Using laser controlled filaments in vanadium dioxide to enhance neural morphology calculations

In a new "Progress in Science" study, scientists from the University of Science and Technology of China have developed a dynamic network structure for neural morphology calculations using laser controlled conductive wires.

Neuromorphic computing is an emerging research field that draws inspiration from the human brain to create efficient and intelligent computer systems. The core of neuromorphic computing relies on artificial neural networks, which are computational models inspired by brain neurons and synapses. But when it comes to creating hardware, it can be a bit challenging.

Due to its unique transition characteristics, Mott materials have become a suitable candidate for neural morphology calculations. The Mott transition involves a rapid change in conductivity, usually accompanied by a transition between the insulating state and the metallic state.

Professor Chong Wen Zou, co lead author, explained to Phys.org, "The obvious electron electron behavior in Mott materials leads to several orders of magnitude changes in conductivity within a very narrow temperature range, and even leads to superconductivity
In their study, the research team selected vanadium dioxide (VO2). Co lead author Fang Wen Sun explained their material selection by stating, "VO2 is a typical Mott material with a phase transition temperature close to room temperature, making it feasible for multiple applications.

VO 2 as electrical switch
VO2, like all Mott materials, undergoes a metal insulator transition (MIT) at around 68 ° C (154 ° F). This means that at this specific temperature, VO2 changes from an insulator to a conductor. The ability to switch between these states makes VO 2 suitable for various applications.

VO 2 is very suitable for neuromorphic computing applications because its MIT behavior can mimic the behavior of biological neurons. Simply put, VO2 exhibits changes in conductivity, similar to changes in strength between biological neurons in the human brain.

This similarity to brain plasticity means that VO2 can adapt and change its conductivity, just like the brain adapts and rewires itself. In addition, the excellent ability of VO2 to switch between conductive and non-conductive states makes it an important component of the circuit, just like an efficient switch.

The flow of current and light through VO2 materials can be controlled based on temperature, making them very suitable for other applications. This is particularly useful in applications such as smart windows, which can control the passage of light and heat, thereby improving energy efficiency.

In addition, VO2 can be used to construct dynamic networks where signals can be processed and stored in a way that mimics the functions of the human nervous system, especially in terms of adaptability and response to external stimuli.

Professor Zou and Professor Sun explained that the controlled connection of conductive wires in VO2 devices is similar to the controlled connection of biological synapses. Therefore, we also explored the network of artificial synaptic tissue based on VO2 devices in our research.

In traditional research on artificial synaptic devices, the properties of individual synapses are characterized and these synapses are used as response functions to simulate neural networks. However, the dynamic network we implement through laser controlled conductive wires exists in hardware, which is very similar to the behavior of biological neurons and does not rely on semiconductor circuits, "the researchers explained.

The research team constructed a highly complex experimental setup to study and manipulate conductive wires in VO2 materials. They first grew VO2 thin films with a thickness precisely controlled at 100 nanometers.

In order to gain a deeper understanding of the behavior of VO2 materials, the team used a quantum sensor based on diamond nitrogen vacancy (NV) centers, which is known for its exceptional sensitivity to conductivity changes caused by atomic defects in diamond crystals.

These sensors play a crucial role in detecting changes in the electrical characteristics of VO2. By manipulating the NV center, researchers can observe how conductive wires are formed and controlled. The main objective of their experiment is to accurately control the position of conductive wires within the VO2 device, which serve as pathways for electrical signals.

To achieve this goal, researchers used a precisely oriented focused laser within the VO2 device to manipulate the position of the conductive wire. This level of control is crucial for regulating electrical signal flow, similar to the behavior of biological synapses.
In addition, the team also used a high angle annular dark field scanning transmission electron microscope (STEM) to capture high-resolution images and analyze the structure of VO2 materials, thereby obtaining valuable insights at the nanoscale.

Professor Sun's team utilized the professional knowledge of conducting nanowires based on quantum sensors with diamond NV centers, and together with Professor Zou's team, who focuses on VO2 phase transition and device application research, helped the team successfully achieve image conduction by detecting the current distribution of a filament with a quantum sensor based on diamond NV centers.

Future Work
Researchers have found that artificial synapses exhibit long-term and short-term enhancement effects, with channels that can be re triggered by current for over two hours and exhibit transient resistance changes caused by laser heating. In short, artificial synapses exhibit the ability to strengthen and adjust their connections over time, much like the way our brain's neural networks learn and process information.

Regarding the future application of this work, "in the current demonstration, we established a network with five artificial synapses and used focused lasers to control conductive wires," said Professor Zou.

Our future goal is to use multi-layer electrodes and light fields to establish more complex neural networks to achieve synaptic connections. Creating feedback mechanisms that regulate light intensity still faces challenges, but we are eager to explore the practical applications of Mott materials, "Professor Mott concluded.

Source: Laser Network