A new class of devices based on stressed single and multiple junctions

Recent investigations have shown that stress suitably applied over small areas of p-n junctions causes very large and reversible changes in junction resistance. The active semiconductor volume involved is of the order of a few cubic microns. The stress sensitivity cannot be expressed in conventional terms since the resistance change is a function of both mechanical and electrical bias and also because anisotropic stress is used. Under reverse bias resistance, ratios of 10³- 10⁴have been obtained reproducibly under forces of a few thousand dynes. Stress signals have also been applied to junctions in transistor structures where the stress sensitivity of the transfer characteristics causes a conversion of mechanical to electrical signals. For example, with forces of a few thousand dynes acting on the emitter junction, hfehas been changed by factors of 10- 100. Experimental two- and three-terminal devices which incorporate stressed junctions will be described. These include microphones, hydrophones and phonograph pick-ups. Other device possibilities on the same principles will be discussed.