Porous Silicon Resonators for Improved Vapor Detection

This paper presents a microscale resonant sensor that has been fabricated with nanoscale pores for enhanced sensitivity to chemical vapors. By building resonators that are made of porous silicon, we take advantage of the increased area for molecular binding and improve the sensitivity of the resonators to the vapor concentration of interest. We present results for resonators whose surfaces are entirely porous silicon. We also examine the use of targeted regions of porosity to keep critical parts of the beam nonporous and mechanically stable while still maximizing surface area. Surface micromachining processes were used to fabricate the silicon resonator mass sensor, allowing nanostructured devices to be fabricated using only standard top-down processing techniques. We have demonstrated an improvement up to 261% and 165% in resonator sensitivity to isopropyl alcohol forfully porous resonators and partially porous resonators, respectively, as compared to nonporous silicon resonators. Combining this increased sensitivity with resonator quality factor suggests an improvement in minimum detectable resolution over the nonporous resonators by 41% and 56% for the fully porous and partially porous resonators, respectively.