Thermoreflectance microscopy analysis on self-heating effect of short-channel amorphous In-Ga-Zn-O thin film transistors

Self-heating effect is recently considered to play an essential role in the degradation of amorphous oxide thin film transistors (TFTs). Previous thermal analysis on amorphous oxide TFTs based on conventional infrared thermography, however, had limitations in studying short-channel TFTs due to its low spatial-resolution. Here, we investigated self-heating effect of short-channel amorphous In-Ga-Zn-O TFTs by using high-resolution thermoreflectance microscopy. For the TFT with a channel length of 15μm and a distance of 10.8μm between source and drain electrodes on an etch stopper, the device temperature due to self-heating reached 70-80°C, and local heating arose close to the center of the channel compared to the drain side in the literature. The channel length dependence of thermal distribution revealed that the asymmetry of local heating weakened with the decreasing channel length due to a heat dissipation by the source and drain electrodes. Transient thermal analysis under a bias stress unveiled that the maximum temperature as a function of stress time strongly depends on bias stress conditions. The temporal behavior of temperature is possibly attributed to the interaction between self-heating and local degradation.