Measurement of the Transient Thermal Impedance of MOSFETs Over the Sensitivity of the Threshold Voltage

Transient thermal analysis (TTA) on power MOSFETs using the threshold voltage as sensitivity parameter and the saturation region for component heating is a promising alternative to measure the thermal impedance Zth. Current can be reduced, power losses are fully adjustable and sensitivity is increased compared to established setups using RDSon or the body diode. All three measurement methods differ in several points. The principles and necessary electrical measurement setups will be explained. Also the influence of the different locations and sizes of heat dissipating areas will be discussed on the basis of thermal finite element simulations. To proof the feasibility and to show the advantages of the threshold voltage measurement method 18 MOSFETs were tested. The sensitivity of the threshold voltage was analyzed on stability and value. Afterwards all MOSFETs were TTA tested with a new developed prototype and the results compared to reference measurement on two commercial equipments using the body diode to measure Zth. Transient thermal FE simulations were performed to investigate the influence of the different Layers.