The Spacistor

A brief description is given of several Spacistor structures and the techniques of fabrication. Detailed measurements of the four-pole parameters are reported and described with the aid of physical models. The mutual conductance is shown to depend upon injector-modulator spacing, injector current and modulator bias, with little variation to 25 Mc. Improvement in both g m and shielding is shown to occur when the modulator is injecting charge. Values of g m of the order of several hundred micromhos have been observed. The input resistance depends upon the characteristics of the modulator contact in the space-charge region and upon the dc bias. Under forward-biased modulator conditions (optimum g m ) values of input resistance of the order of several hundred thousand ohms are obtained. Under zero-bias or reverse-bias conditions (somewhat reduced g m ), values of several megohms are obtained. Values of output resistance ranging to several hundred thousand ohms have been observed with possibilities of larger values being obtained with improved design. Low frequency voltage gain of the order of 10 and power gain of the order of several hundred have been exhibited. The reduction of power gain at 25 Mc is attributed mostly to the array of contact and device resistances, and device and header capacities, some of which may be reduced by appropriate design. These prevented the elimination of shunting capacities and precluded higher frequency measurements.