We report on 1.9-GHz performance of the Buried-Channel self-aligned WN/W-gate GaAs MESFET (BC-MESFET) for use in digital mobile telephone handsets with low power consumption. The BC-MESFET incorporates undoped i-GaAs epitaxial-grown surface layer on the ion-implanted channel. Both the power and noise performance of the BC-MESFET are superior to the conventional MESFET. The 0.6-µm gate power BC-MESFET exhibits a high power-added efficiency of 57% at 1-dB gain compression, which leads to low power dissipation of the handset. This power performance is attributed to high breakdown voltage which the undoped i-GaAs surface layer has brought about. The BC-MESFET has also shown a minimum noise figure of below 0.4 dB. Taking the IC-oriented fabrication process of the BC-MESFET into consideration, these FET performances demonstrate that the BC-MESFET is suitable for the single-chip MMIC that integrates RF front-end blocks for the 1.9-GHz small-size mobile telephone handset with long battery lifetime.

A GaAs linear power amplifier operating with a single 3-V supply has been developed for 5.8-GHz ISM band applications. Two kinds of refractory WNx/W self-aligned gate MESFETs, a P-pocket MESFET and an asymmetric MESFET with a buried p-layer (BP- MESFET ) have been compared in terms of DC characteristics, small signal characteristics and power performances at 5.8 GHz. To obtain both high gain and high efficiency in the case of single 3-V supply operation at 5.8 GHz, we used a highly efficient and linear P-pocket MESFET for the output-stage power FET and a high-gain asymmetric MESFET with a buried p-layer (BP- MESFET ) for the driver-stage FET. The bias condition for 1-mm output-stage P-pocket MESFET was set near class-AB, so as to obtain sufficient output power with high PAE. The two-stage power amplifier MMIC module which can include all matching and biasing circuits, has been designed and fabricated. The amplifier exhibits a high power gain of 17.9 dB and a high power-added efficiency of 25.7% with a sufficient output power of 18.7 dBm at the 1-dB compression point. This self-aligned gate GaAs MESFET technology is promising for near-future 5.8-GHz applications, because of such good power performance and good mass-producibility.