Acoustic wave transmission media using silicon plates with micromachined cavities

The author describes the application of micromachining techniques to form two types of cavities useful in silicon acoustic wave oscillators for sensor applications. Under the design conditions described, it is possible in one processing operation to form two kinds of rectangular cavities in the interior of a silicon die: (1) cavities with long perpendicular walls that are suitable for acting as reflecting surfaces for an ultrasonic beam, and (2) cavities with long sloping walls that are suitable for acting as boundary surfaces, confining the divergent lobes of an ultrasonic beam and dissipating unwanted wave energy by a combination of mode conversion and absorption. By combining these two types of cavities with transducers directing an acoustic beam in <110> directions, it is possible to form an acoustic wave oscillator with a relatively long, multisegment propagation path.<>