Computer designers have long desired a universal memory technology to replace the combination of RAM—which is fast but expensive and volatile, meaning it requires a power supply to retain stored information—and flash, which is nonvolatile but relatively slow.
The urgency is increasing as Moore’s Law, which for so long governed the blistering pace at which silicon transistors shrank, begins to peter out. If we can’t fit many more transistors on a RAM chip, we need to find a fast, cheap new nonvolatile memory technology that can store vast amounts of data.
One promising alternative to the combination of RAM and flash is phase-change materials. This new type of memory stores data not by turning electric current on and off in transistors but by switching a type of material called chalcogenide glass between amorphous and crystalline states. Potentially, it is fast like RAM and nonvolatile like flash. Since 2010, Desmond Loke and his colleagues have solved several critical problems holding up its commercialization.
As a result of the advances, the Singapore researcher has now created a version of phase-change memory that is as fast as RAM chips and packs in many times more storage capacity than flash drives.
For years, researchers have been unable to get the speed at which a material changes from an orderly crystal to amorphous glass—the 1 and 0 states—any faster than about 50 nanoseconds, whereas RAM chips take less than a nanosecond to switch transistors on or off. But by applying a small, constant charge to the material, Loke found he could reduce switching time to half a nanosecond. He and his coworkers also reduced the size of a memory-cell bit to just a few nanometers. And he figured out how to vastly reduce power consumption and allow cells to be stacked in three dimensions to pack in even more memory capacity.