Contents I. Introduction
3D-integration (vertical stacking of LSI chips/wafers) has become the most promising technology to realize the high-density, wide-bandwidth systems in smaller form-factor, which drives the more-than-Moore realm. At the same time, the smaller form-factor of 3D-LSIs/ICs makes the stacked chips highly prone to hot-spot problem. These hot-spot due to high power density deteriorates the performance factor of 3D LSIs/ICs, and hence it is important to have a thermal management system in the stacked 3D-LSI/IC [1], [2]. In general, a thermal TSV (TTSV) is employed to transfer the heat produced in the different tiers of 3D-LSI to the heat sink as shown in fig. 1. So far, metal (such as Cu) is used as heat conducting material in the TTSV [3].[4], wherein the excellent thermal conductivity of Si is exploited by using the TSV arrays as heat conduction path via the Cu core to the Si substrate. Recently C-Cu composite material has been used in the Cu-TSVs owing the enhanced mechanical property, thermal compatibility [5]–[7]. For different applications, several different forms of C can be incorporated in the Cu-Tsv during the electroplating process. Although multi-layer graphene (MLG) has one order higher in-plane thermal conductivity (~4000 W/m.K) than Cu (~400 W/m. K) or C-Cu composite, its out-of-plane thermal conductivity MLG is two order smaller [8]. Therefore, the graphene-Cu composite may not well suit for the TTSV. In order to exploit the better in-plane thermal conductivity of MLG, it is important to have a continuous MLG on both top and bottom surface of the stacked chip passing all through the TSV.
