Better Memories

July 3, 2011

Most of us are familiar with the small USB storage drives (sometimes called thumb drives or jump drives) that allow us to transport surprisingly large amounts of data in a compact package.  These devices use NAND flash memory technology to implement non-volatile storage (that is, the contents of memory are retained even without power).  The same technology is used to implement memory for many types of devices, such as digital cameras, smart phones, and digital audio players. The wide adoption  of the technology testifies to its utility; it is not, however, without some problems.  It has a limited lifetime, ranging from 10,000 to 1,000,000 erase/write cycles in commercial devices; and, although its read speed is satisfactory, writing is slow, because data must be erased and then re-written in relatively large blocks.

According to an article at Computer World, IBM has just announced the results of research on a new memory technology that may produce a range of better non-volatile memory devices.  The technology is called phase change memory [PCM].  It uses a glass-like material (an alloy  of germanium [Ge], antimony [Sb], and tellurium [Te] called GST) sandwiched between two electrodes; application of electric pulses can change the state of the material from crystalline (which has a low resistance) to amorphous (which has high resistance), and vice versa.   PCM memories can have write speeds up to 100 times as fast as NAND flash, and also have longer lifetimes, with at least 10 million erase/write cycles

At present, PCM memories can only store one bit of information per cell.  IBM says its Zürich research center has developed a data encoding technique that will allow storage of 2-3 bits of information per cell, resulting in higher memory density and lower cost per byte.  (The IBM press release is here.)   The new version of PCM is not quite ready for deployment; there are some concerns about its electrical power consumption.  Some early work using carbon nanotubes as the cell electrodes has produced significantly lower power consumption, so the power problem will likely be solved in time.

Given the growth in the use of both mobile devices and cloud-based services, the demand for faster, energy-efficient storage devices is bound to grow. PCM technology is a promising candidate to deliver some of that.

Technology Review also has an article on this announcement.

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