Micron and submicron Nb/Al-AlO/sub x//Nb tunnel junctions with high critical current densities

Abstract

To increase superconducting IC speed and density, it is necessary to reduce junction size and increase critical current density. We describe the fabrication and properties of high critical current density micron and submicron Nb/AI-AIOJNb tunnel junctions. Using a 1O:l reduction wafer stepper with I-line photoresist, we obtained a minimum linewidth of 0.6 pm and junctions as small as 0.3 pm'. The critical current densities can be as high as 20 kA/cm* still with low subgap currents. The measured critical current spreads are small. This is due to the use of low-temperature, low-stress ECR (Electron Cyclotron Resonance)-based PECVD (Plasma Enhanced Chemical Vapor Deposition) SiOz insulation layers and light anodization around junction areas. The junctions have potential applications in very high-speed superconducting digital circuits and submillimeter microwave devices.

Development of superconductor electronics technology for high-end computing

“…Junctions are fabricated using NGST wellestablished Nb/Al-AlO x /Nb trilayer process [4]. Light anodization is used to form a protective oxide layer on the junction sidewalls and around the perimeter of the tunnel barrier to minimize potential damage to the tunnel barrier from subsequent processing steps and to relax alignment tolerance [3,5].…”

Fabrication of high-quality submicron Nb/Al-AlO x /Nb tunnel junctions

“…On the other hand, junction fabrication processes based on the trilayer technique, such as selective Nb anodization process (SNAP) and selective Nb etching process (SNEP), have been successfully used to produce the micronsized junctions. [8−13] To fabricate junctions with further reduced size, modified SNAP or SNEP, [14,15] or the shadow evaporation technique, [16] combined with electron-beam lithography (EBL) have been considered by some groups. Chen et al, for instance, have successfully used self-aligned process to fabricate highquality Nb junctions with sizes as small as 0.15 µm.…”

Fabrication of High-Quality Niobium Superconducting Tunnel Junctions

“…[4] Moreover, its excellent stability against both longterm storage and thermal cycles is particularly useful for cryogenic experiments, and the controllability of its critical current density is convenient for designing superconducting devices and circuits. [5] Nb STJs are widely used in studies of terahertz (THz) detection and macroscopic quantum phenomena. [6−8] For astronomical observations, they can be applied as mixers to detect high-frequency weak signals because of their irreplaceable high performance.…”

“…With their advantages of a high intrinsic switching speed and low power dissipation, Nb STJs are considered to be one of the best choices for the next generation of ultra-high performance computers and communications applications. [5] Therefore, it is essential to establish more reliable techniques for producing high-quality Nb/(Al-)AlO 𝑥 -Al/Nb STJs to realize the various kinds of applications of Nb STJs in the near future.…”