Bloor, David

Donnelly, Kenneth P.

Hands, Philip J.W.

Laughlin, Paul J.

Noble, Mark

Edinburgh Research Explorer

     Edinburgh Research Explorer                                      Quantum tunnelling conductive metal-polymer compositesCitation for published version:Hands, PJW, Donnelly, KP, Noble, M, Laughlin, PJ & Bloor, D 2001, 'Quantum tunnelling conductive metal-polymer composites' SET for Britain 2001, London, United Kingdom, 19/03/01 - 19/03/01, .Link:Link to publication record in Edinburgh Research ExplorerDocument Version:Peer reviewed versionGeneral rightsCopyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s)and / or other copyright owners and it is a condition of accessing these publications that users recognise andabide by the legal requirements associated with these rights.Take down policyThe University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorercontent complies with UK legislation. If you believe that the public display of this file breaches copyright pleasecontact openaccess@ed.ac.uk providing details, and we will remove access to the work immediately andinvestigate your claim.Download date: 28. Apr. 2017Philip Hands, David Bloor, Kenneth Donnelly, Paul Laughlin†, Mark NobleOptoelectronics Research Group, Department of Physics, University of Durham, South Road, Durham, DH1 3LE†Peratech Ltd., G3 Morton Park Way, Darlington, Co.Durham, DL1 4PJUniversity of DurhamDepartment of Physics Researched for over 40 years Metal particles usually have smooth, rounded shape Electrical conduction when neighbouring particles touch each other Conduction by “percolation”Electrical conduction via “percolation” within a ‘conventional’ composite Pressure / tension sensors Re-usable fuses Conductive adhesives Electromagnetic interference (EMI) shielding Touch sensitive fabrics – wearable electronics Interactive aids for the visually impaired, or for those with ----------- coordination difficulties Gas and vapour sensors / electronic nosesMaking fabrics and surfaces touch sensitive: - An interface for an MP3 player in the sleeve of a jacket and a power-drill ‘easy-grip’ variable speed control Micron-sized conducting (metal) particles mixed randomly within a ----- non-conducting (polymer) matrix Metal particles have irregular, spiky surface structure Spikes generate high charge densities Conduction by quantum mechanical tunnelling of electrons via spikes Accounts for high electrical sensitivity to applied pressureSEM and TEM images of metal particles within the Peratech compositeMetal       Oxide    Polymer    Oxide      MetalSchottky barrierEFEFElectrons tunnel through resonant double barrierSurface energy statesElectrical conduction mechanism via the tunnelling of electrons from spikesFor more information about this work, please visit or Intrinsically electrically non-conducting Conductivity increases dramatically when compressed or stretched  ----(1012Ω to 1Ω under only fingertip pressure) Far greater sensitivity than ‘conventional’ composites Destruction of spikes leads to decreased sensitivity Highly non-linear current-voltage characteristics with hysteresisTypical electrical characteristics of the Peratech composite00.050.10.150.20.250.30.350.40 5 10 15 20 25 30Voltage / VCurrent / A00.10.20.30.40.50.60.70.80.9200 250 300 350 400Pressure / kPaResistivity / MΩ mAwards:  Tees Valley Technology Award, SMART Award Winner, Millennium Product Status, Saatchi & Saatchi International Award for Innovation in CommunicationA small, local, high technology materials development company, Peratech, has invented a new type of metal-polymer composite using a metallic powder encapsulated within a siliconerubber matrix. Compared to other insulator-conductor composites, the Peratech material displays unique and fascinating electrical characteristics. In 1996, collaborative work beganbetween Peratech and the University of Durham on this new breed of ‘smart’ material, with the aim of understanding its complex physics and to aid in the development of commercialapplications. Since then, Peratech have received numerous awards for their new composite and innovative ideas.The micron-sized metallic particles within the Peratech material have a uniquely spiky surface morphology. The resulting composite is intrinsically highly electrically insulating, butdisplays a drastic reduction in resistivity to a value close to that of metals when compressed under only finger pressure. Contrary to ‘conventional’ composites, the resistivity also dropswhen the material is subjected to tension, or any type of mechanical deformation. In addition, the current-voltage characteristics of the composite are highly non-linear and displayhysteresis, giving rise to switching behaviour and a negative differential resistance regime. The composite also displays a thermostatic positive temperature coefficient (PTC) effect, andis capable of carrying currents as large as 3A without observable damage. The cause of such phenomena is thought to be due to the quantum-mechanical tunnelling of electronsbetween adjacent metallic particles.This new breed of material has paved the way for a new family of quantum tunnelling composites (QTCs). Such materials can be woven into fabrics or coated onto virtually any surface,enabling new and exciting “touch sensitive” technologies such as wearable electronics to be developed. Other applications include electromagnetic interference (EMI) shielding, pressuresensors, reusable fuses, conductive adhesives and artificial olfactory systems.I acknowledge the members of Peratech Ltd., the Optoelectronics Research Group and Andrew Yates of the Durham Semiconductor Research Group for his microscopy work. 

Quantum tunnelling conductive metal-polymer composites

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