以雙閘極多晶矽薄膜電晶體作為酸鹼感測器之研究

Abstract

隨著生物醫學半導體技術的發展進步，許多研究開始探討將雙閘極結構應用在可量測酸鹼值的離子感測器上，但是這些研究都使用單晶矽作為雙閘極離子感測器的載子通道，而非多晶矽的載子通道。我們首先提出採用新穎的雙閘極多晶矽薄膜電晶體結構作為可量測酸鹼值的離子感測器，並以二氧化矽薄膜作為離子感測膜之材料。 在本篇論文中，我們探討在雙閘極多晶矽離子感測器擁有不同離子感測膜之厚度時對於上方液態參考電極以及下方底部閘極的酸鹼敏感度之影響。在這裡我們成功的驗證了採用雙閘極多晶矽薄膜電晶體結構作為可量測酸鹼值的離子感測器之可行性。此外，在掃動液態參考電極和底部閘極電壓的操作條件下所得到之酸鹼敏感度之相關性也在此篇研究中被觀察到並加以詮釋。 從實驗結果可得到，當雙閘極離子感測器經過一道氫氣熱退火製程後，酸鹼敏感度會得到一定程度的提升。同時，我們可以發現將離子感測器浸泡在滲透水中並不會提升酸鹼敏感度，但卻可以提供一個排除掉不理想效應像是漂移效應(Drift)等，因而擁有較穩定的酸鹼量測環境。最重要的是，藉由雙閘極離子感測器的上方閘極氧化層以及下方閘極氧化層厚度之不對稱性，因而造成受到酸鹼值改變時的底部閘極電壓變化之影響也被觀察到並加以探討。隨著離子感測膜厚度的上升，在掃動底部閘極電壓的操作條件下所得到之酸鹼敏感度將會逐漸衰退，同時在掃動液態參考閘極電壓下的酸鹼敏感度則會固定定值，並將被能斯特定律所限制。再者，我們提出了一種量測方法來以此驗證在掃動底部閘極和液態參考閘極此兩種操作條件下時，所得到的酸鹼敏感度之間的相關性。因此我們確信在此篇論文中的實驗結果是可信並具有參考價值的。

As the development of the biomedical semiconductor technology, the double-gated structure applied on pH sensing of ISFET has been researched in several studies. However, all the researches of double-gated ISFET above were based on single crystalline silicon channel rather than poly-Si channel film. For the first time, we proposed the novel double-gated poly-crystalline silicon thin film transistors (DG poly-Si TFT) structure as a ion-sensitive filed effect transistor (pH-ISFET) for pH sensing, and adopted silicon-dioxide (SiO2) as the sensing membrane. In this thesis, we investigated on the pH sensitivity of the liquid-gate and bottom-gate by utilizing a DG poly-Si TFT with various sensing membrane thickness as a pH-ISFET. Here we have successfully demonstrated the feasibility of applying the DG poly-Si TFT as a pH-ISFET. Besides, the relationship between the pH sensitivity of the liquid-gate and bottom-gate operation mode were also observed and illustrated in this study. From the experiment results, the pH sensitivity of the DG-ISFET is obviously improved after a H2 sinter process. Also, it can be found that the immersion of ISFET devices with the RO water is not expected to improve the pH sensitivity of ISFET but may provide a more stable measurement of pH sensitivity precluding the influence of the non-ideal phenomena such as drift. Most importantly, the pH-induced bottom-gate voltage shift per pH depending on the asymmetric between the top oxide and back oxide thickness of double-gated ISFET is observed and presented. The pH sensitivity of bottom-gate operation mode will degenerate with the increased sensing membrane thickness, while the pH sensitivity of the liquid-gate operation mode is independent of the sensing membrane thickness and limited by the Nernst limit. Furthermore, a measuring method was raised to confirm the relation between the pH response of the bottom-gate and liquid-gate operation mode. Hence we believed that the experiment results in this thesis are credible and valuable.