Covalent Grafting of Low-k Magnolol Films on Si(111) Using Aryldiazonium Salts

The continuous miniaturization and high integration of integrated circuits (ICs) make low-dielectric constant (low-k) materials a critical bottleneck for further performance enhancement. This study explores magnolol, a biobased compound extracted from the natural plant Magnolia officinalis, as a novel dielectric material. Compared to traditional fossil-based dielectric materials, this new material aligns with sustainable development goals. The successful co-grafting of 4-nitrobenzenediazonium tetrafluoroborate (NBD) and magnolol onto the silicon surface is confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). As the amount of magnolol increases to 0.15 g, the arithmetic mean roughness (R_a) of the film decreases to 0.51 nm, the k value can be as low as 2.41, and the dielectric loss can be as low as 0.033. These improvements are predominantly ascribed to the rigid biphenyl structure of magnolol, whose steric hindrance inhibits the close packing of molecular chains to generate nanoscale free volume while facilitating sufficient monomer cross-linking to form a dense, continuous molecular network. The film incorporating 0.15 g of magnolol exhibits excellent thermal stability (T_5% = 302 °C) and electrical insulation (breakdown field strength = 260.34 MV/m, leakage current = 2.34 × 10^-11 A). The films are systematically characterized using XPS, FTIR, atomic force microscopy (AFM), spectroscopic ellipsometry, thermogravimetric analysis (TGA), and a semiconductor parameter analyzer. This work develops a high-performance biobased low-k dielectric material based on magnolol, provides a sustainable alternative to fossil-based dielectric materials, and opens a new technological pathway for green IC fabrication.