Three-dimensional epitaxial silicon microprobe array integrated on highly functional smart sensing chip

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Three-dimensional silicon microprobes are integrated with MOSFET circuits for use in electrical neural interface applications with microelectronics. We have proposed a vapor-liquid-solid(VLS) method to realize microprobes after the fabrication of on-chip MOSFETs using Si(111) substrate. We investigated the characteristics of the on-chip MOSFETs fabricated on Si(111) substrate. Even though the increased interface state density in the Si(111) MOS system causes low-performance of the MOFET, we have improved the electrical characteristics of the MOSFETs on Si(111) using subsequent processes of fluorine implantation and long-time Hydrogen annealing, that exhibits comparable electrical characteristics of MOSFETs to that on Si (100)substrate. In-situ doping method during the VLS growth is one possibility to realize doped-silicon probes by low-temperature process with less than 700℃. We used PH_3 or B_2H_6 mixed with silicon gas source of Si_2H_6, in order to realize n- or p-type of silicon probes, respectively. Both n- and p-types of silicon probe grown by the in-situ doping process showed low electrical resistance characteristics. Although the above VLS growth method provides probe arrays with a same probe length due to same parameters of the VLS growth, individually controlled length of probe in a same array was still problematic. To realize the different lengths of probes, we also demonstrated a repeated selective VLS growth of silicon microprobes using the catalysis of gold remaining at the tip of a preliminary VLS-grown microprobe, resulting in different probe lengths. Additionally, we have realized the integration of silicon dioxide microtube arrays and the silicon micoroprobe arrays with MOSFETs, for use in simultaneous electrical neural recordings and drug delivery into local neuronal tissue, and this proposed device could be an efficient electrical/chemical neural interface for use in numerous neuroscience applications.