pcm.html

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			Phase Change Memories(PCM) utilize the unique propoerty of some material to remain in multiple states as the basics of information storage. Since the change induced in the state remain until the state is again changed to some other state, or reverted back, the storage is non-volatile.
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			The material that is commonly used is <i>Chalcogenide glass</i>, which can stay in amorphous as well as crystalline solid state. In older generation of PRAM, the state of the Chalcogenide glass was changed by production of heat by passing current through a heating element. This heating element is made of TiN, and was used to change the state of the glass to amorphous solid state by quick application (heated over 600 celcuis). Holding the heat for some time in the crystallization temperature range (cooled) would switch the state back to the crystalline state. Alternative technologies for changing states using laser have been proposed in research <a href="https://doi.org/10.1038/nnano.2011.96">(ref)</a>.
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			Amorphous state offers more resistance and thus represents a binary 0 state while crystalline state represents a binary 1 state.
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			The material used in the PCM can exhibit multiple intermediate states between the amorphous and crystalline solid state. This allows for multiple bits storage in a single cell of the PCM. Intel and ST Microelectronis are currently working on a design with four states, two of which are partially crystalline state in addition to the previous two states. <a href="https://en.wikipedia.org/wiki/Phase-change_memory">(ref)</a>.
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			PRAMs are highly temperature sensitive as data can be lost with application of high temperature. However, they offer fast write times and have an endurance of about 100 million write cycles.
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