Low-Current-Density Magnetic Tunnel Junctions for STT-RAM Application Using MgO $_{{x}}$ N $_{\text{1}-{x}}\,\,({x}=\text{0.57}$ ) Tunnel Barrier

High switching speed, endurance, and low-current-based perpendicular magnetic tunnel junction (p-MTJ) memory is attracting wide interest as a key promising candidate for next-generation spintronic memory technology. p-MTJ-based spin-transfer torque RAM (STT-RAM) has been extensively investigated, and despite the promise, there is concern about the high switching current density and low stability with regard to scaling. In this work, the current controllability of p-MTJ in iron (Fe)-enriched Co₂₀Fe₆₀B₂₀ with a newly designed MgO_xN_1-x tunnel layer is systematically investigated, with the expectation that the introduction of N minimizes the oxidation of Fe to improve the performance of the device. A facile, plasma-based oxynitridation (MgO_x=0.57N_1-x=0.43) of MgO through RF-sputter deposition serves as a reliable procedure to establish a tunnel barrier for an MTJ structure fabricated with ~300-nm diameter and pinned with synthetic antiferromagnetic (SAF) [Co/Pt]n multilayer stack. Current-controlled tunneling magnetoresistance (TMR) up to ~65% was observed at room temperature (RT) with ultralow switching current density (J_c) of 136 ± 17 kA/cm². TMR along with tunnel conductance (g(V)) was measured to be highly stable in the read-bias regime (-200 to +200 mV) for MgO_xN_1-x as compared to the reported MgO barrier. The analogous MgO_xN_1-x-based MTJ structures were modeled using the nonequilibrium Green's function (NEGF) with appropriate tunnel barrier parameters and incorporating modulated barrier height as compared with the MgO barrier. The current-voltage characteristics of the modeled device showed close agreement with experimental data indicating high spin current. Based on the field-induced magnetization analysis, the macro-magnetic reversal analysis suggests the free-layer switching duration of ~3 ns. These observations show the strong candidature of MgO_xN_1-x (x = 0.57) MTJs for STT-RAM device application.

I. Introduction

Magnetic tunnel junction (MTJ)-based spintronic devices have gained huge attention due to their improved performance and broad panel of applications [1]–[3]. In particular, recent developments in MTJ-based devices have shown a path for futuristic low-power memory applications [4], [5]. In particular, the perpendicular MTJ (p-MTJ) with spin-transfer torque (STT)-based switching possesses nonvolatile behavior with high endurance, fast switching, and simple device structure [6], [7]. On the other hand, as the cell area is scaled down to meet density and power demands, conventional STT-RAM suffers from endurance and reliability issues due to the aging of the ultrathin tunnel barrier and read current disturbance [6]. Furthermore, there is an imperative need to lower STT switching current densities to further reduce power consumption that has still not yet been met [4], [8].