Flash storage faces challenge from Crossbar's RRAM
The hunt for memory technology to replace NAND flash storage within the next 10 years is under way, and startup Crossbar is planning to bringing its version of RRAM (resistive random-access memory) technology to market next year.
RRAM, a form of nonvolatile memory that is not available commercially yet, will be cheaper, smaller and more power-efficient than NAND flash, which is being used in solid-state drives and mobile flash drives, said Tanmay Kumar, vice president of device engineering at Crossbar.
The company on Monday announced a RRAM array for servers and appliances that will be able to store terabytes of data. The move comes after the first prototype RRAM chip for small and embedded devices like smartphones, tablets and set-top boxes was announced in August last year.
RRAM will be able to store data even after a computer is turned off, much like NAND flash storage. Crossbar said its RRAM can be 20 times faster and more power-efficient than NAND flash. However, the company did not provide specific IOPS (input/output per second), a common metric used to measure the performance of flash memory.
“[RRAM] is much faster on read and write compared to other nonvolatile memory,” Kumar said.
The first RRAM units with 8MB capacity of more will be available for evaluation starting in 2016, with the larger terabyte-range chips shipping a few years later. Information about specific storage capabilities were not provided, though Kumar said the server memory arrays could have 1TB or more per chip.
The latest RRAM array could sit next to DRAM in servers, Kumar said. RRAM could replace the NAND flash already being used in servers for caching or temporary data storage. However, it won’t get rid of DRAM, which is volatile but offers faster throughput for applications like in-memory databases
Crossbar’s RRAM has solid technological foundations and the potential to replace NAND, which may last a decade before manufacturing challenges catch up, said Jim Handy, principal analyst at Objective Analysis.
It is becoming more complex to make NAND flash, with chips getting smaller and with a wider array of defects being exposed in factories. Samsung has now started stacking NAND flash chips to add storage capacity, speed and power-efficiency, but there’s a limit to that as well, Handy said.
“Once NAND flash runs out of steam, some new technology is going to come and take its place,” Handy said. “Crossbar’s making sure that [its] version of RRAM has a shot.”
RRAM could find use in data centers where “gobs” of data are processed, but also in mobile devices, Handy said.
“It would equally at home in an iPhone,” Handy said.
The biggest problem is that Crossbar hasn’t started shipping RRAM yet, Handy said.
“Until they reach that milestone, all bets are off,” Handy said.
Other forms of nonvolatile memory under development being considered as possible NAND replacements include phase-change memory and FRAM (ferroelectric RAM), which have been under development for decades, but according to Handy, are losing support.
Startup Everspin is already shipping a form of MRAM (magnetoresistive random access memory) in small volumes to some customers that need fast write capabilities. Everspin’s MRAM is being used in products like ATMs, gambling machines and storage cards, where data retention is key in case of a power loss. Hewlett-Packard has announced its own form of memory called Memristor, which is another form of RRAM.
Crossbar’s brand of RRAM looks for a change of resistance to read data in the form of 1s and 0s, which differs from NAND flash and other forms of memory. Crossbar’s RRAM takes a layered approach to storing data as opposed to trapping a charge or using transistors. The three layers include a switch sandwiched between metallic and non-metallic electrodes. Positive or negative charges can be passed to read, write and delete data.
The initial design involved putting memory cells in a planar status, placing them right next to each other. But Crossbar has managed to layer memory cells to add more storage capacity, while keeping power consumption down, Kumar said.
Crossbar’s RRAM will be made using conventional CMOS (complementary metal oxide semiconductor) technology, commonly used to make chips. The first RRAM chips will be made using the 40-nanometer process, followed by an upgrade to the smaller and more power-efficient 28-nm process.