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Humidity Sensing Properties of Carbon Nano-Tube Thin Films

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In this article, the electrical properties of carbon nanotubes (CNTs) films were studied by fabricating Ag/CNT/Ag devices. The nominal thickness of the grown CNTs films was ∼12 μm, and the diameter of multiwalled carbon nanotubes (MWCNTs) varied between 10–30 nm. The current–voltage (IV) characteristics of the fabricated devices exhibited rectification behaviour (3 at ±1 V). The effect of humidity on MWCNTs films was investigated by evaluating capacitance and dissipation of the samples at two different frequencies, i.e., 120 Hz and 1 kHz. It is observed that the capacitance and resistance change with changing values of relative humidity (RH) as a function of frequency (f). At f = 120 Hz, RH = 90%, the observed increases in the capacitance of the sensor was ∼366 times and it was only ∼36 times when measured at f = 1 kHz. Under the same experimental conditions, the observed decrease in the resistance values was ∼656 and ∼627 times respectively. It is assumed that the humidity based electrical response of the cell is associated with doping of the nano-particles by water molecules. To evaluate the dynamics of the water vapour absorption and desorption processes, the average response (2 s/percent) and recovery (8 s/percent) times of the fabricated devices were obtained by capacitance-time measurements. The experimental results have been simulated by defining the device equivalent circuit and capacitance-humidity relationship.


Document Type: Research Article


Publication date: 2011-10-01

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