TLC NAND, which stores 3 bits of data per NAND cell, is not truly new. It existed for years in many generations of planar 2D NAND. 3D NAND’s evolution started with SLC NAND (i.e., 1-bit-per-cell NAND); eventually, MLC NAND (i.e., 2-bits-per-cell NAND) was adopted in most of the market. To further improve the cost per bit, TLC NAND successfully achieved market niches, but it prevailed mostly where low-cost took precedence over high-reliability.
Planar NAND technology progressed from generation to generation through lithography shrinking, which means that the flash array progressively became smaller. As the flash array shrinks, there are fewer electrons per data bit, and the capacitive coupling between adjacent flash cells degrades.
With the advent of 3D NAND, TLC is radically different. When 3D NAND advances from one generation to the next, the size of the NAND cells don’t change. The idioms “lithography shrink” and “lithography scaling” do not apply as 3D NAND technology nodes advance. The progression of 3D NAND is analogous to building taller skyscrapers because the NAND flash cells are stacked vertically. The number of NAND cells in the stack increases from generation to generation, which means the cell size and the isolation between adjacent cells is essentially constant.
3D NAND uses a larger cell size than the most recent planar NAND flash generations. With this larger cell size, the number of electrons per bit of data in TLC 3D NAND is the same or better than the latest nodes of MLC 2D NAND, so the endurance and data retention is roughly equivalent. TLC 3D NAND has demonstrated more than 10,000 program/erase cycles with robustness suitable for many applications. For automotive applications with extremely rugged usage environments, the requisite 3000 program/erase cycles can be achieved across a very broad temperature range, with prolong product life.
With evolving Advanced Driver-Assistance Systems (ADAS) and In-Vehicle Infotainment (IVI), the automotive industry is pushing the need for higher storage densities with a corresponding need for high performance while reducing cost. Higher speed host interfaces are also emerging, including UFS and PCIe. To support these high-speed interfaces, the number of internal NAND channels is increasing as well. And while high-speed NAND-based solutions such as PCIe are ubiquitous for cloud storage, automotive solutions seem to be taking a different evolutionary path. The automotive solutions focus on smaller form factors, lower power, higher performance per virtual machine, and higher performance per unit of energy.
Micron is at the forefront of meeting these requirements with the recent announcement of 2100 SSD based on 64 layer TLC for automotive and industrial applications This DRAM-less SSD available in both BGA and 22.30 M.2 form factors takes on the low-cost and low-power advantages of incumbent solutions (i.e. eMMC & UFS) with an enterprise-class host interface (PCIe Gen3) that offers significantly higher performance while supporting the full automotive temperature range from -40C to 105C (Tc).
For further details, see: