Thermally Robust Perpendicular SOT-MTJ Memory Cells With STT-Assisted Field-Free Switching
Ya-Jui Tsou, Wei-Jen Chen, Huan-Chi Shih, Pang-Chun Liu, C. W. Liu, Kai-Shin Li, Jia‐Min Shieh, Yu-Shen Yen, Chih‐Huang Lai, Jeng−Hua Wei, Denny D. Tang, Jack Yuan-Chen Sun
Abstract
A back-end-of-line compatible 400 °C thermally robust perpendicular spin-orbit torque magnetic tunnel junction (p-SOT-MTJ) memory cell with a tunnel magnetoresistance ratio of 130% is demonstrated. It features an energy-efficient spin-transfer-torque-assisted field-free spin-orbit torque (SOT) switching and a novel interface-enhanced synthetic antiferromagnet (SAF). The optimal SAF with a Ru (9 Å) spacer sandwiched by Co/Pt multilayers has a high SAF coupling field of 2.8 kOe. The parallel magnetic coupling between the CoFeB-based reference layer and the bottom Co/Pt multilayer is enhanced by a magnet-coupling face-centered cubic textured Co/Pt (5 Å) multilayer buffer. The thermally induced Pt–Fe interdiffusion is effectively reduced by the W (3 Å) trilayers of texture-decoupling diffusion multibarrier. The Ta/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -W and TaN/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -W composite SOT channels are thick enough to be the etching stop and sustain 400 °C annealing without transforming to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> -W. Using the harmonic Hall voltage measurement, the Ta/W and TaN/W channels exhibit the large effective spin Hall angle of approximately −0.21 and −0.27, respectively. Scaling magnetic tunnel junction (MTJ) down to 30 nm size can reduce the switching time due to single-domain switching based on the micromagnetic simulation. The damping constant of ~0.018 is obtained by the ferromagnetic resonance measurement. A bigger damping constant reduces the switching time as predicted by the calibrated simulation.