Phaw noise study of AlGaN/GaN HEMT X-band oscillator

AlGaM/GaN high electron mobility transistor (HEMT) heterostructures were investigated by noise spectral density measurements. The heterostructure layers are grown without intentionally doping the barrier material and two-dimensional gas appears at the interface only due to polarization effects. Low-frequency noise spectra of the HEMT were studied in a wide range of applied voltages. They demonstrated a deviation from 1/f dependence at high applied drain-source voltages due to increasing dissipated power. The phase noise of a monolithic microwave integrated circuit oscillator based on the AlGaN/GaN HEMT amplifier was investigated. In spite of the low value of the resonator quality factor of 20, a low level of the phase noise of the oscillator was registered. The up-conversion factor was found to be as low as 15 MHz/V for frequency offset 100 kHz, demonstrating that AlGaN/GaN HEMTs offer an excellent potential for a wide range of microwave applications. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.