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We derived an analytical model, focused on injected charge storage, for electron current density J n , hole current density J p s , current gain β, and forward transit time τ f for heavily doped base and emitter with non-uniform band structures. This model can apply in high-level injection regions before the onset of the Kirk effect. By comparing with those results obtained from Sukuki's low-level injection model, it is observed that a new high-level injection term, proportional to the square of the hole current density, appears in the injected hole concentration in the polycrystalline silicon emitter and this term vanishes in the limit of low-level injection. As bias increases, J n and J p s of high-level injection model are less than those of the low-level injection model. In addition, for low-level injection model, β, τ f , the base transit time τ b , the crystalline silicon emitter transit time τ se , and the polycrystalline silicon emitter transit time τ pe keep constant for all injection region. However, for high-level injection model, β and τ b decreases as bias increases, while τ se and τ pe increase with increasing bias. τ f reaches a minimum and then increases. We conclude that the high-level injection model offers significant information for device operations at various electron current levels.

This paper reports high-level injection influence on the high frequency performance in the polycrystalline silicon emitter bipolar transistors. Under high-level injection, the transconductance is not proportional to collector current. From the analysis, both the base resistance and the cutoff frequency are functions of terminal voltage, i.e. applied bias, and the maximum oscillation frequency is also a function of terminal voltage. By comparing these results obtained from the self-consistent high-level injection model considering injected charge storage (i.e. injected electron and hole concentrations comparable to doping concentrations in the base and emitter region) and base resistance with those results obtained from models which neglect the injected charge storage effect and/or the base resistance, it is found that both the injected charge storage effect and the base resistance must be considered to get accurate aforementioned device parameters.

Dr. Tak H. Ning to Deliver Keynote Address BCTM 2007 will feature keynote speaker Tak H. Ning on the "Historical Development of Devices Based on Bipolar Phenomena." The conference will offer two full days of technical papers, including a session on emerging technologies, and a short course on bipolar IC design.

We report on a theoretical investigation of the effect of interfacial oxide on both static and dynamic performance in polycrystalline silicon emitter bipolar transistors. The calculation is carried out up to 0.9 V, before the onset of the Kirk effect. From the model, it is found that the current gain increases and the forward transit time decreases as interfacial oxide thickness increases. Furthermore, both the current gain and the forward transit time decrease as recombination velocity increases. In addition, the intrinsic base resistance remains almost constant as interfacial oxide thickness increases, and increases as recombination velocity increases. Compared with the conventional low-level injection model, the improved model provides much more accurate expressions for electrical characteristics of bipolar transistors operating under high-level injection.

We report the theoretical investigation of the effect of Ge concentration on both static and high-frequency performances in polycrystalline silicon emitter Ge x Si1- x heterojunction bipolar transistors (HBTs). The calculation is carried out up to 0.95 V, before the onset of the Kirk effect [C. T. Kirk: IEEE Trans. Electron Devices ED-9 (1962) 164]. From this model, we find that the current gain, transconductance, cutoff frequency, and maximum oscillation frequency increase with increasing Ge concentration. In addition, the base transit time and the switching delay time in the emitter-coupled logic circuit slightly decrease as Ge content increases. Furthermore, it shows that the high-level injection effect becomes more pronounced in the Ge x Si1- x HBT as Ge concentration increases. Compared with the conventional low-level injection model, the improved model provides much more accurate expressions for electrical characteristics of Ge x Si1- x HBTs operating under high-level injection.