Materials used in CDs and DVDs form the basis of a technology that one day could replace flash memory cards used in laptops, cellphones, cameras and other electronic devices.
Flash memory cards store data in the form of electrical charge, with the presence of charge signifying a 1 and its absence a 0. The charge is stored in a combination of a capacitor and a transistor, etched into silicon chips. So far, chip makers have relied on making these elements ever smaller - today's flash memory transistors are just 65 nanometers wide and the next generation will be a mere 45 nanometers.
Experts say that serious issues begin to arrise when dimensions get below 20 nanometres as parasitic charge builds up on the transistor every time new data is written, limiting the cards' use to around 10 000 write and erase cycles. As the transistor gets smaller the problems increase.
Engineers from Numonyx, a spin off company from STMicroelectronics and Intel Corporation, have been working on Phase Change Memory since 2003. Phase Change Memory (PCM), is a promising new memory technology providing very fast read and write speeds at lower power than conventional flash, and allows for bit alterability normally seen in RAM. It incorporates the best of existing memory technologies and combines into one memory device.
It is not based on floating gate technology but chalcogenide material known as GST which is used in rewritable CDs and DVDs. A chalcogenide is a compound consisting of at least one chalcogen ion and at least one more electropositive element. All Group 16 elements of the periodic table are defined as chalcogens but the term is more commonly reserved for sulfides, selenides, and tellurides, rather than oxides.
PCM Improves as it scales to smaller dimensions. As the PCM memory cell shrinks the volume of GST material also shrinks requiring less power to affect the state change. This savings in power will enable PCs and chips to increase in performance relative to existing technologies. It will lower memory costs and generate new applications and memory uses in a wide range of systems.
Like flash, PCM is a non-volatile memory that can store bits even without a power supply. But unlike flash, data can be written to cells much faster, at rates comparable to the dynamic and static random-access memory (DRAM and SRAM) used in all computers and cell phones today. Numonyx engineers have used this technique to build a chip with 128 megabits of what they call PCM.
According to the New Scientist, researchers at IBM have already demonstrated that a PCM memory cell can be shrunk down to about 5 nanometers wide. As PCM does not accumulate parasitic charge, it can be rewritten at least a million times. PCMs will not be economically viable for awhile.