Thermally Stable Colorless Copolyimides with a Low Dielectric Constant and Dissipation Factor and Their Organic Field-Effect Transistor Applications

• Published in: ACS applied polymer materials 2021-06, Vol.3 (6), p.3153-3163
• Main Authors: Miyane, Satoshi, Chen, Chun-Kai, Lin, Yan-Cheng, Ueda, Mitsuru, Chen, Wen-Chang
• Format: Article
• Language: English
• ISSN: 2637-6105; 2637-6105
• DOI: 10.1021/acsapm.1c00351

We developed highly thermally resistant and colorless polyimides (CPIs) with an ultralow coefficient of thermal expansion (CTE) and sufficient mechanical durability as a flexible substrate for organic field-effect transistors (OFETs). The CPIs were synthesized from trans-1,4-cyclohexyl diamine (t-CHDA) with different ratios of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and pyromellitic dianhydride (PMDA). The effects of the composition of s-BPDA and PMDA on the thermal, mechanical, electrical, and optical properties of CPIs were investigated. The optimized CPI, PI-3 with 90 mol % s-BPDA and 10 mol % PMDA, showed a relatively high elongation at break (8%) with a low CTE of 14 ppm K–1, a high glass transition temperature (T g) of 340 °C, and a large tensile modulus (E) of 4.1 GPa, respectively. Besides, PI-3 possessed a high transparency with a light transmittance at 400 nm (T 400) of 81% and a low cutoff wavelength (λcutoff) of 349 nm. Next, the dimer diamine of DDA (Priamine 1074) was introduced into the PI-3 structure to reduce the dielectric constant and enhance the stretchability. For example, PI-6C, with 85 mol % t-CHDA and 15 mol % DDA, showed a low dielectric constant (D k) of 2.8, a low dissipation factor (D f) of 0.004, and a high T 400 of 86% with maintained thermal and mechanical properties. Finally, a flexible OFET device using PI-3 as the substrate and dielectric was fabricated and characterized and exhibited an outstanding performance preservation after 1000 bending cycles or the high-temperature heating test, suggesting its excellent durability. The experimental results indicate that the CPIs studied have potential applications for transparent organic electronic devices.