Heavily Damped Precessional Switching with Very Low Write-Error Rate in Elliptical-Cylinder Magnetic Tunnel Junctions

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 nonvolatile memory with ultralow power consumption. In conventional dynamic switching, the width of subnanosecond 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 MTJs can be several orders of magnitude smaller than that in usual circular-cylinder MTJs when the external magnetic field is applied parallel to the minor axis of the ellipse. The reduction in the 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.