Temperature and geometry dependence of the electrothermal instability of bipolar transistors

We present an extensive investigation into the temperature and geometry dependence of the electrothermal instability of bipolar transistors. It is shown that the stable operating region increases with decreasing transistor size, which is explained by the geometry dependence of the thermal and base resistances. Next, data taken over a large range of temperatures (-40 to 150 ^oC) are analyzed. It is shown that, for the technology at hand, an additional margin of ~1V above BVCEO is present for the full temperature range. Moreover, it is shown that the temperature-dependent data can be reduced to a single `master curve´ by plotting the instability point versus the collector current at V_CB =0 V. This leads to a simple rule-of-thumb that can be used by circuit designers to estimate the limit of stable operation at all temperatures.