Ultra-fast Thermoreflectance Imaging for Electronic, Optoelectronic, and Thermal Devices

We review the recent advances in thermal characterization of micro/nanoscale electronic, optoelectronic, thermal devices based on thermoreflectance imaging. Thermoreflectance imaging is a non-invasive optical technique that can visualize surface thermal response of devices and integrated circuits (IC). Recent advances of the technique have enabled high-resolution, ultra-fast transient thermal imaging with 800 ps temporal resolution. Using visible or UV illumination, spatial resolution of about 200-250 nm can be achieved. Many IC substrates, e.g. Si, GaAs, are transparent to near IR illumination in 1-1.5 μm wavelength range. Through-substrate thermal imaging of flip-chip bonded ICs with micron spatial resolution has been demonstrated. We provide key examples of various devices characterized by the technique such as CMOS ICs, GaN HEMT, nanowire transistors, thin-film solar cells, and micro-thermal cloaking devices. In addition to the validation of electrothermal models, material and fabrication defects can be identified. Finally we discuss the advantages/limitations, and perspective of thermoreflectance imaging technique.