Periodic Reporting for period 3 - NEW_FUN (New era of printed paper electronics based on advanced functional cellulose)
Reporting period: 2018-09-01 to 2020-02-29
While the vision of the proposal is a very ambitious one, my ground-breaking research work to date, related to oxide based transistors on paper (from which I am one of the co-inventors), has contributed to the basic technological breakthroughs needed to create the key elements to establish a new era of paper electronics. Field effect transistors (FETs), memory and CMOS devices, with excellent electronic performance and using paper as substrate and dielectric have resulted from my recent work. What I am proposing now is to reinvent the concept of paper electronics. In NEW_FUN I want to develop a completely new and disruptive approach where functionalized cellulose fibers will be used not only as dielectric but also as semiconductor and conductor able to coexist in a multilayered paper structure. That is, to assemble paper that can have different functionalities locally, on each face or even along its entire thickness/bulk. This way, issues such as failure under bending, mechanical robustness and stability can be minimized. With this approach, electronic and electrochemical devices can be produced not only on paper but also from paper. The outputs of NEW_FUN will open the door to render paper a real electronic material, making disposable/recyclable electronic products possible, such as smart labels/packages (e.g. food and drug industries), sensors for air quality control (car, house and industrial environments); disposable electronic devices such as bio-detection platforms, lab-on-paper systems, among others.
Concerning the functional materials being combined with cellulose, the emphasis has been on carbon nanostructures and oxide nanoparticles. This way we are avoiding stability issues normally observed when conducting polymers are used. Some of the approaches being used in NewFun project to combine cellulose with carbon or inorganic nanoparticles are completely disruptive allowing to locally pattern functionalized areas in paper substrates. Another approach being explored along the project involves the direct growth of oxide nanostructures on discrete cellulose fibbers that can then be used to create functionalized paper sheets or to be locally combined with other paper substrates to create a semiconductor layer based on these cellulose nanocomposites.
Finally, new cellulose-based solid electrolytes with high ionic conductivity and with improved recyclability potential were also developed where cellulose constitutes almost 100% of the electrolyte matrix.
In summary, the main achievements of this project so far were:
• Direct synthesis of ZnO nanostructures on cellulose fibers
• Development conductive lines with embedded nanocarbon in cellulose.
• Development of printable cellulose/ZnO pastes
• Cellulose/ZnO composites for application in field effect transistors (FETs)
• Highly ionic conductive cellulose based electrolytes
• Integration of all the above in devices such as transistors, sensors and electrochemical devices
As a general remark, I believe the project is running according to the DoA, surpassing in some cases the ambitious objectives initially proposed, such as the remarkable results obtained on cellulose based electrolytes with high ionic conductivity (in the range of 10^-3 S.cm-1) and cellulose based inks with incorporation carbon fibers or ZnO nanoparticles that allow for fully printed transistors and sensors. These developments have resulted in publications in high impact journals and some were also considered among the highlights of these journals.
Carbon fibers (CFs) and multiwall carbon nanotubes (MWCNTs) were combined with cellulose derivative (carboxymethyl cellulose – CMC) towards development of screen-printed printed temperature sensor. This work as resulted in the publication “Printable cellulose-based electroconductive composites for sensing elements in paper electronics” (doi.org/10.1088/2058-8585/aa5ef9) in the journal “Flexible and Printed Electronics” and was considered one of the highlights of 2017 (please see (http://iopscience.iop.org/journal/2058-8585/page/featured-articles-2017?utm_medium=email&utm_source=iop&utm_term=&utm_campaign=13482-37469&utm_content=Click%20to%20read%20the%20Highlights)
Development of cost-effective and up scalable-printing technologies
Having always in mind the simplification of the processing technologies used to create electrical and electrochemical devices on paper I have proposed for the first time the pen-on-paper approach to deposit semiconductor layers on paper at low temperature. This way it is possible to, literally, “write” electronic components. These layers are being used for UV sensors and FETs on paper and resulted in a publication (doi.org/10.1002/admt.201700009)
Paper substrates with surface and bulk embedded functionalities
Development of cellulose-based hydrogel electrolytes (CHEs) from dissolution of microcrystalline cellulose (MCC) at low temperature in aqueous lithium hydroxide (LiOH)/urea solvent systems. The CHEs were successfully implemented as high-capacitance gate dielectrics in oxide based transistors. Part of this work was already published in a high impact journal – Advanced Functional Materials (DOI: 10.1002/adfm.201606755)
Paper layers/substrates from functional cellulose nanocomposites
The precursor for the formation of the cellulose based hydrogel electrolytes has been used to impregnate paper matrices made of pure cellulose fibers. The goal is to create a paper-like structure with high ionic conductivity capable of being used as high capacitance dielectrics in FETs. Work submitted for publication.
Production of optimized of FETs on paper
Dual-phase semiconductor layers obtained by pen-on-paper method, as already described were used in FETs on paper. Published in Advanced Functional Materials (DOI: 10.1002/adfm.201606755).
Development of new strategies to implement electrochromic materials in transistors. It was demonstrated that tungsten oxide (WO3) can be successfully used in electrochromic transistors (ECTs) where the channel layer color changes when the current passing through it is modulated.This work has resulted in a publication in Advanced Electronic Materials (10.1002/aelm.201500414).
The final objective of the NewFun will be the development of an integrated platform to demonstrate the potentiality and validate all the new approaches on materials and devices proposed along the project. This will be achieved by combining printed FETs and electrochromic devices with paper microfluidics technology. The goal is to detect to detect pH variations since it is an indicator for diagnosing diseases, optimizing medical treatments and monitoring biochemical and biological processes. I'm now on the beginning of the first trials on making the integration of the first building blocks already developed. Fully printed EGTs with excellent characteristics (mobility in the range of 10 cm2V-1s-1 and On/Off ratio of 10^5, operating below 2V) are now possible on modified paper substrates. Electrochromic displays printed on paper were also developed. Both devices are using the cellulose based electrolyte developed in the project. All this are being integrated in modified cellulosic matrices (paper-like) that allow microfluidics within its volume having simultaneously a smooth surface for printed electronic components. All the efforts are now on the proper integration of all the functionalities and optimization of the sensing layer for pH detection.