Humidity sensors based on silica nanoparticle aerogel thin films

Abstract Humidity sensors were fabricated with thin films of silica nanoparticles aerogel on gold-patterned alumina substrates by sol–gel colloid spin coating and supercritical drying. The aerogel silica possesses average pore size of 20.5 nm, particle size around 30 nm, film thickness within 142 nm, and specific surface area of 866 m 2 /g. Both impedance and capacitance responses of the mesoporous film sensor were sensitive to moisture and operation temperature at 40% RH and higher, and with a hysteresis within 3.3% RH. Electrical resistance markedly decreased with humidity at low frequency. Porosity, surface hydroxyls, and film uniformity of silica were directly related to the sensors performance. The operation stability and reproducibility over time make the aerogel films potentially viable for use in ceramics integrated humidity sensors.

[1]  R. K. Nahar.  Study of the performance degradation of thin film aluminum oxide sensor at high humidity , 2000 .

[2]  T. Troczynski,et al.  Sol–gel BaTiO3 thin film for humidity sensors , 2003 .

[3]  W. Li,et al.  Stability of hydroxyl and methoxy surface groups on silica aerogels , 1997 .

[4]  F. Uchikawa,et al.  Time variability of surface ionic conduction on humidity-sensitive SiO2 films , 1985 .

[5]  E. Traversa,et al.  Relative humidity and alcohol sensors based on mesoporous silica thin films synthesised from block copolymers , 2003 .

[6]  Ko-Shao Chen,et al.  Humidity sensors using polyvinyl alcohol mixed with electrolytes , 1998 .

[7]  J. Rayss,et al.  Ion adsorption in the porous sol–gel silica layer in the fibre optic pH sensor , 2002 .

[8]  G. A. Parks,et al.  Electrical conductivity of silica gel in the presence of adsorbed water , 1968 .

[9]  R. C. Weast.  CRC Handbook of Chemistry and Physics , 1973 .

[10]  Mechanical properties of aerogel-like thin films used for MEMS , 2004 .

[11]  C. Wan,et al.  Sol–gel processed TiO2–K2O–LiZnVO4 ceramic thin films as innovative humidity sensors , 2000 .

[12]  Jun Liu,et al.  Chemical sensors based on dielectric response of functionalized mesoporous silica films , 2001 .

[13]  Jing Wang,et al.  Humidity sensors based on composite material of nano-BaTiO3 and polymer RMX , 2002 .

[14]  R. Willey,et al.  Mechanistic aspects of methanol partial oxidation over supported iron oxide aerogels , 2001 .

[15]  Hongmin Kim,et al.  The effect of sol viscosity on the sol-gel derived low density SiO2 xerogel film for intermetal dielectric application , 1998 .

[16]  S. Yoda,et al.  Supercritical drying media modification for silica aerogel preparation , 1999 .

[17]  Joseph R. Stetter,et al.  Humidity sensing properties of Nation and sol-gel derived SiO2/Nafion composite thin films , 1997 .

[18]  Huan-Da Chen,et al.  Humidity sensitive characteristics of Zn2SnO4–LiZnVO4 thick films prepared by the sol–gel method , 2002 .

[19]  G. Neri,et al.  Gold promoted Li–Fe2O3 thin films for humidity sensors , 2003 .

[20]  C. Prestidge,et al.  Water adsorption kinetics and contact angles of silica particles , 2001 .

[21]  Plinio Innocenzi,et al.  Humidity sensors based on mesoporous silica thin films synthesised by block copolymers , 2004 .

[22]  K. Uchida,et al.  Effects of ethanolamines catalysts on properties and microstructures of silica aerogels , 1996 .