A 2D Chamber-Free Micro Droplet Generator Array Controlled by Dynamic Virtual Walls

This paper presents an innovative micro droplet generator array controlled by dynamic virtual walls. The heaters for bubble generation can be arranged into a dense two-dimensional (2D) array by removing the chamber wall structures. The micro droplet generator array was fabricated by heater lithography and direct nozzle formation on a laminated SU-8 dry film without any solid chamber wall among heaters. With precise time-delayed control among microheaters, droplets could be ejected out by the thrust generated from the bubbles around the ejection site under the specific configuration. The volume of the droplet was about 3.8 pL and the initial speed can approach 15 m/s, meeting the standard of commercial printheads. In addition, we carried out the meniscus control by precise sequential control of bubble generations, so the micro droplet generator is free of satellite droplets throughout the whole traveling distance. It showed that the meniscus undergoes a “push-pull-push” progress which can effectively cut the liquid column short. To summarize, a 330 dpi chamber-free micro droplet generator prototype has been realized, and it has the potential for the application to large 2D format, high frequency, high resolution printing.