Multiscale Simulation of Phase Change Memory (PCM)

Manjeri P. Anantram, University of Washington, DMR 1006182

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To probe the ultimate scalability of phase change material, we applied ab initio simulation to investigate electron transport properties of GeTe ultrathin films which are sandwiched by realistic electrode material TiN (Fig. 3). It is shown that the ultrathin films can be scaled to 3.3 nm (11 atomic layers) and still support one order of magnitude electrical conductance ON/OFF ratio, suggesting extremely promising scaling scenario.

The ab initio simulation consists of four steps: (1) amorphous GeTe is obtained using melt-quench ab initio molecular dynamics; (2) TiN-GeTe-TiN systems are created using conjugate gradient algorithm; (3) density functional theory is used to obtain tight binding Hamiltonian; and (4) Green’s function is used to obtain low-bias conductance.

J. Liu, M.P Anantram, “Low-bias electron transport properties of GeTe ultrathin films”. (submitted).

Fig 3. Simulation model (upper) and result (below) of GeTe ultrathin films. The amorphous (Ga) and crystalline (Gc) phase conductance are in S/Å2.

The PCM technology is one of the most promising candidates for future-generation ultra-dense memory and logic devices. Under the support of NSF, we are actively performing research on material scalability, energy efficiency, and multi-level data storage behavior of PCM technology.

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J. Liu, B. Yu, M.P Anantram, IEEE Elect. Dev. Lett. 32, 1340, 2011.

Multiscale Simulation of Phase Change Memory (PCM)

Manjeri P. Anantram, University of Washington, DMR 1006182

To investigate energy efficiency during scaling, finite element method (FEM) has been used to analyze Ge2Sb2Te5 (abbr. GST; most widely-used phase change material for PCM devices) model shown above. It is shown that more than 90% of the operation energy is wasted in the current PCM design. This ratio will largely remain the same if the device is scaled by k (k>1) times (left figure). Our results indicate that the energy efficiency of PCM devices can be significantly increased by enhancing thermal insulation, e.g. increasing thermal boundary resistance (TBR).

Fig 2. RESET energy consumption if PCM device is isotropically downscaled by k times (k>1).

Fig 1. Model geometry and material parameters used in the scaling simulation of PCM devices.

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Broader Impacts

Manjeri P. Anantram, University of Washington, DMR 1006182

Undergraduate Research:•Three undergraduate students were involved in research•Simulation framework developed by graduate student was used to undergraduate students to model Phase Change Memory•Two undergraduate students presented posters on their work during a campus wide Undergraduate Research Symposium

Courses:•The operation principle of Phase Change Memory was covered in a Devices class taught by the PI •Phase Change Memory was one of the topics offered in the Devices course as a project. Students wrote reports on the principles of phase change materials and application to memory devices.