Some Microelectromechanical Systems And Related LIGA Techniques

With the MEMS sensors widely applied in fields of physics,chemistry,biology and medicine,etc.,the related microfabricaton technology has become a hot point in the current micro-system research.The micro-processing technology of MEMS relates to micro-electronics,materials,physics(mechanics and fluid mechanics,etc.),chemistry, biology,mechanics and many other subjects,it is the product of multidisciplinary subjects.All of the parts in MEMS devices are produced almost at the same time using micro-electronics and micro-machining technology under overall consideration, the parts and the systems are closely linked,it is a top-down approach.Therefore,the developments of MEMS devices require new concepts and have to be designed and manufactured in the system-level.Since the demands of micro structures with high aspect ratio in micro systems, the LIGA process has the potential to become a popular technique in microfabrication fields.Unlike the micro-electronics technique,the micro-machining technology has to be specific during three-dimensional micro-processing,to overcome the effect of high aspect ratio,and sometimes it also has to be compatible with integrated circuit technology.It is necessary for researchers to make great efforts to solve this series of problems,and develop and improve MEMS manufacturing technology.For every specific MEMS device,there is a separate micro-machining process required to be designed,and the parameters in every process step are needed to be re-explored and determined to meet the demands of special performance of the microstructures.In order to investigate the micro-machining processes in detail and summarize some MEMS design rules,and furthermore to develop the MEMS products with high aspect ratio structures,and do the corresponding performance evaluation and analysis,the main thesis works are carried out in the following areas:1.Improve the X-ray lithography and ultraviolet lithography processA high-precision synchrotron radiation mask fabricating methods is developed by using the silicon substrate fenestration.The microstructures with high aspect ratio are successfully obtained by using X-ray lithography technology and ultraviolet lithography technology.The processing details in UV lithography technique and SU-8 thick resist technique are studied in detail,the inner stress in SU-8 resist structures is reduced effectively by the low-temperature post baking,and the developing efficiency of micro structures with high aspect ratio is obviously improved by using megasonic agitation assistance.2.The application of thick sacrificial layer of zinc in LIGA processThe zinc electrochemical depositing process,the effects of the seed layers to the adhesion of sacrificial layer on silicon substrate,and the release process of the sacrificial layer,are investigated in detail.And the thick zinc sacrificial layer process is developed to be a mature sacrificial layer technology.The zinc sacrificial layer technology is also introduced into the fabrication of the weapon's fuze device,and some microstructures used in the plane frame insurance device are successfully obtained.3.Micro electroforming with utmost high aspect ratio structuresThe micro electroforming technique with utmost high aspect ratio structures is explored in the experiment;the effect of metallic ion transmission condition in the electrolyte to deposition status is studied.A very high aspect ratio metallic structure is obtained successfully by using megasonic agitation assistance which effectively improves the transmission ability of metallic ion in the electrolyte.4.Fabrication of nickel base composite microstructures with Al₂O₃ nanoparticlesIn order to deposit the alumina nanopartMes uniformly in the composite micro structures and obtain the composite microstructures with good distribution of the alumina nanoparticles,an effective and low cost spraying assistance circulation system is set up in the experiment to improve the dispersing and depositing condition of the nanoparticles in the electrolyte.The analysis on the micromechanical hardness and wearing property shows that the composite components' hardness are improved form HV_0.2 300to HV_0.2 500 compared with pure nickel components,their wearing resistance are also increased nearly 100 percent,and the average compressive stress reaches 960Mpa.The micromechanical properties of composite components are significantly improved in comparison with the pure nickel components.The hydrokinetic flow field during the spraying assistance deposition process is also simulated presumably by using hydrokinetics finite element analysis.The simulated results also show that the spraying riptides in electrolyte would be helpful to promote the nanoparticles to disperse in the electrolyte and deposit onto the cathode uniformly. 5.Fabrication of micro acceleration trigger switch combined with LIGA /UV-LIGA technology and thick zinc sacrificial layer technologyA cantilever-type micro acceleration switch is fabricated successfully by using the X-ray deep lithography process,combined with thick Zn sacrificial layer technology developed in this thesis.The electroforming defects in plating very high aspect ratio microstructures are studied,and the yield of the microstructures is counted and analyzed.On the basis of these experimental data,the design of the microstructures and the fabrication process flow are optimized,and the micro acceleration switch samples with high aspect ratio structures are fabricated.The movement testing results of the microstructures shows that the micro system accords with the design requirements.A spiral type micro-acceleration switch is fabricated successfully by using the ultraviolet lithography technology,combined with SU-8 thick photoresist technique. The properties of sacrificial layer materials are analyzed and experimented to solve the desquamating problem of microstructures,and through process optimization,the planar micro spiral spring structures are obtained.The test results of the switching threshold(1g～10g) and the elasticity coefficient(140～200μN/nm) show that the microstructures accords with the designer's demands of the low frequency response.6.Development of millimeter-wave rectangular accelerating channel.A millimeter-wave rectangular accelerating channel with complex internal cavity is fabricated successfully by using the UV-LIGA technology,combined with multi-layer SU-8 lithography and microelectroforming process.The micro-machining process of SU-8 lithography,SU-8 pyrolysis removal,and internal cavity ultrasonic cleaning are studied in detail.