Emerging printed and flexible electronics have great potential for customised consumer, medical and communication applications. In the lab they show ever-increasing performance as designer materials with specific properties are being developed. For these technologies to bridge the gap to volume production, consistency of performance and high production yield are essential, yet current progress has largely focused on individual device performance. A type of electronic device, the source-gated transistor (SGT), was developed and patented at Surrey and operates on different principles to a conventional thin-film transistor. This device has the potential to produce uniform performance (especially drain current) despite significant parameter variation which may occur during manufacturing. SGTs can be made in a variety of technologies and in principle can be combined with conventional transistors to create high performance printed and large area electronic circuits without resorting to complicated compensation circuitry to repeatedly achieve the desired characteristics. SGTs would be ideal devices for routine operations in mass-market, low-cost printed electronics, in which their energy efficiency and uniformity of performance would outweigh the comparatively low operating speeds. This project would be the first systematic study of both devices and low cost circuits deliberately designed to take advantage of the uniformity benefits of SGTs, with a focus on organic materials. The field of organic transistor research is particularly attractive due to the comparative ease of fabrication, rich palette of designer materials materials - both current and future, flexible substrate compatibility and low capital investment in equipment. This research has, however, now reached a plateau with the development of high-performance semiconductors, where significant improvements are likely to arise chiefly through the synthesis of improved materials. The principal hurdles for high-volume manufacturability are now the comparatively low yield and significant variations in performance, particularly over a large area. We will demonstrate the next important innovation, bringing high-volume yield to the manufacturing of low-power organic electronic technologies, by addressing these challenges. Project partners NeuDrive (materials and devices), Silvaco (simulation), and Altro (smart living spaces) will provide essential know how in order to help achieve the project aims: to verify theoretical SGT properties by device fabrication and characterisation; to optimise the designs and assess the performance of electronic circuit blocks made with source-gated transistors; to support our findings with numerical modelling; to create design guidelines and documentation, facilitating the uptake of this new technology in both the academic and industrial environments. CPI, the national facility for research into advanced manufacturing processes for electronics, will be subcontracted for part of the fabrication, allowing research staff to concentrate on process development, device optimisation and circuit design. We expect the greatest value of the project to be in making possible the efficient high volume manufacturing of a wide variety of printed and flexible electronics used for wearables, sensor arrays and internet-of-things (IoT) devices, which are priorities for development in both the research community and industry. Our contribution will allow consistent performance to be obtained from printed and flexible circuits, directly increasing the market viability of a variety of cost-effective applications.

This multidisciplinary project will exploit an established UK based team's track record comprising RF & bio-sensing engineers, battery & materials scientists, and CPI, the UK National Catapult for Printed Electronics. Centred around Additive Manufacture and aimed towards scale-up, we will transform nascent wireless skin-based sensing to the high data rate capacity offered by upcoming communications systems using license-free 24 GHz channels. This will enable new streaming of biodata for remote diagnostics, monitoring and care, as well as ultra-low impact wireless EEG for forehead/ear/hair free regions. It will make possible the use of multiple sensing tags on multiple people simultaneously monitoring physiological parameters such as accelerometery (for activity tracking), photoplesmography (for heart rate monitoring), and sweat (for metabolite monitoring). At high data rate, this represents a step change over available technologies. Manufactured on highly flexible, potentially stretchable, substrates the skin tags take the form factor of temporary tattoos and are highly long lasting, discrete for social acceptability, and can follow the micro-contours of the skin to give a large contact surface area and consequently sensing signal-to-noise ratio. To achieve our aims, we will advance wireless mmWave devices, on-skin electronics, low-power bio-sensing, and additive manufacture. Additionally, through CPI, we will develop scale-up processes for these mmWave devices. Through existing investments the applicant team is positioning the UK for the large scale manufacture of on-skin sensor tags. EP/P027075/1 is creating an inkjet printing based manufacturing process for sensors on flexible substrates which avoids cleanrooms, uses graphene based ink formulations for biodegradability, and can be scaled up large run roll-to-roll screen printing. EP/R02331X/1 added the capability to print TiO2/LiFePO4 batteries integrated into the platform, removing a key integration bottleneck. This new proposal 'MultiSense' seeks to build upon the manufacturing base created by these two projects, extending it to overcome the key sensing limitation of current on skin tags: that they can only monitor one parameter from one person at a time, and at a comparatively low data rate. These projects are further limited to producing first principle non-elastic, low capacity integrated batteries and UHF frequency (868 MHz) RF devices which require print resolutions similar to conventional masks for wet etching (typically 200 um). Further, our experience of UHF RFID reveals transmission delays of 6 ms, and a reliable data rate upper limit of only 400 bps (corresponding to a sample rate of just 30 Hz for a modality such as accelerometry). In MultiSense, we propose to overcome these limitations by moving from RFID to 24 GHz ISM (Industrial, Scientific Medical) band transmission, where very substantial uncongested bandwidth is available, offering orders of magnitude higher bit rates than UHF. In addition, the smaller wavelengths will increase antenna miniaturisation on integrated elastic substrate batteries, requiring print resolutions of 50 um. The new batteries will be solid state and polymer based with elastic current collectors. We will also investigate the mmWave signal surface guiding over the skin as a mechanism to allow for inter-patch communications. Sensing robustness will be improved as minor variations/misplacements in the sensor positions could be captured, and potentially corrected for in software. This will impact on diagnostic EEG measurements where currently entire datasets (from cabled electrodes) might be abandoned when individual electrodes disconnect. To enable the measurement of skin-based transmission between patches with new dry electrode designs, we will work with International Research Visitor Professor Koichi Ito of Chiba university, an expert in human phantom design.