Transient thermal imaging of pulsed-operation superlattice micro-refrigerators

Thermoreflectance thermal imaging is a proven method for obtaining quantitative temperature maps of active semiconductor devices in the nanometer to millimeter size. The resolution of such images obtained using a charge coupled device (CCD) based thermoreflectance system in a reasonable time, has been shown to be 200 nanometer spatial (visible light diffraction limit), 0.1 K temperature sensitivity, and 10 microsecond temporal. We show an improved method for obtaining thermal transient temperature maps with 100 nanosecond resolution, and obtain results on SiGe based superlattice micro-cooler devices of different sizes. The results, previously predicted but not measured, indicate that under moderate current value, in pulsed-operation, the microrefrigerator device can momentarily cool, even though steady state measurements show heating.