Effect of emitter-base reverse bias stress on high frequency parameters of bipolar transistors

Bipolar transistors fabricated using the stripe process with deep submicron emitters were used to study the effect. Variation in the h parameters was studied as a function of frequency after emitter-base (E-B) stress in the frequency range 100 MHz to 10 GHz. Variation of parameter h/sub 21/ (magnitude and phase), initially and after the final stress, is shown. The transistor parameters showing maximum sensitivity to E-B stress are the input impedance parameter h/sub 11/ and h/sub 21/. Analysis of h/sub 11/ data reveals that base resistance R/sub b/ increases after E-B stress. The effect of E-B stress upon h/sub 21/ leads to degradation of the peak cutoff frequency of the transistor. The peak f/sub t/ degradation was found to be more severe for the transistors with narrow emitters. A qualitative model to explain the results is proposed.<>