Fujistu Semiconductor Ltd. has become the first manufacturer to announce it is mass producing a new RAM that boasts 1,000 times the performance of DRAM but stores data like NAND flash memory.
The new non-volatile memory known as Nano-RAM (NRAM) was first announced last year and is based on carbon nanotube technology.
Fujitsu Semiconductor plans to develop a custom embedded storage-class memory module using the DDR4 interface by the end of 2018, with the goal of expanding the product line-up into a stand-alone NRAM product family from Fujitsu's foundry, Mie Fujitsu Semiconductor Ltd.; the stand-alone memory module will be sold through resellers, who'll rebrand it.
According to Nantero, the company that invented NRAM, seven fabrication plants in various parts of the world experimented with the new memory last year. And other as-yet unannounced chipmakers are already ramping up production behind the scenes.
Fujitsu plans to initially manufacture the NRAM using a 55-nanometer (nm) process, which refers to the size of the transistors used to store bits of data. At that size, the initial memory modules will only be able to store megabytes of data. However, the company also plans a next-generation 40nm-process NRAM version, according to Greg Schmergel, CEO of Nantero.
Initially, NRAM products will likely be aimed at the data center and servers. But over time they could find their way into the consumer market -- and even into mobile devices. Because it uses power in femtoJoules (1015 of a Joule) and requires no data clean-up operations in the background, as NAND flash does, NRAM could extend the battery life of a mobile device in standby mode for months, Schmergel said.
Fujitsu has not specified whether its initial NRAM product will be produced as a DIMM (dual in-line memory module), but Schmergel said one of the other fabrication partners "is definitely doing just that...for a DDR4 compatible chip in product design.
"There are several others [fabricators] we are still working with, and one, for example, is focused on a 28nm process and that's a multi-gigabyte stand-alone memory product," Schmergel said, referring to the DIMM manufacturer.
Currently, NRAM is being produced as a planar memory product, meaning memory cells are laid out horizontally across a two-dimensional plane. However, just as the NAND flash industry has, Nantero is developing a three dimensional (3D) multilayer architecture that will greatly increase the memory's density.
"We were forced to go into 3D multilayer technology maybe sooner than we realized because customers want those higher densities," Schmergel said. "We expect densities will vary from fab to fab. Most of them will produce four to eight layers. We can do more than that. Nanotube technology is not the limiting factor."
Currenty, NRAM can be produced for about half the cost of DRAM, Schmergel said, adding that with greater densities production costs will also shrink -- just as they have for the NAND flash industry.
"My understanding is that Nantero plans to bring NRAM to the market as an embedded memory in MCUs and ASICs for the time being," Jim Handy, principal analyst with semiconductor research firm Objective Analysis, said in an email reply to Computerworld. "This is a good strategy, since flash processes are having trouble keeping pace with the logic processes that are used to make MCUs and ASICs.
"An alternative technology like NRAM then stands a chance of getting into high volumes on the back of the MCU and ASIC markets," Handy added. "After that, it could challenge DRAM, but it will have some trouble getting to cost parity with DRAM until its unit volume rises to a number close to that of DRAM."
Should DRAM stop scaling, though, NRAM will encounter a big opportunity since it promises to scale at lower prices than DRAM will be able to reach, according to Handy.
Because of its potential to store increasingly more data as its density increases, NRAM could also someday replace NAND flash as the price to produce it drops along with economies of scale, Schmergel said.
"We're really focused in the next few years on competing with DRAM where costs don't need to be as low as NAND flash," Schmergel said.
One big advantage NRAM has over traditional flash memory is its endurance. Flash memory can only sustain a finite number of program/erase (P/E) cycles -- typically around 5,000 to 8,000 per flash cell before the memory begins to fail. The best NAND flash, with error correction code and wear-leveling software, can withstand about 100,000 P/E cycles.
Carbon nanotubes are strong -- very strong. In fact, they're 50 times stronger than steel, and they're only 1/50,000th the size a human hair. Because of carbon nanotubes' strength, NRAM has far greater write endurance compared to NAND flash; the program/erase (P/E) cycles it can endure are practically infinite, according to Schmergel.
NRAM has been tested by Nantero to withstand 1012 P/E cycles and 1015 read cycles, Schmergel said.
In 2014, a team of researchers of at Chuo University in Tokyo tested Nantero's NRAM tested it up to 1011 P/E (program/erase) cycles which represents more than one billion write cycles.
"We expect it to have unlimited endurance," Schmergel said.
Another advantage is that NRAM is being built using the DDR4 specification interface, so it could sport up to 3.2 billion data transfers per second or 2,400 Mbps -- more than twice as fast as NAND flash. Natively, however, the NRAM's read/write capability is thousands of times faster than NAND flash, Schmergel said; the bottleneck is the computer BUS interface.
"Nanotube switch [states] in picoseconds -- going off to on and on to off," Schmergal said. A picosecond is one trillionth of a second.
Because the company designed the memory using the DDR4 interface, speeds will be limited by the bus interface; thus, it only has the potential to be 1,000 times faster than DRAM on a technical specification sheet.
Another advantage is that NRAM is resistant to extreme heat. It can withstand up to 300 degrees Celsius. Nantero claims its memory can last thousands of years at 85 degrees Celsius and has been tested at 300 degrees Celsius for 10 years. Not one bit of data was lost, the company claims.
How NRAM works
Carbon nanotubes are grown from catalyst particles, most commonly iron.
NRAM is made up of an interlocking fabric matrix of carbon nanotubes that can either be touching or slightly separated. Each NRAM "cell" or transistor is made up by a network of the carbon nanotubes that exist between two metal electrodes. The memory acts the same way as other resistive non-volatile RAM technologies.
Carbon nanotubes that are not in contact with each other are in the high resistance state that represents the "off" or "0" state. When the carbon nanotube contact each other, they take on the low-resistance state of "on" or "1."
In terms of new memories, NRAM is up against an abundant field of emerging technologies that are expected to challenge NAND flash in speed, endurance and capacity, according to Handy.
For example, Ferroelectric RAM (FRAM) has shipped in high volume; IBM has developed Racetrack Memory; Intel, IBM and Numonyx have all produced Phase-Change Memory (PCM); Magnetoresistive Random-Access Memory (MRAM) has been under development since the 1990s; Hewlett-Packard and Hynix have been developing ReRAM, also called Memristor; and Infineon Technologies has been developing Conductive-Bridging RAM (CBRAM).
Another potential NRAM competitor, however, could be 3D XPoint memory, which will be released this year by development partners Intel and Micron.
Micron, which will market it under the name QuantX (and Intel under the name Octane), is targeting NAND flash because the technology is primarily a mass storage-class memory that, while slower, is cheaper to produce than DRAM and vastly faster than NAND.
"We're at DRAM speed. We have far greater endurance," Schmergel said.
"It should be superior to 3D XPoint, which wears and has a slower write than read cycle," Handy said. "If this is true, and if its costs can be brought to something similar to DRAM's costs, then it is positioned to replace DRAM. Cost is the big issue here though, since it takes very high unit volumes for prices to get close to those of DRAM.
"It's a chicken-and-egg problem: Costs will drop once volumes get high enough, and volume will get high if the cost is competitive with DRAM costs."