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/Job opportunities/Novel magnetic tunnel junction concept for spin logic application

Novel magnetic tunnel junction concept for spin logic application

PhD - Leuven | More than two weeks ago

Explore spintronic devices for tomorrow’s computer architecture 

Background:
 
Fast domain wall (DW) motion governed by spin-orbit torque (SOT) and the Dzyaloshinskii-Moriya interaction (DMI) in ultrathin magnetic layers on heavy metals is crucial for future spin logic devices [1].
Spin logic devices based on DW motion offer flexible architectures to store and carry logic information in a circuit. In this device concept, logic information is encoded in the magnetic state of a magnetic track shared by multiple magnetic tunnel junctions (MTJs) and is processed by DW motion. Such devices combine unique properties such as non-volatility, fast operation, and ultra-low energy consumption. Therefore, they are currently explored to enable functional rather than dimensional scaling devices. 
 
Challenges
 
To date, writing of DWs has mainly been performed via magnetic field and read out via either Hall bar devices or magnetic imaging techniques [1]. These schemes play a crucial role to characterize material properties, but their applicability to real DW devices is limited. Therefore, the lack of all-electrical control of DW at nanoscale devices impedes practical applications of spin logic devices. In this context, MTJs with fast reading and low writing current as demonstrated in current STT-MRAM technology, can be used to electrically control a DW device. Nevertheless, DW-based logic devices require an additional scheme to electrically move the DW in a circuit for logic operation. Therefore, the conventional MTJ devices based on CoFeB/MgO free layer posse a major challenge to realize such devices which are related to the slow DW speed in CoFeB/MgO free layer and difficulties of device integration using industrial platforms [2]. At imec, we have recently developed and demonstrated a novel concept of MTJ devices that enables the synthetic antiferromagnetic (i.e., two thin ferromagnetic layers are antiferromagnetically coupled via a non-magnetic layer) as magnetic free layer into the MTJ devices [3, 4]. This novel design is promising to overcome many hurdles to achieve the full technological realization of spin logic devices thanks to the special properties of synthetic antiferromagnetic materials (robust against perturbation of external field, produce no stray fields, ultra-fast DW speed) compared to conventional ferromagnetic layer.
 

  • [1]. Zhaochu., et al., “Current-driven magnetic domain-wall logic” Nature 579, 214 (2020).
  • [2]. Raymenants, Couet, Nguyen et al., “Scaled spintronic logic device based on domain wall motion in magnetically interconnected tunnel junctions” 2018 IEDM, 36.4.
  • [3]. Raymenants, Couet, Nguyen et al., “All-electrical control of scaled spin logic devices based on domain wall motion” 2020 IEDM, 21.5.
  • [4]. Raymenants, Couet, Nguyen et al., “Nanoscale domain wall devices with magnetic tunnel junction read and write” Nature Electronics 2021 (in review).

 
Key aspects of this PhD:
To develop spin logic devices, imec uses a dedicated 300-mm wafer platform. Devices are fabricated in imec’s 300 mm CMOS fab on full wafers. The purpose of this PhD project is to pave the path towards integration of this novel MTJ concept in a viable technological process for spin logic applications. This dissertation will focus on the understanding of the physical mechanism of DW dynamics at nanoscale devices by means of advanced electrical and physical characterizations. This experimental works will be performed in close collaboration with micromagnetic modeling (OOMMF, Mumax) activities to support the experimental findings. This study will be finally focused on designing and investigating a fully functional spin logic devices, addressing both fundamental and technological challenges.
An extensive toolset for structural, magnetic and electrical characterization is available including: material characterizations as XRR, XRD, magnetic characterizations as VSM, PMOKE, magnetic imaging techniques as MFM, Magneto-optical Kerr microscopy, magneto-transport characterizations as Hprobe electrical prober and a SOT electrical characterization setup. 
 
Key to the PhD research is to:
 

  1. Study DW motion in magnetic materials and their compatibility with perpendicular magnetic tunnel junction.
  2. Characterize magnetic and transport properties of novel MTJ devices.
  3. Integrate novel MTJ concept in fully functional spin logic devices.
  4. Study dynamics of DW propagation and demonstrated logic functionality in fully integrated devices.
  5. Perform micromagnetic simulations to support for the explanation of experimental results. 

Required background: Nanophysics, Engineering Science, Nanotechnology or equivalent 

Type of work: 70% experimental work, 20% simulation/modeling, 10% literature  

Supervisor: Kristiaan Temst 

Daily advisors: Van Dai Nguyen and Sebastien Couet 

The reference code for this position is 2021-135. Mention this reference code on your application form.