Optimizing field-free magnetization switching through surface roughness engineering in T-type structures

Chun-Yi Lin^1*, Shih-Che Kao¹, Wei-Bang Liao¹, Po-Chuan Wang¹, Chi-Feng Pai^1,2

¹Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan
²Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, Taiwan

* Presenter:Chun-Yi Lin, email:d10527001@ntu.edu.tw

In the quest for practical spin-orbit torque magnetic random access memory (SOT-MRAM) deployment, achieving current-induced magnetization switching without an external bias field is paramount. Our investigative journey into this critical realm of memory technology is mapped out through the exploration of the CoFeB/W/CoFeB T-type structures. Such structures align with the widely adopted CoFeB/MgO-based magnetic tunnel junctions and are robust against high-temperature processes. Initial SOT characterization shows a sizable zero-field SOT efficacy (χ_(Hx = 0)) for such T-type devices, marking a stride toward field-free operation. Through field-free angle-dependent SOT measurements, the parallel orientation between the built-in bias field and the magnetization of the in-plane magnetized CoFeB layer is affirmed. Our investigations unveil the dominant role of the Néel orange-peel effect in enabling current-induced SOT switching correlated with the deposited film surface roughness. Based on this discovery, the switching performance in T-type structures is further optimized via film roughness tuning and examined with pillar-shaped devices. Our findings shed light on emerging strategies to enhance field-free switching with T-type devices and explore the potential for down-scaling.

Keywords: Spin-orbit torque, Thin films and heterostructures, Perpendicular magnetic anisotropy, Field-free switching