Junctionless silicon nanowire transistors for the tunable operation of a highly sensitive, low power sensor

Silicon nanowire (SiNW) field effect transistors (FETs) have been widely investigated as biological sensors for their remarkable sensitivity due to their large surface to volume ratio (S/V) and high selectivity towards a myriad of analytes through functionalization. In this work, we propose a long channel (L > 500 nm) junctionless nanowire transistor (JNT) SiNW sensor based on a highly doped, ultrathin body field-effect transistor with an organic gate dielectric ε_r = 1.7. The operation regime (threshold voltage V_th) and electrical characteristics of JNTs can be directly tuned by the careful design of the NW/Fin FET. JNTs are investigated through 3D Technology Computer Aided Design (TCAD) simulations performed as a function of geometrical dimensions and channel doping concentration N_d for a p-type tri-gated structure. Two different materials, namely, an oxide and an organic monolayer, with varying dielectric constants ε_r provide surface passivation. Mildly doped N_d = 1 × 10¹⁹ cm^-3, thin bodied structures (fin width F_w < 20 nm) with an organic dielectric (ε_r = 1.7) were found to have promising electrical characteristics for FET sensor structures such as V _th ~ 0 V, high relative sensitivities in the subthreshold regime S > 95%, high transconductance values at threshold g_{m,Vfg=0 V} > 10 nS, low subthreshold slopes SS ~ 60 mV/dec, high saturation currents I _d,max ~ 1-10 μA and high I_on/I_off > 10⁴-10¹⁰ ratios. Our results provide useful guidelines for the design of junctionless FET nanowire sensors that can be integrated into miniaturized, low power biosensing systems.