Pixel-based biosensor for enhanced control: silicon nanowires monolithically integrated with field-effect transistors...

Silicon nanowires (SiNWs) are a widely used technology for sensing applications. Complementary metal-oxide-semiconductor (CMOS) integration of SiNWs advances lab-on-chip (LOC) technology and offers opportunities for read-out circuit integration, selective and multiplexed detection. In this work, we propose novel scalable pixel-based biosensors exploiting the integration of SiNWs with CMOS in fully-depleted silicon-on-insulator technology. A detailed description of the wafer-scale fabrication of SiNW pixels using the CMOS compatible sidewall-transfer-lithography as an alternative to widely investigated time inefficient e-beam lithography is presented. Each 60 nm wide SiNWs sensor is monolithically connected to a control transistor and novel on-chip fluid-gate forming an individual pixel that can be operated in two modes: biasing transistor frontgate (V _G) or substrate backgate (V _BG). We also present the first electrical results of single N and P-type SiNW pixels. In frontgate mode, N and P-type SiNW pixels exhibit subthreshold slope (SS) ≈ 70-80 mV/dec and I _on/I _off ≈ 10⁵. The N-type and P-type pixels have an average threshold voltage, Vth of -1.7 V and 0.85 V respectively. In the backgate mode, N and P-type SiNW pixels exhibit SS ≈ 100-150 mV/dec and I _on/I _off ≈ 10⁶. The N and P-type pixels have an average V _th of 5 V and -2.5 V respectively. Further, the influence of the backgate and frontgate voltage on the switching characteristics of the SiNW pixels is also studied. In the frontgate mode, the V _th of the SiNW pixels can be tuned at 0.2 V for 1 V change in V _BG for N-type or at -0.2 V for -1 V change in V _BG for P-type pixels. In the backgate mode, it is found that for stable operation of the pixels, the V _G of the N and P-type transistors must be in the range 0.5-2.5 V and 0 V to -2.5 V respectively.