Thermal limitations of CW and pulsed silicon TRAPATT diodes

The power density distribution in the avalanche zone of a TRAPATT-diode is approximated by a rectangular pulse in order to consider it as a source function in the heat equation. Heat generation is considered to be periodic, and the dissipation is taken with a thermal time constant larger than the period. The increase in frequency needs a decrease in depletion width, improving the thermal conduction to the heat sink. The power density needed increases with frequency, thus raising the maximum temperature in the depletion region with frequency. The criteria for the best performance is that the two processes of heat generation and conduction to the heat sink are to be so adjusted as to lead to a mininum rise in temperature. The steady state temperature rise in CW operation comes out to be , while in the pulsed case this expression is related to the maximum temperature. The maximum temperature allowable in the depletion region should be lower than that required for any failure to occur. Using these criteria the thermal limitations for CW and pulsed operations of the TRAPATT diode have been analyzed.