Silicon-based ultrasonic microsensors and micropumps

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Abstract
With the addition of a thin piezoelectric zinc oxide film and transducing electrodes, a thin membrane of low-stress silicon nitride formed in a silicon die can be made into a versatile ultrasonic sensor and actuator. We will describe the fabrication and application of this device, which typically operates in the low megahertz frequency range and can perform many functions: measuring the viscosity of microliter volumes of liquids; measuring the densities of gases and liquids; serving, with the addition of a thin polymer film, as a sensor for measuring the concentrations of organic gases; determining, when immersed in a liquid, the mass per unit membrane area of adsorbed protein molecules, cells and bacteria; pumping air at velocitities of centimerters per second and pumping water at hundreds of microns per second; and stirring microliter volumes of fluids.

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