Controllers for eMMC storage devices come embedded with a flash chip. This makes the choice of an eMMC controller...
a third-party decision, where the flash vendor may change vendors between models. This would be a minor issue if all controllers were equal in function and performance, but that isn't the case.
For example, issues regarding the TRIM command, which clears up bad and erased blocks, can compromise safe erasure of data. This often doesn't matter, but as soon as data, like phone directories and passwords, is stored in the eMMC on a mobile device, safe erasure takes on a whole new dimension.
Performance is another issue. Adding some dynamic RAM to the flash configuration allows for much faster write performance, but not all chips have this.
Data integrity management is also a concern with an eMMC controller. With NAND flash, the variations in flash devices complicate how data protection is delivered. Flash has different failure modes, both digital and analog, requiring a resilient controller design to deliver long-term integrity, good write wear characteristics and solid failure detection.
Technical issues are just part of the picture. The eMMC industry is seeing major changes on both the business and the political front. More than 90% of the industry is concentrated in the hands of just four vendors: market leader Samsung, Toshiba, SK Hynix and SanDisk.
These vendors have both huge momentum and vast investment pools. They are applying intense market stress to the dozen or so Taiwanese eMMC flash memory vendors, which is shrinking the already small market for controllers.
At the same time, China has stated that most of its semiconductors, and especially their memory components, will be built in the country in an attempt to reduce its dependency on foreign technology sources. The aim is to decrease external supply from the current 80% to 25% in a decade.
The result is that China will be investing deeply in eMMC controller design and core technology and will likely acquire some of the Taiwanese intellectual property. The upshot is that China-based corporations intend to give the four eMMC flash giants a run for their money. With domestic demand being high (iPhones are made in China), this will change market dynamics quite a bit.
Back to the tech
The mainstay of the flash industry, 2D NAND, is rapidly giving way to 3D NAND alternatives. This change has been slowed by technical issues, but the transition should be complete for Samsung, Toshiba, SK Hynix and SanDisk (as well as Intel and Micron) in early 2017. This will have a major impact on eMMC host controller design, since the capacity of the largest eMMC devices will increase significantly. This would yield tablets with a terabyte of storage and smartphones with 256 GB or more, making room for background downloads and other user-facing features that offer a substantial boost in a saturated market.
Few eMMC controller companies have the exposure to 3D NAND that is needed to enter the game. These companies will be late to the party, including the Chinese ones. This will concentrate sales for a year or two into the hands of Samsung, Toshiba, SK Hynix and SanDisk, since they are all into 3D NAND. Samsung is particularly strong in this area, with around a six-month lead in the market.
Most of the market aligns with the eMMC 4.5 specification from JEDEC, but revisions 5.0 and 5.1 have been released and address much higher transfer rates and random access performance. In fact, these perform at more than twice that of today's most common standard, revision 4.5. This is a controller hit, with new designs needed, and the best-positioned players are the giants.
To complicate this, recognition that a good many of the CPUs that eMMC attaches to now support a SATA interface has led to the Universal Flash Storage (UFS) specification. This applies a SATA-like interface to the flash controller, which is serial rather than the eMMC 8-bit parallel interface. Clearly, a new eMMC controller design is needed, and Samsung has already stepped up to the plate, releasing a UFS product in early 2016.
The eMMC market will shift over the next five years as technical and business/political stresses come into play. Purchasing a controller/flash memory combo will likely lean toward the four giants, with Micron perhaps adding some volume. The impact of China is several years out -- in the 2019/2020 timeframe -- when the dynamics of the market will change again. We may also see internal shifts within vendors to focus on segments of the flash market, which might move their focus from embedded to, for example, enterprise SSD flash needs.
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