以ZrO2和聚合物做為ISFET/REFET之感測材料應用於讀出電路設計之特性與考量研究

Abstract

讀出電路的發展是為了微小化離子感測場效電晶體(Ion-sensitive Field Effect Transistor)的體積。讀出電路除了能夠微小化之外，它也擁有積體化和精確的輸出訊號的優點。為了能夠達簡便設計出電路的目的。我們必須對讀出電路中的高靈敏性的ISFET和低靈敏性的參考電晶體(REFET)這兩個基本元件有更多的了解。 在本篇論文中，我們先研究以二氧化鋯作為閘極的ISFET。我們相當在意ISFET中兩樣重要的參數：靈敏度以及漂移。p型的ISFET具有57.08mV/pH的靈敏度而n型的ISFET也具有58.73mV/pH的靈敏度。這種高的ISFET靈敏度能夠在量測中為我們帶來更高的判別度。除此之外，我們也對ISFET另一項重要參數：漂移有興趣。漂移指的是ISFET中臨限電壓的改變。當ISFET浸泡在化學溶液時，漂移就變成了一種必然發生的物理現象。在本篇論文中，我們提出一個可行的方法用來降低漂移量帶來的影響。藉著使用我們所提出的方式，最後確實成功的增加了訊號雜訊比例。 在研究的第二個部分，我們找到了一種合適的REFET材料。我們選擇了一種Nafion和polyimide比例為一比一的混合物•此種物質的靈敏度為8.12 mV/pH而飄移速率為9.74 mV/hr。這種選定的材料在電導率上面的表現也和ZrO2 作為閘極之ISFET極為相似。上面提到的REFET特性：低的靈敏度、可接受的漂移速率、和ZrO2 作為閘極之ISFET匹配的電導率，都為我們在降低差動型ISFET/ REFET讀出電路上的設計複雜度上帶來便捷的影響性。

Readout circuit was developed to miniaturize the volume of ISFET (Ion-sensitive Field Effect Transistor). Besides the miniaturization, it also has advantages such as integration and the accurate output signal. To achieve the goal of design simplicity, we must know more about the basic devices including a high sensitive structure (ISFET) and a low sensitive structure (REFET). In this thesis, we first investigated the ZrO2 gate ISFET. We are interested in sensitivity and drift which are two important parameters for ISFET. The sensitivities are 57.08mV/pH for the p-type ISFET and 58.73mV/pH for the n-type ISFET respectively. The high sensitivity for the ISFET can bring the high resolution while measuring. Furthermore, we also interested in drift the other significant parameter of ISFET. Drift is the change of the threshold voltage of an ISFET. It is an unavoidable physical phenomenon while an ISFET immersed in the chemical solutions. To reduce the influence of drift, we introduce a feasible method in this thesis. We can successfully increase the signal-to-noise ratio with the use of the proposed method. In the second part of this study, we found the suitable REFET material. We select the mixture of Nafion and polyimide with the 1/1 ratio of Nafion comparing to polyimide. The sensitivity and drift rate of this chosen material are 8.12 mV/pH and 9.74 mV/hr respectively. The transconductance of this material is also similar to the ZrO2 gate ISFET. It is convenient for us to reduce the complexity of differential ISFET/REFET readout circuit because of the above properties of REFET.