Sensitivity Studies Of Love Wave Immunosensors

This dissertation is on the researches of Love wave sensors, which mainly includes three parts:(1) Theoretical analysis of Love wave devices;(2) Love wave devices are fabricated and elastic constants of SiO2and ZnO guiding layers are studied;(3) Studies on gravimetric sensitivities of Love wave immunosensors are carried out.There are five chapters in this dissertation as follows:In the first chapter, it mainly describes the research progress of surface acoustic wave (SAW) sensors. Several different types of SAW sensors and various advantages of SAW sensors are also presented. Finally, the development of the Love-mode sensors is briefly introduced. In the end of this chapter, the primary coverage and the basic frame of this dissertation is outlined.In the second chapter, theories on elastic waves propagating in mutilayer structures are introduced. The chapter contains the following four parts:Firstly, a theory on elastic waves propagating in two layer structure is introduced. The fundamental wave equations in piezoelectric materials are derived from the Newtonian equations of motion and Maxwell’s equations, intercoupled by the piezo-electric tensors. The partial wave theories are presented in details and the solutions to the wave equations in the substrate and guiding layer are obtained. Secondly, in order to study Love-wave immunosensors consisting a Love wave device and a sensitive film, we developed a theoretical model of three layer structure Love-wave immunosensors. Thirdly, based on boundary conditions at each interface of the three layers, twenty homogeneous equations are got. Finally, procedures of numerical calculations are introduced to solve anisotropy media problems.In the third chapter, studies on elastic constants of SiO2and ZnO guiding layers are presented. This chapter contains the following parts:Firstly, Love wave delay lines are fabricated based on36°YX-LiTaO3substrates and interdigital transducers. Secondly, amorphous SiO2thin films and c-axis orientated ZnO thin films are made on Love wave delay lines using RF magnetron sputtering techniques, and several Love-wave devices based on SiO2/36°YX-LiTaO3、ZnO/36°YX-LiTaO3structures are fabricated with different SiO2and ZnO guiding layer thicknesses. Thirdly, two experimental measurement systems include a network analyzer and a close-loop oscllator consisting of an amplifier, a Love-wave device and a frequency counter are constructed and the frequencies of the Love-wave devices based on SiO2/36°YX-LiTaO3and ZnO/36°YX-LiTaO3structures are measured when the thicknesses of the SiO2and ZnO guiding layers are changed. Thus the variation in phase velocities as a function of thicknesses of the SiO2and ZnO guiding layers is obtained. Finally, using the theories on elastic waves propagating in three layers structures, the elastic constants of the SiO2and ZnO guiding layers are evaluated by theoretical fitting to the experimental data. The results show that the physical parameters of SiO2and ZnO thin film materials are different from that of their bulk counterparts, and the elastic constants of thin film materials are much smaller than that of their bulk counterparts, which indicates that the determination of the elastic constants of the SiO2and ZnO guiding layers is critically important for theoretical analysis on Love-wave devices.In the fourth chapter, studies on gravimetric sensitivities of Love wave immunosensors are described. This chapter includes the following three parts:Firstly, the basic structure of the Love wave immunosensor is introduced and the principles of its operation are also presented. Secondly, the sensitive film and Love wave immunosensors are mentioned in detail. The experimental results show that sensitivities of Love-wave immunosensors based on SiO2/36°YX-LiTaO3and ZnO/36°YX-LiTaO3structures both increase with increasing the guiding layer thicknesses, and after reaching a maximum, the sensitivities decrease with increasing the guiding layer thicknesses. Thirdly, using the determined elastic constants of the SiO2and ZnO guiding layers and theories on elastic waves propagating in three layers structures, the gravimetric sensitivities of the Love wave immunosensors based on SiO2/36°YX-LiTaO3and ZnO/36°YX-LiTaO3structures are calculated. The numerical calculations show that when the normalized guiding layer thickness is in a restricted range, the sensitivities of the Love immunosensors increase firstly with thicknesses increase of the guiding layers, then decrease with the thicknesses further increase, and there are optimum guiding layer thicknesses for the Love-mode immunosensors. This is because when the guiding layer thickness is small, more acoustic energy is confined to the surface when the guiding layer thickness increases, and this leads to a higher sensitivity; when the guiding layer thickness is large, the acoustic energy is distributed evenly in the whole guiding layer, which leads to a decrease in the sensitivity.In the last chapter, the conclusions, prospects and suggestions for future work are presented.