Experimental Study On Fracture Damage Of Polyimide-supported Nanometric Films With A Transition Layer Under Biaxial Tension

SSIF(Soft Substrate Interlayer Film)structure is widely used in thin film transistors,flexible electronic components,aerospace,biomedicine and other fields,due to its high flexibility,ductility,high efficiency and low cost.Compared with the single-layer thin film structure,the SSIF structure improves the mechanical properties of the structure,and deeply affects the damage behavior of the membrane structure.The SSIF structure is subjected to more complex loads during its service life,which results in the phenomena such as debonding,buckling and fracture of the thin film,which affects the service life of the device and bring loss to the application of the structure.In order to simulate the actual application environment of structural components,the biaxial load state is closer to the actual force of the device.Therefore,it is very important to study the fracture damage of SSIF under biaxial load.In this paper,the experimental specimen is designed based on the homogeneity of strain in the central region of the biaxial tensioned cross specimen,and the size of the uniform strain region under different loading ratios is given.At the same time,the mold of independent research has a simple molding operation,low cost,compact structure,high precision and mass production.The SSIF structures with different structures were prepared by magnetron sputtering using a PI substrate.According to the experimental requirements,a biaxial tensile system was designed and developed.The system has many advantages,such as large range,small increment,high precision,low cost,adjustable loading ratio and centering loading,etc.,And can cooperate with measurement of micro-scale film in situ.The load device is mainly through the single-chip microcomputer control two stepper motor synchronous drive lead screw,and through the mechanical transmission system to achieve the variable ratio biaxial loading of the specimen.And the displacement and force are measured by S-sensor and dial gauge.This paper describes the working process of each component,data collection and the use of load ratio adjustment device.The experimental device has been verified by experiments to meet the micro-nano-scale film material measurement,with a certain reliability.The influence of different loading ratio and Poisson ratio of interlayer on the biaxial stress ratio and its transfer is analyzed by finite element method.The fracture behavior of the upper layer was observed under high power optical microscope,and the crack morphology under biaxial tensile loading was studied.And the crack morphology under different loading ratio and different film structures were analyzed.Finally,the crack angle of the secondary crack is analyzed by the minimum strain energy density factor theory.