| Thin film bulk acoustic resonator (FBAR), as a novel radio frequency MEMS device, has received extensive attention and research in recent years. FBAR has made huge commercial success in the field of wireless communications (radio frequency devices such as filters and duplexers), for its small volume, high resonant frequency as well as compatibility with CMOS process. Besides, with high resonant frequency, FBAR shows excellent sensing sensitivity, and has broad application prospects in the fields of micro mass sensors, pressure sensors, temperature sensors, as well as biosensors. FBAR sensors are gradually becoming new research hotspots of FBAR technologies.According to the bulk acoustic wave models, FBAR devices can be divided into longitudinal wave mode and shear wave mode. Due to the large damping of longitudinal wave and almost no damping of shear wave in the liquid, shear wave mode FBAR is more suitable for the application of biological sensing in the liquid environment. Excitations of shear wave mode FBAR include two main forms, thickness excitation and lateral field excitation. Compared with the thickness excited FBAR which needs to control the growth of piezoelectric thin film at c axis tilt angle, lateral field excited FBAR has relatively simple structure, and good repeatability of preparation process, therefore it is considered to be one of the most promising biological sensing technologies. In order to improve the Q value and obtain pure shear wave mode FBAR, this paper explored the lateral field excited FBAR with embedded electrode structure. The main work and results of this paper are as follows:1. Summarizing the research status of FBAR technology at home and abroad in detail. The sound field distribution and electrical resonant characteristics of the lateral field excited FBAR were theoretically derived based on the analysis of the traditional longitudinal wave mode FBAR.2. Using COMSOL Multiphysics finite element simulation software, we have carried out theoretical analysis on three kinds of novel acoustic piezoelectric devices systematically.1) Surface acoustic wave devices on flexible substrate; 2) FBAR devices on any substrate with polyimide as support layer; 3) the lateral field excited FBAR with embedded electrodes structure. The former two were verified by experiments, and the experimental results were in good agreement with the simulation predictions. We have carried out the detailed modeling analysis on the lateral field excited FBAR with embedded electrodes, and systematically studied the effect of electrode gaps, electrode widths, electrode sets and embedded depths on the performance of the devices in order to obtain the optimized design scheme.3. Studying the preparation process of FBAR devices with lateral field excitation. A series of lateral field excited FBAR masks was designed according to the simulation results, and we prepared back-etching lateral field excited FBAR devices based on ZnO piezoelectric thin films through micro nano processing platform. The resonant frequency was about 1.16 GHz which was detected by the network analyzer, and it showed great agreement with simulation analysis. The Q value of the devices was 470. By 0.4% dilute hydrochloric acid corrosion of the piezoelectric layer selectively, we successfully prepared lateral field excited FBAR with embedded electrodes. The resonant frequency was 741 MHZ, and Q value was 119.The above related results have been published in the journals of Scientific Reports and Piezoelectrics and Acoustooptics. |
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