5. New Techniques and Phenomena
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.
Kwan, Sze-Hon; White, Richard M.; and Muller, Richard S., "Integrated Ultrasonic Transducer" (1978). Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, September 1976–June 1977. 25.