Study on induced work-function variation of titanium metal gate on various electrical parameters for delta-doped layer germanium source vertical tunnel FET

Abstract

Workfunction variation (WFV) in a high-k/titanium metal gate stack vertical tunnel field-effect transistor (FET) with a delta-doped layer in the germanium source is explored using technology computer-aided design simulations. The field-induced quantum confinement effect is also evaluated for the vertical tunnel FET. The impact of the gate area on various electrical parameters such as the ON-current (σION), OFF current (σIOFF), current ratio [σ(ION/IOFF)], subthreshold swing (σSS), threshold voltage (σVT), and analog performance parameters such as the total gate capacitance (σCgg), transconductance (σgm), and cutoff frequency (σfT) due to WFV of the titanium gate metal is evaluated. The results show that the variability in ION and IOFF increases when decreasing the overall transistor gate area for different metal grain sizes. In addition, the variations in the subthreshold swing and threshold voltage also decrease for a larger gate area. The distributions of the electrical parameters show that, when the grain size is comparable to the gate dimension, the distribution is not Gaussian bounded. In addition, the plot of the ratio of the average grain size to the gate area reveals that a slope of more than ~ 120 mV is attained.