Piezoresistance of silicon and strained Si0.9Ge0.1

Abstract We present experimentally obtained results of the piezoresistive effect in p-type silicon and strained Si 0.9 Ge 0.1 . Today, strained Si 1− x Ge x is used for high speed electronic devices. This paper investigates if this area of use can be expanded to also cover piezoresistive micro electro mechanical systems (MEMS) devices. The measurements are performed on microfabricated test chips where resistors are defined in layers grown by molecular beam epitaxy on (0 0 1) silicon substrates. A uniaxial stress along the [1 1 0] direction is applied to the chip, with the use of a four point bending fixture. The investigation covers materials with doping levels of N A  = 10 18  cm −3 and N A  = 10 19  cm −3 , respectively. The results show that the π 66 piezoresistive coefficient in strained Si 0.9 Ge 0.1 is approximately 30% larger than the comparable π 44 piezoresistive coefficient in silicon at a doping level of N A =  10 18  cm −3 . Thus, strained Si 0.9 Ge 0.1 holds promise for use in high sensitivity MEMS devices.