Integrated AlGaAs/GaAs HBT high speed operational amplifier

We report the fabrication and testing of a wideband and high slew-rate voltage-mode operational amplifier using AlGaAs/GaAs HBTs. The fabrication process showed that a higher carbon doping concentration is more effective to reducing base resistance and gives a good steadiness of process. The specific contact resistivity of base measured by TLM was 6.4/spl times/10/sup -7/ /spl Omega/.cm/sup 2/ at the base doping concentration 4/spl times/10/sup 19/ cm/sup 3/ by using a AuZu/Au alloy. The HBT operational amplifier has provided 500 v//spl mu/s high slew-rate, only 8 ns settling time and about 2 GHz unity-gain frequency. The circuit structure gave CMRR values in the order of 70 dB.