Piezoelectric Switching of Bistable MEMS Membranes in Fluids

In this paper, we demonstrate bistable switching of micromachined membranes with integrated piezoelectric thin film actuators in liquids with a dynamic viscosity up to 286 mPa·s. The membranes have diameters between 600 to 800 µm and a total layer stack thickness of 3.3 µm, thus enabling membrane displacements up to 20 µm, when switching from one ground state to the other. To predict the switching behavior in fluids, pre-evaluation was carried out in air. The resonance frequency of the first vibrational mode f res1 provided information, if such a membrane is switchable. In contrast, in liquids only the membrane center velocity at f res1 showed a tendency to predict the switching behavior of the membranes. However, neither the viscosity nor the density affected the displacement heights between the two ground states during switching procedures. By stimulating the switching process purely electrically, a great variety of new applications of such membranes is unlocked like as fluid valves, PMUTs in fluids or bio-sensors.