Browsing by Author "Chen, Kuan-Ming"

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Effects of synthetic antiferromagnetic coupling on back-hopping of spin-transfer torque devices
(2020-08-17)
Chen, Kuan-Ming
;
Cheng, Chih-Wei
;
Wei, Jeng-Hua
;
Hsin, Yu-Chen
;
Tseng, Yuan-Chieh
A synthetic antiferromagnetic (SAF) layer is a key component in spin-transfer torque magneto-resistive random-access memory devices. This study reveals that slight fluctuations in SAF coupling at the margin of the reference layer and hard layer (i.e., concurrent reversal) can lead to write errors in the form of back-hopping (BH). It appears that variable BH behavior can be attributed to competition between antiparallel (AP) -> parallel (P) and P -> AP transitions associated with SAF coupling. Our conclusions are supported by careful analysis of switching phase diagrams and measurements of self-heating and voltage-controlled magnetic anisotropy. We also observed that one form of coupling provided higher perpendicular magnetic anisotropic energy and thermal stability, which is likely due to the Dzyaloshinskii-Moriya interaction (DMI) effect. Thus, minimizing variations in DMI by optimizing SAF coupling is crucial for minimizing write error rates.
Study of Al interdiffusion in ultrathin beta-Ta/Co2FeAl/MgO heterostructures for enhanced spin-orbit torque
(2019-12-01)
Bhardwaj, Vishal
;
Chen, Kuan-Ming
;
Tseng, Yuan-Chieh
;
Chatterjee, Ratnamala
;
材料科學與工程學系
In this work perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films is achieved using rapid thermal annealing under N-2/H-2 gas flow in Si/beta-Ta(6.5 nm)/CFA(0.6-2 nm)/MgO(1.15 nm)/Pd(1 nm) heterostructures. The Al interdiffusion into MgO layer plays an important role in determining perpendicular magnetic anisotropy(PMA) and increasing the damping constant (alpha) of ultrathin CFA samples. The time of flight SIMS depth profiling along with XPS is used to study interdiffusion of Al across CFA/MgO interface. XPS analysis of Al-2p and Mg-1s spectra indicate the formation of A1(2)O(3) and MgAl2Ox oxide phases at CFA/MgO interface in addition to pure Al metal. The Slonczewski-like and the field-like SOT effective fields are quantified using second harmonics measurements. An effective spin hall angle of beta-Ta (6.5 nm) is estimated in range - 0.02 to - 0.06 for CFA layer thickness varied from 0.8 nm to 1.5 nm.