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Ô-GST: Materials Science for Phase Change Memories

CEMES joins STMicroelectronics within the EC IPCEI Project on Microelectronics.

by PREVOTS Evelyne - published on , updated on

The ambition of the project is to provide European microelectronics companies with a foundation of knowledge in materials science to optimize the composition and processing of GeSbTe-based alloys used in the manufacture of phase change memories.


The standard built-in flash memory devices used in the automotive and Internet Of Things (IOT) industries are facing, at the most advanced technology nodes (28 nm and below), difficult physical challenges limiting switching speed, energy consumption and costs. Phase change memories (PCMs) are emerging as a promising alternative technology to overcome these limitations. These PCM memories use thin layers of chalcogenide materials, a GeSbTe alloy (GST), which is locally and reversibly switched between its crystalline and amorphous states using electrical pulses (Joule heating). The information is contained in the marked difference in electrical conductivity between the crystalline and amorphous phases of this alloy.


Le projet Ô-GST :

Very little is known about the physical and chemical changes that result in the electrical switching of the cell and the degradation mechanisms that affect it. For this reason, a fundamental work is needed to understand the mechanisms by which the material passes from amorphous to crystalline (and vice versa), the impact of the geometry, size, and surrounding support of the cell on the final characteristics of the cell. material and associated device. In addition, the desired characteristics are obtained using GST materials of clearly non-stoichiometric compositions, which further increases the need to understand in depth the atomic mechanisms involved and therefore to characterize them at the nanoscale.

In this context, CEMES is collaborating today with STMicroelectronics as part of a major European project (IPCEI, nano2022). Together, as part of the "O-GST" project, we will aim to:

  1. Understand the mechanisms and parameters governing phase transitions in PCM GST materials and resulting changes in electrical conductivity.
  2. Understand the influence of the morphology of GST domains (particle size, multiphases, etc.) on the electrical performance and reliability (drift, retention / cycle) of PCM.
  3. Feed in the models: study and measure the diffusivity of Ge, possibly Te and Sb, in amorphous and crystalline GST alloys.
  4. Scalability of the PCM: highlighting and understanding the effects of the environment (containment, stress, oxidation, interfaces, etc.) on the properties of GST cells.

The project (2019-2022) will be based on two Cifre theses and six years of postdoctoral contract.



M. Agati, F. Renaud, D. Benoit, A. Claverie, In-situ transmission electron microscopy studies of the crystallization of N-doped Ge-rich GeSbTe materials, MRS Comm. 8, 1145 (2018).

Marta Agati, Maxime Vallet, Sébastien Joulie´, Daniel Benoit and Alain Claverie, Chemical phase segregation during the crystallization of Ge-rich GeSbTe alloys, J. Mater. Chem. C, 2019, 7, 8720. DOI: 10.1039/c9tc02302j

R. Sinha-⁠Roy, A. Louiset, M. Benoit, and L. Calmels, Electronic structure and conductivity of off-⁠stoichiometric and Si-⁠doped Ge2Sb2Te5 crystals from multiple-⁠scattering theory, Phys. Rev. B 99, 245124 (2019).


RElated links IPCEI Microelectronic






Dr. Alain Claverie