What's the Difference Between Commodity and Embedded NAND Flash Memory?

NAND flash memory has been on the market for decades and many of electronic products we use on a daily basis feature some form of NAND —from wireless phones to automobiles— but the function this memory serves can be vastly different. This difference in function has caused a divergence in the evolution of NAND flash memory, leading to two distinct memory product categories: commodity and embedded NAND.

NAND Flash Memory for Commodity

Commodity NAND flash memory is commonly used in consumer devices; these devices are price sensitive and require mass storage for music, videos, books, photos, games and other user data. Over time, the demand for storage has increased, but the sensitivity towards price has stayed the same. As a result, there is a never ending urgency for commodity NAND suppliers to continuously reduce cost.

This cost reduction battle is fought on two fronts. On one hand, memory suppliers are reducing cost by sacrificing performance and quality. Instead of selling higher quality and performance single-level cell (SLC) NAND, this segment uses lower quality and performance multi-level cell (MLC) NAND and, in some cases, even lower quality and performance three-level cell (TLC) NAND. Consumer devices accommodate this degradation by either setting lower expectations, for example in USB flash drives or solid state drives (Fig. 1), or by managing around it with complex controller technologies, like those used in SSDs. Memory suppliers also combat cost reduction by hopping from one technology node to the next at a very fast pace.

Figure 1. OCZ's forthcoming solid state disk utilizes three-level cell (TLC) NAND flash storage.

The cost reduction battle is true for commodity NAND flash memory makers and for DRAM memory suppliers, but because the commodity NAND market is growing along with a very large consumer-driven industry, it is a magnet for the lion share of the NAND supply.

NAND Flash Memory for Embedded

Devices in the embedded market, like set-top boxes, automobiles, industrial meters, sensors and GPS navigation systems, do not follow the same storage/cost cycle as those within the commodity NAND flash market. These devices require NAND flash memory that focuses more on reliability than large storage space The important function of embedded NAND flash memory is to provide predictable performance and long term product support. Embedded NAND suppliers are held to a higher standard than commodity NAND suppliers, who are driven by the agenda of driving down cost.

Long term product support is vital for embedded applications as the technology it powers is expected to last many years, for example: wireless companies use embedded NAND in 4G LTE base stations and when companies deploy this technology they want to be sure they don’t have to send people out to service the stations frequently. Similarly, cable providers use embedded NAND in TV set-top boxes as they don’t want to have to swap out boxes frequently, and automotive manufacturers need the NAND flash memory they use within in-vehicle infotainment systems to run as long as the car does, which averages ten years.

The Difference Between NAND Flash

The key differentiators between commodity NAND and embedded NAND are performance, reliability, extended temperature support and long term product support. Embedded NAND flash memory is SLC based; SLC NAND read performance is approximately 3X faster than MLC NAND read performance, and SLC NAND program performance is 7X to 10X faster than MLC NAND.

Each physical memory location in an embedded NAND flash memory device can be written at least 10X more than memory locations in a commodity NAND flash memory device. Commodity devices manufacturers make up for this lack of reliability by adding more density to their device. Embedded NAND does not need the additional density, and typically does not have the necessary space needed to add additional capacity.

Embedded NAND flash memory devices need to operate at a consistent level for a long time, because embedded platforms are used by their customers for many years. The 10X amount of write into an embedded NAND is a key enabler of long life. Embedded NAND flash memory also comes with -40C to 85C or more extended temperature support, which is highly desirable in automotive, industrial and many consumer electronic applications.

Last but not least, embedded platform designs do not change as often as commodity platforms. These platforms cannot keep pace with technology nodes changing once every year and a half. A serious embedded NAND supplier needs to support a product for at least five years in the roadmap.

NAND Evolution

Embedded NAND demand has been growing over time, partly because it is complemented by development in silicon systems (processors and controllers), which have made NAND easier and more efficient to work with. Additionally, NAND’s inherent ability to achieve higher densities quickly has lead to its inclusion in embedded systems as applications grow beyond where NOR flash is today. Other reasons include the simple fact that as features and functions increase – and devices become more connected and graphically rich – the needs for both commodity and embedded NAND grow.

Communication media is rapidly changing with more and more people getting connected every day. Network memory modules and wireless communication are on the rise and embedded NAND will play an essential part in the future of this technology. With the influx of smart TVs and new set-top boxes, our living rooms and homes are getting smarter. We are also seeing a large amount of growth in automotive infotainment, which requires more memory. Additionally, more industrial sensors and timers will be required as the demand for smarter, more efficient systems grows across industries.

This thirst for information and richer user experiences will push both NOR and embedded NAND demand; parallel and serial NOR flash will provide fast boot and rich and interactive user experience, while NAND will provide bandwidth and storage for application and data. In the next five to ten years, the growth will almost double in this market.

Commodity NAND demand is growing even faster and it is growing with the tremendous pressure on cost, for example: the USB and SD card markets have to meet $10 to $20 price points for consumers at retail stores, and SSDs have to compete against cost per GB of hard disk drives. They also have to support capacity levels that are meaningful to customers, which are continuing to increase. Just look at smartphones, they have capacities ranging from 8GB to 64GB, and 1GB can only store approximately 50 10MP pictures.

Commodity NAND is also running into technical obstacles as manufacturers strive to reach higher densities. There is a general consensus that few years from now commodity NAND makers will have to find a new approach beyond today’s Floating Gate technology as they strive to meet consumer needs for space. One alternative approach is Charge Trapping, a potential bridge before a next new generation memory technology emerges. Charge Trapping devices have a more planar structure, creating a scaling advantage over Floating Gate technology, and MirrorBit technology on top of Charge Trapping can be used to extend density range by allowing two bits to share the same memory cell. The scalability and flexibility of MirrorBit and Charge Trapping technologies will continue to deliver the benefits of smaller process lithographies combined with market-leading capabilities in logic integration.

The industry is also investing in the development of other technologies. Scientists are looking into the scalability of technologies like MRAM, PCMS and RRAM. MRAM has unlimited and fast writes, but this technology comes up against challenges in scaling as well as reaching the cost structure for broad market adaptation. RRAM is intended for extremely high density and has the potential to be more cost efficient than other memory, but a number of breakthroughs are still needed before it becomes a viable alternative. Additionally, both MRAM and RRAM use materials that can create challenges in the manufacturing process. These, and other new alternative memory technologies, are still in the development phase and it doesn’t appear as though there will be a cost-effective commodity NAND alternative for at least five to eight years.