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Samsung Electronics have announced that it has begun mass production of a new kind of memory chip that stores information by melting and freezing tiny crystals. Called the phase-change memory (PCM), the idea was first proposed by physicists in the 1960s, but it took long for them to develop the chip. The scientists now expect that PCM would change mobile phones forever. PCM rests on a simple concept- atoms that are neatly arranged in crystals conduct electrons better than those jumbled up in a glass. Unlike conventional memory, which involves moving electrons around a chip, PCM data would literally be frozen in place, even when the machine is off, which means these devices could switch on nearly instantaneously. But Matthias Wuttig, a physicist at RWTH Aachen University in Germany, says that PCM, though simple in principle, is much harder to implement. The main problem is with writing the information into the material-to write in a one or a zero, the crystalline material has to be heated to high temperatures and refrozen, either in a crystal or glassy form. In the 1970s and 1980s, scientists developed new classes of crystalline materials in which the atoms were held together via very weak bonds and thus the materials could shift from crystal to glass very quickly. But turning that breakthrough into a working device was not easy and thus other kinds of transistor-based memory, such as the flash memory currently installed in most mobile phones and mp3 players, were closer to the market. Wuttig said that at transistor sizes of a few tens of nanometres, a quantum mechanical phenomenon called 'tunnelling' begins to come into play, which allows electrons to leak out of the transistor, effectively destroying the memory. Because PCM memory doesn't rely on charge, it can theoretically be used to create ever-smaller devices. In fact, because the speed of PCM memory depends on how long it takes to melt and refreeze the crystal, the smaller each crystal cell in the device, the faster it becomes. Wuttig's group has recently conducted experiments with cells just 20 nanometres across, which can be switched in just 16 nanoseconds - far faster than existing technology. And very soon, these memory chips may start appearing in mobile phones.