Bioinspired Hierarchically Porous Polyimide Films with Moisture-Resistant Low-κ Dielectric Performance

Achieving polymer dielectric films with simultaneously a low dielectric constant, suppressed moisture uptake, and robust mechanical integrity remains a long-standing challenge for advanced interfacial dielectric layers in microelectronic and high-frequency applications. Herein, we report a bioinspired dual-template self-assembly strategy to fabricate hierarchically porous polyimide (PI) films with a moisture-resistant low-κ dielectric performance. Condensed water droplets are employed as dynamic microscale templates to generate ordered honeycomb-like porous surfaces, while poly(ethylene glycol) (PEG) acts as a sacrificial nanoscale porogen to introduce abundant nanoporosity along the pore walls. The synergistic integration of micro- and nanoscale porosity results in a well-defined hierarchical architecture that effectively increases the air fraction, suppresses moisture diffusion, and mitigates interfacial polarization. Benefiting from the combined effects of hierarchical porosity and the intrinsically low polarity of fluorinated PI, the optimized porous film exhibits a significantly reduced dielectric constant of 2.3220 and a low dielectric loss of 0.00314, together with a markedly decreased water uptake of 0.483%. Notably, after water immersion and under humid conditions, the dielectric constant increases only marginally (Δκ = 0.0630), demonstrating excellent moisture-tolerant dielectric stability. Meanwhile, the hierarchically porous PI films maintain enhanced mechanical performance, achieving a tensile strength of 125.69 MPa and an elongation at break of 64.48%, which are substantially higher than those of dense PI films. Importantly, both the porous architecture and the resulting dielectric and mechanical properties can be readily tuned by controlling key processing parameters, including the ambient humidity and PEG content. This work highlights a versatile material and interface design strategy for constructing hierarchically porous polymer dielectric films and provides insights into the development of moisture-stable low-κ materials through the rational control of multiscale porosity.