Microwave Operation of Drift Transistors in Transit-Time Mode

The transit-time transistor and its operation was first proposed by Weinreich in relation to a diffusion transistor. The similarity to the diffusion-delay diode and the existence of a negative resistance has been pointed out in accord with the original theoretical work by Shockley . In this paper the drift transistor is analyzed in respect to transit-time effects of minority carriers across the base region, which appear at frequencies above the normal cutoff frequency and are more favorable than in a diffusion transistor due to larger excess phase shifts in the base transport factor. Amplification and power-generation properties at frequencies properly related to the base transit time are theoretically predicted and lie within frequency bands above the cutoff frequency. Experimental vertification of gain and power have been obtained with some commercial and developmental high-frequency mesa-type drift transistors. The results are reported, together with the special microwave circuitry utilized in the experiments. Although realization of gain and power in the microwave region with present transistor encapsulations encounters difficulties in the form of parasitic circuit elements, e.g., lead inductances, and interelectrode capacities, a promising application of suitably designed and packaged drift transistors in the microwave-frequency region will be demonstrated. The operation of the drift transit-time transistor is similar to its vacuum-tube counterpart. Microwave performance to date is very encouraging, and certain advantages over its vacuum-tube equivalent are indicated.