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Using Graphene for Storage

The average consumer flash memory will store data in polysilicon layers as an electric charge. Polysilicon is a single continuous material and this means that if there is anything wrong with the material, like a dent, then it can cause interference with the desired charge movement. This is a problem because it can limit how much data is retained and also the density of it.

Researchers have been trying to overcome this problem for a while. One method they tried was to store charge in discrete charge traps, like nanocrystals, rather than the polysilicon layers. A discrete charge trap material is not as sensitive to defects and thus it can help stop unwanted charge movement. As such, there is the opportunity for them to be used in high-density flash memories.

A new study published in the academic journal Nanotechnology by South Korean researchers Soong Sin Joo, et al., at Kyung Hee University and technology giant Samsung looks into the use of another material. Instead of using nanocrystals as the discrete charge trap material, the scientists used graphene quantum dots.

In the material industry, graphene is popular for next-generation electronics and photonics due to the unique properties that it holds. However, using the material for memory is still in its infancy, especially graphene quantum dots. These are pieces of graphene that have been extracted from bulk carbon; they can then be altered with certain electronic and optical properties in order to be used for other things.

In this case, the scientists used three different sizes of graphene quantum dots (6, 12 and 27 nm in diameter) between silicon dioxide layers. They found that the metal properties changed dependant on the size. The 12 nm dots had the highest program speed, but the 27 nm dots had the highest erase speed and stability.

“This is the first report of charge-trap flash nonvolatile memories made by employing structurally characterized graphene quantum dots, even though their nonvolatile memory properties are currently below the commercial standard,” Suk-Ho Choi at Kyung Hee University said to Phys.org in an interview. “Actually, this is first successful application of graphene quantum dots in practical devices, including electronic and optical devices, as far as I know, even though there are many reports on physical and chemical characterizations of graphene quantum dots.”

The electron density is similar to that of other memory devices that are based on semiconductor and metal nanocrystals. Although there is still further research that needs to be carried out, there is hope that in the future there will be even greater performance and a range of different applications.

“If flexible dielectrics (insulators) are used instead of silicon dioxides as tunnel and control barriers on plastic substrates, then they can be used in flexible (or wearable) electronic devices,” Choi said. “Metal nanoparticles also offer several advantages similar to graphene quantum dots, such as higher density of states, flexibility in choosing the work function, etc., for charge-trap flash nonvolatile memories, but may potentially degrade the device performance due to their thermal instabilities and are not useful for transparent and flexible electronics and photonics.”

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