New chip architecture with CPU, storage & sensors in one package

Read an article the other day in MIT news, (3D chip combines computing and data storage) about a new 3D chip out of Stanford and MIT research, which includes CPU, RRAM (resistive RAM) storage class memories and sensors in one single package. Such a chip architecture vastly minimizes the off chip bottleneck to access storage and sensors.

Chip componentry

The chip’s sensors are based on carbon nanotubes. Aside from a layer of silicon at the bottom, all the rest of transistors used in the chip are also based off of carbon nanotube FET (field effect transistors).

The RRAM storage class memory is a based on a dielectric material which uses electrical resistance to store non-volatile data.

The bottom layer is a silicon based CPU. On top of the silicon is a carbon nanotube layer. Next comes the RRAM and the top layer is more carbon nanotubes making up the sensor array.

Architectural benefits

One obvious benefit is having data storage directly accessible to the CPU is that there’s no longer a need to go off chip to access data. The 2nd major advantage to the chip architecture is that the sensor array can write directly to RRAM storage, so there’s no off chip delay to provide sensor readout and storage.

Another advantage to using carbon nanotube FET’s is that they can be an order of magnitude more energy efficient than silicon transistors. Moreover, RRAM has the potential to be much denser than DRAM.

Finally, another major advantage is that this can all be built in one 3D chip because carbon nanotube and RRAM fabrication can be done at relatively cooler temperatures (~200C) vs. silicon fabrication which requires relatively high temperatures (1000C). Silicon cannot be readily fabricated in multiple layers because of the high temperatures required which will harm lower layers. But you could fabricate the lowest layer in silicon and then the rest as either carbon nanotube FETs or RRAM without harming the silicon layer.

Transistor/RRAM counts

The chip as fabricated has a million RRAM cells (bits?) and 2 million nanotube FETs. In contrast, in 2014, Intel’s 15-core Xeon Ivy Bridge EX had 4.3B transistors and current DRAM chips offer 64Gb. So there’s a ways to go before carbon nanotube and RRAM densities can get to a level available from silicon today.

However, as they have a bottom layer of silicon they can have all the CPU complexity of an Intel processor and still build RRAM and carbon nanotubes FETs on top of that. Which makes this chip architecture compatible with current CMOS fabrication techniques and a very interesting addition to current CPU architectures.

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Unclear to me why they stopped at 4 layers (1-silicon FET, 1 carbon nanotubes FET, 1 RRAM and 1 carbon nanotubes FET [sensor array]). If they can do 4 why not do 5 or more. That way they could pack in even more RRAM storage and perhaps more sensor layers.

Also, not sure what the bottom most layer of carbon nanotubes is doing. If I had to hazard a guess, it’s being used for RRAM control logic. But I could be wrong.

I could see how these chips could be used for very specialized sensor applications, with a limited need for data storage. The researchers claim many types of sensors can be created using carbon nanotubes. If that’s the case, maybe we might see these sorts of chips showing up all over the place.

Comments?

Photo Credit(s): Three dimensional integration of nanotechnologies for computing and data storage on a single chip, Nature magazine. 

Nanterro emerges from stealth with CNT based NRAM

512px-Types_of_Carbon_NanotubesNanterro just came out of stealth this week and bagged $31.5M in a Series E funding round. Apparently, Nanterro has been developing a new form of non-volatile RAM (NRAM), based on Carbon Nanotubes (CNT), which seems to work like an old T-bar switch, only in the NM sphere and using CNT for the wiring.

They were founded in 2001, and are finally  ready to emerge from stealth. Nanterro already has 175+ issued patents, with another 200 patents pending. The NRAM is currently in production at 7 CMOS fabs already and they are sampling 4Mb NRAM chips  to a number of customers.

NRAM vs. NAND

Performance of the NRAM is on a par with DRAM (~100 times faster than NAND), can be configured in 3D and supports MLC (multi-bits per cell) configurations.  NRAM also supports orders of magnitude more (assume they mean writes) accesses and stores data much longer than NAND.

The only question is the capacity, with shipping NAND on the order of 200Gb, NRAM is  about 2**14X behind NAND. Nanterre claims that their CNT-NRAM CMOS process can be scaled down to <5nm. Which is one or two generations below the current NAND scale factor and assuming they can pack as many bits in the same area, should be able to compete well with NAND.They claim that their NRAM technology is capable of Terabit capacities (assumed to be at the 5nm node).

The other nice thing is that Nanterro says the new NRAM uses less power than DRAM, which means that in addition to attaining higher capacities, DRAM like access times, it will also reduce power consumption.

It seems a natural for mobile applications. The press release claims it was already tested in space and there are customers looking at the technology for automobiles. The company claims the total addressable market is ~$170B USD. Which probably includes DRAM and NAND together.

CNT in CMOS chips?

Key to Nanterro’s technology was incorporating the use of CNT in CMOS processes, so that chips can be manufactured on current fab lines. It’s probably just the start of the use of CNT in electronic chips but it’s one that could potentially pay for the technology development many times over. CNT has a number of characteristics which would be beneficial to other electronic circuitry beyond NRAM.

How quickly they can ramp the capacity up from 4Mb seems to be a significant factor. Which is no doubt, why they went out for Series E funding.

So we have another new non-volatile memory technology.On the other hand, these guys seem to be a long ways away from the lab, with something that works today and the potential to go all the way down to 5nm.

It should interesting as the other NV technologies start to emerge to see which one generates sufficient market traction to succeed in the long run. Especially as NAND doesn’t seem to be slowing down much.

Comments?

Picture Credits: Wikimedia.com