  We propose superconducting-semiconducting (super-semi) qubit and coupler
designs based on high-quality, compact through-silicon vias (TSVs). An
interposer "probe" wafer containing TSVs is used to contact a sample wafer
with, for example, a superconductor-proximitized, epitaxially-grown, germanium
quantum well. By utilizing the capacitance of the probe wafer TSVs, the
majority of the electric field in the qubits is pulled away from lossy regions
in the semiconducting wafer. Through simulations, we find that the probe wafer
can reduce the qubit's electric field participation in the sample wafer by an
order of magnitude for thin substrates and remains small even when the
epitaxial layer thickness approaches 100 $\mu$m. We also show how this scheme
is extensible to multi-qubit systems which have tunable qubit-qubit couplings
without magnetic fields. This approach shrinks the on-chip footprint of
voltage-tunable superconducting qubits and promises to accelerate the
understanding of super-semi heterostructures in a variety of systems.
