This The best solid state drive Currently using TLC or QLC memory. Kioxia (formerly Toshiba Memory) is the first 3D NAND manufacturer Start talking about 5 digits per unit (5 bpc) PLC (five-level unit) 3D NAND memory as early as 2019. Kioxia’s scientists and engineers certainly don’t want to be satisfied with their laurels. This year they demonstrated 6 bpc — six-level cell or HLC — 3D operating NAND memory, and believe that even 8 bpc — eight-level cell, or OLD — 3D NAND is also possible of. But there are some important nuances.
In order to store more than one bit per cell, NAND memory must maintain multiple different voltage levels in the cell. For example, MLC has four states per cell, TLC uses eight voltage levels, QLC has 16 voltage levels, and PLC has 32 voltage states. In other words, no matter what cell level you are talking about, both are affected. To store 6 bits per cell (HLC), the cell must store 2^6 or 64 voltage levels.
To build 3D NAND using such cells, manufacturers must overcome multiple challenges. They must find the right material that can handle and store 64 different voltage states, while also being able to distinguish between these states. This means that the voltage states cannot interfere with each other. Controlling temperature is also important, and it becomes more and more difficult as the number of bits per cell is higher.
To prove the possibility of HLC memory, Kioxia scientists immersed one of the company’s existing 3D NAND memory chips in liquid nitrogen (77K, -196°C) to eliminate cell degradation caused by rewrite cycles. The extremely low temperature also helps reduce the need for tunnel insulating films, lower voltage requirements, and stabilize materials. In short, this improves the physical properties and processes that occur in the IC.
Kioxia’s scientists stated that they not only managed to write and read 6-bit data from a cell and reliably hold it for 100 minutes, but they also achieved 1,000 program/erase (P/E) cycles durability. Of course, this is largely due to the temperature of -196C. According to its estimates, under normal conditions, the durability of 3D HLC NAND memory is about 100 P/E cycles.Kioxia presented the experimental results at the 5th IEEE Electronic Device Technology and Manufacturing Conference (EDTM 2021) in April 2021 (exhibition number: WE2P4-5), report Computer watch.
3D PLC NAND has not been commercialized yet, Western Digital (Kioxia manufacturing partner) I believe it will only make sense for some SSDs after 2025Western Digital further claimed that only 25% increase in density of 3D PLC caused too many problems.
In contrast, 3D HLC NAND increases the density of flash memory by 50% compared to 3D QLC NAND, so it is more likely to be commercially viable. In addition, Kioxia scientists believe that even an OLC 3D NAND with 8 bits per cell with 256 voltage levels is technically possible. The task of scientists and developers now is to find the right materials, designs and controllers to make 3D HLC and 3D OLC NAND run and commercially viable at room temperature.
If it fails, the development of multi-level cell 3D NAND will stop on the PLC, and flash memory manufacturers will have to focus on increasing the number of layers of 3D NAND flash memory to increase storage density.Of course, Samsung and SK Hynix believe that 600 arrive 1,000 floors It is feasible, which has opened the door to ultra-high capacity SSDs.
Even if Kioxia scientists succeed in making HLC and OLC NAND work at room temperature, they must develop suitable controllers that can reliably read and write data from such flash memory. Such controllers must support extremely complex ECC algorithms, which require powerful computing power. Will such a controller be too expensive and will offset the capacity advantages of 3D HLC and 3D OLC NAND? What kind of performance can even future HLC drives provide? We already know that even QLC drives tend to perform poorly in heavier use cases. Only time will tell, but we don’t expect TLC to disappear anytime soon.