Wave transmission lines and networks – Coupling networks – Electromechanical filter
Patent
1997-05-07
1999-07-27
Pascal, Robert
Wave transmission lines and networks
Coupling networks
Electromechanical filter
310313R, 310363, H03H 9145, H03H 964
Patent
active
059297239
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention is related to a surface acoustic wave apparatus and its manufacturing method. More particularly, the present invention relates to a surface acoustic wave apparatus including electrode films having an improved electric power-durability, and to a method for manufacturing the surface acoustic wave apparatus.
BACKGROUND ART
A surface acoustic wave apparatus, in particular a surface acoustic wave filter has found a wide use for a RF band-pass filter in a mobile telephone and/or a handy telephone, etc. in place of a dielectric band-pass filter. The reasons for that may be that surface acoustic wave apparatus, in particular surface acoustic wave filters are smaller in size than dielectric filters, and also shows improved electric characteristics as compared with dielectric filters of the same sizes.
A surface acoustic wave apparatus includes at least a piezoelectric substrate, an electrode pattern consisting of a metal film formed on a surface of the piezoelectric substrate, and a package accommodating the piezoelectric substrate and the electrode pattern. The piezoelectric substrate is made of a material, such as a lithium niobate, a lithium tantalate, or a quartz, an electrode pattern of a film of a metal, such as aluminum being formed thereon and accommodated into the package.
In FIG. 5, there is shown a manufacturing process of a conventional prior art surface acoustic wave apparatus. First, a piezoelectric substrate 50 is provided by being cleaned in the process (a), and a metal film 51 is formed thereon by means of a vapor-deposition or a sputtering to provide an electrode material in the process (b). A coating of a photoresist is then provided thereon, for example, by means of a spin coat method. Then, as shown in the process (c), exposure to a desired pattern is made by an exposing machine, and after development, obtain a photoresist pattern 52. Thereafter, in the process (d), a wet-etching or a dry-etching method is carried out to form a metal film of a desired electrode pattern 53. The photoresist used for the pattern formation is, in the process (e), removed using a removing agent, or by means of an ashing method. Thus, a pre-process, which is so-called photo-process, has been completed. Thereafter, in the process (f), the piezoelectric substrate formed with the electrode pattern thereon is cut into chips by dicing. Then, in the process (g), after having fixed the cut chips on the package using an adhesive, bonding wires are attached thereto in the process (h). Finally, in order to secure a hermeticity, a lid is welded to the package in the process (i), an electrical characteristic test is made in the process (j) to complete the post-process.
The surface acoustic wave apparatus has a problem such that, when in use for the RF band around 1 GHz, an electrode width and an electrode gap of a comb-shaped electrode must be of very small values, such as about 1 micrometer, thereby its life time (hereinafter, referred to as life) is very short. A factor of determining the life for the surface acoustic wave apparatus is mainly a power-durability of the electrode film. Placing the surface acoustic wave apparatus in an operating state, the electrode film on the piezoelectric substrate is subjected to a stress which is repeated with a frequency that is equal to an operating frequency. Due to this repetitive stress applied to the electrode film, defects such as hillocks (projections) and voids (depletions) will be generated on the electrode film by migrations, thereby significantly degrading the characteristics of the surface acoustic wave apparatus. This degradation phenomena of electrode film will be more pronounced for higher operating frequency, and for larger applied electric powers. Further, as a matter of design, for higher operating frequency, it is necessary to make the electrode film thinner and to make the electrode width narrower. With such additional factors, in a design for higher operating frequency, defects would be easily generated on the electrode film, an
REFERENCES:
patent: 4775814 (1988-10-01), Yuhara et al.
patent: 4906885 (1990-03-01), Kojima et al.
patent: 5144185 (1992-09-01), Yuhara et al.
patent: 5162690 (1992-11-01), Ieki t al.
patent: 5558711 (1996-09-01), Sakurai
patent: 5773917 (1998-06-01), Satoh et al.
"Improved Metallization for Surface Acoustic Wave Devices", J.I. Latham, W.R. Shreve, N.J. Tolar and P.B. Ghate, thin Solid Films, vol. 64, pp. 9-15, Apr. 1979.
"Power Aging Test of SAW Filter for Portable Telephone Antenna Duplexer", T. Tabuchi, K. Kurosawa, H. Kojima, Y. Ishida and M. Hikita, Technical Reports of Institute of Electronics and Information Communication Engineers of Japan, US 87-18, Jul. 23, 1987.
"FEM Estimation of Equivalent Stress in SAW Device Electrodes", T. Kawakatsu, T. Okada and H. Ieki, Technical Reports of Institute of Electronics and Information Communication Engineers of Japan, US 90-70/EA-90-83, Jan. 25, 1991.
Kimura Noritoshi
Nakano Masahiro
Nakazawa Michiyuki
Sato Katsuo
Pascal Robert
Summons Barbara
TDK Corporation
LandOfFree
Surface acoustic wave apparatus having an electrode that is a do 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 having an electrode that is a do, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface acoustic wave apparatus having an electrode that is a do will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-883551