Performance Analysis of 60-nm Gate-Length III-V InGaAs HEMTs: Simulations Versus Experiments
Date of this Version7-2009
This document has been peer-reviewed.
An analysis of recent experimental data for high-performance In0.7Ga0.3As high electron mobility transistors (HEMTs) for logic applications is presented. By using a fully quantum mechanical ballistic model, we simulate In0.7Ga0.3As HEMTs with gate lengths of L-G = 60, 85, and 135 nm and compare the result to the measured I-V characteristics, including drain-induced barrier lowering, subthreshold swing, and threshold voltage variation with gate insulator (wide-bandgap barrier layer) thickness, as well as on-current performance. To first order, devices with three different oxide thicknesses and channel lengths can all be described by a ballistic model for the channel with appropriate values of parasitic series resistance. For high gate and drain voltages (V-GS - V-T = 0.5 V and V-DS = 0.5 V), however, the ballistic simulations consistently overestimate the measured on-current (a sign of higher transconductance), and they do not show the experimentally observed decrease in on-current with increasing gate length. With no parasitic series resistance at all, the simulated on-current of the L-G = 60 nm device is about twice the measured current. According to the simulation, the estimated ballistic carrier injection velocity for this device is about 2.7 x 10(7) cm/s. Because of the importance of the semiconductor capacitance, the simulated gate capacitance is about 2.5 times less than the insulator/barrier capacitance. Possible causes of the transconductance degradation observed experimentally under high gate voltages in these devices are also explored. In addition to a possible gate-voltage-dependent scattering mechanism, the limited ability of the source to supply carriers to the channel and the effect of nonparabolicity are likely to play a role. The drop in the on-current at higher gate biases with increasing gate length, is an indication that the devices operate below the ballistic limit.
Engineering | Nanoscience and Nanotechnology