Optimizing performance to achieve multi-terahertz operating frequencies in pseudomorphic HEMTs



High-electron mobility transistors (HEMTs) are important for high frequency applications, and they now operate in the range of several hundred GHz for the cut-off frequency, fT and even higher for the maximum frequency of oscillation, fmax. To study the question of how much higher these frequencies can be pushed, we have used a full-band, cellular Monte Carlo transport program to study scaled pseudomorphic HEMTs and their response at high frequency. Building on a previous study on fT, we have obtained the unilateral power gain for gate lengths ranging from 10 to 50 nm, extracted the corresponding fmax's and extrapolated the results to determine an ultimate frequency limit for the 300 nm long device shown here.. We find that fmax can exceed 4 THz, ∼25% higher than the limit for fT that was previously obtained. We also examine the effect of varying the gate to channel spacing has on the operation of these devices. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)