturing method described below further requires an additional new step for producing this dielectric thin film 5, which makes the manufacturing method troublesome.
First, as shown in
Then, as shown in
Further, as shown in
Furthermore, as shown in
Next, as shown in
Dielectric thin film 34 is deposited on piezoelectric body 31 by sputtering a silicon oxide target, and simultaneously part of dielectric thin film 34 on piezoelectric body 31 is sputtered with a bias voltage. That is to say, part of dielectric thin film 34 is shaved while depositing film 34 to control the shape of film 34. To control the shape of dielectric thin film 34, the following means can be used. That is, the ratio of a bias voltage applied to piezoelectric body 31 to sputtering power is changed during the process of depositing dielectric thin film 34. Another means is, a film is formed without applying a bias voltage on piezoelectric body 31 in the initial period of film-forming; a bias voltage is applied simultaneously with film-forming from halfway through the process. In this case, the temperature of piezoelectric body 31 is controlled as well.
Further, as shown in
Furthermore, as shown in
Next, as shown in
Finally, piezoelectric body 31 is divided into pieces by dicing to produce acoustic wave resonators 1.
As described above, the inventors have confirmed that a desired shape can be achieved by film-forming dielectric thin film 34 by bias sputtering under appropriate conditions.
The characteristics of acoustic wave resonator 1 according to the fourth embodiment described above are the same as those of acoustic wave resonator 1 according to the first embodiment shown in
Further, acoustic wave resonator 1 of the first embodiment may be applied to a filter (e.g. a ladder-type filter or a DMS filter, not shown). Furthermore, resonator 1 may be applied to a duplexer (not shown) including a transmission filter and a reception filter. Resonator 1 may be applied to an electronic device including the filter, a semiconductor integrated circuit element (not shown) connected to the filter, and a reproducing device connected to the semiconductor integrated circuit element (not shown).
An acoustic wave resonator and a duplexer according to the present invention have an advantage of reducing transverse-mode spurious emission, which is applicable to an electronic device such as a mobile phone.
Number | Date | Country | Kind |
---|---|---|---|
2009-127346 | May 2009 | JP | national |
2010-047432 | Mar 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2010/003459 | 5/24/2010 | WO | 00 | 11/7/2011 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2010/137279 | 12/2/2010 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
7812688 | Nakamura et al. | Oct 2010 | B2 |
7821179 | Nakao et al. | Oct 2010 | B2 |
7965155 | Nakamura et al. | Jun 2011 | B2 |
20040174233 | Takayama et al. | Sep 2004 | A1 |
20070241840 | Takayama et al. | Oct 2007 | A1 |
20100097161 | Nakamura et al. | Apr 2010 | A1 |
Number | Date | Country |
---|---|---|
1 962 424 | Aug 2008 | EP |
8-316781 | Nov 1996 | JP |
03088483 | Oct 2003 | WO |
2006003933 | Jan 2006 | WO |
2008059780 | May 2008 | WO |
2008078573 | Jul 2008 | WO |
Entry |
---|
International Search Report issued Aug. 17, 2010 in International (PCT) Application No. PCT/JP2010/003459. |
Number | Date | Country | |
---|---|---|---|
20120044027 A1 | Feb 2012 | US |