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Abstract

A nonvolatile magnetic random access memory (MRAM) is an array of individual magnetic memory cells. Each memory cell is a magnetic tunnel junction (MTJ) element and a diode electrically connected in series. Each MTJ is formed of a pinned ferromagnetic layer whose magnetization direction is prevented from rotating, a free ferromagnetic layer whose magnetization direction is free to rotate between states of parallel and antiparallel to the fixed magnetization of the pinned ferromagnetic layer, and an insulating tunnel barrier between and in contact with the two ferromagnetic layers. Each memory cell has a high resistance that is achieved in a very small surface area by controlling the thickness, and thus the electrical barrier height, of the tunnel barrier layer. The memory cells in the array are controlled by only two lines, and the write currents to change the magnetic state of an MTJ, by use of the write currents' inherent magnetic fields to rotate the magnetization of the free layer, do not pass through the tunnel barrier layer. All MTJ elements, diodes, and contacts are vertically arranged at the intersection regions of the two lines and between the two lines to minimize the total MRAM surface area. The power expended to read or sense the memory cell's magnetic state is reduced by the high resistance of the MTJ and by directing the sensing current through a single memory cell.

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First Claim