A microjet array cooling system for thermal management of active radars and high-brightness LEDs

Advancement in high heat thermal management technology and its successful integration into emerging GaN-based amplifiers is imperative to meet the long-term requirement of future X-band radar systems. It is also known that the efficiency and reliability of light emitting diode (LED) strongly rely on successful thermal management due to its inherit low junction temperature in the LED chip. In this paper, a new cooling solution for thermal management of GaN based power amplifiers for X-band radars (XBR) and high-brightness LEDs, by a closed microjet array cooling system, is proposed and investigated by experiments. For the active radar part, we developed a circuit consisting of Si resistor chips to generate heat. The resistor chip has a resistance of 10 Ohm. It has a chip dimension of 2.4 mm times 2.4 mm times 0.50 mm, with a top side 4 mum Al and bottom side 1 mum Al/Ti/Ni/Ag. The testing results are shown to achieve a thermal resistance of 0.192degC/W under a flow pressure of 32psi. For LED packaging, the tests show that it can achieve good cooling effect, for a 16.4W input power, the surface temperature of 2times2 LED array is just 44.2 degC after 10 minutes' operation, much lower than 112.2degC, which is measured without any active cooling techniques at the same input power. To compare its performance with conventional thermal management means, three cooling methods for LED array such as natural convection, heat sink and heat pipe, are also experimentally studied. The comparison results demonstrate that present microjet cooling system has the best cooling performance. To fully understand present cooling system for real world applications, the cost, reliability and volume comparison and analyses among different cooling means are also briefly conducted in the final section of this paper