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Reference : UPR8011-ALACLA-004
Workplace : TOULOUSE
Date of publication : Tuesday, September 01, 2020
Type of Contract : FTC Scientist
Contract Period : 12 months
Expected date of employment : 19 October 2020
Proportion of work : Full time
Remuneration : 2500-4000 monthly gross depending on experience
Desired level of education : PhD
Experience required : 1 to 4 years
To contribute to the various objectives of the project using different techniques, notably but not only advanced transmission electron microscopy techniques such as STEM/HAADF, ELS and EDX. This “expert” will interact with the group members (permanent and postdocs) and complement their findings by providing information on the redistribution of chemical elements following thermal annealing or PCM cell operation.
The one-year contract is renewable up to 2 times.
- Preparation of samples for TEM, by conventional techniques (mechanical, PIPS ...) and FIB.
- Operation of electron microscopes in complete autonomy and mastery of STEM, HAADF, EELS and EDX techniques.
- Data extraction and visualization.
- Writing reports and articles.
We are looking for a doctor in Physics or Materials Science with demonstrated experience in metallurgy and/or microelectronics using advanced transmission electron microscopy techniques (HREM, STEM, HAADF, ELS, EDX …). Open minded and autonomous, he/she is willing to interact with others scientists and contribute to a common goal. He is motivated by the development of fundamental and applied research in collaboration with a major industrial player in the field of advanced electronic devices.
Standard embedded flash memories used for automotive and IOT businesses are facing for the most advanced nodes (28 nm and below) physical challenges limiting the reduction of switching speed, power consumption and eventually cost. Phase Change Memory (PCM) appears as a promising alternative technology to overcome the limitations of flash memories. Phase Change Memories employ thin films of chalcogenide materials, a GeSbTe (GST) alloy, that is locally and reversibly switched between its crystalline and amorphous phase states using heating pulses (i.e. through electrical pulses). Information is contained in the pronounced difference of electrical conductivity between crystalline and amorphous phases of the GeSbTe alloy.
Despite huge potentiality, developing and industrializing PCMs for advanced nodes still require in depth understanding of the physical phenomena involved in the switching mechanisms, this in the frame of scaled down dimensions. At the moment, most IC manufacturers are exploring the potential of such materials, in collaboration with academics, and this project is no exception.
In fact very little is known of the physical and chemical changes which result in the electrical switch of the cell and on the degradation mechanisms which affect it. For this reason, some fundamental work is needed to understand the mechanisms by which the material transits from the amorphous to crystalline phases (and vice versa), the impact of the geometry, of the size, and on the surrounding media of the cell onto the final characteristics of the material and associated device. Moreover, desired cell characteristics are obtained using GST materials of clearly non-stoichiometric compositions, what increases even more the need for in-depth understanding of the atomic mechanisms involved and thus of nanometer scale characterization. During the last year, we have already explored some metallurgical aspects of the amorphous to crystalline transition in Ge-rich GST alloys, got some experience and noticeable results (1-5).
In this context, CEMES is now collaborating with STMicroelectronics within a large project from which this position is granted. The project goals focus at:
1) Identifying the mechanisms and parameters governing crystallization in Ge-GST materials and the changes resulting from doping with N and H.
2) Understanding the influence of morphology of GST domains (phases, grain sizes…) on the electrical characteristics of the material and on the performance and reliability (drift, retention / cycling) of PCMs based on these materials.
3) Scaling and extracting from dedicated experiments Ge, Sb and Te self-diffusivities in GST alloys.
4) Highlighting and understanding the effects of the environment (confinement, stress, oxidation, interfaces ...) on the properties of GST cells.
To reach these objectives, we have set up a group of three permanent scientists of complementary expertise (experiments and theory, materials science, structural and electrical properties), one expert engineer from STMicroelectronics, 2 postdocs and one PhD student. While already extensively using XRD, SIMS, C(V), CTEM (in situ and ex situ), HREM and EDX, we are willing to extend the characterization skills of the group by integrating a new postdoc with excellent and recognized expertise in advanced TEM techniques, notably for elemental mapping at the nanoscale
The work will be carried out under the guidance of Alain CLAVERIE, within the MEM group at CEMES / CNRS in Toulouse. (www.cemes.fr)
Publications from our group:
1) M. Agati et al., MRS Communications (2018), doi:10.1557/mrc.2018.168
2) M. Agati et al., J. Mat. Chem. (2019), doi: 10.1039/c9tc02302
3) R. Sinha Roy et al., Phys. Rev. B, 99, 245124 (2019).
4) M. Agati et al., Applied Surface Science 518 (2020) 146227, doi : 10.1016/j.apsusc.2020.146227
5) A. Bourgine et al., Solid State Electronics, in print. doi.org/10.1016/j.sse.2020.107871
Constraints and risks
No specific risks identified.
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