Versatility

We can control current in both vertical and horizontal directions. This flexibility unlocks more complex circuit integration like stacked chip architectures. Advanced semiconductor researchers are developing vertical structures like IBM and Samsung’s new Vertical Transport Field Effect Transistors (VTFETs) to improve performance and energy-efficiency of semiconducting circuits. Ambature’s a-axis HTS trilayer JJs can bring similar benefits to superconducting circuits.

Scalability

High-volume manufacturing is critical to the competitiveness of superconducting circuits in a mature semiconductor market. With the a-axis, we have successfully shifted the complexity of HTS JJ manufacturing from fabrication to epitaxial growth of the wafer. Our JJs can be accurately manufactured in high volumes using standard silicon fabrication equipment. We deliberately use standard silicon fab equipment to make it easy for foundries to adopt our technology. Regardless of stacked chip architectures, tunnel junctions also have smaller functional footprints than other types of junctions (like step-edge or ramp-edge junctions), enabling greater chip densities.

Performance

Tunnel junctions exhibit high characteristic frequencies. High frequencies are useful in superconducting circuits for high-performance computing (HPC) because they can clock hundreds of gigahertz. While clock speed is by no means the only factor that determines the performance of a processor, higher clock speeds do enable more basic operations to be performed per second.

LTS tunnel junctions made of niobium have been commercially available for some time, but there were no commercial HTS alternatives until very recently, when Ambature created vertical HTS tunnel junctions with a-axis cuprates. A-axis epitaxy enables HTS trilayer devices because current can flow vertically through the layers.

There are three major advantages of a-axis HTS JJs over conventional LTS JJs. The first is simply the reduced cooling requirement. In a field where practical applications are often held back by cooling overhead, order-of-magnitude improvements in material costs and power consumption can be the difference between feasibility and infeasibility or profitability and unprofitability.

The second advantage is nuanced, and represents an exciting new body of research: HTS materials like cuprates are more variable than LTS materials like niobium. We can change material properties and device characteristics by doping materials, varying layer thicknesses, substituting layer materials and so on to optimize the composition and characteristics of specific JJs for specific applications. This flexibility makes electrical properties like coherence length and IcRn, a determining factor of the frequency of a Josephson junction switching process, tunable in HTS materials. The properties of niobium JJs are comparatively rigid.

Finally, a-axis epitaxial growth requires extremely high-quality crystal growth, so our HTS crystal structures are of higher quality than typical LTS crystal structures in LTS tunnel junctions. This quality can positively affect device performance by, for example, minimizing defects that can adversely affect the superconducting state of a material.

In summary, a-axis HTS trilayer JJs are a confluence of operational advantages over LTS and c-axis HTS counterparts: temperature, speed, density, tunability, throughput and fabrication.

Josephson Junctions, SQUIDs, JPUs

Quantum Computing

Josephson junctions and SQUIDs fulfill various roles in quantum circuits. The superconducting qubits favored by large organizations like Google and IBM are often made of SQUIDs.

High-Performance Computing, Energy-Efficient Computing, Machine Learning & Artificial Intelligence, Data Centers

Superconducting circuits can implement high-frequency or energy-efficient classical computer logic. A form of Rapid Single Flux Quantum (RSFQ) logic is typically implemented for high-frequency processing with clock rates in the hundreds of GHz. While clock speed is by no means the only factor that determines the performance of a processor, higher clock speeds do enable more basic operations to be performed per second. A form of Adiabatic Superconductor Logic (ASL) like Adiabatic Quantum-Flux-Parametron (AQFP) logic is typically implemented for energy-efficient processing, where system efficiencies including cooling overhead can be as much as two orders of magnitude better than CMOS counterparts. For data center applications, For data center applications, HTS cable systems, Superconducting Magnetic Energy Storage (SMES) and superconducting flywheels can further improve system efficiencies by reducing power losses, balancing loads and providing overload and fire protection. For sensing applications, co-located processing of sensor data within the same cooled environment can make each installation more effective and reduce communication network requirements.

Metrology

Josephson junctions can be precise frequency to voltage converters. The National Institute of Standards and Technology (NIST) takes advantage of this property to define the standard volt using thousands of JJs in series.

SQUID Sensor Arrays

Medical Imaging

Superconducting coils are used to generate the magnetic field in magnetic resonance imaging (MRI). SQUIDs are more sensitive alternatives to conventional radiofrequency coils for readout in MRI, magnetoencephalography (MEG), magnetocardiography (MCG) and other imaging applications. Replacing LTS coils with HTS coils also reduces cooling requirements for lower cost and power consumption.

Non-Destructive Testing

Following similar principles of magnetic imaging, SQUIDs can be used to find problems in aircraft, bridges and so on before they lead to failures.

Magnetic Anomaly Detection

Militaries use SQUIDs to detect underwater submarines and other vessels by the disturbances they create in the Earth’s magnetic field. Magnetic navigation follows the same principles and can provide an unjammable supplement or alternative to the Global Positioning System (GPS). Magnetic navigation would also be useful for civilian research operations like ocean monitoring because the GPS does not work underwater.

Telecommunications

SQUID filters are excellent front-end detectors for software-defined radio in digital signal applications. They improve quality factors and signal-to-noise ratios in cellular base stations and therefore increase the minimum feasible distance between towers. SQUIDs are well-suited for ultra-wideband 5G connectivity.

Wires, Tapes, Powders

Wind Turbines

The larger a wind turbine is, the more it benefits from direct-drive technology using HTS permanent magnets rather than a conventional gearbox. Direct-drive systems generate electricity more efficiently and require less maintenance than gearbox systems. Direct-drive and gearbox systems are comparable below 10 megawatts, but direct-drive is preferable for larger turbines, and the largest turbines are only feasible with direct-drive.

Cable Systems

Superconducting technologies offer electrical grids higher capacities, inherent overload protection, and environmentally-conscious coolants. HTS wires carry as much as two orders of magnitude more current than conventional wires of the same size. HTS cable systems cooled by liquid nitrogen typically carry an order of magnitude more current than comparable conventional cable systems. HTS cable systems are mostly used to connect substations in high-demand urban areas because they require less space and accommodate much higher future demand. Larger projects like the Munich SuperLink are underway.

HTS wires also have built-in overload protection because they become resistive if their critical current is exceeded. Superconducting fault current limiters (FCLs) are useful for the same reason and provide compact, passive, and automatic protection.

Conventional transformers are cooled by flammable, environmentally hazardous oils. HTS transformers are cooled by nonflammable, abundant, benign liquid nitrogen.

High Magnetic Fields

Particle accelerators like CERN’s Large Hadron Collider and prototype fusion reactor components like CFS and MIT’s 20-tesla magnet use LTS coils and HTS plates, respectively.