Laser Irradiation Effect on Saw Properties of Layered Structure of Oxide/Piezoelectric Substrate
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O
Amorphous Ti-O, Si-
and Si-X-O, where X is other metal elements, films were formed on the surface of the SAW device
composed of quartz or LiTaO 3 substrate and several hundred Al electrode fingers for oscillating and detecting the SAW.
A KrF excimer laser with 248nm in wavelength was used for the irradiation. The center
frequency of the SAW devices was immediately decreased by the irradiation of the laser pulses.
Although
the response to the irradiation was reversible for lower laser energy, the change of the center frequency was irreversible for the laser energy density higher than 20mJ/cm 2.
It is considered that the response appeared in
the frequency shift is generated by a change of an elastic stiffness of the films lowered by an absorption of the laser energy. INTRODUCTION SAW devices are widely applied to components of high frequency communication systems.
Especially,
for SAW filters, a control of operating frequency (center frequency) is a serious problem because the frequency is defined by the accuracy of the device dimension. The center frequency of SAW filter is strongly dependent on the thickness of the electrodes. thickness increases.
In general, the frequency linearly decreases as the
Therefore, development of an in-situ frequency controlling method is desirable for
improving the efficiency of device processing.
On the other hand, studies on the interaction between
ceramic materials and UV light for improving the materials are interesting because most materials have an optical band gap in UV region. to ceramic substrates [1, 2].
Irradiation with UV light can enhance the adhesion strength of metal films
In the study of irradiation using a XeCI excimer laser with 308nm wavelength
on Al-O substrates, the generation of point defects during laser irradiation was suggested experimentally [3]. Laser irradiation can be expected to be used for a selective improvement of oxide thin films for electronic devices.
As is well known, SAW devices have a high sensitivity to surface conditions of a piezoelectric
substrate where an acoustic wave propagates.
In this study, for preliminary experiments, dielectric thin
films of amorphous Ti-O and Si-O induced other metal elements were deposited on SAW filters, and effects of the irradiation on the operational properties of the SAW filters have been investigated using UV laser
237 Mat. Res. Soc. Symp. Proc. Vol. 459 0 1997 Materials Research Society
pulses of KrF excimer laser with 248nm wavelength in order to develop an frequency controlling method. EXPERIMENTAL TECHNIQUES Oxide thin films were prepared by using ion beam sputtering [4] on surfaces of SAW filters, which are very sensitive to the conditions of the substrate surface [5-7].
Sputtering conditions are shown in Table I.
An ion source was the Kaufman-type (Commonwealth Co.) with beam diameter of 30mm at outlet of the source.
The oxide films were formed reactively by supplying oxygen gas to the substrate from a nozzle.
Si-X-O films were prepared by sputtering the Pyrex glass (Coming c
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