Determination Of Mechanical Properties Of Thin Films Hanging In The Air Based On Bulge Test

Thin film is a kind of nanometer semiconductor material which has excellent mechanical,thermal,optical and electrical properties.At the same time,it has created the necessary conditions for the miniaturization and integration of the MEMS/NEMS devices.Thin film can often work as field effect transistors,thin film light-emitting diodes,protective layers,and window materials of solar cells etc.The suspended thin film structure comprises a linear one-dimensional suspended film and a planar two-dimensional suspended film.It is an important part of micro/nano-electro-mechaincal system(MEMS/NEMS)and has become frontier topic and research hotspot.Characterization of mechanical properties such as elastic modulus and residual stress of the thin film is the key to improve stability and reliability of the thin film device.However,due to the particularity in size,shape and structure of the impending film,many traditional testing device's the reliability needs to be verified or is no longer applicable,and it is necessary to establish new testing technologies.Firstly,the existing methods and the devices for measuring mechanical properties of thin films are reviewed.Then the principle of the testing method,experimental setup and the problems were introduced.Bulge test experiment equipment in conjunction with Michelson interferometry displacement measuring system was made,which overcomes the clamping problems of the tensile testing,and the substrate effect problems of the nanoindentation method.The proposed method can obtain many mechanical parameters at the same time by one testing.The application of optical interference and image processing technology make the system with high sensitivity,high resolution,no contact testing,simple equipment,easy measurement,and etc.To determine the mechanical properties of thin films by obtaining the relation curve of continuous bugling deformation and corresponding load,bulge test experiment equipment in conjunction with Michelson interferometry displacement measuring system was made.Firstly,the current status of bulge test methods for measuring mechanical properties of thin films is reviewed.Then the principle of the testing method,the design of blister experiment in the test is introduced.Lastly,finite element method was used to simulate the bulge test of the samples.To determine the mechanical properties of thin films,combining with proper mechanics model,the relation curve of continuous bugling deformation and corresponding load was obtained.In order to validate our method,Al thin films(purity:99.9%)were tested by our developed method.The elastic modulus E of the Al film was measured to be 68.6 Gpa,which is in an agreement with the given material reference values.It can thus be concluded that it is feasible to measure mechanical properties of thin films by our devised bulge testing setup.It is vitally significant for the application of our developed experiment setup to characterize thin films widely used in the field of MEMS/NEMS.