Toshiba’s new quadruple-level 3D cells could be the next big thing in low-cost flash memory
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
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