Direct On-Chip IGBT Thermal Sensing Using Adhesive Bonded FBG Sensors

This article investigates the application of adhesive bonded fiber Bragg grating (FBG) sensors for insulated gate bipolar transistor (IGBT) direct on- chip thermal sensing. The influence of the physical properties of different adhesives on the sensor's calibrated wavelength-to-temperature characteristic is first investigated. The thermal sensing performance of the bonded FBG sensor is then tested under various current levels in laboratory experiments on a commercial IGBT module. It is found that the bonding adhesive's curing temperature, glass transition temperature, coefficient of thermal expansion, and hardness can modify the sensor's calibration characteristic. The adhesive's glass transition temperature needs careful consideration to ensure an effective match to the IGBT's thermal operating range of interest and the hardness of the solid bond required for a given application. Operation within the adhesive's linear working region is shown to be sufficient to provide accurate sensing performance while ensuring the retention of a solid physical bond between the sensor and the chip.