High Tunneling Magnetoresistance in Magnetic Tunnel Junctions with Subnanometer Thick Al₂O₃ Tunnel Barriers Fabricated Using Atomic Layer Deposition

Abstract

Pinhole-free and defect-free ultrathin dielectric tunnel barriers (TBs) are a key to obtaining high-tunneling magnetoresistance (TMR) and efficient switching in magnetic tunnel junctions (MTJs). Among others, atomic layer deposition (ALD) provides a unique approach for the fabrication of ultrathin TBs with several advantages including atomic-scale control over the TB thickness, conformal coating, and a low defect density. Motivated by this, this work explores the fabrication and characterization of spin-valve Fe/ALD-Al₂O₃/Fe MTJs with an ALD-Al₂O₃ TB thickness of 0.55 nm using in situ ALD. Remarkably, high TMR values of ∼77 and ∼90% have been obtained, respectively, at room temperature and at 100 K, which are comparable to the best reported values on MTJs having thermal AlO_<i>x</i> TBs with optimized device structures. In situ scanning tunneling spectroscopy characterization of the ALD-Al₂O₃ TBs has revealed a higher TB height (<i>E</i>_b) of 1.33 ± 0.06 eV, in contrast to <i>E</i>_b ∼ 0.3-0.6 eV for their AlO_<i>x</i> TB counterparts, indicative of significantly lower defect concentrations in the former. This first success of the MTJs with subnanometer thick ALD-Al₂O₃ TBs demonstrates the feasibility of in situ ALD for the fabrication of pinhole-free and low-defect ultrathin TBs for practical applications, and the performance could be further improved through device optimization.