Micro Biosensor Research Based On Film Bulk Acoustic Resonator

With the development of modern detection technology, people have increasingly demanding micro-biosensors. Biosensors toward the development of miniaturized, trace detection, high-sensitive and specific detection. In many cases, this type of biosensor needs to work in the liquid environment. However the quartz crystal microbalance (QCM) and surface acoustic wave sensors as typical piezoelectric biosensor can not meet requirement in the development market. According to the literature and analysis, there need a piezoelectric biosensor which should be high-sensitive, micrometer scale and micro material test, work in the liquid environment and integrated into the chip.Thin film bulk acoustic resonator which is a new developed resonant device achieved great commercial success as filters in the RF field of communication, its high resonant frequency and integrated advantage make it become a new generation of piezoelectric biosensor research hotspot.In order to improve a micro, high-sensitive sensor based on FBAR by used the knowledge of the existing study, there have three critical questions:(1) theoretical deduction and modeling;(2) workmanship and integrated with other devices;(3) test and application. The first question is the main study in this paper.Firstly, starting from piezoelectric crystal’s elasticity and dielectric properties, working principle, typical structure and fabrication process of the thin film bulk acoustic resonator are described, and the theoretical model of FBAR is studied and analyzed. Then there has a deduction and builds a model of the matching sensor and obtains its Mason equivalent model. On this basis, we do research on the longitudinal wave mode FBAR sensor with vertical c-axis orientation, create FBAR sensor model with five-layer structure, and simulate achieving FBAR sensor with quality of the mass loudness per unit area which is up to0.28pg/Hz/cm2, that means adsorption layer with per square centimeter adsorbing0.28pg substance leads to resonant frequency of FBAR drifting to1Hz. We researched the influence by mass loading layer’s material properties of FBAR sensor on resonance characteristics, it is verified that it can fit well with classic Suaerbrey formula. Then we study on FBAR sensor’s characteristics in liquid environment, found that the sound attenuation of FBAR is more serious in the longitudinal wave mode. So we propose to use microfluidic technology in order to add microfluidic structure on FBAR sensor which can reduce acoustic waves losing in the liquid environment. We make deeper research on FBAR sensor with titled c-axis orientation; found that when the c-axis inclined, there are two piezoelectric thin film acoustic modes:longitudinal modes and shear modes. We derive an expression of its electrical impedance and simulate resonance characteristics when the c-axis tilt angle is different. It shows that only longitudinal modes occurred when the c-axis tilt angle was0°or66.5°,only shear modes occurred when the c-axis tilt angle at39.4°or90°.The maximum electromechanical coupling coefficient of longitudinal appears at0°and shear modes at32.3°. Then we derive the electrical impedance formula of the FBAR sensor with titled c-axis orientation which have five-layer structure. Finally use the ANSYS finite element analysis software, we simulate the research on FBAR sensor with vertical c-axis orientation and tilted c-axis orientation, finally get its admittance characteristic curve. We find that it is consistent between simulation results and matlab simulation results which are derived by the theoretical formula. It verifies the correctness of the theoretical model and formula deduction result.The study of this paper are instructive for the study, development and application of the sensor which is similar micro-type, trace materials, high-sensitive and working in the liquid environment.