Research On Simulation And Fabrication Of FBAR Filter

With the rapid growing of mobile communication technology RF filter has been the fastest developed core module in the RF front-end chip.The fifth generation of mobile communication(5G)driven the huge eager for filters with small volume,high power capacity and excellent performance.The film bulk acoustic resonator(FBAR)filter exhibits good and reliable transmission performance,reduced in size and power,ability to integrated to CMOS circuit,which is considered as the best solution of filter in mobile communication terminal like cellphones and tablets.A few companies had made worldwide success in commercial FBAR filters that based on polycrystalline AlN film playing as piezoelectric.Researchers purpose to develop the wideband filters working on higher frequency.To cope with these demands for high frequency and high power capacity,piezoelectric films below to several hundred nanometers but stable in mechanical structure and released stress are required.This study proposed an innovative process route,researched on film deposition,photolithograph,dry &wet etching process in micromachining technology(MEMS),subsequently fabricated FBAR chip and tested its transmission performance.In addition,we established equivalent circuit model and finite element analysis method of FBAR.This research study focus on 1D and 3D simulation,device processing and on-chip testing,achieved such results and innovation as follows:Firstly,we utilized goal and optimization in ADS(advanced design system)software to adjust each resonator's thickness and area in 4th-ladder FBAR filter schematic.We built the 2D and 3D modeling of FBAR by COMSOL and simulated potential distribution and displacement characteristic,contrasted admittance grids to 1D modeling by ADS as well.Furthermore,we come up with the bonding and flip process that exploited monocrystalline AlN film as piezoelectric material,taking advantages of its low mechanical loss and thermal loss.In practice,we solved the large residue stress problem that make AlN/Si hard to machine,and discussed the AuSn bonding condition.We found titanium as barrier metal,a substitute for platinum,researched on mixed acid wet-etching and ICP(induce coupled plasma)etching process to release rest silicon substrate.Eventually,we tested the impedance properties of Ti/AlN/Si films and the transmission curves of the finished air-gap FBAR.The results show response but the process still remains to be improved.