High-frequency properties of four-terminal field-effect transistors

The high-frequency properties of the four-terminal field-effect transistor are examined. Using the device charge equations, various intrinsic capacitances are defined, and expressions are obtained for their variation with voltage. From these equations and a knowledge of the intrinsic and extrinsic structure of these devices, an equivalent circuit is proposed, which is shown to be in reasonable agreement with experimental observations. The intergate capacitance is examined in some detail, and an explanation of the very abrupt capacitance changes observed experimentally is given. Careful attention is paid to distinguishing between the device's intrinsic and extrinsic properties and correctly comparing experimental and theoretical results.