Scientists from IBM, Macronix and Qimonda today disclosed joint
research results that detail a new type of computer memory with the potential
to be the successor to flash memory chips. The advancement is "phase-change"
non-volatile memory, which appears to be much faster and can be scaled to
dimensions smaller than flash. Non-volatile memories do not require electrical
power to retain their information. By combining non-volatility with good
performance and reliability, this phase-change technology may one day be a
universal memory for mobile applications.
Working together at IBM Research labs on both U.S. coasts,
the scientists designed, built and demonstrated a prototype phase-change memory
device that switched more than 500 times faster than flash while using less
than one-half the power to write data into a cell. The device’s cross-section
is a minuscule 3 by 20 nanometers in size, far smaller than flash can be built
today and equivalent to the industry’s chip-making capabilities targeted for
2015. This new result shows that unlike flash, phase-change memory technology
can improve as it gets smaller with Moore’s Law advancements.
Flash memory cells, while also non-volatile, degrade and
become unreliable after being rewritten about 100,000 times. This is not a problem for many consumer uses, but is a showstopper in applications that must be
frequently rewritten, such as computer main memories or the buffer memories in
network storage systems. A third concern for flash’s future is that it may
become extremely difficult to keep its current cell design non-volatile as designs shrink below 45 nanometers.
The IBM/Macronix/Qimonda joint project’s phase-change memory
achievement is important because it demonstrates a new non-volatile
phase-change material that can switch more than 500 times faster than flash
memory, with less than one-half the power consumption, and most significantly,
achieves these desirable properties when scaled down to at least the 22-nanometer
node, two chip-processing generations beyond floating-gate flash’s predicted
At the heart of phase-change memory is a tiny chunk of a
semiconductor alloy that can be changed rapidly between an ordered, crystalline
phase having lower electrical resistance to a disordered, amorphous phase with
much higher electrical resistance. Because no electrical power is required to
maintain either phase of the material, phase-change memory is non-volatile.
The material’s phase is set by the amplitude and duration of
an electrical pulse that heats the material. When heated to a temperature just
above melting, the alloy’s energized atoms move around into random
arrangements. Suddenly stopping the electrical pulse freezes the atoms into a
random, amorphous phase. Turning the pulse off more gradually – over about 10
nanoseconds – allows enough time for the atoms to rearrange themselves back
into the well-ordered crystalline phase they prefer.
The new memory material is a germanium-antimony alloy (GeSb)
to which small amounts of other elements have been added (doped) to enhance its
properties. Simulation studies enabled the researchers to fine-tune and
optimize the material’s properties and to study the details of its
crystallization behavior. A patent has been filed covering the composition of
the new material.
The view a couple animations of how phase-change memory works, click here. The technical details of this research will be presented
this week at the IEEE’s 2006
International Electron Devices Meeting in San Francisco.