Applied Physics

More Memory Please

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Science  11 Apr 2014:
Vol. 344, Issue 6180, pp. 129
DOI: 10.1126/science.344.6180.129-c

The storage density of digital media has soared by many orders of magnitude over the past several decades, but still there is demand to store even more on an even smaller scale. Doing so, however, has its bounds, as engineering capabilities or fundamental physical limitations may hinder further size reduction. Phase-change memory materials provide a platform to store digital information in the form of bits, the state of the bit being distinguished by the different reflective properties of the amorphous and crystalline state. The state of the bit typically is set by optical, electrical, or thermal pulses that change the phase of the materials. Instead of shrinking the size of the bit, Wang et al. show that such a phase-change memory bit can access several levels. Using a series of ultrafast laser pulses to the control the amount of energy pumped into the bit, they show that a ladder (or gray scale) of stable states can be accessed. Such a multilevel approach could be useful for enhancing effective storage density without the need to shrink the device size. “What I know can be written on the back of a postage stamp” may actually turn out to be a rather showy feat of memory recall, and not a self-deprecating claim of modest knowledge as intended.

Appl. Phys. Lett. 104, 121105 (2014).

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