Development of thermal test chip for GaN-on-Si device hotspot characterization

The design and fabrication of thermal test chip, specifically for electronic hotspot cooling solution development and characterization are presented. The silicon thermal test chip is designed to simulate a working GaN-on-Si high power device and consists of two main components, which are heater and temperature sensor diode. Highly doped resistors are built on the thermal chip (7 × 7 × 0.2 mm³) to represent groups of HEMT gate fingers. Intense heat can be generated to create localized hotspots when current passes through these tiny resistors. These heaters vary in size, from 40 × 350 μm² to 450 × 5280 μm²; designed to dissipate an averaged chip level heat load from 100 to 300 W/cm². The localized heat flux on the heater itself can be as high as 10 kW/cm². On the other hand, temperature diode sensors are placed at 5-10 μm away from the heaters to measure its peak temperature. The temperature diode sensor operates as a p-n junction with its forward voltage drop having a negative temperature dependency. The resistors (150 × 350 μm²) are demonstrated to function well at very high hotspot heat flux at 11.9 kW/cm².