A Look at the MicroSD Card of the Future: Speed and Capacity meet Reliability
Manufacturers recently released the largest capacity and fastest microSD cards ever made. The 128 GB cards demonstrate more than a 1,000-fold increase in storage density over the last decade, and the fastest speeds of these microSD cards now rival other high-speed options for wireless computing.
The SD Association is made up of application developers and microSD and component manufacturers. The organization determines microSD technology specifications and sets standards and roadmaps for the industry. SD Association President Brian Kumagai explained some of the new features and recent technology trends that help ensure microSD cards remain relevant and offer viable storage for many products and markets in the future.
Markets driving standardization
MicroSD cards are predominantly used in smartphones and other mobile devices that have limited space. When microSD cards first arrived on the scene, they quickly became the most popular form factor for mobile devices, and according to Kumagai, that is what drove their success. The microSD market is rapidly growing as more smartphones ship with microSD card slots. Even though the newest phones made by industry giant Apple do not currently accommodate microSD cards, those made by Samsung and many others do.
Over time, smartphone manufacturers have reduced the amount of on-board memory that ships with smartphones, thus lowering their hardware costs. Consumers have compensated by adding additional storage, often using 8 GB microSD cards. In fact, the bulk of microSD cards sold is used in smartphones, but sales of larger cards (16 and 32 GB) continue to grow. MicroSD card use is also growing in other devices that need small form factors, such as consumer digital imaging and video cameras like the GoPro action camera, night-vision IP security cameras, nanny cameras, automotive in-dash cameras and tablets. MicroSD is still the storage space of choice as devices become smaller and cards gain higher capacity, become faster and exhibit better performance.
Capacity: It’s all in the flash memory technology
The fundamental technology in all SD cards and any type of solid-state storage device today is NAND flash memory. Current NAND flash memory chips use floating-gate processes that all manufacturers support. Over the years, decreasing the horizontal line width of the lithography technology used in NAND memory production has created higher density storage capacities. The industry roadmap shrank design-rule dimensions for memory features from 110 nm down to the current size of 19 nm, making smaller NAND chips and allowing microSD cards to use more of them to hold more data. At these thin-line widths, there are only a few electrons of charge inside a single level cell. NAND chips using 16 nm line widths will be coming soon, but Kumagai says the industry is starting to see the limitations of scaling to smaller lithography.
Within the next year, NAND suppliers are expected to roll out the next generation technology that will go vertical and offer much higher densities than the current technology. The 3-D concept involves grinding individual cells so they are much thinner and stacking more of them so there is more than one cell in the same horizontal plane. “This technology is more difficult to produce. The thinner it is, the more difficult it is to read all the different levels, and error correction becomes needed,” says Kumagai.
All major NAND suppliers have 3-D technologies in development now. “The microSD card will look the same on the outside and at the interface, but the new 3-D NAND processes may help reliability and have other impacts on the industry if the technology is cheaper,” Kumagai says.
One way higher reliability processes will change the industry is that it will create new uses for microSD cards. They will be used in high-end automotive or industrial applications such as bar-code readers and scanners that need to store important data.
Strategies for higher speeds
While memory manufacturers are increasing the storage capacity by improving NAND technologies, they are also increasing microSD card speed with a combination of hardware and software strategies. One way is through the interface. A new high-speed serial interface (UH-II) handles the speed by having a second row of pins connect to the outside world and a new file system that supports much larger micro XSDHC or SDXC cards that are 32 GB to 2 TB. The newest second-generation ultra-high-speed (UHS2) cards using this interface have much faster read and write times at up to 312 mbps, up from 104 mbps on older generation cards.
Another area where speed can be gained is in the flash-memory controllers. This component manages the NANDs and does a handshake to the outside world. The controllers in the fastest-speed-class microSD cards use strategies to help both functions, such as using multiple channels and interleaving data.
Suppliers in the microSD card space include Delkin Devices, Greenliant, Intel, Kingston Technology, Micron, OCZ Technology, Panasonic, PNY Technologies, Samsung and Toshiba. The microSD card industry is now integrating more features into the card itself. A few years ago SDIO stacks provided Wi-Fi capabilities in microSD cards. The newest trend is to combine security features with wireless capabilities, so microSD cards can be used by themselves to transmit secure data. Through the use of Smart microSD technology, shoppers may soon be able to make purchases securely and wirelessly through their microSD card without needing a SIM card or mobile provider. In these instances, financial organizations, such as credit card companies, would work independently with the microSD card maker so users could complete transactions with more flexible and less expensive financial packages.
Fig. 1: X-ray of the rectangular Kingston microSDHC/SDXC card – such as the Kingston SDC10/32GB – on a panel during the SMT production process before being separated and cut into the more familiar shape. The two + (plus) signs on top are the edges of one card, and portions of another card are viewable to the left and right. The large gold rectangle with a cross separating it into four parts is the NAND Flash. The smaller silver rectangle below with the gold wires coming out it is the controller. The gold wiring goes into the strata. (Source: Kingston Technology)