Direct pattering of porous Mg₂SiO₄ films through electrochemical polymerization using low-conducting electrolytes and study of their microwave dielectric properties

This paper reports on the novel use of polymerization reactions using low-conductivity electrolytes, induced by a high electric field (≈10¹¹ V/m) built at a sharp tungsten tip to achieve direct patterning of pure porous Mg₂SiO₄ films. The establishment of an edge-point-to-center-point electrochemical configuration enables local deposition with easy and versatile control of the growth rate, thickness, and quality of the films by simply adjusting the associated experimental parameters, such as the precursor amount, deposition time, annealing temperature, and pH value. Hypothetical mechanisms for both polymerization of precursor solutions and film deposition are proposed based on results of various characterizations, including zeta potential, Fourier-transform infrared spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, small-angle X-ray scattering, X-ray diffraction, and X-ray photoelectron spectroscopy. The resulting Mg₂SiO₄ films were peeled and sandwiched between polyimides for dielectric measurements at 28 −80 GHz. The dielectric constants and loss values exhibited by favorable samples were approximately 2.4 and 0.015 at up to 80 GHz, respectively. Furthermore, moisture absorption increased by approximately 0.14 wt% after 24 h. Our encouraging results highlight the potential of these samples as substrates for applications beyond 5 G or 6 G.