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

In this article, 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-
$\mu \text{m}$
-diameter, 50-
$\mu \text{m}$
-tall signal TSV from its semicoaxial 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.