探針式延伸式閘極場效電晶體於生醫感測研究

Abstract

本研究主要探討探針式延伸式閘極場效電晶體於酸鹼度量測上的生醫感測器應用。首先使用原子層沉積 (ALD) 氧化鋁 (Al2O3) 包覆直徑0.5 mm的鋁線，成長溫度設定經過測試之後固定在250 ℃，以改變成長圈數從100到300圈來增加氧化鋁的包覆度，並透過電化學阻抗分析 (EIS) 的方式，Fitting出電阻，再利用歐姆定律計算出單位表面積的漏電值，之後再比較平面式電極與探針式電極的成長差異，找到一個最合適的氧化鋁成長圈數，最後，利用壓克力設計出一款可以方便更換、簡單使用的量測裝置，將鋁線作為延伸式閘極與電晶體做結合，應用於pH量測的研究。 在成長氧化鋁的實驗過程中，經過EIS分析發現ALD成長200圈的參數有較低的漏電值，有較接近於電容的性質，因此實驗參數定為250 ℃、200圈，並將整合後的探針式延伸式閘極場效電晶體應用於pH量測的方面，理論上的靈敏度為59.16 mV/pH，而本研究得到55至58.5 mV/pH的靈敏度，而且因為只需要購買鋁線以及成長介電材料的價格，所以成本較低，而3D立體結構的優勢是表面積較大以及感測位點較集中，這可以讓感測時的靈敏度大幅提升，所以這個技術提供了高靈敏度以及3D立體結構的探針式延伸式閘極場效電晶體的生醫感測應用，是一個很有潛力的發展。 本實驗成功的利用ALD成長氧化鋁包覆3D結構的材料，並初步使用此探針式延伸式閘極場效電晶體量測到酸鹼值的即時 (Real-time) 變化，提供一個新穎的量測技術。

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.