Single chip integration of MWCNTs/SiO2 thin film humidity sensor based on standard CMOS IC process

Miniaturization, integration and high performance are key requirements for the present humidity sensor development. One kind of single chip integrated MWCNTs thin film humidity sensor based on standard CMOS IC process was proposed in this paper. The sensor was designed and realized with MWCNTs/SiO2 thin film coated on exposed interdigital electrodes on chip, which was achieved by arrange PADs (bond pad opening) array on the top layer of layout by 0.5 μm DMDP 18 V process, at maximum exposure of the interdigital patterned metal2 electrodes. The sensor was surrounded by the heating cells formed by paralleled polysilicon resistors, which can accelerate desorption of condensed vapors and thus lower the humidity hysteresis, and provide good long time stability at high humidity environments. As the film was fabricated onto the electrodes in post process, it has great IC compatibility. The sensor has high sensitivity of 270% at 200 kHz and 120% at 50 kHz under sine source signal, and a fast response and recovery of 5 s and 7 s, respectively. It was found that nano SiO2 dispersed in film and middle frequency AC source on sensor can both reduce fluctuation of electron waves, and further lower the sensor's inherent noise. Besides, given the 30 μm interdigital finger gap, sensors with MWCNTs of 4-6 μm length has apparently lower current noise than those with 1-2 μm tubes under 4 kHz source signal. The chip is simple and compact, and low cost, and has good long time endurance in high humidity environments.