Thin film heat flux sensors fabricated on copper substrates for thermal measurements in microfluidic environments

Micro-scale heat flux sensors are fabricated on bulk copper surfaces using a combination of lithography-based microfabrication and micro end milling. The heat flux sensors are designed to enable heat transfer measurements on an individual pin in a copper micro pin fin heat sink. Direct fabrication of the sensors on copper substrates minimizes the thermal resistance between the sensor and pin. To fabricate the devices, copper wafers were polished to a flatness and roughness suitable for microfabrication and standard processes, including photolithography, polyimide deposition via spinning, and metal deposition through physical vapor deposition were tailored for use on the unique copper substrates. Micro end milling was then used to create 3D pin features and segment the devices from the copper substrate. Temperature calibrations of the sensors were performed using a tube furnace and the heat flux sensing performance was assessed through laser-based tests. This paper describes the design, fabrication and calibration of these integrated heat flux sensors.