Electrical transport through single molecules has been investigated previously but problems remain with reliability, stability and yield, preventing further progress in the integration of discrete molecular junctions into circuits. A multi-disciplinary team of scientists from the Netherlands, Belgium and Italy presents a breakthrough technology to simultaneously fabricate over 20000 molecular junctions on a single 150-mm silicon wafer. Their integration is demonstrated in so-called strings where up to 200 junctions are connected in series with a yield of 100%. The team’s findings are published online, and scheduled for publication in the November issue of Nature Nanotechnology.
The vision of using a single molecule or a small number of molecules to build electronic devices has led to a new research field called molecular electronics. A molecular junction typically consists of a single molecule of only a few nanometers sandwiched between two electrodes. Molecular electronics holds the potential to fabricate elements for electronic circuits with a functionality that is embedded in just a single layer of molecules. Instead of using photolithography or printing techniques to etch or print nano-scale circuit features, molecular electronics can be engineered to use organic molecules that spontaneously form the correct structures via self-organization in self-assembled monolayers (SAM) of only several nanometers thick. Molecular electronics is envisaged as the next disruptive technology in electronics.
Discrete molecular junctions have been processed and characterized previously. However the progress in molecular electronics is severely hampered by the limited reliability, reproducibility and, especially, the yield. Electrical shorts are generally formed upon vapor deposition of the top electrode. The formation of shorts can be prevented by applying a conducting barrier layer between the SAM and the top electrode.
However, crucial for any application is a process technology that allows for integration of the discrete molecular junctions. This requires additional patterning of the bottom and top electrode, as well as introduction of a second layer of interconnects. A bottleneck is the limited processing window; the process temperature had to be limited to room temperature to prevent deterioration of the organic self-assembled monolayer. A process flow chart for processing simultaneously over 20000 molecular junctions on 150-mm silicon wafers is presented. The molecular junction consists of a gold bottom electrode, a self-assembled alkanethiol monolayer, a conducting polymer and a gold top electrode. Integration is demonstrated in so-called strings where up to 200 junctions are connected in series. Detailed information on fabrication technology is presented to allow other research groups to reproduce and benchmark the experimental data.
See the Nature Nanotechnology publication: Upscaling, integration and electrical characterisation of molecular junctions, Paul A. van Hal1, Edsger C. P. Smits1,2,3, Tom C. T. Geuns1, Hylke B. Akkerman2, Bianca C. de Brito1, Stefano Perissinotto4, Guglielmo Lanzani4, Auke J. Kronemeijer2, Victor Geskin5, Jérôme Cornil5, Paul W. M. Blom2, Bert de Boer2, and Dago M. de Leeuw1,2
1 Philips Research Laboratories, High Tech Campus 4, 5656 AE Eindhoven, the Netherlands.
2 Molecular Electronics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands.
3 Dutch Polymer Institute,
, 5600 AX Eindhoven, The Netherlands.
4 IIT Istituto Italiano di Tecnologia, Dipartimento di Fisica, Politecnico di Milano, P.za L. da Vinci 32, 20133, Milano, Italy.
5 Service de Chimie des Materiaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, Mons, Belgium.
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