Hybrid ternary composites of hyperbranched and linear polyimides with SiO2: a research for low dielectric constant and optimized properties

Based on a hydroxyl-terminated hyperbranched polyimide (HBPIBPADA-TAP(OH)), two series of hybrid ternary composites composed of a linear polyimide (PI6FDA-APB), HBPIBPADA-TAP(OH) (10% and 20%), and various concentrations of SiO2 were fabricated by sol-gel method. Research showed that properties of the composites are closely related with the ratio of HBPIBPADA-TAP(OH) to SiO2, which can be optimized by proper choice of the compositions. Under optimized conditions, the hybrid ternary composites show properties complementary to the drawbacks of unary or binary systems. The dielectric constant (D-k) of the PI6FDA-APB_HBPIBPADA-TAP(OH)-10%_SiO2-10% composite reaches the lowest value of 2.26. The silica loading and reinforcement binding with PI6FDA-APB_HBPIBPADA-TAP(OH) matrix are confirmed by the SEM morphology of the hybrid ternary composite films. When a suitable amount (20%) of HBPIBPADA-TAP(OH) is added into the PI6FDA-APB_SiO2-10% composite, the optical transmittance is significantly improved to be 63% at the wavelength of 450 nm. With increase in the content of SiO2, the thermal expansion is obviously reduced. For the PI6FDA-APB_HBPIBPADA-TAP(OH)-10%_SiO2-30% composite, the coefficient of thermal expansion (CTE) of the film is reduced to 15.9 ppm degrees C-1 compared to 37.1 ppm degrees C-1 for the PI6FDA-APB film (reducing about 59%). Due to these optimized properties, hybrid ternary composite films are expected to have potential applications in micro-electronic insulator fields such as interlayer dielectric of advanced electronic devices.