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 impla nted MESFETs and epitaxially grown PHEMTs fabricated with the same geo metry in order to identify the suitability of these technologies for t he manufacture of hand-held personal communications products. We exami ne the microwave performance of the devices under low power operating conditions and we analyse the critical factors contributing to the noi se performance. In the high current regime we have found that the MESF ETs and PHEMTs have equivalent noise figures and gains at the bias poi nt, 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 adv antages over the MESFET, including higher associated gain, lower R(n), and lower \Gamma(opt)\. We believe these advantages result from the s harpness of the doping profile in the epitaxial material and the rapid decrease in carrier concentration at the buried heterojunction, rathe r than the two-dimensional electron gas effect. Under 1 mW of d.c. bia s (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.