Various aspects of the theory and applications of one and two-gate field-effect transistors (F.E.T.) are examined in this work.

A general theory of double-gate F.E.T.ts is developed which is applied to two idealized impurity distributions. It is shown that F.E.T.'s made by the double diffusion pro-cess can be reasonably accurately approximated by an abrupt-linear distribution, and that on the basis of this model good agreement with experimental results can be obtained.

In order to account for the anomalous behaviour of the I_d/g_m characteristics, experimentally observed for certain units, a general second order theory is developed. This theory is based on that developed by Dacey and Ross (1955) to account for field dependent mobility effects. On the basis of this theory, a reasonable account of the experimental observations is obtained.

The effects of temperature on the gate leakage current and channel are examined in considerable detail, and it is shown that the first order theory is in good accord with experimental results. However, the voltage dependence of the gate leakage current appears to involve phenomena which are not well understood and, while a semi-quantitative theory is . presented, the observed effects at higher voltages are not satisfactorily accounted for.

A brief account of switching phenomena in one and two-gate structures is presented. General charge equations are derived and applied to the double-gate, abrupt, symmetrical F.E.T. It is shown that an equivalent inter-gate capacity exists, and a proposal is presented regarding the equivalent circuit of double-gate F.E.T.

Finally, the application of F.E.T.'s to the design of a neutralized input capacity amplifier suitable for measuring biological inter-membrane potentials is described. With this unity voltage gain amplifier an equivalent input capacity of ~0.3 pF and an input resistance of >10¹¹ ohms is obtained.