High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications

Jun-Yang Chen,Mo Li,Jian-Ping Wang,J M D Coey,Yong-Chang Lau

doi:10.1038/srep42001

Abstract

The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices‘ robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications.

Highlights

Barrier magnetic tunnel junction (MTJ) were patterned using standard UV lithography and ion-milling; After post-annealing, (c) a layer of S1813 photoresist was spin-coated onto the device surface; (d) The sample was turned over, mounted onto a four-inch silicon wafer covered with photoresist; (e) A deep trench etching process with SF6 and Ar plasma was performed to thin the back side of the silicon; (f) After carefully removing the photoresist with acetone, the flexible MgO-barrier MTJs were released
MTJs with a crystalline MgO barrier have been intensely studied[24,25] and tunneling magnetoresistance (TMR) as large as 600% at room temperature has been reported in pseudo spin valve stacks[26]
In order to prepare the flexible MgO-barrier MTJs, we used a double-side polished silicon wafer with a norminal thickness of 150 μm having a 300 nm SiO2 layer on one side of the substrate

Summary

Introduction

Barrier MTJs were patterned using standard UV lithography and ion-milling; After post-annealing, (c) a layer of S1813 photoresist was spin-coated onto the device surface; (d) The sample was turned over, mounted onto a four-inch silicon wafer covered with photoresist; (e) A deep trench etching process with SF6 and Ar plasma was performed to thin the back side of the silicon; (f) After carefully removing the photoresist with acetone, the flexible MgO-barrier MTJs were released. We have developed a different method and successfully demonstrate the intergration of high performance flexible MgO-barrier MTJs directly onto ultrathin flexible silicon membranes. Both MTJ stacks and fabrication methods are different from those in ref. The fabricated MgO-barrier MTJs exhibit a room-temperature TMR ratio of up to ~190% with various bending radii, which is much higher than achieved with the previous developed flexible GMR or Al2O3 barrier MTJs on organic substrates[16,17,18,19,20,21,22,23] These flexible MgO-barrier MTJs open a way to realize high performance spintronic devices in flexible and wearable device applications

Methods

Results

Conclusion