Current gain variability in normal and I2L bipolar transistors

This paper studies the nature and degree of variation in current gain caused by perturbations in processing and material parameters in normal and I2L (inverse) transistors, formed by the double-diffusion process. The influence of predeposition and drive-in cycle, surface recombination velocity, emitter contact area and epitaxial-layer concentration has been estimated. It is shown that it is possible to recover a change in gain caused by perturbation in a particular parameter. Current-gain variability is found to be a characteristic of device design. It is desirable to optimise the design, both from the viewpoint of the specified gain and its expected variability.