In this letter, we present an Rx core chip and a Tx core chip for Ku‐band phased arrays, which are designed and fabricated using the commercial 0.25‐μm GaAs pHEMT foundry service. Each of the Rx core chip and the Tx core chip has a 4‐bit phase shifter driven by an on‐chip serial‐to‐parallel (SPC) converter. The on‐chip SPC provides the serial interface with an external controller. The Rx core chip shows a gain >10 dB, a noise figure less than 2 dB at a frequency range of 10.7 to 12.75 GHz and for all phase states of the 4‐bit Rx phase shifter. The Tx core chip shows a gain >10 dB, an output P1dB of about 13 dBm at a frequency range of 13.5 to 15.5 GHz and for all phase states of the 4‐bit Tx phase shifter. The Rx core chip and the Tx core chip have the same size of 1.75 × 1.75 mm2, which we believe the state of the art size among the presented GaAs core chips.

AlGaN/GaN‐based normally‐off GaN MOSFET with stress controlled 2DEG source and drain was proposed and fabricated using Al2O3 gate oxide deposited on the fully recessed gate region. The proposed normally‐off Al2O3/GaN MOSFET utilized AlGaN/GaN heterostructure source and drain with extremely high 2DEG density of 1.87×1014 cm2 with mobility of 120 cm2V‐1s‐1 and the device results were compared to those obtained from the reference device with normal AlGaN/GaN heterostructure source and drain with 2DEG density of 1.33×1013 cm2 and mobility of 1070 cm2V‐1s‐1. The maximum drain current and maximum transconductance of the proposed device were 263 mA/mm and 72 mS/mm, respectively, about 7.3‐times and 5‐times larger than those of the reference device, which are comparable to or even higher than one of the best results obtained from various GaN MOSFETs reported by others. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)