Heavily Damped Precessional Switching with Very Low Write-error Rate in Elliptical-cylinder Magnetic Tunnel Junction

TL;DR

This paper investigates how the shape of elliptical-cylinder magnetic tunnel junctions and the direction of applied magnetic fields can significantly reduce write-error rates in voltage-induced magnetic switching, enhancing VCMRAM reliability.

Contribution

It demonstrates that elliptical shape and specific magnetic field orientation drastically lower WER in heavily damped precessional switching, improving VCMRAM performance.

Findings

WERS in elliptical MTJs can be several orders lower than in circular ones.

Applying magnetic field parallel to the ellipse's minor axis reduces WER.

Demagnetization fields narrow magnetization distribution, aiding switching reliability.

Abstract

Voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a writing technique for voltage-controlled magnetoresistive random access memory (VCMRAM), which is expected to be an ultimate non-volatile memory with ultra-low power consumption. In conventional dynamic switching, the width of sub-nanosecond write voltage pulses must be precisely controlled to achieve a sufficiently low write-error rate (WER). This very narrow tolerance of pulse width is the biggest technical difficulty in developing VCMRAM. Heavily damped precessional switching is a writing scheme for VCMRAM with a substantially high tolerance of pulse width although the minimum WER has been much higher than that of conventional dynamic switching with an optimum pulse width. In this study, we theoretically investigate the effect of MTJ shape and the direction of the applied magnetic field on the WER of heavily damped precessional switching. The results show that the WER in elliptical-cylinder MTJ can be several orders of magnitude smaller than that in usual circular-cylinder MTJ when the external magnetic field is applied parallel to the minor axis of the ellipse. The reduction in WER is due to the fact that the demagnetization field narrows the component of the magnetization distribution perpendicular to the plane direction immediately before the voltage is applied.