Micromachined rayleigh, lamb, and bulk wave capacitive ultrasonic transducers

Abstract

A micromachined capacitive ultrasonic transducer is used to generate and detect Rayleigh, Lamb, and bulk waves in a solid substrate. The transducer contains a substrate with a conductive back electrode, a support material on the substrate, a membrane supported above the substrate by the support material, and a conductive film on the membrane. The support material contains parallel edges defining elongated gaps over which the membrane is supported. Unsupported free regions of the membrane above the gaps are vibrated by applying an electrical signal between the conductive film and conductive back electrode, and stresses are coupled into the substrate at the attachment edges of the membrane. Acoustic modes of the substrate are excited by the stresses, and ultrasonic waves propagate in a direction perpendicular to the parallel edges. By properly choosing the membrane width, material, and thickness, the gap separation distance, and the support material height and thickness, a particular acoustic mode can be selected for a required operating frequency. The gaps may be separated by a distance equal to the wavelength or half-wavelength of the desired acoustic mode. Alternately, the gaps may be grouped, with each group separated by a wavelength or half-wavelength. The transducer can be used in many applications, including filtering and chemical sensing.

Dependencies are inferred from the claim text.