液相沈積製程應用於高靈敏度多孔性二氧化錫氣體感測器之研究

Abstract

運用各種不同薄膜製程技術製作出一具有多孔性二氧化錫感測膜之微機電式氣體感測器之製作上，目前已有廣泛的研究，因其具有微型化、低消耗功率、高靈敏度與反應速度快等優點。氣體感測器的靈敏度與響應特性是取決於觸媒與感測薄膜的結構特性，其可藉由選擇適當的觸媒或添加物進行最佳化處理。本論文為首先提出利用低溫液相沈積技術備製摻雜二氧化矽添加物之二氧化錫薄膜及純二氧化錫薄膜。此方法具有可量產、低製程溫度與不需真空設備等優點。此外、本論文將討論二氧化錫摻雜銅、金觸媒與晶粒抑制劑(SiO2)對H2S感測效果之研究。在二氧化錫感測膜製作方面，於液相沈積法中透過添加不同濃度的H2SiF6至成長溶液裡，可成功製作出不同多孔性二氧化錫薄膜。隨著H2SiF6濃度的增加，此SiO2-doped SnO2感測薄膜將獲得好的反應穩定性及高靈敏度。另一方面，當銅、金觸媒添加至含有SiO2之二氧化錫表面時，可大大提高其靈敏度。在薄膜的特性分析方面，本論文是利用低掠角X光繞射儀、電子顯微鏡與原子力顯微鏡對薄膜表面進行形貌量測與材料晶粒尺寸分析。在化學定性定量分析方面，利用高解析度X光光電子頻譜儀進行二氧化錫薄膜中矽元素的含量測定。在Cu-Au-SnO2氣體感測器的特性分析方面，結果顯示在感測薄膜中添加二氧化矽可以有效改善其感測響應、靈敏度、響應與回復時間。實驗結果指出Cu-Au-SDS (Si/Sn = 0.5)氣體感測器可以獲得最佳的敏靈敏度(S = 67)和最快的反應時間(t90% < 3s)。此外，本論文提出利用微機電製程技術成功的製作出微加熱平板整合液相沈積多孔性感測薄膜之微機電氣體感測器。本論文中，此氣體感測器的加熱機制有兩種設計分別為蛇狀結構與環狀結構，為了分析其加熱特性，我們設計不同大小的加熱器尺寸並討論加熱器大小對薄膜感測特性的影響。實驗結果顯示當感測薄膜尺寸小於200 um2以下時，環狀加熱器的氣體感測器靈敏度比蛇狀加熱器的氣體感測器靈敏度好。

MEMS-based gas sensors with porously SnO2 sensing film have been studied extensively due to their have advantages including miniaturized structure, low-power consumption, high sensitivity and short response time. Sensitivity and response time of the sensing film is very important condition in gas sensors, which can be optimized by proper choice of dopants and additives. In this thesis, we fist time reported that the preparation of SnO2 thin film doped with or without SiO2 additive by the liquid phase deposition (LPD) method. This method has several advantages in fabrication process, such as high throughput, low processing temperature and not need for a vacuum system. The effectiveness of copper and gold as a dopant and H2SiF6 solution as an additive to tin oxide for sensing H2S in air was studied. In preparation of sensing film, the SnO2 film can form different porous structure and grain size easily in LPD method through adding various concentration of H2SiF6 in the growth solution. The SiO2-doped SnO2 sensing film can obtain good stability and high sensitivity with increasing H2SiF6 concentration. On the other hand, the sensitivity of SiO2-doped SnO2 sensing film can be drastically raised by adding Cu and Au catalysts on the surface. In the characterization of the thin films, surface morphology and grain size of the pure and doped films were investigated by GIAXRD, SEM and AFM. The stoichiometric analysis of Si content in the SnO2 film prepared from various Si/Sn molar ratios has also been estimated by HRXPS. In the characteristics of sensing response, the sensitivity, response and recovery time had been improved by the presence of SiO2 additive in the Cu-Au-SnO2 sensing films. Experimental results indicated that the Cu-Au-SDS gas sensors (Si/Sn = 0.5) can obtain good sensitivity (S = 67) and response time (t90% < 3s). In fabrication of miniaturized gas sensor, a MEMS-based gas sensor with porously SnO2 sensing film prepared by liquid phase deposition (LPD) was successfully implemented by utilizing MEMS fabrication technology. In this thesis, the two types of heating mechanism are designed, including serpentine structure and annular structure. The heating behavior of heaters had been described by using different dimension of sensing films. Experimental results indicate that the annular heater has a better sensitivity than serpentine heater when the dimension of sensing film is designed at below 200 um2.