The piezoelectric semiconductor and acoustoelectronic device development in the sixties

In the 1960´s the properties of piezoelectric semiconductors, group III-V zinc-blende and group II-VI wurtzite structure, were explored for the development of acoustoelectronic, (AE), devices. Bulk acoustic wave, (BAW), delay lines, traveling wave amplifiers, and oscillators were developed. Although these elegant functional devices never made it into the realm of full-scale production and application, the piezoelectric semiconductor developments of the 1960´s provided an exciting time for theoretical explanations and creative experimentation to explore device capabilities for electronic systems applications. Delay lines were formed from rectangular parallelepiped blocks of piezoelectric semiconductors with integral input and output transducers depleted of carriers at each end of the block. The ultrasonic traveling wave amplifier was based on the interaction of electrons under a bias field moving with a velocity faster than the piezoelectric field accompanying the acoustic traveling wave. The gain factor in a piezoelectric semiconductor under direct current bias was used to develop oscillators. This historical presentation will be illustrated by experimental work done at Motorola in the period from 1962 to 1969 to introduce piezoelectric semiconductor components and devices into electronic systems.