| Summary: | 碩士 === 國立交通大學 === 生醫工程研究所 === 105 === In this thesis, tip-based extended gate field effect transistor is studied as the biosensor. Atomic layer deposition (ALD) was adopted to grow ultra-thin aluminum oxide (Al2O3) film to cover the 0.5 mm aluminum wires with high conformality at 250 C. After Al2O3 deposition, electrochemical impedance spectroscopy (EIS) was adopted to check the surface coverage so that a near ideal capacitive behavior can be achieved. Moreover, the resistance of the tip-based capacitor can be obtained via EIS measurement. The electrical characteristics of tip-based capacitor were also compared to those of planar device to assure its qualification in later sensing applications. Next, the tip-based extended gate was connected to field-effect transistor for pH detection.
From the growth of aluminum oxide by ALD and check by the EIS, we found that the parameter of 200 cycles had the minimal leakage current and transform conductive Al wire into capacitor. In pH detection, sensitivities around 55 to 58.5 mV/pH can be achieved, which is very close to the Nernst limit 59.16 mV/pH.
For the first time, the tip-based extended gate was demonstrated in sensing application with high sensitivity and low cost. Based on the structure proposed, non-specific binding outside extended gate can be avoided so that a lower detection limit can be expected.
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