Superconducting Vacuum-Gap Crossovers for High Performance Microwave Applications

TL;DR

This paper presents a novel fabrication method for superconducting vacuum-gap crossovers that significantly reduce losses in high-frequency microwave applications, enabling improved performance in millimeter wave devices.

Contribution

It introduces a new fabrication process for superconducting vacuum-gap crossovers compatible with micro-machining and detector integration, enhancing microwave device performance.

Findings

Vacuum-gap crossovers reduce ohmic and parasitic losses.

The fabrication process is compatible with wafer-level micro-machining.

The method enables integration with waveguide-coupled detectors.

Abstract

The design and fabrication of low-loss wide-bandwidth superconducting vacuum-gap crossovers for high performance millimeter wave applications are described. In order to reduce ohmic and parasitic losses at millimeter wavelengths a vacuum gap is preferred relative to dielectric spacer. Here, vacuum-gap crossovers were realized by using a sacrificial polymer layer followed by niobium sputter deposition optimized for coating coverage over an underlying niobium signal layer. Both coplanar waveguide and microstrip crossover topologies have been explored in detail. The resulting fabrication process is compatible with a bulk micro-machining process for realizing waveguide coupled detectors, which includes sacrificial wax bonding, and wafer backside deep reactive ion etching for creation of leg isolated silicon membrane structures. Release of the vacuum gap structures along with the wax bonded wafer after DRIE is implemented in the same process step used to complete the detector fabrication