Replacing the tunnel barrier in a flash memory device with a series of quantum dots can increase the write speed a thousand-fold
Flash memory offers high-density, low-cost data storage, but it suffers from poor write speeds. To write a bit of data in one of these devices, which are essentially metal-oxide-semiconductor field-effect transistors, electric charge has to be injected onto a ‘floating gate’. However, this involves electrons tunnelling through the thick insulating barrier that isolates the floating gate, which is a slow process.
To increase this write speed, Claes Thelander and co-workers1 at Lund University in Sweden have fabricated a new type of floating gate in a nanowire flash memory device. They replaced the thick barrier with a series of 17-nm quantum dots made of indium arsenide that are separated by thin (3–4 nm) tunnel barriers made of indium phosphide. The electrons are able to tunnel through the InAs/InP heterostructure much faster than they can through a single thick barrier.
The new structure permits write speeds of as little as 10 ns — nearly one thousand times faster than before. Although the device only works below 150 K at present, Thelander and co-workers hope that the use of smaller quantum dots and a different barrier material might make room-temperature operation possible.
Nillson, H. A., Thelander, C., Fröberg, L. E., Wagner, J. B. & Samuelson, L. Appl. Phys. Lett. (2006). 10.1063/1.2362594