Researches On Vibration Theory And Experiment Of Thin Film/substrate Structure

With the rapid development of modern science and technology,all kinds of highly integrated and multi-functional industrial products have been manufactured.The thin film/substrate structure as the key component of the above application,it has become one of the research hotspots and it has been widely used in the fields of microelectronics,optics,physics and materials science.Specially,the thin film/substrate structure in the integrated circuit,micro-electromechanical systems(MEMS)and other micro-device applications greatly promote the development of human society.The thin film substrate materials are usually composed of nano scale thin-films and micron scale substrates and the overall structure is quite simple.However,strain mismatch between the film and the substrate due to interfacial misfit strain and the deformation of thin films caused by the non uniform temperature distribution,both of them had become the important research directions in field of mechanics.As early as 1909,Stoney established the relationship between the stress and curvature of the film,thus laid the basic framework of thin film stress research,that is,by measuring the curvature of the film to calculate stress distribution of the whole field.Later,a large number of scholars through the relaxation of Stoney basic assumptions to achieve the expansion of the Stoney formula,but as of now these studies are mainly considering the film in the quasi-static state of the mechanical behavior,while the vibration characteristics of thin film/substrate structure rarely involved that it has been become a difficult problem for the safety design of the thin film/substrate.To solve this problem,in this thesis,the free vibration equations of the thin film/substrate structure under axisymmetric and non axisymmetric conditions are established and the analytical expression of the film stress on the curvature is obtained.Then,taking the high temperature superconducting thin film as an example,the temporal evolution of the full field stress of superconducting thin films was abtained for the first time,which by using the Coherent Gradient Sensing(CGS)technique in the low temperature environment and then according to the theory of film stress-curvature that deriving from this thesis,and it provides a basis for further study of the mechanical response of superconducting films in electromagnetic fields.The works of this paper are listed as follows:(1).By analyzing the film substrate interface shear stress,the free vibration equation of the thin film/substrate structure under the axisymmetric condition is established.The analytic expression of the film stress-curvature is obtained.We also discussed the deflection mode shapes and corresponding solutions of natural frequencies.(2).By considering the film substrate interface shear stress,free vibration equation is established at the film substrate structure axisymmetric case.In this thesis,the expression of thin film displacement,stress and interface shear stress are obtained,meanwhile,the theoretical relationship between of film stress and curvature is given.(3).Using the Coherent Gradient Sensing technique at low temperature,the full-field curvature change of the superconducting thin films caused by the electromagnetic pulse was measured.Using the theoretical relationship of the thin film and the curvature derived from this thesis,we first obtained the full-field stress varied with time about the superconducting thin films.At the same time,this thesis makes a correlation analysis and discussion on the measurement results.