Geometry, Temperature, and Body Bias Dependence of Statistical Variability in 20-nm Bulk CMOS Technology: A Comprehensive Simulation Analysis

Abstract

Abstract-Conventional bulk CMOS, which is arguably most vulnerable to statistical variability, has been the workhorse of the electronic industry for more than three decades. In this paper, the dependence of the statistical variability of key figures of merit on gate geometry, temperature and body bias in 25nm gate-length MOSFETs, representative for the 20nm CMOS technology generation, are systematically investigated using 3D statistical simulations. The impact of all relevant sources of statistical variability is taken into account. The geometry dependence of the threshold voltage dispersion (and indeed the dispersion of other key transistor figures of merit) does not necessarily follow the Pelgrom's law due to the complex non-uniform channel doping and the interplay of different statistical-variability sources. The DIBL variation for example follows a log-normal distribution. The temperature significantly affects the magnitudes of threshold-voltage, sub-threshold slope, on/off currents and the corresponding statistical distributions. Reverse body bias increases the threshold voltage and its fluctuation while forward body bias reduces both of them.

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].…”

Drain bias effects on statistical variability and reliability and related subthreshold variability in 20-nm bulk planar MOSFETs

“…It features a hafnium--based high--κ gate dielectric and TiN metal gate with equivalent oxide thickness of 0.85 nm. The complex doping profiles of this device were optimized in [6], in terms of both nominal device performance and variability. A retrograde doping profile reduces the effective channel doping near the interface, which in turn reduces the RDD--induced variability.…”

“…However in figures 12 (a) and (b) the proportion of acceptors at the drain--side is high. As drain bias, and hence the drain side electric field, increases, the effect of these drain--side dopants in providing a barrier to current is constrained, and the overall source drain potential barrier is significantly reduced [6]. Thus the transistors in figures 12 (a) and (b) exhibit high DIBL values.…”

“…For example, the drain--bias has a strong effect on subthreshold electrostatics, and DIBL is an indicator of the drain bias dependence of the short--channel effects. The geometry, body bias and temperature impact on statistical variability for the 20--nm bulk planar technology was presented in [6]. To the best of our knowledge, there are few systematic studies of the impact of the drain--bias on the statistical variability and reliability of bulk MOSFETs [6][7] [8].…”

“…The geometry, body bias and temperature impact on statistical variability for the 20--nm bulk planar technology was presented in [6]. To the best of our knowledge, there are few systematic studies of the impact of the drain--bias on the statistical variability and reliability of bulk MOSFETs [6][7] [8]. In this paper the impact of drain--bias on bulk MOSFET threshold--voltage and subthreshold variability is studied in detail, taking into account the individual impact of all relevant major statistical variability sources: random discrete dopants (RDD), line edge roughness (LER) and metal gate granularity (MGG), as well as the random interface trapped charges (ITC) responsible for the bias temperature instability degradation.…”