Apparatus for creating re-entrant nozzles

#The present invention relates to methods and apparatus of manufacturing ink-jet printheads, and in particular to the formation of re-entrant nozzles through which ink is discharged from the printhead.

#Thermal ink-jet printers operate by rapidly heating a small volume of ink and causing the ink to vaporize into a bubble which ejects a droplet of ink through an orifice nozzle to strike a recording medium, such as a sheet of paper. Typically, a number of orifices are arranged in a pattern upon a printhead. Thus, a properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper. In this print method, a major component of print quality depends upon the physical characteristics of the orifices in the printhead. For example, the geometry of the orifice affects the size, shape, trajectory, and speed of the ink drop ejected.

#An ideal printhead includes nozzle members having re-entrant orifice nozzle profiles. Affixed to a back surface of the nozzle members is a substrate, which channels liquid ink into a vaporization chamber. Liquid ink within the vaporization chamber is vaporized by the energization of a thin film resistor formed on the surface of the substrate that causes a droplet of ink to be ejected from the orifice nozzle. Preferably, nozzle members are formed of a polymer material or a photoresist material using photolithography, laser ablation or other similar techniques to minimize cost and wafer process capability.

#FIG. 1A illustrates a cross-sectional view of a conventional nozzle on a substrate.

#FIG. 1B illustrates a cross-sectional view of a re-entrant nozzle on a substrate.

#FIG. 2A illustrates the ray distribution of a conventional optical system.

#FIG. 1A is a cross-section of a conventional etched nozzle 10 in a polyimide film 50 on a substrate 30 that has been exposed and developed. The nozzle 10 has positive sidewalls 12 that expand the nozzle from the top surface of the substrate 30 to the top surface of the polyimide film 50. This type of nozzle has the disadvantage in that when ink is ejected from it, the speed and direction of the ink are difficult to control.

#FIG. 1B is a cross-section of a desirable type of re-entrant orifice or nozzle 20 required for high quality ink-jet printing. The polyimide film 50 on substrate 30 has negative sidewalls 11, which form the re-entrant nozzle 20. This re-entrant nozzle 20 is difficult to manufacture using conventional orifice manufacturing techniques for monolithic structures.

#FIG. 2A illustrates the properties of conventional optical systems. The conventional optical system 17 is shown about its optical axis 15. Electromagnetic energy, such as light, enters the conventional optical system 17 in a series of rays, each at a ray height 14, h, from the optical axis 15. The conventional optical system 17 then redirects and focuses the electromagnetic rays on an process plane 24 to a common focal point on the optical axis 15 at a distance F which is called the focal length 18 of the conventional optical system 17. The amount of deflection of the electromagnetic rays is represented by the angle of incidence 16, θ′. This angle of incidence 16 changes in a tangential relationship with the ray height 14. However, to make re-entrant nozzles that have uniform conical angles over the full printhead it is necessary to have a constant angle of incidence 16 over the full process plane of the optical system. This requirement is not possible to achieve with the conventional optical system 17 as its angle of incidence 16 varies with the ray height 14.