Research team led by Singaporean scientists breaks new ground in memory technology

An international research team led by scientists from the National University of Singapore (NUS) pioneered the development of a novel thin, organic film that supports a million more times read-write cycles and consumes 1,000 times less power than commercial flash memories.

The novel organic film can store and process data for 1 trillion cycles and has the potential to be made even smaller than its current size of 60 square nanometers, with potential to be sub-25 square nanometres.

"The novel properties of our invention opens up a new field in the design and development of flexible and lightweight devices. Our work shifts the paradigm on how the industry has traditionally viewed organic electronics, and expands the application of such technologies into new territories," said Professor T Venky Venkatesan, Director of NUS Nanoscience and Nanotechnology Institute (NUSNNI), the overall coordinator for this groundbreaking project.

The invention of this novel memory device was first reported online in the journal Nature Materials on 23 October 2017.

Global demand for better electronic memory devices
With the emergence of the digital age, data is constantly generated and shared in devices ranging from mobile phones to industrial machines. Driven by this need to store data, silicon-based flash memories have become ubiquitous.

For years, the computer industry has sought to develop memory technologies with higher endurance, lower cost, and better energy efficiency than commercial flash memories. The industry has kept away from using organic systems in memories due to their limitations in performance, questionable claims of reproducibility, and the lack of scientific clarity on mechanisms through which they exhibit their behaviour.

To address these challenges, Sreetosh Goswami, a researcher from NUSNNI, successfully fabricated a novel organic resistive memory device that outperforms commercial flash memory in terms of endurance, energy efficiency and cost. He developed 600 working devices which demonstrated impeccable reproducibility.

Goswami explains, "For the first time an organic device is looking industrially competitive. Also, we have developed a clear picture of the molecular mechanism based on our in-situ studies which organic devices have always been lacking." He is also a graduate student from the NUS School of Integrative Sciences and Engineering who is under the supervision of Prof Venkatesan.

The new device utilises a transition metal complex which was designed and synthesised by Professor Sreebrata Goswami and his team, comprising graduate students Santi Prasad Rath and Debabrata Sengupta, from the Indian Association for Cultivation of Sciences. Prof Goswami says, "We have been working on this unique family of metal complexes over the past few decades, to understand the chemical and physical properties which are controlled by ligand redox. Our understanding is now at a stage where we can engineer new materials by bringing together different variations in the molecules, adding active functions and using right counter ions. This opens up new avenues to address many scientific problems."

In order to understand the science behind the device performance, Prof Venkatesan established a collaboration with Professor Victor Batista from Yale University. Besides simulating the spectral behaviour of the molecules, Dr Svante Hedstrom and Adam Matula, who are from Prof Batista's team, were able to identify the role of the counter ions in the molecule which gave rise to a non-volatile memory behaviour.

"The counter ions surrounding the molecules act like the ratchets on a wrench, and offer stability to the various electronic states of the molecule which are necessary to achieve the memory effect. This molecular-level understanding that we have helped to generate is unprecedented in a memory device, and allow us to create design principles for the next generation of devices," commented Prof Batista.

Pushing the frontiers of memory technologies
The research team is planning to partner a consumer electronics company to commercialise the new technology. In addition, the researchers are also looking at fabricating multi-state memories to produce neuromorphic memory devices (that resemble the brain) for artificial intelligence (AI) applications, one of the fastest growing technology fields today.

Prof Venkatesan elaborates, "AI relies on neuromorphic computing to simulate the architecture of the human brain. Therefore, the development of neuromorphic memory devices that can embody the concept of learning endemic to biological memory is crucial. Given the success of our current work, I believe we are on the right track to fabricate innovative memories which will have more than two states while maintaining all the fascinating properties of the device we currently have."