噴印鈦酸鋇奈米顆粒之表面型態研究及應用於複合介電層可撓式電容元件

Abstract

軟性電子是現今的研究趨勢，其中噴墨的製程技術有許多的優勢。薄膜的均勻性常是影響元件性能的關鍵，然而噴墨液滴在基板上容易形成的環型沉積會造成薄膜的品質不佳，因此本研究的主旨為開發噴墨均勻的鈦酸鋇墨水。應用方面，噴墨奈米複合材料作為全噴墨式軟性電容的介電層，以達到可撓取、低成本、高電容值及低漏電流的目的。以水、乙二醇及二甘醇作為墨水溶劑，使用球磨法及加入分散劑，成功製備出兩種不同混合溶劑、粒徑500 nm以下且懸浮良好的鈦酸鋇墨水。其黏度與表面張力在25 oC下分別為8.7、2.3 cps及51.5、56 mN/m，皆能順利的用於噴墨。用SEM及白光繞射觀察得知，我們使用混合溶劑系統，成功在25oC基板上噴墨出均勻的液滴，改善咖啡環(Coffee Ring)效應的產生。且當液滴的均勻度變好，噴墨線及薄膜的品質也會跟著改善。最後，噴墨自製的鈦酸鋇墨水與市售的負光阻SU-8結合製作出全噴墨式複合介電層軟性電容。電容值最高為8.28 pF/mm2，且有高介電常數12.44，然而因厚度較厚因此比文獻中其他有機電容元件的電容值小。未來若降低厚度，對於提高電容值仍有很大的空間。

Recently, ink-jet printing technology has become an important production means for flexible electronics. It is recognized that the topography of the inkjet-printed droplet on the substrate is very critical because its uniformity and distribution have tremendous influence over the resulting device performance. The objective of this thesis is to develop an uniformly-deposited barium titanate ink for the purpose of fabricating an all-inkjet-printed flexible capacitor with a nanocomposite dielectric to achieve low-cost, high capacitance, and low current-leakage. With the addition of suitable dispersant and the adoption of a ball-milling process, we successfully prepare a homogeneous barium titanate dispersion with barium titanate in less than 500 nm size. The formulation is optimized so the barium titanate ink can be properly printed. Observations from scanning electron microscope and white light interferometer, the undesirable “coffee ring effect” is largely mitigated when we identify a mixture including a solvent with low-boiling-point and high surface tension and another solvent with high-boiling-point and low surface tension. Without the “coffee ring” pattern, we are able to ink-jet print two-dimensional line and three-dimensional surface/plane reproducibly. By ink-jet printing barium titanate nanoparticles and commercially available negative photoresist (SU-8) sequentially on a flexible PI substrate, a nanostructured composite dielectric is successfully demonstrated. The flexible capacitor exhibits a capacitance of 8.28 pF/mm2 and a relative permittivity of 12.44. However, due to its relatively larger thickness, the recorded capacitance is less than that of organic capacitors reported in the literatures.