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

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 VFBfor GaAs dioxide films. Electrical characteristics are strongly dependent on the oxide film. Although the transconductance gmdeteriorates compared to MESFET´s due to the potential drop through the oxide layer, the deterioration in gmis found to be small for oxide films with large dielectric constant εOX. Furthermore, it is clarified that cutoff frequency fTfor IGFET´s is greater than for MESFET´s because the input capacitance Cgsin 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 gm, 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.