三氧化鎢/氧化銥二極體元件對二氧化碳氣體感測機制之探討

Abstract

在一對白金微電極上，先後濺鍍上三氧化鎢及氧化銥電色材料薄膜， 薄膜中間部份重疊形成二極體界面，於薄膜表面上覆蓋一層固態聚合物電 解質－PVA/KHCO3，製作成光/電開關二極體元件，可於一大氣壓及室溫中 工作，並能對二氧化碳氣體進行感測。由於此元件對二氧化碳感測時，電 流方向的改變並非一定，因此，我們利用遮蓋實驗、改變薄膜厚度實驗及 薄膜光學穿透率量測實驗，來研究其感測機制。所得的結論有：（1）於 二氧化碳吹入時，固態電解質中 H+ 離子濃度會升高，三氧化鎢及氧化銥 縴 □犒q位皆往正方向位移，但由於薄膜特性不同，造成氧化銥薄膜的實 際電位位移大於三氧化鎢薄膜，經由兩薄膜間的電位差值可決定元件的感 測機制。（2）於遮蓋實驗中，遮蓋氧化銥薄膜上方使二氧化碳氣體僅能 與三氧化鎢薄膜發生氧化還原反應，此二極體電流增減的趨勢與遮蓋三氧 化鎢薄膜上方時為相反的結果，所以此二極體的氣體感測之電流值變化， 可經由遮蓋兩薄膜其中之一上方所控制。（3）薄膜本身導電度變化值大 小會受薄膜厚度不同所影響，造成此二極體界面電壓降的變化，利用我們 所建立的電壓降模型，可解釋其感測機制。（4）利用光學系統量測薄膜 穿透率的改變，能得知二極體工作時薄膜的導電度變化，可與電學結果相 互說明與印證。此外，施加順、逆向偏壓時，元件對二氧化碳氣體都能做 出正確且具高重覆的可逆反應，對於氣體的濃度變化，也具有良好的感測 能力。 We have sputtered WO3 and IrO2 thin films on individual Pt electrodes.Part of the films were stacked and the films were coated with a polymer electrolyte（PVA/KHCO3）. This device can function as an optical/electrical switch/diode at 1 atm and room temperature. When configured as a CO2 sensing microdiode, the current in the diodes tend to fall mostly with occasional rises in some devices. We investigated this current behavior in three experiments in the hope to disclose its mechanism. They showed that：（1）The potential shift in IrO2 under CO2（which increases the H+ concentration in the electrolyte）is larger than that in WO3, therefore causing the current to fall normally.（2）When we shielded the IrO2 side with epoxy, the current tends to rise, opposite to that observed when the WO3 side is shielded instead. This means that we can control the trend in sensing current change by this one-sided shielding technique.（3）The film thickness has an impact on the trend in the current change. The distribution of voltage in the diode can be established by modelling the voltage drop to explain the current mechanism.（4）We can confirm the above current mechanism by measuring the transmittance change in the films to corroborate our results.