Tunable dielectric and other properties in high-performance sandwich-type polyimide films achieved by adjusting the porous structure

The preparation and performance adjustment of low-dielectric polyimide (PI) play important roles in the development and application of next-generation dielectric materials used in high-speed integrated circuits. Herein, composite polyimide films with sandwich-type porous structures were fabricated via a microemulsion method, in which the self-assembly of water droplets was involved. Decreases in the dielectric constant and water absorption and increases in the tensile strength and tensile modulus were simultaneously realized due to the presence of symmetrical porous structures and a dense PI layer upon the introduction of the sandwich-type porous structure. The dielectric, mechanical and water resistance properties of the composite PI films could be further regulated by controlling the porous structure using different conditions for film formation. By varying the temperature, humidity, concentrations of polymer and surfactant in the microemulsion method, we obtained the low dielectric constants of 2.24-2.81 and the low water absorptions of 0.49-0.59%, with decreases from 15.73% to 32.81% and 76.02% to 80.08%, respectively, as compared to the case of the flat PI film; we also achieved the high tensile strengths of 97.7-103.2 MPa and high tensile moduli of 1.2-1.4 GPa, with the increases of 4.83-10.73% and 6.57-16.43%, respectively, as compared to the case of the flat PI film. Moreover, excellent durability of the low dielectric constant under high humidity condition was demonstrated by the very small increase in the dielectric constant (0.02-1%) in a moist environment. These results provide useful information for the structural design of high-performance dielectric materials. Excellent dielectric and other properties of PI films were realized and tuned through the introduction of a sandwich-type porous structure.