As the processing speed of the electronic components increased with technology advances, the overall performance of the system is limited by the propagation delay in the interconnections, while the propagation speed of signal in interconnections is depended on the dielectric materials. The current dielectric materials such as silicon dioxide have dielectric constant of 3.9-4.2. Future generation of electronic devices require the material to have ultralow dielectric constant below 2. To increase signal propagation speed and reduce propagation delay, ultralow dielectric constant material has to be developed. The industry has targeted at the development of ultralow dielectric materials since 2005 but there is still no available solution.

In this study, porous polyimide (PPI) as an...[ Read more ]

As the processing speed of the electronic components increased with technology advances, the overall performance of the system is limited by the propagation delay in the interconnections, while the propagation speed of signal in interconnections is depended on the dielectric materials. The current dielectric materials such as silicon dioxide have dielectric constant of 3.9-4.2. Future generation of electronic devices require the material to have ultralow dielectric constant below 2. To increase signal propagation speed and reduce propagation delay, ultralow dielectric constant material has to be developed. The industry has targeted at the development of ultralow dielectric materials since 2005 but there is still no available solution.

In this study, porous polyimide (PPI) as an ultralow dielectric material for device application is investigated. Porous polyimide is prepared via a Vapor Induced Phase Separation (VIPS) method. The porous structure of the film was found to be affected by the concentration of polyimide (PI) in the casting solution and the processing conditions. Dielectric measurement showed that dielectric constant is depended on the porosity of the fabricated films. Microporous polyimide films with 70% porosity and dielectric constant as low as 1.5 were successfully fabricated.

To evaluate the performance of porous polyimide as a dielectric material, circuits were built on microporous polyimide substrate with etching process. The dielectric constant of the microporous substrate was remained stable in value of 1.5 after exposure to 95% relative humidity for 3 hours. Electrical measurements showed that the ultralow dielectric constant of the microporous film increased the signal propagation speed by 35% in the circuits on microporous polyimide substrate than the circuits on dense polyimide substrate. Impedance tests on copper circuits built on the substrates showed that a 23% increase in impedance for circuits on microporous substrate. Considering the same impedance, the ultralow dielectric constant of microporous polyimide enabled 37% reduction in line spacing. With higher wiring density, miniaturization of electronic devices can be achieved.