What is 3D Flash Memory?

Slowly, but steadily, the memory market is veering away from magnetic disc storage systems to solid-state drives or SSDs. Not only are prices falling fast, manufacturers are producing SSDs with improved technologies, leading to denser memories, higher reliability and lower costs. For example, Samsung has recently announced SSD and systems designs that will drive their new 3-D NAND into mass markets.

Samsung’s latest SSDs are the 850 EVO series. According to Jim Eliot, a marketing executive for Samsung, these are 48-layer, 256 Gbit 3-D NAND cells, with 3-bits per cell. The new chips show more than 50% better power efficiency and twice the performance when compared to the 32-layer chips Samsung is now producing. In the future, Samsung is targeting Tbit-class chips made with more than 100 layers.

On a similar note, an engineer with SK Hynix says that by the third quarter, the company will start production of 3-D NAND chips with more than 30 layers. By 2019, SK Hynix will be making chips containing more than 190 layers.

At present, 3-D NAND production is still low in yield and the cost of production is higher than for producing traditional planar flash chips. However, these dense chips bring promises of several generations of continuing decreases in costs and improvements in the performance of flash. According to analysts and vendors, it might take another year or so before the new technology is ready for use in the mainstream.

Samsung was the first to announce 3-D NAND production, with rivals catching up fast. Toshiba has already announced its intentions of producing 256 Gbit 3-D NAND chips in September. These will also have 48 layers and 3-bits per cell.

According to Jim Handy, an analyst at the Objective Analysis, Los Gatos, California, sales of the 3-D NAND will not pick up before 2017. With Samsung shipping its V-NAND SSDs at a loss, they are gearing up to put the 48-layer devices in volume production. This will enable them to beat the cost of traditional flash.

The reason is not hard to find. Wafers of 3-D chips with 32-layers cost 70% higher than wafers for traditional flash. On the other hand, wafers for 48-layer versions cost only 5-10% higher, but have 50% more layers. Therefore, although the 48-layer chips tend to start with a 50% yield, they will easily approach the planar flash yield levels with a year or so.

According to expert analysts, it takes a couple of years for any new technology to mature. Therefore, the prediction that 3D NAND will reach a majority of flash bit sales only after 2018.

The number of 3D layers providing an optimal product is still under experimentation. Also, included is the development of a new class of controllers and firmware for managing the larger block sizes. Vendors are still exploring other unique characteristics of these 3D chips.

For example, Samsung has designed controllers and firmware that addresses the unique requirements of 3-D NAND and is selling its chips only in SSD form. According to the head of Samsung’s Memory Solutions Lab, Bob Brennan, SSDs provide higher profit margins as compared to merchant chips, and are the fastest way to market.