Abstract:
A fluid ejector, such as a printhead for an inkjet printer, comprising a substrate that includes a primary via formed therein, and a nozzle member overlying the substrate and including vertical nozzle chambers at least partially overlying the primary via and a corresponding fluid actuator (e.g., a heater) associated with the substrate.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed to fluid ejection and, more specifically, to fluid ejectors having nozzles and/or nozzle chambers that vertically overlie a primary via within a substrate.  
       RELATED ART  
       [0002]     Inkjet printing apparatus, such as printers and multi-function devices, rely on the transfer of ink from a source to a nozzle chamber where the ink is ejected through an orifice of the nozzle chamber and onto a print medium. Common conduit systems for delivering ink to nozzles of an inkjet printer include a primary via formed within a silicon substrate that provides the sole on-chip source of ink. A series of horizontal channels are fabricated during the printhead fabrication sequence to provide fluid communication between the primary via and respective nozzle chambers in order to allow ink from the primary via to refill each nozzle chamber subsequent to the firing of a respective fluid actuator.  
         [0003]     Thermal inkjet printers utilize fluid actuators that comprise electrical resistors (referred to hereinafter as “heaters”) that are “fired” by passing an electrical current through each heater in order to generate thermal energy. The thermal energy generated upon firing of a heater is relatively local and sufficient to vaporize a small fraction of ink in thermal communication with the heater, preferably to vaporize ink within the nozzle chamber. The pressure differential and expansion of fluid to a gaseous state within the nozzle chamber forces the remaining liquid ink within the chamber through the nozzle orifice and onto the print medium.  
         [0004]     Referencing U.S. Pat. No. 6,409,312, fabrication of these exemplary inkjet printheads requires forming the primary via within the substrate, as well as forming the heaters to be substantially offset from the primary ink via. Thereafter, a first photo-imageable layer is applied over the substrate to cover the primary ink via and thereafter developed to create horizontal channels connecting the primary via to the eventual nozzle chamber. A second photo-imageable layer is applied over the first photo-imageable material and thereafter developed to create the vertical nozzle chambers. It should be noted, however, that the nozzle chambers do not overly the primary ink via and therefore are dependent upon the horizontal chamber for fluid communication with the primary ink via and its associated fluid dynamics for refill characteristics.  
         [0005]     Other exemplary printheads are constructed using heater bridges. For example, U.S. Pat. No. 6,676,244 discloses a heater assembly adapted to generate bubbles of ink vapor in a direction opposite that of the nozzle orifice. These printheads may suffer from insufficient heat capacity surrounding the heater and the associated complexity of fabricating the electrical leads and bridging structure. Those of ordinary skill are familiar with the problems associated with the drawbacks with utilizing a bridge structure such as insufficient heater cooling that may lead to inadvertent ink ejection.  
         [0006]     Exemplary embodiments of the present invention obviate the need for horizontal channels to provide fluid communication between a primary via and a nozzle chamber, and simplify the fabrication process (e.g., by eliminating the process step to form the horizontal channel between the nozzle chamber and the primary via). Exemplary embodiments of the present invention also do not rely on a complex bridging structure incorporating the heater, but instead mount the heater to the bulk substrate.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to fluid ejection and, more specifically, to fluid ejectors having nozzles and/or nozzle chambers that vertically overly a primary via within a substrate. Exemplary embodiments of the present invention include forming nozzle chambers within a nozzle plate that vertically overly the primary via and/or vertical conduits fed by the primary via, as well as the heaters mounted on or associated with the substrate. The walls of the nozzle chambers may be tapered to increase the cross-sectional area of the chamber as the distance from the nozzle increases. In exemplary form, the nozzle chamber defines a frustoconical region, where a base of the frustoconical region overlies the primary via or a vertical conduit associated with the primary via.  
         [0008]     Embodiments of the present invention might also include methods and resulting devices having chamfered edges to meter the fluid (e.g., ink) between the nozzle chamber and the primary via. Those of ordinary skill will readily understand that the chamfered nature of the edges may be manipulated during fabrication to achieve the desired metering.  
         [0009]     It is a first aspect of the present invention to provide a fluid ejector comprising: (i) a substrate that includes a primary via formed therein; and (ii) a nozzle member overlying the substrate and including vertical nozzle chambers at least partially overlying the primary via and a corresponding fluid actuator associated with the substrate  
         [0010]     In a more detailed embodiment of the first aspect, the nozzle member and substrate cooperate to form a constriction that is adapted to meter the flow of fluid between the primary via and at least one vertical nozzle chamber. In yet another more detailed embodiment, at least one of the nozzle member and substrate that cooperate to form the constriction are chamfered. In a further detailed embodiment, at least one of the fluid actuators is recessively mounted to the substrate. In still a further detailed embodiment, fluid from the primary via is adapted to vertically refill each of the vertical nozzle chambers. In a more detailed embodiment, at least one of the vertical nozzle chambers includes a tapered wall. In a more detailed embodiment, the at least one vertical nozzle chamber includes at least two tapered walls, the first tapered wall is angled greater than the second tapered wall, and the first tapered wall at least partially overlies the primary via.  
         [0011]     In yet another more detailed embodiment of the first aspect, the tapered wall at least partially defines a frustoconical region. In still another more detailed embodiment, at least one of the vertical nozzle chambers includes a nozzle orifice at least partially overlying the primary via. In a further detailed embodiment, the primary via is horizontally staggered, the fluid actuators are horizontally staggered, and the vertical nozzle chambers are correspondingly horizontally staggered to match the orientation of the fluid actuators and primary via. In still a further detailed embodiment, the nozzle member is photolithographically developed to define the vertical nozzle chambers. In a more detailed embodiment, the nozzle member comprises a metallic material, and the vertical nozzle chambers are formed through the nozzle member utilizing at least one of laser ablation and electroplating. In a more detailed embodiment, the substrate includes a conduit formed between the primary via and at least one of the vertical nozzle chambers to regulate the refill of fluid into the at least one vertical nozzle chamber. In another more detailed embodiment, the substrate includes a plurality of conduits formed between the primary via and at least one of the vertical nozzle chambers to regulate the refill of fluid into the at least one vertical nozzle chamber.  
         [0012]     It is a second aspect of the present invention to provide a method of fabricating a printhead for an inkjet printing apparatus comprising: (i) forming an ink via within a substrate; (ii) overlying the substrate with a nozzle plate; and (iii) forming a plurality of orifices through the nozzle plate, where the plurality of orifices are adapted to overly at least a portion of the ink via and a corresponding heater mounted to the substrate to provide a plurality of overhanging nozzles.  
         [0013]     In a more detailed embodiment of the second aspect, the nozzle plate comprises a photosensitive material, and the photosensitive material is exposed to light and developed in order to form the plurality of overhanging nozzles. In yet another more detailed embodiment, the act of forming a plurality of orifices through the photosensitive material includes utilizing a photolithographic gray scale mask. In a further detailed embodiment, the act of forming the plurality of orifices through the nozzle plate includes utilization of at least one of laser ablation and electroplating. In still a further detailed embodiment, the act of forming the ink via within the substrate occurs prior to overlying the substrate with the nozzle plate. In a more detailed embodiment, the act of overlying the substrate with the nozzle plate occurs prior to the act of forming the plurality of orifices through the second material.  
         [0014]     In yet another more detailed embodiment of the second aspect, the act of forming the ink via within the substrate occurs subsequent to overlying the substrate with the nozzle plate, the act of forming the ink via within the substrate includes utilization of at least one of reactive ion etching and chemical etching, and the nozzle plate is operative as an etch stop. In still another more detailed embodiment, the act of overlying the substrate with the nozzle plate includes at least one of: (i) laminating a nozzle plate film onto the substrate, and (ii) applying a spin-on liquid composition and subsequently developing the spin-on liquid composition to form a nozzle plate film overlying the substrate. In a further detailed embodiment, the act of overlying the substrate with the nozzle plate occurs subsequent to the act of forming the plurality of orifices through the nozzle plate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a cross-sectional view of a first exemplary printhead in accordance with the present invention;  
         [0016]      FIG. 2  is an overhead view of the first exemplary printhead of  FIG. 1 ;  
         [0017]      FIG. 3  is an overhead view of a first alternate exemplary printhead in accordance with the present invention;  
         [0018]      FIG. 4  is a cross-sectional view of a second alternate exemplary printhead in accordance with the present invention;  
         [0019]      FIG. 5  is a cross-sectional view of a third alternate exemplary printhead in accordance with the present invention;  
         [0020]      FIG. 6  is a cross-sectional view of a fourth alternate exemplary printhead in accordance with the present invention;  
         [0021]      FIG. 7  is an overhead view of a second exemplary printhead in accordance with the present invention;  
         [0022]      FIG. 8  is an overhead view of an alternate exemplary printhead in accordance with the present invention;  
         [0023]      FIG. 9  is an overhead view of a third exemplary printhead in accordance with the present invention; and  
         [0024]      FIG. 10  is a cross-sectional view of the third exemplary printhead of  FIG. 9 . 
     
    
     DETAILED DESCRIPTION  
       [0025]     The exemplary embodiments of the present invention are described and illustrated below to encompass exemplary inkjet printheads. Of course, it will be apparent to those of ordinary skill in the art that the preferred embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the present invention. However, for clarity and precision, the exemplary embodiments as discussed below include optional steps, methods, features, and apparatuses that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present invention.  
         [0026]     Referencing  FIGS. 1 and 2 , a first exemplary printhead  10  includes a silicon substrate  12  and a nozzle plate  14  having a plurality of horizontally aligned nozzles  16  through which a fluid such as ink is ejected. The nozzle plate  14  includes a series of vertical shafts  18  formed through the nozzle plate  14  that are vertically aligned over at least a portion of a primary ink via  20  formed within the substrate  12 . Each shaft  18  includes tapered walls  22  having a circular cross-section that increases in area as the distance from the corresponding nozzle  16  increases to define a frustoconical nozzle chamber  24 . At least a portion of the frustoconical nozzle chamber  24  vertically overlies a corresponding heater  26  recessively mounted within the substrate  12 .  
         [0027]     In this exemplary orientation, the primary via  20  includes vertical walls  30  that are blocked off to provide a normal edge  32 . The normal edge  32  of the via  20  and the tapered walls  22  of the frustoconical nozzle chamber  24  define a constriction  34  through which ink must pass from the via  20  prior to entering the frustoconical nozzle chamber  24 . As will be described in more detail below, the geometries associated with the walls  30  of the via  20  and the walls  22  of the shafts  18  can be varied to accommodate predetermined rates of refilling.  
         [0028]     In an exemplary operational sequence of an exemplary inkjet printer (not shown), a printer controller (not shown) is operative to selectively fire one or more heaters  26  associated with the printhead  10 . The firing of a heater  26  generates a local area of higher thermal energy that is transferred to the substrate  12  and the ink directly above the heater. The extent to which this thermal energy is transferred to particular aspects of the printhead  10  is accounted for in this exemplary embodiment by the orientation and location of the heater  26  with respect to the substrate  12 , via  20 , and nozzle chambers  24 .  
         [0029]     For example, prior art designs included a horizontal conduit linking the primary ink via with the vertically oriented nozzle chamber, where the heater was spaced a considerable distance from the via. The nozzle chamber of some of these prior art designs included a heater mounted to a thin bridge extending into the nozzle chamber. While some of these prior art designs included heaters facing the nozzle or heaters facing away from the nozzle, a common theme remained that the heater and backside of the bridge were each in contact with ink within the nozzle chamber or the atmosphere, but in any event were not in intimate thermal communication with the silicon substrate. These prior art bridge designs have suffered from an insufficient thermal capacity of the bridge, resulting in overheating of the silicon supporting the heater. Likewise, such bridges having the backside exposed to the atmosphere have also suffered from insufficient heat sink capacity. Without a proper heat sink, unintended bubble formation on the backside of the bridge or on the front side of the heater may result that hinders ink from being properly ejected through the nozzle and degrades the filling characteristics of the nozzle chamber.  
         [0030]     Referring again to  FIG. 1 , the design of the exemplary printhead  10  is mindful of thermal energy transfer considerations, particularly where the primary ink via  20  directly feeds the nozzle chamber  24 . When an exemplary heater  26  is fired, thermal energy is transferred to ink directly above the heater and within the nozzle chamber  24  to generate a bubble that forces the remainder of the ink within the chamber  24  through the nozzle. By mounting the heater  26  to the bulk substrate  12 , as opposed to prior art bridge designs, each heater may be closer to the primary via  20  without transferring sufficient thermal energy to the ink within the primary via  20  to generate bubbles therein that might become lodged within the constriction  34  or slow the refilling of ink within the nozzle chamber  24 .  
         [0031]     A first exemplary process for fabricating of the first exemplary printhead  10  includes forming a primary ink via  20  within a silicon substrate  12 . Exemplary techniques for forming an ink via  20  within the substrate include, without limitation, deep reactive ion etching (DRIE) and chemical etching. Resistors on the substrate  12  are electrically connected to provide an array of heaters that will generate the thermal energy required for bubble formation. A heater overcoat is applied over the resistors to inhibit intimate fluid communication between the resistors and ink. The heater overcoat can comprise a dielectric layer and a passivation layer. The dielectric layer, which insulates the ink from the current in the heater may comprise silicon oxide, silicon nitride, silicon carbide, diamond like carbon, tantalum oxide or some combination of these, for example. The passivation layer, which protects the heater from the collapse of the vapor bubble—commonly known as cavitation, may comprise, for example, tantalum. These layers are deposited through standard PECVD or sputtering processes, then patterned with standard masked etching techniques. A photolithographic film that will eventually comprise the nozzle plate  14  is layered over the substrate  12 , via  20 , and heaters  26  on the order of 25 μm and may be applied using spin-on or spray on films such as, without limitation, SU8 available from Microchem Corporation or dry laminate films such as, without limitation, Vacrel or Riston available from Dupont Corporation. The photolithographic film  14  is developed using conventional techniques to create shafts  18  extending completely through the film that define the nozzles  16  and the nozzle chambers  24  that overly at least a portion of the via  20 . Those of ordinary skill are familiar with the techniques for developing photolithographic material that include, without limitation, positive photo development and negative photo development, with or without the utilization of a gray scale mask. In this exemplary embodiment, a positive photo development technique is utilized with a gray scale mask to selectively develop the film. A solvent is applied to the surface of the film to dissolve those portions left undeveloped by exposure to light, thereby creating the tapered walls  22  defining the frustoconical area of the nozzle chamber  24 .  
         [0032]     A second exemplary process for fabricating of the first exemplary printhead  10  includes first etching the recesses in the substrate  12  that are adapted to accommodate the heaters  26  and the associated electrical contacts. The heaters  26  and the associated electrical contacts are thereafter mounted to the substrate  12 , followed by a heater overcoat and a photolithographic film being applied over the substrate  12  that covers the heater overcoat, heaters  26 , and associated electrical contacts. At this point, the via  20  within the substrate has not been formed, nor have the plurality of shafts  18  through the film been formed that will eventually define the nozzles  16  and nozzle chambers  24 . Subsequent to the photolithographic film being applied to the substrate  12 , the ink via  20  is formed within the substrate, optionally utilizing the photolithographic film as an etch stop for deep reactive ion etching (DRIE) and/or chemical etching. After the via  20  has been formed, the shafts  18  within the photolithographic film are created as discussed above and known to those of ordinary skill.  
         [0033]     It is also within the scope of the invention to fabricate the shafts  18  within a nozzle plate  14  prior to the nozzle plate being applied to the substrate  12 . An exemplary nozzle plate  14  may be fabricated from a metallic substrate and include forming the shafts  18  therethrough using techniques such as, without limitation, laser ablation and electroplating. Laser ablated metallic nozzle plates  14  typically have nozzle chamber sidewalls angled at 7°, but may be increased to at least 20° by using a gray scale mask. Likewise, electroplated nozzle chambers may be fabricated with wall angles exceeding 40°. Another exemplary nozzle plate  14  may be fabricated from a polymer photolithographic film that is developed to define the shafts  18 . Using either the metallic or polymer film nozzle plate  14 , the shafts  18  through the plate are formed completely independent of recess and/or via  20  formation within the substrate  12 . In this manner, via  20  and recess formation can occur prior to, concurrent with, or subsequent to shaft  18  formation. The shafts  18  of the nozzle plate  14  may be aligned with preexisting recesses and vias  20 , or be aligned with locations where the vias  20  and recesses will be subsequently formed to ensure that the resulting nozzle chambers  24  vertically overly at least a portion of the via  20  to provide direct vertical communication between the via  20  and nozzle chamber  24 . It is also within the scope of the invention that the nozzles  16  themselves overly the via  20 .  
         [0034]     Referring to  FIG. 3 , it is also within the scope of the present invention to provide a shaft  18 ′ defining an area other than a frustoconical area by utilization of geometries incorporating cross-sectional areas other than circular cross-sections. In this first alternate exemplary printhead  10 ′, the shafts  18 ′ are defined by two opposite and linear parallel tapered walls  50 ,  52  that are connected to one another by mirror image conical walls  54 ,  56 . At least one of the conical walls  54  vertically overlies the primary ink via  20 ′ formed within the substrate  12 ′ in order to provide direct communication between the via  20 ′ and nozzle chamber  24 ′. It should also be noted that each nozzle chamber  24 ′ also overlies the corresponding heater  26 ′. Presuming the nozzle plate includes a photolithographic composition, the conical walls  54 ,  56  may be formed by exposing the shafts,  18 ′ to a gray scale mask or a stepper.  
         [0035]     It is further within the scope of the present invention to provide a shaft having a sidewall perpendicular or orthogonal to the surface of the substrate. In this manner, nozzle chambers may be fabricated to define a cylindrical area, and elongated cylindrical area, or any other area where the vertical walls of the nozzle chamber are substantially perpendicular to the substrate.  
         [0036]     Referring to  FIG. 4 , it is also within the scope of the present invention to provide a shaft  18 ″ having walls that are tapered or angled in a non-uniform manner. In this second alternate exemplary printhead  10 ″, at least one wall  60  of the shaft  18 ″ is angled or tapered more so than an opposite wall  62 . In an exemplary orientation, the wall  60  overlying the primary ink via  20 ″ is angled more so than the wall  62  overlying the substrate  12 ″, however, it is also within the scope of the present invention to angle the wall  62  overlying the substrate more so than the wall  60  overlying the primary via  20 ″.  
         [0037]     Referring to  FIGS. 5 and 6 , it is also within the scope of the present invention to fabricate a printhead  10 ′″ that eliminates the normal edges associated with the walls  30 ′″ of the ink via  20 ′″, as well as fabricating a printhead  10 ′″ that concurrently eliminates the normal edges associated with the walls  30 ″″ of the ink via  20 ″″ and the sharp edges associated with the walls  22 ″″ of the shafts  18 ″″ by chamfering such edges. By chamfering the walls bounding the constriction  34 ′″,  34 ″″, it is possible to manipulate the refill characteristics of the nozzle chamber  24 ′″,  24 ″″ without substantially modifying the orientation of the walls bounding the nozzle chamber and the via. Likewise, the volume of the via and each nozzle chambers is substantially unchanged, but provides for various metering of ink between the via and nozzle chamber. For example, by chamfering the walls bounded the constriction, the cross-sectional area of the constriction is increased, which reduces the refill time of the nozzle chamber.  
         [0038]     Referencing to  FIGS. 7 and 8 , a second exemplary printhead  100  and second alternate exemplary printhead  100 ′ each include nozzles  102 ,  102 ′ that overhang the primary ink via  104 ,  104 ′ and are horizontally staggered. For purposes of explanation, staggered nozzles  102 ,  102 ′ include nozzles that are not linearly aligned and are not perpendicular to an edge of the printhead  100 ,  100 ′. Staggering of the nozzles reduces the number of heaters  106 ,  106 ′ that need to fire at the same time in a vertical line printing situation, which advantageously reduces the number of sequential heaters that are fired. The exemplary nozzles  102 ,  102 ′ and nozzle chambers  108 ,  108 ′ may be fabricated consistent with any one of the above explanations for fabricating an exemplary embodiment in accordance with the present invention, with the locations of the heaters,  106 ,  106 ′ being predetermined and eventually dictating the modification of the ink via  104 ,  104 ′ and the nozzle changers  108 ,  108 ′.  
         [0039]     Referencing to  FIGS. 9 and 10 , a third exemplary printhead  200  includes series of nozzles  202  through a nozzle plate  204 , where the nozzles  202  overhang a series of orthogonal conduits  206  vertically overlying a primary ink via  208  formed within a silicon substrate  210 . The nozzle chambers  214  also vertically overly heaters  218  recessively mounted within the substrate  210 . Unlike the exemplary embodiments discussed above that utilize the constriction to primarily meter the ink between the via and the nozzle chamber, this third exemplary printhead  200  utilizes the constriction  212  and associated conduit  206  prefacing the constriction to meter ink between the via  208  and a respective nozzle chamber  214 . In this manner, the dimensions of the constriction  212  and the conduit  206  work in tandem to dampen the volumetric flow rate of ink between the primary ink via  208  and the nozzle chambers  214  to prevent ink flooding in proximity to the nozzle  202  prior to ink jetting.  
         [0040]     While the exemplary printhead  200  is shown with each nozzle chamber  214  having tapered sidewalls  216  to define a frustoconical area, it is also within the scope of the invention that the walls are oriented normal to the surface of the substrate  210  and/or have cross-sectional areas that are not circular. Likewise, it is within the scope of the invention to eliminate or substantially reduce the sharp and normal edges of the substrate  210  and nozzle plate  204  by chamfering such edges to define the constriction  212  consistent with the explanation above for chamfering constriction boundaries. It is further within the scope of the invention to provide a plurality of conduits  206  feeding a single overhanging nozzle  202 .  
         [0041]     Fabrication of the second exemplary printhead  200  includes utilization of deep reactive ion etching (DRIE) to define the primary via  208 , along with the respective conduits  206  feeding the overhanging nozzle chambers  214 . A photolithographic film, that will eventually comprise the nozzle plate  204 , is mounted to the substrate  210  and developed to define the nozzles  202  and associated nozzle chambers  214 . As discussed above, this film  204  may be a preexisting metallic or polymer film, or a liquid spun deposited over the substrate  210  and thereafter cured to provide a film. The etching utilized to fabricate the via  208  and conduits  206  can occur prior to, subsequent to, or concurrently with the formation of the nozzles  202  and nozzle chambers  214 . Those of ordinary skill will be understand the exemplary teachings of the present invention to fabricate obvious variations of the aforementioned exemplary embodiments.  
         [0042]     Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the invention contained herein is not limited to this precise embodiment and that changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.