Reduction of unwanted light reflection from a surface of a substance is very essential for the improvement of the performance of optical and photonic devices. Anti-reflection (AR) surface textures can be created on the surface of lenses and other optical elements to reduce the intensity of surface reflections. AR textures are indispensable in numerous applications, both low and high power, and are increasingly demanded on highly curved optical components.
Nanofabrication involves the fabrication of devices at the nanometer scale. In this work, we used nanofabrication to design and fabricate nanostructures of squares and hexagons of different spatial pitch and gap width in Gallium Arsenide (GaAs). These structures have a gap of 300nm, 400nm, and pitch of 900nm, 1000nm and 1100nm. The fabrication process involves solvent cleaning, deposition of silicon oxide, soft and hard bake, photolithography and development. Both wet and dry etching were used to fabricate the expected structures. Results from scanning electron microscopy (SEM) to examine the shapes of the fabricated arrays are presented in this study. By combining dry and wet etches, we obtained the desired shapes and depth of hexagons and squares with rounded edges. We report detailed fabrication processes and their corresponding results at each step.
Electroencephalogram (EEG) recording is a widely used method to measure electrical activity in the brain. Rodent EEG brain recording not only is noninvasive but also has the advantages to accomplish full brain monitoring, compared with that of the invasive techniques like micro-electrode-arrays. In comparison to other noninvasive recording techniques, EEG is the only technique that can achieve sub-ms scale time resolution, which is essential to obtain causal relationship. In this work, we demonstrated a simple microfabrication process for developing a high-density polyimide-based rodent EEG recording cap. A 34-channel rodent electrode array with a total size of 11mmx8mm, individual electrode diameter 240μm and interconnect wire linewidth 35μm was designed and fabricated. For the fabrication process, we first deposit 350nm SiO2 on a silicon substrate. We then fabricate 6-7μm thick first layer polyimide caps with fingers and contact holes. Gold deposition and then lithography etching of 34 channel contact-electrodes and their interconnects were fabricated in the second step. The third step was to cover metal interconnects with a 10μm thick second layer polyimide, which was fabricated with photolithography before the final film released by HF undercutting etching of SiO2 layer. Then the fabricated EEG cap is interfaced with a commercial 34-channel female connector, which is soldered with 34-line wires. These wires are then connected to an ADC to record the EEG data in computer for post-processing. With polyimide, the EEG cap is biocompatible, and flexible which makes it suitable for good contact with rodent skulls.
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