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Investigation and improvement of spin-orbit torque for magnetic commutation of advanced mRAM elements (H/F).

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Français - Anglais

Date Limite Candidature : lundi 4 juillet 2022

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General information

Reference : UMR137-HENJAF-007
Workplace : PALAISEAU
Date of publication : Monday, June 13, 2022
Scientific Responsible name : Henri JAFFRES
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

This thesis program concerns the experimental study of the spin-orbit torque (SOT) for magnetic switching by SOT-MRAM. The SOT results from the interaction between a spin current and the local magnetization acting as a memory bit. It is currently a hot topic in spintronics, both for the fundamental aspect and for the realization of a new generation of spintronic devices such as memories or logics.
SOT can be associated to several spin-charge conversion mechanisms that we are trying to optimize from the spin-orbit interaction (SOI) such as the spin Hall effect (SHE) of heavy metals (e.g. 5d series such as Pt, Ta, W), or the Rashba Edelstein effect (REE) acting on surface states of topological insulators (such as Bi). These effects control the amplitude and symmetries of the SOT components for magnetic reversal for typical critical current densities of the order of jc = 10^11 A/m2.
A major goal of the thesis will be to reduce this critical current density Jc by an order of magnitude that would represent a significant net benefit. This thesis program addresses these perspectives by developing new dedicated multilayers.

The thesis will be mainly developed at the Unité Mixte de Physique CNRS, Thales, U. Paris-Saclay (UMPhy) and will require the use of different equipments (sputtering; micro-nano lithography; Kerr effect, MFM, THz-TDS spectroscopy, f-2f second harmonic methods, switching measurements with possible use of a 9T cryostat). This thesis will be conducted in close collaboration with Kevin Garello from the SPINTEC laboratory (Grenoble) for the fabrication and measurements of nanometric magnetic tunnel junctions.

Work Context

A) Optimization of SO Torques amplitudes and control of their symmetry (UMPhy)

These tasks will be realized on experimental devices with micronic size elements elaborated at UMPhy : sputtering growth, lithography, characterization methods like THz spectroscopy in the time domain (THz-TDS), f-2f second harmonic measurements of SOT. The experiments will be accompanied by numerical analyses and calculation of material/multilayers/heterostructures spin-orbit properties and spin-charge conversion efficiency required for SOT.

Several parameters and issues will be addressed to this aim:

1) SHE materials made of 5d heavy materials combination
2) SHE materials made of Bi-based topological insulators (Bi2Se3)
3) Improvement of properties of the magnetic material
4) Investigation of multilayered stacks to improve SOT amplitude

B) Investigation of the magnetic switching by optimized SOT (UMPhy/SPINTEC)

The SOT-driven switching of magnetization will be performed in sub-micronic elements (device size < 200 nm) realized at SPINTEC (or UMPhy) prepared in optimized material system from Task 1. The switching detection will be realized through electrical (Anomalous Hall effect) and optical means (Kerr effect or MFM).
- Design and fabrication by e-beam lithography of SOT elements with dimension less than 200 nm
- Study of the magnetization reversal by SOT vs. the elliptical shape and corresponding size.
- Study of the reversal modes by SOT (experimental and modelling)

C) Technology transfer on SOT-MRAM bits and study of writing operation in SOT-MTJ (SPINTEC/UMPhy)

- Sputtering deposition of optimized heterostructures on large scale wafers (100 mm)
- E-beam lithography and MTJ fabrication at the nanometer scale (less than 100 nm)
- Characterization of switching performance by improved SOT (investigation of the mode reversal) and benchmarking.

Constraints and risks

No constraint
No risks

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