柔性可延展电子有转角印戳转印的力学机理与模型研究

Transfer printing is the key technology used to fabricate eletronic devices. The challenge for high-yield and efficient transfer printing is to use the same stamp for both inking and printing, which have contradictory requirements of strong and low adhesions, respectively. Inspired by the oriented adhesion of Gecko feet, angled stamp, a new type of stamp with tilt angle, will be adopted to make transfer printing in a high-yield and efficient manner with the same stamp by applying shear displacement in different directions during inking and printing, respectively. Theoretical and experimental studies as well as finite element analysis will provide insights into the basic mechanism of adhesion. The experiments of adhesion of the interface between the stamp and electronics device will be performed. The mechanical mechanism of adhesion and peeling off between the stamp and electronic devices will be investigated based on finite deformation and viscoelasticity theories. Then the critical criterions of adhesion and peeling off and critical condition during different finite deformation stage of hyperelastic stamp will be established. The law, reflecting the influence of the geometric parameters of angled stamp and the lateral shear displacement on the adhesion between stamp and electronic devices, can direct the geometric parameter choices for stamp and loading control. Finally, the mechanical model of angled stamp transfer printing, which will be validated by experiments and can describe the finite deformation and viscoelastic characteristics of stamp during transfer printing, will be established. The research results are beneficial to improve the yield and efficiency of transfer printing and to promote the commercialization of flexible and stretchable electronics.

转印是制备柔性电子器件的关键环节。为了提高转印的效率和成功率，必须解决好上墨和印刷过程中印戳/电子元件界面粘附作用由强到弱的转换。受壁虎脚掌定向吸附机理的启发，本申请项目将采用一种具有倾斜角度的新型印戳，在上墨和印刷中沿不同方向施加剪切载荷，从而通过同一个印戳实现高效率的转印。拟采用理论分析、试验和有限元分析相结合的方法，开展印戳/电子元件界面粘附力的试验研究，基于有限变形理论和粘弹性理论分析超弹性印戳与刚性电子元件粘附、剥离的力学机理，建立粘附和剥离的临界准则，明确超弹性印戳有限变形不同阶段的临界条件；揭示印戳几何参数及横向剪切载荷对印戳/电子元件界面粘附力影响的规律，为印戳的参数选择和载荷控制提供理论依据，最终建立经试验验证的、能够反映粘弹性印戳的有限变形特征的有转角印戳转印的力学模型。研究成果对于提高转印的效率和成功率，促进柔性可延展电子的实用具有重要意义。

本项目开展了无倾角印戳/薄膜界面以及有倾角印戳/薄膜界面粘附力的试验研究，获得了不同剪切位移作用下的界面粘附力。开展了印戳超弹性大变形本构模型的研究，发现二阶Ogden模型的模拟结果与实验结果最为接近。基于粘弹性断裂理论，以G=Gc 作为判据，进行了印戳几何参数对印戳/电子元件界面粘附力影响的力学机理的研究，研究了剪切载荷辅助转印中印戳粘弹性特性对转印机理的影响，并且分析了有转角印戳的几何形状对界面粘附力的影响。研究发现有限元计算的印戳和电子元件界面粘附力在有横向剪切位移时与试验结果存在较大差距。为此，基于转印中印戳/基底界面的粘附作用源于范德华力这一认识，建立了基于范德华力的印戳/薄膜界面内聚力模型，该模型表明印戳和薄膜间只有法向作用力，切向作用力为零，由此建立了由弹簧元表示的界面断裂力学模型，此模型与传统的界面断裂准则不同。基于新型断裂模型建立了转印力学模型，对于提高转印的效率和成功率，促进柔性可延展电子的实用具有重要意义。建立的内聚力模型除了应用于本项目转印力学模型的建立，还可应用于微纳制造、生物力学及仿生力学（特别是生物粘附）领域力学机理的分析。