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URN etd-0109113-155311 Statistics This thesis had been viewed 1841 times. Download 1119 times. Author Cheng-Hsiu Ho Author's Email Address email@example.com Department Mechanical Engineering Year 2012 Semester 1 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 77 Title Surface Acoustic Wave Sensors for UV and CO detections Keyword SnOx poly ethylene glycol ZnO nanorod two-port SAW resonator two-port SAW resonator ZnO nanorod poly ethylene glycol SnOx Abstract Surface acoustic wave (SAW) devices are widely utilized in various sensing applications because of several advantages like high sensitivity, small size, and simple fabrication. Therefore, the thesis aims to develop ultraviolet (UV) and carbon monoxide (CO) sensors which can operate at room temperature by applying SAW devices. First of all, two-port SAW resonators with a central frequency of 145 MHz were designed and fabricated based on 128˚YX LiNbO3 substrates. ZnO nanorods and SnOx organic-like films coated with poly ethylene glycol (PEG) films were chosen to be sensing films of UV and CO sensors, respectively. ZnO nanorods were synthesized by aqueous solution method. The SnOx organic-like films were deposited with TMT (Tetramethyltin) and O2 (oxygen) gas mixtures by plasma-enhanced chemical vapor deposition (PECVD) and then coated with PEG films for enhancing sensing ability. Further, the external amplifier was designed by circuit simulation software, and a dual delay line configuration was constructed to reduce interferences from environmental temperature and humidity variations.
In UV sensing experiments, a bright white light that closely mimics natural sunlight was produced via an Xe lamp and a monochromator. The UV light of 380 nm (UV-A) and 300 nm (UV-B) wavelengthes were reserved by filters. The UV sensor modules were tested by illuminating UV light of various power densities. Results show that frequency shift increases with power density and the sensitivities to UV-A and UV-B light are 19 and 406 Hz•cm2/μW. The UV sensor module is more sensitive to UV-B than UV-A. In CO sensing experiments, the CO sensor modules were immerged in CO gas of different concentrations (200~100 ppm) to measure their sensitivities. Results show that the sensitivities of pure SnOx film and SnOx film coated with PEG were 0.75 and 1.68 Hz/ppm, indicating the post treatment with PEG film is useful for enhancing sensitivity.
In conclusion, the sensor modules developed herein have been successfully applied to measure UV light and CO gas at room temperature without additional heating module. The sensor modules exhibit promising features like great linear relation, repeatability, and stability as well as high sensitivity. In the future, the developed sensor modulus can be extended to detect other kinds of items by changing the sensing film.
Advisor Committee Yung-Yu Chen - advisor
Jia-Hong Sun - co-chair
Wen-Ching Shih - co-chair
Files Date of Defense 2012-07-28 Date of Submission 2013-01-09