| Metal film interconnects are widely used in flexible electronic devices.The characteristic size of metal film interconnects has been reduced to micron and submicron.Thin films of flexible electronic devices are subjected to high current density,high temperature and cyclic thermal strain during the service process.Mechanical fatigue,electromigration and thermal fatigue are affected by the combined mechanical,electrical and thermal fields,which seriously affect the service reliability of flexible electronic devices.At present,most studies only consider the effect of single physical field on the fatigue properties of thin films,which are quite different from the actual service environments of metal films on flexible substrates.In order to solve the above problems,a fatigue model of metal film on flexible substrates in multiphysics fields is established,which provides new analysis and calculation methods for the degradation analysis of fatigue performance and service reliability evaluation of metal films in multiphysics fields.The main work and research results are as follows:1.According to the actual service environment of flexible electronic devices,the combined effects of mechanical field,electric field and temperature field are considered to affect the fatigue properties of metal films.Based on the continuum damage mechanics theory,damage of metal films is characterized from two aspects: deteriorations of mechanical properties and electrical conductivity.By introducing the effect of electric field and temperature field into the Coffin-Manson relationship,the law of fatigue accumulation of metal films considering multiphysics fields is established.2.Neglecting the influence of the microstructure of the material on the deformation,the metal film is regarded as a continuous,homogeneous and isotropic material.Based on COMSOL Multiphysics platform,the finite element model of fatigue properties of metal films in multiphysics fields is established.Based on the model,the response of copper film under different load conditions is calculated,and the influence of electrothermal behavior on the fatigue properties of copper film is analyzed.The results show that due to the weak effect of electrothermal behavior the fatigue life of thin metal films has almost no change;For thicker films,the effect of electrothermal behavior is strong,which can result in a significant decrease in fatigue life.3.The degradation of mechanical properties of metal films caused by damage is ignored,and the degradation of conductive properties of thin films is only considered.The fatigue damage analysis method for flexible electronic metal films is proposed.Taking 0.7μm thick copper films as an example,the degradation process of electrical properties of thin films caused by cumulative fatigue damage in multiphysics fields is simulated and analyzed.The results show that the effect of electric field and temperature field will aggravate the damage of the film,which can lead to early failures of metal films.In summary,a finite element model of metal film on flexible substrates in multiphysics fields established in this paper can introduce the influence of multiphysics fields in the actual service environment of the metal films,and simulate the mechanical behavior of the thin films under the coupling of multiphysics fields.The proposed fatigue law of metal films considering multiphysics fields can describe the degradation of fatigue properties and predict the fatigue life of thin films in multiphysics fields.The fatigue damage analysis method for flexible electronic metal films is proposed,and the degradation of electrical properties of thin films caused by damage accumulation in multiphysics fields is simulated and analyzed.The above work can make the fatigue degradation and reliability analysis of the metal films more in line with the actual situation,and provide reference for the evaluation of the service reliability of flexible electronic devices in multiphysics fields. |
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