Unipolar Transistors: Some Aspects Related to Their Inclusion in Electronics Curricula

Some considerations related to including material on unipolar transistors in electronics curricula are presented. Techniques for estimating the ultimate capabilities of the unipolar transistor and a simple method for deriving circuit models are described. Important aspects of the processing are treated, and the speed and gain capabilities of unipolar and bipolar transistors are compared in terms of basic structural and material parameters. In the estimation of the ultimate capabilities of the unipolar transistor, the maximum charge that can be induced in the channel sets the upper limits for the static performance and the limiting carrier velocity sets the upper limits for the dynamicperformance. The details of pinch-off operation receive attention, particularly those that could yield confusion in a classroom presentation. Where possible, for clarity as well as for conciseness, the analysis uses a basic unipolar structure of which the junction-gate FET and the MOS transistor are special cases. Throughout, consideration is given to the application of unipolar transistors in integrated circuits.