Fabrication And Characterization Of Silicon Microwire Neural Electrode Arrays On Flexible Substrates

Neuroprosthetic devices are widely employed in clinical and research settings. However, most of these devices suffer from diminishing device performance over time, likely due to the reactive tissue response of the central nervous system and scarring to biological tissue from the implantation procedure. In an effort to minimize acute tissue trauma while maintaining high spatial resolution, this thesis presents a novel miniaturized neural implant device capable of recording high-density neural signals from cortical tissue with penetrating silicon microwire sensing elements on a flexible conformable substrate. In addition to reduced tissue scarring, it is possible to improve on current commercially available neural probe designs by reducing the mechanical property mismatch between the electrode interface and neural tissue. Neural electrodes fabricated on flexible substrates have received an increase in attention in recent years; however, these designs offer moderate spatial resolution because signals are typically recorded from the surface of neural tissue in thin film style electrode designs. The MEA presented in this thesis is fabricated by a hybrid integration technology that takes advantage of both rigid penetrating pillars, similar yet smaller than commercially available technology, and is fabricated on thin film polyimide substrates. The thin film polyimide substrate allows for the electrode to make intimate contact with surrounding cortical tissue around sulci and gyri of the brain, and the silicon microwire sensing elements, which penetrate into the cortex, enable this MEA to have the potential for the best spatial resolution. The impedance of these MEAs was characterized and found to be in the range of a few hundred kilohms making them suitable for both local field potentials and single unit recordings.