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Micron bets on 3D NAND flash for the future of storage

Interview Working on memory cells stacked vertically
Mon Aug 05 2013, 08:40

THE NEXT REVOLUTION in data storage will be 3D NAND flash, claims memory chipmaker Micron.

Speaking with Micron VP of NAND Solutions Glen Hawk, The INQUIRER learned that Micron is working on what it calls the "next major revolution in flash technologies".

Dubbed 3D NAND flash, the technology - which is also being worked on by many other chip manufacturers at present such as Sandisk and Intel - enables memory cells to be stacked on top of each other vertically instead of spread out in a two dimensional (2D) horizontal grid.

"The flash cell largely exists in two dimensions and for the last 20 years when we've scaled, we've simply made the X dimension and the Y dimension smaller to develop from one chip [generation] to the next," Hawk explained.

"We're now dealing with the difference between states within a memory cell, in the order of 10 or 20 electrons. It's very small and electrons are very poorly behaved in small numbers, so we are reaching some fundamental limits."

Hawk said that Micron could keep going for a number of generations with this 2D technology, but what it is also working on in terms of the future, along with others in the industry, is 3D NAND flash technology.

"The concept here is that now we take the NAND memory string out of flatland and we use the third dimension and start to stack the memory cells on top of one another," he said.

Hawk made it clear that he doesn't mean the stacking of chips, which is very common today, but rather stacking memory cells on a single chip.

"It's analogous to the difference to maybe suburban sprawl versus a skyscraper," Hawk said. "We're starting to make skyscrapers now and that's very exciting because it gives us a third dimension to scale into and the game will be how many memory cells will you stack on top of one another."

3D NAND flash allows memory makers to back off on the X and Y dimensions of the cell and make it a little bigger in those terms because they are instead going higher.

"When we do that we turn the clock back from the flash cell perspective and now we're once again dealing with tens of thousands of electrons between the states and that's a much better place to be," Hawk explained.

"This will increase the reliability, performance and gives us an excellent path for continued scaling because once 3D NAND technology comes around and 'resets the clock', so we have so many more electrons to play with.

"That's going to open up a new era of scaling for us, so the future is pretty bright for continued NAND scaling."

The construction of 3D NAND flash scaling doesn't come cheap. Hawk noted that the "secret recipe" that Micron and its competitors are seeking at the moment is how you can, as efficiently as possible, put down multiple layers on one chip and create an array of NAND flash transistors from that.

"It's a big costly transition to do this, but it will happen," Hawk said and, referring to Micron's competitors, acknowledged that everyone is "very closed-lipped about their solutions".

Micron plans to make the transition from 2D NAND flash to 3D NAND flash when it's more cost effective. Because Micron already has a good scaling path for 2D NAND flash, it needs to add a lot of layers to 3D NAND flash before it makes economic sense to change over, so it is pursuing both formats in parallel.

"We're not sure whether it's one generation or two before that crossover point occurs," Hawk said. "But it is in the near future, so we're getting there." µ


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