Low dielectric and thermally stable hybrid ternary composites of hyperbranched and linear polyimides with SiO2

Abstract

A hydroxyl-terminated hyperbranched polyimide was synthesized via the A₂ + B₃ reaction between dianhydride and triamine monomers. The hydroxyl groups at the peripheral positions were then introduced by modification of the anhydride end groups via a reaction with 4-aminophenol. Based on the hydroxyl-terminated hyperbranched polyimide, HBPI_{BPADA-TAP(OH)}, we successfully fabricated hybrid ternary composites, which were comprised of a linear polyimide (PI_6FDA-APB), HBPI_{BPADA-TAP(OH)}, and an inorganic SiO₂ component. The material was designed to satisfy the requirement for cutting-edge insulators with a low dielectric constant and a high thermal stability. Because of the appropriate choice of the hybrid ternary composite systems with HBPI_{BPADA-TAP(OH)} and inorganic silica, it is sensible to improve the dielectric properties and thermal resistant properties of unary systems or improve the disadvantages of the dielectric and optical properties of binary systems. For an optimized composition, the dielectric constant (D_k) of the PI_6FDA-APB–HBPI_{BPADA-TAP(OH)}-30%–SiO₂-20% composite reaches the lowest value of 2.24 at 100 kHz. Research also showed that the optical transparency is significantly improved with the increase of the HBPI_{BPADA-TAP(OH)} content in the composite. Compared with the binary linear PI _6FDA-APB–SiO₂ composite, the transmittance increases from 1% to 75% at the wavelength of 450 nm. The incorporation of SiO₂ can preserve the good thermal properties of the hybrid composites containing HBPI_{BPADA-TAP(OH)}. By adding 10% of HBPI_{BPADA-TAP(OH)} to the PI_6FDA-APB–SiO₂-20% system, the coefficient of thermal expansion of the hybrid ternary composite is 20.9 ppm °C⁻¹ in the temperature range from 100 to 150 °C, which is significantly lower than that of the linear polyimide (37.1 ppm °C⁻¹ for PI_6FDA-APB). Because of these optimized properties, hybrid ternary composites have the potential for use in applications in the micro-electronic insulator fields, such as interlayer dielectrics of advanced electronic devices.