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Patent Issued for Electronic Device Incorporating Memristor Made from Metallic Nanowire

May 21, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Strachan, Douglas R. (Lexington, KY); Johnson, Stephen L. (Lexington, KY), filed on February 25, 2011, was published online on May 6, 2014.

The assignee for this patent, patent number 8716688, is The University of Kentucky Research Foundation (Lexington, KY).

Reporters obtained the following quote from the background information supplied by the inventors: "Metals have long been used to form resistors, capacitors, and inductors--the three classical passive circuit elements in which geometry determines the principle behavior of the device. A fourth passive circuit element, the memristor, has generated significant recent interest due to its potential use in nanoscale logic and memory devices. Among the presently demonstrated memristors are those whose resistance depends on state variables such as coupled ionic and electronic conduction, phase transistions, redox reactions in organic semiconductors, and the configuration of molecular heterostructures.

"U.S. Pat. No. 6,636,433 discloses an electronic device incorporating a memory core comprising either a material that can be electromigrated or a carbon nanotube having a hollow core holding a material that can be electromigrated which alters the overall conduction based on its position. To electromigrate the material, the approach disclosed in U.S. Pat. No. 6,636,433 is to utilize the Joule heating within the material or nanotube itself in order to increase the rate of electromigration, which depends sensitively on the mobility of the atoms. However, achieving an applied Joule heating that can be used to help controllably electromigrate atoms without causing catastrophic runaway is non-trivial.

"Memristor devices are presented in this document containing a feedback configuration. The memristors consist of conductors which are stable in at least two states which can be accessed through the application of an applied voltage and current. The applied voltage and current induce migration of material within the memristor which changes its state. This effect can be used to store non-volatile memory. The feedback included in this configuration permits a specific voltage to be applied directly across a nanowire which allows it to be reproducibly switched between states and prevents thermal runaway breakdown of the memristive device. This configuration can be implemented with a single component nanowire and electrode geometry.

"Advantageously, the feedback system of the current document permits precise and controllable Joule heating to the nanowire memristive element without thermal destruction of the device. The current feedback system also permits consistent voltage application to all nanowire memristive elements in applications where a plurality is utilized. This consistent voltage application, regardless of physical changes occurring in the memristive elements, could result in significant improvements to device performances, reproducibility among nominally identical memristive elements, and lifetime."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "This document describes an electronic device comprising a first electrode, a second electrode and a nanowire connected between the first and second electrodes to allow electric current flow. The nanowire is made from a conductive material exhibiting variable resistance R.sub.N due to electromigration. The nanowire is repeatedly switchable between a first state having a first physical geometry producing a first resistance R.sub.1 and a second state having a second physical geometry producing a second resistance R.sub.2 where R.sub.1>R.sub.2. In addition, the device includes a voltage clamp, operating through feedback control, connected to the nanowire. The voltage clamp produces a bias voltage V.sub.tot that maintains the applied voltage V across the nanowire regardless of the resistance R.sub.N and prevents thermal run away and nonreversible device failure.

"The voltage clamp may comprise a circuit including a combination of an operational amplifier, an instrumentation amplifier, a follower and transistors connected to the first electrode by a first lead and to the second electrode by a second lead. In an alternative embodiment the voltage clamp comprises an integrated voltage control device that may include, for example, at least one transistor.

"The electronic device includes a sense electrode for sensing electric resistance of the nanowire. In an alternative embodiment a first sense electrode may be connected to the first electrode and a second sense electrode may be connected to the second electrode. Further, in one useful embodiment the nanowire, the first electrode and the second electrode are all made from a single component material.

"In accordance with an additional aspect, an integrated electronic device comprises a plurality of memristors arranged on a single substrate. Each of the plurality of memristors includes a first electrode, a second electrode and a nanowire connected between the first electrode and the second electrode to allow electric current flow. The nanowire is made from a conductive material exhibiting variable resistance R.sub.N due to electromigration. The nanowire is repeatably switchable between a first state having a first physical geometry producing a first resistance R.sub.1 and a second state having a second physical geometry producing a second resistance R.sub.2 where R.sub.1>R.sub.2. In addition, the integrated electronic device includes a voltage clamp, operating through feedback control, connected to the nanowires of the plurality of memristors. The voltage clamp produces a bias voltage V.sub.tot that maintains the applied voltage V across the nanowires regardless of resistance R.sub.N and presents thermal runaway.

"In the following description there is shown and described several different embodiments of electronic devices, simply by way of illustration of some of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive."

For more information, see this patent: Strachan, Douglas R.; Johnson, Stephen L.. Electronic Device Incorporating Memristor Made from Metallic Nanowire. U.S. Patent Number 8716688, filed February 25, 2011, and published online on May 6, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=76&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3783&f=G&l=50&co1=AND&d=PTXT&s1=20140506.PD.&OS=ISD/20140506&RS=ISD/20140506

Keywords for this news article include: Nanowire, Nanotechnology, Emerging Technologies, The University of Kentucky Research Foundation.

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Source: Journal of Engineering


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