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 mum and 3.6 mum 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 mum inner diameter and 29 mum 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 mum diameter and 30 mum height, measured at 1 kHz in a saline environment is 2 MOmega. Insertion into a gelatin membrane confirms that both the tube and the probe show sufficient penetration capabilities.