Novel Tunnel Magnetoresistive Sensor Functionalities via Oblique-Incidence Deposition.

Svenja Willing,Tatiana Gurieva,Ralf Röhlsberger,Kai Schlage,Guido Meier,Mohammad Mehdi Ramin Moayed,Lars Bocklage

doi:10.1021/acsami.1c03084

Abstract

Controlling the magnetic properties of ultrathin films remains one of the main challenges to the further development of tunnel magnetoresistive (TMR) device applications. The magnetic response in such devices is mainly governed by extending the primary TMR trilayer with the use of suitable contact materials. The transfer of magnetic anisotropy to ferromagnetic electrodes consisting of CoFeB layers results in a field-dependent TMR response, which is determined by the magnetic properties of the CoFeB as well as the contact materials. We flexibly apply oblique-incidence deposition (OID) to introduce arbitrary intrinsic in-plane anisotropy profiles into the magnetic layers. The OID-induced anisotropy shapes the magnetic response and eliminates the requirement of additional magnetic contact materials. Functional control is achieved via an adjustable shape anisotropy that is selectively tailored for the ultrathin CoFeB layers. This approach circumvents previous limitations on TMR devices and allows for the design of new sensing functionalities, which can be precisely customized to a specific application, even in the high field regime. The resulting sensors maintain the typical TMR signal strength as well as a superb thermal stability of the tunnel junction, revealing a striking advantage in functional TMR design using anisotropic interfacial roughness.

Highlights

Since the discovery of spin-dependent tunneling[1] and tunnel magnetoresistance[2,3] the race for ever increasing effect strengths of magnetic tunnel junctions (MTJs) has been ongoing.[4,5] A huge leap forward was made with the invention of grain-to-grain epitaxy in amorphous CoFeB layers annealed in contact with MgO
We found that unlike for polycrystalline films the magnetic properties of the CoFeB layers depend on layer thickness and polar deposition angle and the annealing temperature and contact material
We have shown that the additional shape anisotropy induced via oblique-incidence deposition (OID) enables tuning of the magnetic properties of annealed CoFeB layers

Summary

Introduction

Since the discovery of spin-dependent tunneling[1] and tunnel magnetoresistance[2,3] the race for ever increasing effect strengths of magnetic tunnel junctions (MTJs) has been ongoing.[4,5] A huge leap forward was made with the invention of grain-to-grain epitaxy in amorphous CoFeB layers annealed in contact with MgO This approach combines the advantages of smooth amorphous materials with the spin-selective properties of epitaxial interfaces and a crystalline tunnel barrier.[6] Sensors based on the tunnel magnetoresistive (TMR) effect benefit from the resulting high effect strength exceeding 600% at room temperature.[7] In addition, such sensors can be small, are robust, provide contact-free measurement, and excel in energy efficiency due to an inherently large resistance. TMR sensors are widely used in a variety of different applications ranging from the detection of magnetic fields in the read heads of computer hard disk drives or e-compass hardware to electric current sensing and precision angle, position, and motion measurements in industrial robotics and especially automotive environments

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