Nantero is exploring a new class of memory devices it calls nanoRAM

By Brian Santo, contributing writer

Nantero appears to be pulling away from the pack of companies that are exploring
potential successors to silicon storage with a new class of memory devices it
calls nanoRAM. Non-volatile random access memory (NRAM) is based on carbon nanotubes (CNT). 

Image source: Nantero.

When interest in carbon nanotubes was revived in the early 1990s, it was
understood CNT might make good semiconductors. That initial excitement was
rekindled in 2004, when CNT was discovered to exhibit electron mobility far
superior to silicon
. At the time, indications were that circuitry based on CNT could be easily
assembled with little regard for impurities. That all lead to speculation that
CNT could replace silicon relatively quickly.

That excitement early in the century was followed by more than a decade of
disappointment. It turns out the assumption that impurities were barely
relevant was wrong. It was discovered that impurities had to be reduced to 10
parts per billion, according to Nantero, as reported by IEEE Spectrum. The company now has
patented processing technology that gets impurities down to 1 part per billion.

The setback in processing gave the company time to conduct research in
semiconductor technology. Nantero’s original semiconductor device had three
terminals, one of them for switching. The company eventually devised a
two-terminal device, which was not only inherently smaller, but is also subject
to scaling down in size. Furthermore, Nantero developed a way to assemble
nanotubes on silicon.

This allows Nantero to make use of transistors on the silicon substrate as
drivers. As important, if not more so, Nantero’s CNT-based devices can be
fabricated on standard CMOS production equipment. This is a tremendous
advantage, as semiconductor manufacturers will have to do minimal, if any,
retooling. Keep in mind that it costs more to build a leading edge fab than the
GDPs of several dozen countries.

Though CNT is exotic, NRAMs should behave a little different from any other
random access memory, such as, flash memory or ferroelectric RAM.

In fact, flash appears to be approaching a wall in terms of density (FRAM
is, too, but it always has been a niche product). Flash vendors are searching
for a potential replacement.

It turns out that NRAM could be that replacement. Like flash, NRAM is
nonvolatile. Nantero believes NRAM will be able to match the densities of
current flash memories, and said that theoretically it could be made far denser
than that.

Because NRAMs will be based on carbon, which is cheap, and use standard
CMOS production equipment processes (which won’t add much in the way of cost),
NRAM is almost certain to be relatively inexpensive.

Nantero announced a set of products aimed at applications that might
otherwise have used flash. They include the following:

  • A multi-gigabyte DDR4-compatible nonvolatile standalone memory
  • A standalone chip designed as a cache for solid state drives (SSD) or hard
    disk drives (HDD)
  • A line of embedded memories.

Nantero said its DDR4-like product will have speed comparable to DRAM at a
lower price per gigabyte. (DDR4 is a double data rate fourth-generation
synchronous dynamic random-access memory, or SDRAM.)

The cache, based on nonvolatile technology, will remove the need for battery
backup. Nantero said this allows for a dramatic expansion of cache size,
substantially speeding up the SSD or HDD.

Embedded memory will eventually be able to scale to 5 nm in size (the most
advanced semiconductors are being produced at the 10 nm and 7 nm nodes); operate
at DRAM-like speeds, and operate at very high temperature, said Nantero. The
company said the embedded memory devices will be well-suited for several IoT
applications, including automotive.

CNT has disappointed before, but there are signs that this time around
Nantero might come through. Recently, some of the world’s biggest industrial
companies invested in Nantero, including Dell, Cisco,
Kingston Technology, Schlumberger and three “global” semiconductor
manufacturers that Nantero won’t name yet.

Most encouraging, however, may be that Fujitsu licensed Nantero’s
technology
. Fujitsu also is co-developing the technology, and has agreed to act as a
foundry. Fujitsu expects to introduce NRAM embedded LSI in mass production in
2019, an extraordinary claim to make if it wasn’t confident it can deliver.

In a video
discussing NRAM technology, Matsumiya Masato, Fujitsu vice president, head of
the company’s system memory operation, said Fujitsu is preparing to mass
produce NRAMs in 2019 using a 55-nm process. Masato explained that NRAMs share
the very fast write times and low power consumption of FRAM, with similar write
endurance, but NRAM is also robust at high temperatures. He said that if
NRAM read/write density and memory density is improved, NRAM could replace
DRAM. 

There are many alternative memory proposals with promise, but Nantero
appears to have been able to reap CNT’s potential while putative rivals are
still doing basic R&D on various materials and device architectures.

Silicon hasn’t hit a dead end yet. Intel’s 3D XPoint SSDs (solid state
drive) are hailed as some of the fastest memory available. But the
manufacturing process is complicated and the devices are expensive.

The number of possible alternatives to common silicon-based memory is
boggling. Some are based on different materials; others on different
architectures; some on both. They include a magnetic RAM based on gadolinium and iron; a new, unspecified
ferroelectric material that is one of the first in its category to exhibit all
the characteristics useful for computer memory; and diselenides and molybdenite.

One new approach is vacuum-channel
transistors
; another is embedding semiconductors with
nanostructures. And then there is a fairly well-stocked category of possible
devices based on exotic physics phenomena, such as quantum bits (Qbits), nanoscale optical quantum
effects
, and skyrmions.

Any or all of these technologies could eventually prove to be commercially
viable, but most of them are at the stage where researchers are still
characterizing the basic physics.