INKJET PRINTED CONDUCTIVE INKS FOR THE FABRICATION OF ORGANIC THIN FILM TRANSISTORS

Abstract

<p>In recent years, there has been a strong interest in the use of drop-on-demand inkjet printing for the fabrication of organic thin-film transistors (OTFTs). This method would allow for roll-to-roll fabrication of low-end, disposable, and large-area electronics such as RFID tags, sensors, and flexible displays at a small fraction of the current costs. A great deal of research has already yielded new materials which are solution processable and have demonstrated excellent perfonnance when incorporated into OTFTs. One of the largest obstacles to the commercialization of this technology is the development of a successful strategy for the inkjet printing process. In order for this printing process to be successful, it must be able to deposit the components of the OTFTs such that they have sufficient resolution, excellent film thickness unifonnity and excellent perfonnance.</p> <p>Here a strategy is developed which allows for high resolution printing of source and drain electrodes with excellent film uniformity. By simultaneously optimizing dot-to-dot spacing and solvent composition, near-perfect film uniformity and very high resolution can be obtained. Resolution is further improved via increasing the viscosity of the ink and decreasing the surface roughness of the substrate.</p> <p>The inkjet printing system is further investigated and optimized for printing with silver nanoparticle ink. By using the design of experiments method, we detennined the independent influence of silver nanoparticle mass fraction, solvent composition, substrate surface energy, substrate temperature and dot-to-dot spacing on printed line width, line thickness and film uniformity. Furthennore, this method also allowed for the detennination of the influence of variable interaction, allowing a complete understanding of the system to be developed. This knowledge was used to develop a non-linear computer optimization program such that optimal variable settings could be detennined. As a result of this study, highly conductive silver lines with excellent resolution and film uniformity were inkjet printed and incorporated in high perfonnance OTFTs.</p> <p>A novel method for printing source and drain electrodes with a very small channel length was also developed. A silver nanoparticle ink with a large concentration of free alkylamine stabilizer was used in this study. The excess alkylamine formed a hydrophobic boundary around printed silver features, which repelled any ink subsequently deposited near the original feature. This allowed for source and drain electrodes to be printed with very narrow channel length with no need for any intelmediate processing steps. Furthennore, the self-alignment nature of this technique allowed the process to automatically correct for slight printing errors, resulting in transistor arrays with very narrow channel length distributions.</p>