Abstract
Floating-emitter potential measurement indicates the surface condition and therefore is used for the detection of defects on the surface. So far the cause of excess floating-emitter potential has been given due to channel formation only. The present paper deals with experiments which have revealed that external conducting paths provided by the adsorbed or condensed layer of water on the encapsulation of the transistor is also equally or even more responsible for performance degradation. A mathematical equation has been formulated which correlates floating potential under humid conditions to the initial floating potential, applied collector reverse bias and leakage path resistances. Variation of floating-emitter potential with collector reverse bias and temperature have been shown graphically. The effect of 100 per cent relative humidity at 40°C on this potential has been studied.
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