Noise and gain comparison of 0.25 mu m gate MESFETS and PHEMTS for low power wireless communication circuits

We compare the low power, low noise performance of 0.25 mu m ion implanted MESFETs and epitaxially grown PHEMTs fabricated with the same geometry in order to identify the suitability of these technologies for the manufacture of hand-held personal communications products. We examine the microwave performance of the devices under low power operating conditions and we analyse the critical factors contributing to the noise performance. In the high current regime we have found that the MESFETs and PHEMTs have equivalent noise figures and gains at the bias point, which results in the lowest noise figure (V(d)s = 1.5 V and I-ds = 14 mA). Under low power bias, the PHEMT shows several performance advantages over the MESFET, including higher associated gain, lower R(n), and lower \Gamma(opt)\. We believe these advantages result from the sharpness of the doping profile in the epitaxial material and the rapid decrease in carrier concentration at the buried heterojunction, rather than the two-dimensional electron gas effect. Under 1 mW of d.c. bias (V-ds = 0.5 V, I-ds = 2 mA) at 6 GHz, the MESFET's noise figure was 0.5 dB and its associated gain was 8 dB. The noise figure of the PHEMT for the same conditions was 0.6 dB and its associated gain was 10 dB.