Bonding Mechanism And Process Investigation On Plasma Modification Of SAW Microfluidic Chip

The surface acoustic wave（SAW）microfluidic technology has good scientific value and application prospect in the separation of micro-nano particles and biological particles.However,the long time,low strength,and unstable quality of the bonding between the PDMS chip and Li Nb O₃ substrate have limited the development of SAW devices.To solve this problem,oxygen-nitrogen dual plasma modification technology was proposed in this paper to efficiently bond PDMS chip and Li Nb O₃ substrate.The bonding mechanism and process were studied,and the bonding quality was evaluated with microfluidic device as the application object.The main work and conclusions are as follows:（1）The wettability,morphology and chemical composition of plasma-modified surface were characterized,and the bonding mechanism was revealed.Plasma modification introduced active chemical groups into the surface,which increased the surface hydrophilicity,but did not etch the surface.The oxygen plasma introduced-OH groups at the surface,and nitrogen plasma introduced not only-NH₂ groups,but also=N-OH groups.Compared with single plasma modification,oxygen-nitrogen dual modification could further increase the content of active groups.（2）The bonding experiments of different modification parameters were carried out to study the bonding process of plasma modification.The bonding strength of air plasma modification was about 300k Pa,that of oxygen or nitrogen plasma modification was about 1MPa,and that of secondary plasma modification could reach 1.3MPa.The orthogonal test was designed to optimize the oxygen plasma modification bonding process.For the dual plasma modification bonding process,the bonding strength could be improved only when both plasma modification were sufficient.（3）The bonding quality of SAW microfluidic devices was evaluated.The results of interface characterization of the bonded device modified by dual plasma indicated that an irreversible bonding was formed between the PDMS chip and Li Nb O₃ substrate.The leakage test and sorting function verification based on the actual working condition showed that the dual plasma modification bonding process could meet the normal use requirements of the device.The dual plasma modified bonding technology proposed in this paper achieved the stable bonding between PDMS chip and Li Nb O₃ substrate at room temperature,which shortened the bonding period from several hours to 5min and increased the bonding strength from 300k Pa to 1.3MPa.It well solved the bonding problems of SAW devices,and promoted the further development of SAW microfluidic technology.