Study On InGaP/GaAs Microwave HBT And VCO

With good high frequency and power performance, as well as comparatively mature material preparation and process technologies. InGaP/GaAs HBT has become a promising device for wireless communication, fiber optic communication and other electronic systems. Summarizing the primary progress and research results on HBT and combined with the present experiment condition, this dissertation focused on design and fabrication of InGaP/GaAs HBT and VCO. The main research work done includes the followings:The principal of HBT and design essentials of each epi-layer in HBT were analyzed. Then MEDICI, a two dimensional device simulator of Synopsys, was used to simulate a series of epilayer structures of InGaP/GaAs HBT. Some key factors such as the thickness of spacer and the thickness of base layer were changed to find their effect on the device characteristics. The current gain and frequency performance were simulated and optimized. The InGaP/GaAs HBTs with three different epilayer structures were fabricated and their DC characteristics were tested. The experimental results were in good agreement with the simulation.The key design points of HBT layout were presented. A layout was designed to fabricate InGaP/GaAs HBTs with different scale and passive components including thin film resistors, overlay capacitors, spiral inductors and varactors. Their equivalent models were given and the process was discussed.HBT process was introduced in great details. The uniformity of InGaP/GaAs heterointerface after wet etching by citric acid and HC1 based etchant was studied experimentally and a simple improved method was found.InGaAs capping layer was used in InGaP/GaAs HBT to improve the Ohmic contact character, but in the mean while,it brought problems on device isolation.This work studied wet etching and proton implantation to achieve good device isolation Other process including emitter ledge, ohmic contact and air bridge technologies were also presented. A full process flow was established based on the practical conditions of our lab.and InGaP/GaAs HBT was developed. The characteristic of the fabricated HBT devices were measured and analyzed.It accumulated valuable experience for future's optimization of HBT.Finally, the HBT equivalent circuit models were introduced,and an X-band HBT VCO was designed by using ADS.