Study On Electromechanical Fa-Tigue Simulation And Reliability Of Movable Micro/Nano Devices

In the era of artificial intelligence and Internet of Things,micro and nano devices(MEMS/NEMS)are the main hardware forces in this information revolution war,undertaking a series of important tasks such as information monitoring,transmission and recording.The 5G network information era has accelerated the development of artificial intelligence and Internet of Things revolution,but the contradiction between mature IC preparation and advanced conceptual design and device reliability has greatly slowed down the advance of devices from laboratory to market.In this paper,the functional failure and fracture failure of microelectronic devices under mechanical load and thermal-mechanical load are studied by using the theory of damage and fracture mechanics.Of three kinds of typical devices as cases study,the electro-mechanical fatigue damage modeling analysis of flexible electronics interconnections,thermal fatigue performance simulation analysis of MEMS thermal actuators,fatigue failure simulation analysis of MEMS polycrystalline silicon resonators,and the reliability analysis of zero-power micro/nano switch sensors are carried out.The main research results of this paper are as follows:(1)The fatigue reliability analysis method of a kind of microelectronic devices(flexible electronic devices)with mechanical fatigue loading failure is discussed.Based on continuum damage mechanics theory,fatigue damage models of microcrack evolution for two grain fracture mechanisms of small scale metal films were established respectively.Considering the resistance degradation mechanism of small scale thin films,a resistance degradation model caused by mechanical fatigue damage was established,and the relationship between the resistance change of silver and copper films with thickness of 100nm-1000 nm and the increase of loading times under different strain tensile loads was analyzed.Several groups of experimental data were fitted with the established model,and then the model parameters were inverse calculated,and the fatigue life of the device was predicted.(2)The fatigue reliability analysis method of microelectronic polysilicon thin films under mechanical fatigue loading was discussed.Based on the existing observation test,data were analyzed.For the first time,using the continuum damage mechanics method to represent MEMS resonators damage and the microcrack evolution model was developed.At the same time,considering the common effects of oxidative damage and mechanical damage,a polycrystalline silicon resonant frequency of the resonator degradation model was further established.The fatigue damage distribution was simulated by jump-in-cycles algorithm,and the frequency variation of comb resonator was calculated.The microcracks of comb-tooth resonator were determined by damage simulation.(3)The fatigue reliability of movable micro/nano devices under thermo-mechanical coupling loading was studied.Based on the thermodynamic framework,the thermodynamic constitutive equation with damage was derived.Taking the micro/nano thermal actuator as a case study,the creep damage model of the device under thermal loading caused by structural defects and material properties was established by using continuum damage mechanics.Considering the thermodynamic coupling behavior under fatigue condition,a set of effective thermodynamic coupling calculation method was proposed.The damage was introduced into the thermodynamic constitutive equations of the material.The fatigue cyclic block algorithm was used to calculate the change of thermal performance under long-term load.The damage distribution of the thermal actuator was obtained by finite element simulation,so as to determine the maximum position of irreversible deformation.(4)The fracture mechanics problem of damaged films was solved.Considering the damage of thin film,the damage model was established and substituted into the constitutive equation to determine the effective stress.The semi-inverse method and the indirect Trefftz method were used to derive the plane fracture problem of rectangular plate with central crack,and the direct Trefftz method of piezoelectric rectangular plate was used as numerical method to solve the plane and anti-plane fracture problem of(piezoelectric)thin film.The stress intensity factors and energy release rates of several different boundary conditions were derived.For the first time,continuum damage mechanics combined with boundary element numerical method was used to solve fracture problem with material damage.The effects of crack location and film geometry on crack propagation were studied.The results were verified by comparison with analytical solutions,and more accurate solutions were obtained than ideal linear elastic fracture mechanics method.(5)The fatigue reliability of a new type of micro/nano switch sensor is investigated.First,based on the existing sourcemeters,electronic devices,microprobe,computer and Labview software,using Labview software to compile the fatigue loading program,and record the fatigue data.The specimens were scanned by electron microscope,and the fatigue reliability was analyzed qualitatively based on the fatigue data.Furthermore,wear fatigue modeling and analysis were carried out on the surface of contact head of micro/nano switch,and the three-dimensional wear problem was simplified to the one-dimensional defect evolution problem.A resistance degradation model was established by using damage mechanics method.At last,the fatigue reliability of the device was qualitatively evaluated based on the theoretical analysis in previous chapters.