SILICON-BASED ULTRASONIC MICROSENSORS AND MICROPUMPS

With the addition of a thin piezoelectric zinc oxide film and transduc ing electrodes, a thin membrane of low-stress silicon nitride formed i n a silicon die can be made into a versatile ultrasonic sensor and act uator. We will describe the fabrication and application of this device , which typically operates in the low megahertz frequency range and ca n perform many functions: measuring the viscosity of microliter volume s of liquids; measuring the densities of gases and liquids; serving, w ith the addition of a thin polymer film, as a sensor for measuring the concentrations of organic gases; determining, when immersed in a liqu id, the mass per unit membrane area of adsorbed protein molecules, cel ls and bacteria; pumping air at velocitities of centimerters per secon d and pumping water at hundreds of microns per second; and stirring mi croliter volumes of fluids.