Electrical Characterization of Shielded TSVs with Airgap Isolation for RF/mmWave Applications

In this paper, shielded and airgap-isolated through-silicon vias (TSVs) are fabricated and measured up to 50 GHz. The unique TSV configuration is low-loss and electrically shielded, and the fabrication process includes a trench encapsulation process, improving surface planarity. TSV is an essential technology in heterogeneous integration, allowing chip manufacturers to stack disaggregated chiplets in a cost-efficient manner. Today’s mobile and networking needs are growing and require even faster communication links, calling for systems that can support higher-frequency signals in the radio spectrum. Using standard semiconductor manufacturing processes, ring-shaped airgap trenches were etched and encapsulated, surrounding the 10 μm-diameter, 50 μm-tall signal TSV from its semi-coaxial shielding TSVs. Once encapsulated, the surface is planar and allows subsequent photolithography steps to be performed. Simulation results showed that TSV shielding reduced noise coupling from -30.6 to -62.4 dB compared to GSG TSVs. Measurement results indicated that the airgap isolation reduced total capacitance from 12.9 to 7.95 fF, a 38.4% reduction, and conductance from 1.31 to 0.634 mS, a 51.6% reduction.