Deposition of organic and inorganic layers on polymer substrates by R2R coating in vacuum

Roll-to-roll coating is a low-cost high-throughput manufacturing method for deposition of thin layers onto flexible substrates - this is an important methodology for developments in wearable and flexible technologies. Such technologies may favour vacuum-deposited layers for high quality physical properties and the widest range of materials.

The aims of this project will be to develop materials and device structures that are suitable for high-throughput roll-to-roll coating in vacuum. A particular focus will be on organic thin film transistors (OTFTs), and circuits made from them, for example for low cost disposable sensor 'plasters' for wearable technologies e.g. in health monitoring. The work will continue our approach using floating gate OTFTs through an OTFT-based transimpedance amplifier circuit.

Areas to investigate will be to (i) explore novel in-line patterning technologies for manufacture of circuits and (ii) novel sensing areas to control chemical selectivity of the sensor. Under (i) the main approach will be use of 'liquid masking' as an in-line patterning method to vacuum deposit electrical contacts and circuit tracks. This is a commercial technology for producing decorative packaging, but we are extending the concept to its use in electronics. In particular, this allows us to produce highly conducting electrodes from a wider variety of materials than with printed inks, and superior conductivity with thin layers (desirable for thin film technologies for the avoidance of 'steps'). This project will allow us to investigate the performance of devices and circuits using this approach, and we will investigate its application using a method we have recently patented that shows promise for higher resolution printing. This method may allow us to produce OTFTs with small source-drain gaps using a continuous high-throughput manufacturing method, rather than being reliant on photolithography, which is not suitable for high speed roll-to-roll throughput. Under (ii), the 'floating gate' approach allows us to decouple the delicate semicondutor materials and circuit from contact with the analyte (allowing them to be encapsulated from the environment), and uses a simple metal electrode as the basis of the sensing element. From there we will seek to develop selective sensing materials that can be thin-film deposited on this metal patch. Our initial approach will be based on thiophene copolymers attached to a gold electrode that can bond to specific enzymes, and hence the selectivity of the sensor can be ensured by the specific biochemical interaction with the enzyme.

No formal collaborators are involved, but this comes within the remit of our 'Wearable and Flexible Technologies' project (EP/MO15173/1) with the cluster of companies involved with this. In addition, we collaborate with the Hamlyn Centre, Imperial College London, and with Prof Manish, University College London, on the medical sensing aspects of the work.

This project falls within the EPSRC 'manufacturing the future' and 'healthcare technologies' research areas.