Lab talk
Mar 22, 2013
Simple high-performance nanotube-based WORM memories
In a recent study, researchers in Brazil, Mexico and South Africa have investigated write-once-read-many times (WORM) memory devices based on multiwalled carbon nanotubes embedded in a poly(vinyl alcohol) matrix. These devices change their conductance by five or six orders of magnitude when a voltage pulse is applied, irreversibly going from an electrically high resistive OFF state to a highly conductive ON one. These states are the equivalent of the "0" and "1" states in conventional memories and so satisfy logic digital circuitry requirements.
Applications for these simple and potentially inexpensive memories include electronic identification. Such devices must be able to change one of their measurable electrical characteristics in a controlled and reproducible way following an intentional external input, ideally maintaining this change ad eternum.
Poly(vinyl alcohol) is a relatively inexpensive and commonly used material and the amount of carbon nanotubes embedded in the device composite film is very low. The best performance is obtained when the composite contains less than 0.5% carbon nanotubes.
We observed memory behaviour in nominally undoped, nitrogen-doped and boron-doped carbon nanotubes, suggesting that impurities in the carbon nanotubes do not play a crucial rule in the memory phenomenon. An added advantage comes from the fact that very little energy is required to switch the device from the OFF to the ON state.
More details of the work can be found in the journal Nanotechnology.
About the author
The study was conducted by research teams in the Physics Department of the Federal University of Paraná (UFPR) in Brazil and DST/NRF Centre of Excellence in Strong Materials and Molecular Sciences of the School of Chemistry at the University of the Witwatersrand in South Africa. The team operates under the India-Brazil-South Africa (IBSA) Initiative in Nanotechnology. The work was funded by CNPq-Brazil and NRF-South Africa. Messai A Mamo was a postdoctoral fellow at UFPR and is currently at the University of Johannesburg. Alan O Sustaita is a PhD student at the IPICYT in San Luis Potosí, Mexico, and performed the work in a doctoral internship at UFPR. Zikhona Tetana is a PhD student supervised by Prof. Neil J Coville at the University of the Witwatersrand. Prof. Ivo A Hümmelgen is the head of the Group of Organic Optoelectronic Devices – UFPR in Curitiba, Brazil.
