Superconducting PVD Thin Films for Quantum Applications; Qubits & Josephson Junctions

In the race to realize the possibility of quantum information processing far surpassing that of modern supercomputers, one of the most technologically advanced approaches taken to date relies on superconducting circuits that have quantum mechanics at their core. Their basic units, quantum bits or qubits, contain Josephson junctions (JJs) which are fabricated commonly from thin films of Nb or Al using Physical Vapor Deposition (PVD) techniques such as magnetron sputtering or electron beam evaporation.

A superconductor is a material, that when cooled, goes from a normal state where there is electrical resistance through to a superconducting state where there is essentially no resistance to the flow of direct electrical current. The promise of superconductivity has been to revolutionize applications including power transmission, magnetic sensors, quantum computing and SQUIDs (superconducting quantum interference devices).

There are two temperature regimes currently for superconductors, with metallic superconductors which go through a resistive/non-resistive transition below 30K and 'high temperature' compound superconductors where the transition temperature can be as high as 100K.

Kurt J. Lesker has been manufacturing PVD tools for superconductors since the 1980's, having supplied hundreds of tools to the world's leading quantum research institutions. Because of this, our team of dedicated applications, design and vacuum experts have developed unrivaled know-how about the creation and application of this exciting class of thin films that include Niobium tri-layer JJs, Aluminum-based JJs, transition edge sensors, NbTiN kinetic inductance detectors and other exciting quantum technologies.

For superconductor qubit technology the focus is primarily on the PVD (sputtering and evaporation) of tunnel junctions/Josephson Junctions. Atomic Layer Deposition (ALD) is also a promising technique for producing JJs with lower defect densities for qubit applications along with Pulsed Laser Deposition (PLD).

The requirements of the quantum research community are varied. We know this and fully understand the need for high purity vacuum tools, control of film stress, temperature control of deposited films, controlled oxidation capability and ever shrinking feature sizes.

In the case of the fabrication of Josephson Junctions, used in superconducting circuits for quantum computing, this requires that the thin film deposition tool be capable of producing high purity, highly controlled thin films and tunnel barriers, yet also be flexible enough to allow for 'materials engineering and personalization' of the films based on the particular and often unique application.

Josephson Junctions are highly sensitive to contaminants and the superconducting layers are contained within one deposition module, with a separate load lock and substrate preparation module used for the precision fabrication (using static or dynamic oxidation) of ultra-thin tunnel barriers needed for high performing qubits.

We understand that tool personalization that addresses a researcher's unique requirements is critically important and we have therefore developed and support an extensive capabilities portfolio including:

• VHV and UHV base pressure process chamber options for very low film impurities
• Multiple UHV magnetron sputter sources with both high and low deposition rate capability
• Single and multiple substrate load-locks with water cooled or cryogenic temperature - controlled oxidation plus precise gas handling solutions for static and dynamic oxidation
• Pulsed DC and DC power supplies for magnetron sputtering (e.g. of Nb, Al, Ti, etc)
• HiPIMS power supplies for deposition of very smooth (low surface roughness) films
• Ion sources for substrate cleaning prior to deposition
• VHV and UHV Electron Beam Sources for evaporation (e.g. of Al)
• Patented MagKeeper sputter sources with low sputtering pressure, high deposition rate and low contamination operation
• Upstream and downstream multi-channel pressure control allowing repeatable, stable sputtering conditions
• Heating and cooling substrate platens
• In-situ film measurement to accurately monitor real-time deposition parameters
• Fully integrated film recipe and system control using our Lesker eKLipse™ process control platform for precise, repeatable deposition conditions

We want to hear from you. Our thin film experts and service support team are eager to help enable your important quantum research.