Thermal stability for domain wall mediated magnetization reversal in perpendicular STT MRAM cells with W insertion layers

TL;DR

This paper develops an analytical model to evaluate the thermal stability of domain wall-mediated magnetization reversal in perpendicular STT MRAM cells with W insertion layers, revealing how W thickness affects stability and the key role of coercive field.

Contribution

It introduces a new analytical approach to assess thermal stability in MRAM cells considering W layer effects, emphasizing the importance of coercive field over PMA field.

Findings

Increasing W thickness raises PMA energy density.

Thermal stability factor Δ decreases with W thickness.

Coercive field H_c is more influential on Δ than PMA field H_k.

Abstract

We present an analytical model for calculating energy barrier for the magnetic field-driven domain wall-mediated magnetization reversal of a magneto-resistive random access memory (MRAM) cell and apply it to study thermal stability factor $\Delta$ for various thicknesses of W layers inserted into the free layer (FL) as a function of the cell size and temperature. We find that, by increasing W thickness, the effective perpendicular magnetic anisotropy (PMA) energy density of the FL film monotonically increases, but at the same time, $\Delta$ of the cell mainly decreases. Our analysis shows that, in addition to saturation magnetization $M_s$ and exchange stiffness constant $A_\mathrm{ex}$ of the FL film, the parameter that quantifies the $\Delta$ of the cell is its coercive field $H_c$, rather than the net PMA field $H_k$ of the FL film comprising the cell.