臺灣博碩士論文加值系統

近年來氧化鋅廣泛的被應用在表面聲波元件，它已經成功的被成長在quartz, Si、GaAs、InP、sapphire (Al2O3) 和diamond 基板上，其中成長 sapphire 基板更被廣泛的應用在高頻表面聲波元件，其主要原因為 sapphire 基板具有高聲速的之優點，然而由於 sapphire 基板價格較 Si 基板昂貴且不利於大面積化，在本研究中，我們成長氧化鋅在Al2O3 緩衝層上以達高頻表面聲波元件應用。
本研究成功地利用射頻磁控濺鍍法在 Al2O3 緩衝層上成長具有優選方向之氧化鋅薄膜，並且在氧化鋅薄膜表面上使用舉離法製作對指型換能器，氧化鋅成長在 Al2O3 (4.8μm)/SiO2/Si 結構上，所量測到表面聲波濾波器之中心頻率由無Al2O3 緩衝層之265 MHz 提升至 408 MHz，而與其操作頻率接近ZnO/sapphire中心頻率，並且將來有利於高頻表面聲波元件應用。

Among recently developed piezoelectric thin film materials, ZnO has been considered to be very promising for fabricating thin film surface acoustic wave (SAW) devices. ZnO thin films have been deposited on quartz, Si, GaAs, InP, sapphire (Al2O3), and diamond substrates. In these substrates materials, sapphire is widely used for high frequency SAW device due its high acoustic velocity. However, the sapphire substrate is more expensive than Si wafer, and it is still very difficult to grow large size of Al2O3 single crystal. In this study, the Al2O3 buffer layer was served as a lower-price alternative to the expensive sapphire substrates. We adopt the ZnO thin film on SiO2/Si substrate with Al2O3 buffer layer as a promising substrate for high-frequency SAW device.
In this work, we have been successfully developed the ZnO on Al2O3 buffer by RF magnetron sputtering. Interdigital transducers (IDTs) were fabricated on ZnO thin film surface by a conventional photolithographic technique. The center frequency of SAW device with Al2O3 (4.8μm) buffer was measured to be about 408 MHz, which was much higher than that (265 MHz) of ZnO/SiO2/Si SAW device. The center frequency of ZnO/Al2O3/SiO2/Si SAW device is approach to that of the ZnO/sapphire SAW device. It is beneficial to replace sapphire substrate for high frequency SAW device. And we believe that the SAW devices based on Al2O3 buffer will be applied on high frequency devices in the future.

CHAPTER 1
1.1 Introduction 1 1.2 Motive 2

CHAPTER 2 Fundamental Theories and Background Topics
2.1 Historical Background 4
2.2 Characteristics of Ferroelectric 5
2.3 Piezoelectric Effect 8
2.3.1 Direct Piezoelectric Effect 8
2.3.2 Converse Piezoelectric Effect 9
2.3.3 Piezoelectric Materials 10
2.4 Techniques for Fabricating Thin Films 11
2.4.1 RF Magnetron Sputtering 11
2.5 Surface Acoustic Waves 15
2.6 SAW Excitation and Operation Properties 18
2.6.1 Interdigital Transducer (IDT) 18
2.6.2 Coupling Coefficient 21


CHAPTER 3 Growth ZnO and Al2O3 Buffer layer on Si
Substrates by RF Magnetron Sputtering
3.1 Introduction 23
3.2 RF Magnetron Sputtering System 23
3.3 Preparation of Substrates 24
3.3.1 Clean Procedure for Si(100) Substrate 24
3.4 Growth and Evaluation Al2O3 Buffer Layer 25
3.4.1 Deposition Condition 25
3.4.2 Thickness 26
3.5 Growth and Evaluation ZnO Thin Film 27
3.6 Properties Measurements 29
3.6.1 α-step 29
3.6.2 X-ray Diffraction (XRD) 29
3.6.3 Scanning Electron Microscopy (SEM) 29
3.6.4 Atom Force Microscopy (AFM) 29
3.7 Interdigital Transducer Fabrication 30
3.7.1 Pattern Design 30
3.7.2 Photolithographic Process 31
3.8 Measurement and Inspection of SAWDevice 39

CHAPTER 4 Results and Discussion
4.1 ZnO/Al2O3/SiO2/Si 40
4.1.1 Al2O3 Deposition Condition 40
4.1.2 ZnO/Al2O3/SiO2/Si 47
4.2 ZnO/NCD/Si 50
4.3 ZnO/Substrates 55

CHAPTER 5 Surface Acoustic Wave Properties of ZnO
Thin Film with Different Buffer Layer
5.1 Introduction 60
5.2 General Principle 60
5.3 Deviation Factors from Ideal SAW Response 62
5.3.1 Electromagnetic Feedthrough (crosstalk) 63
5.3.2 Triple Transit Interference 63
5.3.3 Bulk Wave Interference 64
5.3.4 Circuit Factor Loading 64
5.3.5 Impedance Mismatch 64
5.3.6 Harmonic Response 65
5.4 SAW Properties 65
5.4.1 Frequency Response of SAW Filter 65

CHAPTER 6 Conclusion 78

REFERENCE 79

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