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UMass Engineers Made Crossbar Arrays of the Smallest Memristors

Qiangfei Xia

Qiangfei Xia

A research team led by Qiangfei Xia of the Electrical and Computer Engineering Department at the University of Massachusetts Amherst has just published a paper in the prestigious journal Nature Nanotechnology about research into a promising building block for the next generation of nonvolatile random access memory and bio-inspired computing systems. The research team says that its working memristor crossbar arrays are “to the best of our knowledge, the first high-density electronic circuits with individually addressable components scaled down to two-nanometer dimension built with foundry-compatible fabrication technologies.”

The title of the Nature Nanotechnology paper is “Memristor crossbar arrays with six-nanometer half-pitch and two-nanometer critical dimension." One nanometer is one billionth of a meter. The diameter of a human hair is on the order of a hundred micrometers, or a hundred thousand of nanometers. Two nanometers are just a few atoms wide.

“This work will lead to high-density memristor arrays with low power consumption for both memory and unconventional computing applications,” says Xia. “The working circuits have been made with technologies that are widely used to build a computer chip.”

According to the researchers, “Organizing memristors into high-density crossbar arrays, although challenging, is critical to meet the ever-growing high capacity and low-energy demands of these applications, especially in the big data era.”

In this research the team has constructed memristor crossbars with a single-layer density up to 4.5 terabits per inch square, comparable with the information density achieved using the state-of-the-art, 64-layer, triple-level cell NAND flash technology.

“The densely packed crossbars of extremely small working devices provide a power-efficient solution for high-density information storage and processing,” as the researchers explain.

An earlier version of the Nature Nanotechnology manuscript, posted on arXiv.org (a repository of electronic preprints) was chosen by MIT Technology Review as one of “This week’s [five] most thought-provoking papers from the Physics arXiv.

The pioneering research is one outgrowth of Xia’s 2013, five-year, $400,000 grant from the National Science Foundation (NSF) Faculty Early Career Development (CAREER) Program to develop emerging nanoelectronic devices. Xia’s NSF research has been addressing the biggest obstacle for the continued operation of Moore’s Law, which states that the number of transistors on integrated circuits doubles approximately every two years.

“[Moore’s Law] worked perfectly for more than 40 years, but now we’re reaching its fundamental limit, due to the quantum effects related to electron flow,” says Xia. “So we absolutely need new devices that can do a better job.”

In the Nature Nanotechnology paper, Xia’s research team explains that “Organizing small memristors into high-density crossbar arrays is critical to meet the ever-growing demands in high capacity and low energy consumption, but is challenging because of difficulties in making highly ordered conductive nanoelectrodes.”

The researchers go on to explain that “Here we demonstrate memristor crossbar arrays with a two-nanometer feature size and a single-layer density up to 4.5 terabits per inch square, comparable with the information density achieved by using three-dimensional stacking in the state-of-the-art, 64-layer, and multilevel 3D-NAND flash memory. Memristors in the arrays switch at tens of nanoampere electric current with nonlinear behavior.”

As the research team concludes, “The densely packed crossbar arrays of individually accessible, extremely small, functional memristors provide a power-efficient solution for information storage and processing.”

In addition to Xia, the other authors of the Nature Nanotechnology paper are Shuang Pi, Can Li, Hao Jiang, Weiwei Xia, Joshua Yang, and Huolin Xin. (November 2018)