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Memory Components

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MRAM Technology

In an attempt to combine the speed of the faster volatile memory with the benefits of non-volatile memory, a new type of non-volatile memory - Magnetoresistive Random Access Memory (MRAM) - was created. The roots of MRAM can be traced back to the 1940's at Harvard when physicists An Wang and Way-Dong Woo and later Jay Forrester and colleagues at MIT worked on developments that led to Magnetic Core Memory and later on to the discovery of the "giant magnetoresistive effect" in thin-film structures by researchers from IBM in the late 1980's. Like Flash, MRAM retains data after a power supply is cut off, potentially eliminating that seemingly endless boot time of conventional computers when data from the hard drive is transferred to RAM, as well as loss of data when the computer is suddenly shut off. MRAM has much faster write speeds than Flash and has an unlimited endurance, meaning that MRAM is not subject to the degradation suffered by Flash.

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Magnetic Tunnel Junction (MTJ) deposited on standard 180nm logic process
Simple 1T-1MTJ Cell Structure
Information is stored as magnetic polarization, not charge
The state of the bit is detected as a change in resistance

Conventional RAM memory is made of transistors and capacitors that are paired to create a memory cell, which represents one bit of data (0 or 1).

Memory cells are aligned in columns and rows, the intersections of which are known as addresses in which information is stored.

Reading and writing information occurs by measuring or changing the charge at a specific address, accordingly.

MRAM works in a different way, more like the read/write head of a hard drive. But unlike a hard drive, which includes mechanical parts (the moving arm holding the read/write head and the rotating plates on which the information is stored), MRAM is a solid state device and, as such, has much greater speed and durability. Like conventional RAM, MRAM is composed of transistors but, instead of electrical charges, it uses magnetic charges to store information. An MRAM chip is made up of millions of pairs of tiny ferromagnetic plates (like the one covering hard drives) called memory cells, i.e., magnetic sandwiches consisting of two magnetic layers separated by a very thin insulating layer. Each magnetic layer has a polarity – a north pole and a south pole. These can be oriented in a parallel orientation, meaning that both have their respective poles (or 'magnetic moments') in the same orientation, or in an anti-parallel fashion, meaning that their poles/magnetic moments are oriented in opposite directions. These relative magnetic pole orientations correspond to the binary memory states, either 0 or 1.

Read Mode

An MRAM chip reads information by measuring the electrical resistance of a specific cell that, in turn, depends upon the alignment of the magnetic moments of the layers of the cell. To read a bit of information, a current is passed through the memory cell. If the magnetic moments are in a parallel orientation, then the detected resistance would be smaller than if they were in an anti-parallel orientation.

Write Mode

Write is achieved by the alignment of the magnetic moments of the two memory layers into one or the other relative orientation. Current is passed through two sets of parallel wires or write lines (called a bit line and a digit or word line), which pass over and beneath the memory cells, respectively.The bit lines and the digit lines run perpendicular to one another and at their intersections lie the magnetic memory cells, each defined by one particular bit line and one particular digit line. To write to a particular memory cell (bit), current is passed through the two wires that intersect at that memory cell. The magnetic field that is generated from current passing through a wire can change the orientation of the magnetic moments of the particular memory cell.

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