Porous Silicon for Chemical Sensors

Abstract

In this work we highlight the advantages of using Porous Silicon (PS) as a material for chemical sensors. Two different applications of PS are investigated: (a) as a matrix for the inclusion of catalytic materials, such as Pd or Pt, and (b) as a material for the fabrication of suspended micro hotplates, for improved thermal isolation. For the first application, the catalytic behavior of Pd-doped PS samples is estimated and the parameters that influence the kinetics of the chemical reaction are evaluated. It is found that the catalytic activity of Pd-doped porous silicon is significantly higher than that of a planar surface covered with Pd. On the other hand, the effectiveness of PS for local thermal isolation on a silicon substrate is examined and the thermal properties of suspended porous silicon (PS) micro-hotplates are investigated. The micro-hotplates are fabricated by a novel technique, based on the isotropic etching of silicon under a PS layer, in a high density plasma reactor. Very high local temperatures on the micro-hotplates (higher than 600°C) with very low power consumption (only a few tens of mW) have been obtained, due to the very low thermal conductivity of PS, which is comparable to that of thermal oxide and it is much lower than that of silicon nitride, typically used for thermal sensor applications.