1/f noise due to temperature fluctuations in heat conduction in bipolar transistors

Noise is an important consideration in the reliability of microelectronic circuits and often sets a lower bound on their sensitivity and limits operation. High device temperature which result from high power operation is shown to result in an additional noise source or mechanism which can become important, become a limiting factor on circuit operation, and limit reliability. Power dissipation at high currents and voltages in bipolar transistors results in significant heat generation and heat conduction towards the heat sink. As might be expected the device temperature is only an average value and there are, as a consequence of the diffusion equation for heat flow itself, temperature fluctuations about this average value. It will be shown that these temperature fluctuations can result in l//ʹnoise at moderately low frequencies where these frequencies are determined by the physical dimensions over which the heat flows and the diffusion transit time. This physical phenomena is another mechanism which can be explained by the equivalent circuit representations to obtain frequency dependent solutions to the diffusion equation. The results presented here are then related to the shot noise or white noise due to the collector current allowing a determination of the 1/f noise corner frequency. © 1999 Elsevier Science Ltd. All rights reserved.