Demonstration of CVD Diamond Heat Spreaders for Performance Improvement of a 400 W AlGaN/GaN S-Band Power Amplifier MMIC

The performance of high power GaN HPAs in terms of output power, efficiency and maximum reliable pulse width/duty cycle is thermally limited. The power dissipation of such amplifiers is mainly concentrated below the output stage transistors, resulting in a very high-power dissipation density and high thermal resistance. Diamond heat spreaders can be used to lower the dissipation density and provide a lower thermal resistance to a defined base-plate temperature. This paper shows quantitative measurement results of the effectiveness of diamond heat spreaders for a realistic S-band HPA designed for pulsed radar applications. The diamond heat spreaders help to reduce the MMIC temperature by 20-30% and provide an almost 30% reduction in thermal resistance of the package. Alternatively, the diamond heat spreaders can be applied to increase the pulse width of the used RF signal with a factor of 30-100, while maintaining the same maximum junction temperature.