二氧化鋯感測層在N型及P型pH-離子感測場效電晶體上之研究與比較

Abstract

就我們所知離子感測場效電晶體(ISFET)是種生物感測器,它是利用浸泡在溶液中再去偵測其pH值，許多論文已經指出在長時間的操作下會有“漂移”現象的產生，“漂移”正如其名，就是閘極電壓在固定的店留下隨著時間會跟著變動，這種效性可能會造不準確性當我們在量測的時候，我們發現再“漂移”之後pH-ISFET的靈敏度會有變化，這是因為“漂移”所造成的，此效應便成了阻礙這產品再應用上的發展。 於本論文我們提出了一個方法去消除“漂移”這效應，我們發現“漂移”和溶液的pH值有一定的關係，然而“漂移”對於兩種不同型態的pH-ISFET所表現的特性是相反的，基於這個原因我們可以透過電路利用這不同的效應去做補償而且補償之後的靈敏度會變成兩種型態pH-ISFET的平均,透過這種方法我們可以將“漂移”變成一個定值不管經過多少時間或是用任何的pH溶液。為了實現這個想法，我們選用二氧化鋯去當N型和P型ISFET的感測層是基於它的高靈敏度，實驗的結果表示可以把“漂移”變成接近-26mV的定值，它可以看成pH-ISFET的初始點的位移,這樣子就更容易補償透過其他電路方式，這種方法的優點在於不但可以消除“漂移”現象也可以維持高的靈敏度。 此外磁滯現象也會影響pH-ISFET的準確性，所以在本論文我們也會去討論此效應，我們選用二氧化鋯去當pH-ISFET的感測層，在實驗中發現它具有良好的磁滯特性，其最大的誤差大概是0.111pH值,所以我們可以知道二氧化鋯在pH-ISFET上是種很實用的材料。

So far as we know, the ion-sensitive field effect transistor (ISFET) is a biosensor which via immersed the aqueous solution to detect the pH value. Some papers have already reported that at the long-term operation will cause a detrimental effect “Drift”. According to the meaning of “Drift” is that VG shifts a value with time under the fixed current. The effect may cause the pH-ISFET inaccurately while measuring. We have already found the sensitivity of pH-ISFET variants after “Drift”, this situation is caused by “Drift”. The effect is one of the main reasons to obstruct the development of application. In this study we propose a method to eliminate the “Drift”, we find that the “Drift” relates to the different pH value of aqueous solution. The “Drift” to different type of pH-ISFET reveal opposite characteristic, to base on the situation we can compensate this effect through the circuit and the sensitivity to pH-ISFET become the average sensitivity of N-type and P-type pH-ISFETs, and then the “Drift” can be held to be a constant no matter how much time or any pH value of aqueous solution. To realize the idea, we prepare the ZrO2 sensing film due to its high sensitivity which is based on the N-type and P-type pH-ISFETs. The results show that the “Drift” can be held nearly -26mv to any pH value aqueous for 6 hours, it can seem the offset of pH-ISFETs, and however it is more easily to compensate the offset through the other circuit. The advantages of this method are the elimination of “Drift” and keep the high sensitivity. The hysteresis also causes the inaccuracy of pH-ISFETs, in our study we also discuss the effect to the pH-ISFET. It shows a good hysteresis characteristic to ZrO2 based pH-ISFET from the results; its maximum error is 0.111pH value. It appears the ZrO2 is a useful material to the pH-ISFET.