Experimental and theoretical study of physical mechanisms governing oxide-based Resistive Memory devices operation

Post-doc starting date: mid 2011 (flexible); Duration: 1 year

The Applicants :

The Post-Doc Topic Description:

Context - The ITRS (International Technology Roadmap for Semiconductors) pushes toward the development of new microelectronic devices based on original physical mechanisms, offering new memory functions and optimized performances. In particular, recently, resistive memories (RRAM) have attracted a lot of attention: a commutation effect inside metal oxides is responsible for the switching between a low and a high resistance state and suitable for non volatile memory applications. However, the basic physical mechanisms at the heart of this type of resistive memories are still unclear and controversial. Various mechanisms are invoked to describe the resistive switching: phonon assisted tunnelling, creation and annihilation of one or several conductive filaments, oxygen diffusion assisted by an electric field, electrode solubility etc. Thus the understanding has to be largely improved in order to sustain the development of this new technology.

Post-Doc work - The aim of the postdoctoral position will be to couple an experimental and theoretical study of the physical mechanisms governing the Resistive switching memory operation. The candidate will have two tasks: (1) electrical characterization and (2) physical simulations of the memory devices. In particular:
1) The candidate will analyze the performances of the memory samples using electrical characterization setups (located both in CEA-LETI and in IMEP-LAHC) at the state of the art. In particular, a strong attention will be devoted to the evaluation of switching power versus retention compromise, necessary before Resistive switching memories could be put in production. These measurements of memory will be associated with the material features, obtained in collaboration with the characterization laboratory, and using a panel of physical characterization techniques (XRR, XRD, XPS, SIMS, MIR, TEM/EELS).
2) Then the experimental results will be coupled with an in depth theoretical study, comprising:
- Ab initio simulations in combination with Molecular Dynamics to study the “on-state’ to “off-state” switching. In particular, formation and disruption processes of the filament will be addressed, by studying anions and cations migration inside the oxide matrix. The role of electrodes and Oxygen charge effects will also have to be clarified. Finally the activation energy for this switching will have to be evaluated to analyze the reliability and retention issue.
- Based on this previous study at the atomistic scale, a multi physical model will be developed, including the top and bottom electrodes for the switching, with expectation in providing a guiding principle for the combination of RRAM oxides and electrodes.
The studied memory devices will be processed at CEA LETI MINATEC, investigating various technological configurations: insulator and electrodes materials, process conditions.

The Post-Doc Framework

The Post-Doc will be founded by the Nanosciences Foundation in the frame of the Prof. Nishi Chair of Excellence Project. The Prof. Nishi  Chair of Excellence Project deals with Resistive Memory Devices and aim to bring an important contribution to resistive memory technology assessment for new applications, especially for reconfigurable circuits, through the establishment of reliable electrical characterization methodologies, reliable physical models of switching elements for circuit design, proposition of reprogrammable circuits implementing resistive switching elements, proposition of new circuit architectures implementing nanoscale switching elements. The combination of the technological know-how and facilities of Leti, the electrical characterization knowledge of IMEP-LAHC with the scientific expertise of Prof. Nishi from Stanford University will allow to reach those targets.

The Laboratory

Under the direction of Prof. Nishi, the PhD work will be performed in the Advanced Memory Technologies Laboratory of CEA-LETI (http://www-leti.cea.fr/en), a world leader laboratory in the creation and transfer of innovation from technologies to applications within Europe. The student will work in strict collaboration with the IMEP-LAHC academic laboratory (http://imep-lahc.grenoble-inp.fr/index.jsp).  LETI and IMEP-LAHC are part of the Grenoble MINATEC innovation campus (http://www.minatec.com/en), which is home to 2,400 researchers, 1,200 students, and 600 technology transfer experts on a state-of-the-art 20-hectare campus offering 10,000 square meters of clean room space. MINATEC is located in the Grenoble-Isère French region, otherwise known as France’s Silicon Valley, A unique scientific, industrial and cultural environment, With its research centers, university campus, 500 foreign companies and 40,000 scientists, engineers and technicians employed in the area.

The Post-Doc Advisors

Prof. NISHI Yoshio

Stanford University

(650) 723-9508

Email:     Yoshio.nishi@stanford.edu

Dr. MOLAS Gabriel
Advanced Memory Technology Laboratory
CEA LETI MINATEC Campus
17 rue des Martyrs, 38054 Grenoble CEDEX 9
+33 4 38 78 92 56
Email : gabriel.molas@cea.fr 

Dr. BLAISE Philippe
Laboratory of Simulation and Modeling
CEA LETI MINATEC Campus
17 rue des Martyrs, 38054 Grenoble CEDEX 9
+33 4 38 78 48 94
Email : philippe.blaise@cea.fr

Prof. GHIBAUDO Gérard
IMEP-LAHC MINATEC Campus
+33 4 38 78 48 94
Email : ghibaudo@minatec.inpg.fr