The aim of this work is to calculation and fabrication silicon membranes for acoustic sensors with operating ranges of resonant frequencies from 10 kHz to 100 MHz and pressures from 0.1 to 103 kPa. In this paper, analytical dependences of pressure and resonance frequency on geometrical parameters of membranes are presented. The ranges of the thickness (30-50 μm) and the length of the edge membranes (0.2-1.0 mm) were defined. Experimental studies of the etching of the silicon wafer with a solution of 30% KOH were carried out and the etching rate was found to be 1.2-1.8 μm/min. Anisotropic wet etching was used to form square-shaped silicon membranes with a thickness of 30-50 μm and an edge length of 0.2 to 1.0 mm with resonant frequencies in the range of 0.7 to 30 MHz. The obtained results can be used in the development of acoustic sensors based on of monocrystalline silicon.
Multi-electrode microprobes fabrication process based on silicon substrate was developed using surface micromachining and anisotropic wet etching. The process flow consists of 20 main operations, including 4 lithography steps using 4 photomasks. The minimum size of the elements is 2 μm. The effect of the solution concentration (from 10 to 40% at 80°C) on the etching rate and surface roughness was studied. The optimal value of solution concentration leading to the formation of surface with the lowest root mean square roughness value was determined. The etching rates of monocrystalline silicon (100) face and silicon oxide were 1.5 μm/min and 10 nm/min, respectively. Rapid thermal annealing at 600 °C for 3 min increased the resistance of silicon oxide to the action of an alkaline solution by 2 times. As a result, the neural probe structure including two microprobes and electrical interface of 10 electrodes was fabricated.
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