It might not be as tasty as chocolate and peanut butter together, but the mixture of NOR and NAND flash might make a lot of sense for some applications, including the Internet of Things (IoT), which is one reason Winbond Electronics Corp. recently introduced its family of stackable SpiFlash memory.

The company’s SpiStack W25M Series stacks homogeneous or heterogeneous flash to provide memories of varying densities for code and/or data storage. The mixing and stacking capabilities provide designers with added flexibility to meet needs for a variety of small machine-to-machine (M2M) and IoT devices, said Mike Chen, Winbond’s director of technical marketing.

In a telephone interview with EE Times, Chen said Winbond wanted to innovate around the well-established 8-pin 8x6mm WSON package designers are already comfortable with, as well as the multi-IO SpiFlash interface and command set. “The small form factor has become popular as electronic devices are getting smaller.”

Each die can be used according to its specifically beneficial characteristics, Chen explained. SpiStack homogeneous memories are achieved by stacking SpiFlash dies, each with density ranging from 16Mb to 2Gb. For example, two 256Mb dies can be combined to form a single SpiFlash 512Mb NOR memory in the 8-pin package. Meanwhile, SpiStack heterogeneous memories stack a NOR memory with a NAND die, such as a 64Mb SpiFlash NOR blended with a 1Gb Serial NAND die, so designers can store code in the NOR die and data in the NAND memory.

Chen said Winbond sees a strong, growing market that marries NOR to store machine boot up code, as it can deliver better endurance and retention with fast random access time, with NAND flash to store data, as well as back up the boot up code. Customers have different criteria for flash memory application use. Some are prioritizing density, with others are more focused on performance aspects, such as erase times, which is a key feature in the PC accessory segment. He said customers expect high reliability from the NOR that handles code, while there is more room for error on data stored on NAND.

Chen said Winbond is not focused on having the highest capacity, and it’s looking how it might incorporate 3D NAND down the road.

Jim Handy, principal analyst with Objective Analysis, said it’s the first time he’s encountered a company that’s mixed NOR and NAND SPI in a single package. “It’s an interesting approach,” Handy said.

While much of the focus on NAND production has been about the 3D technology and increasing storage capacities for smartphones, tablets and enterprise storage to support exponential growth in data and large file sizes for things like 4K video, “there's a market for low capacity NAND and Winbond supports that market,” Handy said.

While Winbod’s package can’t accommodate 3D NAND, said Handy, for small devices such as those worn on the wrist, it’s more than enough space for the flash memory required. “This lets people use NOR flash for the code and NAND for their data.”

NAND in still significantly less expensive than NOR, Handy said, but NOR remains a good choice for a lot of applications, much as SRAM and EEPROM have endured. And although all of these memories are more expensive per byte, “they end up the cheapest chip you can buy.”

By: DocMemory
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