Metallic air-bridges on non-planar transport structures

Abstract

Peculiarities of metallic air bridge fabrication on non-planar surfaces along a step or across a trench were investigated. These particular reliefs feature prominently in many geometries used to study electron transport in nanostructures. The bridges were fabricated by a one-step electron beam exposure followed by metal evaporation and subsequent lift-off using a three-layer positive electron resist system. The method is based on varying the exposure dose for the pillars and the span of the air-bridge. The peculiarities for a substrate with a relief are directly associated to a topography induced thickness variation of the resist layers after spin-coating. In case of a step, the dose redistribution and the correct location are sufficient to form a stable bridge. To fabricate a stable air-bridge across a trench, it is very desirable that the bottom layer of the resist system provides good planarization of the substrate.