Investigation of Intensive Pulsed Light Sintering for Conductive Hybrid Copper Ink
Date
2019-09-03
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Abstract
With the increasing demand for flexible electronic devices in applications such as OLED screens and wearable technologies, there is a large need to find improved manufacturing methods in order to reduce costs and increase reliability. With traditional photolithography methods relying on slow and costly processes, the printed electronics industry is becoming a popular alternative. The deposition of flexible, electrically conductive electrodes and circuits onto polymeric materials via a printing technology such as, screen and inkjet printing, is becoming an attractive alternative due to ease of use, system adaptability, processing time, and roll to roll scalability. Most conductive nanoparticle-based ink technologies rely on silver nanoparticles due to their low electrical resistivity and high oxidation resistance; however, this method creates inks that are relatively expensive. In this study, a novel copper nanoparticle-based conductive ink is developed for use with conductive ink-based printing technologies and is designed to replace silver nanoparticles due to the immense cost savings. Novel processing techniques are used to increase oxidation resistance and flexibility along with minimizing resistivity. To prevent thermal damages to low glass transition temperature polymeric substrates, an intensive pulsed light (IPL) technique is used to sinter the hybrid ink in order to induce conductivity. To optimize the sintering process, the IPL technique is then modeled in order to determine the thermal characteristics during the sintering process and to illustrate the geometric changes that occur during sintering. These simulations are then used to predict a resistivity for pure copper nanoparticle films of 6.8 μΩ·cm (~4x bulk copper). Copper ink on its own is also prone to thermal cracking, resistivity increases with bending, and oxidation over time. To mitigate these issues, a hybrid copper ink is created by adding various components such as graphene nanoplatelets (GNP) and silver. This hybrid ink demonstrated an improvement in flexibility and durability for bending performance along with greatly increased oxidation resistance. Another variation of the hybrid copper-silver-graphene (CSG) ink is also explored by doping the material with various low melting temperature metals, known as field metals. These field metals are shown to increase overall flexibility and demonstrate self-healing characteristics. Since stretching and bending processes in printed electronics result in microcracking over time, the inks need to be healed in order to maintain resistance properties. To achieve this self-healing, IPL re-sintering is done on the field metal infused inks. The process is shown to demonstrate complete self-healing without damage to the remaining film and underlying substrate. In order to make these films useful for circuit applications, a process called selective IPL sintering is utilized to micropattern the hybrid ink films into useful conductive patterns. The proposed method is then demonstrated by producing strain sensors in a simple two-step process. Therefore, this work presents the creation and optimization of a novel copper based conductive ink that can be used in various printed electronic applications. The various additives in the ink create a flexible, low cost, oxidation resistant, and even healable conductive ink that will aid in reducing industry costs and increase reliability for various electronics.
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Keywords
Nano-particles, printed electronics, intensive pulsed light, copper, graphene, conductive ink, Flexible electronics
Citation
Kockerbeck, Z. (2019). Investigation of Intensive Pulsed Light Sintering for Conductive Hybrid Copper Ink (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.