China’s Memory Ambitions Intensify NAND Competition

Article By : Gary Hilson

The "Made in China 2025” initiative is bearing fruit, with a homegrown company demonstrating success with proprietary architecture for 3D NAND flash memory chips.

There’s been lots of chatter about China’s ambitions to become more semiconductor self-sufficient in recent years. The country’s “Made in China 2025” initiative is bearing fruit, with a homegrown company demonstrating further success with its proprietary architecture for 3D NAND flash memory chips.

Yangtze Memory Technologies Co.’s (YMTC) 3D 64L Xtacking TLC NAND device is already drawing considerable analysis by Ottawa, Canada-based TechInsights, which specializes in the reverse-engineering of semiconductors in advanced technology products. In a telephone interview with EE Times, senior technical fellow Jeongdong Choe said YMTC’s device will disrupt the $52 billion NAND memory market and its big players such as Micron, Samsung, SK Hynix, Kioxia, Western Digital, and Intel — not only by being a new entrant but because of its Xtacking architecture. “It’s very unique and it’s different from the others.”

Cross-section SEM image along BL direction showing YMTC Xtacking architecture (Source: TechInsights)

Among TechInsight’s early observations are that YMTC’s 3D 64L Xtacking TLC NAND devices comprise 73 gates in total for a vertical NAND string with nine vertical channel (VC) holes, including one dummy hole between common source line contacts. Choe said it’s likely that five select gates (one SSG and four DSGs) and four dummy gates are also used.

In YMTC’s proprietary Xtacking architecture, he said, periphery circuits and memory cell operations are processed on a separate wafer, that allows for higher array efficiency and memory bit density than conventional 3D NAND solutions, such as the 64-layer BiCS NAND from Western Digital and Kioxia and Samsung’s 64-layer V-NAND. For example, said Choe, the YMTC 256 Gb die bit density is 4.41 Gb/mm, which is higher than the Samsung equivalent 256 Gb die at 3.42 Gb/mm. YMTC’s Xtacking is quite similar to Micron’s, but distinguishes itself overall by using wafer-to-wafer hybrid bonding, which means the NAND array is upside-down on periphery circuits.

As different as Xtacking architecture is from the incumbent NAND players, until quite recently YMTC was still considered to be lagging behind other companies which had already unveiled 96-layer NAND, even 128-layer. However, YMTC recently announced it has developed the X2-6070, a 128-layer 1.33 Tb QLC 3D NAND memory chip, based on its Xtacking architecture. The company also has plans for a 128-layer 512 Gb TLC chip.

Objective Analysis’ annual report, China’s Memory Ambitions 2019, extrapolates what the country’s monthly semiconductor sales might be broken out as its own region from Asia-Pacific. (Source: Objective Analysis)

There’s been a lot of speculation about when China would be able to make an impact in the semiconductor market, as well as the quality of the technology itself. As Jim Handy, principal analyst at Objective Analysis told EE Times last fall, it won’t be the country’s lack of funds that get in the way so much as its lack of experience and sophistication in semiconductor manufacturing. The research released its annual, deep dive report on the factors affecting China’s memory ambitions, including comparisons to investments in other industries in the country and how other countries have kickstarted market entry, such as Korea and Japan.

As noted by the Objective Analysis report, Asia Pacific’s sales have clearly grown to account for more than half of world semiconductor sales as all other regions have decreased over the past four decades; China accounts for a growing portion of the region. Less than 20% of the chips consumed in China in 2015 were domestically produced, and the “Made in China 2025” plan is to reach to reach 40% by 2020 and 70% by 2025.

YMTC was founded in 2015 and is part of the Tsinghua Unigroup. It designed and manufactured the first 3D NAND flash chip in China in 2017.


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