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Thermal issues are among the major concerns for 3D stacked ICs, and Through silicon vias (TSVs) are used to effectively reduce the temperature of 3D ICs. Normally, TSV is considered as a good thermal conductor in its vertical direction, and its vertical thermal resistance has been studied extensively. However, lateral heat transfer of TSVs, which is also important, was largely ignored in the past. In this paper, we propose an accurate physics-based model for lateral resistance of TSVs in terms of physical and material parameters, and discuss the conditions valid for model accuracy. In addition to modeling the lateral thermal resistance of a single TSV, the proposed thermal model is also applicable to TSV arrays or TSV farms. We show that the TSV insulation linear and space between TSVs could impose a significant impact on TSV thermal behavior. The new TSV thermal model can be easily integrated into a finite difference based thermal analysis framework to improve analysis efficiency. The accuracy of the model is validated against a commercial finite element tool -COMSOL. Experimental results show that the proposed TSV lateral thermal resistance model is very accurate for both a single TSV and TSV arrays.

This paper studies the thermal impact and characterization of Through Silicon Vias (TSVs) in stacked three dimensional (3D) integrated circuits (ICs) through finiteelement based numerical analysis. Realistic 3D stacked ICs are built using a commercial finite-element based modeling and analysis tool, COMSOL. Thermal profiles along with thermal impact of TSVs are studied for two layer and three layer stacked IC structures under practical power inputs. Experimental results show that there is a significant temperature gradient across the stacked dies for both two layer and three layer structures. The cross-layer temperature is seen to grow rapidly from two layer structures to three layer structures with the same power and TSV densities. As a result, stacking of active layers will not be scalable as the maximum temperature can quickly reach the 105 degree Centigrade limit for CMOS technology. Elevated temperatures can make thermal-sensitive reliability issues a major challenge for 3D stacked ICs. Advanced cooling, low power design, better thermal management and new architecture techniques are hence required to keep the temperature in a safe range for stacking more layers onto the chip.

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