Electric fields have been applied to the surface over a planar silicon junction by means of a metallic control-ring electrode on the oxide surface. Capacitance measurements have indicated that a large, positive, immobile charge is present at or near the interface between the silicon dioxide and the silicon. An improvement in breakdown voltage occurs when the control ring is biased negatively, producing a field that opposes the field of the immobile charge. Positive control-ring voltages are shown to produce very large junction leakage currents. The leakage current is shown to be sensitive to a high-temperature reverse bias treatment and a model for this effect is suggested. Transistors with base contracts that extend over the oxide-protected collector junction are shown to have higher breakdown voltages than do those that lack the base electrode extension. This effect is consistent with the improvement in breakdown voltage found in control-ring diode measurements.
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