本論文探討高性能3D奈米結構堆疊式異質接面(Pd /BaTiO3-CuO /Ag /BaTiO3-CuO /P-Si)二氧化碳(CO2)感測器的研製。吾人利用兩種不同濕式蝕刻方式來完成3D奈米結構：(一)混合硝酸銀及氫氟酸之蝕刻溶液於P型(100)矽基板上成長奈米柱狀結構、(二)混合氫氧化鉀、異丙醇及去離子水之蝕刻溶液於P型(100)矽基板上成長奈米尖端結構。並使用射頻濺鍍系統(RF sputtering system)沉積單層或複層BaTiO3-CuO薄膜作為感測層，以及在複層感測層間沉積不同金屬薄膜(Ag、Au、Cu)。最後再蒸鍍金屬鈀(Pd)及鋁(Al)分別於矽基板最上層及背面作為催化層及金屬接觸層完成Pd/BaTiO3-CuO/P-Si/Al元件製作。
本論文利用AFM、SEM、EDX分別量測薄膜結晶及觀察表面結構和厚度藉以探討BaTiO3-CuO薄膜材料的特性及做最佳製程選擇。元件I-V特性則以HP4145半導體量測分析儀來進行量測。主要探討研究含：有無3D奈米結構的影響及在複層感測層間添加不同金屬(Ag、Au、Cu)之影響。實驗結果發現：使用3D奈米結構及添加不同金屬的感測層可提升靈敏度。前者是因可有效增加感測氣體接觸之面積/體積比，後者則歸致於感測層的阻值降低、提高BaTiO3-CuO化學活性以及增強對CO2的吸附反應。如在奈米尖端結構添加Ag的元件在溫度200℃，逆向偏壓3V及CO2氣體濃度3000ppm條件下，靈敏度可由2D平面的610.53%提升至1141.75%。而添加Ag的奈米柱狀結構者靈敏度更可提升到2017.28%。而感測能力也隨著操作溫度升高而增加。但高到300℃時，會因元件整流特性遭到破壞，導致漏電流急速增加而降低靈敏度。
此外，吾人發現在溫度200℃，濃度3000ppm環境下，反應時間可由一般電阻式元件數分鐘縮短為26秒。也對CO及酒精氣體無明顯反應。

In this thesis, we developed the tandem heterojunction with 3D nano structures for CO2 gas sensing applications. Two different wet etching methods were used to form the 3D nano-structures firstly, i.e., (a) use of the AgNO3 mixed HF solution to form the nano rods on a P (100) Si substrate, and (b) to form the nano tips by etching the P (100) Si substrate with the KOH mixed IPA and DI water solution. Next, sputter a BaTiO3-CuO thin film as the sensing layer and BaTiO3-CuO/ various metals (Ag, Au, and Cu)/ BaTiO3-CuO as single and multi-layer sensing layer on the etched substrate, respectively. Finally, to complete the Pd/BaTiO3-CuO/P-Si/Al devices by evaporate Pd and Al on the top of sensing layer and the bottom of the silicon substrate, respectively. The sensing layers were examined using EDX、AFM and SEM, respectively for crystallinity, surface roughness and morphology, while I-V curves were characterized with HP4145 semiconductor parameter analyzer.
We have focused our studies on：(1) the effect of the 3D nano-structures on sensing performances；(2) the impact of inserting metals (Ag、Au、Cu) between the multi-layer sensing layer on sensing performances. The experimental results found that use of the 3D nano-structures and addition of metal indeed can effectively increase the sensing ability. For example, under the condition of 200℃, -3V and 3000ppm CO2 ambient, the sensor with nanotip structure and Ag added improves sensitivity from 610.53% of the 2D plane and without the metal insertion one to 1141.75%. The improvement even increases up to 2017.28% for the nanorod structure. The reason for the 3D structure is due to the increase of the absorption area, while the addition of metal can reduce BaTiO3-CuO resistance, improving chemical activity and the adsorption of CO2.
In general, the sensitivity of the 3D sensors increases with increasing operating temperature up to 300℃, beyond that, the sensitivity start to reduce for the rapid increase of the leakage current caused by the degradation of the rectifying characteristics of the hetero junction. Besides, the response time is also improved from few minutes of the conventional resistive type to 26 seconds at 200℃, and 3000ppm concentration.

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