On the futility of thermal through-silicon-vias

Thermal integrity is one of the most important challenges faced by three-dimensional integrated circuits (3D ICs). Towards this, thermal through-silicon-vias (TTSVs) have been widely used to assist heat dissipation. The metal inside TTSVs can conduct heat more effectively than the silicon substrate, and the metal bumps underneath TTSVs can help heat penetrate through the inter-layer thermal interface material (TIM). However, the surrounding silicon dioxide blocks the heat flowing into them. This makes the effectiveness of TTSVs questionable. In this paper, we argue that some existing TTSV models fail to capture those effects. Experimental results based on finite element simulations verify and confirm that the temperature reduction is indeed brought by the metal bumps underneath the TTSVs rather than the TTSVs themselves. We demonstrate that it is sufficient to add bumps between tiers to reduce temperature without wasting silicon area.