2D acoustically actuated micromachined droplet ejector array

Most of the semiconductor and MEMS fabrication processes require deposition of organic polymers on wafers. The current state-of-the-art method is the spin coating. However, more than 95% of the expensive coating material is wasted. To reduce waste, we proposed to use a novel two-dimensional micromachined droplet ejector array to deposit photoresist and other spin-on materials used in IC manufacturing. Each element of the two-dimensional ejector array consists of flexurally vibrating circular membranes with orifices etched at their centers. Droplets are ejected through these orifices. The actuation is performed by a piezoelectric transducer placed parallel to the array. We observed that achieving simultaneous ejection from all the array membranes was difficult. The problem was associated with non-uniform membrane displacements across the array due to an uneven pressure distribution within the individual fluid reservoirs. Finite element method (FEM) modeling was used to investigate the problem. Our simulation results showed that in the presence of individual fluid reservoirs the membrane resonance frequency shifted and the quality factor of the resonance is decreased. These simulations indicated that an ejector design free of individual reservoirs would achieve more uniform membrane displacements across the array. The simulation results of two designs were verified by vibrometer measurements.