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Molybdenum Disulfide Could Help Memristors Mimic Neurons

2-D material offers way to produce third-terminal memristive devices, potentially key to new brain-like computers

2 min read
Molybdenum Disulfide Could Help Memristors Mimic Neurons
Illustration: iStockphoto

The memristor seems to generate fairly polarized debate, especially here on this website in the comments on stories covering the technology. The controversy seems to fall along the lines that the device that HP Labs’ Stan Williams and Greg Snider developed back in 2008 doesn’t exactly line up with the original theory of the memristor proposed by Leon Chua back in 1971.

While this debate will not likely abate, research is continuing in developing two-terminal non-volatile memory devices based on resistance switching.

Along these lines, researchers at Northwestern University have pushed the envelope of the two-terminal device—which can only control one voltage channel—by creating a third terminal. The researchers believe that this will expand the capabilities of memristors into more complex electronics, paving the way for computers to more closely mimic the neurons of the human brain.

“Computers are very impressive in many ways, but they're not equal to the mind," said Mark Hersam, of Northwestern University's McCormick School of Engineering, in a press release. "Neurons can achieve very complicated computation with very low power consumption compared to a digital computer.”

To achieve this biomimetic capability, sometimes called neuromorphic computing, Hersam believes that the use of memristors as a memory element in an integrated circuit or computer could be the key because of their stability and ability to remember their state even if there’s no power.

The Northwestern researchers turned to the two-dimensional material molybdenum disulfide (MoS2) to create the third terminal for the memristor.

In research published in the journal Nature Nanotechnology, the team found that the grain boundaries of MoS2 provided a better way to modulate resistance than can be achieved with memristors consisting of metal–insulator–metal structures with insulating oxides.

Grains are essentially the direction that atoms are arranged in a material; the grain boundaries are the interface where these grains come together and meet. In MoS2 these grain boundaries are well-defined.

"Because the atoms are not in the same orientation, there are unsatisfied chemical bonds at that interface," Hersam explained in the release. "These grain boundaries influence the flow of current, so they can serve as a means of tuning resistance."

In actual practice, when a voltage is applied to the MoS2-based memristor the grain boundaries physically move, which is the mechanism that changes the device’s resistance. The result is a three-terminal memristive device that can be tuned by a gate electrode.

Hersam added: "With a memristor that can be tuned with a third electrode, we have the possibility to realize a function you could not previously achieve,” Hersam said.

He added that with a three-terminal memristor in hand, his research team will be actively pursuing the potential for brain-like computing.

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3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD

A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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