GAAS BIPOLAR-TRANSISTORS FOR MICROWAVE AND DIGITAL CIRCUITS

The GaAs/GaAlAs heterojunction bipolar transistor is a promising device for use in fibre-optic communications and advanced radar systems that need high-speed digital circuits combined with microwave analogue functions. The interest in GaAs bipolar processes is that they combine the microwave advantages of GaAs with the circuit performance of bipolar transistors. The availability of a high performance, high yield GaAs/GaAlAs heterojunction bipolar transistor (HBT) process opens up a wide field of potential applications, ranging from power amplifiers through to gate arrays. Particular examples within this paper are high-speed laser driving and microwave logic circuits for frequency synthesizers. The ability to mix logic and microwave functions within one circuit is an advantage of our HBT process. Further strides in performance will come by applying self-alignment to the HBT. This self-aligned process could be used in systems operating at millimetre-wave frequencies.