Abstract:
A fluid ejection device comprises a substrate including a fluid ejector thereon, and an orifice member positioned over said substrate. The orifice member has a fluid-transfer bore extending therethrough and corresponding to the fluid ejector. The orifice member further has a counter-bore about the fluid-transfer bore.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to fluid ejection devices, and more particularly to a counter-bore of a fluid ejection device.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various inkjet printing arrangements include both thermally actuated printheads and mechanically actuated printheads. Thermally actuated printheads tend to use resistive elements or the like to achieve ink expulsion, while mechanically actuated printheads tend to use piezoelectric transducers or the like.  
           [0003]    A representative thermal inkjet printhead of a print cartridge has a plurality of thin film resistors provided on a semiconductor substrate. A barrier layer is deposited over thin film layers on the substrate. The barrier layer defines firing chambers about each of the resistors, an orifice corresponding to each firing chamber, and an entrance or fluid channel to each firing chamber. Often, ink is provided through a slot in the substrate and flows through the fluid channel to the firing chamber. Actuation of a heater resistor by a “fire signal” causes ink in the corresponding firing chamber to be heated and expelled through the corresponding orifice.  
           [0004]    In order to provide high print quality, each nozzle (or orifice) of the printhead should be able to repeatably deposit the desired amount of ink in the proper pixel location on a medium, producing round spots or dots. However, printhead aberrations and the effects of aging can adversely affect ink drop placement. The actual location of misplaced drops can visibly differ from the desired location, much like missing the bulls-eye of a target. The location error can have a component in the direction in which the print cartridge is scanned; such error is known as scan axis directionality (“SAD”) error. The location error can also have a component in the direction in which the medium is advanced; such error is often called paper axis directionality (“PAD”) error.  
           [0005]    Another form of drop placement error also occurs because fluid is typically not ejected from a nozzle in the form of a single drop, but rather as a main drop followed by one or more satellite drops. All of these drops would ideally be deposited in the same pixel location; however, because the main and satellite drops are ejected at slightly different times with slightly different velocities, satellite drops often land downstream in the scan direction from the main drop. Instead of printing a round spot on the medium, non-coincident main and satellite drops can produce a non-round spot with a “tail”, or even more than one spot on the medium. As the scanning speed of the printhead with respect to the medium increases, the time separation between the main and satellite drops has a greater effect, and it becomes more likely that the main and satellite drops will not result in round spots as desired.  
           [0006]    Drop placement errors generally cause a visually significant print quality defect known as banding: strip-shaped nonuniformities that are visible throughout the printed image. Banding is particularly noticeable when the drop placement errors are not consistent from nozzle to nozzle on the printhead. Banding is also particularly noticeable when the drop placement errors for a single nozzle vary between consecutive drops, such as when the main and satellite drops sometimes coincide, but other times don&#39;t coincide. Furthermore, a combination of round and non-round spot shapes in an area on the medium which is intended to be printed with a uniform color and intensity can result in an undesirable variation of lightness and darkness within the supposedly uniform area. Accordingly, it would be desirable to deposit drops of fluid in a repeatably accurate and/or precise manner.  
         SUMMARY  
         [0007]    A fluid ejection device comprises a substrate including a fluid ejector thereon, and an orifice member positioned over said substrate. The orifice member has a fluid-transfer bore extending therethrough and corresponding to the fluid ejector. The orifice member further has a counter-bore about the fluid-transfer bore.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of a printer according to an embodiment of the present invention.  
         [0009]    [0009]FIG. 2 illustrates a perspective view of an embodiment of a fluid ejection cartridge of the present invention.  
         [0010]    [0010]FIG. 3 is a perspective view of an embodiment of a fluid ejector.  
         [0011]    [0011]FIG. 4 is a schematic isometric view of an embodiment of an orifice with a counterbore.  
         [0012]    [0012]FIG. 5 is a cross-sectional view of the orifice and the counterbore of FIG. 4.  
         [0013]    [0013]FIG. 6 is a schematic representation of drop placement errors with respect to the scan axis and medium advance axis.  
         [0014]    [0014]FIG. 7A is a plan view of a counter-bore embodiment shown symmetrically with a fluid transfer bore.  
         [0015]    [0015]FIG. 7B is a plan view of a counter-bore embodiment shown asymmetrically with a fluid transfer bore. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Overview of a Fluid Ejection Device Embodiment  
         [0017]    Referring now to the drawings, there is illustrated a fluid ejection system  10  constructed in accordance with an embodiment of the present invention and operated in accordance with an embodiment of a fluid ejection method which provides accurate and/or precise drop placement at high scanning speeds so as to minimize visual printing defects such as banding. The system  10  includes at least one ejection device  110  having ejection nozzle features which reduce drop placement error in the medium advance direction  4  (known as PAD error) and/or in the scan axis direction  2  (known as SAD error). In one embodiment, objectionable banding is minimized, thereby maximizing the quality of the output produced by the system  10 .  
         [0018]    The system  10  generally includes a frame  14  to which a carriage  20  is moveably mounted along a sliding rail  22 . The carriage  20  is capable of holding one or more ejection devices  110  and moves them relative to the surface of a medium  18  such as paper, transparency film, textiles, or any other medium. The medium is often placed in input tray  12 . In this embodiment shown, the ink or fluid supply is separate from the ejection device  110 . Embodiments of the present invention may use fluid supply that is separate from the ejection device as shown in FIG. 1, or fluid supply that is coupled with the ejection device within a cartridge, such as the cartridge  101  shown in FIG. 2.  
         [0019]    [0019]FIG. 2 is a perspective view of an embodiment of a cartridge  101  having a fluid ejection device  103 , such as a printhead. The cartridge houses a fluid supply, such as ink. In this embodiment, visible at the outer surface of the printhead are a plurality of bores, such as orifices or nozzles,  105  through which fluid is selectively expelled. In one embodiment, the fluid is expelled upon commands of a printer (not shown), which commands are communicated to the printhead through electrical connections  107 .  
         [0020]    In the embodiment of FIG. 3, a thin film stack  115  (such as an active layer, an electrically conductive layer, or a layer with micro-electronics) is formed or deposited on a front or first side (or surface) of a substrate. The thin film stack can include, in one embodiment, layers to form an ejection element  201 , such as a fluid ejector, a resistor, a heating element, or a bubble generator.  
         [0021]    In one embodiment, a top layer  124  is deposited over the thin film stack  115 . In one embodiment, the top layer  124  is a layer comprised of a fast cross-linking polymer such as photoimagable epoxy (such as SU8 developed by IBM), photoimagable polymer or photosensitive silicone dielectrics, such as SINR-3010 manufactured by ShinEtsu™. In another embodiment, the top layer  124  is made of a blend of organic polymers which is substantially inert to the corrosive action of ink. Polymers suitable for this purpose include products sold under the trademarks VACREL and RISTON by E. I. DuPont de Nemours and Co. of Wilmington, Del. In yet another embodiment, the top layer  124  includes a polymer barrier layer defining firing chamber  202  and an orifice plate defining the corresponding orifice  105 .  
         [0022]    In a particular embodiment, the top layer  124  defines the firing chamber  202  where fluid is heated by the corresponding ejection element  201  and defines the corresponding nozzle orifice  105 , such as a fluid-transfer bore, through which the heated fluid is ejected. Fluid  209  flows into the firing chamber  202  via a channel  203  defined by the top layer  124 . Flow of a current or a “fire signal” through the resistor causes fluid in the corresponding firing chamber to be heated and expelled through the corresponding nozzle  105 .  
         [0023]    In one embodiment, the top layer  124  is an orifice member. The orifice member has a top surface that defines a top opening for the fluid-transfer bore. In one embodiment, the counter-bore  205  extends around the top opening for the fluid transfer bore  105 . In another embodiment, a counterbore  205  is disposed in the outer surface of the layer  124  about the nozzle  105 . In an inner surface of the layer  124 , such as a bottom surface of the orifice member, is a bottom opening of the orifice  105 . The bottom opening is adjacent the corresponding firing chamber.  
         [0024]    In one embodiment, the fluid transfer bore  105  is substantially circular. The orifice  105  has a diameter “a” in a range of about 10 to 14 microns, in one particular embodiment about 12 microns, to its top edge  106 . In another embodiment, the nozzle  105  is non-circular in shape. For this non-circular shape, the area of the counterbore is substantially similar to the range of circular areas.  
         [0025]    Embodiments of Reduced Drop Placement Error  
         [0026]    As will be explained subsequently in greater detail, the nozzles  105  and counter-bores  205  can be constructed with geometric features according to one of the present embodiments that reduce drop placement errors on a medium  18 .  
         [0027]    [0027]FIG. 4 is an isometric view of the orifice  105  and counterbore  205  of FIG. 3. FIG. 5 is a cross-sectional view of the counterbore  205  of FIG. 4. The counterbore  205  is disposed in the orifice member about a top surface of the orifice  105 . The depth w 1  of the counterbore is less than the depth or height w 2  of the orifice through the orifice member in this embodiment. In one embodiment, the depth w 1  of the counterbore is about 0.5 to 10 microns, in a particular embodiment: 1 micron. In one embodiment, the depth w 2  of the orifice in the orifice member  124  ranges from about 10 microns to 50 microns. In particular embodiments, the depth w 2  is one of 10, 25, 37, and 50 microns.  
         [0028]    In one embodiment, during operation of the fluid ejector, when a fluid drop is ejected from the top surface of the orifice  105 , some fluid  209  breaks off from the drop to set on the top surface of the orifice, within the counterbore. The fluid  209  within the counter-bore creates puddling, which can affect drop placement error, and thus, print quality in some embodiments.  
         [0029]    When puddling occurs in a counter-bore  205  corresponding with a fluid ejection nozzle  105 , there are three general scenarios. In a first scenario, there is not enough puddling in the counterbore  205  to affect the direction of the fluid being ejected from nozzle  105 . After some amount of firing of the ejection device, a puddle begins to form in the counterbore in a second ‘transitional’ scenario. In this second ‘transitional’ scenario, there is an amount of puddling in the counterbore  205  that may affect the direction that fluid is being ejected from the nozzle  105 . In one embodiment, this puddle uniformly surrounds the bore, and has no substantial impact on drop trajectory. In another embodiment, there is an asymmetric puddle about the bore, and accordingly, an impact on drop trajectory. Generally, in this asymmetric transition state, the direction of dot placement error is directed towards (a) the highest puddle of fluid  209  in the counterbore  205  surrounding the orifice  105  and/or (b) the fluid first touching the bore. In one embodiment, during this transitional scenario, the entire puddle pulls the drop toward the area of the initially highest puddle, thereby misdirecting the drop substantially consistently in that general direction. The counterbore fills starting at the area of the initially highest puddle and moving around the nozzle in both directions with two advancing fluid fronts. As the puddle increases in size about the nozzle, the sum of the misdirection remains substantially in the same direction, but the magnitude of the misdirection decreases.  
         [0030]    In a third ‘steady state’ scenario, the puddle expands until the entire counterbore is substantially evenly filled with a layer of fluid approximately 1 μm thick. After the fluid fronts meet, the misdirection forces from the puddle are substantially equal in all directions, and the puddle no longer affects dot placement.  
         [0031]    In one embodiment, the counterbore surface is highly wettable. In another embodiment, the counterbore surface is non-wettable. In yet another embodiment, the counterbore surface is part wettable and part non-wettable. Those of skill in the art appreciate that modifications of the counterbore surface wetting can be substantially equivalent to modifications of the counterbore dimensions with respect to the bore.  
         [0032]    In one embodiment, the ejected fluid is affected by the puddled fluid in the counterbore such that the ejected fluid may be misdirected in a random direction, i.e. no preferred direction for tail break-off. In most embodiments discussed herein, the second ‘transitional’ scenario is being considered. In a particular embodiment, it is desired to bias or influence the location of highest fluid puddle, and thus the direction of dot placement error.  
         [0033]    In a particular embodiment, fluid  209  builds up more quickly in the narrowest areas of the counterbore  205 ; i.e. a shortest distance between a top edge  106  of the orifice  105  and an outer edge  206  of the counterbore  205 . In one embodiment, the fluid tends to build up in the narrowest area because the bottom surface of the counterbore is not perfectly flat, and tends to have a slightly domed shape. The slightly domed shape causes the top surface of the orifice to be slightly pointed away from the center of the counterbore, which can cause the tail of the drop to break off in this same direction. The top surface of the orifice points toward the narrowest region due to this doming effect. In an additional embodiment, the fluid tends to build up in the narrowest area because the counterbore is generally highly wettable to certain fluids. Fluid in the counterbore spreads out in a thin layer on the bottom surface. The fluid collects, growing thicker, in any groove or other capillary in the bottom surface. In a particular embodiment, fluid collects around the substantially orthogonal outside edge  206  of the counterbore. As this ring of fluid expands, fluid first touches the bore near the area where the bore is closest to the counterbore edge, i.e. the narrowest region.  
         [0034]    Considering now with reference to FIG. 6, the drop placement error (also known as directionality error or concentricity error) associated with the main and satellite drops ejected from the ejection chamber (such as the firing chamber)  202  is defined as the distance between the actual drop location  19 ′, and the intended pixel location  19 . The drop placement error can have a scan axis directionality (“SAD”) component in the direction along the scan axis  2 , and a medium (such as paper) axis directionality (“PAD”) component in the direction along the medium advance axis  4 . Where the main  6  and satellite  8  drops are not coincident on the medium  18  (as in FIG. 6), the drop placement error may be determined with respect to a centroidal position of the two drops  6 , 8 . Alternatively, the drop placement error of the drops  6 , 8  may be measured with respect to the drops  6 , 8  individually, with the main drop  6  having a drop placement error  53  with a PAD component  51  and a SAD component  52  relative to the intended location  19 , and the satellite drop  8  having a drop placement error  56  with a PAD component  54  and a SAD component  55  with respect to the main drop  6 .  
         [0035]    In embodiments described herein, some types of errors can often be compensated for so as to more closely align the main drop  6  to the desired location  19 . However, in some ejection devices the drop placement error of the satellite drop  8  tends to have variable amounts of SAD and PAD error from chamber to chamber, and from drop to drop from the same chamber. This variable drop placement error may become worse at higher scanning speeds.  
         [0036]    Because PAD error is typically more perceptible to the human eye than SAD error, in one preferred embodiment PAD error is minimized. Accordingly, the dot placement error has less of an impact on print quality in embodiments where the error is primarily in the scan axis  2 .  
         [0037]    Alignment of Counterbores to Bores  
         [0038]    The embodiment of FIG. 7A illustrates a plan view of a counter-bore  205  being substantially symmetrical to a corresponding orifice  105 . The counterbore  205  is aligned with the bore  105  when symmetrically placed about the bore, as shown in this embodiment. However, it is often difficult to align the counter-bore with the bore to within a certain tolerance, with some embodiments. FIG. 7B illustrates a plan view of an embodiment with a counter-bore  205  being asymmetrical to the corresponding orifice  105 .  
         [0039]    In one embodiment, the distance between the actual location of the counterbore  205  with respect to the bore  105 , and the intended location of the counterbore with respect to the bore is considered an offset in radial alignment. In one counterbore embodiment, a radial alignment tolerance is about 0 to 10 microns. In another counterbore embodiment, the radial alignment tolerance is about 7 microns. In yet another counterbore embodiment, the tolerance is less than about 5 microns. One skilled in the art would understand that tolerances outside this range are within the purview of these embodiments. In several embodiments, the SAD and PAD errors are affected by the degree or amount of misalignment of the counterbore  205  with respect to the bore  105 . In one embodiment, this misalignment is substantially the same as the amount of counterbore radial offset. In the embodiment of FIG. 7A, there is substantially no counterborelbore misalignment. As the counterbore  205  of FIG. 7A fills with fluid  209 , the fluid is filled about the bore  105  with substantial symmetry. This fluidic symmetry, in one embodiment in the “transitional” state, renders a counterbore without any significant fluid high spots. Accordingly, the drop placement upon the media is substantially unaffected by the fluid in the counterbore, and thus, there are no significant SAD or PAD errors in this embodiment.  
         [0040]    Counter-Bore Embodiments  
         [0041]    In one embodiment, the shape and size of the counterbore  205  depends upon the shape and size of the bore  105 . The counterbore and bore are configured in size and shape such that a fluid puddle is formed in the narrowest region to maximize drop placement accuracy and/or precision, such that print quality is maximized in one embodiment.  
         [0042]    In the embodiments shown in FIGS. 7A and 7B, the counter-bore  205  is stadium shaped. In another embodiment, the outer edges  206  of the counter-bore  205  are shaped as an oval race track. In yet another embodiment, the counter-bore  205  is oblong. In another embodiment, the counter bore  205  is substantially a circle with multiple substantially flat spots  207  in edges  206  of the counter-bore. In one embodiment, one flat spot  207  is substantially in the scan axis  2  direction. In another embodiment, the flat spot is substantially aligned with the medium axis  4  direction.  
         [0043]    As shown in the embodiments of FIGS. 7A and 7B, the counterbore has straight or flat sides  207  and rounded ends  208 . In another embodiment, the sides  207  are curvilinear. In yet another embodiment, the counter-bore is a shape with narrow sides in first direction, and elongated sides in a second direction perpendicular to the first direction. In one embodiment, the counter-bore is one of race-track shaped, rectangular, and hourglass shaped.  
         [0044]    In the embodiment of FIGS. 7A and 7B, the counterbore is two semi-circles connected by a bridge. The end semi-circles have radii of curvature of r 1  and r 2 , respectively. The radii of curvature r 1  and r 2  range from between about 17 and 19 microns (the diameter is about 34 to 37 microns). In one embodiment, r 1  and r 2  are substantially the same length. In another embodiment, r 1  and r 2  are different lengths. The range of radii r 1 , r 2  is about 1.5 to about 5 times the nozzle/bore diameter, in a particular embodiment. In a more particular embodiment, the radii of curvature r 1  and r 2  is about three times the nozzle diameter.  
         [0045]    In one embodiment, at least a substantial portion of the fluid-transfer bore  105  is within the bridge section of the counterbore  205  (as shown best in FIG. 7A). The bridge in between the two semi-circles has a length  1  that is about 5 microns in one embodiment. In a particular embodiment, the side length  1  is about 0.25 to about 1.5 times the nozzle diameter. In a more particular embodiment, the side length is about 0.5 times the nozzle diameter. In one embodiment, the counter-bore shape has a surface area of about 1260 square microns.  
         [0046]    In the embodiments of FIGS. 7A and 7B, between the top edge  106  of the orifice and outer edges  206  of the counter-bore is the bottom of the counterbore. A distance “d” is measured along the bottom of the counterbore between the top edge  106  of the orifice  105  and the closest corresponding outer edge  206  of the counterbore  205 . In the embodiment shown in FIG. 7A, d 1  and d 4  are substantially aligned with the scan axis (or short axis), while d 2  and d 3  are substantially aligned with the medium axis (or long axis). In the embodiment shown, distances d 1  and d 4  are substantially the same, and are in the range of about 6 to 16 microns. In this embodiment, distances d 2  and d 3  are substantially the same, and are in the range of about 8.5 to 18.5 microns.  
         [0047]    In some embodiments, the counter-bore is symmetrical in the scan axis  2  direction and/or the medium axis  4  direction. For example, in one embodiment, d 1  is substantially the same as d 4 , and the bore is substantially symmetrical to the counterbore in the scan axis direction. In another embodiment, d 2  is substantially the same as d 3 , and the bore is substantially symmetrical to the counterbore in the medium axis direction. In some embodiments, the counter-bore is asymmetrical in the scan axis  2  direction and/or the medium axis  4  direction. For example, d 1  is not substantially the same as d 4 ; and/or d 2  is not substantially the same as d 3 .  
         [0048]    In the embodiment of FIG. 7B, the bore  105  is asymmetrical with the counterbore  205  in both the scan and medium axes. The fluid-transfer bore (or orifice)  105  is non-concentric with respect to the counterbore  205  in this embodiment. In embodiments of the present invention, the direction or misdirection of the fluid caused by the puddling of the fluid  209  in the narrowest region is biased or influenced by the asymmetry of the counterbore relative to the bore. In particular embodiments, the narrowest region of the counterbore bottom (and corresponding puddle) is in the scan axis direction.  
         [0049]    An edge  206  of the counterbore  205  is closest to an edge  106  of the fluid-transfer bore  105  in a first direction, in the first region. In the embodiment shown in FIG. 7B, distances d 1  and d 4  are each shorter than distances d 2  or d 3 , and distance d 4  is longer than d 1 . In this embodiment, the narrowest region (closest edges  106 ,  206 ) is therefore located along the distance d 1 , with the first direction being substantially in the scan axis  2  direction. Consequently, the counterbore region of d 1  fills up more quickly with fluid  209  than in the other directions. Accordingly, in one embodiment where the puddling is in the transitional state, the misdirection  300  is substantially towards d 1 , as shown in FIG. 7B.  
         [0050]    In embodiments of the present invention, the shape of the counterbore allows the capillary action of the fluid to bias any puddling-related misdirection in the least harmful directions, which allows a much larger tolerance for bore-counterbore alignment and thus, a more robust product and higher yield. Because the narrowest regions of this embodiment are in the scan axis direction, where errors may be unavoidable, dot placement errors are thereby biased substantially in the scan axis direction in this embodiment. Therefore, the counterbores  205  have increased robustness to misalignment in the medium axis  4 , and less robustness to misalignment in the scan axis  2  direction, in this embodiment.  
         [0051]    In other embodiments, the first direction (where edges  106 ,  206  are closest) is in any direction, including in the direction of the medium axis or a combination of the scan and medium axes. In these other embodiments, the ejected fluid is biased in primarily the medium axis  4  or in both the scan and medium axes. In one of these other embodiments, d 2  is the shortest distance between edges  106 ,  206  and the misdirection  300  of the dot placement is biased towards the area of d 2 . In another embodiment, d 3  is shortest and the misdirection  300  is biased towards d 3 . In another embodiment, d 4  is shortest and the misdirection  300  is biased towards d 4 .  
         [0052]    It is therefore to be understood that this invention may be practiced otherwise than as specifically described. For example, the present invention is not limited to thermally actuated fluid ejection devices, but may also include, for example, piezoelectric activated fluid ejection devices, and other mechanically actuated printheads, as well as other fluid ejection devices. Thus, the present embodiments of the invention should be considered in all respects as illustrative and not restrictive, the scope of the invention to be indicated by the appended claims rather than the foregoing description. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.