利用臨場共製的ReFET與ISFET來改善飄移特性之研究

Abstract

ISFET最早是由P.Bergveld在1970年所提出的，其結構是將傳統的金氧半場效電晶體中的金屬閘極以待測溶液與參考電極所取代之。一旦待測溶液中的離子被感測層(sensing layer)表面的斷鍵所束縛住時，將會對下面的通道做出調變的效應，進而改變通道的電阻。如此一來，元件的電性將會隨著溶液的不同而產生變化，我們也同時藉由電性的變化來判定溶液的性質。 然而在我們的量測過程之中，輸出電壓的飄移效應是對元件穩定度影響最大的原因之一。如何去改善ISFET本身的飄移效應是目前所遇到的最大問題之一，這將會直接影響元件的使用壽命以及量測的準確度。不同的感測層，其本身的性質亦不盡相同。在本篇論文中，我們引入幾種與目前CMOS製程匹配的材料來做為感測層，結合適當的輸出電路的設計，以求可以將元件的飄移效應的影響降到最低。 實驗結果顯示，HfO2-Si3N4對有最佳的飄移特性(0.19mv/hr)，可以大幅的減低飄移現象的影響。而在配合輸出電路後，TiO2-ZrO2對則有最佳的修正率(98%以上)。在最後並討論如何藉由本文的結果，在將飄移效應減至最低的前提之下，來適當的選取ReFET。

The ion-sensitive field effect transistor (ISFET) was first introduced by P.Bergveld in 1970. The metal gate is replaced by a reference electrode and the electrolyte . Once the ions in electrolyte are trapped by the dangling bond at the surface of sensing layer , which will induce the modulation of channel resistance . Therefore, the electric characteristics are changed by different kinds of electrolyte , and we can distinguish the properties of electrolyte . During measurement , the drift characteristics is a major problem for stability of device . That will directly affect the lifetime of device and accuracy of measurement . Depending on different sensing layers, the property of sensing layers varies . In this thesis , we use some kinds of CMOS-compatible materials as sensing layers combining output differential measurement circuit in order to reduce the drift effect . According to our results , the S-HfO2-Si3N4 pair has the best result of drift characteristic (0.19mv/hr after 10000 s) . And the TiO2-ZrO2 pair has the best of drift correction up to 98 % . At last , we will discuss that how to use the results here to choose proper ReFET in order to reduce the drift characteristics .