Research On High Quality Factor Piezoelectric Micromechanical Resonator

The micromechanical resonator is a type of acoustic resonator designed and manufactured based on MEMS?Micro-Electro-Mechanical Systems?technology.Compared with traditional electrical resonator,the size of micromechanical resonator can be greatly reduced,and it also has the advantages of low power consumption and integration with CMOS circuits.Therefore,with the trend of miniaturization and high integration of electronic equipment,micromechanical resonators have broad application prospects in the fields of sensors and wireless communication system.However,the low quality factor of piezoelectric micromechanical resonator severely limits its practical application in various fields,because resonator with high quality factor is the core device of low phase noise oscillators,high sensitivity sensors and narrowband filters.Based on this,in order to promote the practical application of piezoelectric micromechanical resonator,it is necessary to research high quality factor micromechanical resonator.Among various types of piezoelectric micromechanical resonators,this article mainly studies the thin-film piezoelectric-on-silicon?TPoS?structure because it has high electromechanical coupling coefficient and can achieve multi-frequency output on a chip.The anchor loss generated during the electromechanical conversion process of TPoS resonator is the main reason for low quality factor.In order to improve the quality factor by reducing anchor loss,this article has made an in-depth study of the phononic crystal,because the acoustic band gap generated by the phononic crystal can prevent the propagation of acoustic waves.So,placing the phononic crystal in a suitable position on the resonator can significantly reduce the anchor loss.Specific research contents include:Firstly,this article designed and fabricated a one-dimensional bulk phononic crystal integrated on the tethers of resonator.By simulating the bandgap structure of the phononic crystal,it is verified that there is a part of the acoustic bandgap at the resonance frequency,which can prevent the propagation of acoustic waves in some specific directions.Then,by analyzing the test results,it is proved that the part of the acoustic bandgap can improve the quality factor of the resonator by about 2.8 times,but the improvement is slight.Therefore,by optimizing the structure of the phononic crystal,a one-dimensional cross-type phononic crystal with low frequency and small size and wide band gap characteristics was designed.Through simulation verification,the complete bandgap of the one-dimensional cross-type phononic crystal contains the resonant frequency,which can significantly improve the quality factor of the resonator,Q_ancnc increased from 10,100to 404,000.Secondly,this article proposed a strategy to suppress anchor loss by integrating the two-dimensional phononic crystal array on the resonant body.Through simulation analysis,the placement and number of two-dimensional phononic crystal arrays on the resonant body are studied in detail.In addition,by simulating the displacement distribution of the resonator and the S21 transmission characteristic curve,it is proved that compared with the traditional design method of placing a two-dimensional phononic crystal array on the substrate,the proposed strategy not only improve the quality factor of the resonator by about 3 times,but also don't increase the area of the entire device.In summary,this article mainly studies the structure of the one-dimensional phononic crystal tether and the two-dimensional phononic crystal array on the resonant body to improve the quality factor of the TPoS resonator.It is verified that the proposed structure can effectively improve the quality factor of the resonator through theoretical analysis,simulation and test.Through theoretical analysis,simulation design and experimental testing,it is verified that the proposed structure can effectively improve the quality factor of the resonator.