Research Highlight

Ultra-thin, ultra-fast, low-power memory devices

doi:10.1038/nindia.2021.77 Published online 22 May 2021

A computer-based simulation study has shown how a non-volatile memory effect emerges because of atomic rearrangement in a single-layer molybdenum disulphide1. This new type of memory, known as resistive memory, retains data even after power is turned off. 

Understanding the mechanism behind such a memory in this material may help design reliable, high-performance, low-power devices that could process and store data on a single device, a team of electronics engineers from the Indian Institute of Science in Bangalore says.

The most common defects in a single-layer molybdenum disulphide are missing sulphur atoms. Such defects make this material change resistance under a strong electric field. What triggers such a non-volatile and reversible resistance change is not well understood.

To find out, the scientists conducted a reactive molecular dynamics simulation of bond breaking and formation in a single-layer molybdenum-disulphide-based device with inert electrode systems.

The researchers, led by Santanu Mahapatra, found that most sulphur atoms directly above the sulphur vacancies vertically move to form stronger bonds with the neighbouring atoms at a critical electric field. This creates a localised metallic state, forming a conducting virtual filament between the electrodes.

The bonds between the sulphur atoms and the neighbouring atoms remain even in the absence of an electric field. This creates a non-volatile memory effect that could be used for developing non-volatile memory devices, the researchers say.

Applying a suitable electric field and a local high temperature weakens the bonds, bringing the sulphur atoms back to their original position. This resets the device, removing the memory effect, they note.


References

1. Mitra, S. et al. Theory of nonvolatile resistive switching in monolayer molybdenum disulfide with passive electrodes. npj. 2D. Mater. & Appl. 5, 33 (2021) DOI: 10.1038/s41699-021-00209-0