Stable GaAs oxide films were grown successfully using LPCEO(Liquid Phase Chemical Enhanced Oxidation) which had been proposed in Taiwan for the first time. The developed LPCEO technology shows a high oxidation rate($\approx680Å/hr$) at optimum pH and temperature. Side oxidation, selective oxidation, and metal evaporation were investigated. GaAs oxide films were characterized based on results of EDS and AFM. Especially, leakage current and breakdown field of GaAs oxide films were $2.4×10^{-6} A/㎠$ and 3.8 MV/cm,respectively.
A new GaAs MOS varactor is proposed for the first time utilizing LPCEO. In GaAs HBT MMIC process, varactors have been fabricated using base-collector junctions. When the performance is optimized for the HBT, that of PN junction varactor is degraded. However, for the case of the proposed GaAs MOS varactor, the performance of the HBT and varactor can be optimized simultaneously. From a theoretical analysis, it is estimated that the GaAs MOS varactor shows higher capacitance ratio than PN junction varactor. The fabricated PN junction varactor shows a capacitance ratio of 1.5. On the other hand, the fabricated GaAs MOS varactor shows a 35% improved capacitance ratio of 2. Both GaAs MOS and PN junction varactor have the same series resistance of 2.4 Ohm.
The capacitance ratio of GaAs MOS varactor is expected to be more increased by reducing the thickness of GaAs oxide.
