Die-Level Transient Thermal Imaging Based on Fourier Series Reconstruction for Power Industrial Electronics

A novel solution for off-chip electrothermal studies in power devices at die level and short timescales is reported. The proposed method involves acquiring a sequence of thermal images on the top of the die with an infrared (IR) camera, while the device is biased under a periodic nonharmonic modulated current. Fourier coefficients are then extracted using lock-in strategies, and the time evolution of the device thermal map is reconstructed using Fourier series. To evaluate and showcase its potential, the conventional approach of boxcar averaging is implemented and used as a reference. As a case study, a reverse-conducting insulated gate bipolar transistor (RC-IGBT) is thermally measured under both forward and reverse modes. The proposed strategy significantly improves the thermal and time resolution, overcoming the limitations of the camera’s frame rate and noise resolution. Moreover, the impact of current crowding on the power device is studied at the millisecond timescale, considering both biasing modes.