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|Type of Document
||The study of BaTiO3-gated pH-ISFET using sol-gel processes|
|Date of Defense
||Flat band voltage
||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℃ and 850℃.
The flat-band voltage(ΔVBF) 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℃, 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℃ and 550℃are 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 μA and VDS＝0.2 V), and -11~-24.8 μA/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.
||Wei-Hsing Tuan - chair|
Chen-Chia Chou - co-chair
Cheng-Fu Yang - co-chair
Mau-Phon Houng - co-chair
Ying-Chung Chen - advisor
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|Date of Submission