R&D: Team Led by National University of Singapore Scientists Breaks New Ground in Memory Technology

From the National University of Singapore (NUS)

An international research team led by scientists from the 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 one 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 nanometers.

Researchers from NUS led the invention of a novel organic resistive memory device
that is cheaper and has higher endurance as well as better energy efficiency
than commercial flash memories. The overall coordinator for the project is
Professor T Venky Venkatesan, Director of NUS Nanoscience and Nanotechnology
Institute (extreme right).

“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, 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. (see below)

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, researcher, 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 explained, “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 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, Indian Association for Cultivation of Sciences.

Goswami said, “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 bring 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, Venkatesan established a collaboration with Professor Victor Batista, 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 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 AI applications, one of the fastest growing technology fields today.

Venkatesan elaborated, “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.”

Article: Robust resistive memory devices using solution-processable metal-coordinated azo aromatics

Nature Materials as published an article written by Sreetosh Goswami, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, and NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore, Adam J. Matula, Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA, Santi P. Rath, Department of Inorganic Chemistry, Indian Association for the Cultivation of Science (IACS), Jadavpur, Kolkata 700032, India, Svante Hedström, Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA, Surajit Saha, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, present addresses: Fysikum, Stockholm University, 10691 Stockholm, Sweden (S.H.); Department of Physics, Indian Institute of Science Education and Research (IISER), Bhopal 462066, India (S.Saha), Meenakshi Annamalai, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, Debabrata Sengupta, Department of Inorganic Chemistry, Indian Association for the Cultivation of Science (IACS), Jadavpur, Kolkata 700032, India, Abhijeet Patra, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, and NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore, Siddhartha Ghosh, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, Hariom Jani, Soumya Sarkar, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, and NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore, Mallikarjuna Rao Motapothula, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, Christian A. Nijhuis, Department of Chemistry, National University of Singapore, Singapore 117543, Singapore, and Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore, Jens Martin, Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore, and Department of Physics, National University of Singapore, Singapore 117542, Singapore, Sreebrata Goswami, Department of Inorganic Chemistry, Indian Association for the Cultivation of Science (IACS), Jadavpur, Kolkata 700032, India, Victor S. Batista, Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA, and T. Venkatesan, NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore, NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore, Department of Physics, National University of Singapore, Singapore 117542, Singapore, Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore, and Materials Science and Engineering Department, National University of Singapore, Singapore 117575, Singapore.

Abstract: “Non-volatile memories will play a decisive role in the next generation of digital technology. Flash memories are currently the key player in the field, yet they fail to meet the commercial demands of scalability and endurance. Resistive memory devices, and in particular memories based on low-cost, solution-processable and chemically tunable organic materials, are promising alternatives explored by the industry. However, to date, they have been lacking the performance and mechanistic understanding required for commercial translation. Here we report a resistive memory device based on a spin-coated active layer of a transition-metal complex, which shows high reproducibility (∼350 devices), fast switching (≤30 ns), excellent endurance (∼10¹² cycles), stability (>10⁶ s) and scalability (down to ∼60nm²). In situ Raman and ultraviolet–visible spectroscopy alongside spectroelectrochemistry and quantum chemical calculations demonstrate that the redox state of the ligands determines the switching states of the device whereas the counterions control the hysteresis. This insight may accelerate the technological deployment of organic resistive memories.“