Feasibility of silicon nanowire's electrical characteristics modulation using substrate bias for tunable biosensor design

Abstract

We report a feasibility study of using silicon (Si) nanowire (NW) as a tunable biosensor through substrate bias arrangement. 75nm, 50nm and 25nm thick Si NWs having channel length of 1pm with doping concentrations of 1016/cm3, 1017/cm3 and 1018/cm3 respectively are investigated for different substrate voltages. For 75 nm and 50 nm thick NWs, application of substrate bias has been found to significantly affect NW's sub-threshold characteristics for body doping values of 1016/cm3, 1017/cm3 and a sub-threshold slope of 63 mV/dec can be achieved by using 7 V of substrate bias. For a body doping of 1018/cm3 an insignificant effect is observed with a degraded sub-threshold slope around 3402.2 mV/decade for all substrate voltages. This result indicate that 75 nm and 50 nm thick Si NWs can be used as tunable biosensor with a body doping of 1016/cm3 or 1017/cm3 but a body doping of 1018/cm3 is not suitable for viable biosensor operation. A drastic change in behavior is observed for 25 nm thick Si NW which exhibits excellent subthreshold slope around 64mV/dec for body doping values of 1016/cm3, 1017/cm3 and 1018/cm3 with an appropriate substrate voltage. This result implies that scaling of NW thickness at 25 nm and/or below would allow tunable biosensor design using both low and high doping with doping concentration within the range of 1016/cm3 to 1018/cm3 for single molecule detection.