Characterization of a-SiCx:H thin films as an encapsulation material for integrated silicon based neural interface devices

A fully integrated, wireless neural interface device is being developed to free patients from the restriction and risk of infection associated with a transcutaneous wired connection. This device requires a hermetic, biocompatible encapsulation layer at the interface between the device and the neural tissue to maintain long-term recording/stimulating performance of the device. Hydrogenated amorphous silicon carbide (a-SiCx:H) films deposited by a plasma enhanced chemical vapor deposition using SiH4, CH4, and H2 precursors were investigated as the encapsulation layer for such device. Si–C bond density, measured by Fourier transform infrared absorption spectrometer, suggests that deposition conditions with increased hydrogen dilution, increased temperature, and low silane flow typically result in increase of Si–C bond density. From the variable angle spectroscopic ellipsometry measurement, no dissolution of a-SiCx:H was observed during soaking tests in 90 °C phosphate buffered saline. Conformal coating of the a-SiCx:H in Utah electrode array was observed by scanning electron microscope. Electrical properties were studied by impedance spectroscopy to investigate the performance of a-SiCx:H as an encapsulation layer, and the results showed long term stability of the material.