Physical Description of the Anisotropic Stress Effect in the Silicon P-N Junction Cantilever Transducer

Abstract

A silicon p‐n junction device using the anisotropic stress effect has been constructed. The device exhibits a change in reverse leakage current on application of a bending force. The device consists of a narrow bar of silicon into which a sharp notch is cut electrolytically. On the opposite surface, a shallow p‐n junction is produced by diffusion. Sensitivity to bending is achieved when mechanical damage is produced at the surface of the shallow junction in a controlled fashion. The corresponding change in the forward and reverse characteristics of the device after scribing is described. Methods of testing the device and changes in operating characteristics are discussed. A theory of device operation is proposed. This theory presents a model of generation of dislocation loops from Frank‐Read sources produced during the plastic deformation phase. The dislocation loops, on application of stress, enter the depletion region of the junction creating a generation current according to the Sah‐Noyce‐Shockley generation‐recombination theory. A mathematical model of the device is developed. Operating characteristics are then compared with the mathematical model. The sensitizing operation produces noise sources within the device. The spectrum of these sources is described and the intensity is compared to device sensitivity during the scribing operation. Device noise is reduced by a decrease in the emitter perimeter. Operating characteristics of the device are discussed. These include linearity of the stress‐ leakage current curve, change of sensitivity with voltage, deflection with applied force, a‐c impedance, junction capacity, mechanical stiffness, effective minority carrier lifetime, and fundamental vibration frequency.