Numonyx BV, a joint venture between Intel and STMicroelectronics, last week announced that its Omneo range of phase change memory products has entered mass production.
“Not since flash memory was introduced in 1988 has the industry seen a new, high-density memory technology,” said Glen Hawk, Numonyx VP and GM of the Embedded Business Group. “Today, designers have to use different memory types for code storage and execution, as well as data storage. Now, with Numonyx Omneo PCM, they have a simple, one-device solution.”
The company’s 16 megabyte P5Q and P8P phase change chips offer an SPI and parallel NOR interface, respectively. The latter interface is ideal for SD cards or a motherboard’s BIOS, while the former is ideal for embedded storage, where a device might need to change one byte of data at random.
Reality check
What is phase change memory?
Phase change memory is a fascinating technology that relies on the the curious properties of chalcogenide glass, which changes phases of matter with the application of voltage. Early attempts at developing PCM defined two states of matter: the first being an amorphous solid, the second a hard crystalline structure. In the case of the former, the high resistance of the amorphous state indicates a binary zero, and the low-resistance crystalline state represents a binary one.
More recent research has developed two additional states, for a total of four. Four states of matter permits a PCM cell to assume four combinations of binary one and zero (00, 01, 10 and 11), which leads two two bits of storage. Two bits of storage is equal to what you would find in the cell of an average SSD, with thousands of two-bit cells packed into a single multi-megabyte chip.
Why phase change memory?
PCM’s characteristics make it something of a Holy Grail amongst memory researchers. For starters, the current crop of NAND-based storage devices, like SSDs or memory cards, represent their data by trapping electrons. Scientists believe that it will not be possible to store electrons in NAND cells manufactured on a process node any smaller than 20nm. The electrons will be bigger than the cell at this size. PCM, however, is seen as a viable technology down to the 5nm level.
PCM also trumps the write endurance debate, which continues to shroud NAND technology in a shadow of concern. In just five years of development, PCM has already achieved 1,000,000 write cycles–NAND took 30 years to hit the same number. In fact, researchers are expecting PCM’s write endurance to be so high that PCM will be more likely to die from general microelectronic phenomena like electromigration. In other words, the endurance of the medium itself is not likely to ever be in question.
“This is important as traditional flash memory technologies face certain physical limits and reliability issues, yet demand for memory continues to rise in everything from mobile phones to data centers,” said Greg Atwood, Senior Technology Fellow at Numonyx.
PCM may even unify mass and volatile storage technologies by replacing DRAM, as Al Fazio, Intel Fellow and Director of Memory Technology Development once explained: “You have a memory technology that looks like memory–in other words, hardware can do a load/store because it can act on a small chunk of data with a low latency, yet it’s non-volatile so that it has the non-volatile aspects of storage.”
This means that memory modules based on PCM could operate at the speed of DRAM, but retain their data even through power loss. Imagine how quickly a PC might boot if the operating system’s last environment state was ready to go in memory the moment the PC was powered on.
Finally, because PCM cells can be addressed one byte at a time, rather than 512KB blocks as with NAND, PCM-based storage solutions could offer the mass storage of NAND at the speed of PC memory. PCM can also write new data without first erasing existing information, something NAND cannot do. Such qualities would put an end to optimal write sizes, write amplification and trading between IOPS and throughput.
The final word
The Numonyx announcement is for 16 megabyte chips on a 90nm process. The current state of NAND technology offers 256MB (or larger) chips on a 25nm process–considerably higher density and cost effectiveness, by any standard.
PCM is a very young technology that will, for now, start where NAND started: embedded memory for devices like programmable appliances, feature phones, firmware stores and the like. PCM is not ready to replace SSDs, memory cards or PC memory, not by a long shot.
The important thing to keep in mind about PCM is that it is the memory technology to watch, because the biggest movers and shakers in the semiconductor industry (chiefly Intel) are throwing their weight behind it. PCM may not be ready now, but it will be in the next five to ten years.
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