Nanostructured Metal Oxide Thin Films for Humidity Sensors

Capacitive humidity sensors were fabricated using countersunk interdigitated electrodes coated with amorphous nanostructured TiO2, SiO2, and Al2O3 thin films grown by glancing angle deposition. The capacitive response and response times for each sensor were measured. The sensor utilizing TiO2 exhibited the largest change in capacitance, increasing exponentially from ~ 1 nF to ~ 1muF for an increase in relative humidity from 2% to 92%. Adsorption and desorption response times were measured using flow rates of 2.5 l/min and were between 90 ms and 300 ms for the sensors studied here. A simple model of the capacitive response of the devices has been developed and used to calculate the dielectric constant of the combined system of our films and adsorbed water. The obtained dielectric constants are found to be much higher than bulk or literature values for similar systems.

[1]  S. Fonash,et al.  Biomedical/analytical applications of deposited nanostructured Si films , 2005 .

[2]  Kevin Barraclough,et al.  I and i , 2001, BMJ : British Medical Journal.

[3]  Enrico Traversa,et al.  Ceramic sensors for humidity detection: the state-of-the-art and future developments , 1995 .

[4]  R. K. Nahar,et al.  Surface conduction mechanisms and the electrical properties of Al2O3 humidity sensor , 1987 .

[5]  Michael A. Henderson,et al.  The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited , 2002 .

[6]  Weng Cho Chew,et al.  Dielectric enhancement due to electrochemical double layer: Thin double layer approximation , 1982 .

[7]  Nathan S. Lewis,et al.  Characterization of the temporal response profile of carbon black-polymer composite detectors to volatile organic vapors , 2003 .

[8]  L. Greenspan.  Humidity Fixed Points of Binary Saturated Aqueous Solutions , 1977, Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry.

[9]  Jörg-Uwe Meyer,et al.  A novel thick-film ceramic humidity sensor , 1997 .

[10]  J. Fagan,et al.  Reliability and reproducibility of ceramic sensors. III: Humidity sensors , 1993 .

[11]  B. M. Wright,et al.  Measurement of respiratory rate in the newborn. , 1983, British medical journal.

[12]  Kensall D. Wise,et al.  A high-speed capacitive humidity sensor with on-chip thermal reset , 2000 .

[13]  S. Fonash,et al.  Nanocrystalline Si thin films with arrayed void-column network deposited by high density plasma , 2000 .

[14]  J. Hasted.  Water: a Comprehensive Treatise (Volume 6) , 1980 .

[15]  Hélène Debéda,et al.  Evidence of a correlation between the non-linearity of chemical sensors and the asymmetry of their response and recovery curves , 2005 .

[16]  Ettore Massera,et al.  A very sensitive porous silicon based humidity sensor , 2005 .

[17]  S. Gevorgian,et al.  Modelling of thin-film HTS/ferroelectric interdigital capacitors , 1996 .

[18]  Jeremy C. Sit,et al.  Nanostructured gradient index optical filter for high-speed humidity sensing , 2006 .

[19]  S. Fonash,et al.  A rapid-response, high-sensitivity nanophase humidity sensor for respiratory monitoring , 2004, IEEE Electron Device Letters.

[20]  William J. Fleming,et al.  A Physical Understanding of Solid State Humidity Sensors , 1981 .

[21]  C. Kolb,et al.  Spectroscopic water vapor sensor for rapid response measurements of humidity in the troposphere , 2002 .

[22]  T. Morimoto,et al.  Dielectric behavior of adsorbed water. 3. Measurement at room temperature on zinc oxide , 1987 .

[23]  Chi-En Lu,et al.  Humidity Sensors: A Review of Materials and Mechanisms , 2005 .

[24]  M. Brett,et al.  Capacitive Humidity Sensors With High Sensitivity and Subsecond Response Times , 2007, IEEE Sensors Journal.

[25]  J. Berg,et al.  Durable microfabricated high-speed humidity sensors. , 2004, Analytical chemistry.

[26]  Z. M. Rittersma,et al.  Recent achievements in miniaturised humidity sensors—a review of transduction techniques , 2002 .

[27]  Mahiko Nagao,et al.  Relation between the amounts of chemisorbed and physisorbed water on metal oxides , 1969 .

[28]  M.J.A.M. van Putten,et al.  Multisensor microsystem for pulmonary function diagnostics , 2002 .

[29]  T. Tatara,et al.  An Apnea Monitor Using a Rapid-Response Hygrometer , 2004, Journal of Clinical Monitoring.

[30]  V. Pravdić,et al.  Dielectric behaviour of adsorbed water films on the α-Fe2O3 surface , 1970 .

[31]  Noboru Yamazoe,et al.  Humidity sensors: Principles and applications , 1986 .

[32]  Claude Pellet,et al.  Comparison of three humidity sensors for a pulmonary function diagnosis microsystem , 2002 .

[33]  R. Igreja,et al.  Analytical evaluation of the interdigital electrodes capacitance for a multi-layered structure , 2004 .

[34]  J. T. Ranney,et al.  The Surface Science of Metal Oxides , 1995 .

[35]  Wojtek Wlodarski,et al.  Comparative study on micromorphology and humidity sensitive properties of thin-film and thick-film humidity sensors based on semiconducting MnWO4 , 2000 .

[36]  J. Lepage,et al.  Porous silica-water interactions. II. Mechanical and dielectric effects , 1997 .

[37]  P. R. Wiederhold,et al.  Water vapor measurement , 1997 .

[38]  A. N. Papathanassiou,et al.  Dependence of the electrical conductivity and the low-frequency dielectric constant upon pressure in porous media containing a small quantity of humidity , 2002 .

[39]  S. Gevorgian,et al.  CAD models for multilayered substrate interdigital capacitors , 1996 .

[40]  T. Morimoto,et al.  Dielectric behaviour of adsorbed water. Part 1.—Measurement at room temperature on TiO2 , 1987 .

[41]  Y. Li,et al.  A novel highly reversible humidity sensor based on poly(2-propyn-2-furoate) , 2002 .

[42]  Michael J. Brett,et al.  Nanostructure engineering in porous columnar thin films: recent advances , 2007 .

[43]  S. Kondo,et al.  The Dielectric Relaxation of ?-Alumina , 1973 .

[44]  J. Maczuk,et al.  ON THE LOW-FREQUENCY DIELECTRIC DISPERSION OF COLLOIDAL PARTICLES IN ELECTROLYTE SOLUTION1 , 1962 .

[45]  J. C. Morrow,et al.  Dielectric Behavior of Water Adsorbed on Alumina , 1962 .

[46]  B. Fubini,et al.  The reactivity of oxides with water vapor , 1988 .

[47]  K. G. Ong,et al.  Highly Ordered Nanoporous Alumina Films: Effect of Pore Size and Uniformity on Sensing Performance , 2002 .

[48]  Gwo-Bin Lee,et al.  Humidity Sensors: A Review , 2005 .

[49]  M. Brett,et al.  Arrays of self-sealed microchambers and channels , 2002 .

[50]  Honeywell,et al.  Humidity Sensors , 2002 .

[51]  E. Zdankiewicz,et al.  Micromachined water vapor sensors: a review of sensing technologies , 2001 .

[52]  R. Glang,et al.  Handbook of Thin Film Technology , 1970 .