Junctionless Silicon and In_0.53Ga_0.47As Transistors—Part II: Device Variability From Random Dopant Fluctuation

Abstract

Random dopant fluctuation (RDF) variability in nanoscale junctionless FETs (JLFETs) utilizing either Si orIn 0.53 Ga 0.47 As channels has been studied using technology computer-aided design (TCAD) simulations. The 15nm node Si and InGaAs JLFETs are equivalently designed and calibrated using nonequilibrium Green's function simulations for statistical TCAD analysis. We find that n-InGaAs JLFETs exhibit reduced RDF variability compared with n-Si JLFETs in terms of threshold voltage, subthreshold swing, and drain-induced barrier lowering as a result of high degeneracy effects. By contrast, the variability of p-InGaAs JLFETs is comparable with that of n-and p-Si JLFETs because of the larger valence band density of states (DOS). The normalized variations in ON-state drive current are roughly equal (∼16%) for all device types, because the major effects of degenerate screening on current transport effectively cancel one another. From these results, we find that high carrier degeneracy in small DOS materials can have a significant effect on the electrostatic integrity of JLFETs in the presence of RDF (especially in subthreshold), and that degenerately doped n-InGaAs devices are slightly (and inherently) more immune to RDF compared with Si JLFETs.

Junctionless Silicon and In0.53Ga0.47As Transistors—Part I: Nominal Device Evaluation With Quantum Simulations

“…6, we see that E TOB ∼ 0.4 eV in InGaAs and 0.2 eV in silicon in the OFF-state, leading to roughly equivalent SS in agreement with what was observed in our NEGF simulations. We also note that, at higher nominal barrier heights, the SS is less sensitive to changes in E TOB because of a smaller |(d SS/d E TOB )|, which is consistent with the reduced SS variability found in InGaAs JLFETs [11]. Since these findings only rely on a generic channel potential model and the presence of strong degeneracy in the source and the drain, they may also apply to other types of III-V transistors besides JLFETs.…”

“…As expected, the trends, though quantitatively different, are qualitatively preserved across dimensions. The electrostatic effects of degeneracy affect the nominal device characteristics, and also have a major impact on the resilience of different channel materials to device variability, as seen in Part II of this paper [11].…”

“…We give an analytical discussion of barrier height-dependent subthreshold swing (SS) characteristics in the Appendix. In Part II of this paper [11], we build on these nominal device findings to examine the variability of silicon and InGaAs JLFETs induced by random dopant fluctuations.…”

Threshold Voltage Statistical Variability and Its Sensitivity to Critical Geometrical Parameters in Ultrascaled InGaAs and Silicon FETs

“…The methodology used in our analysis is an advancement over the approaches previously reported in literature, in that we simultaneously considered all the relevant sources of statistical variability, as well as their dependence on the most critical geometrical parameters. Previous works considered only Si channel material [12,[14][15][16][17][18][19][20], fewer variability sources and/or sensitivity parameters [17,[19][20][21][22][23][24], and devices not as aggressively scaled as in our investigation [12,15,17].…”

Enhancement of off-state characteristics in junctionless field effect transistor using a field plate

“…[1][2][3] One of the main reasons is that the rapid down-scaling of conventional bulk MOSFETs below 45 nm requires an ultrasteep doping profile at the metallurgical junction and a high thermal budget corresponding to the post-anneal dopant activation,which leads to extreme troubles in device fabrication. [4,5] To overcome this limitation, various alternative devices are being proposed, and a new class of field effect device called the junctionless field-effect transistor (JLFET) has attract lots of research attention in recent years. [6][7][8][9][10][11][12][13][14] The basic structure of a JLFET consists of a uniformly highly doped silicon channel controlled by at least an on gate electrode.…”