On Friday October 10th, at 14:00, Kuldeep RAY (SPINTEC) will defend his PhD thesis entitled : Development of SOT-MRAM technology for integration in functional devices
Place : IRIG/SPINTEC, CEA Building 10.05, auditorium 445 (presential access to the conference room at CEA in Grenoble requires an entry authorization, request it before October 1th to admin.spintec@cea.fr)
video conference : https://cnrs.zoom.us/j/98644075579?pwd=0o4l1QT16KpPU3u3taN8kGQblIk4K3.1
Meeeting ID : 986 4407 5579
Passcode: NDPu00
Abstract : The explosive growth of data and sub-10 nm transistor scaling have driven up chip power, making it attractive to bring non-volatile memory closer to the CPU. Magnetic random-access memory (MRAM), based on magnetic tunnel junctions, is a leading contender. While STT-MRAM is already in production, spin–orbit torque MRAM (SOT-MRAM), based on spin currents from the spin Hall and Rashba effects, offers faster sub-nanosecond switching and superior endurance.
A key challenge, however, is deterministic switching. Even with external fields, write probability can collapse at high currents due to intrinsic backswitching. We systematically investigate this phenomenon in sub-100 nm CoFeB pillars on β-W using statistical measurements and macrospin simulations that reproduce experiments. The results suggest practical mitigation strategies, including free layers with high damping, interface engineering to tune the field-like/damping-like torque balance, and tailored pulse shapes.
To eliminate the external-field requirement, we examine combined SOT and STT writing. While this boosts practicality, it introduces reliability concerns linked to reference-layer imperfections. Through write error rate (WER) experiments and improved stack, we identify optimal pulsing strategies and demonstrate low WER at sub-critical currents. We also disentangle contributions from stray fields, VCMA, STT, and Joule heating, and highlight the fundamental difference in symmetry-breaking mechanisms of external field and STT.
Finally, we explore orbital torques in Co/Pt/Ta trilayers, revealing a damping-like torque efficiency more than twice that of Co/Pt, which increases with temperature, alongside a sizable field-like component. By decoupling spin and orbital contributions, we uncover their relaxation mechanisms. These results highlight new pathways toward robust, deterministic, and energy-efficient SOT-MRAM.
Jury :
- Stéphane MANGIN, Professeure des Universités, Université de Lorraine, Rapporteur
- Pietro GAMBARDELLA, Full Professor, ETH Zürich, Rapporteur
- Liliana BUDA-PREJBEANU, Professeure des Universités, Grenoble INP-UGA, Examinatrice
- Yoshichika OTANI ; Full Professor, University of Tokyo, Examinateur
- Sébastien COUET, Vertical Compute, Examinateur
Thesis supervisors :
- Gilles GAUDIN, Directeur de Thèse
- Marc DROUARD, Weebit Nano Ltd, Encadrant de thèse
