Experimental method to thermally deembed pads from R/sub TH/ measurements

Both compound semiconductor and silicon-based bipolar junction transistors or heterojunction bipolar transistors (HBTs) require the efficient removal of heat in order to achieve a maximum level of performance and reliability. In order to satisfy both of these criteria, the electrothermal behavior of each device must be captured in a compact model. The model parameter that determines the junction temperature is R _TH, the thermal resistance. Experimental methods to determine R_TH often require a relatively small device with a large R _TH to be attached to a set of relatively large metal pads with a low R_TH. The pads act as a thermal shunt to the substrate and artificially lower the measured R_TH. In order to obtain a suitable R_TH value for a device located in an IC, the pads must be deembedded from the measured data, much like pad deembedding for an S-parameter measurement. Test structures with various width metal traces between the emitter pad and device´s emitter have been fabricated in a 200-GHz InP double HBT process. A method of using the measured R_TH of these structures and a simple resistive network model to deembed the pads is presented. It is shown that deembedded values can be as much as 30% higher than the measured R_TH