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In the area of data storage, no universal solution exists to give every desired function.
Among the most popular types of memory are DRAM (dynamic random access memory) and flash memory, but each has its own drawbacks.
Some memories boast high speeds at the expense of higher voltages.
Others have the advantage of being non-volatile (the memory maintains its state) but suffer from shortened durability.
However, emerging memory solutions have the potential of being universal solutions.
Researchers and developers have utilized the size and excellent properties of nanoparticles to create small non-volatile, endurable, and relatively high speed memory technology.
MRAM stands for magnetoresistive random access memory.
Unlike other types of memory, MRAM does not store memory as the presence or absence of electric charge.
Instead, MRAM stores a bit of data through polarizing a magnetic layer in opposite directions to represent a "0" or a "1" bit value.
When the magnetic layer changes polarization, the resistance of the bit cell changes and, therefore, can be sensed by complimenting transistors.
A cell which represents a single bit is composed of a few different layers.
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Other layers below the fixed magnetic layer are not shown — the extra layers are anti-ferromagnetic which help isolate the layers from accidental writing.
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At the heart of the device are two magnetic layers, one of which is a permanently polarized in one direction while the other can be changed (the fixed layer acts more as a reference for the top free layer, which represents the bit value).
Between the two layers is an barrier layer, such as aluminum oxide (Al2O3), which isolates the two ferromagnetic layers.
The combination of the magnetic layers and the barrier is called a magnetic tunneling junction (the MTJ).
When the directions of the two magnetic layers are parallel, the magnetoresistance of the MTJ is small.
Conversely, the magnetoresistance is larger when the directions are opposite.
A read operation can be performed by passing a sense current through a transistor connected to the bit cell.
Thus, a relatively large voltage drop on the bit line indicates a certain bit value, and a smaller voltage drop indicates a different value.
A word line connects all the bottom permanent magnetic layers of each bit cell in the word.
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Image recreated from www.research.ibm.com
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The top magnetic layer is connected to a bit line which connects the corresponding bit numbers of each adjacent word in the grid.
A write operation is accomplished by first activating the correct word with a current.
Then, current is passed through the bit line in the correct direction.
The magnetic field generated by the current line changes the direction of the free magnetic layer.
Changing the direction of the current will change the polarization of the free layer and, thus, the magnetoresistance of the MTJ.
The density of the memory unit depends on the strength of the current through the word and bit lines.
A bit line current should only produce a field which effects a single bit cell.
A current which is too strong may change a nearby cell.
Likewise, the current through a word line should only effect a single word and not an adjacent word.
The current strength of both the word and bit lines are necessary to change the free magnetic layer.
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