NAND flash devices, available in 128Mb to 2Tb densities, are used to store data and code. Low-density NAND flash is ideal for applications like STBs, digital televisions (DTVs), and DSCs while high-density NAND flash is most commonly used in data-heavy applications like SSDs, tablets, and USB drives. There is a continuous effort to reduce the cost/GB of NAND devices, so device life cycles tend to be shorter with more frequent process lithography shrinks. NAND requires a controller, either internal or external, and specific firmware for error code correction (ECC), bad block management, and wear leveling.
There are two primary types of NAND: raw and managed. Raw NAND comes in different flavors, including single-level cell (SLC), multilevel cell (MLC) and triple-level cell (TLC). Raw NAND requires external management but is the lowest cost/GB NAND flash available. Managed NAND incorporates memory management into the package, simplifying the design-in process.
Raw NAND provides the lowest cost per bit but requires an external host controller (not contained within the package) to perform all manage¬ment functions (e.g., ECC, FTL).
- One bit per cell; high performance and write endurance; designed for high-end, high-density, mission-critical systems where NAND high performance standards and reliability are required and cost reduction is not a major driver
- Low-density SLC devices with a NOR-like serial interface to simplify system design
- Two bits per cell; a good balanced of performance and write endurance for a wide range of cost-sensitive, high-density applications
Embedded MLC+ NAND
- Uses special programming algorithms to extend write endurance; typically used in high-write workloads like time shifting (pausing live TV)
- Three bits per cell; high cell density, but lower performance and endurance specifications; most often used in mass storage consumer applications (e.g., client SSDs, USB drives or SD cards) with very high cost sensitivity
Managed NAND provides simpler solutions and speeds time-to-market because the controller is embedded within the package to handle wear leveling, bad block management and ECC.
- High-capacity NAND flash device combined with a high-speed MultiMediaCard (MMC) controller in a single BGA package; suitable for designers looking for a fully managed device and ease of design for MMC-like, application-to-application interoperability for a wide range of networking, industrial, and automotive applications
On-die ECC NAND
- Hybrid between raw and fully managed NAND; ECC is integrated while wear leveling and bad block management are handled by the host controller
- NAND-based drives that enhance reliability, reduce power, and provide faster performance compared to hard disk drives (HDDs)
- Embedded USB bring the density and reliability of an SSD to networking and embedded applications with a simple universal serial bus (USB) connector. An embedded USB is physically smaller than a 1.8-inch HDD, costs far less to implement than even the cheapest hard drive, draws a mere 330mW of power when it’s actively reading or writing data, and will boot much faster than most hard drives.
- UFS is a high-performance storage interface for applications that require faster sequential & random performance over eMMC with low power consumption
- SD,microSD cards and USB flash drives are ideal for applications that require flash memory to be easily removed or installed
- More and more NAND Flash memory is being used in multichip packages (MCPs) where it is paired with Mobile LPDRAM in a variety of form factors. NAND/LPDRAM MCPs are offered in densities of 1GB to 4GB for SLC NAND and 1GB to 8GB for e.MMC™ Embedded Memory.
A basic knowledge of the various kinds NAND Flash-based memory solutions available can help designers make informed decisions about which NAND Flash device to specify for a particular design. This article's general description of each of the NAND Flash options helps illustrate what makes them better suited for some applications than others. More technical information about each memory type can be found in the Products section of our Web site.
- Jim Cooke, “Flash Memory 101: An Introduction to NAND Flash,” CommsDesign (March 20, 2006)
- Open NAND Flash Interface