Nanostructuring of polycrystalline silicon thin films

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Supervisor:
Dr. Juhász László
Department of Electron Devices

Brain tissue responses to chronically implanted neural microelectrodes by insulating the probe itself from the biological system due to the inevitable action of glial cells. Such cell proliferation inherently causes reduced recording capabilities, however, surface nanostructuring of recording sites can significantly improve signal-yield in case the extracellular matrix is mimicked. Several experimental results in literature proves that not only the immune response can be reduced, but signal-to-noise ratio can be also increased since specific surface of the recording sites is changed beneficially.

Commonly used microelectrodes are fabricated from silicon, which implies that a nanostructuring method compatible with silicon technology is preferred. The so-called black silicon, which can be realized by deep reactive ion etching at cryogenic temperature, is a promising candidate. In my study, I had the opportunity to work on this topic in the Institute for Technical Physics and Materials Science, RCNS, HAS. The main goal of my work was to determine the effect of the cryogenic temperature of the vacuum chamber, the rate ratio of etching gases (SF6, O2) and the RF power of the plasma on the resulting surface morphology. My manuscript also containsI was also involved in the in-depth investigation on loading and on the grain structure of the polycrystalline silicon film. The morphological investigation is supported byFor the investigation of the morphology scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis was used. Cyclic voltammetry and electrochemical impedance spectroscopy of blacksilicon layers covered by sputtered platinum thin film is applied and evaluated to reveal surface enhancement and resulting electrochemical properties provided by the proposed method.

Besides the improvement inbetter recording quality of the electrophysiological measurements the long-term stability of the implanted electrodes in chronic recording sessions may be improved, reducing the number of the sacrificed laboratory animals can also be limited as the long-term stability of the implanted electrodes in chronic recording sessions may be inherently improved.

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