CMOS-Compatible MESFETs for High Power RF Integrated Circuits

Metal semiconductor field effect transistors (MESFETs) have been fabricated using a 45-nm silicon-on-insulator CMOS technology available from Global Foundries. MESFETs with gate lengths of 200 nm show good manufacturability with well-controlled run-to-run variations. The DC and RF performance of devices with different drain access lengths are compared to illustrate the design trades between high breakdown voltage and high frequency operation. Two applications of the MESFETs for RF integrated circuit design are presented. The first demonstrates integrated n-channel MOSFET–MESFET cascode amplifiers that combine the enhanced voltage operation of the MESFET with the high frequency capability of the scaled MOSFET. The resulting small-signal amplifiers demonstrate cut-off frequencies of 50 GHz when operated with supply voltages of 6 V, significantly higher than the nominal 1 V breakdown voltage of the CMOS transistors. The second application demonstrates a watt-level MESFET power amplifier integrated with a CMOS current steering digital-to-analog converter (DAC). The MESFET serves as the RF output device, while the 4-bit CMOS DAC enables average power tracking. Both examples demonstrate the design flexibility enabled by the CMOS-compatible MESFETs.