Tunable Dielectric and Other Properties in High-Performance Sandwich-type Polyimide Film by Adjusting the Porous Structure
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, a composite polyimide film with sandwich-type porous structure was fabricated through the microemulsion method, in which the self-assembly of water droplets was involved. The reductions of dielectric constant and water absorption, and increases of tensile strength and tensile modulus were realized simultaneously due to the presence of symmetrical porous structure and the dense PI layer upon the introduction of sandwich-type porous structure. The dielectric, mechanical and water resistance properties of composite PI film could be further regulated through controlling the porous structure by using different conditions for film formation. Through varying the temperature, humidity, concentration of polymer and surfactant in microemulsion method, the low dielectric constants of 2.24–2.81 and low water absorptions of 0.49–0.59%, with 15.73–32.81% and 76.02–80.08% of decreases, respectively, while high tensile strength of 97.7–103.2 MPa and high tensile modulus of 1.2–1.4 GPa with 4.83–10.73% and 6.57–16.43% of increases, respectively, compared to flat PI film were shown. Meanwhile, excellent durability of low dielectric constant under high humidity was demonstrated by the tiny increase of dielectric constant (0.02–1%) upon moist environment. These results provide useful information for the structural design of high-performance dielectric materials.