This paper proposes a synthesis of different electrical methods used to estimate the temperature of power semiconductor devices. The following measurement methods are introduced: the voltage under low current levels, the threshold voltage, the voltage under high current levels, the gate-emitter voltage, the saturation current and the switching times. All these methods are then compared in terms of sensitivity, linearity, accuracy, genericity, calibration needs and possibility of characterizing the thermal impedance or the temperature during the operation of the converter. The measurement of thermo-sensitive parameters of wide band gap semi conductors is also discussed.

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The measurement of the junction temperature with thermo-sensitive electrical parameters (TSEPs) is largely used by electrical engineers or researchers but the obtained temperature value is generally not verified by any referential information of the actual chip temperature distribution. In this paper, we propose to use infrared (IR) measurements in order to evaluate the relevance of three commonly used TSEPs with IGBT chips: the saturation voltage under a low current, the gate-emitter voltage and the saturation current. The IR measurements are presented in details with an estimation of the emissivity of the black paint deposited on the power module. The temperatures obtained with IR measurements and with the different TSEPs are then compared in two cases: the use of only one chip and the use of two paralleled chips.

We report in this paper studies on a mixture of nematic liquid crystal (5CB) and BaTiO3 ferroelectric nanoparticles (NPs). Apart a drastic change in the electro-optical (EO) properties of this mixture, which is reported as a conclusion, we focused our attention onto the characteristics of those NPs. The initial powder obtained by solid way is first analyzed: this material is crystallized in the ferroelectric phase as shown by x-ray diffraction and Raman spectroscopy. A high speed second milling was performed to obtain NPs: they have been characterized by high resolution transmission electron microscopy (size and structural characterizations) and by dynamic light scattering. Then these NPs were blended with a nematic liquid crystal (5CB). Raman spectroscopy measurements were used to measure and compare the scalar order parameter of both samples. The EO properties were measured in planar liquid crystal cell configuration by using classical EO setup. We amazingly found a significant decrease in the Freedericksz threshold, compared to the pure material. This is to be compared to the Glushchenko’s measurement, who observed no variation, for a similar mixture in concentration, but for smaller NPs. Switching times were measured using the same setup and we noticed a decrease in the “τon” for the 5CB+BTO mixture compared to the pure 5CB one.