BCB with nano-filled BaSrTiO3 for thin film capacitors

A BaSrTiO₃-BCB composite was developed for spin-coating to integrate capacitors into multilayer wiring for Wafer Level Packaging (WLP) and System in Package (SiP). The size of nanoscale barium strontium titanate crystallite size was measured as 24 nm. The matrix for the composite was BCB with 63 wt.-% solids dissolved in mesitylene. Various dispersants were tested to find the best surfactant for the stabilization of BaSrTiO₃ in mesitylene, which is compatible with BCB. The optimum dispersant was used for preparation of suspensions with a solid loading of 20 - 35 wt.-% BaSrTiO₃ dispersed in mesitylene using 5.0 - 10 wt.-% dispersant. The resulting average layer thickness of the cured composite is in the range of 1.7 mum. These films can be easily integrated into existing thin film multilayer built-up wiring structures. The relative dielectric constant epsiv_r of the investigated BaSrTiO₃-BCB composite is 31. The breakdown voltage of the exceeds 170 V for 1.7 mum thickness which equals a dielectric strength of 1.0 MV/cm. High reliability was proven for humidity storage (85degC and 85% rel. humidity, 2000 hrs) and thermal cycling from (AATC from -55degC to +125degC, 2000 cycles).