Memory

Does Vertical Flash NAND memory offer scalability?

6th August 2014
Nat Bowers

3D Vertical NAND (V-NAND) flash memory is breaking through the current scaling limit for existing NAND flash technology. Achieving gains in performance and area ratio, the new 3D V-NAND is developed for a wide range of consumer electronics and enterprise applications, including embedded NAND storage and solid state drives (SSDs).

For the past 40 years, conventional flash memory has been based on planar structures that make use of floating gates. As manufacturing process technology has proceeded to the 10nm-class and beyond, concern for a scaling limit arose due to the cell-to-cell interference that causes a trade-off in the reliability of NAND flash products. This also led to added development time and costs. Samsung has address this hurdle with 3D V-NAND solutions based on cylinder-shaped 3D Charge Trap Flash Cell architecture and vertical interconnect process technology.

By vertically stacking planar cell layers, a new 3D structure has been successfully developed. To do this, Samsung revamped its cylinder-shaped Charge Trap Flash (CTF) architecture, which was first developed in 2006. In Samsung’s CTF-based NAND flash architecture, an electric charge is temporarily placed in a holding chamber of the non-conductive layer of flash that is composed of silicon nitride (SiN), instead of using a floating gate to prevent interference between neighbouring cells. By making this CTF layer three-dimensional, the reliability and speed of the NAND memory have improved sharply.

Vertical interconnect

One of the most important technological achievements of V-NAND is the proprietary vertical interconnect process technology, which can stack as many as 24 cell layers vertically using a special etching technology that connects the layers electronically, by punching holes from the highest layer to the bottom. With the new vertical structure, Samsung can enable higher density NAND flash memory products by increasing the 3D cell layers without having to continue planar scaling, which has become incredibly difficult to achieve. This 3D CTF architecture and vertical interconnect process technology can overcome the technical challenges for finer process technology and higher areal density. By stacking many more layers vertically, Samsung can continue to aggressively develop next-generation NAND flash products that provide higher memory storage.

Typically, the reliability of NAND flash memory refers to the program erase cycles that the device can endure during its lifespan. The 3D V-NAND technology shows an increase of a minimum of two times to a maximum of ten times higher reliability, which means the number of program erase cycle has increased up to 10 times compared to planar NAND flash memory chips, depending on target applications.

Additionally, write performance is improved 100% over conventional 10nm-class floating gate NAND flash memory, meaning one of the most critical performance parameters, tPROG (programming time), is twice as fast as that of planar NAND flash memory. Although bandwidth is also used as a typical performance metric, program time really shows the intrinsic cell characteristics.

The technology has been used in the industry’s first 3D V-NAND based SSD, introduced in August 2013, designed for use in enterprise servers and data centres. The SSD provides over a 20% performance increase and over 40% improvement in power consumption, which can bring huge benefits to enterprise servers and data centres. Available in 960 and 480GB versions., the 960GB version boasts the highest level of performance, offering more than 20% increase in sequential and random write speeds by utilising 64 dies of MLC 3D V-NAND flash, each offering 128Gbit of storage, with a 6Gbps SATA interface controller. The new V-NAND SSD also offers 35K program erase cycles and is available in a 2.5" form factor with x, y and z-heights of 10cm, 7cm and 7mm, which provides server manufacturers with more design flexibility and scalability.

After nearly 10 years of research on 3D Vertical NAND, Samsung now has more than 300 patent-pending 3D memory technologies worldwide. With the industry’s first completely functional 3D Vertical NAND memory, Samsung has strengthened its competitiveness in the memory industry as well as set the foundation for more advanced products including one terabit (Tb) NAND flash, while setting a faster pace for industry growth. According to IHS iSuppli, the global NAND flash memory market is expected to reach approximately $30.8bn (USD) in revenues by the end of 2016, from approximately $23.6bn (USD) in 2013 with a CAGR of 11%, in leading growth of the entire memory industry.

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