A neuronal microneedle, a single-crystalline silicon microneedle with fluidic

The processes for the neuronal microneedle are performed with only one ordinary double-polished (100) silicon wafer. The buried microchannel in the neuronal microneedle is fabricated using the processes of anisotropic dry etching, sidewall passivation, isotropic dry etching, and trench-refilling with a LPCVD polysilicon film. Because the microchannel fabrication process in this thesis uses the isotropic dry etch, the direction of microchannels can be oriented to any crystallographic direction in-plane. The gold microelectrodes in the neuronal microneedle are formed on top of a polysilicon film which is deposited on top of a silicon dioxide film. This process significantly increases the roughness of the polysilicon film, and then the effective surface area of microelectrodes is increased. Therefore, the electrode-electrolyte interface impedance is significantly lowered. Finally, a fluid reservoir, a handling body, and a microneedle shank of the neuronal microneedle structure is defined and released from the silicon substrate by using the process of anisotropic dry etch on both sides of the wafer.