Abstract:
An ink jet nozzle. The ink jet nozzle includes a substrate having an upper surface in which an ink energizing element is attached to the upper surface of the substrate. The ink jet nozzle further includes an oxide-nitride or oxide-carbide composite orifice layer. The oxide-nitride composite orifice layer includes a lower surface conformally connected to the upper surface of the substrate, and an exterior surface facing away from the substrate. The oxide-nitride composite orifice layer defines a firing chamber. The firing chamber opens through a nozzle aperture in the exterior surface, and extends downward with a negative slope through the oxide-nitride orifice layer to expose the ink energizing element.

Description:
This application is a continuation under 37 CFR 1.53(b) or application Ser. No. 09/005,319 filed on Jan. 9, 1998 which is hereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to an ink jet print nozzle. In particular, it relates to an ink jet print nozzle in which inner walls of the ink jet print nozzle are formed from an oxide-nitride or oxide-carbide composition. 
     BACKGROUND 
     Ink jet printing mechanisms use pens that shoot droplets of ink onto a printable surface to generate an image. Ink jet printing mechanisms may be used in a wide variety of applications, including computer printers, plotters, copiers, and facsimile machines. For convenience, the concepts of the invention are discussed in the context of a printer. 
     An ink jet printer typically includes a print head having a multitude of independently addressable firing units. Each firing unit includes an ink chamber connected to a common ink source, and to an ink jet print nozzle. A transducer within each ink chamber provides the impetus for expelling ink droplets through the associated ink jet print nozzle. Typically, the transducer is a firing resistor which heats the ink until the ink droplets are expelled through the ink jet print nozzle. 
     Generally, a substrate supports the firing resistors. An orifice layer which includes the ink jet nozzles is attached to the substrate so that each ink jet nozzle corresponds with an associated firing resistor and forms an ink chamber. 
     To obtain a high resolution printed output, it is desirable to maximize the density of the firing units, requiring miniaturization of the print head components. The substrate that supports the firing resistors and the orifice layer that provides the ink jet nozzle above each resistor are subject to small dimensional variations that can accumulate and limit miniaturization. 
     Monolithic print heads have been developed through print head manufacturing processes which use photo imaging techniques similar to those used in semiconductor manufacturing. The components are constructed on a flat wafer by selectively adding and subtracting layers of various materials. Using photo-imaging techniques, dimensional variations are limited. Further variations do not accumulate because each layer is registered to an original reference on the wafer. 
     Existing monolithic print heads are complex to manufacture. Further, the ink jet nozzles are formed from either a polymer or metal material. Polymer and metal materials offer limited performance because the surfaces of these materials can be rough, and because these materials react corrosively with the ink. It is important that the surface of the ink jet nozzle be smooth so as to not interrupt the flow of ink through the ink jet nozzles. Further, corrosive reactions to the ink cause the ink jet nozzles to break down and deteriorate. 
     It is desirable to have an ink jet nozzle in which the surface of the ink jet nozzle is formed from a material which is smoother than presently existing materials. Further, the material would not react to ink which flows through the ink jet nozzle thereby increasing the useful life of the ink jet nozzle. 
     SUMMARY OF THE INVENTION 
     The present invention provides a monolithic ink jet nozzle which is formed from an oxide-nitride or oxide carbide composition. These compositions provide an ink jet nozzle which includes a smoother re-entrance surface than presently existing ink jet nozzles. Further, the compositions do not corrosively react to ink passing through the ink jet nozzle. Therefore, the ink jet nozzle is useful for a longer period of time than presently existing ink jet nozzles. 
     A first embodiment of the invention includes an ink jet nozzle. The ink jet nozzle includes a substrate having an upper surface in which an ink energizing element is attached to the upper surface of the substrate. The ink jet nozzle further includes an oxide-nitride or oxide-carbide composite orifice layer. The composite orifice layer includes a lower surface conformally connected to the upper surface of the substrate, and an exterior surface facing away from the substrate. The composite orifice layer defines a firing chamber. The firing chamber opens through a nozzle aperture in the exterior surface, and extends downward with a negative slope through the composite orifice layer to expose the ink energizing element. 
     Another embodiment of the invention includes a method of forming an ink jet nozzle over an ink energizing element on an upper surface of a substrate. The method includes the following steps. First, a positive sloped sacrificial oxide bump is created on the surface. Next, a nitride or carbide composite layer and an oxide layer are deposited over the surface and the sacrificial bump. The oxide and composite layers are polished forming an orfice layer. An opening in the orifice layer is created over the sacrificial oxide bump. Finally, the sacrificial oxide bump is removed yielding an ink jet nozzle. 
     Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an ink jet pen having a print head which includes ink jet nozzles according to the invention. 
     FIG. 2 is a cross-sectional view of an embodiment of the invention. 
     FIG. 3 is a perspective view of the embodiment of the invention shown in FIG.  2 . 
     FIGS. 4A-4H show a series of steps in the formation of an embodiment of the invention. 
     FIGS. 5A,  5 B show alternative processing steps to the processing steps shown in FIGS. 4A-4C. 
    
    
     DETAILED DESCRIPTION 
     As shown in the drawings for purposes of illustration, the invention is embodied in a monolithic ink jet nozzle. The ink jet nozzle is formed from an oxide-nitride or oxide carbide composition. The composition provides an ink jet nozzle which is smoother than presently used polymer ink jet nozzles. Further, the composition does not react to ink passing through the ink jet nozzle. Therefore, the ink jet nozzle lasts longer than presently existing ink jet nozzles. 
     FIG. 1 is a perspective view of an ink jet pen  10  having a print head  12  which includes ink jet nozzles  18  according to the invention. The ink jet pen  10  also includes a lower portion  14  containing an ink reservoir that supplies ink to the print head  12 . 
     FIG. 2 is a cross-sectional view of an embodiment of the invention. This embodiment includes an ink jet nozzle  18 . The ink jet nozzle  18  is formed by a fructoconical firing chamber  36  of an orifice layer  30  attached to a silicon substrate  20 . The substrate  20  includes a top surface  22  that is typically coated with a passivation layer  24 . A thin film resistor  26  is typically formed over the top surface  22 . The top surface  22  of the substrate forms a bottom section of the ink jet nozzle  18  which receives ink. The orifice layer  30  has a lower surface  32  that conformally rests above the top surface  22 . 
     The ink jet nozzle  18  include walls  41  which are negatively sloped from a smaller circular external orifice  16  to a larger circular base periphery  40 . The larger circular base periphery  40  is centered around the thin film resistor  26 . The ink jet nozzle  18  is aligned on an axis of the thin film resistor  26 . 
     The passivation layer  24  defines several ink supply vias  42  dedicated to the ink jet nozzle  18 . The vias  42  are entirely encircled by the lower periphery  40  of the ink jet nozzle  18 . 
     The walls  41  of the ink jet nozzle  18  are formed from a oxide-nitride or oxide-carbide material. The oxide-nitride or oxide-carbide material allows the walls  41  to be smoother than previously possible. Polymer walls, for example, are rougher. Rough walls impede the flow of ink flowing through the ink jet nozzle  18 . The smooth walls  41  of the ink jet nozzle  18  of the invention do not impede the flow of ink passing through the fructoconical firing chamber  36  as much as rough polymer or rough metal walls. 
     The oxide-nitride or oxide-carbide walls  41  of the ink jet nozzle of the invention do not react to ink passing though the fructoconical firing chamber  36 . Prior art ink jet nozzles are generally formed from materials which react to ink which makes physical contact with the surface of the nozzles. The reactions reduce the useable life time of the ink jet nozzle. That is, the material of the ink jet nozzle begins to break down, thereby reducing the performance of the ink jet nozzle. 
     The substrate  20  includes a tapered trench  44  which provides a path for ink to flow between the reservoir  14  and the ink jet nozzle  18 . 
     FIG. 3 is a perspective view of an embodiment of the invention. A conductor  46  provides a conductive path for current flowing through the thin film resistor  26 . The thin film resistor  26  is a firing resistor which heats the ink until the ink droplets are expelled through the ink jet print nozzle  18 . 
     FIGS. 4A-4H show a series of processing steps in the formation of an embodiment of the invention. First, a structure as shown in FIG. 4A is formed which includes a substrate  50 , a first silicon-oxide (SiO 2 ) layer  52  and tantalum (Ta) layer  54 . A second silicon-oxide layer  56  is deposited over the Ta layer  54 . A poly-silicon layer  58  is deposited over the second-silicon oxide layer  56 . Finally, a photo-resist layer  60  is deposited over the poly-silicon layer  58 . The photo-resist layer  60  is patterned so that an island  62  of photo-resist is located where an ink jet nozzle is to be formed over the substrate  50 . The photo-resist layer  60  pattern can be formed by a standard lithography process. 
     FIG. 4B shows the structure of FIG. 4A in which portions of the poly-silicon layer  58  and the photo-resist layer  60  have been removed through dry etching. Dry etching the poly-silicon layer  60  forms a pattern in the poly-silicon layer  58  as determined by the pattern originally formed in the photo-resist layer  60 . 
     FIG. 4C shows the structure of FIG. 4B in which the second silicon-oxide layer  56  has been wet oxide isotopically etched. An aperture  64  is formed in the silicon-oxide layer as determined by the pattern of the poly-silicon layer  58 . The aperture  64  encircles a sacrificial bump  66 . The sacrificial bump  66  is located where the ink jet nozzle is to be formed. The sacrificial bump  66  include positively sloped edges  68  which define the negatively sloped edges of the ink jet nozzle to be formed. 
     FIG. 4D shows the structure of FIG. 4C in which the poly-silicon layer  58  has been etched away, and a silicon-nitride (Si 3 N 4 ) or, silicon-carbide (SiC) layer  70  has been deposited over the second silicon-oxide layer  56 . 
     FIG. 4E shows the structure of FIG. 4D in which a third silicon-oxide layer  72  has been deposited over the silicon-nitride layer  70 . 
     FIG. 4F shows the structure of FIG. 4E in which the third silicon-oxide layer  72  has been chemically-mechanically polished (CMP). The third silicon-oxide layer  72  is chemically-mechanically polished down to the silicon-nitride or silicon-carbide layer  70  forming an orifice layer  74 . The orifice layer  74  includes the second silicon-oxide layer  56 , the silicon-nitride or silicon-carbide layer  70 , and portions of the third silicon-oxide layer  72 . 
     FIG. 4G shows the structure of FIG. 4F in which a protective layer  75  and second photo-resist layer  76  have been deposited over the orifice layer  74 . The protective layer  75  and the second photo-resist  76  include an opening  78  aligned with the sacrificial bump  66 . A portion of the silicon-nitride layer  70  which is aligned with the opening  78  is nitride dry etched down to the silicon-oxide layer  56  leaving the sacrificial bump  66  exposed. The protective layer is either a silicon-carbide and a silicon-nitride. Silicon-carbide may be the preferred protective layer  75  material because silicon-carbide provides a very hard surface. 
     FIG. 4H shows the structure of FIG. 4G in which the exposed sacrificial bump  66  and the second photo-resist layer  76  have been removed through wet oxide etching. Removing the sacrificial bump  66  results in the formation of an ink jet nozzle  80  in the orifice layer  74 . 
     FIGS. 5A,  5 B show alternative processing steps to the processing steps shown in FIGS. 4A,  4 B,  4 C. First, a structure as shown in FIG. 5A is formed which includes a substrate  50 , a first silicon-oxide (SiO 2 ) layer  52  and tantalum (Ta) layer  54 . A second silicon-oxide layer  56  is deposited over the Ta layer  54 . Finally, a photo-resist layer  60  is deposited over the silicon-oxide layer  56 . The photo-resist layer  60  is patterned so that an island  62  of photo-resist is located where an ink jet nozzle is to be formed over the substrate  50 . The photo-resist layer  60  pattern can be formed by a standard lithography process. 
     FIG. 5B shows the structure of FIG. 5A in which the second silicon-oxide layer  56  has been dry etched. An aperture  64  is formed in the silicon-oxide layer as determined by the pattern of the photo-resist layer  60 . The aperture  64  encircles a sacrificial bump  66 . The sacrificial bump  66  is located where the ink jet nozzle is to be formed. The sacrificial bump  66  include positively sloped edges  68  which define the negatively sloped edges of the ink jet nozzle to be formed. 
     Subsequent processing steps to the structure shown in FIG. 5B are the same as those shown in FIGS. 4D-4H. 
     Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The invention is limited only by the claims.