Research On Rate Dependent Effects And Cohesive Zone Model In Transfer Printing

The ability to pick up functional elements and devices fabricated onsemiconductor wafers and place them safely onto flexible or curvilinear surfaces inefficient and low-cost way is of increasingly high demand in microelectronictechniques such as large-scale integration, wearable electronic devices and flexiblesolar cells. The kinetically-controlled transfer printing method (KCTPM) based onthe rate dependent adhesion of the stamp/device interface is easy to implement andlow in cost. This method is promising to become the mainstream solution that meetsthe demand mentioned above and therefore attracts intensive attention.Experiments in which silicon ribbons are etched on SOI wafers and peeled awayby a PDMS stamp is conducted. The results show that transfer efficiency increaseswith the peeling velocity. Cohesive element modelings are conducted to simulate thisprocess. The simulation results show the distribution and evolution of Mises stressin the Si ribbons during peeling and yields the relation between transfer efficiencyand peeling velocity, which is in good qualitative agreement with experimental results.In addtion, the simulatios also indicate the influences of viscoelastic parameters of thestamp on the transfer efficiency, which decreases with the instantaneous relaxationmodulous and increases with the relaxation ratio, while the relaxation time has nodistinguished effects on the transfer efficiency.Two mechanism of the angle dependency of interface fracture energy in peeltests are discussed. The first is that at the same peel velocity, the viscous dissipationzone grows when the peel angle increases, leading to the increase of interface fractureenergy, which if verified by FEM simulations. However, the mode-mixed fractureenergy is not taken into account in FEM simulations. The second mechanism is thatthe intrinsic interface fracture energy is mode-mixed. Peel test of PP tape-arcylicadhesive/PMMA indicates that under the same peel velocity as the peel anglebecomes larger, the interface fracture energy increase initially and then fall down andreaches its peak at90degree. The relation between the intrinsic interface fracture energy and peel angle takes the same form. These experiments verified the secondmechanism and discloses the complexity of angle dependent interface fracture energyin actual situations.Finally, the relation between the peel force of elastic peel arm/rigid substrate andpeel angle, peel arm geometry and mechanical properties as well as the cohesive lawis deduced. Based on this relation, a cohesive parameter identification framework isproposed, which is the fundamental of a method to identify the cohesive parametersdirectly from peel test results in the future.