Fabrication and Characterization of Nanoporous Silicon Relative Humidity Sensors

Abstract

This work describes a porous, silicon-based humidity sensor operating under the capacitive transduction principle. One of the aims of this work is to determine the main parameters such as sensitivity, linearity, hysteresis, and time response to step humidity changes of four samples via measurements of their capacitance. The parameters gauged by capacitance measurements were used to explain the dynamics of its operation. The most sensitive sample caused changes in relative humidity of $74\hbox { nF}{\cdot }\%\hbox {rh}^{-1}$. Hysteresis of at least 3.6 % to 4.6 % was found to occur. Humidity sensor samples synthesized from nanoporous silicon were also analyzed by scanning electron microscopy, image processing, and Raman spectra red shifts. As a result of these measurement and analysis of this work, the best synthesis conditions and nanopore surface and sub-surface diameters for producing high performing humidity sensors were identified. Another aim of this work is to find the optimal pore size from the analysis of image processing and Raman spectra. The optimal porous sizes in relation to the analyzed sensor’s characteristics were found to be between 4 nm and 26 nm. The novelty of this work is to establish the relationship between the capacitance measurements with image processing of SEM images and Raman spectral measurements. The mechanical stability of the samples was also gauged over 3 months utilizing both capacitance and Raman spectral measurements.