結合聲電效應之板波與表面聲波感測器研製

Abstract

由於體積小、敏感度高，表面聲波與板波感測器已廣泛應用於各式感測，而聲電效應即為其重要感測機制之ㄧ。然由於板波之傳播機制較徹體波或表面聲波複雜許多，現存文獻中仍缺聲電效應與板波波傳之互制行為探討。有鑑於此，本論文分析聲電效應作用下，表面波與板波感測器之特性，並藉以為研製微尺寸板波感測器之基礎。在實驗方面，文中首度研製以氧化鋅奈米結構為感測材料之表面聲波紫外光感測器，更以氧化鋅薄板同時激發板波與作為感測層，製作出一板波紫外光感測器，並分別探討其特性。 本文首先介紹表面聲波傳遞時受聲電效應影響之理論模型，並討論當一壓電半導體材料與自由載子產生交互作用時，其表面波波速、衰減係數與壓電半導體導電度之變化。接著，針對板波，對聲電效應理論模型引入頻散關係，並以此修正之聲電效應理論，探討板波受自由載子影響時之傳播特性。文中以氧化鋅材料為例，研究在聲電效應影響下單層板與多層板板波之傳遞行為。 為了探討聲電效應於表面波傳遞時之影響，本文製作一以氧化鋅奈米柱為感測材料之表面聲波紫外光感測系統，並針對其即時監測之效能、靈敏度、重複性與穩定性做測試與討論。此外，亦首度將量測到的頻率漂移代入聲電效應之理論模型，反算出受紫外光照射一段時間後之氧化鋅導電度，並與理論做一比較與研究。 以第二章板波頻散關係與聲電效應互制之分析為基礎，本文研製一新型板波紫外光感測器。文中，分別製作出氧化鋅/氮化矽/矽結構與氧化鋅/氮化矽薄板之板波紫外光感測器，並對此兩種感測器做量測與比較。研究成果顯示在0.06mWcm-2的紫外光照射下，以氧化鋅/氮化矽薄板為結構之板波紫外光感測器有明顯的波傳損失。表示引入板波頻散關係後，此修正之聲電效應理論可成功設計出感測效能優異之板波感測器。 綜言之，本文提出一分析聲電效應與板波波傳之理論模式，可用於設計單層或多層板板波感測器。在實驗方面，本文基於理論分析設計，亦首度製作出以氧化鋅奈米柱為感測層之表面聲波紫外光感測器以及氧化鋅/氮化矽薄板之板波紫外光感測器。

Surface and Lamb wave sensors, with advantages such as small volume and high sensitivity, have been widely used in various sensing applications. Acoustoelectric effect, which arises from the interaction of acoustic waves and mobile carriers, is one of important sensing mechanisms of acoustic wave sensors. Nevertheless, Lamb wave propagation is much more complex than bulk and surface waves; in the meanwhile, discussions of the influences of acoustoelectric effect on Lamb wave propagation in the literatures remain little thus far. In this regard, characteristics of surface and Lamb wave sensors affected by acoustoelectric interaction are theoretically investigated, which provide a principle and method for designing Lamb wave microsensors for further applications. In addition, a ZnO-nanorods surface acoustic wave UV sensor and a silicon-based ZnO-membrane Lamb wave UV microsensor both employing acoustoelectric effect are realized and demonstrated respectively for the first time. First, an acoustoelectric effect model which has been employed surface wave propagation is briefly introduced. Characteristics of a piezoelectric semiconductor interacting with mobile carriers, such as velocity change, attenuation and conductivity are discussed. In particular, by introducing dispersion relations, a model associated with the acoustoelectric effect is modified to deal with interactions of Lamb waves and mobile carriers. A piezoelectric semiconducting ZnO material is used as a numerical example to discuss Lamb wave propagation influenced by acoustoelectric interaction in a single and multi-layered plate respectively. Next, to reveal the effect of the acoustoelectric interactions on surface wave propagation, a ZnO-nanorod based UV detector system is demonstrated. Characteristics of this UV detector such as real-time response, sensitivity, repeatability and stability are discussed. In addition, ZnO conductivities under 365nm illuminations for a period of time are derived and discussed by substituting measured frequency shifts into the acoustoelectric model for the first time. Finally, based on the analysis of the acoustoelectric-effect model for Lamb wave propagation presented in chapter 2, a novel silicon-based Lamb wave UV microsensor is demonstrated for the first time. For comparison, two types of Lamb wave UV microsensors, based on a ZnO/Si3N4/Si structure and an ultra-thin ZnO/Si3N4 membrane respectively, are realized and discussed. Results show that the ZnO/Si3N4 membrane has obvious acoustic losses when the sensor is under a 0.06mWcm-2 UV illumination, which implies through proper design, a Lamb wave microsensor is a promising candidate for sensing application using acoustoelectric effect. In brief, influences of acoustoelectric effect on surface and Lamb waves are theoretically investigated. For experimental verifications, a ZnO-nanorod based surface-wave UV sensor and a Lamb wave UV detector based on an ultra-thin ZnO/Si3N4 membrane are designed and realized for the first time.