Abstract:
In one embodiment, a fluid ejector structure includes: a chamber; a bridge spanning at least part of the chamber; a channel through which fluid may enter the chamber; a fluid ejector element on the bridge; and an outlet through which fluid may be ejected from the chamber at the urging of the fluid ejector element. The outlet is disposed opposite the fluid ejector element across a depth of the chamber and the chamber, ejector element and outlet are configured with respect to one another such that substantially all of the fluid in the chamber is ejected through the outlet upon actuation of the ejector element.

Description:
BACKGROUND 
     Thermal inkjet printers typically utilize a printhead that includes an array of orifices (also sometimes called nozzles) through which ink is ejected on to paper or other print media. Ink filled channels feed ink to a firing chamber at each orifice. As a signal is applied individually to addressable thermal elements, resistors for example, ink within a firing chamber is heated, causing the ink to bubble and thus expel ink from the chamber out through the orifice. As ink is expelled, more ink fills the chamber through a channel from the reservoir, allowing for repetition of the ink expulsion sequence. The use of thermal inkjet printing in high throughput commercial applications presents special challenges for maintaining good print quality. 
     Small droplets released during break-up of the tail of more elongated ink drops ejected by conventional inkjet printheads typically travel more slowly to the print medium than does the main drop (the head of the ejected ink drop). Thus, these trailing, “satellite” droplets land on the print medium away from the main drop, forming extraneous marks along the edges or in the background of the desired images. Such print quality defects often make the images appear fuzzy or smeared. This undesirable characteristic of ejecting elongated ink drops may become more pronounced as printing speed increases and the printhead and print medium move faster and faster with respect to one another. 
     Clear mode printing, in which substantially all of the ink in the firing chamber is ejected, has been used to eject tail free drops. However, the rate at which ink refills the firing chamber after each ejection in preparation for the next ejection is significantly slower than for printing with elongated ink drops. In “normal”, non-clear mode printing, the collapsing ink bubble tends to drag ink into the firing chamber to help speed refill. In clear mode printing, since the ink bubble is vented completely out through the orifice, there is no collapsing bubble to help draw in refill ink, thus slowing refill. Consequently, conventional clear mode printhead architectures have not proven suitable for inkjet web printing presses and other high speed printing applications. 
    
    
     
       DRAWINGS 
         FIG. 1  is a perspective section view illustrating a thermal inkjet printhead structure according to one embodiment of the disclosure. 
         FIG. 2  is a plan view of an individual ejector structure embodiment from the printhead structure of  FIG. 1 . 
         FIGS. 3 and 4  are section views of the ejector structure embodiment of  FIG. 2  taken along the lines  3 - 3  and  4 - 4 , respectively, in  FIG. 2 . 
         FIG. 5  is a perspective section view of the ejector structure embodiment of  FIG. 2  corresponding to section line  3 - 3  in  FIG. 2 . 
         FIG. 6  is a perspective section view of an ejector structure according to another embodiment of the disclosure in which the bridge part is configured as a more narrow strip extending through only a center portion of the firing chamber. 
         FIG. 7  is a perspective section view of an ejector structure according to another embodiment of the disclosure in which the bridge part is integral to the substrate. 
         FIG. 8  is a graph illustrating clear mode and non-clear mode printing embodiments. 
         FIGS. 9-11  illustrate drop shapes for different printhead embodiments. 
     
    
    
     The structures shown in the figures, which are not to scale, are presented in an illustrative manner to help show pertinent features of the disclosure 
     DESCRIPTION 
     Embodiments of the present disclosure were developed in an effort to improve print quality and firing resistor reliability for high throughput commercial inkjet printing applications. It has been discovered that combining firing chamber configurations typical of those used in clear mode printing with a bridge type, dual feed channel printhead architecture allows for ejecting compact, substantially tail free ink drops at frequencies needed to support inkjet web printing presses and other high speed printing applications. Embodiments of the disclosure will be described with reference to a thermal inkjet printhead structure. Embodiments, however, are not limited to thermal inkjet printhead structures, or even inkjet printhead structures in general, but may include other fluid ejector structures. Hence, the following description should not be construed to limit the scope of the disclosure. 
       FIG. 1  is a perspective section view illustrating a thermal inkjet printhead structure  10  according to one embodiment of the disclosure. Printhead structure  10  represents more generally a fluid-jet precision dispensing device or fluid ejector structure for precisely dispensing a fluid, such as ink, as described in more detail below. Printhead structure  10  includes an array of individual ejector structures  12  each configured to eject drops of ink or other fluid.  FIGS. 2-5  illustrate an individual ejector structure  12  from  FIG. 1 .  FIG. 2  is a plan view of ejector structure  12 .  FIGS. 3 and 4  are section views of ejector structure  12  taken along the lines  3 - 3  and  4 - 4 , respectively, in  FIG. 2 .  FIG. 5  is a perspective section view of ejector structure  12  corresponding to section line  3 - 3  in  FIG. 2 . Conventional techniques well known to those skilled in the art of printhead fabrication and semiconductor processing may be used to form the structures described below. 
     While thermal inkjet printing devices designed to eject ink onto media are described, those of ordinary skill within the art can appreciate that embodiments of the present disclosure are not so limited. In general, embodiments of the present disclosure may pertain to any type of fluid-jet precision dispensing device or ejector structure for dispensing a substantially liquid fluid. A fluid-jet precision dispensing device is a drop-on-demand device in which printing, or dispensing, of the substantially liquid fluid in question is achieved by precisely printing or dispensing in accurately specified locations, with or without making a particular image on that which is being printed or dispensed on. As such, a fluid-jet precision dispensing device is in comparison to a continuous precision dispensing device, in which a substantially liquid fluid is continuously dispensed. An example of a continuous precision dispensing device is a continuous inkjet printing device. The fluid-jet precision dispensing device precisely prints or dispenses a substantially liquid fluid in that the latter is not substantially or primarily composed of gases such as air. Examples of such substantially liquid fluids include inks in the case of inkjet printing devices. Other examples of substantially liquid fluids include drugs, cellular products, organisms, chemicals, and fuel which are not substantially or primarily composed of gases such as air and other types of gases. Therefore, while the following description is described in relation to an inkjet printhead structure for ejecting ink onto media, embodiments of the present disclosure more generally may pertain to any type of fluid-jet precision dispensing device or fluid ejector structure for dispensing a substantially liquid fluid. 
     Referring now to  FIGS. 1-5 , firing resistors  14  and signal traces  16 ,  18  ( FIGS. 2 and 4 ) in ejector structure  12  are formed as part of a thin film stack  20  on a substrate  22 . Signal traces  16  and  18  carry electrical firing signals to selectively actuate or “fire” a corresponding resistor  14  as directed by the printer controller during printing operations. Although a silicon substrate  22  is typical, other suitable substrate materials could be used. In addition to firing resistors  14  and traces  16 ,  18 , thin-film stack  20  usually also will include layers/films that electrically insulate resistor  14  from surrounding structures, provide conductive paths to resistors  14  (including traces  16  and  18 ), and help protect against contamination, corrosion and wear (such protection is often referred to as passivation). In the embodiment shown in  FIGS. 1-5 , film stack  20  includes an oxide layer  24  on substrate  22  and a passivation dielectric layer  26  over resistors  14  and traces  16 ,  18 . The specific composition and configuration of film stack  20 , however, are not important to the innovative aspects of this disclosure except with regard to the configuration of resistors  14  described below. 
     Passages  28  in substrate  22  carry ink to ink inlet channels  30  that extend through film stack  20  near resistors  18 . Ink enters a firing chamber  32  associated with each firing resistor  18  through a corresponding pair of channels  30 . Ink drops are expelled or “fired” from each chamber  32  through an orifice  34 . Orifices  34  are formed in an orifice sub-structure  36  made of silicon or other suitable material formed on or bonded to the underlying ejector element sub-structure  38 . Orifice sub-structure  36  is sometimes referred to as an orifice plate. A dielectric or other suitable passivation layer (not shown) may be formed on those areas of orifice sub-structure  36  exposed to ink to inhibit corrosion from prolonged exposure to the ink, for example at firing chambers  32  and orifices  34 . The specific composition and configuration of orifice sub-structure  36 , however, are not important to the innovative aspects of this disclosure except with regard to the configuration of firing chambers  32  and orifices  34  described below. 
     Each resistor  14  is supported on a bridge  40  that at least partially spans firing chamber  32 . The span of bridge  40  is defined by a pair of ink inlet channels  30  positioned opposite one another across chamber  32  as best seen in  FIG. 2 . Bridge  40  may made from a metal or other suitable high thermal conductivity part  42  embedded in substrate  22 , as shown in  FIG. 1-5 , to facilitate cooling. In the embodiment shown in  FIGS. 1-5 , inlet channels  30  are formed fully within a bridge part  42  that surrounds firing chamber  32 . In an alternative embodiment shown in  FIG. 6 , bridge part  42  is configured as a more narrow strip extending through only a center portion of firing chamber  32  such that the outboard part  44  of each inlet channel  30  is formed in substrate  22 . In an alternative embodiment shown in  FIG. 7 , bridge part  42  is integral to substrate  22 . The specific material for and configuration of bridge  40  and bridge part  44  may be varied as desirable for a particular printhead application. For example, the added cost of a metal bridge  40  may be desirable for some printing applications or fabrication process flows while a silicon bridge  40  integral to substrate  22  may be desirable for other printing applications or fabrication process flows. 
     Referring again to  FIGS. 1-5 , the relative sizes of resistor  14 , firing chamber  32  and orifice plate  36  may be configured to control the shape of ink drops ejected through orifice  34 . There is a region of dimensions within firing chamber  32  that can deliver compact, substantially tail free ink drops with no or few satellite drops trailing the main drop and still maintain refill rates for high speed printing, firing frequencies of 30 kHz for example. As used in this document, a “compact” drop means a drop in which 80% or more of the mass of each drop, on average, is contained in the main drop and, correspondingly, 20% or less of the mass of the drop is contained in a tail and/or in satellite droplets, (in conventional inkjet printing, by contrast, typically only about 50% of the mass of the drop is contained in the main drop.) Compact drop printing may be achieved where the sum of the depth of firing chamber  32  plus the depth of orifice  34  approximates the height of the ink bubble formed upon actuation of resistor  14  such that substantially all of the ink is ejected from firing chamber  32  through orifice  34 . In a typical printing operation, for example, the ink bubble expands to about 20 μm in height but may be up to 30 μm high. Therefore, it is expected that the combined depth of chamber  32  and orifice  34  will not be greater than 30 μm for a typical implementation of ejector structure  12 . Approximate in this context means the combined depth of chamber  32  and orifice  34  is such that the bubble height exceeds the depth of chamber  32  without necessarily extending to the full depth of orifice  34 . For some implementations ejecting compact drops it may be desirable that the combined depth of chamber  32  and orifice  34  is such that the bubble height only slightly exceeds the depth of chamber  32 , allowing the bubble to push just into orifice  34 , while in other implementations the bubble height should approach the full depth of orifice  34 , allowing the bubble to push through to (or close to) the exterior of orifice  34 . 
     The dimensions of one example configuration for compact drop printing are noted below with reference to  FIGS. 2-4  for a rectangular firing chamber  32  51 μm long (L c =51 μm) and 33 μm wide (W c =33 μm) and a circular orifice  34  18 μm in diameter,
         L r  Length of resistor  14 =26 μm   W r  Width of resistor  14 =26 μm   D c  Depth of chamber  32 =6 μm   D o  Depth of orifice  34 =9 μm
 
Increasing chamber depth D c  to 9 μm will produce satellite droplets but still within the range of clear mode printing. However, increasing chamber depth D c  to 13 μm will result in non-clear mode printing. Similarly, increasing orifice depth D o  will also affect the shape of the drop ejected from chamber  32 .
       

     The effect of different chamber depths D c  and orifice depths D o  on drop shape is illustrated in the graph of  FIG. 8  for a 51 μm long, 33 μm wide rectangular firing chamber  32 . Referring to  FIG. 8 , an area  46  of satellite free “full” compact drop printing appears in the lower left hand part of the graph bounded by a chamber depth D c  of about 7.5 μm along the vertical axis and an orifice depth D o  of about 9.5 μm along the horizontal axis. An area  48  of “partial” compact drop printing heavily weighted to the main drop appears in the middle of the graph bounded along the upper end by a chamber depth D c  of about 14 μm at a an orifice depth D o  of 6 μm down to about 10.5 μm at an orifice depth D o  of 13 μm. Elongated drop printing area  50  occurs at chamber depths D c  greater than about 14 μm at a an orifice depth D o  of 6 μm and greater than about 10.5 μm at an orifice depth D o  of 13 μm. The different depths D c  and D o  and the corresponding changes in the configuration of firing chamber  32  near each of the four corners of the graph are depicted structurally by small generalized representations of ejector structure  12  designated by part numbers  52 ,  54 ,  56  and  58  in  FIG. 8 . 
     Ink drop shapes corresponding to some of the data points on the graph of  FIG. 8  are illustrated in  FIG. 9 . Referring to  FIG. 9 , for a chamber depth D o  of 6 μm, satellite free full compact ink drops  60  and  62  are ejected for orifice depths D o  of 6 μm and 9 μm and a partial compact drop  64  heavily weighted to the main drop is ejected for an orifice depth D o  of 13 μm. Drop  60  at the shallower D o  of 6 μm, however, shatters when ejected while drop  62  at the deeper D o  of 9 μm remains intact. For a chamber depth D o  of 9 μm, partial compact ink drops  66 ,  68  and  70  are ejected for orifice depths D o  of 6 μm, 9 μm and 13 μm, with each drop  66 ,  68  and  70  becoming more and more heavily weighted to the satellite droplets until a distinct tail begins to form on drop  70 . For a chamber depth D o  of 13 μm, a partial clear mode ink drop  72  is ejected for an orifice depth D o  of 6 μm and non-clear mode drops  74  and  76  are ejected for orifice depths D o  of 9 μm and 13 μm. 
       FIGS. 10 and 11  show ink drop shapes for narrower (W r =20 μm) and wider (W r =32 μm) resistors  14 , respectively. Ink drops are indicated by part numbers  78 - 94  in  FIG. 10  and part numbers  96 - 112  in  FIG. 11 . Drop shapes  78 - 112  in  FIGS. 10 and 11  are similar to those corresponding to a square (W r =26 μm) resistor  14  in  FIG. 9  with a tail on the main drop developing at somewhat shallower orifice depths D o  for the narrower resistor  14  in  FIG. 10  and at somewhat deeper orifice depths D o  for the wider resistor  14  in  FIG. 11 . 
     Referring again to  FIGS. 1-5 , the close proximity of dual ink inlet channels  30  to chamber  32  and resistor  14  allows a greater volume of ink to reach chamber  32  and resistor  14  faster than in conventional clear mode printing architectures. It is desirable, therefore, to position inlet channels  30  as dose as possible to resistor  14 , within a few microns for example, and that the volume of inlet channels  30  match the volume of the drop ejected through orifice  34 . Referring specifically to  FIG. 2 , the area of orifice  34  should approximate the area of resistor  14  to help balance ink drop ejection with blowback. Blowback refers to the phenomenon in which ink tends to be pushed back out of inlet channels  30  away from firing chamber  32  upon actuation of resistor  14  to eject an ink drop through orifice  34 . Also, and referring now also to  FIGS. 3-5 , the volume of inlet channels  30  should be sized appropriately to balance blowback with refill. A thicker/deeper beam  40  reduces blowback but increases drag, thus slowing refill. A thinner/shallower beam  40  reduces drag and speeds refill, but increases blowback. For a typical implementation of ejector structure  12 , it is expected that a bridge thickness/depth 10-50 μm, usually about 15 μm, and an inlet volume 0.5-2.0 times the sum of the volume of orifice  34  and the volume of firing chamber  32  will inhibit excessive blowback while still allowing refill rates sufficient to support high speed clear mode printing. 
     This bridge type architecture for ejector structure  12 , with dual inlet channels  30  positioned in dose proximity to firing resistor  14 , significantly reduces the mechanical impact on resistor  14  of the ink refilling chamber  32 —the incoming ink does not hit the resistor with as much force as in a conventional printhead architecture. Also, since the ink bubble is vented out through orifice  34  during each ejection, there is no collapsing bubble and, accordingly, no cavitation damage to resistor  14  caused by collapsing ink bubbles. Thermal modeling for a metal bridge  40  in the configuration shown in  FIG. 2-5  indicates the steady state temperature in both the ink and the surrounding structure are lower than in a conventional thermal inkjet printhead structure with the same resistor turn-on energy of 1 μJ. It is believed that the lower temperature is achieved at least in part by the more effective convective cooling of the dual inlet channel, metal bridge structure. Each of these factors helps improve the reliability of the firing resistors and extend the useful life of the printhead. 
     As used in this document, one part formed “over” another part does not necessarily mean one part formed above the other part. A first part formed over a second part will mean the first part formed above, below and/or to the side of the second part depending on the orientation of the parts. Also, “over” includes a first part formed on a second part or formed above, below or to the side of the second part with one or more other parts in between the first part and the second part. 
     As noted at the beginning of this Description, the example embodiments shown in the figures and described above illustrate but do not limit the disclosure. Other forms, details, and embodiments may be made and implemented. Therefore, the foregoing description should not be construed to limit the scope of the disclosure, which is defined in the following claims.