Magnetic Random Access Memory (MRAM)

                          MRAM is a nonvolatile random access memory which uses magnetic storage and magnetoresistance (MR) to read the stored data. Magnetoresistive material is a resistor made of common ferromagnetic material which will change in resistance in the presence of a magnetic field. The magnetoresistive property gives a small but sufficient signal to distinguish between a “1” and “0”. MRAM results from combining MR storage elements with standard semiconductor fabrication processes. The magnetic devices are integrated with support circuits on a single silicon chip to duplicate the function of a static semiconductor RAM chip. The magnetic storage elements are formed from a layer of permalloy thin film where the
intersection of the permalloy (sense line) and metal layer (word line) form a memory bit.

The general attributes of MRAM are:
• Nonvolatility
• Infinite write cycling without wearout
• Fast write (few nanoseconds for advanced modes)
• Low write energy
• Nondestructive read.

When combined with the high density of advanced GMR cells, these attributes lead to the “perfect memory” with speed, density and limited cycling of SRAM and DRAM and the nonvolatility of EEPROM, flash and other nonvolatile memories. In random access magnetoresistive memories (MRAM), storing data is accomplished by applying magnetic fields and thereby causing a magnetic material in a cell to be magnetized into either of two possible memory states. Recalling data is accomplished by sensing resistance changes in the cell when magnetic fields are applied. The magnetic fields are created by passing currents through strip lines (word lines) external to the magnetic structure, or through the magnetic structures themselves (sense lines). MRAM cells are narrow stripes etched into a multi-layer thin film stack of permalloy–copper–permalloy. Data is stored by magnetizing the stripe.

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