以二氧化鋯為感測層之離子場效電晶體其離子偵測與干擾之特性研究

Abstract

這篇論文我們將利用一個建構基礎在傳統的參考電極(RE)以及金屬場效電晶體(MOSFET)的電子感測元件，離子感測場效電晶體(ISFET)來處理一個多種離子混合之反面議題；這個議題正是ISFET的離子干擾與離子偵測現象的研究。其中由於感測層ZrO2對某些離子有較高的感測性與選擇性，以及氫離子(H+)、鉀離子(K+)與鈉離子(Na+)對人體機能的影響有相當的重要性，所以這篇文章將著重探討於由薄膜二氧化鋯(ZrO2)做成的離子感測場效電晶體(ISFET)之技術製程與其對於氫離子(H+)、鉀離子(K+)以及鈉離子(Na+)偵測的電性分析。而該電子感測元件對於多種的，甚至是不同的離子之感測度的獲得，是利用參考電極、電解液及特定的感測層來取代傳統場效電晶體的金屬閘極結構，其中參考電極的部份將會直接接觸並浸泡在溶液之中去決定待測溶液的酸鹼值(pH值)的大小，甚至是其他離子的濃度。 正如我們所知，這個由薄膜二氧化鋯(ZrO2)做成的離子感測場效電晶體(ISFET)化學電子元件的感測度表現出大約為58 mV/pH，這個偵測能力與理論中能士特方程式的吻合度高達百分之九十八左右。不過pH的響應並不是我們的主要研究目標，並且ZrO2這個薄膜(也就是感測層)對離子的選擇性在含有較多且複雜的離子溶液之中，其主要離子的感測度將會被次要離子們所影響。因此，在這篇論文中，我們將會先研究在酸鹼溶液中的鉀離子與鈉離子的電性量測與感測度分析，也就是pK以及pNa的量測實驗。而經由實驗結果的討論與驗證，鈉離子與鉀離子的感測度兩者大致上都低於20 mV/pH左右，並且氫離子的感測度在較高的鈉離子與鉀離子濃度(pK以及pNa的值低於3)之中會比較不明顯。這個結果也就表示，氫離子(H+)、鉀離子(K+)以及鈉離子(Na+)的感測度會彼此相互影響的原因就是高濃度離子所造成的飽和現象。

This article deals with an inverse problem of ion mixture composition estimation using electronic sensors based on conventional reference electrode (RE) and MOS transistors; this topic exactly is ion detection and interference of ISFET. As a result of higher sensitivity as well as selectivity of the sensing layer ZrO2 for some ion and the importance of H+, K+ and Na+ ions to human body mechanism, it reports the technological fabrication and the electrical characterization of ZrO2 ion sensitive field effect transistors (ISFET) for the detection of H+, K+ and Na+ ions. The device sensitivity to various ions is obtained by replacing the traditional transistor metal gate electrode with the series combination of the reference electrode, electrolyte and specific sensing layers, the first one is immersed the aqueous solution to detect the pH value and sensitive to the other ions in an electrolyte flowing over the gate. So far as we know, ZrO2 ISFET chemical sensors show quasi-nernstian pH response with sensitivities around 58 mV/pH. Its detection yield is 98% compared to the Nernst equation. However, it is not our main goal for pH response as well as selectivity of the membrane (i.e. sensing layer) ZrO2 is limited and ions other than the main one also influence the measurement in complex solutions. Therefore, in this study, we will first investigate K+ and Na+ ions measurement in acid or base solution, that is, pK and pNa measurement. By way of evidencing, sensitivities of K+ and Na+ ions is lower than 20 mV/pH and non-nernstian pH-dependent phenomena for highest K+ or Na+ ions concentrations (pK and pNa lower than about 3). It is shown that the detection properties of H+, K+ and Na+ ions are dependent on each other, being responsible for saturation effects for the highest concentrations.