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-SiC(x):H) films deposited by a plasma enhanced chemical vapor deposition using SiH(4), CH(4), and H(2) 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-SiC(x):H was observed during soaking tests in 90°C phosphate buffered saline. Conformal coating of the a-SiC(x):H in Utah electrode array was observed by scanning electron microscope. Electrical properties were studied by impedance spectroscopy to investigate the performance of a-SiC(x):H as an encapsulation layer, and the results showed long term stability of the material.