Abstract
Bipolar microwave transistors with Ti/Pt/Au contact metallization show a reversible degradation in current gain (hFE) due to high temperature storage (HTS) stress at 240 °C. This is an elusive effect that occurs only in certain very small cavity, strip-line packages and only on devices with very shallow emitter-base junctions (∼1200 Å). A model for current gain in shallow-junction bipolar transistors is described. The model shows that hFE of such devices is very dependent on the properties of the metal–silicon interface at the emitter. The cause of the reversible hFE degradation was found to be hydrogen absorption and desorption in the Ti contact metallization. This causes shifts in the Schottky barrier of the Ti/Si contact with consequent changes in the surface recombination velocity at the emitter. A new contact metallization of W:10 wt. % Ti/Au was developed which is hFE drift free.
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Schedule a callMore From: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
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