Authors: Y. Kanda and K. Matsuda
Affilation: Kojundo Chemical Laboratory Co. LTD, Japan
Pages: 153 - 156
Keywords: silicon MEMS piezoresistance, stress
The PR in silicon has been widely used in the framework of micro-electro mechanical systems (MEMS). Origin of the shear PR effect even in n-type Si was not always explained completely in despite of simpler band structure than that of p-type Si. Many of the features of the PR effect observed by Smith in n-type materials were explained very successfully by Herring in terms of the strain-induced transfer of electrons between the conduction band valleys. The electron transfer theory gives the three independent PR coefficients of the cubic crystal under simplifying assumptions on the relaxation time. This theory predicts the shear piezoresistance coefficient π44 of n-type Si to vanish. However the observed π44 differs from zero beyond experimental error π44=－13.6・10-11 Pa-1 as we pointed out that a shear stress destroys the rotational symmetry of the ellipsoidal valleys and induces large effective mass changes. We pay attention to the ellipsoid on the kα axis under shear stress exy. In this case, the energy surface becomes an ellipsoid with three different radii along its principal axes. A similar effect was detected in N-channel MOS transistors.