Laser Micromachining of Nanocomposite-Based Flexible Embedded Capacitors

This paper discusses laser micromachining of barium titanate (BaTiO₃)-polymer nanocomposites and sol-gel thin films. In particular, recent developments on high capacitance, large area, and thin flexible embedded capacitors are highlighted. A variety of flexible nanocomposite thin films ranging from 2 microns to 25 microns thick were processed on copper or organic substrates by large area (13 inch times 18.5 inch, or 19.5 inch times 24 inch) liquid coating processes. SEM micrographs showed uniform particle distribution in the coatings. Nanocomposites resulted in high capacitance density (10-100 nF/inch²) and low loss (0.02-0.04) at 1 MHz. The remarkably increased flexibility of the nanocomposite is due to uniform mixing of nanoparticles in the polymer matrix, resulting in an improved polymer-ceramic interface. BaTiO₃-epoxy polymer nanocomposites modified with nanomaterials were also fabricated and were investigated with SEM analysis. Capacitance density of nanomaterial-modified films was increased up to 500 nF/inch2, about 5-10 times higher than BaTiO₃-epoxy nanocomposites. A frequency-tripled Nd:YAG laser operating at a wavelength of 355 nm was used for the micromachining study. The micromachining was used to generate arrays of variable-thickness capacitors from the nanocomposites. The resultant thickness of the capacitors depends on the number laser pulses applied. Laser micromachining was also used to make discrete capacitors from a capacitance layer. In the case of sol-gel thin films, micromachining results in various surface morphologies. It can make a sharp step, cavity-based wavy structure, or can make individual capacitors by complete ablation. Altogether, this is a new direction for development of multifunctional embedded capacitors.