Abstract:
A micro-fluid ejection head structure having multiple arrays of fluid ejection actuators. The structure includes a semiconductor substrate having a first array of fluid ejection actuators for ejecting a first fluid therefrom, and a second array of fluid ejection actuators for ejecting a second fluid therefrom. The first array of fluid ejection actuators is disposed in a first location on the substrate, and the second array of fluid ejection actuators is disposed in a second location on the substrate. A thick film layer having a thickness is attached adjacent the semiconductor substrate. The thick film layer has fluid flow channels formed therein solely for the first array of fluid ejection actuators. A nozzle plate is attached to the thick film layer opposite the semiconductor substrate. The nozzle plate has fluid flow channels formed therein for both the first array of fluid ejection actuators and the second array of fluid ejection actuators.

Description:
FIELD OF THE INVENTION 
     The invention relates to micro-fluid ejection devices such as ink jet printheads and methods for making micro-fluid ejection devices having improved fluid flow characteristics. 
     BACKGROUND 
     A conventional micro-fluid ejection device such as an ink jet printhead generally has flow features either formed in a thick film layer deposited on a semiconductor substrate containing ink ejection devices or flow features ablated along with nozzle holes in a polymeric nozzle plate material. The term “flow features” is used to refer to fluid flow channels, fluid ejection chambers, and other physical features that provide a fluid such as ink to ejection devices on the semiconductor substrate. When both the nozzle holes and flow features are ablated in the nozzle plate material, a thick film material is typically not present. A disadvantage of forming the flow features and nozzle holes in the nozzle plate material is that the flow feature height and nozzle bore length are constrained by the nozzle plate material thickness. For micro-fluid ejection heads having a separate thick film layer and nozzle plate with the flow features formed in a thick film layer, the nozzle bore length is constrained to equal to the nozzle plate material thickness and the flow feature dimensions are determined by the thickness of the thick film layer. 
     With a trend toward increasing the functionality of micro-fluid ejection devices, it is desirable to provide fluid ejection devices on a single semiconductor substrate for ejecting different fluids having different drop masses. However, for largely disparate drop masses, the above constraints make the design of a single semiconductor substrate for multiple fluids difficult. For example, smaller droplet masses may be accommodated using flow features ablated in a nozzle plate material of a particular thickness. However, the larger droplet masses require additional flow features that cannot be ablated in a nozzle plate material suitable only for smaller drop masses. Alternatively, larger droplet masses may be accommodated using flow features formed in a thick film layer with nozzles ablated in a nozzle plate. However, the combined thickness of the thick film layer and nozzle plate degrades the ejection efficiency of the smaller droplet masses ejected from the same semiconductor substrate. 
     As the speed of micro-fluid ejection devices such as ink jet printers, increases the frequency of fluid ejection by individual ejection actuator elements must also increase requiring more rapid refilling of fluid ejection chambers. The requirement for more rapid refilling provides an incentive to devise a novel approach to providing flow features suitable for fluid ejection actuators for multiple size droplet masses on a single semiconductor substrate. Hence, there exists a need for improved micro-fluid ejection devices and methods for making the devices. 
     SUMMARY OF THE DISCLOSURE 
     With regard to the foregoing, the disclosure provides an improved micro-fluid ejection head structure having multiple arrays of fluid ejection actuators. The structure includes a semiconductor substrate having a first array of fluid ejection actuators for ejecting a first fluid therefrom, and a second array of fluid ejection actuators for ejecting a second fluid therefrom. The first array of fluid ejection actuators is disposed in a first location on the substrate, and the second array of fluid ejection actuators is disposed in a second location on the substrate. A thick film layer having a thickness is attached adjacent the semiconductor substrate. The thick film layer has fluid flow channels formed therein solely for the first array of fluid ejection actuators. A nozzle plate is attached to the thick film layer opposite the semiconductor substrate. The nozzle plate having fluid flow channels formed therein for both the first array of fluid ejection actuators and the second array of fluid ejection actuators. 
     In another embodiment, there is provided a method of making a micro-fluid ejection head structure. The method includes the steps of providing a semiconductor substrate and forming a first array of fluid ejection actuators for ejecting a first fluid therefrom in a first location on the semiconductor substrate. At least a second array of fluid ejection actuators for ejecting a second fluid therefrom is formed in a second location on the semiconductor substrate. A thick film layer is deposited with a thickness adjacent the first and second arrays of fluid ejection actuators on the semiconductor substrate. Fluid flow channels are formed in the thick film layer solely for the first array of fluid ejection actuators. A nozzle plate material is provided for attachment to the thick film layer. Fluid flow channels are formed in the nozzle plate material for both the first and second arrays of fluid ejection actuators. The nozzle plate is attached to the thick film layer opposite the semiconductor substrate to provide the micro-fluid ejection head structure. 
     An advantage of the embodiments described herein is that it enables independent variation of fluid flow characteristics for multiple arrays of fluid ejection actuators on a single substrate. Independent variation of fluid flow characteristics is provided by combining fluid flow channels formed in thick film layer with fluid flow channels and nozzle holes formed in a nozzle plate material for at least one array of fluid ejection actuators. As a result of embodiments, fluid ejector arrays of different ejection volumes may be included on a single ejection head. For example, an ink ejection head may include ejection actuators for black ink that eject about four times the volume of ink ejected from cyan, magenta, and yellow ejection actuators on the same ejection head. Another advantage is that an ejection head having two different size ejection actuator arrays for a single fluid may be provided with a single fluid source without deleteriously affecting the fluid flow to the two actuator arrays. Such advantages are not easily provided by conventional ejection heads and fabrication methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages of the embodiments may be better understood by reference to the detailed description when considered in conjunction with the figures, which are not to scale and which are provided to illustrate the principle features described herein. In the drawings, like reference numbers indicate like elements through the several views. 
         FIG. 1  is a perspective view, not to scale, of a fluid cartridge and micro-fluid ejection head according to the invention; 
         FIG. 2  is plan view, not to scale, of a semiconductor substrate containing multiple arrays of fluid ejection actuators adjacent fluid supply slots; 
         FIG. 3  is plan view, not to scale, of a portion of a micro-fluid ejection head structure according to the disclosure; 
         FIGS. 4 and 5  are a cross-sectional views, not to scale, of portions of a micro-fluid ejection head structure according to one embodiment of the disclosure; 
         FIGS. 6 and 7  are perspective views, not to scale, of portion of a micro-fluid ejection head according to disclosure; 
         FIG. 8  is a cross-sectional view, not to scale, of a portion of fluid flow channels for a micro-fluid ejection head structure according to the disclosure; and 
         FIG. 9  is a plan view, not to scale, of a portion of a thick film layer containing fluid chambers and fluid flow channels for adjacent fluid ejectors. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     With reference to  FIG. 1 , a fluid supply cartridge  10  for use with a device such as an ink jet printer includes a micro-fluid ejection head  12  fixedly attached to a fluid supply container  14 , as shown in  FIG. 1 , or removably attached to a fluid supply container either adjacent to the ejection head  12  or remote from the ejection head  12 . In order to simplify the description, reference may be made to inks and ink jet printheads. However, the invention is adaptable to a wide variety of micro-fluid ejecting devices other than for use in ink jet printers and thus is not intended to be limited to ink jet printers. 
     The ejection head  12  preferably contains a nozzle plate  16  containing a plurality of nozzle holes  18  each of which are in fluid flow communication with a fluid in the supply container  14 . The nozzle plate  16  is preferably made of an ink resistant, durable material such as polyimide and is attached to a semiconductor substrate  20  that contains fluid ejection actuators as described in more detail below. The semiconductor substrate  20  is preferably a silicon semiconductor substrate. 
     Fluid ejection actuators on the semiconductor substrate  20  are activated by providing an electrical signal from a controller to the ejection head  12 . The controller is preferably provided in a device to which the supply container  14  is attached, such as an ink jet printer. The semiconductor substrate  20  is electrically coupled to a flexible circuit or TAB circuit  22  using a TAB bonder or wires to connect electrical traces  24  on the flexible or TAB circuit  22  with connection pads on the semiconductor substrate  20 . Contact pads  26  on the flexible circuit or TAB circuit  22  provide electrical connection to the controller in the printer for activating the fluid ejection actuators on the ejection head  12 . 
     During a fluid ejection operation such as printing with an ink, an electrical impulse is provided from the controller to activate one or more of the fluid ejection actuators on the ejection head  12  thereby forcing fluid through the nozzles holes  18  toward a media. Fluid is caused to refill ink chambers in the ejection head  12  by capillary action between actuator activation. The fluid flows from a fluid supply in container  14  to the ejection head  12 . 
     It will be appreciated that micro-fluid ejection devices such as ink jet printers continue to be improved to provide higher quality images. Such improvements include increasing the number of nozzle holes  18  and ejection actuators on a semiconductor substrate  20 , reducing the size of the nozzle holes  18  and substrate  20 , and increasing the frequency of operation of the ejection actuators. 
     One improvement includes providing an ejection head capable of ejecting multiple different fluids. Such an ejection head is provided by a substrate  28  containing multiple fluid supply slots  30 ,  32 ,  34 , and  36  ( FIG. 2 ) and corresponding arrays  38 ,  40 ,  42 ,  44 , and  46  of fluid ejection actuators  47 . An “array” of fluid ejection actuators is defined as a substantially linear plurality of actuators  47  adjacent one or both sides of a fluid supply slot  30 ,  32 ,  34 , or  36 . 
     The frequency of fluid ejection from each of the arrays  38 – 46  depends on fluid flow characteristics of an ejection head containing the substrate  28 . For example, the operational frequency of fluid ejection from each nozzle in a nozzle plate is limited by the time required to replenish fluid to a fluid chamber adjacent the fluid actuator  47 . Fluid refill times are affected by the flow feature dimensions of the ejection head. 
     A portion of an ejection head  48  containing the substrate  28  and a nozzle plate  50  is illustrated in  FIG. 3 . As will be appreciated from  FIG. 3 , each array  38 ,  40 , and  42  of fluid ejection actuators  47  contains a staggered array of actuators  47 . Accordingly, adjacent fluid chambers, such as chambers  52  and  54  are disposed a different distance from the fluid supply slot  30 . Accordingly, the length of fluid supply channels  59  and  61  for adjacent fluid chambers  52  and  54  is different thereby resulting in different fluid flow characteristics to the chambers  52  and  54 . The distance D between a fluid supply slot edge  56  and an entrance  58  to the fluid flow channel  59  is referred to herein as the “shelf length.” ( FIGS. 3 and 6 ). 
     A cross-sectional view, not to scale, of a portion of the ejection head  48  is illustrated in  FIG. 4 . The ejection head  48  includes the semiconductor substrate  28  containing fluid ejection actuators  47  disposed thereon. For simplicity, the fluid ejection actuators  47 , as described herein, are thermal fluid ejection actuators. However, the embodiments of the disclosure are applicable to other types of fluid ejection actuators, including but not limited to, piezoelectric fluid ejection actuators, electrostatic ejection actuators, and the like. 
     As shown in  FIG. 4 , a portion of the fluid flow channel  64  from the fluid supply slot  30  to a fluid chamber  66  is formed in both a thick film layer  68  and in the nozzle plate  50 . In contrast, fluid flow channel  70  for ejector array  42  is formed only in the nozzle plate  50  as shown in  FIG. 5 . Because the thick film layer  68  does not provide a portion of the fluid flow channels  70  for ejector array  42 , a fluid ejection actuator  47  is disposed in a recessed area  76  of the thick film layer  68 . The recessed actuator  47  may be referred to herein as a “tub actuator” as the actuator is essentially surrounded by the thick film layer  68 . 
     The flow features formed in the nozzle plate  50  may be formed as by laser ablating the nozzle plate material. Typically, the nozzle plate  50  is made of a polyimide material that is readily laser ablatable. Materials suitable for nozzle plate  56  according to the invention are generally available in thicknesses ranging from about 10 to about 70 microns. Commercially available nozzle plate materials have thicknesses of 25.4 microns, 27.9 microns, 38.1 microns, or 63.5 microns. Of the total thickness of the nozzle plate material, 2.54 or 12.7 microns may include an adhesive layer that is applied by the manufacturer to the nozzle plate material. It will be understood however, that the invention is also applicable to a nozzle plate material that is provided absent the adhesive layer. In this case, an adhesive may be applied separately to attach the nozzle plate  50  to the thick film layer  68 . 
     The flow features may be formed in the thick film layer  68  as by a photolithographic technique. Typically, the thick film layer  68  is made of a photoresist material, either positive or negative photoresist, that is spin coated onto the substrate  28 . In  FIGS. 4 and 5 , a single thick film layer  68  is illustrated. However, the thick film layer  68  may include a photoresist planarizing layer having a thickness ranging from about 0.5 to about 5.0 microns and a separate thick film layer having a thickness ranging from about 5 to about 15 microns. 
     A perspective view of arrays  38  and  42  is illustrated in  FIGS. 6–7 . As shown in  FIG. 6 , array  38  includes nozzle holes  78  that are substantially larger than nozzle holes  80 ,  FIG. 7 . Accordingly, arrays  38  and  40  are configured for ejecting a larger volume of fluid, for example from about 15 to about 35 nanograms of fluid, as opposed to array  42  that is designed to eject from about 1 to about 8 nanograms of fluid. 
     Having a single ejection head  48  containing multiple size fluid ejection actuators  47  and nozzle holes  78  and  80  provides increased versatility for use of the ejection head  48 . For example, a multi-color ink jet printhead may include the ejection head  48 , wherein black, cyan, magenta, and yellow inks are ejected from the ejection head  48 . Each of the inks may have a different flow characteristic or volume requirement which may be achieved by variation in the fluid flow feature design of the ejection head  48  for each of the inks. 
     As will be further appreciated, providing a suitable thick film layer  68  and ablatable nozzle plate  50  enables tuning fluid flow characteristics for more efficient fluid ejection at higher frequencies. In embodiments described herein, the flow features for the fluid ejection arrays  38 – 46  are relatively independent of either of the thickness of the thick film layer  68  or of the thickness of the nozzle plate  50 . 
     Variations in the flow feature dimensions between adjacent fluid flow channels  59  and  61  enable tuning of fluid flow to the fluid chambers  52  and  54 . For example, even though fluid chamber  52  is relatively further away from the fluid supply slot  30  than fluid chamber  54 , refill times for the fluid chambers  52  and  54  can be made similar by varying certain dimensions of the fluid flow channels  59  and  61  as herein described. With reference of  FIGS. 8 and 9 , fluid flow channel  59  includes a choke dimension CD 1  and an inlet channel dimension CD 2 . A length L 1  of the channel  59  having choke dimension CD 1  is selected so that the fluid flow characteristics to chamber  52  are similar to the fluid flow characteristics to chamber  54 . In this case, chamber  54  has fluid flow channel  61  having a length L 2  and a choke dimension CD 3 . However, channel  61  may have a choke dimension CD 3  that is the same or different from choke dimension CD 1  depending on the length L 2  of the channel  61 . In this case, inlet channel dimension CD 2  for channel  59  is made as large as possible so as to avoid restricting the flow to channel  59 . 
     The foregoing modification of the fluid flow channel  59  is possible because the fluid flow channel  59  is formed in both the thick film  68  and in the nozzle plate  50 . By contrast, the fluid flow channels  86  and  88  for nozzle holes  80  are formed only in the nozzle plate  50 .  FIG. 8  is a cross-sectional view, not to scale, of a portion of the fluid flow channels  59 ,  61 , and  90  for fluid chambers  52 ,  54 , and  92  ( FIG. 3 ). As illustrated in  FIG. 8 , fluid flow channels  59 ,  61 , and  90  are formed in both the thick film layer  68  and in the nozzle plate  50 . However, fluid flow channels  59  and  90  have an increased inlet channel dimension CD 2  provided in the thick film layer  68 . 
     For further clarification, let CD 4  ( FIG. 8 ) be the width of the ablated region of the fluid flow channel  59  in the nozzle plate  50 . CD 2  is the width of the inlet channel dimension for fluid flow channel  59 , CD 1  is the width of the choke region of the fluid flow channel  59 , and CD 3  is the width of the choke region of the fluid flow channel  61  in the thick film layer  68 . The depth or height of the ablated region of the fluid flow channels  59  and  61  in the nozzle plate  50  is HA. The thickness of the thick film layer is TF. The center to center spacing between adjacent fluid flow channels  59  and  61  is the pitch P. Accordingly, the width WTF of a thick film layer  68  wall remaining between fluid flow channels  59  and  61  is defined by P−(½CD 2 +½CD 3 )=WTF. 
     To assure the most robust adhesion of the thick film layer  68  to the substrate  28 , it is desirable to size CD 2  such that WTF is greater than or equal to TF, where WTF is at least about 12 microns. 
     With regard to the above relationships, a comparison of the dimensions for ejector arrays  38  and  42  with reference to  FIGS. 8 and 9  is provided by way of the following non-limiting example. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Dimensions (Nozzle Plate 50 
                 Ejector Array 
                 Ejector Array 
               
               
                 and Thick film layer 68) 
                 38 (microns) 
                 42 (microns) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Thick Film thickness (TF) 
                 9 
                 9 
               
               
                 Nozzle Plate Thickness (NP) 
                 38.1 
                 38.1 
               
               
                 Nozzle Plate Ablation Depth (HA) 
                 9 
                 18 
               
               
                 Nozzle Bore Length 
                 29.1 
                 20.1 
               
               
                 Thick Film Choke Length (L 1 ) 
                 16 
                 None 
               
               
                 Thick Film Choke Length (L 2 ) 
                 22 
                 None 
               
               
                 Thick Film Choke Width (CD 1 ) 
                 18 
                 None 
               
               
                 Thick Film Channel Inlet 
                 35 
                 None 
               
               
                 Width (CD 2 ) 
               
               
                 Thick Film Choke Width (CD 3 ) 
                 18 
                 None 
               
               
                 Nozzle Plate Choke Width (CD 4 ) 
                 18 
                 16 
               
               
                 Nozzle Plate Choke Length 
                 22 
                 22 
               
               
                 (near nozzle) 
               
               
                 Nozzle Plate Choke Length 
                 16 
                 16 
               
               
                 (far nozzle) 
               
               
                 Nozzle Plate Channel Inlet Width 
                 35 
                 35 
               
               
                   
               
             
          
         
       
     
     In order to provide similar flow characteristics for chambers  52  and  54  in ejector arrays  38  and  40  ( FIGS. 8 and 9 ), the following dimensions are provided, by way of example only and are not intended to limit the embodiments described herein in any material way. 
     
       
         
               
               
               
             
               
               
               
             
               
               
             
           
               
                   
               
               
                   
                 Flow Channel 
                 Flow Channel 
               
               
                 Dimensions 
                 59 (microns) 
                 61 (microns) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Thick Film Thickness (TF) 
                 9 
                 9 
               
               
                 Nozzle Plate Ablation Depth (HA) 
                 9 
                 9 
               
               
                 Thick Film Choke Length (L) 
                 16 (L 1 ) 
                 22 (L 2 ) 
               
               
                 Thick Film Choke Width (CD) 
                  18 (CD 1 ) 
                  18 (CD 3 ) 
               
               
                 Thick Film Channel Entrance (CD 2 ) 
                 35 
                 18 
               
             
          
           
               
                 Pitch (P) 
                 42.3  
               
               
                 Thick Film Wall (WTF) 
                 15.8  
               
               
                 Flow resistance ratio 
                  0.998 
               
               
                 (flow channels 61 to 59) 
               
               
                   
               
             
          
         
       
     
     For flow channels  59  and  61 , the resistance of each channel is substantially the same as evidenced by the flow resistance ratio of about 1.0. Accordingly, the ejected mass of fluid from each channel  59  and  61  is approximately the same. It will be appreciated that the thick film layer  68  thickness (TF) may be decreased by increasing the choke widths (CD 1  and CD 3 ) for the channels and/or decreasing the choke lengths (L 1  and L 2 ). A reduced choke length (L 1  and L 2 ) enables use of a narrower substrate  28 , thereby reducing the cost of a substrate  28  containing multiple fluid supply slots  30 – 36  for multiple fluids. However, the flow resistance of adjacent fluid flow channels  59  and  6   i  can be made substantially the same by varying the choke widths (CD 1  and CD 3 ) in the thick film layer  68  to provide equivalent jetting performance for the adjacent fluid chambers  52  and  54 . Furthermore, an ejection head  48  for ejecting different volumes of different fluids may be provided using a combination of the thick film layer  68  of minimum thickness and the nozzle plate  50  wherein the fluid flow channels may be specifically configured for each array of fluid ejection actuators  38 – 46 . 
     Having described various aspects and embodiments of the disclosure and several advantages thereof, it will be recognized by those of ordinary skills that the embodiments described herein are susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.