Everyone always wants more storage space, whether you have a 16GB iPhone or a 60TB SSD. The good news is, 3D NAND flash memory is here, and that’s going to be a great thing for bigger, faster, and cheaper memory. Wondering what 3D NAND is? Curious for what the flash drives of the future might look like? Read on.
How does flash memory work now?
Excellent question! Flash memory — the type of memory in SD cards, solid state hard drives, and your smartphone — works by having a series of floating gate transistors, which are assigned a charge value of "on" and "off" (1 and 0). These memory blocks are then arranged in a two-dimensional layout, side-by-side. As technology has improved, we’ve been able to fit more and more memory blocks onto a single die, resulting in higher capacity flash memory. Via Moore’s Law, ideally this would mean every two years, the number of transistors would double, allowing storage density to increase.
The single bit per cell method described above is a Single Level Cell (SLC), with each cell only having one bit per cell, but allows for higher speeds and endurance. Cells can also be divided up into 4 levels of charge, for two bits per cell (known as Multi Level Cell or MLC), or even eight levels of charge (Triple Level Cell or TLC), allowing for 3 bits of data per cell. MLC and TLC both increase storage density, but decreases the speed (since there are more levels of charge that need to be differentiated) and durability. But whether SLC, MLC, or TLC, the cells themselves are all on a flat plane in all of our flash memory today.
So why do we need a new technology?
there is a physical limit to how much smaller we can go
The problem as, as we try and cram as many memory cells onto a die, we start running into physical problems. Despite the ideals of Moore’s Law, there is a physical limit to how much smaller than 15nm (the current size of most NAND transistors) we can go. As cell size decreases, the walls between cells becomes smaller, and electrons leaking out becomes more of a problem — especially with MLC and TLC, where it’s already more difficult to determine the exact charge level. Scaling down to 13nm and beyond for flash memory has been difficult for manufacturers to accomplish without suffering loses in performance.
Alright, so how does 3D NAND help?
3D NAND, as the name implies, involves cutting multiple layers into the silicon, stacking memory cells to increase storage density. By stacking cells in 32 layers, we can reach much higher storage density in each die, as well as allowing the cells to space out more on each plane, helping reduce interference issues between the cells. Additionally, with 3D NAND, the stacked cells can still be MLC and TLC cells, leading to huge increases in storage. With MLC and TLC, the memory cells are stacked 32 levels deep for up to 256 gigabit MLC dies, and 384 gigabit TLC dies.
3D NAND technology allows for production of memory with three times the capacity
Intel and Micron, who have been working together on 3D NAND, hope to one day have these advances lead to SSDs the size of a stick of gum with over 3.5TB of storage, or 2.5-inch laptop sized SSDs with over 10TB of storage. Today, current 3D NAND technology allows for production of dies with three times the capacity of any 2D NAND, and it’s still very early days for the technology as a whole.
The disadvantage of 3D NAND is that it requires an incredible level of precision to produce, since each column needs to be perfectly aligned so that the memory blocks are still in a continuous series.
Those sound great! When can I buy it?
The good news is that while 3D NAND was first announced over a year ago, the first purchasable consumer models are coming out now. Intel is releasing its 600p Series of 3D NAND SSDs for consumers next week (as well as some other, more enterprise focused models), while ADATA’s Ultimate SU800 SSDs were announced earlier this week. The bad news is that both are available in the familiar sizes of 128GB, 256GB, 512GB, or 1TB of memory — so no 10TB laptops just yet — but the drives claim to offer higher speeds and reliability than a comparable planar NAND SSD. So those hoping to buy a 3TB thumb drive today will have to wait a bit.
As mentioned earlier, it’s still very early on for 3D NAND as a whole. But by allowing the number of transistors per die to continue to double it's given a reprieve to Moore’s Law, allowing it to continue onward for the time being. And these early advances in production of 3D NAND could hopefully mean even cheaper, more reliable, and higher-capacity storage for all our devices in the future. (At least, until the whole "atomic memory" thing works out.)