The materials used in rewritable CDs and DVDs also show promise as electronic memories systems. They believe they could make 1 million read/write material (50-100 times longer than current flash) and with 4-20 times higher density than flash and faster writing times. New materials for flash could be more competitive and Numonyx must make their new memory cheap enough to displace flash memeory.
New Scientist magazine provides details of the work of Greg Atwood and his colleagues at Numonyx, a flash memory chip maker in Santa Clara, California.
Numonyx has devised a novel microchip memory cell in which a blob of GST (an alloy of tellurium, antimony and germanium used for CDs and DVDs) sits atop a simple resistor. Different current pulses applied to the resistor heat the blob and change its state, and a second, much lower (non-heating) current can sense the blob’s resistance.
This Phase Change Memory (PCM) appears to work reliably. Numonyx – a spinoff from Intel – has built a 128-megabit flash memory and is currently allowing unnamed gadget makers to assess its potential.
Numonyx believes PCM offers new scaling possibilities. They believe they can change and stably hold the phase states in GST cell sizes down to 5 nanometres and below. This would 4-20 times more dense than flash might become.
And, without the parasitic charge problems of today’s flash, it can be written to at least 1 million times. And, unlike flash, individual bits in PCM can be changed at will: flash has to rewrite chunks of data each time, slowing the writing process.
Today, most flash memory transistors are about 65 nanometres wide, with the next generation set for 45 nm. “But serious issues will begin to arise when dimensions get below 20 nanometres due to the retention of electric charge in the flash transistor,” warns Atwood.
Current limitation are around 10,000 write-and-erase cycles. But with 20 nanometre transistors that effect worsens considerably, limiting lifetime even further.