Verification of Differences in Thermal Resistance of Cascode Device Packages due to Heating Power Ratio of Heat Sources

In thermal transient measurement of cascode devices, depending on the thermal transient measurement method can result in significant difference in the thermal resistance values from junction to the package. The model calibration technique was applied to investigate variation in thermal resistance values. The study revealed that the thermal resistance varied considerably because of the differences in heating amount of the JFET and MOSFET in each thermal transient measurement method. In MOS Saturation (Channel Resistor) mode, JFET behaves mainly as a heat source. However, in Body Diode mode, both JFET and MOSFET behave as the heat sources. The thermal structural difference in two heat sources resulting difference in the thermal resistance from each heat source leading consequently in the measured <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta_{\text{jc}}$</tex> values.