04-03-2021 | By Robin Mitchell
Recently, researchers from MIT are soon to present a paper on research involving superconducting wires, and how they can be used in next-generation electronics. What is a Cryotron, what have the researchers done, and how can it help shape the future of electronics?
Superconductors play an important role in high-tech devices thanks to their resistive and magnetic properties (i.e. having no resistance). However, superconductors don’t just have zero resistance; an external magnetic field can destroy their superconductive qualities.
This effect can be exploited in a device called a Cryotron which is essentially a superconducting transistor. Instead of using semiconductor materials to create a conductive channel whose resistance can be altered with current or voltage, a Cryotron utilises two superconductive materials to control current flow.
An insulated straight wire of tantalum has a coil of insulated niobium wire wrapped around it. Both materials have superconductive properties, but the tantalum has a lower Tc than niobium (the temperature where it becomes superconductive).
When the setup is submerged into liquid helium, both wires have superconductive properties. If no current is passed through the niobium then the tantalum wire retains its superconductive properties, and therefore has no resistance. However, if current is passed through the niobium wire, a magnetic field is generated, destroying the superconductive properties of the tantalum wire, thus increasing its resistance.
Thus, a transistor-like device can be realised without the use of semiconductor material.
Recently, researchers from MIT announced that they are to release a paper whereby they describe superconducting nanowires' construction. However, while the paper is yet to be released, details surround what has been achieved has been made public.
Firstly, the researchers have successfully demonstrated the development of superconducting nanowires with widths of 80nm and 60nm spacing. Secondly, these wires have been used to demonstrate multiple devices showing that superconducting wires can be used for practical applications. According to the researchers, they have created a memory cell based on Cryotron action, and an artificial neuron that exhibits spiking properties.
The memory cell utilises a Cryotron whereby the control nanowire can retain its magnetic state (as superconducting loops can hold current indefinitely). From there, data can be stored as magnetic flux, and since the conductivity of tantalum greatly varies depending on its superconducting state, the memory cell can retain information.
According to the researchers, the spiking neuron takes advantage of two nanowires for creating a relaxation oscillator. This supposedly reflects how ion channels work in neurons and could allow for high-speed processing of AI systems.
It is important to understand that superconducting devices are very unlikely to make their way into consumer devices for the foreseeable future unless a major breakthrough is made with room-temperature superconductors. However, superconductive systems are already in deployment in high-tech equipment such as MRI.
As such, there is a very real possibility that superconductive electronics could become mainstream in data processing centres that can afford the cooling infrastructure needed for superconductive materials.
But why use superconductive electronics? Simply put, superconductive electronics have been proven to work at speeds well over anything possible by common room-temperature devices. For example, superconductive Josephson junctions have been demonstrated to operate at 770GHz. If this can be used in Cryotron devices, a processor using such tech would operate on orders of magnitude greater than current technology.
Superconducting devices can also see massive reductions in energy consumption thanks to superconductive materials having zero resistance. Thus, low energy servers with extremely fast processors could readily handle large quantities of data that could power the next-generation IoT, Smart Homes, and AI services globally.