Multi-laver Encapsulation And Viscoelastic Effect Analvsis For Flexible Electronics

Stretchable/Flexible Electronics combines the electronic performance of conventional wafer-based semiconductor devices and mechanical properties of a rubber band, and thus would have a wider range of applications than the current hard, planar integrated circuits. For non-coplanar film/substrate structures, the research work which combined theoretical and computational efforts in this paper is finished from three aspects:Firstly, In order to reduce degradation of stretchability, we proposed a multi-layer encapsulation design and investigated the stretchability. This design was achieved by adopting Polydimethylsiloxane (PDMS) with different mechanical properties near the upper and lower film surfaces. By simplifying the structure of film, upper and lower encapsulation layers to tensile-bending composite beam, the influences of thickness, elastic modulus and other related parameters of the layers on the overall stretchability are analyzed by Finite Element Method (FEM). The results show that the upper encapsulation layer with high thickness or\and low elastic modulus is benefit to improve the stretchability. Meanwhile, the stretchability can be considerably improved when the lower layer’s modulus is moderately higher than that of the basic encapsulation material and the thickness is suitable. Nevertheless, the stretchability may decrease significantly when the lower layer’s modulus is too high or the thickness is too large.Secondly, it is the first time that researcher in this field took into consideration inclusion existing in the encapsulation layers and discussed the effects on the mechanical properties of non-coplanar film structures. We discussed the inclusion effect on the stretchability of flexible electronics structures from three aspects:the stiffness of inclusion, the position of inclusion and ways of encapsulation. The finite element results show that when the stiffness of inclusion increases, the maximum strain of bridge strengthens, but the maximum stretchability decreases up to30%:As the depth of the inclusion increases, the whole strain level of local bridge top area increases and the maximum stretchability of the bridge reduced about20%; Compared with the hard encapsulation, the same inclusion in the soft encapsulation has the larger influence in weakening the maximum stretchability.Finally, we investigated the influence of viscoelasticity of substrate and encapsulation materials on the stress and deformation of thin film during dynamic stretching. Meanwhile, to represent the degradation of stretchability we proposed a non-dimension function and obtain its curve versus stain rate. When the ratio of the maximum instantaneous young’s modulus of encapsulation materials and substrate materials induced by dynamic load becomes larger, the maximum principal strain becomes larger but the height of the film decrease smaller:the maximum principal strain and the height of film decrease gradually until the status of static loading during the stage of relaxation.The results in this paper have important theoretical and practical significances for the design and safe use of non-coplanar film/flexible substrate structure.