Piezoelectrically actuated droplet ejector

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Abstract
This article presents a novel piezoelectric fluid ejector that is based on a variation of the design of a flextensional transducer that excites axisymmetric resonant modes in a clamped circular membrane. The transducer is made by bonding a thin piezoelectric ring to a thin, fully supported, circular membrane. The transducer design is optimized for maximum flexure at the lowest order resonant frequency using finite element modeling. The fluid ejector is formed by placing a fluid, at atmospheric pressure, behind one face of the membrane and an orifice in its center. We achieve continuous or drop-on-demand ejection of the fluid by applying the appropriate voltage to the piezoelectric transducer. We present results of ejection of water, ink, powder, and photoresist. The application of photoresist with minimum waste on silicon wafers is one of the motivations for developing this device. In present applications, over 95% of the photoresist is wasted and has to be disposed as a toxic material, thus making this one of the more expensive steps in integrated circuit manufacturing. The ejector is harmless to sensitive fluids and can also be used to eject fuels, chemical and biological samples. The ejector configuration is unique in that it can be implemented using silicon micromachining as a microelectromechanical system, thus allowing the manufacture of true two-dimensional arrays of ejectors.

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