All five discussed delay line devices are fabricated
using a planar ( IC-compatible) technology. Rayleigh,
APM and STW devices are fabricated in a piezoelectric
crystal such as quartz or LiNbO,. A thin metal film
(e.g. aluminum) is deposited on the crystal and interdigi-
tal patterns are etched using photolithographic tech-
niques. For the Love wave device, an extra process step
is required for the realization of the thin wave guide
film (e.g. silicon dioxide) on top of an ST-quartz crystal.
For devices having a period of about 30 pm, an optimum
sensitivity is obtained for a guiding layer of about 5 pm
thick. The silicon dioxide film should not exhibit too
much stress in order to prevent cracks and peeling of
the film. After deposition, windows are etched to reach
the bonding flaps of the metal transducers which are
located at the interface of the crystal and the guiding
film