Laser Micromachining of Branching Networks

摘要

We describe maskless rapid prototyping of a micro-fluidic branching network on a silicon wafer with laser direct writing (LDW). The branching micro-channel network is designed as a blood oxygenator following Murray's law and satisfying the necessity of equal path lengths. In development of such micro-fluidic structures, this maskless process will reduce time and cost compared with the conventional photolithography based technique. The flexibility of laser direct writing facilitates creating a multi-depth structure of the branching network, ranging from a few microns to a few hundred microns in depth. In order to create such a wide range of feature sizes, a nanosecond pulsed Nd-YAG laser and a femtosecond pulsed fiber laser are used together. The femtosecond fiber laser is used to create micro-channels with a depth of less than 50um. As post-processing, a chemical etching in a solution of HF and HNO3 is applied to smooth the laser ablated surface. To realize an optimized design of micro-fluidic structures, influences of operating parameters, such as the pulse energy, the focal position, the transverse speed, and the number of passes, on the depth of micro-channels and their surface quality are investigated. Using the laser machined silicon structures as a mold, a Poly(dimethylsiloxane) (PDMS) replica is created.