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

• Long channel (L > 500 nm) junctionless NW/fin transistors were investigated through 3D TCAD simulations.
• Mildly doped Nd = 1 × 1019 cm−3 structures with Fw < 20 nm and εr = 1.7 have promising characteristics for sensors.
• These structures have Vth ~ 0 V and high relative sensitivities in the subthreshold regime SS > 95%.
• They also have high transconductance values at threshold gm,Vfg=0 V > 10 nS, and low subthreshold slopes SS ~ 60 mV/dec.
• Finally they were found to have high saturation currents Id,max ~ 1–10 μA and high Ion/Ioff > 104–1010 ratios.

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 εr = 1.7. The operation regime (threshold voltage Vth) 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 Nd for a p-type tri-gated structure. Two different materials, namely, an oxide and an organic monolayer, with varying dielectric constants εr provide surface passivation. Mildly doped Nd = 1 × 1019 cm−3, thin bodied structures (fin width Fw < 20 nm) with an organic dielectric (εr = 1.7) were found to have promising electrical characteristics for FET sensor structures such as Vth ~ 0 V, high relative sensitivities in the subthreshold regime S > 95%, high transconductance values at threshold gm,Vfg=0 V > 10 nS, low subthreshold slopes SS ~ 60 mV/dec, high saturation currents Id,max ~ 1–10 μA and high Ion/Ioff > 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.