Brain-inspired memory device for flexible electronics

Researchers have devised a new memory device inspired by the neuron connections of the human brain which may pave the way for next-generation soft electronics attached to clothes or body.
The research from the Institute for Basic Science (IBS) in South Korea highlights the device's highly reliable performance, long retention time and endurance.
Its stretchability and flexibility makes it a promising tool for the soft electronics attached to clothes or body, researchers said.
The brain is able to learn and memorise thanks to a huge number of connections between neurons. The information you memorise is transmitted through synapses from one neuron to the next as an electro-chemical signal.

Inspired by these connections, scientists constructed a memory called two-terminal tunnelling random access memory (TRAM), where two electrodes, referred to as drain and source, resemble the two communicating neurons of the synapse.
While mainstream mobile electronics, like digital cameras and mobile phones use the so-called three-terminal flash memory, the advantage of two-terminal memories like TRAM is that two-terminal memories do not need a thick and rigid oxide layer.

"Flash memory is still more reliable and has better performance, but TRAM is more flexible and can be scalable," said Professor YU Woo Jong from Sungkyunkwan University.
TRAM is made up of a stack of one-atom-thick or a few atom-thick 2D crystal layers: One layer of the semiconductor molybdenum disulfide (MoS2) with two electrodes (drain and source), an insulating layer of hexagonal boron nitride (h-BN) and a graphene layer.

In simple terms, memory is created, read and erased by the flowing of charges through these layers.
TRAM stores data by keeping electrons on its graphene layer. By applying different voltages between the electrodes, electrons flow from the drain to the graphene layer tunnelling through the insulating h-BN layer.
The graphene layer becomes negatively charged and memory is written and stored and vice versa, when positive charges are introduced in the graphene layer, memory is erased.
Scientists carefully selected the thickness of the insulating h-BN layer as they found that a thickness of 7.5 nanometres allows the electrons to tunnel from the drain electrode to the graphene layer without leakages and without losing flexibility.

When TRAM is fabricated on flexible plastic (PET) and stretchable silicone materials (PDMS), it could be strained up to 0.5 per cent and 20 per cent, respectively.
In the future, TRAM can be useful to save data from flexible or wearable smartphones, eye cameras, smart surgical gloves, and body-attachable biomedical devices, researchers said.
The study was published in the journal Nature Communications.