Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-12-02
2001-07-10
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S364000
Reexamination Certificate
active
06259185
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to the field of radio frequency apparatus, in particular to radio frequency filters and more particularly to radio frequency filters employing surface acoustic wave devices.
BACKGROUND OF THE INVENTION
There is an ongoing need for component miniaturization in radio communication devices. For example, smaller and more efficient components are needed for light-weight, hand-portable cellular telephones, wireless local area networks for linking computer systems within office buildings in a readily reconfigurable fashion, pager devices and other devices for promoting rapid, efficient and flexible voice and data communication.
Filters are needed for a variety of such communications applications wherein small size, light weight and high performance are simultaneously required. Increasing numbers of products seek to employ fixed spectral resources, often to achieve tasks not previously envisioned. Examples include cellular telephones, computer and ancillary equipment linkages as well as a host of other, increasingly complex personal or equipment information sharing requirements. The desire to render increasingly complicated communications nodes portable places extreme demands on filtering technology in the context of increasingly crowded radio frequency resources.
Surface acoustic wave (SAW) ladder filters used in duplexers are a popular choice for radios because of their better performance and small size. However, a small device such as a SAW duplexer is required to handle relatively high power levels. For example, a standard specification for a SAW duplexer requires the duplexer to be able to handle 1 watt of power for a lifetime of 50,000 hours. However, existing SAW technologies have had a difficult time meeting this requirement due to the high power densities involved.
One prior art method of addressing the power handling problem included providing a three layer electrode metallization consisting of a first layer of an aluminum-copper alloy, a second layer of pure copper, and a third layer of another aluminum-copper alloy. However, this method has the drawbacks of proving is difficult to etch, being susceptible to corrosion, and requiring an additional annealing step at 400° C.
Another prior art method includes depositing a single-crystal electrode of an aluminum-titanium alloy at one time using an ion beam sputtering technique. However, ion beam sputtering is a slow process, as is known in the art, and is not suitable for mass production.
Associated prior art relating to flat panel display technology has used a layer of aluminum on a layer of titanium. This was done to control electromigration. However, this technology requires the further deposition of a dielectric film on the metal layer, a preheating step of over 300° C., and a glass substrate which is critical in defining the metallization thickness.
What is needed is a method to provide electrode metallization for a SAW device which provides good mechanical strength, stable frequency response, long lifetime at rated power, has good adhesion to a piezoelectric substrate, and is easily mass produced at a low cost.
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CTS Corporation
Medley Peter
Ramirez Nestor
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