Design, fabrication and testing of CNT based ISFET for Nano pH sensor application: A preliminary study

In recent years, there has been increasing interest in monitoring and controlling of pH. It has become an important aspect of many industrial wastewater treatment processes. At the same time, the demand for smaller electronic devices used for various industrial and commercial applications has greatly increased. Micro and nano materials, such as Carbon Nanotubes (CNTs), are known for their excellent electrical and mechanical properties, as well as for their small size, therefore they are good candidates to manufacture micro or nano electronic devices. These devices can be used for pH control. However, this cannot be achieved unless CNTs with metallic or semiconducting band structures can be successfully deposited and separated. In these processes, microchip fabrication and deposition of CNTs using Dielectrophoresis (DEP) are involved. Comparing with some traditional pH sensors, which mainly consist of Ion-Sensitive Field Effect Transistor (ISFET), signal operational amplifier and Analog Digital Convert (ADC), Nano pH sensor with CNTs may provide more benefits owing to their unique properties. For example, 70-80% of multi-walled CNTs (MWCNTs) are metallic and have high current density, which means this kind of micro device has a linear relationship of I-V characteristic and can produce signal strong enough to make operational amplifying circuits unnecessary. In addition, to manufacture smaller devices more functional becomes possible as CNTs are tiny and compact.