Experimental and modeling study of CO2 laser writing induced polyimide carbonization process

The emerging technique of direct laser writing carbonization (DLWc) of polymers, such as polyimide, receives great attention for its flexibility, versatility, and ease-of-patterning capability in creating a variety of functional materials and devices. To fully take advantage of this novel method for consistently fabricating different types of functional devices, it is necessary to understand the complicated photo-thermal conversion and heat transfer process involved in DLWc. In the present study, we focus on the carbonized dot features created by DLWc on a polyimide substrate to address this issue and investigate its implications on the related processing-structure relationships. Both experimental and theoretical results reveal that the laser power, irradiation duration and the extent-of-focus all have significant effect to dictate the size, morphology and porous structures of the carbonized features created by DLWc. The Gaussian beam characteristics of the laser source used in DLWc is responsible for the highly localized and non-uniformly distributed heating source density that causes the finally formed carbon structures with strong composition/morphology gradients. The no-free-parameter photo-thermal model and its FEA implementation presented in our study offer a platform for better understanding, controlling and optimizing the complicated but highly promising DLWc technique.