Electro-hydrodynamic printing using hole-type electrode

Additive direct writing has many advantages compared with the subtractive conventional MEMS fabrication process. With its reduced manufacturing steps, the processing time is shortened and the overall process costs less. Also, the process is non-toxic and its flexibility in the manufacturing gives the capability to alter printing patterns promptly. Among many direct writing methods, electro-hydrodynamic (EHD) printing is also receiving a huge interest due to its capability of high resolution printing. However, there are still many issues to be resolved for the high volume fabrication process, such as the realization of multi-nozzle drop on demand system, etc. In this work, EHD printing was demonstrated using a hole-type electrode with stainless steel nozzle to which the liquid is supplied from a constant pressure reservoir. With varying square voltage pulses between the nozzle and the electrode, three types of jet emission modes are observed; continuous mode, fine jet pulsating mode and droplet pulsating mode. Among these modes, the droplet pulsating mode and the fine jet pulsating mode were optimized to print relatively large patterns and high resolution patterns, respectively. In addition, to demonstrate near field printing for high position accuracy, EHD printing was carried out with a nozzle penetrating the hole-type electrode, so that the distance between nozzle tip and the substrate could be shortened.