Sensitivity Improvement of SAW NO2 Sensors by p-n Heterojunction Nanocomposite Based on MWNTs Skeleton

As one of the major air pollutants, nitrogen dioxide (NO2) is seriously harmful to humans and the environment. The development of surface acoustic wave ( SAW) sensors provides great potential for manufacturing miniaturized NO2 sensor with high sensitivity, and high stability. In this paper, a SAW NO2 sensor with a sensing layer formed by nanocomposite materials mixed with multi-walled carbon nanotubes (MWNTs) is presented. The SAW device used in this paper is a commercialized two-port Rayleigh wave resonator and the main sensitive material to NO2 is phthalocyanine copper (CuPc). In order to increase the sensitivity of CuPc to NO2 at relative low temperature, MWNTs and metal-oxide nanoparticles are doped into the sensitive films. The p-n heterojunctions formed between the metal-oxide-semiconductor and the CuPc/MWNTs sensitive materials improve the performance of the sensor at low temperature down to 50 degrees C. The sensor shows good linearity and repeatability to NO2 with bulk concentration of 1-80 ppm, and the sensitivity is 50.5 Hz/ppm at 50 degrees C.