  State-of-the-art microfabricated ion traps for quantum information research
are approaching nearly one hundred control electrodes. We report here on the
development and testing of a new architecture for microfabricated ion traps,
built around ball-grid array (BGA) connections, that is suitable for
increasingly complex trap designs. In the BGA trap, through-substrate vias
bring electrical signals from the back side of the trap die to the surface trap
structure on the top side. Gold-ball bump bonds connect the back side of the
trap die to an interposer for signal routing from the carrier. Trench
capacitors fabricated into the trap die replace area-intensive surface or edge
capacitors. Wirebonds in the BGA architecture are moved to the interposer.
These last two features allow the trap die to be reduced to only the area
required to produce trapping fields. The smaller trap dimensions allow tight
focusing of an addressing laser beam for fast single-qubit rotations.
Performance of the BGA trap as characterized with $^{40}$Ca$^+$ ions is
comparable to previous surface-electrode traps in terms of ion heating rate,
mode frequency stability, and storage lifetime. We demonstrate two-qubit
entanglement operations with $^{171}$Yb$^+$ ions in a second BGA trap.
