Scientists at Infineon have built what they claim is the world’s smallest non-volatile flash memory cell. The new memory cell measures 20 nanometres and could make non-volatile memory chips with a capacity of 32 Gbit possible within a few years.
Non-volatile flash memories are becoming increasingly popular as mass storage media for devices such as digital cameras, camcorders and USB sticks. The most advanced non-volatile flash memory devices available today can permanently store one or two bits of information per memory cell without a supply voltage.
Such memories have a feature size of around 90 nanometres, and shrinking this feature size using typical techniques to half that size has posed many problems because of nanoscale physical effects. In particular, fabricating 20 nanometre-sized flash memory cells has been considered impossible because these physical effects would make the memory cells extremely unreliable.
The Infineon researchers overcame this challenge by creating a three-dimensional structure with a fin for the transistor that acts as the heart of the memory cell. The special geometry minimises unwanted effects and improves electrostatic control compared to today’s flat transistors.
Called a FinFET (Fin Field Effect Transistor), the Infineon device stores the electrons which carry the information in a nitride layer that lies electrically isolated between the silicon fin and the gate electrode. Just eight nanometres thin, the fin is controlled by the 20 nanometre-wide gate electrode.
The FinFET is also said to be extremely durable and possesses excellent electrical characteristics. The most advanced memories on the market today need approximately 1,000 electrons in order to reliably remember one bit. The new Infineon memory cell uses just 100 electrons; an additional 100 electrons stores a second bit in the same transistor. One hundred electrons roughly correspond to the number of electrons in a single gold atom. Despite these minimal charge levels, the sample at Infineon’s Munich laboratories showed excellent electrical characteristics.
Details about the new flash memory were presented at the IEEE’s International Electron Devices Meeting in San Francisco yesterday.