Phase change materials could enable energy efficient computing

Modelling and tests of PCM based devices have shown that logic processing operations can be performed in non volatile memory cells using particular combinations of ultra short voltage pulses, something which is not possible with silicon based devices. The processors, designed by a research team which also included the Singapore A*STAR Data Storage Institute and the Singapore University of Technology and Design, use a chalcogenide glass, which can be melted and recrystallised in as little as 0.5ns. Whilst the use of PCMs in electronic devices isn't new, the researchers say those recently demonstrated to perform in memory logic have shortcomings: not only do they not perform calculations at the same speeds as silicon, they also exhibit a lack of stability in the starting amorphous phase. However, the team found that, by performing the logic operation process in reverse – starting from the crystalline phase and then melting the PCMs in the cells to perform the logic operations – the materials were more stable and could perform operations more quickly. "As demand for faster computers continues to increase, we are rapidly reaching the limits of silicon's capabilities," said Professor Stephen Elliott, pictured, of Cambridge's Department of Chemistry. In particular, PCM devices can overcome silicon's scaling limit and can function down to about 2nm. "Eventually, what we really want to do is to replace both DRAM and logic processors in computers by new PCM based non volatile devices," said Prof Elliott. "But, for that, we need switching speeds approaching 1ns. Currently, refreshing DRAM leaks a huge amount of energy, which is costly, both financially and environmentally. Faster PCM switching times would greatly reduce this, resulting in computers which are not just faster, but also much 'greener'."