Laser Micromachining of Barium Titanate $({\hbox {BaTiO}}_{3})$ -Epoxy Nanocomposite-Based Flexible/Rollable Capacitors: New Approach for Making Library of Capacitors

This paper discusses laser micromachining of barium titanate (BaTiO₃)-polymer nanocomposite thin films. In particular, recent developments on high-capacitance, large-area, thin, flexible, embedded capacitors are highlighted. A variety of barium titanate (BaTiO₃)-epoxy polymer nanocomposite-based flexible/rollable thin films ranging from 2 to 25 mum thick were processed on large-area substrates (330 mm times 470 mm, or 495 mm times 607 mm) by liquid coating processes. The electrical performance of composites was characterized by dielectric constant (Dk), capacitance, and dissipation factor (loss) measurements. Nanocomposites provided high capacitance density (10-100 nF/in²) and low loss (0.02-0.04) at 1 MHz. Scanning electron microscopy (SEM) micrographs showed uniform particle distribution in the coatings. Uniform mixing of nanoparticles in the epoxy matrix results in high dielectric (> 3 times 10⁷ V/m) and mechanical strengths (> 3700 PSI). Reliability of the capacitor was ascertained by thermal cycling. Capacitance change was less than 5% after baking at 140degC for 4 h, and 1100 cycles from -55degC to 125degC (deep thermal cycle). 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.