Ion-sensitive field effect transistors (ISFET's) have many advantages than the conventional ion selective electrodes. There exhibt the advantages of small size, fast response and compatible with conventional IC technologies. The general structure of ISFET is the same as that of MOSFET. However, the main difference is that the metal gate in MOSFET is replaced by reference electrode/electrolyte/sensing insulator structure in ISFET. The insulator surface will suffer the change of potential as the sample is immersed into electrolyte, by which, we can measure the pH or other ionic concentration. Amorphous barium titanate (a-BaTiO3) thin film as the pH-sensing layer of the ion-sensitive field-effect transistor is prepared by a sol-gel technique. The stock solution in a concentration about 0.42M is obtained. The barium titanate thin films are deposited on SiO2(1000Å)/p-Si substrates, and the EIS structure is frabricated. The fabrication parameters of BaTiO3 thin films are made up of the thickness of 120-360 nm and the firing temperature between 350¢J and 850¢J. The flat-band voltage(£GVBF) is shifted by C-V measurement. The pH sensitivity is on the downside because the thin films thickness and defect increase. The results reveal the MIS C-V curve. The optimum conditions are found that the annealing temperature is about 350¢J, and the sensitivity of about 59.02 mV/pH with regression of 0.9991. The pH response of 40-59 mV/pH in the range of pH 2-12 exists when the a-BaTiO3 thin film with thickness of about 120-360nm at the firing temperature between 350¢J and 550¢Jare prepared. To decrease the fabrication cost, so the numbers of mask and fabrication steps should be minimized, which are reduced to two from four and 10 from 16 steps. Two masks were used to accomplish a-BaTiO3 gated ISFET. I-V curve shows that the a-BaTiO3 gated ISFET exhibits pH responses of about 38 ~48.7 mV/pH in the linear region(IDS=30 £gA and VDS¡×0.2 V), and -11~-24.8 £gA/pH in the satiation region(VGS=3 V and VDS¡×3.5 V), and the regression of above 0.997 was achieved. Both of C-V and I-V curves revealed the BaTiO3 thin films could be used in the ISFET gate.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18470号 / 工博第3906号 / 新制||工||1600(附属図書館) / 31348 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 北野 正雄, 教授 和田 修己, 准教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20892号 / 理博第4344号 / 新制||理||1624(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 高橋 義朗, 教授 川上 則雄, 教授 田中 耕一郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The work deals with the measurement of CV characteristics of photovoltaic cells and the consequent derivation of the free / bound charge in the volume. It also discusses factors that influence these measurements.

For the past few decades, a frenzy of attention has been given towards the development of an assortment of photocatalysts as a solution for various environmental problems. TiO2 is the most widely used photocatalyst. TiO2 is biocompatible, chemically and thermally stable but TiO2 and a vast majority other photocatalysts have large band gaps, and hence they find applicability only in the UV region of the solar spectrum. These large band gap photocatalysts suffer a severe limitation with regard to their overall process efficiency as the UV region contributes to about 3 to 4 % of the solar spectrum in terms of energy. This thesis concentrates on the progress towards the generation of visible light active photocatalysts. Lanthanum transition metal perovskites were synthesized to incorporate B site doping in the following fashion; LaCrxFe1-xO3, LaMnxFe1-xO3 and LaCrxMn1-xO3 (x= {1, 0.25, 0.5, 0.75}). These perovskites configurations were selected as LaCrO3 has a conduction band edge suitable to activate most photocatalytic reactions, but LaCrO3’s large band gap energetically hinders the photocatalysis. Doping LaCrO3 with Fe and Mn allowed for tuning their band gaps and made various photocatalytic reactions feasible, namely CO2 reduction and photoassisted dye degradation. Validation of the perovskite's crystal structure was established through the study of their XRD patterns. The perovskite exhibited crystallinity throughout all doping concentrations. At some doping concentrations, due to low or high degree of tolerance factor, the presence of hexagonal and rhombohedral crystal phases was seen. Analysis of the electronic structure of these perovskites was conducted through diffuse reflectance spectroscopy measurements and electrochemical impedance spectroscopy. Doping transition metals in B site of the perovskite led to the narrowing of band gap energy with the increase in the concentration of the higher atomic number transition metal. About 38% reduction in band gap was achieved in LaCrxFe1-xO3. The band gap constituted of Mott- Hubbard gap and charge transfer gap. For the species LaCrxFe1-xO3, interband states exist with an energy gap as large as 1.3 eV for X=1 and 0.75. These states manifested as Urbach tails and are clearly documented in the absorption spectrum data. At x=0.5 and below, evidence of mixing is seen in LaCrxFe1-xO3, leading to the diminution of these interband states, although not to full extent, their energy was reduced by about 0.5 eV. In LaCrxMn1-xO3 and LaMnxFe1-XO3, the absence of Urbach tail and absorption edge is observed. The band edge positions of most of these perovskites provided a large enough over potential to cause the reduction of CO2. Future efforts on the photocatalytic activity study of these perovskites through dye degradation and CO2 reduction are in progress. Preliminary results of photoassisted dye degradation are shared in this thesis.

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