14 DAY TRIAL // Forget about transistor based flash memories, say researchers working for the flash memory chip maker Numonyx; future ultrahigh-capacity solid state information storage devices are most likely to be made out of the same materials used to manufacture CDs and DVDs. It may be just a matter of time before nonvolatile memories are built through the new process, since the technology behind the concept has already been proven to work.
Almost anybody today carries in their pocket a device using flash memory as a medium to store information, starting from mp3 players all the way to cellular phones and digital cameras. However, as technology evolves, flash memories must also grow in capacity. To keep pace with this tendency, chip manufacturers must resort to even more advanced fabrication methods. The vast majority of solid state storing devices use transistors 65 nanometers wide, closely followed by chips created through the 45 nm technology.
"But serious issues will begin to arise when dimensions get below 20 nanometres due to the retention of electric charge in the flash transistor," says Greg Atwood of Numonyx.
The most troublesome of these issues is the 'parasitic' charge that appears during the data recording process, limiting the lifespan of typical flash memories to about 10,000 write cycles. In the case of the 20 nm manufacturing process, the number of write cycles drops even more, making solid state memories too unreliable.
The alternative could have already been found in the form of the GST coating used in optical storing devices. GST is an alloy of tellurium, antimony and germanium used in the fabrication of CDs and DVDs as a recording medium. It can exist in two states, disordered and crystalline, both of which can be altered depending on the speed at which the alloy cools, allowing the lasers of optical writing devices to record information. However, the two states also have different characteristic reflectivity levels, which can become extremely important during the reading process.
What makes GST really special is that information recorded on it can be read with the help of electricity as well, due to the fact that the two states have different resistivities. By exploiting this property, Numonyx created a Phase Change Memory with a capacity of 128 megabits that is currently in its testing stage.
"We believe PCM offers new scaling possibilities. You can change and stably hold the phase states in GST cell sizes down to 5 nanometres and below," added Atwood. Not only that PCM could increase the lifespan of solid state memories by at least 100 times, but it would also be much faster being able to write individual bits at a time. If the new solid state device succeeds in replacing flash, it would be the first time in more than three decades that memory manufacturing processes go through a significant change in technology.
"We don't see the classic field-effect transistor running out of Steam for at least 10 years. While it's true that some materials are misbehaving, new materials are always coming along to fix things. It's going to be cost, not technology, that will be the driving factor. That's the bottom line Numonyx has to address," says Malcolm Penn of the Future Horizons.