表面聲波元件應用於光感測器之設計、分析與量測

Investigation on Characterization of Surface Acoustic Wave Based Photodetector

黃采如(Tsai-Ju Huang)

指導教授 ： 馬劍清

國立臺灣大學/工學院/機械工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.02552

摘要

由於表面聲波元件特性的優勢，對於溫度、壓力、表面粗糙度、表面液體黏度及表面電導率等特性均相當敏感，目前利用表面聲波技術來製作感測器元件，無論在氣體、液體，或是生物方面的檢測都已有相當多的研究成果以及產品。表面聲波光感測器可藉由在表面聲波元件上沈積適當的光電感測薄膜來實現，元件具有優異的靈敏度，再加上以微機電製程製作使得感測面積得以大幅縮小，可增加量測的空間解析度，對於感測微小區域的光強密度的感測具有相當大的應用潛力。
本文利用鈮酸鋰壓電基板製作表面聲波元件，在表面波傳路徑上沈積光電材料薄膜（氧化鋅或導電高分子P3HT）作為光感測區，對於元件的感光波長、響應與光強密度的關係、元件動態響應及溫度光電特性等均作深入且詳細探討。除了單一型式的表面聲波光感測器之外，並進一步利用斜指叉轉能器製作寬頻表面聲波元件，藉由元件中空間位置與響應頻率相關的特性，沈積多個獨立的光感測區，來發展陣列式光感測器，感測器可在一次的量測中同時獲得空間中多點位置的光強資訊，可提高光場量測應用時的空間解析度並減少量測時間。
本研究亦建立表面聲波元件聲電效應的模擬分析，詳細探討表面電導率改變、感測區尺寸的變化、指叉狀電極的設計、多點感測區的設計等各項設計參數對元件頻率響應變化的影響，並與實驗結果對照比較，以期對於表面聲波光感測器的元件特性與響應更加瞭解，並發展最佳化的設計方法與流程。

關鍵字

表面聲波 ； 光感測器 ； 延遲線 ； 斜指叉轉能器 ； 聲電效應

並列摘要

Surface acoustic wave (SAW) propagation has a longitudinal and a vertical shear component that can couple with a medium in contact with the device’s surface. Such coupling strongly affects the amplitude and velocity of the wave. This feature enables SAW sensors to directly sense a large number of physical and chemical traits. These include temperature, pressure, acceleration, stress, roughness, density, viscoselastic properties, and electrical conductivity. Mass loading, viscoelastic or acoustoelectric perturbation cohering to SAW propagation will induce changes in response. Therefore, SAW devices can be used for thin film characterization and sensing applications.
A SAW photodetector can be developed by a well-design SAW device and delicate deposited photoconductive film on the SAW propagation surface. In this study, the coupling-of-mode simulation is applied to the characterization of the optical response of a surface acoustic wave photodetector. To verify the simulation results, a LiNbO3-based SAW delay line deposited with a ZnO or P3HT photoconductive overlayer is fabricated. The bilayer system is proved to be a good light-sensing structure where bulk LiNbO3 is used to excite the surface wave and the ZnO and P3HT overlayers are photosensitive layers. The optical characteristics (i.e., optical spectrum, dynamic responses and thermal properties) of the SAW delay line are determined and the simulation and experimental responses show a good agreement.
An ultraviolet array photodetector is also developed in this study by the application of a LiNbO3-based slanted finger interdigital transducer (SFIT) and several ZnO optically active areas. The array photodetector can obtain multiple ultraviolet light intensities within a single measurement and is proved to be capable of measuring a distributed light-field. The acoustoelectric effect is introduced in the SFIT coupling-of-mode (COM) simulation to evaluate the performance of the array photodetector. The simulated results have good agreement with the experimental responses. An optimum design of the slanted finger interdigital transducer and ZnO for the performance of the array photodetector is analyzed and is discussed in detail.

並列關鍵字

SAW ； Photodetector ； Delay Line ； SFIT ； Acoustoelectric

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