Design And Fabrication Of A Pulse Voltage-driven Electrohydro Dynamics Printing Head

Recent years,with electrohydrodynamic(EHD)development,electrostatic printing has been widely used in fields of microelectronics manufacturing and packaging,MEMS actuator and sensor,new energy technology for its advantages such as convenient operation,high printing precision and efficiency and low cost.Many researchers have done remarkable work due to its application potential.Now,most electrohydrodynamic printing obtains high printing resolution by decreasing printing nozzle’s inner diameter.However,when the diameter is lower than 5μm,blocking often occurs during operation which hampers printing and increases the printing cost and difficulty.In this work,we design a new structure of printing head using silicon tip to generate droplet instead of printing nozzle,and electrohydrodynamic simulation is carried out by Comsol Multiphysics to study the effects of silicon tip’s shape,curvature radius and surface wettbility on printing performance.Then,high frequency pulse electrostatic printing head is fabricated by MEMS process on silicon substrate.In the printing head,to generate droplets,silicon tip is prepared through wet-etching in KOH sol using SiO2 layer as mask which is lithographed by UV.The silicon tip is based on a crossbeam of 100μm width fabricated using wet-etching process.Afterwards,the Pt electrodes,by which voltage and pulse signal are applied,are prepared by magnetron spurting and sacrificial layer technologies.SEM technology is applied to test and analyze the size,structure and morphology of silicon tip.To avoid electric breakdown,polyimide(PI)thin film is prepared by spin-coating and imidization.Positive photoresist PI solution is used as precursor which is lithographed to form special structure.Then breakdown experiments are carried out under DC mode and pulse voltage mode by electric breakdown experiment system.The effect of imidization temperature on PI breakdown voltage(Vbd)is also discussed.Results show that higher temperature(ranging from 280 to 350℃)can improve breakdown strength because of higher crystallization degree.The biggest Vbd is 2650 V of PI thin film imidized at 350℃ and average Vbd is 343Kv*mm-1.