  This paper presents the design, fabrication and preliminary experimental
results of a flexure plate wave (FPW) resonator using sol-gel derived lead
zirconate titanates (PZT) thin films. The resonator adopts a two-port structure
with reflecting grates on the composite membrane of PZT and SiNx. The design of
the reflecting grate is derived from a SAW resonator model using COM theory to
produce a sharp resonant peak. The comparison between the mass and the
viscosity effects from the theoretical expression illustrates the applications
and the constraints of the proposed device in liquid sensing. Multiple coatings
of sol-gel derived PZT films are adopted because of the cost advantage and the
high electromechanical coupling effect over other piezoelectric films. The
fabrication issues of the proposed material structure are addressed.
Theoretical estimations of the mass and the viscosity effects are compared with
the experimental results. The resonant frequency has a good linear correlation
with the density of low viscosity liquids, which demonstrate the feasibility of
the proposed device.
