Efficient integration of self-assembled organic monolayer tunnel barriers in large area pinhole-free magnetic tunnel junctions

TL;DR

This paper demonstrates a method to fabricate large-area, pinhole-free magnetic tunnel junctions with self-assembled monolayer barriers, enhancing the understanding and control of interfaces for molecular spintronics.

Contribution

It introduces a novel ultra-high vacuum fabrication process with soft-landing deposition for homogeneous FM/SAM interfaces in hybrid MTJs.

Findings

Homogeneous Co/SAM interfaces achieved without metal diffusion.

Large-area MTJs with electron tunneling through SAM demonstrated.

Optimal deposition conditions enable pinhole-free organic barriers.

Abstract

Magneto-transport properties in hybrid magnetic tunnel junctions (MTJs) integrating self-assembled monolayers (SAMs) as tunnel barriers are critically influenced by spinterface effects, which arise from the electronic properties at ferromagnet (FM)/SAM interfaces. Understanding the mechanisms governing spinterface formation in well-controlled model systems is essential for the rational design of efficient molecular spintronic devices. However, the fabrication of FM/SAM/FM systems remains a significant challenge due to the difficulty in preventing electrical shorts through the SAM tunnel barrier during top FM electrode deposition. In this study, we address these challenges by developing model hybrid MTJs incorporating alkanethiol SAM tunnel barriers grafted under ultra-high vacuum conditions onto single-crystalline Fe(001) bottom electrodes. A soft-landing deposition method is used for the deposition of a top Co FM electrode. The deposition process and the electronic properties of the FM/SAM interfaces are first studied by spatially integrated X-ray photoelectron spectroscopy. Furthermore, ballistic electron emission microscopy (BEEM) and spectroscopy are used to investigate the lateral homogeneity of the organic barrier. Optimal soft-landing deposition conditions allows the preparation of homogeneous Co/SAM interfaces with no evidence of metal diffusion through the SAM at the nanoscale. These observations are further confirmed at the micron-scale by the high-yield patterning of large area (5*5um2) MTJs presenting fingerprints of electron tunneling through the SAM. These findings provide critical insights into the fabrication and optimization of molecular spintronic devices, paving the way for advancements in hybrid MTJ technology.