Ultra-Sensitive FBAR Simulation Design Based On Micro-Pillar Structure

The rapid development in the field of micro-quality inspection puts forward higher requirements on the sensitivity of the sensor device.Film bulk acoustic resonator(FBAR)has attracted wide attention because of its advantages of high sensitivity,small size,high resonant frequency,low power consumption,and integration with CMOS.FBAR can be used to make a micro-quality sensor with low-cost,mass production,real-time measurement.FBAR has shown broad application prospects in the fields of gas and biomolecule detection.Although the main advantage of traditional FBAR devices is its relatively high mass sensitivity.it is still difficult to meet the ultra-high requirements of sensitivity(100 pg/cm2)proposed by most biomolecule interaction analysis applications.In particular,when the sensor exposes in an environment with a small sample volume and a low target concentration,the biomolecules adsorbed on the sensor surface will be few and thereby difficult to be distinguished.Recently proposed methods such as reducing the thickness of piezoelectric films and mass enlargement have the problems of complex process,high cost and unfavorable mass production.In this paper,a scheme is proposed to improve the sensitivity of the coupled resonance system by adding a micro-pillar array on the upper electrode surface of the FBAR.The coupling resonance effect is used to increase the resonance frequency change of the FBAR,thereby the mass sensitivity of the FBAR will be improved.For one,this structure innovation increases the contact area and adsorption space of FBAR.For another,it has the advantages of low cost and easy operation.The content of this article mainly includes the following three points:1.Firstly,the working principle,basic structure and working mode of FBAR were described.Then,tacking the traditional longitudinal wave mode FBAR as the research object,the elastic wave equation was derived based on solid's acoustic characteristics and sound wave transmission characteristics,and the basic characteristics of the piezoelectric material and the coupled wave equation were studied.Finally,Two-degree-of-freedom mechanical model was constructed to theoretically analysis the feasibility of a coupled resonance system based on the principle of mechanical vibration and the law of motion.2.The theoretical model of traditional FBAR was established,and the FBAR electrode and piezoelectric film were optimized by the finite element method.Analyzing the influence of material and thickness of the electrode and the piezoelectric film on the device performance based on simulation and comparison.It was proved that with the same structure of the device,the quality factor of the device was higher when gold was used as the electrode material,indicating that the energy loss was smaller.There was a linear relationship between resonance frequency change and electrode thickness.When the piezoelectric film was aluminum nitride,the quality factor of the device reached 1053.The quality factor decreased with the increase of piezoelectric film thickness3.The finite element method was used to optimize the structural parameters of the micro-pillar array.Multiple sets of simulation experiments were designed to study the influence of micro-pillar array height,diameter,and spacing on the device performance.The results show that the micro-pillar height has a great influence on the resonance frequency,which in turn improve the mass sensitivity of the FBAR device.Plus,these conclusions also prove that it is feasible to form a coupled resonance system by the FBAR device and the micro-pillar array.When the micro-pillar diameter is too large,the quality factor of the device will decrease because of the influence of parasitic wave.The micro-pillar spacing had little effect on the resonance frequency and the quality factor.The mass sensitivity of the FBAR device can reach 5.295 KHz.cm2/ng,when the micro-pillar height is 0.114 ?m,the micro-pillar diameter is 5 ?m,and the micro-pillar spacing is 1.3 ?m.Compared with the traditional FBAR,the sensor designed in this paper has high quality sensitivity and low detection limit,which means that it can detect gas and biomolecule better.The simulation results show that the change of resonant frequency can be increased and the performance of the device can be improved by choosing the appropriate material and thickness for the electrode and piezoelectric film of FBAR.The coupling resonance effect is used to improve the quality sensitivity of the device by optimizing the structural parameters of the micro-pillar array.The ways provide a reasonable design scheme for FBAR device manufacturing.The FBAR device based on the micro-pillar structure has the potential for application in the field of micro-quality inspection.