| Summary: | 碩士 === 國立交通大學 === 電子工程學系 電子研究所 === 103 === With the special material features, such as the high electrical conductivity, high surface-to-volume ratio, strong mechanical strength, and excellent chemical resistivity, the carbon nanotube (CNT) has been regarded as a promising candidate for the applications in the pH sensing. However, in the present CNT-based pH sensors, some significant restrictions, such as the low pH sensitivity, inevitable high-temperature processes, and some contaminations, limiting their applications. In order to conquer these challenges, the high-performance pH sensors based on the extended-gate field-effect transistors (EGFETs) were proposed in this thesis via the low-temperature ultrasonic spraying method and the surface modification of the CNTs by the plasma treatments.
In the first part of this thesis, by utilizing the argon plasma treatment on CNTs, high-performance pH-EGFET sensors with the sensitivity of 54.62 mV/pH and the linearity of 0.995 were successfully fabricated by means of optimizing the plasma treatment time and the bias power. A series of material analyses including scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were demonstrated. By comparing the results of the material analyses with the pH sensitivities of the fabricated sensors, a possible pH-sensing mechanism of the plasma-treated CNTFs was proposed. At first, the weakest π bonds of the CNTs were broken up by the ion bombardment of the argon plasma, becoming the free radicals sited on the surface. Then, the free radicals bound with the active oxygen species in the air and became the oxygen-containing functional groups. It was the oxygen-containing functional groups that acted as the sensing sites for the pH sensing. Hence, the increased amounts of these functional groups resulted in the improvement of the pH sensitivity. In view of the importance of the oxygen-containing functional groups, improved ways were proposed. After treated by the argon plasma, the CNTFs were sent into an oxygen furnace at 200oC to generate the functional groups. The sensitivity of such pH-EGFET sensors could increase from 54.6 mV/pH to 56.4 mV/pH.
Furthermore, the oxygen-containing functional groups were also produced through the oxygen plasma treatment. The oxygen plasma could play the role in not only the generation of the free radicals but also the formation of the oxygen-containing functional groups, and it was more effective to functionalize the CNTFs. The fabricated pH-EGFET sensors with the oxygen-plasma-treated CNTFs (OPT-CNTFs) exhibited the excellent sensitivity of 56.9 mV/pH with the linearity of 0.9995.
Seeing the success on the glass substrates, the OPT-CNTFs were further implemented on the flexible polyimide substrates. The fabricated pH sensors also presented outstanding pH-sensing characteristics of the high sensitivity of 55.7 mV/pH with the linearity of 0.9996. Besides, after bending test, the pH sensors still preserved excellent sensing characteristics, making them promising in the future developments for the flexible biosensors.
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