Semiconductor Strain Transducers

Around the end of 1958, considerable interest developed among experimenters and transducer manufacturers in the possible application of highly sensitive piezoresistive elements as subminiature sensing devices for displacements, strains and forces. For dynamic problems, piezoelectric pickups consisting of quartz or barium titanate had previously found their way into numerous applications for the measurement of vibrations, shock intensities and stress waves. However, similar lightweight instruments that could handle dc or near-dc signals as well as dynamic ones were yet to be found. Piezoresistive semiconductor materials do just that. The present paper is intended to give a summary of established facts about them and indicate some of their potentialities. The history of research in piezoresistive phenomena dates back to the 1920's, when some of the earliest observations were made by Bridgman on single and polycrystalline metal specimens. 2 These results were augmented by several contributions in the 1930's from Allen and Cookson,'" who measured the effects that were subsequently utilized in wire strain gages. To the authors' knowledge, the first piezoresistive measure705