In this paper

the major factor which affects the noise of a device is theoretically analysed from the equivalent circuit in which the trap effects at the interface between the GaAs expitaxial layer and the substrate are considered. The noise figure in the range of device design versus the elements of the equivalent circuit

the geometrical structure of the device

the material parameters and the operation frequency are described. The new planar devices using oxygen implantation are developed. Submicron gate lengths have been fabricated

by using conventional compensated contact photolithography. The microwave noise of the resulted device is much lower than that of the general mesa device. The noise figure of 3.5dB at 12GHz with associated gain of 5dB have been obtained. S-parameters of 2 to 12GHz are also presented. Mean time to failure of the device have been extrapolated to give 2×107 hours. The application experiments

such as that of oscillator

the mixer and the microwave low-noise amplifier at 2 to 12GHz

have been done

and the primary successful results have been achieved.