講演情報
[10p-PB3-40]Exceeding 100% tunnel magnetoresistance in perpendicular magnetic tunnel junctions with cubic GaNx barrier
〇(P)Deepak Kumar1, H Kwon1,2, K Suzuki1,2, S Takaoka1,2, S Miki1, S Mizukami1,3 (1.WPI-AIMR Tohoku Univ., 2.Grad. Sch. Eng., Tohoku Univ., 3.CSIS Tohoku Univ.)
キーワード：
Magnetic Tunnel Junction、、Semiconductor、magnetic materials
Magnetic tunnel junctions (MTJs) are key components in spintronic devices, including hard disk drive (HDD) read heads and magnetic random-access memory (MRAM). Conventional MTJs typically employ CoFeB electrodes and an MgO tunnel barrier; however, alternative materials are actively being investigated to enhance device performance. Although MgO-based MTJs exhibit high tunnel magnetoresistance (TMR), they often have high resistance–area (RA) products due to the large MgO bandgap (7.8 eV). Therefore, there is a growing demand for new tunnel barrier materials that can simultaneously provide high TMR ratios and low resistance. Promising candidates include cubic wide-bandgap oxide semiconductors that can epitaxially grow on the (001) planes of ferromagnetic electrodes. In this study, we investigate metastable cubic-GaN, a wide-bandgap semiconductor with a bandgap of ~3eV, as a tunnel barrier material in perpendicular magnetic tunnel junctions (p-MTJs). The MTJ stacks were deposited on a single-crystal MgO(100) substrate using an ultrahigh-vacuum DC/RF magnetron sputtering system with a base pressure below 5E-7Pa. The stacking structures was substrate/Cr(40)/MnGa(30)/Mg(0.4)/CoMnFe(1.3)/Mg(0.5)/MgO(t)/GaN(0.9)/MgO(1)/CoFeB(1.4)/Ta(3)/Ru(5) (thickness is in nm). Transport measurements were performed using the standard four-probe method at 300K. Figure 1 shows a hysteresis loop for the TMR effect in p-MTJ with a 1 nm bottom MgO layer in the barrier, measured at 300K after annealing at Ta = 300°C. We observed perpendicular magnetization for the top CoFeB layer, indicating that perpendicular magnetic anisotropy remains stable even in the presence of the GaN layer. The maximum TMR ratio of ~120% was observed for the bottom MgO layer with a thickness of ≥ 1 nm in the barrier. We also observed that the resistance-area product (RPA) decreased upon introducing a GaN barrier layer, possibly due to a reduction in barrier height.