Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2002-12-27
2004-12-28
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S195000, C310S31300R
Reexamination Certificate
active
06836196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave apparatus for use in, for example, a resonator, band-pass filter, or other suitable device. In particular, the present invention relates to a surface acoustic wave apparatus using a rotated Y plate X-propagating LiTaO
3
substrate and a method for manufacturing the same.
2. Description of the Related Art
In mobile communication apparatuses, for example, cellular phones, surface acoustic wave filters have been used as RF stage band-pass filters and duplexers. As this sort of surface acoustic wave filter, a surface acoustic wave filter using a leaky surface acoustic wave has been used and includes an IDT (Interdigital Transducer) made of Al arranged on a 30° to 50°-rotated Y plate X-propagating LiTaO
3
substrate.
However, this surface acoustic wave filter has a poor frequency temperature characteristic of −30 ppm/° C. to −40 ppm/° C. and, therefore, improvements thereto are required. In order to improve the frequency temperature characteristic, a structure has been suggested, in which an IDT made of Al has been formed on the 30° to 50°-rotated Y plate X-propagating LiTaO
3
substrate and, thereafter, a SiO
2
film has been further laminated. The frequency temperature characteristic is improved by the arrangement of the SiO
2
film.
When the IDT made of Al is formed, the electrode film thickness H/&lgr; (H denotes a film thickness and &lgr; denotes a wavelength of a surface acoustic wave) of the IDT is significantly increased to 0.08 to 0.10 in order to increase the reflection coefficient and electromechanical coefficient K
2
. Since the IDT made of Al was allowed to have a significant thickness as described above, regarding the portion shown in
FIG. 18A
, when the SiO
2
film was formed thereon in order to improve the frequency temperature characteristic, large height differences occurred in the SiO
2
film and, thereby, cracks sometimes occurred in the SiO
2
film as shown in FIG.
18
B. Consequently, the filter characteristics of the surface acoustic wave filter were degraded due to the occurrence of the cracks.
In addition, since the electrode film thickness of the IDT made of Al is large, an effect of covering the differences in the electrode surface of the IDT based on the arrangement of the SiO
2
film was not adequate and, thereby, the temperature characteristic was not always improved adequately.
Furthermore, the attenuation constant was increased due to the arrangement of the SiO
2
film and, thereby, degradation of the filter characteristics occurred.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave apparatus and a method for manufacturing the same, wherein the surface acoustic wave apparatus includes a rotated Y plate X-propagating LiTaO
3
substrate having a unique arrangement of a SiO
2
film such that the frequency temperature characteristic is greatly improved, the electrode film thickness of the IDT can be significantly reduced, cracking in the SiO
2
film is prevented and, furthermore, the attenuation constant is reduced by a large degree, so that targeted electrical characteristics, for example, desired filter characteristics, can be attained, and the electromechanical coefficient and reflection coefficient in the IDT are allowed to have adequate values.
According to a preferred embodiment of the present invention, a surface acoustic wave apparatus includes a LiTaO
3
substrate having Euler angles (0±3°, 113° to 136°, 0±3°), at least one IDT which is arranged on the LiTaO
3
substrate and which primarily includes Cu, and a SiO
2
film arranged on the LiTaO
3
substrate to cover the at least one IDT.
In preferred embodiments of the present invention, since the IDT primarily includes Cu, and the SiO
2
film is arranged in a unique manner, the electromechanical coefficient is increased, and the frequency temperature characteristic is improved. Furthermore, since the LiTaO
3
substrate having the specific desired Euler angles is used, the attenuation constant &agr; is greatly reduced.
In another preferred embodiment of the present invention, preferably, the film thickness H/&lgr; of the IDT normalized by the wavelength of the surface acoustic wave is preferably within the range of about 0.01 to about 0.08, and the film thickness H/&lgr; of the SiO
2
film normalized by the wavelength of the surface acoustic wave is preferably within the range of about 0.15 to about 0.40. In that case, according to preferred embodiments of the present invention, a surface acoustic wave apparatus which has a large electromechanical coefficient and reflection coefficient, excellent frequency temperature characteristic, and adequately reduced attenuation constant and in which cracking in the SiO
2
film are prevented from occurring can be provided with reliability.
In a preferred embodiment of the present invention, preferably, the film thickness H/&lgr; of the IDT is about 0.12 or less, and the combination of the normalized film thickness of the SiO
2
and the Euler angles of the LiTaO
3
substrate is any one of the values shown in the following Table.
TABLE 3
SiO
2
film thickness
Euler angles of LiTaO
3
More preferably
0.15 to 0.18
(0, 117 to 137, 0)
(0, 120 to 135, 0)
0.18 to 0.23
(0, 117 to 136, 0)
(0, 118 to 133, 0)
0.23 to 0.28
(0, 115 to 135, 0)
(0, 117 to 133, 0)
0.28 to 0.33
(0, 113 to 133, 0)
(0, 115 to 132, 0)
0.33 to 0.38
(0, 113 to 135, 0)
(0, 115 to 133, 0)
0.38 to 0.40
(0, 113 to 132, 0)
(0, 115 to 130, 0)
In another preferred embodiment of the present invention, preferably, when the normalized film thickness of the SiO
2
film is represented by hs, the &thgr; of the Euler angles (0°, &thgr;, 0°) fall within the range of the following Formula (1):
&thgr;
min
−2°<&thgr;≦&thgr;
min
+2° Formula (1)
where in the Formula (1), when the normalized film thickness H/&lgr; of the IDT is within the range of the following (a) to (e), the value of &thgr;
min
is represented by the following Formulae A to E, respectively.
(a) when 0<H/&lgr;≦0.01
&thgr;
min
=−139.713×hs
3
+43.07132×hs
2
−20.568011×hs+125.8314 Formula A
(b) when 0.01<H/&lgr;≦0.03
&thgr;
min
=−139.660×hs
3
+46.02985×hs
2
−21.141500×hs+127.4181 Formula B
(c) when 0.03<H/&lgr;≦0.05
&thgr;
min
=−139.607×hs
3
+48.98838×hs
2
−21.714900×hs+129.0048 Formula C
(d) when 0.05<H/&lgr;≦0.07
&thgr;
min
=−112.068×hs
3
+39.60355×hs
2
−21.186000×hs+129.9397 Formula D
(e) when 0.07<H/&lgr;≦0.09
&thgr;
min
=−126.954×hs
3
+67.40488×hs
2
−29.432000×hs+131.5686 Formula E
In a preferred embodiment of the present invention, preferably, the combination of the normalized film thickness of the SiO
2
and the Euler angles of the LiTaO
3
substrate is any of the values specified in the following Table.
TABLE 4
SiO
2
film thickness
Euler angles of LiTaO
3
0.15 to 0.18
(0, 117 to 125, 0)
0.18 to 0.23
(0, 117 to 125, 0)
0.23 to 0.28
(0, 115 to 125, 0)
0.28 to 0.33
(0, 113 to 125, 0)
0.33 to 0.38
(0, 113 to 125, 0)
0.38 to 0.40
(0, 113 to 125, 0)
In the case of the combinations shown in the aforementioned Table, that is, in the case where the &thgr; of the Euler angles is specified to be about 125° or less, the electromechanical coefficient K
2
is be further increased.
In the surface acoustic wave apparatus according to a preferred embodiment of the present invention, preferably, a leaky surface acoustic wave including a shear horizontal wave as a main component is used as the surface acoustic wave. According to preferred embodiments of the present invention, a surface acoustic wave apparatus having an excellent frequency temperature characteristic, an IDT with a lar
Kadota Michio
Nakao Takeshi
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Summons Barbara
LandOfFree
Surface acoustic wave apparatus utilizing a leaky surface... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Surface acoustic wave apparatus utilizing a leaky surface..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface acoustic wave apparatus utilizing a leaky surface... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3296674