以NafionTM/PR包埋結構作為REFET參考場效電晶體感測層之研究

Abstract

離子場效電晶體(Ion-sensitive Field Effect Transistor，ISFET)是由Bergveld 在1970年提出，因其元件的特性尺寸小，反應速度快、可承受外部應力，且相容於現今的CMOS製程相容性，所以在現今的感測元件開發中具有極大的潛力。在微小化的技術上，必須要整合一個固態參考電極在ISFET上，然而先天上固態電極的金屬/溶液接面電位不易穩定，使得研究方向朝向開發參考電極場效電晶體(Reference Electrode Field Effect Transistor，REFET)。 REFET本身是一個低靈敏度的ISFET，利用一差動放大量測電路來抑制未經處理之金屬固態電極造成的不穩定參考電位。 為得到一個低靈敏度的ISFET，本篇論文中以利用一質子交換膜NafionT包覆PR(FH6400)的結構來完成一個REFET，成功的降低了感測層對離子的感測能力，從未包覆前的57.5mv/pH降至8mv/pH。此外，本實驗還利用二氧化鋯(ZrO2)和二氧化矽(SiO2)兩種不同的感測層當基底，探討Nafion包埋PR結構降低了對氫離子感測靈敏度的機制與基底材料之間的關係。最後，再利用不同Nafion包埋PR條件來做pH1~pH13的靈敏度(sensitivity)和漂移(Drift)量測，並研究其元件特性的重現性及可靠度。 我們成功地以NafionTM包埋PR結構完成對氫離子感測靈敏度的降低，從實驗結果得到其感測靈敏度從未包覆前的57.5mv/pH降至8mv/pH。目前推論其靈敏度的降低主要來自Nafion所包埋的PR所致，與下層所疊的材料無直接的影響性，且在Nafion混合PR的結構所製作出REFET的感測層可維持在一個穩定且固定的電位且不受外部的離子所影響，由實驗值得到在四小時內的漂移(Drift)量相當穩定。

Ion-sensitive Field Effect Transistor, ISFET is proposed by Bergveld in 1970 since its feature of the component is small size, rapid response, strong robustness and be acceptable to the process of CMOS nowadays, it has the great potential on the development of nowaday’s sensitive component. It has to integrate a solid state reference electrode on the miniaturized technology. However, the metal of solid state reference/electrolyte is not to defined, so the direction of the research moves toward developing Reference Electrode Field Effect Transistor, REFET, which is a low sensitivity ISFET itself using a differential amplifier measuring the circuit to set off the unstable voltage caused by the metal solid state without handling. For attaining a low sensitivity ISFET, this academic essay utilizes the structure of proton exchange membrane. Nafion entrap with PR (FH6400) to finish a REFET which successfully reduce the sensitivity to 8.3mV/pH. Moreover, this experiment use ZrO2 and SiO2 the two different sensing film as the base to discuss the relationship between the mechanism that the structure of Nafion entrap PR reduce the sensitivity to H+ ion and the base material. At the end, it also measures the sensitivity of pH1 to pH13 and Drift on the condition of different Nafion entraps PR and research the repeatability and reliance of the component’s feature. We finish successfully the reduction of the sensitivity to H+ ion with the structure. Nafion entrap PR, and it get its sensitivity reduces from the 57.5mV/pH unentraped to 8.3mV/pH in the experiment result. Now it refer the reduction of sensitivity mainly to Nafion entrap PR and sensing layer beneath Nafion/PR membrane will affect the overall performance in sensitivity and drift. The sensing layer of REFET manufacture on the structure of Nafion mix PR could maintain a stable potential without the effect of the outer ion, the Drift quantity is very stable in four hours according to the experiment data.