Comparison of Heat Sinks in Back-End of Line to reduce Self-Heating in 22FDX® MOSFETs

Abstract

This work compares the effect of different heat sink dimensions in the back-end of line (BEOL) on the self-heating (SH) parameters. To assess the self-heating (SH) parameters, the RF characterization technique is employed, which involves measuring S-parameters across a broad frequency spectrum. In addition to the standard device without a sink, two sinks of different dimensions, both connected to the gate, are considered: one smaller and one bigger in size. We experimentally demonstrate lower self-heating as the sink size increases. By using a smaller and a larger sink, a mean reduction of 4.7% and 8.9% in thermal resistance is observed, showing greater SH reduction with increasing sink size, which is also verified from comparison with previous works. The impact of the sinks on RF figures-of-merit (FoMs), namely the cutoff frequency fT and maximum oscillation frequency fmax is investigated. fT is seen to degrade stronger due to increased gate capacitance whereas fmax degradation is limited because of reduced gate resistance.