Analysis of the temperature rise in PIN diodes caused by microwave pulse dissipation

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Abstract
With the increasing use of PIN diodes in high power, microwave switching components, knowledge of the diode transient thermal response to such pulse dissipation becomes of increasing importance. Thermal models for the microwave dissipation within the diode are proposed for both the forward and reverse biased states. Based on these models, both the maximum and junction temperature step responses and pulse waveforms are determined for both bias states. For the forward bias state, the maximum temperature occurs near the center of the dissipation or I-region and for a step increase in dissipation, initially increases linearly with time then levels off to a constant difference with respect to the junctions. Under the same conditions, the junction temperature (relative to an appropriate heat sink) initially increases linearly also followed by a square root dependence to the steady-state value. The total response is therefore characterized by two fundamental thermal time constants and thermal resistances corresponding to the dissipative and conductive regions. Of major importance is the substantial calculated temperature differences which can occur between the center of the I-region and the junction where the temperature is normally experimentally monitored. For the reverse bias state, the maximum temperature occurs at the junctions because of the more localized dissipation and follows the square root dependence to the steady-state value. With knowledge of the diode thermal parameters, the relations given, and quantitative substantiation of the model proposed, the transient temperature response, together with its imposed component design limitations, are now obtainable.

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