Polyphenol-Functionalized Boron Nitride Nanosheet-Reinforced Sustainable Polyimide Dielectric Films for Antenna-in-Package Applications

Polyimide (PI) nanocomposite films containing two-dimensional boron nitride nanosheets (BNNSs) have been recognized as advanced dielectrics for flexible and miniaturized integrated circuits and communication electronics. However, high-quality BNNSs must be created using lengthy and sophisticated exfoliation and surface functionalization methods, while a PI matrix often undergoes high-temperature imidization, which results in thermosetting properties. These factors pose significant challenges for the manufacture and application of BNNSs/PI dielectrics. Herein, we report a simple yet effective approach to fabricate sustainable BNNSs/PI dielectric films using polyphenol-functionalized BNNSs as the filler and soluble PI (sPI) as the matrix. BNNSs with average size of 2.5 μm in lateral dimension and 2.7 nm in thickness were prepared through a lithium intercalation-assisted liquid-phase exfoliation method. The BNNSs were further modified with polyphenol compounds via noncovalent functionalization. We investigated four different polyphenols, namely, hydroquinone (HQ), dopamine (DP), tannic acid (TA), and tea polyphenol (TP), and found that TP displays a high functionalization density of 0.699 molecule/nm2 on surfaces of BNNSs, which is about 1 order of magnitude larger than that of TA. Accordingly, TP-BNNSs/sPI nanocomposites demonstrate superior properties, including a dielectric constant of 3.08 and loss tangent of 0.006 at 100 kHz, electrical breakdown strength of 185.4 kV/mm, and tensile strength of 87 MPa under the filler loading of 1 wt %. Furthermore, the TP-BNNSs/sPI nanocomposite films can be simply recycled at least four times without losing performance. We also demonstrate a coplanar waveguide antenna with the TP-BNNSs/sPI nanocomposite as the dielectric layer, confirming its great potential for practical applications.