水熱合成二氧化鈦奈米柱及其感測器元件應用

Hydrothermal Synthesis of TiO2 Nanorods and Their Application for Sensor Devices

陳科廷

二氧化鈦 ； 奈米柱 ； 光感測器 ； 濕度感測器 ； 氣體感測器 ； TiO2 ； nanorod ； photodetector ； humidity sensor ； gas sensor

成功大學微電子工程研究所學位論文

2015年

碩士

張守進

英文

本論文以研製和分析二氧化鈦奈米柱感測器應用為主。我們選擇用穩定性較佳的二氧化鈦金紅石晶相奈米柱作為感測層，藉由改變水熱實驗的製程溫度以及溶液酸度等參數，探討不同體表面積和結晶品質的奈米柱應用於紫外光感測器、濕度感測器、氣體感測器之影響。 首先，我們利用水熱法於二氧化鈦晶種層/二氧化矽/矽基板上成長二氧化鈦奈米柱，奈米柱的長度、寬度、結晶品質皆隨著成長溫度提升而增加，而在水熱高酸溶液條件下可獲得最佳的結晶品質，但卻抑制了奈米柱的成長。為了決定最佳化的二氧化鈦奈米柱感測器成長參數，我們製作出在不同水熱酸度下成長的奈米柱感測器與未處理的晶種層薄膜式感測器比較，分別討論其感測器響應大小。 在紫外光感測器的應用中，不同酸度溶液下成長的二氧化鈦奈米柱感測器的響應皆比二氧化鈦薄膜式感測器大。奈米柱感測器表現較優異的主要原因是表面積比較大。奈米柱感測器中最大的響應是薄膜式的6倍大。此外，由於缺陷產生的載子復合率減少的關係，結晶品質最好的感測器有最短的響應時間，最短的時間為4秒。 在溼度感測器的應用中，與未水熱處理過的晶種層薄膜式感測器相比之下，在不同水熱酸度下成長的二氧化鈦奈米柱感測器傾向具有較大的響應。我們同樣發現，表面積的大小顯著影響感測器響應的大小。最佳參數的二氧化鈦奈米柱感測器在相對濕度40%到90%間有11.24倍的響應。 在氣體感測器的應用中，我們同樣也比較了不同酸度下成長的奈米柱感測器與薄膜式感測器。分別在不同溫度下，量測其甲醇、乙醇、丙酮等氣體響應的表現。量測結果顯示，感測器能有較大的響應與其具有較大的表面積有關。其中，最佳參數的二氧化鈦奈米柱感測器有5.42倍的響應，在300 oC下量測200 ppm的酒精氣體。 因為製作出來的氣體感測器相較其他感測器較具有競爭力，我們藉由金奈米粒子進一步提升其感測能力。結果顯示，具有金奈米粒子的二氧化鈦奈米柱氣體感測器表現皆有所提升，對酒精200 ppm的響應是純二氧化鈦氣體感測器的四倍，上升及回復時間都減少了一半。 所有感測器應用都由相同的鈦指叉電極金/半/金結構量測，代表著我們成功製作出了一個多功能且有不錯響應又穩定的二氧化鈦奈米柱感測器。此外，我們也探討了感測器在不同條件下的機制。

This thesis aims at the synthesis and analysis of sensor applications based on TiO2 nanorods. Rutile phase TiO2 nanorods were chosen as sensing material due to its quit stable property. With different hydrothermal temperatures and acidities, the influences on the TiO2 nanorod morphologies and crystalline qualities to photodetector, humidity sensor, and gas sensor were studied. First of all, we reported the growth of TiO2 nanorods on seed layer TiO2/SiO2/Si substrate through hydrothermal treatment. It was found that the length, width, and crystalline quality of TiO2 nanorods were all increased by increasing the hydrothermal temperature. Under high acidity hydrothermal conditions, the greater crystalline quality of nanorods was obtained but the formation of nanorods was inhibited. In order to find out the optimization growth parameters for our TiO2 nanorod sensor devices, the hydrothermally treated TiO2 nanorod sensors under different acidities and untreated TiO2 seed layer film-type sensor were then fabricated, followed by a comparison of their sensor response. In the application of UV photodetector, the TiO2 nanorod sensors with various acidities showed larger response to UV light as compared to the TiO2 film-type sensor. The largest response of nanorod sensor was 6 times larger than film sensor. The nanorod sensors outperform the film sensor mainly for the larger surface area. Besides, the best crystalline quality sensor was found to have the shortest response time due to the reduction of the recombination induced by the defects. The shortest response time was 4 seconds. In the application of humidity sensor, the hydrothermally treated TiO2 nanorod sensors with different acidities tended to give higher response than that of untreated TiO2 seed film sensor. Also, it was found that the humidity response of the sensors significantly depended on the surface area. The optimum TiO2 nanorod humidity sensor response is about 11.24 during RH40%~ RH90%. In the application of gas sensor, the sensing performance of TiO2 nanorod and TiO2 film sensor has also been investigated at different temperatures for various volatile organic compounds (VOCs) such as methanol, ethanol, and acetone. The measuring results showed that the larger response was mainly attributed to the larger surface area. The optimum TiO2 nanorod gas sensor response is around 5.42, measured at 300 oC in 200 ppm ethanol. Since our gas sensor performance was much more competitive than other sensors, we further improved its sensing ability by Au nanoparticles. The result showed that the gas sensing performances of Au nanoparticles/TiO2 nanorod were all promoted. The response of 200 ppm ethanol was four times larger than pristine TiO2 sensor, the rise and decay time was halved. All the sensor applications were performed by the same MSM structure with Ti interdigital electrodes, indicated that we successfully fabricated a multifunctional TiO2 nanorod sensor with stability and good response. The sensing mechanisms under various conditions were also investigated.

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76. Reference in chapter 4
77. [19] B. Lyson-Sypien, M. Radecka, M. Rekas, K. Swierczek, K. Michalow-Mauke, T. Graule, K. Zakrzewska, “Grain-size-dependent gas-sensing properties of TiO2 nanomaterials”, Sens. Actuator B-Chem., vol. 211, pp. 67-76, 2015