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Metal-semiconductor interface for brain-inspired computing

By combining aniobium doped strontium titanate (SrTiO3) semiconductor with ferromagnetic cobalt, physicists at the University of Groningen believe they may be a step closer to integrating storage, memory and processing into one unit.

The SrTiO3 semiconductor is said to have a non-volatile variable resistance when interfaced with cobalt, meaning an electric field can be used to create the electroresistance effect.

A tunablity of the TAMR spin voltage by 1.2 mV was apparently demonstrated when a magnetic field was applied across the same interface, in and out of the plane of the cobalt. The physicists state that this coexistence of both a large change in the value of TAMR and electroresistance across the same device at room temperature has not previously been shown in other material systems.

Professor, Tamalika Banerjee of the University of Groningen, said: “This means we can store additional information in a non-volatile way in the memristor, thus creating a very simple and elegant integrated spin-memristor device that operates at room temperature.”

According to Banerjee and her team, the key to success is the interface between cobalt and the semiconductor. “We have shown that a one-nanometre thick insulating layer of aluminium oxide makes the TAMR effect disappear,” Banerjee explained.

The team adjusted the niobium doping of the semiconductor and therefore, the potential landscape at the interface. It is said that the same coexistence can't be realised with silicon as a semiconductor.

“You need the heavy atoms in SrTiO3 for the spin orbit coupling at the interface that is responsible for the large TAMR effect at room temperature,” Banerjee said.

The Banerjee team hope that eventually, the devices could be used in computer architecture that mimics the brain, acting like the synapses that connect the neurons.

The synapse responds to an external stimulus, but this response also depends on the synapse's memory of previous stimuli. “We are now considering how to create a bio-inspired computer architecture based on our discovery,” Banerjee continued.

This system would aim to move away from Von Neumann architecture. It is suggested by the team that it would use less energy and produce less heat and that this heat reduction could be advantageous for IoT devices.

The next stage for Banerjee and her team is to develop a better understanding of the interface between colbalt and the strontium semiconductor. “Once we understand it better, we will be able to improve the performance of the system” she said. “We are currently working on that. But it works well as it is, so we are also thinking of building a more complex system with such spin-memristors to test actual algorithms for specific cognition capabilities of the human brain.”

Author
Bethan Grylls

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