Analysis of Passivation Techniques in InP HEMTs and Implementation of an Analytical Model of fT Based on the Small Signal Equivalent Circuit.

Abstract

This paper analyses, the influence of Si₃N₄-PECVD and Al₂O₃-ALD surface passivation on the DC and RF characteristics of InP HEMTs with different gate lengths 0.08 μm, 0.1 μm, 0.12 μm, and 0.15 μm. A significant improvement in maximum drain current IDS, MAX, transconductance gm, MAX and oscillation frequency fmax, MAX is obtained by scaling the thickness of the passivation layers An increase in gm, MAX and fmax, MAX, fT, MAX is observed by reducing parasitic capacitance w.r.t. the decrease in gate length. In addition, an analytical model of fT based on a small-signal equivalent circuit is developed, which consist of extrinsic parameters Rs, Rd, Cgs_ext and Cgd_ext and intrinsic parameters Cgsi, Cgdi, gmi and goi. The carrier transport is improved by increasing gmi, thus the transit time τt , the parasitic charging delay τext and the τpar are reduced by lowering the extrinsic capacitances. An excellent fitting between measured and simulated fT is achieved, which inturn leads a realistic way for further improvement in fT.