A new phase looms for memory market
Thursday, April 10, 2008 02:38 PM
Phase change memory could actually make its debut later this year. It's only taken decades to wring out the problems.
It's been a long haul for phase change memory, but the goal is in sight.
Numonyx, the memory joint venture between STMicroelectronics and Intel, is already shipping samples of phase change memory (PCM) chips to customers and will start shipping PCM chips commercially later this year, CEO Brian Harrison said at a press conference last week.
"We expect to bring it to market this year and generate some revenue," Harrison said.
"It is one to two years before it becomes widely commercially available."
Hearing a CEO talk about existing samples and near-term commercial shipments is a big deal for PCM. The technology has been stuck in the proverbial "a few years away" phase for a long time.
"It could be cheaper than flash within a couple of years," analyst Richard Doherty said in 2001, predicting the technology might hit the market in 2003.
"We are making good progress," Stefan Lai, one of Intel's flash memory scientists, said in 2002.
Gordon Moore, co-founder of Intel and the man for whom Moore's Law was named, had an article in the Sept. 28, 1970 issue of Electronics predicting that Ovonics Unified Memory, another name for the same type of memory, could hit the market by the end of that decade.
The delays have largely stemmed from two sources.
First, it's not an easy technology to master. In phase change memory chips, a microscopic bit on a substrate gets heated up to between 150 degrees and 600 degrees Celsius. The substrate is made of the same stuff as CD disks.
The heat melts the bit, which when cooled solidifies into one of two crystalline structures, depending on how fast the cooling takes place. The two different crystalline structures exhibit different levels of resistance to electrical current, and those levels of resistance in turn are then as ones or zeros by a computer. Data is born.
Both Intel and ST made a significant amount of progress in controlling the material in the past few years, Harrison said.
Size matters
Second, the makers of flash memory have continued to improve their technology. Back in 2001, some believed that flash would hit a wall at the 65-nanometer level of chip design. Then that got moved to 45 nanometers.
Today, manufacturers mass-produce flash at 65 nanometers and have samples at 45 nanometers. Numonyx has samples of traditional NOR flash at 32 nanometers. Why switch when the existing technology continues to work?
Again, in the past few years, Intel and ST have made progress and figured out a way to produce PCM chips on the manufacturing lines developed for standard chips. That has eroded the barriers to bringing PCM out.
Although Philips, IBM, and others have made progress in PCM, only Samsung is close to coming out with chips commercially, Harrison said.
Why will the world want PCM?
Performance, says Numonyx CTO Ed Doller. PCM chips can survive tens of millions of read-write cycles, he said, or far more than flash. Reading data to PCM chips takes 70 to 100 nanoseconds, or as fast as NOR flash. Data can be written to the chips at a rate of 1 megabyte a second, or equivalent of NAND flash.
There is also no erase cycle, making it similar to DRAM.
In other words, you have the best attributes of three different types of memory--plus, PCM will potentially use far less power.
The cost premium is also coming down fast. By next year, Numonyx hopes to make PCM chips, using 45-nanometer processes, that can hold two bits of data per cell. If that's possible, those chips would compete in price with single-bit-per-cell NAND flash, the memory that's being put into solid-state drives today, said Doller.
But the most important thing is that scientists believe they will be able to increase the density of these chips comparatively easily. In the future, standard flash chips will need additional circuitry for error correction and other functions. Not so with PCM. The smaller the bits get, the less heat that will be required to flip them, Doller added.
"The most important thing is that it is scalable," Doller said.
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