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                                           PhD position 2020-2023
Simulation of 2D transition metal dichalcogenides for memory devices

at IMEP-LAHC / MINATEC / GRENOBLE UNIVERSITY – FRANCE KEYWORDS

KEYWORDS :
Density functional theory, quantum charge transport, nanoelectronics, numerical simulation.

PROJET DESCRIPTION:
Since the discovery of graphene in 2004, many other layered materials have been synthetized. Among them, transition metal dichalcogenides have attracted a strong interest for applications in nanoelectronics thanks to their semiconducting nature with a variety of band gaps, and their atomic thickness, which allows an excellent electrostatic control. The possibility of stacking different layers has opened the path to innovative vertical devices, such as tunnel field-effect transistors for low-power electronics and printable electronics. The understanding of the electron transport through vertical 2D systems thus represents an important challenge for the future development of 2D electronics.

The goal of the PhD is to theoretically and numerically investigate these vertical structures by exploring their electronic and transport properties. The focus will particularly be on atomristors, which are sandwiches of semiconducting 2D materials and metallic contacts. These systems have been shown to change their electrical resistance to high or low values when traversed by a large current. Such a phenomenon is due to modifications of the atomic structure, which are not clearly identified at present. It allows the use of these devices as memories or in radiofrequency switches, which is the goal of the ANR SWIT project.

These systems have an intrinsically quantum behavior, in the sense that the wave nature of electron governs the transport properties at the interfaces and in the 2D layers. Their simulation thus requires the use of a general electron transport approach, such as the non-equilibrium Green’s function formalism, as well as an ab initio atomistic description of the electronic structure based on the density functional theory.

The student will be asked to:

• Calculate the electronic structure of sandwiches of transition metal dichalcogenides and metallic contacts by means of density functional theory simulations. The height of the resulting Schottky barriers will be estimated.
• Calculate the electronic structure and the transport properties of the vertical structures in the presence of vacancies, substitutional impurities, dislocations or grain boundaries. The results will clarify the role of disorder in determining the resistance of the high-resistance state in atomristors.
• Investigate the energetic stability of islands of the transition metal dichalcogenide with different structural phases or migrated metal atoms, and simulate their impact on the transport properties of the vertical structure. The aim is to understand the physical mechanism of the switching in atomristor and to explore the low-resistance state.

This work will require learning and using numerical codes for ab initio calculations and quantum transport simulations.

There will be regular interactions with the experimental colleagues of CEA-LETI and IEMN in the frame of the SWIT project. The results of the student will be important to identify the ideal combinations of transition metal dichalcogenides and metallic contacts to obtain devices with a very high resistance in the off state, and to clarify the switching mechanism.

CANDIDATE PROFILE :

•  Training in physics and/or electronics, with a solid knowledge of condensed matter physics
• Basic knowledge of computer programming for numerical simulation
•  Previous experience with density functional theory will be a plus

The candidate must hold a master degree (equivalent to a master M2R in France) or an equivalent university degree eligible for the EEATS Doctoral School of Université Grenoble Alpes.

DETAILS :
Co-supervisors: Alessandro CRESTI (IMEP-LaHC), François TRIOZON (CEA-LETI)
Funding: ANR project SWIT (SWItches based on Transition metal dichalcogenides for RF applications)
Thesis starting date: October/November 2020
Thesis duration: 3 years

ABOUT THE RESEARCH INSTITUTES :
IMEP-LaHC  is a “unité mixte de recherche” involving Grenoble INP, Université Grenoble Alpes, Université Savoie Mont Blanc and CNRS.
It is located within the Minatec innovation pole, in Grenoble. The laboratory employs 49 researchers, 15 engineers and technicians, 3 postdoctoral fellows, and 42 PhD students.
It has collaborations with several universities and research centers, large industrial groups (ST-Microelectronics, IBM, Motorola, etc.), and preindustrial microelectronics centers (LETI, LITEN, IMEC, Tyndall).
CEA-LETI  is a research institute for electronics and information technologies employing more than 1000 researchers, engineers and technicians.
It hosts a large technological platform (clean rooms, physico-chemical characterization). It is mainly funded by industrial partnerships.
It relies on a strong scientific expertise: partnerships with CEA/DRF (Fundamental Research Division) and academic institutes (CNRS, Universities) via national and European funding.
The PhD student will work within the team “Composant MicroNanoElectronique” of IMEP-LaHC and in very close collaboration with the team “Simulation et Modélisation” of LETI.

CONTACTS :
Send a CV, a letter of motivation, photocopies of diplomas and academic record with ratings, and two recommendation letters to:
Dr. Alessandro Cresti, CNRS researcher at IMEP-LaHC, email: alessandro.cresti@grenoble-inp.fr
Dr. François Triozon, researcher at CEA-LETI, email: francois.triozon@cea.fr

The position will remain open until it is filled.

• Keywords : Engineering sciences, Electronics and microelectronics - Optoelectronics, FMNT, IMEP-LaHc
• Laboratory : FMNT / IMEP-LaHc
• CEA code : IMEPLAHC-CMNE-08-20-2020
• Contact : alessandro.cresti@grenoble-inp.fr
• This Thesis position has been filled. Thank you for your interest