A Compact Model for Undoped Silicon-Nanowire MOSFETs With Schottky-Barrier Source/Drain

Abstract

Abstract-A comprehensive physics-based compact model for three-terminal undoped Schottky-barrier (SB) gate-all-around silicon-nanowire MOSFETs is formulated based on a quasi-2-D surface-potential solution and the Miller-Good tunneling model. The energy-band model has accounted for the screening of the gate field by the electrons or holes, which has been largely missed in the literature. Although SB-MOSFETs are essentially ambipolar devices, we show that the separate modeling of electron and hole currents is simple yet accurately predicts the final ambipolar current. Thinner oxide thickness is confirmed to be beneficial to SB-MOSFETs for both ON-and OFF-state currents. However, smaller nanowire radius (or thinner body thickness) is found to be only beneficial to SB-MOSFETs with high SB heights (SBHs) despite the OFF-state current being reduced significantly. For SB-MOSFETs with low SBHs, the tunneling-current-density enhancement due to a smaller radius is not able to compensate the reduction in the contact size, which leads to a degradation of the "ON" current. The drift current in the channel is shown to be negligible in SB-MOSFETs, and the tunneling/thermionic current through the SB represents the main current-limiting mechanism.

A surface potential and current model for polarity-controllable silicon nanowire FETs

“…However, it can be addressed by introducing a unified λ as in [11]. For simplicity, the modeling of the bias-dependent λ is not discussed in this work.…”

“…For Schottky-barrier devices, the potential distribution near the contacts is required in addition to φ s,0 to calculate the tunneling through the Schottky barriers. Therefore, we apply a quasi-2-D solution of the surface potential [11]:…”

“…There are many works on the compact modeling of doped source/drain or Schottky-barrier SiNWFETs [10], [11]. Compared to these devices, polarity-controllable SiNWFETs introduce additional gated regions between source and drain.…”

Unification of MOS compact models with the unified regional modeling approach

“…He proposed a unique drain-induced barrier lowering (DIBL) model [9,34] based on quasi-2D solution that accounts for both DIBL and T Si -dependent subthreshold slope (flatband voltage). He also developed a complete model for SB FinFETs [35,36], with the URM for φ s in the intrinsic channel and thermionic and tunneling current, as well as a subcircuit model for dopant-segregated Schottky (DSS) SiNWs [37,38], with the unique convex curvature in the I ds -V ds characteristics at small V ds and large V gs .…”

“…The rest of the equations [e.g., (35), (36), (42), (49), (50)] share the same expressions for both CSA and non-CSA models. The "switch" between the two types of models is some intermediate doping level, around which either model would be applicable.…”