System Bits: Jan. 10

Speeding up computing tasks by turning memory chips into processors
In a development that could lead to data being processed in the same spot where it is stored, for much faster and thinner mobile devices and computers, a team of researchers from Nanyang Technological University, Singapore (NTU Singapore), Germany’s RWTH Aachen University, and interdisciplinary research center Forschungszentrum Juelich has found a way to make memory chips perform computing tasks traditionally done by computer processors.

Their approach is built using state-of-the-art memory chips known as Redox-based resistive switching random access memory (ReRAM). SanDisk and Panasonic are expected to have this type of memory — well suited for IoT applications — available soon.

Interestingly, instead of storing information, NTU Assistant Professor Anupam Chattopadhyay, Professor Rainer Waser from RWTH Aachen University, and Dr Vikas Rana from Forschungszentrum Juelich have demonstrated how ReRAM can also be used to process data.

To explain how their approach works, the researchers reminded that all computer processors on the market today use the binary system, composed of two states – either 0 or 1. The prototype ReRAM circuit built by the team processes data in three states instead of two. For example, it can store and process data as 0, 1, or 2, known as Ternary number system.

And because ReRAM uses different electrical resistance to store information, it could be possible to store the data in an even higher number of states, hence speeding up computing tasks beyond current limitations.

Chattopadhyay said in current computer systems, all information has to be translated into a string of zeros and ones before it can be processed, which is like having a long conversation with someone through a tiny translator, which is a time-consuming and effort-intensive process. “We are now able to increase the capacity of the translator, so it can process data more efficiently.”

The researchers believe that using ReRAM for computing will be more cost-effective than other computing technologies on the horizon, since ReRAMs will be available in the market soon.

Cooling circuits
Another use for graphene: transferring heat. According to Rice University researchers, a few nanoscale adjustments may be all that is required to make graphene-nanotube junctions excel at transferring heat.

The Rice lab of theoretical physicist Boris Yakobson found that putting a cone-like “chimney” between the graphene and nanotube all but eliminates a barrier that blocks heat from escaping.

He reminded that heat is transferred through phonons, quasiparticle waves that also transmit sound, and this new theory offers a strategy to channel damaging heat away from next-generation nano-electronics.

As both graphene and carbon nanotubes consist of six-atom rings, which create a chicken-wire appearance, and both excel at the rapid transfer of electricity and phonons, when a nanotube grows from graphene, atoms facilitate the turn by forming heptagonal (seven-member) rings instead.

Simulations by Rice University scientists show that placing cones between graphene and carbon nanotubes could enhance heat dissipation from nano-electronics. The nano-chimneys become better at conducting heat-carrying phonons by spreading out the number of heptagons required by the graphene-to-nanotube transition. (Source: Rice University)

The researchers have determined that forests of nanotubes grown from graphene are excellent for storing hydrogen for energy applications, but in electronics, the heptagons scatter phonons and hinder the escape of heat through the pillars.

As such, the team discovered through computer simulations that removing atoms here and there from the 2D graphene base would force a cone to form between the graphene and the nanotube. The geometric properties (aka topology) of the graphene-to-cone and cone-to-nanotube transitions require the same total number of heptagons, but they are more sparsely spaced and leave a clear path of hexagons available for heat to race up the chimney.

Yakobson said one way is to use this technology is as building blocks to fill 3D spaces with different designs to create anisotropic, nonuniform scaffolds with properties that none of the current bulk materials have. Here, the team studied a combination of nanotubes and graphene, connected by cones, motivated by seeing such shapes obtained in other experimental labs.

What is fascinating is that the tunability of such structures is virtually limitless, the researchers pointed out, stemming from the vast combinatorial possibilities of arranging the elementary modules. The actual challenge is to find the most useful structures given a vast number of possibilities and then make them in the lab reliably.

Stretchable electronics
According to researchers at Missouri University of Science and Technology, electronic components that can be elongated or twisted – known as “stretchable” electronics – could soon be used to power electronic gadgets, the onboard systems of vehicles, medical devices and other products, and 3D printing-like approaches to manufacturing may help make stretchable electronics more prevalent.

The team assessed the current state of the emerging field of stretchable electronics, focusing on a type of conductor that can be built on or set into the surface of a polymer known as elastomer, that could one day replace the rigid, brittle circuit board that powers many of today’s electronic devices. These could be used, for example, as wearable sensors that adhere to the skin to monitor heart rate or brain activity, as sensors in clothing or as thin solar panels that could be plastered onto curved surfaces, they said.

New bendable electronic devices like the one pictured above could become more common in the future. (Source: Missouri University of Science and Technology)

But the key to the future of stretchable electronics is the surface, or substrate, they said. Elastomer, as its name implies, is a flexible material with high elasticity, which means that it can be bent, stretched, buckled and twisted repeatedly with little impact on its performance but one challenge facing this class of stretchable electronics involves “overcoming mismatches” between the flexible elastomer base and more brittle electronic conductors. However, a relatively new manufacturing technique known as additive manufacturing may help resolve this issue.

Additive manufacturing is a process that allows manufacturers to create 3D objects, layer by layer – much like 3D printing, but with metals, ceramics or other materials. The researchers suggest that additive manufacturing could be used to “print” very thin layers of highly conductive materials onto an elastomer surface. “With the development of additive manufacturing, direct writing techniques are showing up as an alternative to the traditional subtractive patterning methods.”

Subtractive approaches include photolithography, which is commonly used to manufacture semiconductors.

At Missouri S&T, they are testing an approach the researchers call “direct aerosol printing,” which involves spraying a conductive material and integrating with a stretchable substrate to develop sensors that can be placed on skin.

Yet further challenges must be addressed before stretchable electronics become widely used as components in consumer electronics, medical devices or other fields, the researchers say. These challenges include the development of stretchable batteries that can store energy and the need to ensure that stretchable electronics and the malleable surfaces they’re built upon perform and age well together.

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