High Aspect Ratio, Superconducting Vacuum Gap Capacitor NEMS with Plate Distances Down to 32 nm

Abstract

Fabrication of aluminium vacuum gap capacitor based nano electromechanical systems (NEMS) is investigated, where the bottom electrode is fixed, and the top electrode is free to move. To avoid collapse of the top electrode, simultaneous oxidation of both sides of the top electrodes is ensured by the deposition of silicon protection layer without breaking vacuum, intended to be removed with the release process of the membrane with XeF₂ gas. Furthermore, the vertical stress gradient is controlled by optimizing the sputter deposition parameters for the aluminium top electrode to 50 W and 3 µbar for 100 nm. These techniques resulted in wafer-level high-yield fabrication of capacitors with radii between $7\mu m$ and $30\mu m$. A cryostat at 400 mK and an integrated piezoactuator are used to prove electromechanical coupling.