本論文中，主要以射頻磁控濺鍍系統沉積氧化錫鋅作為感測層，改變製程參數並分析薄膜特性後，將其應用在紫外光感測器以及氣體感測器。
首先，我們使用射頻磁控濺射技術來沉積鋅錫氧化物（Zn2SnO4）薄膜。在沉積過程中，我們調整了氧氣與氬氣的比例，並在沉積後進行退火處理，以獲得具有不同特性的薄膜。這些薄膜隨後進行了結構、光學和材料分析。
在結構分析中，我們發現所有的Zn2SnO4薄膜均為非晶態。AFM結果顯示，隨著退火溫度的升高，薄膜表面的粗糙度下降，並在500度時達到最佳均勻度，這證實了退火能夠改善表面缺陷。
在光學分析中，所有薄膜在可見光區域的平均透光率均超過80%，且不受退火溫度和氧氣流量的影響。在材料分析中，X射線光電子能譜顯示，隨著氧氣流量的增加，氧空缺有下降的趨勢。且隨著退火溫度上升，氧空缺比例也會隨之降低。
在第二部分的研究中，我們使用射頻磁控濺鍍技術製作氧化錫鋅光感測器，並調整氧氣流量和退火溫度作為製程參數，具體為0%、4%、10%的氧氣比例以及400度、500度和600度的退火溫度。研究結果表明，當氧氣流量為0%時，元件電阻較大，光電流和暗電流均非常小。經過退火處理後，光感測器的光電流和暗電流有所提升，光響應也得到了增強。隨著氧氣流量增加，在高溫退火下，感測器的時間響應也有所增加。
研究進一步發現，當氧氣流量為4%並在500度真空環境下退火一小時後，光感測器的響應度最佳，其光暗電流比為 9.86×10^(-4)，響應值為7.25×10^(-4) (A/W)，響應拒斥比為 9.67×10^(-3)，但開關時間均超過100秒。為了在保持高響應值的同時獲得較好的開關時間，我們得出當氧氣流量為10%並在500度真空環境下退火一小時後，光感測器的開關時間最佳，其具體參數為光暗電流比8.9×10^(-2)，響應值4.47×10^(-3) (A/W)，響應拒斥比 1.21×10^(-3)，開關時間分別為32秒和13秒。
第三部分，我們使用氧化錫鋅薄膜製作毒害氣體感測器，與常見的氧化錫鋅氣體感測器比較起來，我們藉由調整退火溫度以及氧氣流量改善了感測器對NO₂氣體的響應度，在退火溫度繼續上升時，由於表面粗糙度的降低以及氧空缺的減少對於整體元件的影響降低，元件而對於 NO₂ 的響應反而變差。
最後，我們在MEMS結構上實現了Zn2SnO4薄膜，並用偏壓式金屬加熱電極取代了傳統的加熱載台，以解決加熱載台功率溢散的問題，加快熱傳導的速度。我們也研究了以Zn2SnO4作為感測層的EGFET結構pH傳感器，發現其響應度與其他常見材料相比具有相當的競爭力，未來有潛力成為重要的研究方向。

In this thesis, we focused on depositing Zn2SnO4 as a sensing layer using a radio frequency (RF) magnetron sputtering system. By altering the process parameters and analyzing the film characteristics, we applied this material to UV sensors and gas sensors.
First, we used RF magnetron sputtering to deposit zinc tin oxide (Zn2SnO4) thin films. During the deposition process, we adjusted the ratio of oxygen to argon and performed post-deposition annealing to obtain films with varying properties. These films underwent structural, optical, and material analyses.
In the structural analysis, we found that all Zn2SnO4 films were amorphous. AFM results showed that as the annealing temperature increased, the surface roughness of the films decreased, achieving optimal uniformity at 500°C, confirming that annealing improves surface defects. In the optical analysis, the average transmittance in the visible light region for all films exceeded 80%, unaffected by annealing temperature and oxygen flow rate. Material analysis using X-ray photoelectron spectroscopy indicated that oxygen vacancies decreased with increasing oxygen flow rate. Additionally, as the annealing temperature rose, the proportion of oxygen vacancies further declined.
In the second part of the study, we fabricated Zn2SnO4 UV sensors using RF magnetron sputtering, adjusting the oxygen flow rate and annealing temperature as process parameters, specifically 0%, 4%, and 10% oxygen ratios, and annealing temperatures of 400°C, 500°C, and 600°C. The results showed that at 0% oxygen flow, the devices exhibited high resistance with very low photocurrent and dark current. After annealing, both photocurrent and dark current increased, and the photo response was enhanced. With increasing oxygen flow, the time response of the sensors also increased under high-temperature annealing.
Further investigation revealed that when the oxygen flow was 4% and the sensor was annealed at 500°C in a vacuum for one hour, the photo response was optimal, with a photo-to-dark current ratio of 9.86×10^(-4), a response value of 7.25×10^(-4) (A/W), and a rejection ratio of 9.67×10^(-3), although the switching times exceeded 100 seconds. To achieve a better switching time while maintaining a high response value, we found that with 10% oxygen flow and annealing at 500°C in a vacuum for one hour, the sensor showed the best switching times, with a photo-to-dark current ratio of 8.9×10^(-2), a response value of 4.47×10^(-3) (A/W), a rejection ratio of 1.21×10^(-3), and switching times of 32 seconds and 13 seconds, respectively.
In the third part, we fabricated toxic gas sensors using Zn2SnO4 thin films. Compared to common Zn2SnO4 gas sensors, we improved the response to NO₂ gas by adjusting the annealing temperature and oxygen flow rate. However, as the annealing temperature continued to rise, the decreased surface roughness and reduced oxygen vacancies diminished the overall response to NO₂.
Finally, we implemented Zn2SnO4 thin films in a MEMS structure and replaced the traditional heating stage with a bias-type metal heating electrode to address power dissipation issues and accelerate thermal conduction. We also investigated Zn2SnO4 as the sensing layer in an EGFET structure pH sensor, finding its response to be highly competitive with other common materials, indicating potential for future research directions.

[1] M. Kumar, A. Kumar, and A. C. Abhyankar, "Influence of Texture Coefficient on Surface Morphology and Sensing Properties of W-Doped Nanocrystalline Tin Oxide Thin Films," ACS Appl. Mater. Interfaces, vol. 7, pp. 3571-3580, 2015.
[2] C. Ghofrane, A. Mejda, J. Neila, H. Moez, B. Sandrine, A. Khalifa, T. Najoua, and K. K., "Investigation on thermal annealing effect on the physical properties of CuO-SnO2: F sprayed thin films for NO2 gas sensor and solar cell simulation," Materials Letters, vol. 367, p. 136666, 2024.
[3] Y. Gyuho, K. Dongseok, S. Wonjun, P. Min-Kyu, K. Jae-Joon, L., "Fast-response/recovery In2O3 thin-film transistor-type NO2 gas sensor with floating-gate at low temperature," Sensors and Actuators B, vol. 394, p. 134477, 2023.
[4] Z. Shiqi, L. Wanyi, Z. Tianyang, P. Yong, C. Shixiu, Z. Dachuan, "High response ZnO gas sensor derived from Tb@Zn-MOFs to acetic acid under UV excitation," Sensors and Actuators A, vol. 365, no. 1, p. 114862, 2024.
[5] D. Yanqiao, D. Bingsheng, G. Xuezheng, D. Yingchun, Z. Maozhu, J. Weifeng, G. Cao, P. Di, H. Yong, "An ultrasensitive NO2 gas sensor based on a NiO-SnO2 composite with a sub-ppb detection limit at room temperature," Sensors and Actuators B, vol. 414, no. 1, p. 135916, 2024.
[6] J. Srashti, P. Apurva, S. Satish, B. Monika, B. Satishchandra, "Room-Temperature Ammonia Gas Sensing Using Mixed-Valent CuCo2O4 Nanoplatelets: Performance Enhancement through Stoichiometry Control," ACS Omega, vol. 3, no. 2, pp. 1977-1982, 2018.
[7] H. S. Saeedabada, C. Barattob, F. Rigonib, M. Rozatia, S. Sberveglierib, K. Vojisavljevicc, B. Malicc, "Gas sensing applications of the inverse spinel zinc tin oxide," Materials Science in Semiconductor Processing, vol. 71, pp. 461-469, 2017.
[8] P. Shrikrishna, Y. Sangita, S. Gajanan, T. L. "Tin oxide and zinc oxide based doped humidity sensors," Sensors and Actuators A, vol. 135, no. 2, pp. 388-393, 2007.
[9] Y. Zhu, H. I. Elim, Y.-L. Foo, T. Yu, Y. Liu, W. Ji, J.-Y. Lee, Z. Shen, A. T. S. Wee, J. T. L. Thong, C. H. Sow, "Multiwalled Carbon Nanotubes Beaded with ZnO Nanoparticles for Ultrafast Nonlinear Optical Switching," Advanced Materials, vol. 18, pp. 587-592, 2006.
[10] A. F. Kohan, G. Ceder, D. Morgan, C. G. Van de Walle, "First-principles study of native point defects in ZnO," Physical Review B, vol. 61, pp. 15019-15027, 2000.
[11] C. Supatutkul et al., "Density functional theory investigation of surface defects in Sn-doped ZnO," Surface and Coatings Technology, vol. 298, pp. 53-57, 2016.
[12] K. Satoh et al., "Influence of Oxygen Flow Ratio on Properties of Zn2SnO4 Thin Films Deposited by RF Magnetron Sputtering," Jpn. J. Appl. Phys., vol. 44, no. 1, pp. L34-L37, 2005.
[13] S. Y. Li et al., "Effect of Sn dopant on the properties of ZnO nanowires," Journal of Physics D: Applied Physics, vol. 37, no. 16, p. 2274, 2004.
[14] Y. Han, et al., "High performance UV Photodetector Based On βGa2O3/GaN Heterojunction Fabricated by a Reversed Substitution Growth Method," in 2023 IEEE Nanotechnology Materials and Devices Conference (NMDC). IEEE, 2023.
[15] M. Liao et al., "Comprehensive investigation of single crystal diamond deep-ultraviolet detectors," Japanese Journal of Applied Physics, vol. 51, no. 9R, p. 090115, 2012.
[16] C. Wang et al., "Review of recent progress on graphene-based composite gas sensors," Ceramics International, vol. 47, no. 12, pp. 16367-16384, 2021.
[17] Mirzaei, Ali, et al. "Resistive gas sensors based on metal-oxide nanowires." Journal of Applied Physics, vol. 126, no. 24, 2019.
[18] G. Korotcenkov and B. K. Cho, "Metal oxide composites in conductometric gas sensors: Achievements and challenges," Sensors and Actuators B: Chemical, vol. 244, pp. 182-210, 2017.
[19] Ahmad, R., et al. "Recent progress and perspectives of gas sensors based on vertically oriented ZnO nanomaterials," Advances in Colloid and Interface Science, vol. 270, pp. 1-27, 2019.
[20] Y. Fang, S. Li, L. Wang, and J. Zhang, "Accurate characterization of next-generation thin-film photodetectors," in Nature Photonics, vol. 13, no. 1, pp. 1-4, 2019.
[21] K.-J. Chen, Y.-H. Chang, C.-H. Cheng, and C.-H. Lee, "Optoelectronic characteristics of UV photodetector based on ZnO nanowire thin films," Journal of Alloys and Compounds, vol. 479, no. 1-2, pp. 674-677, 2009.
[22] W. Hu, X. Wu, Y. Li, H. Lin, Z. Zhang, and Q. Chen, "High-Performance Flexible Photodetectors based on High-Quality Perovskite Thin Films by a Vapor-Solution Method," Advanced Materials, vol. 29, no. 43, p. 1703256, 2017.
[23] K. Krishna, G. Kurugundla, et al., "Nanostructured metal oxide semiconductor-based gas sensors: A comprehensive review," Sensors and Actuators A: Physical, vol. 341, p. 113578, 2022.
[24] Li-Yang Chang, "Investigation of Indium Gallium Oxide Thin Film Fabricated by RF Sputtering System and Their Applications," Master's thesis, National Cheng Kung University, Jun. 2017.
[25] E. Monroy, et al., "AlxGa1−xN: Si Schottky barrier photodiodes with fast response and high detectivity," Applied Physics Letters, vol. 73, no. 15, pp. 2146-2148, 1998.
[26] D. A. Neamen, "Semiconductor physics and devices: basic principles," McGraw-Hill, 2003.
[27] A. van der Ziel, "Noise in solid state devices and circuits," Wiley-Interscience, 1986.
[28] D. C. Reynolds, et al., "Neutral-donor–bound-exciton complexes in ZnO crystals," Physical Review B, vol. 57, no. 19, p. 12151, 1998.
[29] M. A. Haque and M. T. A. Saif, "Application of MEMS force sensors for in situ mechanical characterization of nano-scale thin films in SEM and TEM," Sensors and Actuators A: Physical, vol. 97, pp. 239-245, 2002.
[30] The Editors of Encyclopaedia Britannica, "X-ray diffraction," Encyclopedia Britannica, Mar. 31, 2023.
[31] Cha, J. H., Kim, K. H., Park, Y. S., Park, S. J., & Choi, H. W. (2009). Photoluminescence characteristics of nanocrystalline ZnGa2O4 phosphors obtained at different sintering temperatures. Molecular Crystals and Liquid Crystals, 499(1), 85-407.
[32] K. M. Niang, et al., "Zinc tin oxide thin film transistors produced by a high rate reactive sputtering: Effect of tin composition and annealing temperatures," Physica Status Solidi (a), vol. 214, no. 2, p. 1600470, 2017.
[33] S. Han, et al., "Photoconductive gain in solar-blind ultraviolet photodetector based on Mg0. 52Zn0. 48O thin film," Appl. Phys. Lett., vol. 99, no. 24, 2011.
[34] M. G. Yun, Y. J. Chung, J. S. Park, Y. W. Heo, and H. J. Kim, "Effects of channel thickness on electrical properties and stability of zinc tin oxide thin-film transistors," Journal of Physics D: Applied Physics, vol. 46, no. 47, p. 475106, 2013.
[35] W. Ping et al., "Effects of internal gain and illumination-induced stored charges in MgZnO metal–semiconductor–metal photodetectors," IEEE Trans. Electron Devices, vol. 63, no. 4, pp. 1600-1607, 2016.
[36] F. Sun, Y. Zhang, and H. Wang, "Ultraviolet photodetectors fabricated from ZnO p–i–n homojunction structures," Materials Chemistry and Physics, vol. 129, no. 1-2, pp. 27-29, 2011.
[37] J. Yu et al., "ZnO-based ultraviolet avalanche photodetectors," J. Phys. D: Appl. Phys., vol. 46, no. 30, p. 305105, 2013.
[38] N. Al-Khalli, M. Aboud, and N. Debbar, "Theoretical study and design of n-ZnO/p-Si heterojunction MSM photodiode for optimized performance," Opt. Laser Technol., vol. 133, p. 106564, 2021.
[39] C.-Y. Huang, K.-C. Chen, and C.-J. Chang, "Realization of a self-powered ZnSnO MSM UV photodetector that uses surface state controlled photovoltaic effect," Ceramics International, vol. 47, no. 2, pp. 1785-1791, 2021.
[40] Cao, F., Pan, Z., & Ji, X. (2021). An approach for fabrication of micrometer linear ZnO/Ti3C2Tx UV photodetector with high responsivity and EQE. Journal of Applied Physics, 129(20).
[41] J. Kim, et al., "Conversion of an ultra-wide bandgap amorphous oxide insulator to a semiconductor," NPG Asia Mater., vol. 9, no. 3, p. e359, 2017.
[42] S. Soman, A. K. Das, and S. S. Hegedus, "Interface engineering by intermediate hydrogen plasma treatment using DC-PECVD for silicon heterojunction solar cells," ACS Appl. Electron. Mater., vol. 5, no. 2, pp. 803-811, 2023.
[43] V. V. Ganbavle et al., "Development of Zn2SnO4 thin films deposited by spray pyrolysis method and their utility for NO2 gas sensors at moderate operating temperature," Journal of Analytical and Applied Pyrolysis, vol. 107, pp. 233-241, 2014.
[44] M. Fleischer, "Advances in application potential of adsorptive-type solid state gas sensors: high-temperature semiconducting oxides and ambient temperature GasFET devices," Measurement Science and Technology, vol. 19, no. 4, p. 042001, 2008.
[45] S. T. Shishiyanu, T. S. Shishiyanu, and O. I. Lupan, "Sensing characteristics of tin-doped ZnO thin films as NO2 gas sensor," Sensors and Actuators B: Chemical, vol. 107, no. 1, pp. 379-386, 2005.
[46] B. Bergveld, "Development of an ion-sensitive solid-state device for neurophysiological measurements," IEEE Transactions on Biomedical Engineering, vol. 1, pp. 70-71, 1970.
[47] C. D. Ung, P. W. Cheung, and W. H. Ko, "A generalized theory of an electrolyte-insulator-semiconductor field-effect transistor," IEEE Transactions on Electron Devices, vol. 33, no. 1, pp. 8-18, Jan. 1986.
[48] K. Park, J. H. Kim, T. Sung, H. W. Park, J. H. Baeck, J. Bae, K. S. Park, S. Yoon, I. Kang, K. B. Chung, H. S. Kim, and J. Y. Kwon, "Highly Reliable Amorphous In-Ga-Zn-O Thin-Film Transistors Through the Addition of Nitrogen Doping," IEEE Transactions on Electron Devices, vol. 66, no. 1, pp. 457-463, Jan. 2019.