线性缓变SiGe　HBT低温基区滚越时间的研究

Base Transit Time of HBT with Linearly Graded SiGe Base at Low Temperatures

提出了线性缓交ＳＩＧｅＨＢＴ的基区滚越时间τｂ的解析模型，基于该模型研究了基区渡越时问的低温行为。研究发现，τｂ随温度的降低而迅速减小，虽然大的基区Ｇｅ组份级变有利于τｂ的减少，但对小的基区缓变的ＨＢＴ，通过降低温度，也能使τｂ有较大的减小，改善其频率特性。

A base transit time analytical model for linearly graded SiGe base HBT is presented.Based on the model, the low temperature behavior of base transit time, τb, is studied. It is found that re decreases rapidly as the temperature is lowered. While a large base Ge fraction grading can be beneficial to the reduction of τb, for HBT's with small Ge fraction grading,τb can be significantly reduced by lowering temperature.