Micron phases out planar, boosts 3D NAND production

With 3D NAND technology now made available by Micron in multi-level cell (MLC) and triple level cell (TLC) products as well as the increasing demands for higher capacity and performance of laptops and servers, the semiconductor manufacturer has increased its 3D NAND production.

Micron is also looking into phasing out its planar predecessor in favour of 3D NAND come June.

SSDs are the obvious opportunity for 3D NAND, said Kevin Kilbuck, Micron's director of NAND strategic planning, particularly enterprise storage. The company is sampling 3D NAND-based client SSDs this month that will be generally available in June. It will also find its way into embedded markets such as automotive, industrial, and mobile devices as well as IoT devices, he told EE Times in a telephone interview.

The company has begun volume production of 256Gb MLC and 384Gb TLC that can be stacked and put into an SSD. Kilbuck said it can get 3.5 TB into an m.2 form factor and 10 TB in a 2.5-inch (convert to mm except for displays) form factor. He said Micron has made some architectural innovations to further reduce the cost of 3D NAND, noting that XY lithography is now becoming irrelevant.

One of the changes Micron was able to make was the ability to hide more than 75 per cent of the CMOS logic under the array with its 32-tier 256Gb MLC/384Gb TLC 3D NAND products.

Kilbuck said they chose to stick with floating gate technology, which has been around since the early days of flash and used for EEPROM and NOR, noting there have been issues with the charge trap approach, such as charge loss which affect retention. "We didn't want to have to solve those issues while stacking." It made sense to stack a known entity, he said, rather than exponentially stretch the learning curve. "It was a matter of de-risking our schedule and deployment plans."

Micron commences mass production of 256Gb MLC and 384Gb TLC 3D NAND for SSDs that can get 3.5TB into an m.2 form factor.(Image source: Micron)

What will also contribute to 3D NAND's uptake in 2016 is that there is a supporting ecosystem for the technology, said Kilbuck, with companies such as PMC Sierra and Silicon Motion providing controllers. Silicon Motion introduced a turnkey merchant SATA SSD controller supporting 3D NAND from multiple vendors, including Micron, earlier this year at CES. It supports provisioning of higher capacity SSDs, from a broad range of vendors, up to 2TB.

While 3D NAND is often labelled as revolutionary because of its potential for reduced cost and increased density, Kilbuck said in many ways, including from a controller standpoint, it's just a natural evolution from its predecessor. "It's still NAND to the controller. There may be a few more features to deploy but it's still fundamentally a pretty evolutionary change for them."

There are several controllers ready to handle Micron's 3D NAND depending on the market segment for flash cards, client SSD and enterprise SSDs, said Kilbuck. The initial densities Micron is manufacturing are well above what is used in embedded applications. Meanwhile there is lots of room for SSD growth in the notebook segment, he said, and the enterprise space as organisations still haven't completely moved away from spinning disc in the data centre.

Kilbuck said 2016 is the year of 3D NAND, but more specifically, it's an investment year as vendors look to ramp up and make it more cost-effective to produce than 2D NAND. "Planar is hitting the end of its wall. There are still a few more shrinks left."

He acknowledged there are trade-offs when moving to 3D NAND— there are more process steps and wafer costs go up. "Once you get some scale behind it, no wants to be on the old technology."

Micron announced with Intel last March that together they would be second to Samsung with ultra-dense 3D NAND flash chips that will sell as chips and in SSDs. Not long after, Toshiba announced it was shipping samples of its 48-layer 3D Bit Cost Scalable (BiCS) stacked cell structure flash.

-Gary Hilson,??EE Times