Study On Design Principle And Fabrication Process Of Micromachined Butterfly Gyroscope Drived By Tangential Electrostatic Force

Gyroscope is a sensor for rotation measuring,which is an important part in inertia navigation system and has been applied in many military and civil fields.Compared with traditional gyroscopes,MEMS gyroscope has advantages in size,power dissipation,integration and batch fabrication process,presenting the potential in aerospace,unmanned systems,consumer electronics,and high performance MEMS gyroscope products have already been developed aboard.While,the products and technologies are embargoed,forcing us to develop high performance MEMS gyroscope with our own intellectual property.So,design and develop high performance gyroscopes have strategic importance in breaking the monopoly.MEMS butterfly gyroscope has been studied by our group for several years,and many achievements have been made.Now,the butterfly gyroscope is excited by normal electrostatic force,forcing the vibrating mass to vibrate along tangential direction as well as normal direction.Thus,sensitivity cannot be improved by increasing the amplitude of drive mode and decreasing the air gap,simultaneously,which will limit the performance improvements seriously.Therefore,a modified butterfly gyroscope excited by tangential electrostatic force is proposed,and the basic working principles,design and fabrication of the structure,error analysis are studied in detail.1.Basic working principle.Firstly,the normal electrostatic force excited butterfly gyroscope was present,and the restrain effect between drive mode amplitude and air gap was analyzed.Then,the modified structure excited by tangential electrostatic force was designed,and the bending and torsional stiffness of the rectangle beam were analyzed.After that,dynamic performances of the gyroscope were analyzed,showing advantages in mechanical sensitivity improvement and thermal mechanical noise reduction of the modified structure.Finally,working principle of the readout circuit was introduced.2.Structure design.The driving comb was designed,including distribution and size of the comb.Then,key sizes of the structure were obtained based on the mode frequency simulation,and amplitude of drive mode was achieved.Finally,“TGV-silicon-TGV” sandwich structure based on glass reflow process was designed.3.Key fabrication process.Fabrication process of the gyroscope was designed and the key fabrication process was studied.After fabrication process optimization,the etching quality of silicon structure and TGV substrate were improved.Finally,three layers anodic bonding process and wire bonding method were studied.4.Error analysis.The influence of structure errors on mode frequencies were analyzed,including depth error of the silicon wafer,size error of the rectangle beam,vertical deviation of the rectangle beam.Normal electrostatic force error was analyzed,restrain effect of the sandwich structure on normal force error was studied.Temperature error on sensitivity stability was analyzed,and the restrain method was studied.Finally,nonlinear error on drive mode amplitude was studied.5.Performance measurement.Drive and sense mode resonant frequency of device level packaging structure are 3268 Hz and 3477 Hz,and quality factor are 14296 and 4084,and scale factor increases 19 times.Air tightness of wafer level packaging structure is tested and the value reaches between 200 Pa and 240 Pa.