A robust methodology is proposed for determining and assessing measurement uncertainties in thermal imaging systems when the Fourier coefficient-based time-reconstructed method is used. This comprehensive approach addresses factors such as camera-induced noise, setup-related errors, and data postprocessing strategies. As a case study, this methodology is applied to measure a thermal test chip (TTC) using a thermo-reflectance (TR) setup. The results are validated with the stroboscopic boxcar averaging technique. This study yields valuable insights. The camera introduces a Rayleigh-distributed white noise, which is extracted in both postprocessing methods. Image registration mitigates thermo-mechanical displacements during calibration effectively. Key uncertainties are identified for each method. Registration and calibration errors remain under 5%, with camera noise contributing only 0.5 degrees C of measurement uncertainty. These uncertainties allow for accurate thermal measurements with a precision of 2 degrees C and preserving a high spatial resolution ( similar to 1 mu m).

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.

The thermal resistance of a high electron mobility transistor (HEMT) forming part of a monolithic microwave integrated circuit (MMIC) is noninvasively extracted under real working conditions (electrical and thermal) by infrared thermal imaging. The HEMT thermal resistance considers the device local maximum temperature and dissipated power. An experimental approach to this end is currently not available, as the HEMTs thermal interaction does not allow extracting its individual heat generation. Thanks to thermal field confinement offered by heat source frequency modulation, the power dissipation in each device is inferred, making feasible its individual thermal resistance extraction. As a result, reasonable values of the local thermal resistance of each individual HEMT integrated in the MMIC (i.e., 57.8 ± 3.4 °C/W and 24.8 ± 1.4 °C/W) are obtained in agreement with studies on discrete devices available in the literature.