Dielectric properties of on-chip-cured polyimide films

Spin-coated polyimide thin films were locally cured using microelectromechanical system microhotplates as an alternative approach to the conventional wafer-level curing process. The on-chip cured polyimide films were characterized Fourier transform infrared spectroscopy. The polyimide was found to be fully cured at a temperature over 350 oC for 1 h. The dielectric properties of 350 oC-cured polyimide films were measured over broad frequency, temperature, and humidity ranges. As is expected for most polymer materials, the dielectric constant decreased with increasing frequency due to dielectric relaxation, which may be due to the fact that multiple relaxation times (i.e., several types of polarization), rather than a single one are involved. The dissipation factor was very low and nearly flat for excitation frequencies less than 1 MHz. Both the dielectric constant and the dissipation factor increased with increasing temperature from 10 oC to 90 oC, and relative humidity (RH) from 30%RH to 95%RH, with a steeper slope at lower frequencies. These results indicate that on-chip-cured polyimide films have weak low frequency dispersion due to the aging effect at high temperature and humidity.