Phase Change Memory technology – exciting but don’t hold your breath

Every meeting regarding Solid State memory technology includes pre-emptive prognostications about future technology. Phase Change Memory is always included as an alternative to adoption of the current state-of-the-industry NAND FLASH systems. We recently had the opportunity to discuss this really cool (or hot, depending on your perspective) technology with Cliff Smith and Mark Miller of Numonyx, a silicon fabricator with a huge investment in all forms of solid state memory technologies.

 

In a nutshell, Phase Change Memory is based on a radical approach to ‘remembering’ – one that involves no electrons – just a physical change in the substrate material that yields a closed or open circuit. What could be simpler? The devil in the detail involves a physical change in the actual substrate. That is, heat it up and cool it down at a varying rate. Cool it fast equals a one, cool it slow equals a zero (or vice-versa). Literally, PCM involves smelting the substrate on the fly. While the technology is in its infancy, it will certainly be a primary contender for memory systems in the next ten years. The primary advantage of PCM is that, like DRAM, individual bits can be read or written without the erase-write cycle involved in NAND FLASH. There are several disadvantages, including temperature limitations (don’t store the device at temperatures above 85c for long periods), but they are relatively small compared with the well-discussed NAND issues of wear-leveling, write amplification, and endurance.

 

So why are all the smart guys developing NAND FLASH SSD’s? The answer is simple. On the current Moore’s Law flight plan, it will be about a decade before PCM’s can compete on a cost-per-bit basis. DRAMs, on the other hand, will be in jeopardy in five or six years. And remember, PCM’s are non-volatile with power disruptions.

 

We analyze all forms of Solid State memory in context with enterprise and portable applications. In our current assessment, NAND FLASH will remain the pre-dominant technology for at least the next five years. But planning new systems beyond that point will certainly involve a PCM strategy.–Jim Bagley

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