IBM: Phase Change Memory to Operate Beyond 150°C

The patent, which was filed as an application in November 2009 and approved on July 31, 2012, describes a memory cell that uses techniques such as insulation material as well as growth-dominated phase change material to achieve "superior" memory qualities at increasing temperatures. The inventors explain that a current  sent through the phase change material creates ohmic heating and causes the phase change material to melt.

Phase change memory is based on the idea of taking advantage of behavior of chalcogenide glass, which can assume crystalline and amorphous states, depending on the temperature. Gradual cooling results in a crystalline state of the material and abrupt cooling quenches the phase change material into the amorphous state. Once quenched, the crystallization temperature decreases "and the amorphous region is surrounded by a crystalline layer which acts as a seed for growth," the patent states. The problem: "If the phase change memory cell is raised to a higher temperature, the data stored within the memory cell may be lost or degraded due to changes in the size and shape of the amorphous region."

IBM's solution is a phase change memory cell with the characteristics of

• A bottom electrode
• A top electrode separated from the bottom electrode
• Growth-dominated phase change material deposited between the bottom electrode and the top electrode and contacting the bottom electrode and the top electrode and surrounded by insulation material at sidewalls thereof
• The phase change memory cell in a reset state only includes an amorphous phase of the growth-dominated phase change material within an active volume of the phase change memory cell
• The phase change memory cell comprises a current path that includes interface regions between the bottom electrode
• The growth-dominated phase change material and the top electrode such that a reset current at a predetermined value above the nominal reset condition flows along the current path
• The growth-dominated phase change material is fully amorphized after the reset operation, and wherein the interface regions comprise gallium (Ga) atoms

There is no information of a commercial application of the patent.

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