Investigation Of ZnO Piezoelectric Film Resonator And BYFO₃ Ceramic

The ever-increasing development of information technology requires that devices be reduced in size, greater integrated, more modular array and high sensitivity. They are main goals for the future development of sensor devices. Due to the bottleneck in the thickness milling of quartz-crystal microbalance (QCM), the applicability of QCM is limited in obtaining high frequency. In order to solve this problem, researchers are paying great attention in the development of new piezoelectric film resonator to replace traditional QCMs. Based on those reasons, we made extensive investigations on both fabrication and characterization of the ZnO film resonator and its application in biosensors. Our main contributions are listed below.We successfully fabricated zinc oxide (ZnO) based film bulk acoustic resonator by magnetron sputtering method, and it consists of a piezoelectric element (Au/ZnO/Pt) and a Bragg reflector (ZnO/Pt multilayer structure). Under optimized deposition condition, each layer of the device was compact, uniform, well crystallized and highly textural. Through crystallographic test, the orientation fluctuation of ZnO layer decreases slightly. The surface of FBAR is relatively smooth with a root mean square roughness of 7 nm, though many cycles of layer mounting. From the selected area electron diffraction, the ZnO (0002) planes are grown on top of the Pt (111) plane with a very clean interface. It indicates that there is no diffusion between ZnO and Pt layers.It is the first time that we achieved the synthesis of p-type ZnO films by ion beam assisted deposition. We also investigated their optical and electrical properties. It is found that after the 400°C annealing the transmittance of ZnO film becomes higher than that as-deposited. Hall measurements indicated that ZnO film is p-type. Photoconductivity of the p-type ZnO films was also investigated and the conductivity of the films under ultraviolet illumination is about 600 times larger than that in the dark.A series of electrode patterns for standard microwave test were designed and fabricated. In photolithographic process, great effects have been made for the ZnO based device. Through a series of characterization, those films are proved to have good structural, electrical and mechanical properties. Owning to the good quality films, the film resonator will have good properties predictably and have been measured with a resonant frequency of 4.01 GHz.Ansoft, a microwave simulation software, was applied to simulate the behavior of FBAR devices based on piezoelectric resonator formula. Simulation results agree well with experiments. We found that with the increase of the thickness of piezoelectric or electrode layer, the resonant frequency decreases. It acts the same trend as the C₁ and L₁ parameter augment.The ZnO based FBAR was applied in mass detection. Through the deposition of different top electrode thickness and a series of bio-specimen binding, it is found that the resonator frequency shifts sequentially with the loading mass effect. The sensor is demonstrated a candidate for protein detection with a mass sensitivity thousand of times better than that of QCM. Moreover, sandwich structure technique is employed in resonators to enhance the attached mass. The bio-appending mass was estimated by using Sauerbrey Equation. The calculated sensitivity of our biosensor is 8970 Hz-cm²/ng, which is about 8000 times larger by using 20 MHz quartzes, also several times larger than the literature reports. It can be a promising mass sensor as the replacement of QCM.We are the first to fabricate high quality Bi_1-xYb_xFeO₃ multiferroic ceramics by rapid liquid phase sintering method with rare earths Yb³⁺ ions in substitution for Bi³⁺ ions in the BiFeO₃ composition. Their electrical properties are investigated. It is found this method helps reduce leakage current and improve ferroelectricity of the material.