A multinational team of academics unveiled a unique molecular device with remarkable computational capability in a paper published in the journal Nature. The gadget can be changed on the fly for different computing tasks by merely adjusting applied voltages, similar to the flexibility of connections in the human brain.
The brain has the remarkable ability to change its wiring around by making and breaking connections between nerve cells. Achieving something comparable in a physical system has been extremely challenging.
Dr. R. Stanley Williams
Furthermore, much as nerve cells may store memories, the same device can store data for retrieval and processing in the future.
“The brain has the remarkable ability to change its wiring around by making and breaking connections between nerve cells. Achieving something comparable in a physical system has been extremely challenging,” said Dr. R. Stanley Williams, professor in the Department of Electrical and Computer Engineering at Texas A&M University. “We have now created a molecular device with dramatic reconfigurability, which is achieved not by changing physical connections like in the brain, but by reprogramming its logic.”
Dr. T. Venkatesan, director of the University of Oklahoma’s Center for Quantum Research and Technology (CQRT), a Scientific Affiliate at the National Institute of Standards and Technology in Gaithersburg, and an adjunct professor of electrical and computer engineering at the National University of Singapore, added that their molecular device could help design next-generation processing chips in the future.
The von Neumann bottleneck is a frequent adversary of digital technology, whether it’s a simple laptop or a complex supercomputer. The present computer designs, in which the memory, which contains data and programs, is physically separated from the CPU, cause this delay in computational processing.
As a result, computers waste a lot of time transferring data between the two systems, generating a bottleneck. In addition, despite their high CPU speeds, these devices can sit idle for long periods of time during times of data interchange.
Devices such as memristors offer a technique to get around the von Neumann bottleneck as an alternative to traditional electrical elements used in memory units and processors. At a specific temperature, memristors consisting of niobium dioxide and vanadium dioxide change from an insulator to a conductor. These memristors have this characteristic, which allows them to execute calculations and store data.
Despite their numerous benefits, these metal oxide memristors are comprised of rare-earth elements and can only work at specific temperatures. As a result, Williams added, there has been an ongoing hunt for potential organic chemicals that might perform a similar memristive function.
The substance utilized in this project was created by Dr. Sreebrata Goswami, a professor at the Indian Association for the Cultivation of Science. The ligands are three phenyl azo pyridine chemical molecules bound to a central metal atom (iron).
“This behaves like an electron sponge that can absorb as many as six electrons reversibly, resulting in seven different redox states,” said Sreebrata. “The interconnectivity between these states is the key behind the reconfigurability shown in this work.”
Dr. Sreetosh Goswami, a researcher at the National University of Singapore, created this technique by using a 40-nanometer layer of molecular film sandwiched between a layer of gold on top and gold-infused nanodisc and indium tin oxide at the bottom to create a small electrical circuit.
When Sreetosh applied a negative voltage to the gadget, he saw a current-voltage profile that no one had ever seen before. Unlike metal-oxide memristors, which can only transition from metal to insulator at a single fixed voltage, organic molecule devices can switch from insulator to conductor at several distinct voltages.
“So, if you think of the device as an on-off switch, as we were sweeping the voltage more negative, the device first switched from on to off, then off to on, then on to off and then back to on. I’ll say that we were just blown out of our seat,” said Venkatesan. “We had to convince ourselves that what we were seeing was real.”
Using an imaging method called Raman spectroscopy, Sreetosh and Sreebrata studied the chemical processes underlying the strange switching behavior. They were looking for spectral markers in the organic molecule’s vibrational motion that may explain the many transitions.
Swinging the voltage negative prompted the ligands on the molecule to undergo a sequence of reduction, or electron-gaining, processes, causing the molecule to transition between off and on states, according to their findings.
Williams then diverged from the traditional technique of using fundamental physics-based equations to quantitatively characterize the molecular device’s extraordinarily complicated current-voltage profile. Instead, he used a decision tree method containing “if-then-else” statements, a typical line of code in many computer programs, especially digital games, to explain the behavior of the molecules.
“Video games have a structure where you have a character that does something, and then something occurs as a result. And so, if you write that out in a computer algorithm, they are if-then-else statements,” said Williams. “Here, the molecule is switching from on to off as a consequence of applied voltage, and that’s when I had the eureka moment to use decision trees to describe these devices, and it worked very well.”
However, the researchers went one step further and used these molecular devices to run programs for a variety of real-world computing activities. Sreetosh demonstrated that their devices could execute reasonably complicated computations in a single time step and then be reprogrammed to undertake another task in the next moment in an experiment.
“It was quite extraordinary; our device was doing something like what the brain does, but in a very different way,” said Sreetosh. “When you’re learning something new or when you’re deciding, the brain can actually reconfigure and change physical wiring around. Similarly, we can logically reprogram or reconfigure our devices by giving them a different voltage pulse then they’ve seen before.”
Venkatesan pointed out that doing the same computing duties as one of their molecular devices with its several decision trees would require thousands of transistors. As a result, he believes their technology will first be employed in portable devices such as mobile phones and sensors, as well as other low-power applications.
Other contributors to the research include Dr. Abhijeet Patra and Dr. Ariando from the National University of Singapore; Dr. Rajib Pramanick and Dr. Santi Prasad Rath from the Indian Association for the Cultivation of Science; Dr. Martin Foltin from Hewlett Packard Enterprise, Colorado; and Dr. Damien Thompson from the University of Limerick, Ireland.
This finding, according to Venkatesan, is suggestive of future discoveries from this interdisciplinary team, which will comprise the Indian Institute of Science’s Center of Nanoscience and Engineering and the National Institute of Standards and Technology’s Microsystems and Nanotechnology Division.
This multidisciplinary and multinational research was supported by the Singapore National Research Foundation under the Competitive Research Programs; Science and Engineering Research Board, India; the X-Grants Program of the President’s Excellence Fund at Texas A&M; Science, Technology and Research, Singapore, under its Advanced Manufacturing and Engineering Individual Research Grant; startup funds at CQRT University of Oklahoma; and the Science Foundation, Ireland.
