| Summary: | 碩士 === 大葉大學 === 電機工程學系碩士在職專班 === 95 === In this study, porous thick TiO2 films were fabricated by using nanocrystalline TiO2 paste spin-coated on ITO-Glass. The porosity of TiO2 films was controlled by adding PEG(Polyethylene glycol, MW=4000). After annealing at 450℃ for 1 hour under ambient atmosphere, the as-prepared thick films were characterized by DRIFT、EDS、SEM、AFM and XRD, etc. The results analyze by DRIFT reveal that there are three distinct peaks at 2856、2927 and 2960 cm-1 , respectively which could be account for the corresponding bonds of surface hydroxyl group. To analyze the component elements by EDS, the weight of Ti is 53.72% with the atomic ratio of 37.07%, it shows indirectly from the O to Ti ratio that some of lattice oxygen is in deficiency. Besides, the morphology and surface structures of TiO2 films change a lot after the introduction of PEG as characterized by SEM. The films after adding PEG were more rugged as further proved by the Rms index of AFM. Meanwhile, the crystalline of the films were characterized by XRD. The diffraction patterns was identified to be the anatase phase diffracted at (101), (004) and(200) crystal face.
The above structures were further connected to wire and encapsulated to make the extend-gate structures of ion-selective field effect transistor(EGFET) as pH sensor. Because the interface of TiO2 is selective under different activities of H+( different pH), the absorbed ions will further changed the surface potential which will further influence the IDS and VDS of the EGFET under reverse bias.. The results were summary below: when the temperature of the system is 25℃ and buffer solution is pH＝2~12, the structure sensitivity of TiO2(PEG, 1 layer, film thickness is 4μm) is 44μA/pH. However, porous structure sensitivity of TiO2 without adding PEG (no PEG, 1 layer, film thickness is 4μm) is only 27.5μA/pH. When the film thickness is increasing to 7μm, TiO2 (PEG, 2 layers), EGFET has the best sensitivity 69μA/pH. By this result, we know film thickness influences sensitivity a lot. Then when pH＝2~7, TiO2(No PEG, PEG, 1 layer and PEG, 2 layers ),The sensitivity is 20、54 and 84μA/pH, respectively. When pH＝7~12, The sensitivity is 32、34 and 54μA/pH respectively. The sensitivity increased in acid and alkaline solutions, and the characteristic of sensitivity is obviously better in acid buffer than in alkaline buffer.
Because the sensitivity is better in porous film (69μA/pH) than in densely film (27.5μA/pH), porosity adjusting and film thickness increasing of porous film will affect sensitivity in PEG, spin coating and annealing, it's valuable to study.
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