Humidity Sensitivity of Multi-Walled Carbon Nanotube Networks Deposited by Dielectrophoresis

Litao Liu,Zhaoying Zhou,Kang Wu,Rui Han,Xiongying Ye,Tianhong Cui

doi:10.3390/s90301714

Litao Liu, Zhaoying Zhou + Show 4 more

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https://doi.org/10.3390/s90301714

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Journal: Sensors	Publication Date: Mar 11, 2009
Citations: 130	License type: CC BY 4.0

Affiliation: Tsinghua University, University of Minnesota

Abstract

This paper presents an investigation on the humidity sensitivity of deposited multi-walled carbon nanotube (MWCNT) networks using ac dielectrophoresis (DEP) between interdigitated electrodes (IDEs). MWCNTs dispersed in ethanol were trapped and enriched between IDEs on a Si/SiO2 substrate under a positive DEP force. After the DEP process, the ethanol was evaporated and the MWCNT network on a substrate with IDEs was put into a furnace for repeated thermal annealing. It was found that the resistance stability of the network was effectively improved through thermal annealing. The humidity sensitivity was obtained by measuring the resistance of the MWCNT network with different relative humidity at room temperature. The experimental results show the resistance increases linearly with increasing the relative humidity from 25% to 95% RH with a sensitivity of 0.5%/%RH. The MWCNT networks have a reversible humidity sensing capacity with response time and recovery time of about 3 s and 25 s, respectively. The resistance is dependent on temperature with a negative coefficient of about −0.33%/K in a temperature range from 293 K to 393 K.

Highlights

Carbon nanotubes (CNTs) are well-known functional materials with unique electrical, physical, mechanical, and chemical properties
We report an investigation on humidity sensitivity of deposited multi-walled carbon nanotube (MWCNT) networks using ac DEP between interdigitated electrodes (IDEs)
The density of MWCNTs on IDEs can be controlled by the DEP parameters

Summary

Introduction

Carbon nanotubes (CNTs) are well-known functional materials with unique electrical, physical, mechanical, and chemical properties. There have been high expectations for CNTs as novel sensing materials, since their hollow cores with a large surface area to volume ratio are well suited for physical adsorption or chemical interaction with sensed targets. Some reports showed that CNT films could be used as a humidity sensing material due to a drastic change in the electrical conductivity or capacitance upon the adsorption of water molecules. There are mainly two methods to form CNT films for humidity sensors. The CNTs in these films have a high density and/or are random. Their sensitivities are usually not linear, and their response and recovery times are relatively long. Dielectrophoresis (DEP) is an effective method to deposit and align

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