Target bias voltage effect on properties of magnetic tunnel junctions by biased target ion beam deposition

TL;DR

This study investigates how bias voltage during Biased Target Ion Beam Deposition affects magnetic tunnel junction properties, revealing a trade-off between intermixing reduction and surface roughness that influences device performance.

Contribution

It demonstrates the impact of bias voltage on MTJ film quality and provides insights for optimizing fabrication parameters using BTIBD.

Findings

Lower bias voltage reduces interlayer intermixing.

Higher bias voltage improves surface smoothness.

Bias voltage tuning can optimize TMR performance.

Abstract

Magnetic tunnel junctions (MTJ) with AlOx barrier were fabricated by a deposition tool called Biased Target Ion Beam Deposition (BTIBD) using low energy ion source (0-50 eV) and voltage biased targets. The BTIBD system applies bias voltage directly and only on the desired targets, providing enough sputtering energy and avoiding "overspill" contamination during film deposition. The successful deposition of AlOx-MTJs demonstrated the capability of BTIBD to make multilayer structures with good film quality. MTJ thin film surface roughness and intermixing between layers are among the key problems leading to low TMR performance. Here by studying the bias voltage effect on MTJ properties via the measurement of Neel coupling field and TMR, we suggest that the lower bias voltage reduces the intermixing that occurs when top CoFe free layer is deposited on AlOx barrier, but produces relatively high surface roughness. On the other hand, higher energy deposition enhances both interlayer mixing and surface flattening. Such understanding of bias voltage effects on film properties could be used to optimize the MTJ performances.