Fabrication Of Polymer Micro/nanofluidic Chip Based On Plasma Technology

To improve the integration of polymer microfluidic chips,many kinds of metal microelectrodes have been integrated onto the chip.However,fracture of the microelectrode likely happens during the thermal bonding process of the chip.The fracture behaviors are studied.The fracture is mainly caused by the plastic deformation of the electrode plate(the PMMA plate with microelectrodes) and the thermal stress of microelectrodes,which is due to the high bonding temperature.The fracture mechanism is studied by the fractographic analysis.A modified dicing saw is used to fabricate the fracture section successfully.The macroscopic and micro fractographies are conducted by using a stereomicroscope and a scanning electron microscope,and the fracture is a dimple fracture.A novel plasma assisted thermal bonding method is evaluated to reduce the bonding temperature.Before the electrode plate is thermally bonded to the cover plate(the PMMA plate with microchannels),the surface of the cover plate is modified using oxygen plasma. The parameters of the oxygen plasma treatment are optimized by orthogonal factorial design, and the contact angle of PMMA[poly(methylmethacrylate)]is decreased from 71.7°to 43.6°. The surface energy of PMMA increases with the decrease of the contact angle,which is beneficial for reducing the bonding temperature.The effect of the temperature on the contact angle of modified PMMA is also investigated,and then the thermal bonding temperature is optimized,which decreases the thermal bonding temperature from 100℃to 85℃.To demonstrate this bonding method,a PMMA microfluidic chip with integrated copper interdigitated microelectrode arrays for AC electroosmotic pump is fabricated,which presents both completed bonding and continuous metal microelectrode arrays.Recently,nanotechnology is introduced into microfluidic chips to realize nanofluidic chips, and the development of nanofluidics is based on the fabrication of nanochannels.A fabrication method of polymer planar nanochannels based on plasma etching is put forward. First,a Cu protection layer is fabricated by UV-lithography and wet etching.Secondly,the exposed polymer is etched by O₂ plasma using plasma cleaner.Thirdly,the Cu protection layer is removed,and polymer planar nanochannels are achieved.The etching rate for many kinds of polymer materials used for chips is tested,and the corresponding relation curve between the etching depth and time is established.A PMMA micro-nano fluidic chip for ion enrichment is fabricated by combining the fabrication methods for nanochannels and thermal bonding stated above.Two U-shape microchannels are made in one PMMA plate,and 9 parallel nanochannels with 5μm width, 500nm depth and 1mm length are made in another PMMA plate.These two PMMA plates are aligned and thermally boned together to make the nanochannels connect these two U-shape microchannels.The ion enrichment is obviously observed at the end of the nanochannels.