本論文利用不同之聲波元件，包括Rayleigh波共振模態、Sezawa波共振模態之表面聲波以及固態堆疊型薄膜體聲波元件，結合匹配電路和高頻放大器組成振盪器，並將其應用於紫外光感測器。由於不同之聲波元件，其聲波傳遞的方式和波速不同，機電耦合係數及聲波共振特性也不相同，因此其對於紫外光感測的靈敏度及感測的效果也會相對不同。Rayleigh和Sezawa表面聲波元件的結構，雖然皆為以氧化鋅為感測層的雙層結構，但是其產生聲波的共振模態及特性卻不同，所以其感測度也有所不同。而固態堆疊型薄膜體聲波元件的共振模態與表面聲波波速也不相同，體聲波於上下電極與壓電層之三明治結構中產生共振，其塊體波波速及操作頻率也相對表面波來得高，因此其應用於紫外光之感測器，也將預期會有較佳的特性表現。
產生Rayleigh波的表面聲波元件，其結構為氧化鋅/鈮酸鋰基板的雙層元件，氧化鋅薄膜(約3 μm厚)係作為紫外光之感測層，而鈮酸鋰基板(約1~2 mm厚)則係表面聲波產生的主要來源；由於表面聲波傳遞其波能量時，主要集中於壓電材料表面的一個波長(32 μm)深度左右，因此大部分的聲波皆於鈮酸鋰基板傳遞，當紫外光照射於氧化鋅感測薄膜時，其表面聲波僅受到部分的擾動，因此在強度為1250 μW/cm2的紫外光照射下，最大頻率飄移量僅有63.75 kHz。由於氧化鋅薄膜為本研究之紫外光感測層，因此期望藉由調變氧化鋅沉積溫度之濺鍍參數，以改善此結構的感測度，最終於沉積溫度為400 ℃時，其最大頻率飄移量於相同紫外光照射強度下，大幅提升至264 kHz。
產生Sezawa波的表面聲波元件，其結構為氧化鋅/矽基板的雙層元件，氧化鋅薄膜(約4 μm)同時作為紫外光之感測層以及產生表面聲波之壓電層，因此全部的表面聲波皆於氧化鋅薄膜中傳遞，當紫外光照射於氧化鋅薄膜表面時，其相對於氧化鋅/鈮酸鋰基板雙層結構之Rayleigh波表面聲波元件來得較易於受到擾動，因此其感測度也相對來得大，當紫外光照射強度為551 μW/cm2，可得到最大頻率飄移量1017 kHz。
由於固態堆疊型薄膜體聲波元件依照布拉格反射器排列順序之不同，體聲波於壓電層產生共振時可分為½ 和¼ 波長之共振模態，經由探討兩者之頻率共振特性，½ 波長之固態堆疊型薄膜體聲波元件，有較佳之整體表現，因此本論文以½ 波長共振模態之薄膜體聲波元件製作紫外光感測器。由不同紫外光強度之探討可得知，其頻率飄移曲線與表面聲波類似，但是最大頻率飄移量以及最大感測度比表面聲波大很多，其結果可歸因於體聲波元件有較小之共振波長 (2 μm)，因此當紫外光照射於氧化鋅薄膜時，其會造成相對大的擾動，使得其感測度較大且較靈敏，當紫外光強度為212 μW/cm2時，其最大頻率飄移量為552 kHz。

In this thesis, Rayleigh-mode and Sezawa-mode surface acoustic wave devices, and SMR-based (solidly mounted resonator, SMR) thin film bulk acoustic wave devices were employed to construct the UV sensors. The oscillators are composed of acoustic wave devices, high-frequency amplifier and matching networks. Due to the fact that the different acoustic wave devices are associated with the different propagating behaviors, electromechanical coefficient and resonance characteristics, they lead to the diversely sensing properties. Although Rayleigh-mode and Sezawa-mode SAW devices are both constructed by a ZnO sensing layer, they operate with different resonance behaviors and propagate with different phase velocities in the layered structures. Therefore, they result in different frequency shifts and sensitivities while illuminating UV light on the surface of ZnO thin films. As to the SMR device, the acoustic waves are confined within the ZnO piezoelectric layer sandwiched between two metal electrodes and then resonance as standing waves. In general, thin film bulk acoustic wave devices, which are SMR devices in this thesis, possess a higher operating frequency and better frequency response than those of SAW devices. Therefore, it is expected that UV sensors based on SMR devices will lead to an excellent performance.
The Rayleigh-mode SAW-based UV sensors consisted of a 3μm-thickness ZnO thin film for sensing UV light and a 2mm-thickness LiNbO3 substrate for generating surface acoustic waves in the ZnO/ LiNbO3 layered structure. Because surface acoustic waves travel along the surface within the depth of one wavelength, 32 μm herein, most of them propagate in the LiNbO3 substrate. SAWs were perturbed slightly and consequently resulted in an unsatisfactorily maximum frequency shift of 63.75 kHz when a UV light intensity of 1250 μW/cm2 was illuminated on the surface of ZnO thin film. Because ZnO films in this thesis are used as the sensing layer for UV light, we adjusted the sputtering parameter of deposition temperature to improve their crystalline properties and further enhance the sensitivity of ZnO/LiNbO3 layered SAW devices. Finally, the maximum frequency shift was raised to 264 kHz with the same UV light intensity using the deposition temperature of 400 ℃.
The ZnO thin films in the ZnO/Si layered structure were simultaneously employed as the piezoelectric layer for generating SAWs and the sensing layer for UV light. Therefore, all of the acoustic waves propagate within the ZnO thin films and are easier disturbed than the devices operated with the ZnO/LiNbO3 layered structure. This accounts for the relatively large frequency shift of 1017 kHz with the UV light intensity of 551 μW/cm2.
The ½ λ type SMR device was adopted to construct the UV sensor due to their better resonance characteristics than those of ¼ λ type. As can be seen from the results that SMR-based UV sensor presented better UV sensing properties compared with SAW-based UV sensors. The reasons for the considerable frequency shifts and sensitivities can be attributed to that SMR-based sensor possesses a shorter resonance wavelength and a larger electromechanical coefficient than those of SAW-based devices. Finally, the maximum frequency shift of 552 kHz can be obtained when the illumination intensity of UV light was 212 μW/cm2.

摘要 I
ABSTRAT III
CONTENTS VI
FIGURE CAPTIONS VIII
TABLE CAPTIONS XI
CHAPTER 1 INTRODUCTION 1
1.1 HISTORY OF ACOUSTIC WAVE DEVICES 1
1.2 UV SENSOR BASED ON ACOUSTIC WAVE DEVICES 4
1.3 THESIS ORGANIZATION 6
CHAPTER 2 THEORY 8
2.1 PIEZOELECTRICITY 8
2.2 SPUTTERING TECHNIQUE 10
2.3 SURFACE ACOUSTIC WAVE DEVICES 12
2.3.1 The fundamental designs and characteristics of SAW devices 12
2.3.2 Rayleigh wave and Sezawa wave 13
2.4 BULK ACOUSTIC WAVE DEVICES 15
2.4.1 Solidly mounted resonator, SMR 15
2.4.2 The effective electromechanical coupling coefficient, K2eff 19
2.4.3 The quality factor, Q 19
2.4.4 The figure of merit, FOM 20
2.5 ACOUSTIC WAVE OSCILLATOR 20
2.5.1 Oscillator basics 20
2.5.2 The feedback-loop oscillator 21
2.5.3 The negative resistance oscillator 22
2.5.4 Phase noise 24
2.6 SENSING PRINCIPLE 26
2.6.1 UV sensing 26
CHAPTER 3 EXPERIMENTAL PROCEDURES 29
3.1 THIN FILM DEPOSITION BY SPUTTERING SYSTEM 29
3.2 FABRICATION OF SURFACE ACOUSTIC WAVE DEVICES 30
3.3 FABRICATION OF BULK ACOUSTIC WAVE DEVICES 31
3.4 UV LIGHT ILLUMINATION AND MEASUREMENT SYSTEMS 32
3.5 THE ANALYSES FOR THIN FILMS AND THE MEASUREMENTS FOR ACOUSTIC WAVE DEVICES 33
3.5.1 X-ray diffraction (XRD) analysis 33
3.5.2 Scanning electron microscopy (SEM) analysis 34
3.5.3 Atomic force microscopy (AFM) analysis 34
3.5.4 X-ray photoelectron spectroscopy (XPS) analysis 34
3.5.5 Photoluminescence (PL) analysis 36
3.5.6 Network analyzer measurement 36
3.5.7 Spectrum analyzer measurement 36
CHAPTER 4 RESULTS AND DISCUSSION 38
4.1 UV SENSOR BASED ON A ZNO/LINBO3 LAYERED SAW OSCILLATOR CIRCUIT 38
4.1.1 Investigation of ZnO films on LiNbO3 substrates 38
4.1.2 Frequency characteristics of a ZnO/LiNbO3 layered SAW device 39
4.1.3 Transient photoresponse of a ZnO/LiNbO3 layered SAW oscillator 40
4.1.4 Frequency shifts of a ZnO/LiNbO3 layered SAW oscillator as a function of various illumination positions 41
4.1.5 Frequency shifts of a ZnO/LiNbO3 layered SAW oscillator as a function of various ultraviolet light intensities 43
4.1.6 Optimization of the ZnO sensing layer 44
4.1.6.1 Optimizing ZnO films by adjusting deposition temperatures 44
4.1.6.2 Photoluminescence analysis 45
4.1.6.3 XPS analysis 45
4.1.6.4 UV sensing properties of a ZnO/LiNbO3 layered SAW oscillator with ZnO films deposited at various temperatures 46
4.2 UV SENSOR BASED ON ZNO/SI LAYERED SAW DEVICES 48
4.2.1 Investigation of ZnO films on Si substrates 48
4.2.2 Frequency characteristics of a ZnO/Si layered SAW device 49
4.2.3 UV sensing properties of a ZnO/Si layered SAW device 50
4.3 UV SENSOR BASED ON TFBAW DEVICES 52
4.3.1 Comparison of the ½ λ and ¼ λ configurations of SMR devices 53
4.3.2 UV sensing properties of an SMR oscillator 55
4.3.2.1 Frequency characteristics of an SMR device 56
4.3.2.2 Frequency shifts of an SMR oscillator as a function of various UV light intensities 56
CHAPTER 5 CONCLUSION 58
CHAPTER 6 FUTURE WORK 61

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