Solidigm introduced the first working prototype of SSD on PLC NAND memory

Solidigm, the NAND research and manufacturing part sold by Intel to SK hynix, took to the Flash Memory Summit 2022 to show the first working SSD prototype carrying the company's latest NAND technology: Penta-Level Cell (PLC). Samsung's 64G LPDDR4X, on the other hand, builds on NAND density by allowing a single cell to store up to five bits of data (up from QLC's four bits per cell), increasing the amount of storage space in each NAND flash chip.

The new development thus opens the door for even cheaper $/GB ratios on PLC SSDs than what is presently feasible with Quad-Level Cell (QLC) technology (let alone MLC and SLC technologies, which have been mostly relegated to enterprise, data center, and other critical environments).

As data production by humanity rises at an accelerated rate (with forecasts placing daily data generation at 463 exabytes per day by 2025), storage technology will need to develop to accommodate this deluge. With the rise of 5G and AI, all requiring enormous amounts of data storage, Solidigm sees PLC as a solution to scale while keeping costs down.

The idea of PLC is to add new voltage states, which will represent the cell's information bits. SLC only had to cope with two voltage states (a bit was either written or not), whereas MLC had to deal with four additional voltage states (so each cell may contain any combination of both a 0 and a 1).

The 32 voltage states required by PCM NAND technology to distinguish between all conceivable combinations of ones and zeros in the cell puts additional strain on the cells and at the controller level, which must account for the increased possibility of voltage states being improperly written, corrupting the data. To counter this, more advanced error correction methods must be included at the controller level.

Because of the extra bits and higher voltage states, each additional bit per cell necessitates a doubling of the voltage states, which has its own set of problems. To deal with the increasingly finer differences between states, NAND cells' life expectancies are shortened as their bit storage capacity increases. This decrease in NAND cell longevity as a result of an increase in bit storage capacity is one reason why QLC SSDs are commonly thought to be less sturdy (with cell "death" occurring sooner) than flash drives using fewer numbers of bits.

The laws of diminishing returns are obvious in scaling NAND density by adding more bits per cell. Each additional bit of information on a single NAND cell results in a 100 percent increase in voltage states (which adds to the problem), while storage capacity rises by half.

Solidigm's PLC NAND is built on Intel technology, therefore it uses a distinct type of cell than other major NAND makers, such as Micron, have been using. The NAND from Intel was based on floating gate transistors and was designed to boost bits per cell in order to enable the creation of PLC, according to Solidigm. Instead of focusing its manufacturing efforts on charge trap technology like Micron has done.

It's still unclear when PLC-based drives will be available. Western Digital has stated that they will not become commercially available until 2025, yet we are now in 2022 with Solidigm's functional prototype. But when they do arrive, clients can anticipate NAND devices with better $/GB ratios than any QLC drive could ever hope to offer. And if you believe Solidigm should be confined to the $/GB ratio, think again. The SK hynix Platinum P41 is one of the most efficient and rapid SSDs we've ever evaluated, and it's made by Solidigms' parent company. Because controllers and buses continue to develop, PLC SSDs will struggle to compete on performance, but they should provide good performance at a lower price as controllers and buses mature.