Ultrasonic transducers composed of integrated assemblies of double-diffused MOS transistors (DMOST) and thin-film piezoelectric transducing elements are described. The entire transducer is built on a single-crystal silicon wafer and offers a number of attractive features including: small size and correspondingly precise localization of the sensitive element, a response that can be predicted by relatively simple theory, a large bandwidth, and a possibility of producing arrays of sensors together with other signal-processing elements in a single processing sequence. The piezoelectric film (zinc oxide) is sputtered either in the gate region of a double-diffused H6S transistor (making the so-called PI-MOST ) or adjacent to the gate electrode of a double-diffused MOS transistor. The transducer~ be excited in various ways: (1) in a thickness mode from the bare silicon surface opposite the piezoelectric-coated region; (2) in a flexural mode caused by bending the silicon wafer; (3) end excitation by surface motions either normal or transverse to the edge of the wafer; (4) by surface waves. Various of these modes are characterized by high sensitivity to strain, low conversion loss, large bandwidth, and good response at very low or very high frequencies
