A Microfabrication Compatible Method to Fabricate Silicon Nanotubes for Nanoprobe Applications

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Top-down micromanufacturing is the process for fabricating computer chips and microelectromechanical system sensing chips and is the basis for the current semiconductor and sensor industries. However, the emergence of various nanoscale structures and materials can significantly improve the performance of these chips. However, numerous challenges exist to integrate these nanoscale materials and structures on these chips seamlessly due to incompatibility of their fabrication process with standard microfabrication processes. This award supports fundamental research to develop a room-temperature microfabrication process to fabricate silicon nanotubes. The new process allows the manufacturing of silicon nanotubes with other functional elements or electronics on the same chip without thermal damage. Nanotubes and nanotube-enabled functional devices fabricated from a wide variety of materials such as semiconductors, compound semiconductors, and metals have great potential for applications in healthcare, biomedical, energy, aerospace, and chemical industries. Hence, the outcomes from this research benefits the U.S. economy and society. This research involves several disciplines including manufacturing, computation, neuroscience and material science, thereby helping broaden participation of women and underrepresented minority students in research and having a positive impact on engineering and science education. The project seeks to develop a scalable, ambient temperature, top-down process to fabricate single crystal silicon nanotubes. The fabrication of the silicon nanotubes is realized by simply using a series of integrated circuit (IC)-compatible microfabrication processes. Specifically, polystyrene nanosphere (NS) beads are first self-assembled into a close-packed monolayer on a silicon wafer. These NS beads are then tailored by oxygen plasma reactive ion etching (RIE) to shrink their size. Using the NS beads as the mask, the silicon nanotubes are fabricated by inductively coupled plasma (ICP) Bosch process. This research fills the technical knowledge gap on how to realize the large-scale integration and arrangement of a single nanotube or an array of nanotubes in a controlled manner on a chip. The research team plans to perform sharp interface phase-field nanoscale modeling for fundamental understanding and control of the tolerance range of the processing parameters for fabricating robust silicon nanotubes. In addition, the research team plans to develop silicon nanotube-based patch-clamp nanoprobes for neuronal and cellular stimulation and recordings. Specifically, arrays of silicon nanotube-based patch-clamp nanoprobes embedded within microscale cell culture chambers are developed for recording electrophysiological activity in cultures of adult hippocampal progenitor cells that have differentiated into oligodendrocyte, astrocytes or neurons as well as mapping multiple individual synaptic connections between neurons.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.