Semiconductor ultrasonic signal-delay apparatus utilizing integral p-n junctions as electromechanical transducers

1,015,559. Piezoelectric elements; semiconductor devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 28, 1964 [May 28, 1963], No. 22135/64. Headings H1E and H1K. [Also in Division H3] An elongated piece of semi-conductive piezoelectric material (preferably a single crystal) has spaced PN junctions which when biased induce depletion layers around them to act as electrical/ mechanical transducers for propagating ultrasonic waves down the body. Suitable materials are cadmium sulphide, cadmium selenide, cadmium telluride, zinc oxide, indium arsenide, indium antimonide, gallium phosphide and (especially) gallium arsenide. In Fig. 1 the material comprises a P-type circular filament 10 with N-type regions 13, 14 at each end formed, e.g. by diffusion or epitaxial deposition. The filament may be coiled to save space. The junctions 15, 16 are biased by batteries 24, 27 to produce depletion layers which are a half-wavelength long at the working frequency, which may be 300 Mc/s. to several thousand Mc/s. Pulses applied from a source 30 produce stresses in the depletion layer 11 which cause longitudinal stress waves to be propagated down the line to the corresponding layer 14 at the other end. Here the waves generate corresponding electric signals which are passed to a utilizing device 33. Since the depletion layers and the rest of the material have the same geometry and mechanical properties, their mechanical impedances will be the same and no energy loss occurs. Losses due to reflections at the ends of the material are minimized by tapering the ends 17, 18 and enclosing them in absorbing blocks of plastic 19, 20. The material may alternatively be in the form of a flat ribbon (Fig. 2, not shown). The cross-section of the material may be greater or less than the wavelength of the stress wave, or in the case of the ribbon one dimension may be greater and the other less.