Surface acoustic wave filter

Details Surface acoustic wave filter Surface acoustic wave filter

2000-02-28

2001-10-30

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

Reexamination Certificate

active

06310422

ABSTRACT:

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP99/0115005583.
TECHNICAL FIELD
The present invention relates to a surface acoustic wave filter used in frequency filter of portable telephone and other mobile communication device.
BACKGROUND ART
FIG. 5
shows a constitution of a conventional surface acoustic wave filter. In
FIG. 5
, reference numeral
101
is an input terminal,
102
is an output terminal,
103
is a piezoelectric substrate,
105
to
108
are resonators provided on a signal line
104
a
on the piezoelectric substrate
103
, and this surface acoustic wave filter is composed of a comb-shaped electrode pattern (not shown) and reflector patterns (not shown) provided at its both ends. Further, reference numeral
109
is a package,
110
a
to
100
f
are lands formed in the package
109
, and
111
a
to
111
f
are wires for connecting the resonators
105
to
108
in the signal line
104
a
and a ground pattern
104
b.
Herein, by composing the rcsonators
105
to
108
on the piezoelectric substrate
103
by means of the comb-shaped electrode pattern and reflector patterns provided at its both ends, an elastic vibration is induced to the surface. By operating as the resonators by making use of this elastic vibration, the frequency filter, that is, the surface acoustic wave filter is obtained.
In this constitution, however, when a large input signal is applied to the input terminal
101
, a sudden temperature rise takes place in the resonators
105
and
106
, in particular, closer to the input terminal
101
, and it may cause migration in the metal composing the comb-shaped elcctrode pattern (usually aluminum or aluminum alloy), thereby leading to precipitation, oxidation or deterioration, and the desired filter characteristic might not be obtained.
That is, the conventional surface acoustic wave filter has been known as a filter generally capable of obtaining a steep filter characteristic, but it was designed to handle a small signal and limited in the range of use, and hence it was difficult to handle a large signal in the surface acoustic wave filter
SUMMARY OF THE INVENTION
The invention is devised in the light of the above problems, and it is therefore an object thereof to present a surface acoustic wave filter capable of obtaining a stable filter characteristic if a large current is applied in the input terminal.
To achieve the object, the invention comprises resonators formed on a piezoelectric substrate, through-holes provided near the resonators, and a conductive material filling up the through-holes, in which the through-holes filled with the conductive material are electrically grounded. In this constitution, by the through-holes provided near the resonators and filled up with the conductive material, the heat generated in the resonators when a large signal is applied to the input terminal can be released, and a stable filter characteristic may be maintained if a large signal is entered.


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