Toshiba announced today that it has successfully developed what it claims to be the world’s first QLC — quadruple-level cell — 4-bit flash memory in a 3D flash device.
That’s pretty big news for the future of flash memory, creating even higher storage density at cheaper prices. Flash memory (very, very loosely) works by using a series of floating gate transistors with a charge value that is either assigned a “0” or “1” — one bit. These memory blocks are either arranged in a two-dimensional plane (planar NAND) or stacked in a more space efficient column (3D NAND, which is still relatively new).
To maximize storage, either of those memory blocks — whether in a 2D plane or stacked — can be divided up into more charge levels for even more data. Flash memory with four levels of charge per cell, or two bits, is known as multi-level cells or MLC, and memory with eight levels of charge (three bits) is referred to as having triple-level cells, or TLC.
QLC is the obvious next step, allowing even greater storage capacity by dividing each cell into 16 charge levels for four bits of data in each cell. For a while, it looked like reaching that level from TLC would be difficult; the level of precision in manufacturing needed to be able to accurately differentiate between charge levels increases exponentially. But Toshiba has pulled it off for its latest 3D NAND memory, which features 64-layer stacked QLC cells.
The QLC method resulted in a 768 gigabit die capacity, a dramatic improvement over the earlier 512 gigabit TLC dies. Toshiba notes that the new QLC dies can be stacked in a 16-die package to create a single device with 1.5TB of storage, which it claims is the largest capacity in a one unit.
What that means for the average consumer is that higher-capacity flash storage could soon be coming for less money. The advantage of MLC, TLC, and QLC flash is the dramatically increased storage density, which results in cheaper memory, albeit at the cost of speed and durability. Those trade-offs will continue to exist with QLC, given that there are even more levels of charge that need to be differentiated each time the drive is read, but Toshiba’s success is good news for users looking to maximize storage on a budget.
Toshiba has already started shipping the 3D QLC NAND samples to vendors for evaluation earlier this month, but there’s no timeline as to when we’ll see it available for consumers.