A Study Of The Micro Thermal Imprint Process Based On Amorphous Polymer

As one of replication manufacturing technologies of micro-/nano-pattern, thermal imprint process takes many advantages in manufacturing cost, efficiency and resolution, compared to other traditional MEMS (Micro-Electro-Mechnical Systems) techniques. Products fabricated by thermal imprint process have wide range application potential in many areas such as bio-chip, chemical microfluidic chip and optical devices. Thermal imprint process is now attracting more and more attention in the research field and becoming a focal point in the micro-/nano fabrication area. With increasing demands from the market and industrial mass production, it is necessary to have a throughout understanding of the flow behavior of amorphous polymer material near the glass transition temperature region and the relationship between process parameter, material character and final replication quality.In this thesis, flow behavior of amorphous polymer with the change of temperature is studied and viscoelastic material model of amorphous polymer near the glass transition temperature is established. Finite element model of flat-pressing type thermal imprint process is developed to study the effect of process parameter on the imprinting replication quality. Finally, to address the issue of replication of micro-pattern over large area, a roll-to-flat (R2F) micro thermal imprint process is studied. By using the replication ratio for the evaluation of R2F thermal imprint process and basing on the analysis of filling mechanism during rolling process, a theoretical model of replication ratio is established and relationship between process parameters and replication quality is studied. Major research work of this thesis consists of the following parts:1) Investigation of flow behavior and viscoelasticity of amorphous polymerFollowed by the introduction of polymer material flow deformation mechanism in the thermal imprint process, three deformation states of amorphous polymer versus temperature are described. The characterization of viscoelastic property of amorphous polymer near the glass transition temperature (Tg) is carried out to better understand the flow behavior through creep and stress relaxation phenomenon. Viscoelastic material model of amorphous polymer is then introduced. For the polycarbonate (PC) which is used as substrate in this thesis, tensile stress relaxation test is conducted to obtain the material properties. A viscoelastic model of polycarbonate with the set of parameters is then established to describe the deformation flow behavior in thermal imprint process, which establishes the theoretical basis of the analysis of numerical simulation and experimental study in the following chapters.2) Numerical modeling and analysis for flat-pressing type micro thermal imprint processBased on finite element method, numerical simulation modeling and analysis of flat-pressing type thermal imprint process are performed. Material flow behavior of polymer substrate in the thermal imprint process is studied based on the viscoelastic material model. Process analytical model is established to demonstrate the time dependency of viscoelastic material in the thermal imprint process. Major process control parameters such as imprinting temperature, imprinting pressure and pattern density are also discussed based on the numerical simulation, providing theoretical support for the design of practical micro thermal imprint process.3) Experimental study of flat-pressing type micro thermal imprint processUsing two glassy carbon (GC) molds composed with different micro patterns on the surface and polycarbonate substrate, series of experiments of flat-pressing type thermal imprint process are carried out. The material flow behavior in the thermal imprint process is investigated, such as time, temperature and pressure dependency, one GC mold with micro line-groove pattern is used in the experiments for the study on process parameter effect on the final replication quality. The experimental results are also compared with simulation to evaluate the numerical model that is proposed in chapter 3. Another GC mold with micro semi-pyramidal cavity array on the surface is used in the thermal imprint process experiments for the further study on process parameter effect based on the design of experiment method.4) Investigation of continuous roll-to-flat micro thermal imprint processTo address the demands of replicating micro-pattern on large-area substrate, a continuous roll-to-flat (R2F) thermal imprint process is studied. Repliation ratio is firstly defined for the evalutation of R2F thermal imprint process. Base on the analysis of material flow behavior in the continuous R2F imprint process, a theoretical model of replication ratio is established. Furthermore, based on the developed lab-scale R2F micro thermal imprint system, experiments of continuous R2F thermal imprint process are performed by using a SKD-11 flat mold and PC substrate under different process conditions. Effects of process parameter and other factors are discussed through the analysis of measurement of experimental results, in which the analytical model is also evaluated.Focusing on the characteristics of thermal imprint process for the replication of micro-pattern from the mold to the substrate, this thesis performs the study of replicating mechanism and process analysis. Based on the analysis of material flow behavior of amorphous polymer, numerical modeling and experimental analysis are carried out to study traditional flat-pressing type micro thermal imprint process and continuous R2F micro thermal imprint process. These works can provide theoretical basis and guid line for further research on process design, quality control on the replication of micro-pattern on polymer substrate using micro thermal imprint process.