Size dependence of switching current and energy barrier in the magnetization reversal of rectangular magnetic random access memory cell

Write operation in magnetic random access memory (MRAM) with bit density of Gbit/cm2 order has been numerically simulated for low submicron scale magnetic cells. The amplitude of both the switching current Iw and the energy barrier ΔE of the magnetic cell show strong dependence on the width w and the thickness t of the cell. The calculated results show that the amplitude of Iw is proportional to t/w, while that of ΔE is proportional to wt2. To obtain the sufficient energy barrier against a thermal stability (ΔE>80kBT, at 300 K), the thicker magnetic cell is required as the cell is downsized for high-density memory applications, although the thinner one is preferred to lower the switching current. From the calculated results, it appears that the margin of the switching current for selective write operation is decreased with decreasing the lateral aspect ratio of the cell. The addressability for the write operation is also degraded by the formation of structural defect in the cell. In this article, optimum configurations of the magnetic cell applicable for Gbit MRAM are discussed.