Critical Current Distribution in Spin Transfer Switched Magnetic Tunnel Junctions

TL;DR

This study investigates the distribution of critical switching currents in magnetic tunnel junctions, revealing how thermal factors influence variability and providing an analytical model to predict this distribution.

Contribution

It introduces an analytical expression for the critical current distribution considering thermal activation, highlighting the thermal factor's role in variability.

Findings

Distribution width is 7.5% for KuV/kBT=40 and 3.5% for KuV/kBT=65.

Distribution width remains stable across pulse widths from 1 s to 4 ms.

Thermal factor is the key parameter affecting critical current distribution.

Abstract

The spin transfer switching current distribution within a cell was studied in magnetic tunnel junction based structures having alumina barriers with resistance-area product (RA) of 10 to 30 Ohm-um2 and tunneling magneto-resistance (TMR) of ~20%. These were patterned into current perpendicular to plane configured nano-pillars having elliptical cross-sections of area ~0.02 um2. The width of the critical current distribution (sigma/average of distribution), measured using 30 ms current pulse width, was found to be 7.5% and 3.5% for cells with thermal factor (KuV/kBT) of 40 and 65 respectively. The distribution width did not change significantly for pulse widths between 1 s and 4 ms. An analytical expression for probability density function, p(I/Ico) was derived considering the thermally activated spin transfer model, which supports the experimental observation that the thermal factor is the most significant parameter in determining the within cell critical current distribution width.