잉크젯 직접 프린팅 공정을 이용한 전자소자 제작 및 특성 평가

Abstract

Printed electronics has been emerging as a promising alternative to the conventional photolithography process for the implementation of inexpensive large-area and flexible electronics. One of numerous techniques, inkjet printing has received significant attention in printed electronics because of its simplicity, low material consumption, non-contact nature, and the compatibility of printing with flexible substrates. Even though inkjet printing is a versatile technique for fabricating high-resolution patterns, there are still demands to widen the application areas of inkjet printing. Most devices are composed of multi-layer structures: electrode, dielectric, and semiconductor layers. Each layer has different surface properties, leading to difficulty in inkjet-printing multi-layer structures because physical behaviors of printed liquids are sensitively dependent on the surface properties. This dissertation provides reliable strategies for producing all-inkjet-printed electronic devices such as passive components and organic thin film transistor (OTFT). The effect of plasma surface treatment with various approaches on inkjet-printed droplet spreading is investigated to produce inkjet-printed patterns with the desired resolution. The shapes and morphologies of silver lines are observed and analyzed after printing them on the plasma-treated substrates at various overlaps and substrate temperatures. Based on developed fine and stable printing process, various electrical passive components are confirmed to be successfully fabricated. A circuit composed of resistor and capacitor (RC circuit) is also produced; the feasibility of inkjet-printed passive components is discussed. Evaporation behavior of the inkjet-printed semiconductor layers is controlled by various printing conditions, and a proper bottom contact configuration is proposed to obtain well-oriented crystalline structures. The surface physical and chemical characteristics and surface wettability show a clear dependence on radio frequency power and gas pressure of plasma process. Higher fluorine/carbon ratios leads to smaller droplet diameter on the surface, which means the surface becomes more hydrophobic. For the plasma treatment with two precursors, the mixed gas approach is a simpler process, but it shows an irregular tendency toward surface wettability. The sequential approach produces a clear dependency of surface wettability on O2 treatment time. Longer O2 plasma treatment makes the surface more hydrophilic, leading to a larger droplet diameter for the sequentially plasma-treated surfaces. Continuous lines are not guaranteed to be formed due to line instability issue when printed at room temperature. By heating the substrates, continuous lines without bulges could be on the relatively hydrophilic substrate due to the enhanced evaporation rate of solvent. However, the coffee stain effect in the droplets and lines is aggravated as the substrate temperature increases. Using a synthesized dielectric ink of mixed-solvent system, all-inkjet-printed passive components can be fabricated without electrical short circuit. The responses of the printed RC circuits are well consistent with the calculated results. Crystalline structure of inkjet-printed semiconductor layer is mostly influenced by the internal flows and the corresponding contact line movements of drying semiconductor layer. Well-oriented crystalline structure can be obtained using appropriate overlap condition and substrate temperature. A relatively hydrophobic surface is likely to generate better crystallinity of inkjet-printed semiconductor layer. All-inkjet-printed OTFT with well-oriented crystalline structure show high electrical performances. The plasma surface treatment and inkjet printing processes suggested in the dissertation is expected to be effective in the fabrication of high-performance all-inkjet-printed electronic components for the implementation of printed electronics.