Floating-Gate Device may revolutionize computer memory
By Paul Ridden
January 26, 2011
A team of researchers from North Carolina State University claim to have created a memory device that could give computer users the speed advantages of DRAM system memory and the data retention capabilities of flash memory, in one unit. The new device could lead to genuine instant-on computing and machines with improved resiliency. The development may even lead to power-hungry server farms making considerable energy savings by allowing parts of the system to be shut down during periods of inactivity without fear of data loss.
The new scalable, dual-metal device is called a double floating-gate field effect transistor (FET) and is said to combine the advantages offered by two forms of computer memory currently in common usage. Nonvolatile memory, like that used in USB flash drives, allows data to be retained after the power is turned off while the volatile variety, like the memory modules slotted into a mainboard, offers faster read and write access but needs constant power for the retention of stored data.
Currently in the testing phase of development, the new FET device stores data as electric charge and uses a special control gate to quickly get to the stored data. Whereas modern nonvolatile flash memory uses a single floating gate to store the charge for long term data retention, the new device utilizes a second gate which is said to give the device transfer speeds comparable to current volatile DRAM memory. The researchers also believe that the new technology could "have a very long lifetime, when it comes to storing data in the volatile mode."
Unifying volatile and nonvolatile memory
The device's state is determined by its threshold voltage, and can be switched between the volatile and nonvolatile states quickly on a row-by-row basis. In bulk form, the device is said to be scalable to at least the 16nm node and can be three-dimensionally stacked using deposited layers of indium-gallium-zinc-oxide amorphous semiconductors, which have the potential to achieve better performance than amorphous silicon transistors. A stack of four devices could have similar densities to an 8nm node.
The research team believes that the new double floating gate FET device could potentially offer instant-on functionality, as the computer would not need to retrieve startup information from a hard drive. It should also lead to improvements in a computer's ability to withstand and recover from faults and could solve energy-proportional computing problems.
For instance, when a computer or server is just performing background tasks, the double gate allows portions of the memory to be powered down and reactivated as necessary without losing data. This could lead to enormous power savings at server farms, which currently need to maintain constant power throughout the whole system, even at times of low usage.
Authored by Daniel Schinke, Neil Di Spigna, Mihir Shiveshwarkar and Paul Franzon from North Carolina State University, the paper entitled Computing with Novel Floating-Gate Devices has been published in IEEE's journal Computer.