18 September 2007

Phase Change Memory Using Nanowires

The quest to create fast, non-volatile phase-change memory dates to Stanford Ovshinky's 1966 patent application. Since then, many companies such as Intel, have made significant progress toward developing such a potentially revolutionary memory technology. The latest advance comes from a UPenn team that used nanowires to fabricate a phase change memory.
Ritesh Agarwal, an assistant professor in the Department of Materials Science and Engineering, and colleagues developed a self-assembling nanowire of germanium antimony telluride, a phase-changing material that switches between amorphous and crystalline structures, the key to read/write computer memory. Fabrication of the nanoscale devices, roughly 100 atoms in diameter, was performed without conventional lithography, the blunt, top-down manufacturing process that employs strong chemicals and often produces unusable materials with space, size and efficiency limitations.

Instead, researchers used self-assembly, a process by which chemical reactants crystallize at lower temperatures mediated by nanoscale metal catalysts to spontaneously form nanowires that were 30-50 nanometers in diameter and 10 micrometers in length, and then they fabricated memory devices on silicon substrates.

“We measured the resulting nanowires for write-current amplitude, switching speed between amorphous and crystalline phases, long-term durability and data retention time,” Agarwal said.

Tests showed extremely low power consumption for data encoding (0.7mW per bit). They also indicated the data writing, erasing and retrieval (50 nanoseconds) to be 1,000 times faster than conventional Flash memory and indicated the device would not lose data even after approximately 100,000 years of use, all with the potential to realize terabit-level nonvolatile memory device density.

“This new form of memory has the potential to revolutionize the way we share information, transfer data and even download entertainment as consumers,” Agarwal said. “This represents a potential sea-change in the way we access and store data.”

The history of computer memory research is littered with failed concepts that offered great promise, but could not deliver for technical or economic reasons. Phase change memory technology is a relatively simple concept and should not be expensive, once developed. It will be much faster and more radiation resistant than flash memory, and will last much longer. Memory density should also be better than flash, and since it is non-volatile, it may become a replacement for hard disk drives. If it can be made fast enough, it may also replace volatile RAM memory.

In other words, regardless of whether phase change memory is implemented from the top down (lithography) or the bottom up (nano-wires), the underlying technology is likely to come standard, at least in top of the line machines, in the near future.

Hat tip Brian Wang.

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