Models for the JFET and the MESFET
Although from a viewpoint of manufacturing and application the differences between the junction-gate field-effect transistor (JFET) and the metal-gate field-effect transistor (MESFET) are considerable, their physical operation is almost identical. The modelling of these devices is therefore discussed in one chapter. In both cases transistor operation is achieved by depleting an already existing channel region via a gate-controlled p-n junction or a Schottky diode. The channel region can be realized as an n-type epitaxial layer in a p-type substrate (as for instance for the discrete JFET), as an implanted p-type layer in an n-well (bipolar IC-compatible JFET) or as an epitaxial layer on a semi-insulating substrate (GaAs MESFET). In the latter case a channel implant is often added for achieving better process control. Figs. 9.1 a and 9.1 b give a cross-section of the JFET and the MESFET, respectively.
KeywordsDrain Current Saturation Region Gate Bias Velocity Saturation Velocity Overshoot
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