Development of Surface and Lamb Wave Sensors using Acoustoelectric Effect

• Main Authors: Wei-Shan Wang, 王偉姍
• Other Authors: 吳政忠
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/74439444260108676355

博士 === 臺灣大學 === 應用力學研究所 === 98 === 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.