In phase change memory, data are stored by switching small regions of a "phase-change" material between one of two phases: a highly resistive amorphous phase, and a highly conductive crystalline phase. Switching is done by using voltage/current pulses to control time and temperature within this small volume.

Phase change memory has a number of advantages as a prospective next-generation solid-state memory, including

• Solid-state memory array & potential for CMOS compatibility
• Large resistance contrast
• Media familiarity from CD-RW
• Inherently fast transformation

However, there remain a number of open research questions, including

• Will the phase-change still work the same as we scale down?
• To RESET to high-R, we melt a portion of the cell
• Will this take more power than our access device can deliver?
• Will these high temperatures lead to crosstalk? to degradation?
• Can we get both speed and long-term retention?
• Can we integrate this with CMOS & make all the bits identical?
• Is there a long-term roadmap to even higher density, using >1 bit/cell or 3-D?

At Almaden, our work (some of which is done in collaboration with the IBM/Macronix/Qimonda Joint Project on Phase Change Memory) concentrates on:

• Materials science & characterization - we fabricate & characterize new phase-change materials, using a combination of techniques. These include well-established tools such X-ray diffraction, TEM, and AFM, as well as our own custom-built platforms for optical, electrical, and thermal characterization.
• Simulation & modeling - we have developed a custom simulation tool, which uses finite-difference techniques to allow full 3-D modeling of phase-change devices as well as calibration against material characterization experiments.
• Device prototype & testing - we use a combination of cutting-edge e-beam and conventional lithography in order to build both nanostructures for materials characterization as well as nano-devices for prototyping and electrical characterization.

One example of our recent efforts resulted in a recent, well-publicized paper at IEDM 2006. You can read more about this work here.