AN ANALYTICAL SUBTHRESHOLD CURRENT/SWING MODEL FOR JUNCTIONLESS CYLINDRICAL NANOWIRE FETS (JLCNFETS)

Te-Kuang Chiang, Juin J. Liou

Abstract: Based on the parabolic potential approach (PPA), scaling theory, and drift-diffusion approach (DDA) with effective band gap widening (BGW), we propose an analytical subthreshold current/swing model for junctionless (JL) cylindrical nanowire FETs (JLCNFETs). The work indicates that the electron density of Qm that is induced by the current factor minimum central potentialc,minand equivalent quantumpotential QM is used to determine the subthreshold current/swing for JLCNFET. Unlike the junction-based (JB) cylindrical nanowire FETs (JBCNFETs), the subthreshold current for JLCNFET is not linearly proportional to the silicon diameter, but linearly proportional to the current factor due to the depletion-typed operation. Apart from short-channel effects (SCEs), the quantum-mechanics effects (QMEs) are included in the model by accounting for the effective BGW, which decreases the electron density in the subthreshold regime and reduces the subthreshold current consequently. Band-to-band tunneling (BTBT) that impacts the subthreshold current is also discussed in the end of the paper. The model explicitly shows how the bulk doping density, drain bias, channel length, oxide thickness, gate workfunction, and silicon film diameter affect the subthreshold current/swing. The model is verified by its calculated results matching well with the data simulated from the three-dimensional device simulator and can be used to investigate the subthreshold current/swing for JLCNFET.

Key words: Scaling theory, Parabolic potential approach, Subthreshold current, Subthreshold swing, Drift-diffusion approach, Effective bad gap widening, Short-channel effects, Quantum-mechanics effects, BTBT, JLCNFET