PNAS – Nanowire nanocomputer as a finite-state machine Fundamental limits soon may end the decades-long trend in microelectronic computer circuit miniaturization that has led to much technological and economic progress. Nanoelectronic circuits using new materials, devices, and/or fabrication methods face formidable challenges to provide alternatives for future microelectronics. A key advance toward overcoming these hurdles is achieved in this work through the construction of a nanoelectronic finite-state machine (nanoFSM) computer using “bottom–up” methods. The nanoFSM integrates both computing and memory elements, which are organized from individually addressable and functionally identical nanodevices, to perform clocked, multistage logic. Furthermore, the device density is the highest reported to date for any nanoelectronic system. Advances in logic and design in the nanoFSM are scalable and should enable more extensive nanocomputers.
Researchers have arranged a total of 180 such transistor nodes in six crossbar arrays and divided them into three separate tiles to make a finite-state machine capable of performing arithmetical operations. In one configuration, the first tile does the math, while the second tile holds one bit in memory and the third tile holds a second bit. Chemist Charles Lieber, head of the Harvard team, says more tiles can be added in a Lego-like fashion. The version the team built was a two-bit adder. Four tiles would make a four-bit adder, and so on. A four-by-four array of tiles “could function as a pretty sophisticated microprocessor,” he says.
Lieber says the nanowire device will likely surpass CMOS chips only in very specific applications that benefit from low power consumption and operate at megahertz rather than gigahertz clock rates. But Ellenbogen hopes the research will provide hints for where CMOS technology can be improved. “We think some of the approaches are more generally applicable,” he says.
Fabricated nanoelectronic chip. (A) SEM image of the final chip (scale bar, 500 μm). (B) SEM image of the inner layout of the fabricated chip as indicated in the dashed box in A. The red dashed box region corresponds to the chip’s basic three-tile circuit shown. (Scale bar, 100 μm.) (Credit: Jun Yao et al./PNAS)
Implementation of complex computer circuits assembled from the bottom up and integrated on the nanometer scale has long been a goal of electronics research. It requires a design and fabrication strategy that can address individual nanometer-scale electronic devices, while enabling large-scale assembly of those devices into highly organized, integrated computational circuits. We describe how such a strategy has led to the design, construction, and demonstration of a nanoelectronic finite-state machine. The system was fabricated using a design-oriented approach enabled by a deterministic, bottom–up assembly process that does not require individual nanowire registration. This methodology allowed construction of the nanoelectronic finite-state machine through modular design using a multitile architecture. Each tile/module consists of two interconnected crossbar nanowire arrays, with each cross-point consisting of a programmable nanowire transistor node. The nanoelectronic finite-state machine integrates 180 programmable nanowire transistor nodes in three tiles or six total crossbar arrays, and incorporates both sequential and arithmetic logic, with extensive intertile and intratile communication that exhibits rigorous input/output matching. Our system realizes the complete 2-bit logic flow and clocked control over state registration that are required for a finite-state machine or computer. The programmable multitile circuit was also reprogrammed to a functionally distinct 2-bit full adder with 32-set matched and complete logic output. These steps forward and the ability of our unique design-oriented deterministic methodology to yield more extensive multitile systems suggest that proposed general-purpose nanocomputers can be realized in the near future.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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