Research And Fabrication Of Ultra-thin Piezoelectric Crystal Resonator

With the rapid development of 5G communication and Internet of Everything sensing technology,the demand in the emerging consumer electronics market has greatly increased,and new requirements have also been put forward for the MEMS industry based on semiconductor micro-nano processing technology.Among them,film bulk acoustic wave resonator(FBAR)and surface acoustic wave resonator(SAW),as radio frequency MEMS devices,have always attracted attention.On the one hand,5G communication requires an increase in the working frequency of the resonator.Because the resonant frequency of the FBAR device is inversely proportional to the thickness of the piezoelectric film,the thickness of the piezoelectric film can be reduced to make it work at about 5GHz,which greatly reduces the size of the device while at the same time It meets the requirements of 5G communication;on the other hand,the sensing technology based on the 5G Internet of Everything also requires an increase in the range of the strain sensor.The size of the SAW device is comparable to the acoustic wavelength of the signal,so it can be prepared on an ultra-thin quartz wafer The SAW strain sensor not only realizes the ultra-miniaturization of the device,but also increases the strain sensing range to 5000 ??,which is 12 times that of the previous generation SAW strain sensor.In this paper,innovative researches on FBAR and SAW are carried out.Ultra-thin single crystal lithium niobate(LiNbO3)and quartz are selected as the corresponding piezoelectric layer materials,and the development of high-frequency FBAR based on ultra-thin single crystal LiNbO3 is proposed.Flexible SAW strain sensing technology of ultra-thin quartz.The main research contents and current results are as follows:1.Establish design methods for ultra-thin FBAR devices and SAW devices,use finite element software to design FBAR devices and SAW devices through theoretical methods such as piezoelectric equations and wave function analytical calculations,model simulation calculations,including structural design and material selection.2.Research on the preparation process of ultra-thin lithium niobate FB AR,design the structure according to theory,and study the preparation process technology of ultra-thin FBAR.Firstly,based on the piezoelectric material lithium niobate research,the standard stress stripping method was used to obtain the process flow of single crystal LiNbO3;secondly,the back-etched structure based on the LiNbO3 piezoelectric film and the solid-state assembly structure were prepared using the micro-nano processing platform.FBAR device;the resonant frequency of the device measured by the network analyzer is about 5.09GHz and 4.5GHz respectively,which is consistent with the simulation analysis.The Q value of the FBAR device with the back-etched structure exceeds 1800.3.The preparation scheme of flexible SAW based on ultra-thin quartz piezoelectric layer is proposed,and a SAW strain sensor with stable performance and multiple application possibilities is obtained.Firstly,the feasibility of ultra-thin SAW was verified through theoretical analysis;secondly,the preparation of 31?m ultra-thin quartz SAW devices was realized by using deep reactive ion etching and photolithography sputtering stripping process without destroying the performance of piezoelectric film;finally The measured resonance frequency is 156.16MHz,the electromechanical coupling coefficient(kt2)is 1.4%,the hysteresis is less than 0.43%under the linear strain range of 5000 ??,the sensitivity is 186.2 Hz/??,and the temperature coefficient of frequency(TCF)is stable at-1.06 ppm/?,has a huge advantage in the field of strain sensing.