Studies OfMaterial And Designon Micromachined Gyroscope

In this paPer, the material and device related to micromachined gyroscope arepresented.In the joint project named "ElectrOfOrming Materials and ElectroformingTechnologies for Micromachined Sensors and ActUators" by Shanghai InstitUte ofMetallng, Chinese Academy of Science and General Motor Company, UnitedStates, FeNi alloys are selected as the eIectrOforming materials. The technology andmaterial properties of Fe-Ni electropl8tCd and electroformed dePositS arecomprehensively surveyed.Based on the analysis of electrodeposition conditions in Fe-Ni depositions, anovel electrOdePosition method is presenied, which can control the dePositedcompositions accurately. The qualities of dePOsits are very good and stab1e.A novel FeNi/CujSi comPosite canilever is made with the combination ofbulk-silicon micromaching technology and electrodeposition technology. Using thecomposite canilever, the intemal ffiction of Fe-Ni deposit is measured. The intemalffiction of Fe-Ni dePosit (Fe64%, Ni36%) is about l0-3 under resonant frequency247Hz and vacuum l0-2 Torr. This is the first report on the intemal friction of Fe-NidePosits. Average intemal stress of FeNi dePOsit increases with Fe contCnt uP to amaximum of about 300MPa at 64% Fe contCnt, then decreases with Fe content.Based on homemade load-defiection balance method, the Young's modulus ofcomPosite cantilever (Fe57%, Ni43%) is measured to be l.0.l0llN/In2. Thermalexpansion coefficients (TECs) of Fe-Ni dePositS decrease with Fe content down to a..minimum of about 6xl0--6/'C near the comPOsition of Invar alloy. TECs of Fe-Nideposits change with the same trends as those of bulk Fe-Ni alloys, although TECs ofFe-Ni deposits are higher than that of bulk Fe-Ni alloys near the Invar composition.The processes to sPread, exPose and deveIop the positive photoresist used fore1ectroforming metal are oPtimized. The photoresist moulds are made with thethickness of 30mp. Using quasi-LIGA technique the Fe-Ni microstruct'Ures are made.The released Fe-Ni microsmicfores without deformation are fabricated with thethickness of 30pm, width of l0-l5Um and length below 600llm. The microstructUresare parallel to silicon substrate with steep side walls, but its surface aPPearances areneed to be improved.The design of a novel micromacboed comb-gimbal gyroscope is presented forthe first time. Since the electrostatic comb driving and folded-beam smictUres areadopted, the large driving amP1itude can be achieved. The thickness and sensitivity ofgyroscope structure can be increased if the deep reactive ion etching(DmE)tecboque is used. The analysis shows that the comb-gimbal gyroscope has very highmechanical quality, because the effect of daxnping on its performance is small. Also,the dimensions of structure are ophmized. The fabrication sequences of thegyroscope except the DmE process are discussed in detail.