Understanding the Self-Heating Effects Measured With the AC Output Conductance Method in Advanced FinFET Nodes

Accurate determination of thermal resistances having a clear physical interpretation is crucial for analyzing self-heating effects (SHEs) in bulk FinFETs and ensuring reliable circuit operation. In this article, we use extensive electrothermal simulations, calibrated against experiments, to validate a popular method to monitor SHEs based on the measured AC output conductance. The results confirm that nanoscale silicon fins exhibit degraded thermal conductivity compared with the bulk silicon case. Then, we explore the relationship between the temperature extracted by the output conductance method and the maximum temperature inside the fin (which is a useful parameter to study device reliability) as a function of device bias and dimensions, providing a few projections toward scaled technology nodes. Our results show that the following hold: 1) the overtemperature extracted with the AC output conductance method represents an average overtemperature across the device active area and 2) the AC conductance method largely underestimates the peak temperature of long-channel devices; less so for short-channel ones. In this latter case, however, the difference between the above temperatures changes appreciably as a function of gate voltage.