NAND flash memory is the technology behind power-efficient, speedy solid state drives (SSDs) and other storage memory found in personal computers and mobile devices. While it is becoming increasingly common for consumer devices to be sold with SSDs, it is not usually within the same capacity that most standard hard disk drives (HDD) are sold in. Laptops sold with SSDs are in the range of 128 to 256 GB, while a laptop with an HDD is commonly anywhere between 500GB to 1 TB, and the price difference tends to be quite significant.
However, a shortage of NAND memory that began in 2016 has been impacting the electronics industry in a variety of ways. Not only is the already elevated cost of SSDs now rising with the low supply (up to a 16% increase in prices) but some companies are now attempting to take up the mantle to produce more, while others are seeking alternatives. Currently, there is reportedly up to a five month waiting time on flash memory production.
For electronic designers, the volatility of the price of NAND flash memory, and the potential of alternative memory technology on the horizon is certainly a topic to pay attention to in the upcoming few years. Robin Mitchell addresses some of the causes of component shortages and how designers can prepare themselves in his article, “What 2017’s Potential Component Shortage Means for Design Engineers” .
What is flash memory?
For those not familiar, flash memory consists of a series of gates which do not require a charge to retain data that is stored. This is called “non-volatile” memory and it's what is commonly found in mobile devices and SSDs in computers. This is unlike volatile memory, such as RAM, which can not retain memory when power is not being supplied.
Flash memory can be NAND type or NOR type—that is, memory cell arrays based off of NAND (NOT AND) logic or NOR (NOT OR) logic. The two types of flash memory types have their own advantages.
NAND memory is much more suitable for sequential memory access and storage (similar to traditional hard disk drives, and useful for the storage of PC data for applications or files), while NOR functions better as non-sequential memory access (such as Random Access Memory).
NOR flash memory is also useful for execute-in-place functions, allowing programs to run directly from storage memory instead of having to be copied to RAM first. However, it is becoming more common for processors to be designed with the capability to execute-in-place using NAND flash memory. NAND flash memory also has higher memory density than NOR flash memory.
A comparison of NOR and NAND cells. Image courtesy of Toshiba.
Currently, 2D NAND planar flash memory is the most common type used in devices such as SSDs, in Single Level Cell (1 bit of memory per cell), Multi-Level Cell (2 bits of memory per cell), or Triple Level Cell (3 bits of memory per cell) arrangements. Quad Level Cells (4 bits of memory per cell) are also feasible. Access speed, however, tends to decrease with the increase of bit density.
3D NAND Memory to Combat Moore's Law
As 2D planar suggests, the memory blocks are arranged in a 2-dimensional arrangement over the die of the device—flat and side-to-side. While transistors have become increasingly smaller over time to allow more memory blocks to fit on a single die, the components are now reaching a limit in how much smaller they may get. Currently, 13-15nm is roughly the limit. Any smaller is not only difficult to manufacture, but the behavior of the transistors then begins to change at such microscopic sizes, making devices less reliable.
This is where 3D NAND memory comes into play. 3D NAND stacks NAND memory blocks on top of each other in 32 layers, increasing memory capacity significantly. This configuration helps overcome the limitations of transistor size and permits the increase of memory density, with capacities of 10 TB potentially becoming commonplace.
The challenge with 3D NAND memory is that the manufacturing process requires much higher precision than 2D planar NAND memory, due to the necessity of vertical alignment of the memory bit cells.
Samsung has gotten a head start on the production of 3D NAND memory, although other companies such as Intel and Micron are also producing 3D NAND memory.
Cause of the Shortage
The current financial troubles of electronics conglomerate, Toshiba, is one of the likely contributions to the shortage of NAND flash memory. Toshiba is the second largest supplier of flash memory in the global market (second only to Samsung) and also the first company to begin producing NAND flash memory. The company has also struggled with the production of 3D NAND memory, further impacting the company.
However, Toshiba’s woes stem from the acquisition of a company to build nuclear power plants in the USA. The project resulted in the overrun of construction costs, accounting scandals, legal actions, unhappy stockholders, and billions of dollars in debt for the company.
As a result, Toshiba has recently announced that it will be selling off the company’s semiconductor division which produces NAND memory. Likely bidders include Western Digital, Micron Technology, and SK Hynix.
Samsung’s recall of the Galaxy Note 7 smartphone also contributed to the global shortage, as millions of devices had to be returned and replaced in the market, along with each device’s flash memory unit.
In response to the shortage of NAND flash memory over more than a year, an increasing number of companies are now throwing their hats into the memory production ring. While demand is far outstripping supply at this current time, it is possible that the industry may begin to over-produce in an attempt to make up for the long-lasting shortages.
For devices like mobile phones and tablets, cloud memory storage remains a viable alternative without having to increase on-device memory capacity. However, for laptops and PCs, HDD, or HDD/SDD hybrids, remain the most economical options.
Featured image courtesy of Storage Review.