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Materials

Concept A phase change memory (PCM) is a non volatile memory. The PCM adopts a chalcogenide compound, the same being used in CD-RW and DVD, as storage material. Changing the phase of the chalcogenide material results in a change of PCM resistance, which is used for bit storage.

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Materials

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  1. Concept A phase change memory (PCM) is a non volatile memory. The PCM adopts a chalcogenide compound, the same being used in CD-RW and DVD, as storage material. Changing the phase of the chalcogenide material results in a change of PCM resistance, which is used for bit storage. CAMELS explores the feasibility of multilevel storage, that is the capability of storing more than one bit per physical cell. STEM picture of a PCM device, showing amorphous (a) and crystalline (c) phases of the chalcogenide material (GST). Read current level in a 2-bit multilevel PCM. Materials One of the main priorities of CAMELS is the optimization of the chalcogenide material. The PCM operation and reliability are in fact dictated by the physical and electrical properties the chalcogenide. Advanced materials production and deposition techniques, optical/electrical characterization and first-principle calculations are just few of the CAMELS tools to this purpose. In the framework of CAMELS, a first treasure map for phase-change materials has been developed (Nature Mater., in press). Optical power-time-phase characteristics for GeSb2Te4. Red region corresponds to crystalline, black to amorphous phases. Pictorial view of the rock-salt structure of GeSb2Te4, including vacancies. CAMELS ChAlcogenide MEmory with multiLevel Storage Objective The Project aims at demonstrating the feasibility of multilevel storage in chalcogenide-based phase change memory (PCM), and at defining material properties, cell architectures and programming conditions to achieve this objective. Scenario Several emerging technologies compete for high-density and high performance storage in a memory-hungry semiconductor market. CAMELS in numbers A STREP of the EU-FP6, CAMELS started in 2005 and will finish in the fall of 2008. Funding is 1.6M€, for an overall budget of 2.67M€. CAMELS puts together a consortium of 5 industrial/academic institutions with about 35 researchers involved.

  2. Architecture The multilevel approach calls for specific characteristics of the cell, particularly in terms of cell reliability, programming and scaling. To this purpose, improved cell architectures for fast programming, precise write/read of resistance and superior reliability have to be explored. Disturbed cell Programmed cell Numerical simulation of melting in a PCM cell, aimed at assessing possible excess heating (disturb) in neighbour cells in the array. Numerical simulation of a PCM cell. Confinement of the current into a sub-lithographic path is essential for efficient phase change. Algorithms Accurate programming and sensing of stable resistance levels requires improved algorithms. The project aims at exploring this aspect by new characterization techniques, new metrics and new circuits for optimized programming and reliability of the multilevel PCM. Electrical test-bench for integrated multilevel PCM devices. Read-current distributions for a multi-Mb multilevel PCM array, demonstrating the stability after high temperature bake. Consortium Partners Numonyx (I) Politecnico di Milano (I) RWTH Aachen (D) University of Pardubice (CZ) Umicore TFP (FL) Coordinator Roberto Bez Numonyx roberto.bez@numonyx.com Website http://ia.physik.rwth-aachen.de/camels/ 00 01 10 11

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