What is 3D NAND Flash?
Storage drives have been progressing for the past 70 years, to the point of having massive storage sizes at affordable prices, which are reliable enough for consumer and industrial uses. Storage size, however, is just one parameter that drives needed to meet.
Speed became important when CPUs and RAM speeds started increasing, making storage drives a pretty obvious hurdle in the overall performance of computers. Hard drives could only go as fast, leading to solid-state drives or SSDs.
SSDs are faster, have no moving parts, but were more expensive to produce in terms of storage size. Changes had to be made, particularly to the flash memory and the way it is layered in the drive, leading to 3D NAND.
But how is 3D NAND different to planar NAND and what is NAND in the first place?
Understanding NAND – Non Volatile Memory
NAND is a type of flash memory, one of the two types used for storage, the other being NOR. NAND stands for NOT AND. It is not an acronym, as many would infer. NAND uses NAND gates, while NOR uses NOR gates. The gates are used to store data, and are faster and more reliable when it comes to storing data compared to NOR gates.
In storage devices such as USB flash memory, SD cards and SSDs, NAND cells are used as storage units.
How NAND Works
A typical NAND storage cell has a transistor meant for storage and a floating gate and control gate. The floating gate is used to store an electron charge, and an oxide layer keeps the electrons even when the device is not receiving power. This cell sits on top of a semiconductor silicon substrate and the aforementioned oxide layer is used as an insulator.
When the floating gate is charged, it reads a 0 and when it is not charged, it reads a 1. When writing data, high voltage is applied to the control gate through the substrate, which tunnels electrons through the oxide layer (also known as tunneling). This process damages the oxide layer, leading to wear. In a typical configuration for storage, NAND cells are organized in a single plane.
Planar NAND
Planar NAND, as the name implies, sees NAND cells organized one next to another. This worked for a while, but the only way to increase storage size while retaining the same chip size with this technology was to squeeze the cells closer and use smaller cells.
This, however, led to problems with quantum physics, because the cells were so small and too close to one another. Charges would jump from one cell to another at random, causing at best, bit errors, at worst, complete data loss. The solution was 3D NAND.
What is 3D NAND?
Given that expanding storage drives horizontally would go far beyond the already established specifications for drive size (NVME or 2.5 inch SSDs), 3D NAND was the solution. 3D NAND vs v NAND, it was a matter of naming, some manufacturers preferring 3D, others v, which stands for vertical.
With vertical NAND, cells are stacked on top of each other in layers, thus increasing the storage size per chip. There are interconnects between the layers. Due to the layering, the cells can have shorter connections, which boosts performance while retaining stability.
Manufacturers use different types of NAND designs, namely floating gate and charge trap. All larger SSDs, including external SSDs, use 3D NAND or v NAND as a design principle. 3D NAND drives typically use MLC, TLC or QLC (NAND cell layers, or how many bits per cell can be stored, MLC for two, TLC for three and QLC for four).
Price and Performance
3D NAND is cheaper to produce compared to older planar NAND. Customers get more gigabytes per currency, but also a faster drive which is more reliable (which also has to do with SSD development and maturity.
Readily available consumer drives extend to 8TB and in some cases to 15TB. There are special SSDs which go far and beyond these numbers, but are extremely expensive and used in niche scenarios.
The Future of NAND Storage?
3D NAND’s limits have yet to be reached. Given that cells can be only so small before quantum physics ruins everything, 3D NAND is bound to hit a wall at some point, but until that time, the technology is used to produce the best SSDs we currently have on the market.
Looking forward, 3D NAND is expected to mature even more and increase storage size. In the future, quantum computing storage might be a valid substitute, but that might not even be realized, due to the volatility of quantum physics.
Summary and Conclusion – 3D NAND Gives Us Reliable, Cheap and Fast Storage
Vertical stacking of NAND cells enables us to have cheap and fast SSDs, where prices have been equalized with HDDs, which was one of the benefits of hard drives. Solid state drives are looking most likely going to be the future of storage, with v NAND leading the way at the moment.