As NOR flash runs into scaling limitations, the company formerly known as Toshiba Memory thinks planar SLC NAND makes a good alternative for some applications. In the meantime, NOR isn’t disappearing, it’s just moving to satisfy different use cases.

Now officially Kioxia Memory, the company recently unveiled a family of SLC NAND flash memory products for embedded applications that need high-speed data transfers, including flat screen TVs, printers, wearable devices, and robots. Kioxia’s second-generation Serial Interface NAND is compatible with the widely used Serial Peripheral Interface (SPI) and offers increased speeds from 104 MHz to 133 MHz as compared with the previous generation. The new line consists of eight products in total with power supply voltages of 2.70 to 3.60V and 1.70 to 1.95V.

While NOR flash has long been a preferred memory for storing boot and even low-level operating system code, according to Kioxia memory business unit director Brian Kumagai, software requirements are getting more demanding and taking up more space, which makes sticking with NOR flash quite expensive when compared with NAND flash. There’s a cost savings benefit when you start hitting densities of 512 MB and higher, he said, even though some flash management integration work is required. “It's a little bit more work to use NAND Flash, but the cost benefit definitely justifies going to it,” added Kumagai.

While 3D TLC NAND gets a lot of attention for higher density products in larger systems such as enterprise storage, Kioxia senior staff applications engineer Doug Wong said SLC offers the best characteristics for endurance and for data retention for embedded applications that need smaller densities in devices with long life spans, such as TVs and gaming systems. “That's actually one of the reasons why SLC continues to exist.” NOR flash still has its advantages, added Wong. It's fast enough to do execute in place operations. “You can give it an address and get the instruction back fast enough that you don't really have to shadow code from a NAND flash into RAM space.”

However, as people expect more capabilities from the products presently using NOR flash, increased density requirements are going to drive the adoption of alternatives, said Wong, whether it’s an SPI SLC NAND device or MRAM, as it can be function as RAM space or as a non-volatile memory, he said. “There's going to be a general trend away from NOR flash in the future just because people want more capability and that's just going to require more software.”

The diminished used of NOR flash really boils down to its inability to scale, said Gregory Wong, principal analyst with Forward Insights, and for applications requiring one gigabyte and above. It’s expensive and there aren’t a lot options vendor-wise. A NAND option with an SPI interface makes a lot of sense for devices such as set-top boxes and televisions as they get even smarter and require more code.

But neither Kioxia’s Wong nor Forward Insights’ Wong sees NOR completely disappearing. The latter noted that as some applications outgrow NOR, others are popping up because the smaller density is enough for their needs. Many Internet of Things (IoT) devices can use it for code storage; and small devices such as wireless earbuds are opting for serial NOR, as are touch screen applications with finger sensors.

When the jump to NAND flash is necessary, SLC is optimal, said Gregory Wong, because it’s still a relatively small density, and as endurance and error corrections are critical for the applications involved, there’s no cost benefit to using MLC or TLC. “You get a lot of performance degradation and endurance degradation if you move to those capacities, so that's why they're sticking with SLC NAND,” added Gregory Wong.

By: DocMemory
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