Direct imaging of the structural change generated by dielectric breakdown in MgO based magnetic tunnel junctions

TL;DR

This study directly visualizes the structural changes in MgO-based magnetic tunnel junctions caused by dielectric breakdown, revealing more microscopic pinholes compared to alumina-based junctions, and correlates these changes with transport behavior.

Contribution

It provides the first direct TEM imaging of breakdown-induced structural changes in MgO tunnel barriers and compares these with alumina-based junctions.

Findings

MgO barriers exhibit numerous microscopic pinholes after breakdown.

A simple model relates current density to pinhole formation rate.

Transport behavior correlates with structural damage observed.

Abstract

MgO based magnetic tunnel junctions are prepared to investigate the dielectric breakdown of the tunnel barrier. The breakdown is directly visualized by transmission electron microscopy measurements. The broken tunnel junctions are prepared for the microscopy measurements by focussed ion beam out of the junctions characterized by transport investigations. Consequently, a direct comparison of transport behavior and structure of the intact and broken junctions is obtained. Compared to earlier findings in Alumina based junctions, the MgO barrier shows much more microscopic pinholes after breakdown. This can be explained within a simple model assuming a relationship between the current density at the breakdown and the rate of pinhole formation.