- 學位論文
虛擬表面聲波的特性分析及層狀表面聲波元件模擬
Properties of Pseudo-mode Surface Acoustic Waves and Analysis of Layered SAW devices
摘要
表面聲波元件常應用在行動電話、呼叫器、全球定位系統…等通訊元件上，隨著新一代通訊系統的發展，資料傳輸的速度需求越來越快，因此如何有效提升表面聲波元件的操作頻率、降低插入損失…等，是重要的研究方向。表面聲波元件通常由壓電基底材料鍍上指叉電極所組成，而在本論文中主要探討基底材料的表面聲波之波傳性質、及模擬表面聲波元件的頻率響應，以利於表面聲波元件的設計分析。 關於基底材料的分析，本文首先利用矩陣法求解表面聲波在半無限域壓電介質的波傳特性。而利用修正的複數波數，可求出相位速度較表面波高的虛擬表面波及高速虛擬表面波，並在壓電基底上尋求具有較低波傳損失的波傳方向。另外，將表面阻抗及反射張量加入矩陣法中，則可分析層狀壓電介質的波傳性質及頻散效應,本文探討了金屬電極及金屬薄膜厚度對壓電基板的影響，並計算ZnO/Diamond/Si層狀基底的頻散關係。 至於表面聲波元件的模擬，本文先採用脈衝函數模型做初步的分析。再利用Abbott所提出的耦合模型理論來模擬表面聲波濾波器及共振器的頻率響應，並探討指叉換能器的對數、交叉長度、延遲距離..等設計參數對於頻率響應的影響。最後以ZnO/Diamond/Si為基底，考慮ZnO厚度及頻散效應的影響，並利用修正偶合模型的參數，則可在不需要次微米線寬的製程下，設計模擬中心頻率達1.5GHz 的表面聲波濾波器。 綜言之，本文建立了一套完整的表面聲波元件分析理論，在基底方面主要討論具有較快相位速度的虛擬表面聲波及層狀壓電基底；而對於元件的模擬則考慮了包括設計參數及頻散效應..等。這些對於日後實際設計及製作高頻的表面聲波元件，可提供有效分析。
並列摘要
As the development of communication equipments, the demand of faster information transferring is increasing. SAW devices are usually used in the mobile phones, radio system and global positioning systems (GPS). Increasing the frequency and decreasing the insertion loss of SAW become more and more important. SAW devices are usually consist of piezoelectric substrate with interdigital electrodes. The aim of this study is to investigate the propagation characteristics of SAW on substrate and simulate the frequency response of SAW to improve the design of SAW. In the analysis of substrate, the matrix method was used to solve the propagation characterstics of semi-infinite piezoelectric medium. By utilizing the corrected wave number, the pseudo-modes SAW (PSAW) and the high velocity pseudo-modes SAW (HVPSAW) with higher phase velocity can be found and the propagation direction with lower propagation loss in the piezoelectric medium can also be calculated. On the other hand, the surface impedance tensor and the reflection tensor are introduced into the matrix to evaluate the propagation characteristics and dispersion effect of layered piezoelectric substrate. The effect of the thickness of metallic electrode and metallic film on the piezoelectric substrate was investigated, and the relation of dispersion effect in ZnO/Diamond/Si layered substrate was also calculated. For simulation of SAW devices, the delta function model is applied to the preliminary analysis. The COM model that Abbott proposed is then used to simulate frequency responses of SAW filters and resonators, and investigate the effect of the number of IDT pairs and grating, overlap length and delay distance etc.. Finally, based on the ZnO/Diamond/Si substrate, the effect of the thickness of ZnO film and dispersion effect on COM parameters are evaluated. By using parameters of COM model, the SAW device with 1.5GHz center frequency can be designed. In conclusion, the present study established a complete SAW device analysis theory and provided efficient analysis in the design and production of high frequency SAW devices.