Phase Change Memory


Picture Professor Wuttig


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  Simulated structure of a phsae change material. FZ Jülich Simulated structure of a phase change material. On the left side of the cube the chemical composition is depicted while the right side shows the distribution of the density of states.

Phase change memory describes optical and electrical data storage mediums where information is saved by switching locally between an amorphous and crystalline phase in a non-volatile manner. Using der reflectivity or electrical resistivity the state of a storage region can be identified during a reading process.

The materials used in this kind of application are called phase change materials. This material class stands out by having a strong contrast in the optical or electrical properties of the phases which is required for a proper differentiation. Stability of the phases, speed and energy requirement of the transition as well as endurance are critical parameters of the materials used.

Phase change materials are used in all established rewritable optical storage mediums (CD-RW, DVD+-RW, DVD-RAM, BD-RE). The storage region to be switched is heated by a laser pulse which induces a transition. The information can then be read by measuring the reflectivity.

  TEM-Picture of AIST. In the center there ist an amorphous bit visible on a crystalline background. I. Physikalisches Institut Bright field image of an amorphous bit in a crystalline phase change material (AIST). The phases can be easily distinguished optically.

In so-called Phase Change RAM (PCRAM or PRAM) the storage regions are switched and read with an electrical pulse. In the near future memories of this type will be available for advanced memory applications. Potentially low produciton costs, high data densities and high writing speeds make PCRAM very attractive and it does not surprise that well-known companies in the semiconductor industry are intensely working on prototypes.

The phase change memory group of the I. Institute of Physics (IA) stands out in this research field with a broad collection of experimental methods and theoretical models. With an Advanced Grant of the European Research Council with the title Disorder Control we research possibilities to control disorder and thus transportation properties in phase change materials. In the scope of the special research field SFB-917 of the Deutsche Forschungsgesellschaft we work on resistive nanoswitches where the correlation of switching behavior and defects are investigated. Together with further cooperations and promotions we have numerous research possibilities which are potentially ground-breaking for future information technology.