  Although extensively presented as one of the most promising silicon-based
micromachined sensor adapted to real-time measurements in liquid media, the
cantilevered structure still suffers from its quality factor (Q) dramatic
dependence on the liquid viscosity thus lowering the measurement resolution. In
this paper, micromachined piezoelectric membranes are introduced as a potential
alternative to the cantilevers for biological applications. HighQ-factors (up
to 150) of micromachined piezoelectric membranes resonating in various liquid
mixtures (water/glycerol and water/ethanol) are thus reported and a theoretical
model proposed by Lamb [H. Lamb, On the vibrations of an elastic plate in
contact with water, Proc. Roy. Soc. Lond. A 98 (1920) 205?216] is validated for
microscale structures proving that the variation of the liquid viscosity (if
lower than 10 cP) has no effect on the dynamic behavior of the membranes. To
conclude, two types of experiments were performed in water/glycerol mixtures:
in-flow (with liquid continuously flowing on the devices) and in-spot (with
individual membranes oscillating in a 5 $\mu$L volume of liquid). The results
interestingly showed that for the in-spot configuration the Q-factor values are
more than two-fold the ones corresponding to in-flow measurements thus
providing alternative insights into the way to conceive ideal configurations
for real-time biological measurements in liquid media.
