Doping and Thickness Dependent Electrical Characteristics of Backgated Silicon Nanowire Biosensors

Abstract

We performed a feasibility study of Si nanowire as a biosensor through backgate bias arrangement by tuning its electrical characteristics. 75nm, 50nm and 25nm thick Si NW having channel length of 1μm with doping concentrations of 1016cm-3, 1017cm-3 and 1018cm-3 respectively were investigated for different backgate voltages. It is found that backgate bias has a significant effect on the sensitivity of p-type Si-NW. 75nm thick NW shows sub-threshold slope of 70.36mV/dec, 79mV/dec and 3402.2mV/dec at doping values of 1016cm-3, 1017cm-3 and 1018 cm-3 respectively. This result shows that 75nm thick Si NW's sensor characteristics degrade with the increase of body doping values. Application of positive backgate has been found to improve NW's sub-threshold characteristics however this improvement is minor for 75 nm thick Si NW at 1018cm-3 doping. The 25nm thick Si NW exhibited sub-threshold slopes of 64mV/dec, 65.49mV/dec and 66.96mV/dec at doping values of 1016cm-3, 1017cm-3 and 1018cm-3 respectively which implies much better sensor operation of 25nm thick NW in comparison to 75 nm thick NW. Application of +7V of positive backgate bias resulted in the improvement of the sub-threshold slope of the 25nm thick NW with values of 62mV/dec, 62mV/dec and 63.11mV/dec at doping values of 1016cm-3, 1017cm-3 and 1018cm-3 respectively. In all cases application of negative backgate bias generally degrades the sub-threshold behavior of NW's. These results show that backgate bias arrangement has significant effect on NW sensor operation. A typical less sensitive NW can be converted into a sensitive one by choosing the appropriate backgate voltage. However this thesis also gives a data base of NW thickness and doping for sensor design. These results are very important for p-type Si-NW based biosensors fabricated on SOI platform to ensure maximum sensitive operation for molecular level detection.