Displacement Damage in Bipolar Junction Transistors: Beyond Messenger-Spratt

Bipolar junction transistors (BJTs) with relatively large feature sizes, typical of older technologies and high-voltage devices, are susceptible to recombination in the neutral base region when they are damaged by atomic displacement. This results in gain degradation, which, as originally described by Messenger and Spratt, can be modeled as an increase in the ratio of BJT base to collector current (1/β) when the device is exposed to high energy particles (e.g., neutrons). While this also occurs in smaller devices and in those intended for operation at lower voltages, recombination in the emitter-base depletion region typically dominates the radiation-induced gain degradation in these devices. This is a consequence of the recombination rate being highest in regions where the electron and hole concentrations are approximately equal. Recombination in the neutral base and emitter-base depletion region exhibit different dependences on applied voltage, base doping and neutral base width. These dependences result in inaccuracies in the standard Messenger-Spratt equation, even for devices with base widths as large as ~ 10 μm. This paper presents a physics-based modification of the equation which provides a much better fit to experimental data, particularly at low voltages.