Data storage is one of those things where too much is never enough. And as the amount of data generated increases exponentially, the search is on for new memory technologies that tick all the boxes in terms of speed, endurance, non-volatility and endurance. Phase-change memory (PCM) has emerged as a promising candidate, and now IBM Research has worked out how to triple the amount of data bits each cell can hold, edging the technology closer to a cost-effective, blistering fast data storage solution.
PCM materials exist in either an amorphous or a crystalline state, with each state exhibiting different levels of electrical conductivity. Data is stored in binary, so one level can be used to represent a 0 and the other to represent a 1 on each PCM cell, with a low-voltage then applied to read the data bit back.
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IBM scientists have previously been able to optimize this process to write and retrieve data 100 times faster than is possible with flash memory. But when it comes to density, they have been limited to one data bit per each cell.
So while PCM has a number of advantages, which include the ability to last 10 million write cycles compared to the 3,000 of a standard flash-based USB stick, or not lose data when switched off like DRAM, the low density and therefore cost is what has held the technology back.
But IBM Research has now developed a PCM cell that can store three bits. The key was a tweak in how the data is read back when the low-voltage is applied. While more than two states can be stored on each cell, the crystals can drift in response to ambient temperatures making them indecipherable upon retrieval.
The researchers have built a new coding and detection scheme that makes these drifts a non-factor. At the IEEE International Memory Workshop in Paris today, they have presented a 64k-cell array that can successfully store three data bits per cell at elevated temperatures after one million endurance cycles.
The scientists say the new PCM could work alone, storing huge databases for large companies to offer faster processing speeds, or combined with existing storage technologies. These hybrids could see a smartphone's operating system stored in PCM and allow users to fire their devices up within seconds.
"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," says 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."
You can hear from the researchers involved in breakthrough in the video below.