Laser Micromachining of Barium Titanate (BaTiO_3)-Polymer Nanocomposite Based Flexible/Rollable Capacitors

摘要

This paper discusses laser micromachining of thin films. In particular, recent developments on high capacitance, large area, thin, flexible/rollable 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 (330 mm × 470 mm, or 495 mm × 607 mm) liquid coating processes. SEM micrographs showed uniform particle distribution in the coatings. Nanocomposites resulted in high capacitance density (10-100 nF/inch~2) 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. BaTiO_3-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/inch~2, about 5-10 times higher than BaTiO_3-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 of 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.