Artificial Visual System for Future AI

Johnny Chung-yin Ho of the Department of Materials Science and Engineering at CityU looks at a nanowire chip. Developing nanowires for future semiconducting chips is one of his research focuses. (Source: City U. Hong Kong)

A joint research led by City University of Hong Kong (CityU) has built an ultralow-power consumption artificial visual system to mimic the human brain, which success­fully performed data-intensive cognitive tasks. Their experiment results could provide a promising device system for the next generation of arti­ficial intelligence (AI) appli­cations. The research team is led by Johnny Chung-yin Ho, Associate Head and Professor of the Department of Materials Science and Engi­neering (MSE) at CityU.

As the advances in semi­conductor technologies used in digital computing are showing signs of stagnation, the neuro­morphic computing systems have been regarded as one of the alter­natives in future. Scientists have been trying to develop the next generation of advanced AI computers which can be as lightweight, energy-efficient and adaptable as the human brain. “Unfor­tunately, effectively emulating the brain’s neuro­plasticity – the ability to change its neural network connections or re-wire itself – in existing artificial synapses through an ultralow-power manner is still challenging,” said Ho.

Artificial synapse is an artificial version of synapse – the gap across which the two neurons pass through electrical signals to communi­cate with each other in the brain. It is a device that mimics the brain’s efficient neural signal trans­mission and memory formation process. To enhance the energy efficiency of the artificial synapses, Ho’s research team has intro­duced quasi-two-dimensional electron gases (quasi-2DEGs) into arti­ficial neuro­morphic systems for the first time. By utilising oxide superlattice nanowires, they have designed the quasi-2DEG photonic synaptic devices which have achieved a record-low energy consumption down to sub-femtojoule per synaptic event. It means a decrease of 93 % energy consumption when compared with synapses in the human brain.

“Our experiments have demons­trated that the artificial visual system based on our photonic synapses could simultaneously perform light detection, brain-like processing and memory functions in an ultralow-power manner. We believe our findings can provide a promising strategy to build artificial neuro­morphic systems for appli­cations in bionic devices, electronic eyes, and multi­functional robotics in future,” said Ho. He explained that a two-dimensional electron gas occurs when electrons are confined to a two-dimensional interface between two different materials. Since there are no electron-electron inter­actions and electron-ion inter­actions, the electrons move freely in the interface.

Upon exposure to light pulse, a series of reactions between the oxygen molecules from environment absorbed onto the nanowire surface and the free electrons from the two-dimen­sional electron gases inside the oxide super­lattice nanowires were induced. Hence the conductance of the photonic synapses would change. Given the outstanding charge carrier mobility and sensi­tivity to light stimuli of superlattice nanowires, the change of conductance in the photonic synapses resembles that in biological synapse. Hence the quasi-2DEG photonic synapses can mimic how the neurons in the human brain transmit and memorise signals.

“The special properties of the superlattice nanowire materials enable our synapses to have both the photo-detecting and memory functions simul­taneously. In a simple word, the nanowire superlattice cores can detect the light stimulus in a high-sensi­tivity way, and the nanowire shells promote the memory functions. So there is no need to construct addi­tional memory modules for charge storage in an image sensing chip. As a result, our device can save energy,” explained Ho.

With this quasi-2DEG photonic synapse, they have built an artificial visual system which could accurately and efficiently detect a patterned light stimulus and memorise the shape of the stimuli for an hour. “It is just like our brain will remember what we saw for some time,” described Ho. He added that the way the team syn­thesised the photonic synapses and the arti­ficial visual system did not require complex equipment. And the devices could be made on flexible plastics in a scalable and low-cost manner. (Source: City U. Hong Kong)

Reference: Y. Meng et al.: Artificial visual systems enabled by quasi–two-dimensional electron gases in oxide superlattice nanowires, Sci. Adv. 6, eabc6389 (2020); DOI: 10.1126/sciadv.abc6389

Link: State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Hong Kong SAR

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