PIEZOELECTRICALLY ACTUATED DROPLET EJECTOR

This article presents a novel piezoelectric fluid ejector that is base d on a variation of the design of a flextensional transducer that exci tes axisymmetric resonant modes in a clamped circular membrane. The tr ansducer 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 el ement modeling. The fluid ejector is formed by placing a fluid, at atm ospheric pressure, behind one face of the membrane and an orifice in i ts center. We achieve continuous or drop-on-demand ejection of the flu id by applying the appropriate voltage to the piezoelectric transducer . We present results of ejection of water, ink, powder, and photoresis t. The application of photoresist with minimum waste on silicon wafers is one of the motivations for developing this device. In present appl ications, 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 sensi tive fluids and can also be used to eject fuels, chemical and biologic al samples. The ejector configuration is unique in that it can be impl emented using silicon micromachining as a microelectromechanical syste m, thus allowing the manufacture of true two-dimensional arrays of eje ctors. (C) 1997 American Institute of Physics.