Indirect techniques for channel temperature estimation of HEMT microwave transistors: Comparison and limits

This paper presents a critical comparison of three different methods for the estimation of the thermal resistance (RTH) of GaAs pHEMTs: (i) a DC method, based on the use of drain current as a temperature sensitive parameter (TSP); (ii) a pulsed I–V method, based on the evaluation of IDS at different temperature levels, (iii) infrared thermography. DC and pulsed measurements were carried out on several multifinger GaAs pHEMTs characterized by different gate width values. Results provide information on the dependence of the thermal characteristics of the HEMTs on the main device parameters, and on the differences between the methods adopted for RTH extrapolation. Moreover, DC analysis and infrared thermography was extended to complete MMIC structures: experimental results provide information on the cross-thermal resistance existing between the different components of the analyzed circuits, as a function of the operating conditions of each stage.