Sub-threshold behavior assessment of the accumulation and inversion mode silicon nanowires for biosensor application

The subthreshold characteristics of accumulation and inversion mode silicon nanowire (SiNW) transistors are investigated for different drain voltage (VD) polarities, NW thicknesses and substrate voltages (VSUB) to assess their comparative biosensing potential. The accumulation type SiNW transistor demonstrates improved subthreshold characteristic with the positive VSUB whereas the subthreshold characteristic is found to degrade with the negative VSUB. However, this degradation is prominent for thick nanowires whereas in the thinnest nanowire no significant degradation is observed. Accumulation mode SiNWs exhibit relatively superior behavior when the VD is negative. Quite an opposite behavior is found for inversion mode SiNWs. Scaling of the NW thickness results in the significant improvement of the electrical characteristics both for accumulation and inversion mode SiNWs. However, comparative analysis reveals that the inversion mode of operation is preferable for designing sensitive biosensor when the NW thickness ≥ 50 nm whereas an almost similar biosensor performance is achieved both in inversion and accumulation mode SiNWs for the NW thickness ≤ 25 nm if the conventional three-terminal operation (i.e. source, drain and gate) is performed. It is revealed that for the three-terminal operation, the economic benefit of junction less transistors can be exploited for sensitive biosensor design, only in the aggressively scaled NWs. This investigation also reveals that the VSUB can be used to tune the subthreshold behavior of SiNWs and hence, there are available bias conditions whereby thick SiNWs’ can also be used for designing a sensitive biosensor.