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IBM Triples PCM Storage Capacity So It Can Finally Challenge Flash

Tom Jowitt is a leading British tech freelance and long standing contributor to TechWeek Europe

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RIP Flash and DRAM? Big Blue researchers demonstrate reliable phase-change memory (PCM)

Scientists at IBM Research said they have for the first time “reliably stored 3 bits of data per cell and retained the information at elevated temperatures”, a technical advance that makes phase-change memory (PCM) an alternative to flash storage.

The idea is that PCM will be used in future in mobile and IoT devices, as it offers non-volatile and high-density data storage that is 100 times faster and far more durable than Flash.

Long Time Coming

IBMIBM scientists in Zurich first introduced PCM technology way back in 2011, when they presented a whitepaper at the 3rd IEEE International Memory Workshop in Monterey, California. However this demonstration only showed the ability to store 1 bit per cell. Now IBM can now store 3 bits per cell in a 64k-cell array at elevated temperatures and after 1 million endurance cycles.

This development finally makes the technology a cost effective and viable alternative to Flash and DRAM. Researchers believe this means it could be used in either standalone PCM, as well as hybrid applications that combines PCM and flash storage together, with PCM acting as an extremely fast cache.

This is because PCM doesn’t lose data when powered off, unlike DRAM, which means that a phone’s operating system for example could be stored in PCM, allowing it to launch in just seconds. Businesses meanwhile could store their corporate databases for extremely fast query processing, where timing is critical (for example in financial transactions).

Another huge advantage of PCM over Flash is that it is much more durable, as it can endure 10 million write cycles, whereas enterprise-class Flash is only good for 30,000 cycles, and consumer-class Flash typically 3,000 cycles.

The Techy Bit

So how does it work? Well, IBM explains that “PCM materials exhibit two stable states, the amorphous (without a clearly defined structure) and crystalline (with structure) phases, of low and high electrical conductivity, respectively.”

“To store a ‘0’ or a ‘1’, known as bits, on a PCM cell, a high or medium electrical current is applied to the material. A ‘0’ can be programmed to be written in the amorphous phase or a ‘1’ in the crystalline phase, or vice versa. Then to read the bit back, a low voltage is applied. This is how re-writable Blue-ray Discs store videos,” said IBM

“Phase change memory is the first instantiation of a universal memory with properties of both DRAM and flash, thus answering one of the grand challenges of our industry,” said Dr. Haris Pozidis, an author of the paper and the manager of non-volatile memory research at IBM Research – Zurich. “Reaching 3 bits per cell is a significant milestone because at this density the cost of PCM will be significantly less than DRAM and closer to flash.”

The scientists developed a multi-bit PCM chip which they connected to a standard integrated circuit board. The chip consists of a 2 × 2 Mcell array with a 4- bank interleaved architecture. The memory array size is 2 × 1000 μm × 800 μm.

It should be noted that IBM is not the only vendor working on PCM. Intel has also previously worked on the technology.

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