Fabrication of carbon nanotube/titanium dioxide nanomaterials-based hydrogen sensor using novel two-stage dielectrophoresis process

The porosity and large surface area of carbon nanotubes (CNTs) made them a candidate active material for gas sensing applications. However, the responsivity and sensitivity of CNTs toward hydrogen are lower than those of metal oxide semiconductor materials such as TiO2. The addition of TiO2 to CNTs is found to increase the sensitivity of the resulting composite material at the expense of increasing the resistance. This paper presents a new dielectrophoresis (DEP) process to fabricate nanoparticle-based hydrogen sensors at room temperature. The simple and low-cost process is based on tuning the AC signal frequency to deposit different nanoparticles in stages, forming a composite sensing layer across interdigitated electrodes (IDE). The sensing layers have been characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM). Sensors fabricated with only CNTs showed low resistance and weak sensitivity of less than 2%. The sensitivity has increased to 3.42% when CNTs are deposited together with TiO2 in a single stage. However, the sensor shows high resistance because TiO2 particles interrupt the conduction paths of CNTs. A high sensitivity of 15.78% and a low resistance of similar to 524 Omega have been achieved when CNTs are deposited individually in the first stage, and followed by depositing the TiO2 in the second stage. This work provides a proof-of-concept that the two-stage DEP enhances the performance of the sensor in terms of sensitivity and resistance compared to single-stage DEP, which is highly desirable in fabricating composite and multi-layer sensing materials.