This paper demonstrates a highly sensitive humidity sensor based on carbon nanotube and poly (dimethyldiallylammonium chloride) composite films. The composite film is deposited between interdigitated electrodes on a Si/SiO 2 substrate through layer-by-layer self-assembly technique. The resistance stability of the composite film is effectively improved through thermal annealing, and I-V characteristic of the film exhibits a very good linear behavior. The resistance increases exponentially with relative humidity from 20% to 98%, and a much higher sensitivity in comparison with pure carbon nanotube networks is achieved. With temperature increased, the water vapor density versus RH shifts upwards, while the resistance is reduced downwards. The resistance is dependent on temperatures with a negative coefficient. The composite films with multiwalled carbon nanotubes show an adjacent sensitivity, compared with the single-walled carbon nanotube composite films. The experimental results show that the humidity sensors have a fast response and a short recovery time, and their response is reversible. A simple model is proposed to explain the change of composite film resistance with humidity. The carbon nanotubes junctions may play a more important role in the overall resistance change for water molecule absorption.
Bibliographical noteFunding Information:
Manuscript received June 09, 2009; accepted July 13, 2009. Current version published September 02, 2009. This work was supported in part by the National Nature Science Foundation of China (NSFC) under Grant 50675118 and Grant 50730009), in part by the Major State Basic Research Development Program of China (2007CB310500), and in part by the Minnesota/China Collaborative Research Program at the University of Minnesota. The associate editor coordinating the review of this paper and approving it for publication was Prof. Gerald Gerlach.
- Carbon nanotube (CNT)
- Composite film
- Humidity sensitivity
- Layer-by-layer (LbL) self-assembly
- Poly (dimethyldiallylammonium chloride)