Modeling, analysis and simulation of CNT based TSVs for RF applications

This paper presents the development of integrated model of CNT-based TSVs for RF applications by taking into consideration contact pad resistance, substrate effects and kinetic inductance contribution of different parasitics, in addition to quantum mechanical transport effects in these 1D mesoscopic systems. Previously, we developed models for CNT-based TSV for low frequencies that SW-CNT bundles by considering ideal contact pads because CNTs offer tremendous performance based benefits such as excellent current carrying capability (> 10¹⁰ A/cm², three orders of magnitude higher than Cu), negligible electro-migration and good thermal stability. However, in order to realize a 3D IC with CNT based TSVs it is essential to form an interconnection network between the TSVs and 2D interconnects on the die. We have used both Molybdenum (Mo) and gold (Au) contact pads to connect CNT-TSVs with copper trace lines on the die. Modeling was performed on two dies interconnected with CNT-TSVs of height 20 μm, diameter of 5 μm and a pitch of 80 μm. BCB (benzocyclobutane) is used as the insulation layer which provides excellent isolation at high frequencies and also fills the gaps in CNT bundles making the structure thermo-mechanically robust. SW-CNTs of diameter 1nm were used in bundles of 15000 CNTs/bundle. S-parameter simulation of CNT-based TSVs with Mo and Au contact pads was performed and the return loss and transmission was measured at frequencies up to 13 GHz.