Integration of out-of-plane silicon dioxide microtubes, silicon microprobes and on-chip NMOSFETs by selective vapor-liquid-solid growth

Three-dimensional microtubes and microprobes with MOSFET circuits are integrated for use in chemical and electrical neural interface applications with microelectronics. We propose a vapor-liquid-solid (VLS) method to realize both the microtubes and microprobes, which are 2 mu m and 3.6 mu m in diameter, respectively, and can be fabricated after the on-chip MOSFET processes. The on-chip NMOSFET shows electrical characteristics with a threshold voltage of 1.2 V and a subthreshold swing of 145 mV decade(-1), confirming that subsequent fabrications of the tube and probe are compatible with the inclusion of the on-chip circuits. The prototype oxide tube, which has 2.7 mu m inner diameter and 29 mu m height, has a flow rate of 550 nl min(-1) with an external pump pressure of 33.5 kPa. The impedance of the on-chip Si probe, which has 2 mu m diameter and 30 mu m height, measured at 1 kHz in a saline environment is 2 M Omega. Insertion into a gelatin membrane confirms that both the tube and the probe show sufficient penetration capabilities.