High power microwave field effect transistor development

Work is concentrating on gallium arsenide devices rather than silicon to take advantage of the higher mobility. Two fabrication techniques are being used to construct arrays of unit cells on GaAs wafers. The first technique requires realignment of multiple photomasks and has given the best performance but is more costly. The second technique uses only one photomask and the gate is self-aligned between the source and drain metalization. Both unit cells are designed for approximately one watt. The realigned cell has an active length of 1,500 microns, and measures about 8 mils by 12 mils. This cell was tested at 3.5 GHz with .6 watts output, 18 db of gain, and 15% efficiency. The efficiency would be much improved in a better test fixture. The self-aligned gate cell has an active length of 2,500 microns and measures 12.5 mils by 17 mils. This cell was tested at 4 GHz with one watt of power output, 6 db of gain and 39% drain efficiency or 34.7% overall efficiency.