以NafionTM/高分子材料為結構的感測層應用在pH-ISFET離子選擇場效電晶體之研究

Abstract

離子感測場效電晶體(Ion-sensitive Field Effect Transistor)是由Bergveld在1970年首先提出，由於它的尺寸小，反應速度快、可承受外部應力，且與現今的CMOS製程相容，所以在現在的感測元件開發中具有相當大的潛力。 但是由於缺乏一個穩定的固態參考電極使得ISFET的應用受到很大的限制。這個問題在藉由一個ISFET/REFET差動對的輸出後,固態參考電極因為金屬/溶液接面產生的不穩定電壓會以共模訊號的形式而被消除掉。 在本篇論文中，我們首創以Nafio混合光阻(FH6400)的結構來修飾ISFET的感測層，成功地使得原本對氫離子有高靈敏度的ZrO2-pH-ISEFT變成一個對氫離子及鈉離子靈敏度極低的參考電晶體(REFET)。從實驗結果顯示原本氫離子靈敏度有57.89 mV/pH的ZrO2-pH-ISFET經過Nafion與光阻混合物的修飾後可降低到5.8 mV/pH，而鈉離子的靈敏度也可從15.88 mV/pNa降低到11.27 mV/pNa。 為了要實現一個最簡單且小型結構的ISFET，也就是把一個固態電極整合到單一ISFET晶片上，不需額外再使用到REFET或玻璃電極。我們也把Nafion與光阻混合的結構應用到固態參考電極的表面修飾上。因為從前面的實驗結果可知道，Nafion混合PR的結構具有使REFET的感測層維持在一個固定的電位且保護它不受離子的干擾的效果。由實驗結果可看出，令人困擾的電壓不穩問題，大幅地獲得改善。一個單一的ISFET整合固態參考電極在不需搭配REFET或玻璃參考電極的情況下，對氫離子的靈敏度在60秒的量測時間中仍然可達到55.9 mV/pH而且輸出電壓也相當的穩定。

ISFET( Ion-sensitive Field Effect Transistor ) was first developed by Bergveld in 1970s, and because of its small size, fast response, rigidity and compatibility with standard CMOS process, ISFET is an attractive candidate of modern sensor device. But the lack of a stable solid-state reference electrode is detrimental to the luring properties of ISFET. One approach to solve this problem is to use a differential measurement consisting of an ion-sensitive structure (ISFET) and an ion-insensitive structure (REFET). With this arrangement, the common mode unstable voltage generated from the thermodynamically undefined metal/ electrolyte interface can be eliminated. In this thesis, we first apply the Nafion mix PR(FH6400) structure to modify the ISFET sensing layer and successfully make the high H+ sensitivity ZrO2-pH-ISFET become a low H+ and Na+ sensitivity REFET. From the experimental results, the H+ sensitivity of ZrO2-pH-ISFET with the value of 57.89 mV/pH can be decreased to 5.8 mV/pH and Na+ sensitivity is also decreased from 15.88 mV/pNa to 11.27 mV/pNa. When in differential ISFET/REFET measurement, the H+ sensitivity and Na+ sensitivity will be 52.09 mV/pH and 4.61 mV/pNa, respectively. In order to realize the single ISFET integrated with a solid-state reference electrode, the simple and compact structure of ISFET sensor without the additional REFET or glass reference electrode, we also apply the Nafion mix PR structure for the solid-reference electrode. From the previous experimental results, we can know the Nafion mix PR structure can maintain a constant voltage for the sensing layer of REFET and prevent it from the ions disturbing. The experimental results show the troublesome and unstable problem can be greatly improved. Without REFET arrangement in differential measurement or replaced by glass reference electrode, the H+ sensitivity of single ZrO2-pH-ISFET integrated with solid-state reference electrode still can reach to 55.9 mV/pH and the output voltage is also very stable within 60 seconds.