Theoretical characterization and high-speed performance evaluation of GaAs IGFET's

Abstract

Fundamental characterization of GaAs IGFET's is carried out utilizing two-dimensional numerical analysis, and high-speed operation performances are evaluated. Two-dimensional analysis shows that the operational mechanism of GaAs IGFET's is very similar to that of MESFET's, i.e., channel depletion-type operation due to control of the gate depletion layer. But normally-off-type current-voltage characteristics can be easily realized because of positive V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FB</inf> for GaAs dioxide films. Electrical characteristics are strongly dependent on the oxide film. Although the transconductance g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> deteriorates compared to MESFET's due to the potential drop through the oxide layer, the deterioration in g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> is found to be small for oxide films with large dielectric constant ε <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OX</inf> . Furthermore, it is clarified that cutoff frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> for IGFET's is greater than for MESFET's because the input capacitance C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</inf> in depletion-type device operation is found to be much smaller than for MESFET's. In additional, a high-voltage swing is applicable in device operation because of the IG structure, and higher g <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> , is achieved by supplying high gate biases. These features give GaAs IGFET's wide application fields as high-performance devices and make them superior to MESFET's, especially in digital circuits.