Patent Publication Number: US-2006000925-A1

Title: Reduced sized micro-fluid jet nozzle structure

Description:
FIELD OF THE DISCLOSURE  
      The disclosure relates to improved nozzle holes for micro-fluid ejection devices and to methods for making the nozzle holes.  
     BACKGROUND  
      Fluid ejection droplet size from a micro-fluid ejection device is an important parameter for achieving desired results. For example, the quality of images printed by an ink jet printer onto a medium is greatly influenced by the size of the ink droplets ejected by the printhead. Currently, eleven micron diameter nozzles produce a two to five nanogram droplet size. As smaller droplets are desired, the nozzle diameter is decreased along with an ejection actuator size decrease. However, as the nozzle diameter decreases, problems arise in the manufacture and operation of such nozzles. Smaller nozzles are more prone to blockage from contamination. Also, in the case of printing, more droplets are required to be delivered for an image, thereby slowing down the printing process.  
      Attempts have been made to provide multiple smaller nozzle holes for a single fluid chamber. However, these attempts often provide nozzle bores through the nozzle plate material with too high an aspect ratio for efficient fluid ejection.  
      Hence, there continues to be a need for improved nozzle plates for micro-fluid ejection devices.  
     SUMMARY  
      With regard to the foregoing and other objects and advantages there is provided a nozzle plate structure having nozzle bores therein in flow communication with corresponding fluid chambers. The nozzle bores have an overall nozzle bore length dimension and each nozzle bore includes two or more exit bores in fluid flow communication with each nozzle bore. Each of the exit bores having a length dimension ranging from about 5 to about 100 percent of the overall nozzle bore length dimension.  
      In another embodiment there is provided a method of making a nozzle plate for a micro-fluid ejection head. The method includes partially laser ablating a single nozzle bore for each fluid chamber in a nozzle plate material. Multiple exit bores corresponding to each nozzle bore are laser ablated in the nozzle plate material. The exit bores have a length dimension ranging from about 5 to about 100 percent of an overall nozzle bore length dimension.  
      Another embodiment provides a method of reducing fluid droplet size without substantially reducing fluid droplet volume from a micro-fluid ejection head. The method includes partially laser ablating a single nozzle bore for each fluid chamber in a nozzle plate material. Multiple exit bores corresponding to each nozzle bore in the nozzle plate material are also laser ablated in the nozzle plate material. The exit bores have a length dimension ranging from about 5 to about 100 percent of an overall nozzle bore length dimension. The nozzle plate material containing the laser ablated nozzle bores and exit bores is attached to a semiconductor substrate containing fluid ejection actuators. Fluid is ejected from the exit bores of the nozzle plate material by activating the fluid ejection actuators to provide multiple droplets from the exit bores for each nozzle bore having a total volume ranging from about one to about eight nanograms.  
      An advantage of the embodiments described herein can be the ability to provide multiple small fluid droplets during a single fluid ejection actuation step without significantly reducing the total volume of fluid ejected during the actuation step. Such an ability is particularly suitable for ink jet printing operations wherein smaller droplets provide a smoother more desirable image. In the present embodiments, even though smaller droplets are ejected from each corresponding nozzle bore, the volume of fluid remains substantially the same as the volume for a single larger droplet. Accordingly, there is little or no reduction in print speed associated with the production of smaller droplets.  
      The disclosed embodiments also provide a means for ejecting small droplets from a single fluid chamber without significantly affecting the jetting efficiency for the droplets. Unlike other ejection heads having multiple nozzle holes for a single fluid chamber, the multiple exit bores provided in the nozzle plate according to the disclosed embodiments have relatively small aspect ratios thereby reducing fluid resistance.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Further advantages of the disclosed embodiments will become apparent by reference to the detailed description of exemplary embodiments when considered in conjunction with the following drawings illustrating one or more non-limiting aspects of the embodiments, wherein like reference characters designate like or similar elements throughout the several drawings as follows:  
       FIG. 1  is a plan view, not to scale, of a nozzle hole in a nozzle plate according to the prior art;  
       FIG. 2  is a cross-sectional view, not to scale, of a portion of a prior art micro-fluid ejection head;  
       FIG. 3  is a plan view, not to scale, of a nozzle hole in a nozzle plate according an embodiment of the disclosure;  
       FIG. 4  is a cross-sectional view, not to scale, of a portion of a nozzle plate during a manufacturing process therefor according to the disclosure;  
       FIG. 5  is a plan view, not to scale, of a completed nozzle hole in the nozzle plate of  FIG. 4 ;  
       FIG. 6  is a cross-sectional view, not to scale, of a portion of a micro-fluid ejection device containing the completed nozzle plate of  FIG. 5 ;  
       FIG. 7  is a cross-sectional view, not to scale, of a portion of a micro-fluid ejection device containing an alternative nozzle plate of  FIG. 5 ;  
       FIG. 8  is a plan view, not to scale, of a mask for the nozzle plate of  FIG. 5 ;  
       FIG. 9  is a plan view, not to scale, of exit bores in a nozzle plate according to another embodiment of the disclosure;  
       FIG. 10  is a cross-sectional view, not to scale, of a portion of a micro-fluid ejection device containing the nozzle plate of  FIG. 9 ;  
       FIG. 11  is a cross-sectional view, not to scale, of a portion of a micro-fluid ejection device containing an alternative nozzle plate of  FIG. 9 ; and  
       FIG. 12  is a plan view, not to scale, of a nozzle plate according to another embodiment of the disclosure. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      With reference to  FIGS. 1 and 2 , a portion of a prior art micro-fluid ejection head  10  is illustrated. The micro-fluid ejection head  10  includes a nozzle plate  12  containing a nozzle bore  14 , providing nozzle hole  16 . The nozzle plate  12  is typically made of a corrosion resistant polymer, such as polyimide. The nozzle bore  14  is in fluid flow communication with a fluid chamber  18  provided by ablating a portion of the nozzle plate  12  or by providing a separate thick film layer (not shown). A fluid ejection actuator  20  for each of the nozzle holes  16  is provided on a semiconductor substrate  22 . As shown in  FIG. 2 , the nozzle bore  14  is a substantially continuous bore through a thickness T of the nozzle plate  12 . The overall length of the nozzle bore  14  depends on the thickness of the nozzle plate and may range from about 16 to about 65 microns. As the exit diameter D of the nozzle hole  16  is decreased to decrease the amount of fluid ejected, an aspect ratio T/D becomes larger thereby reducing an efficiency of ejection of fluid from the nozzle hole  16 . For fluids such as inks, the volume of fluid ejected from nozzle hole  16  typically ranges from about one to about eight nanograms for high quality printing applications.  
      As the exit diameter D of the nozzle hole  16  decreases, an ink delivery rate from the nozzle hole  16  also decreases. For example, printing applications wherein ink is ejected from the micro-fluid ejection device  10 , require more time to provide the same volume of ink printed thereby slowing down the printing speed.  
      In order to decrease a droplet size ejected from a micro-fluid ejection device without substantially decreasing the total drop volume during one ejection sequence, a two step laser ablation process for forming a nozzle bore and exit bore is illustrated in  FIGS. 3-8 . In  FIGS. 3 and 4 , a nozzle plate  24  according to one embodiment of the disclosure is illustrated. The nozzle plate  24  is ablated to provide a fluid chamber  26  and a nozzle bore  28  that extends part way through the nozzle plate  24  from the ink chamber  26  to an exit surface  30  of the nozzle plate  24 .  
      In a next step of the process, two or more exit bores  32  are laser ablated in the nozzle plate  24 . The exit bores  32  have a length dimension L 1 , referred to herein as the “exit bore length” ranging from about 5 to about 100 percent of the overall nozzle bore  28  length L 2 , which, as set forth above, may range from about 15 to about 65 microns. The exit bores  32  are ablated from the exit surface  30  of the nozzle plate  24  whereas the nozzle bore  28  is ablated from the fluid chamber  26  side of the nozzle plate  24 . Laser ablation of the nozzle bore  28  and exit bores  32  may be conducted using a single laser and flipping the nozzle plate  24  over once the fluid chamber  26  and nozzle bore  28  are ablated in the nozzle plate  24  to complete the formation of the exit bores  32 . Such a nozzle plate may also be provided by using two lasers, one to ablate nozzle bore  28  and one to ablate exit bores  32 . A single laser having a split laser beam may also be used to ablate nozzle bore  28  and exit bores  32 .  
      With reference to  FIG. 7 , a nozzle bore  34  and corresponding exit bores  36  may be ablated in a nozzle plate  38  from the fluid chamber  26  side of the nozzle plate  38 . Such a process eliminates the need to flip the nozzle plate  38  over after forming nozzle bore  34  or exit bores  36 . In this process, a laser beam is focused during ablation of the nozzle plate  38  to provide the partially ablated nozzle bore  34  and exit bore dividing member  40 .  
      In an alternative process, a gray scale mask  42  ( FIG. 8 ) may be used to form the exit bores  32  or  36  and exit bore dividing members  40  ( FIG. 7 ) and  44  ( FIG. 6 ). The gray scale mask  42  includes an opaque area  44 , transparent areas  46 , and a partially opaque area  48  corresponding to the dividing members  40  and  44  in nozzle plates  38  and  24 , respectively. During ablation of the nozzle plate  24  or  38 , the partially opaque area  48  causes ablation of the nozzle plate to proceed more slowly thereby forming dividing members  40  and  44 . Ablation of the nozzle plate  24  or  38  for exit bores  32  or  36 , respectively, would be terminated before ablation of the dividing members  40  or  44  is complete through the thickness T of the nozzle plate  38  or  24 .  
      While nozzle plates  24  and  38  contain four exit bores  32  and  36 , more or fewer exit bores may be provided in a nozzle plate to provide reduced droplet size. However, the overall volume of fluid ejected from exit bores  32  and  36  is substantially the same as the amount of fluid ejected from nozzle hole  16 ,  FIGS. 1 and 2 , e.g., from about one to about eight nanograms total. Also, the exit bores  32  and  36  may have any suitable shape including, but not limited to, semicircular, rectangular, triangular, or a combination of two or more of the foregoing shapes.  
       FIGS. 9-12  illustrate further embodiments of the disclosure.  FIG. 9  is a plan view of substantially rectangular exit bores  50  and  52  having rounded corners formed in a nozzle plate  54  and corresponding to a substantially rectangular nozzle bore  56  having rounded corners. In this case the centers of exit bores  50  and  52  are separated from one another by a distance X ranging from about five to about 30 microns. The separation distance X should be sufficient to prevent droplet recombination upon exit of the droplets from the exit bores  50  and  52 . As the droplets exit from the exit bores  50  and  52 , the droplets tend to become spherical due to a surface tension of the ejected fluid. Accordingly, the distance X should be somewhat larger than a diameter of an individual spherical droplet ejected from the exit bores  50  and  52  when the droplet trajectories are substantially parallel to one another.  
      Also, with the separation distance X between the centers of exit bores  50  and  52 , it may be desirable to provide a split fluid ejection actuator  58  having portions  58 A and  58 B that are connected to one another in series having substantially the same resistance as a single ejection actuator. The split fluid ejection actuator  58  wastes less energy since portions  58 A and  58 B need only heat fluid adjacent the portions  58 A and  58 B for flow through exit bores  50  and  52  respectively.  
      As mentioned above, a problem associated with ejecting multiple droplets of fluid from exit bores  32 ,  36 , and  50  is that the droplets may tend to recombine into a single droplet a short distance from the nozzle plates  24 ,  38  and  54 . Recombination of the individual droplets may occur due to decreased air pressure between the moving droplets or due to the surface tension of the fluid being ejected. If the separation distance X cannot be increased sufficiently to eliminate recombination of the droplets ejected, then exit bores  60  and  62  may be formed in a nozzle plate  64  at diverging angles θ as shown in  FIG. 11 . It will be appreciated that the exit bores  32  and  36  may also be formed with a diverging angle θ which may range from about 90° to about 150° to eliminate recombination of the droplets. Exit bores  60  and  62  may be formed with the diverging angles θ by use of the two-sided ablation process described above.  
      In the alternative, exit bores  66  in nozzle plate  68  may include notches or trenches  70  adjacent the exit bores  66  formed in the exit surface of the nozzle plate  68 . The trenches  70  cause droplets ejected from the exit bores  66  to be misdirected toward the trenches  70 . Accordingly, embodiments as described above provide multiple smaller droplets from a nozzle plate while maintaining substantially the same volume of fluid ejected per ejector activation sequence for each corresponding nozzle bore in the nozzle plate.  
      In the embodiments described above, the exit bore length L 1  may range from about 5 to about 100 percent of the overall nozzle bore length L 2 . Nevertheless, a practical range may be from about 10 to about 80 percent of the nozzle bore length depending on the overall thickness T of the nozzle plate material. In other embodiments the exit bore length L 1  may range from about 10 to about 50 percent of the overall nozzle bore length L 2 .  
      It is contemplated, and will be apparent to those skilled in the art from the preceding description and the accompanying drawings, that modifications and changes may be made in the embodiments of the disclosure. Accordingly, it is expressly intended that the foregoing description and the accompanying drawings are illustrative of preferred embodiments only, not limiting thereto, and that the true spirit and scope of the disclosed embodiments be determined by reference to the appended claims.