Vertical Diaphragm Electrostatic Actuator for a High Density Ink Jet Printer Head

This paper describes the design, fabrication process and preliminaiy evaluation of an electrostatic ink jet printer head with vertical diaphragms in deep trenches. By adopting the novel structure where an ink cavity is surrounded by the vertical diaphragm, the footprint of each unit (40 μm×500 μm) becomes approximately one fifth as small as that of a conventional one. Such small footprint is advantageous in cost, resolution and printing speed. To make the vertical diaphragms, a 0.5 μm thick sacrificial thermally-oxidized layer and a 4.5 pm thick poly-silicon layer are sequentially formed in deep-reactive-ion-etched trenches, and then the sacrificial layer is etched away by fluoric acid. The nozzles are fabricated on a Pyrex glass substrate by femtosecond laser ablation, and the nozzle outside is covered with a water repellant Au/Pt/Ti layer. Impedance measurement found that the electrostatic gaps were in contact or closely approaching. This could be because the diaphragms buckled by compressive stress induced in low pressure chemical vapor deposition (LPCVD). Ink ejection was tried using commercially-available blue ink, but failed. The nozzles were covered with the ink, because the water repellant finish of the nozzle outside was not good.