Carbon nanotube-enhanced capillary condensation for a capacitive humidity sensor

A capacitive humidity sensor is presented for moisture detection at room temperature. The sensor is fabricated by depositing multi-wall carbon nanotubes (MWCNTs) on one of the stainless-steel substrates. When compared to a sensor without CNTs, a CNT-enhanced sensor has an increase of 60–200% in capacitance response when the humidity is under 70% relative humidity (RH), and 300–3000% if the RH level goes over 70%. The performance is comparable to a commercial sensor from Honeywell, which is used as a benchmark throughout the experiments. Our results demonstrate that nano-materials like MWCNTs can naturally form networks of porous nano-structures, which can potentially realize a miniature capacitive humidity sensor with a higher sensitivity. The gain in performance is attributed to the capillary condensation effect.

[1]  Chia-Pin Lin,et al.  Fabrication and Characterization of Low Turn-On Voltage Carbon Nanotube Field Emission Triodes , 2001 .

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

[3]  Gwo-Bin Lee,et al.  Micromachine-based humidity sensors with integrated temperature sensors for signal drift compensation , 2003 .

[4]  Craig A. Grimes,et al.  A wireless, passive carbon nanotube-based gas sensor , 2002 .

[5]  Yao Xi,et al.  Porosity control of humidity-sensitive ceramics and theoretical model of humidity-sensitive characteristics , 1989 .

[6]  J. Kornet,et al.  Long-term tests of capacitive humidity sensors , 1994 .

[7]  G. Hummer,et al.  Water conduction through the hydrophobic channel of a carbon nanotube , 2001, Nature.

[8]  Yasuhiro Shimizu,et al.  Theoretical studies on the impedance-humidity characteristics of ceramic humidity sensors , 1985 .

[9]  Denis Flandre,et al.  High-sensitivity capacitive humidity sensor using 3-layer patterned polyimide sensing film , 2003, Proceedings of IEEE Sensors 2003 (IEEE Cat. No.03CH37498).

[10]  Sungho Jin,et al.  Nucleation and growth of carbon nanotubes by microwave plasma chemical vapor deposition , 2000 .

[11]  Craig A Grimes,et al.  Metal oxide nanoarchitectures for environmental sensing. , 2003, Journal of nanoscience and nanotechnology.

[12]  Desheng Jiang,et al.  Quartz crystal microbalance coated with carbon nanotube films used as humidity sensor , 2005 .

[13]  M. Meyyappan,et al.  Carbon Nanotube Sensors for Gas and Organic Vapor Detection , 2003 .

[14]  Sanjeev K. Manohar,et al.  Flexible vapour sensors using single walled carbon nanotubes , 2006 .

[15]  J. Ocaña,et al.  A theoretical method for the calculation of frequency- and temperature-dependent interaction constants applicable to the predictive assessment of laser materials processing , 2000 .

[16]  Xing Hu,et al.  Capacitive humidity sensing properties of hydrothermally-etched silicon nano-porous pillar array , 2005 .

[17]  J.P.M. She,et al.  Nanotechnology-Enabled Wireless Sensor Networks: From a Device Perspective , 2006, IEEE Sensors Journal.

[18]  M. S. Dresselhaus,et al.  Down the straight and narrow , 1992, Nature.

[19]  P. Milani,et al.  First study of humidity sensors based on nanostructured carbon films produced by supersonic cluster beam deposition , 2004 .

[20]  Karol Nitsch,et al.  Thick-film humidity sensors , 1997 .

[21]  W. S. Khokle,et al.  On the origin of the humidity-sensitive electrical properties of porous aluminium oxide (sensor application) , 1984 .

[22]  S. Iijima.  Helical microtubules of graphitic carbon , 1991, Nature.

[23]  J.P.M. She,et al.  Nanotechnology-enabled wireless sensor networks: overcoming the limitations from a device perspective , 2005, IEEE International Conference Mechatronics and Automation, 2005.

[24]  Ho Jung Hwang,et al.  Gigahertz actuator of multiwall carbon nanotube encapsulating metallic ions: molecular dynamics simulations , 2004 .

[25]  J. F. Stoddart,et al.  Nanoscale molecular-switch crossbar circuits , 2003 .

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

[27]  S. Yi,et al.  Humidity sensors using porous silicon layer with mesa structure , 2000 .

[28]  Karen Twomey,et al.  A Ceramic Thick Film Humidity Sensor Based on MnZn Ferrite , 2002 .

[29]  Khalil Najafi,et al.  A high-sensitivity polyimide capacitive relative humidity sensor for monitoring anodically bonded hermetic micropackages , 2001 .

[30]  Jijun Zhao,et al.  Gas molecule adsorption in carbon nanotubes and nanotube bundles , 2002 .

[31]  Junya Suehiro,et al.  Fabrication of a carbon nanotube-based gas sensor using dielectrophoresis and its application for ammonia detection by impedance spectroscopy , 2003 .