Patent Publication Number: US-9895885-B2

Title: Fluid ejection device with particle tolerant layer extension

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/650,833, filed Jun. 9, 2015, which is a 371 application of PCT Application No. PCT/US2012/070794, filed on Dec. 20, 2012. The contents of both U.S. application Ser. No. 14/650,833 and PCT Application No. PCT/US2012/070794 are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Fluid ejection devices in inkjet printers provide drop-on-demand ejection of fluid drops. Inkjet printers produce images by ejecting ink drops from ink-filled chambers through nozzles onto a print medium, such as a sheet of paper. The nozzles are typically arranged in one or more arrays, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium move relative to each other. In a specific example, a thermal inkjet printhead ejects drops from a nozzle by passing electrical current through a heating element to generate heat and vaporize a small portion of the fluid within the ink-filled chamber. In another example, a piezoelectric inkjet printhead uses a piezoelectric material actuator to generate pressure pulses that force ink drops out of a nozzle. 
     Rapidly refilling the chambers with ink enables increased printing speeds. However, as ink flows into the chambers from a reservoir, small particles in the ink can get lodged in and around the channel inlets that lead to the chambers. These small particles can diminish and/or completely block the flow of ink to the chambers, which can result in the premature failure of heating elements, reduced ink drop size, misdirected ink drops, and so on. As small particles inhibit ink flow to more and more chambers, the resultant failures in corresponding nozzles can noticeably reduce the print quality of a printer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1 a    illustrates a fluid ejection system implemented as an inkjet printing system, according to an embodiment; 
         FIG. 1 b    shows a perspective view of an example inkjet cartridge that includes an inkjet printhead assembly and ink supply assembly, according to an embodiment; 
         FIG. 2  shows a plan view of a portion of an example fluid ejection device, according to an embodiment; 
         FIG. 3  shows a side view taken from the example fluid ejection device shown in  FIG. 2 , according to an embodiment; 
         FIG. 4  shows a plan view of a portion of an example fluid ejection device illustrating how a particle tolerant primer layer extension prevents a long particle from blocking ink flow to fluid chambers, according to an embodiment; 
         FIG. 5  shows a side view taken from the example fluid ejection device shown in  FIG. 4 , according to an embodiment; 
         FIG. 6  shows a plan view of a portion of an example fluid ejection device with a varying design of a particle tolerant primer layer extension, according to an embodiment; 
         FIG. 7  shows a plan view of a portion of an example fluid ejection device with a varying design of a particle tolerant primer layer extension, according to an embodiment; 
         FIG. 8  shows a plan view of a portion of an example fluid ejection device with a varying design of a particle tolerant primer layer extension, according to an embodiment; 
         FIG. 9  shows a plan view of a portion of an example fluid ejection device comprising a recirculation channel and a particle tolerant primer layer extension, according to an embodiment; 
         FIGS. 10-13  show processing steps that illustrate how a particle tolerant primer layer extension coats the edges of a thin-film layer, according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     As noted above, small particles within the fluid ink of inkjet printheads (and other fluid ejection devices) can reduce and/or block the flow of ink into the ink firing chambers, which can reduce the overall print quality in inkjet printers. There are a number of potential sources for the small particles carried within the ink, including ink storage mechanisms such as porous foam material, and materials used in the printhead manufacturing process (e.g., SiN particles from the backside wet etch mask process on the printhead). In one example, the processing of a thin-film layer can leave behind tantalum (Ta) or other metal filaments along the edges of the thin-film layer. The Ta filaments can break off the edges of the thin-film layer, producing both long and short particles that can block the flow of ink. In some cases, longer particles from these sources can block the flow of ink into multiple adjacent chambers and their corresponding nozzles. In such cases, long particles carried by the ink can become lodged on an ink feed hole shelf and across multiple adjacent channel inlets that lead to multiple adjacent corresponding ink chambers. The diminished or blocked ink flow into multiple adjacent ink firing chambers can cause multiple adjacent corresponding nozzles to either not fire ink drops, or to fire misdirected or reduced-size ink drops. These circumstances can cause inkjet printers to produce printed pages that have missing portions of text and/or images and other similar noticeable print defects. 
     Previous approaches for dealing with defects caused by such ink blockages include the use of scanning print modes that enable multiple print passes. While a scanning print mode that uses multiple passes to compensate for defective/blocked nozzles is generally effective, it is not applicable in single-pass print modes (i.e., with page wide array printers), and it has the drawback of decreasing the print speed. Another solution is to employ spare or redundant nozzles. Redundant nozzles can be used in both scanning print modes and single-pass print modes. While the use of redundant nozzles can also effectively compensate for defective/blocked nozzles, this solution adds cost and reduces print resolution by the number of redundant nozzles being used. 
     Other approaches to dealing with defects from ink blockages include the use of multiple channel inlets that lead to the ink firing chambers, which reduces the chances that ink flow to the chambers will be blocked. Still other approaches include the use of barriers that prevent particles from reaching the channel inlets leading to the ink firing chambers. Such barriers can include pillar structures located near the channel inlets. The placement, size, and spacing of the pillars are generally designed to prevent particles of the smallest anticipated size from blocking the inlets to channels that lead to the ink firing chambers. These latter approaches, while beneficial in reducing blockage caused by small particles, are generally less effective for preventing ink blockage caused by longer particles that become lodged on the ink feed hole shelf across multiple adjacent channel inlets, as in the circumstances noted above. 
     Embodiments of the present disclosure help prevent particles, including long filament, metal, and fiber particles, from blocking fluid flow in fluid ejection devices such as inkjet printheads, by employing a particle tolerant architecture that extends an existing primer layer into a fluid slot. While prior particle tolerant architectures prevent smaller particles in the fluid from entering fluid channel inlets that lead to fluidic chambers, the disclosed primer layer extension also prevents longer particles from settling length-wise on a shelf region in front of the channel inlets that lead to fluid chambers. The long particles are therefore prevented from blocking fluid flow into the fluid chambers. In addition to forming particle tolerant architectures that extend into the fluid slot and prevent particles from blocking fluid flow, the primer layer extension also forms a coating over the edges of the thin-film layer. The extension of the primer layer over the etched edges of the thin-film layer coats the thin-film edges and prevents Ta or other metal filaments from breaking off the edges. The primer layer coating over the thin-film edges eliminates a potential source of both long and short particles that can block the flow of ink in the fluid ejection device. 
     In one example, a fluid ejection device includes a thin-film layer formed over a substrate. A primer layer is formed over the thin-film layer, and a chamber layer is formed over the primer layer that defines a fluidic channel leading to a firing chamber. The fluid ejection device includes a slot that extends through the substrate and into the chamber layer through an ink feed hole in the thin-film layer. The fluid ejection device also includes a particle tolerant extension of the primer layer that protrudes into the slot. In some implementations, the particle tolerant primer layer extension extends across a full width of the slot. 
     In another example, a fluid ejection device includes a thin-film layer formed over a substrate. A chamber layer is formed over the thin-film layer, and an ink feed hole is formed through the thin-film layer. The ink feed hole fluidically couples a slot between the substrate and chamber layer. The fluid ejection device also includes an SU-8 primer layer over the thin-film layer that extends into the slot and over edges of the ink feed hole to coat the edges of the ink feed hole. 
     Illustrative Embodiments 
       FIG. 1 a    illustrates a fluid ejection system implemented as an inkjet printing system  100 , according to an embodiment of the disclosure. Inkjet printing system  100  generally includes an inkjet printhead assembly  102 , an ink supply assembly  104 , a mounting assembly  106 , a media transport assembly  108 , an electronic controller  110 , and at least one power supply  112  that provides power to the various electrical components of inkjet printing system  100 . In this embodiment, fluid ejection devices  114  are implemented as fluid drop jetting printheads  114  (i.e., inkjet printheads  114 ). Inkjet printhead assembly  102  includes at least one fluid drop jetting printhead  114  that ejects drops of ink through a plurality of orifices or nozzles  116  toward print media  118  so as to print onto the print media  118 . Nozzles  116  are typically arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  116  causes characters, symbols, and/or other graphics or images to be printed on print media  118  as inkjet printhead assembly  102  and print media  118  are moved relative to each other. Print media  118  can be any type of suitable sheet or roll material, such as paper, card stock, transparencies, Mylar, and the like. As discussed further below, each printhead  114  comprises a particle tolerant primer layer extension  119  that extends a primer layer out into the fluid slot area to prevent particles from blocking ink flow into the fluidic architectures (e.g., fluidic channels and chambers) of the chamber layer. 
     Ink supply assembly  104  supplies fluid ink to printhead assembly  102  and includes a reservoir  120  for storing ink. Ink flows from reservoir  120  to inkjet printhead assembly  102 . Ink supply assembly  104  and inkjet printhead assembly  102  can form either a one-way ink delivery system or a macro-recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to inkjet printhead assembly  102  is consumed during printing. In a macro-recirculating ink delivery system, however, only a portion of the ink supplied to printhead assembly  102  is consumed during printing. Ink not consumed during printing is returned to ink supply assembly  104 . 
     In some implementations, inkjet printhead assembly  102  and ink supply assembly  104  (including reservoir  120 ) are housed together in a replaceable device such as an integrated inkjet printhead cartridge or pen  103 , as shown in  FIG. 1 b   .  FIG. 1 b    shows a perspective view of an example inkjet cartridge  103  that includes inkjet printhead assembly  102  and ink supply assembly  104 , according to an embodiment of the disclosure. In addition to one or more printheads  114 , inkjet cartridge  103  includes electrical contacts  105  and an ink (or other fluid) supply chamber  107 . In some implementations cartridge  103  may have a single supply chamber  107  that stores one color of ink, and in other implementations it may have a number of chambers  107  that each store a different color of ink. Electrical contacts  105  carry electrical signals to and from controller  110 , for example, to cause the ejection of ink drops through nozzles  116 . 
     In other implementations, ink supply assembly  104  is separate from inkjet printhead assembly  102  and it supplies ink to inkjet printhead assembly  102  through an interface connection, such as a supply tube. In either implementation, reservoir  120  of ink supply assembly  104  may be removed, replaced, and/or refilled. Where inkjet printhead assembly  102  and ink supply assembly  104  are housed together in an inkjet cartridge  103 , reservoir  120  can include a local reservoir located within the cartridge as well as a larger reservoir located separately from the cartridge. A separate, larger reservoir serves to refill the local reservoir. Accordingly, a separate, larger reservoir and/or the local reservoir may be removed, replaced, and/or refilled. 
     Mounting assembly  106  positions inkjet printhead assembly  102  relative to media transport assembly  108 , and media transport assembly  108  positions print media  118  relative to inkjet printhead assembly  102 . Thus, a print zone  122  is defined adjacent to nozzles  116  in an area between inkjet printhead assembly  102  and print media  118 . In one implementation, inkjet printhead assembly  102  is a scanning type printhead assembly that includes one printhead  114 . As such, mounting assembly  106  includes a carriage for moving inkjet printhead assembly  102  relative to media transport assembly  108  to scan print media  118 . In another implementation, inkjet printhead assembly  102  is a non-scanning type printhead assembly with multiple printheads  114 , such as a page wide array (PWA) print bar, or carrier. A PWA print bar print bar carries the printheads  114 , provides electrical communication between the printheads  114  and electronic controller  110 , and provides fluidic communication between the printheads  114  and the ink supply assembly  104 . Thus, mounting assembly  106  fixes inkjet printhead assembly  102  at a prescribed position while media transport assembly  108  positions and moves print media  118  relative to inkjet printhead assembly  102 . 
     In one implementation, inkjet printing system  100  is a drop-on-demand thermal bubble inkjet printing system comprising thermal inkjet (TIJ) printhead(s). The TIJ printhead implements a thermal resistor ejection element in an ink chamber to vaporize ink and create bubbles that force ink or other fluid drops out of a nozzle  116 . In another implementation, inkjet printing system  100  is a drop-on-demand piezoelectric inkjet printing system where the printhead(s)  114  is a piezoelectric inkjet (PIJ) printhead that implements a piezoelectric material actuator as an ejection element to generate pressure pulses that force ink drops out of a nozzle. 
     Electronic controller  110  typically includes one or more processors  111 , firmware, software, one or more computer/processor-readable memory components  113  including volatile and non-volatile memory components (i.e., non-transitory tangible media), and other printer electronics for communicating with and controlling inkjet printhead assembly  102 , mounting assembly  106 , and media transport assembly  108 . Electronic controller  110  receives data  124  from a host system, such as a computer, and temporarily stores data  124  in a memory  113 . Typically, data  124  is sent to inkjet printing system  100  along an electronic, infrared, optical, or other information transfer path. Data  124  represents, for example, a document and/or file to be printed. As such, data  124  forms a print job for inkjet printing system  100  and includes one or more print job commands and/or command parameters. 
     In one implementation, electronic controller  110  controls inkjet printhead assembly  102  for ejection of ink drops from nozzles  116 . Thus, electronic controller  110  defines a pattern of ejected ink drops that form characters, symbols, and/or other graphics or images on print media  118 . The pattern of ejected ink drops is determined by the print job commands and/or command parameters. 
       FIG. 2  shows a plan view of a portion of an example fluid ejection device  114  (i.e., printhead  114 ), according to an embodiment of the disclosure. The portion of printhead  114  shown in  FIG. 2  illustrates architectural features from each of several different layers of the printhead  114 . The different layers, components, and architectural features of printhead  114  can be formed using various precision microfabrication and integrated circuit fabrication techniques such as electroforming, laser ablation, anisotropic etching, sputtering, spin coating, dry film lamination, dry etching, photolithography, casting, molding, stamping, machining, and the like.  FIG. 3  shows a side view (view A-A) taken from the example fluid ejection device  114  shown in  FIG. 2 . 
     Referring generally to both  FIGS. 2 and 3 , printhead  114  is formed in part, of a layered architecture that includes a substrate  200  (e.g., glass, silicon) with a fluid slot  202 , or trench, formed therein. Running along either side of the slot  202  are columns of fluid drop ejectors that generally comprise thermal resistors  210 , fluid chambers  220 , and nozzles  116 . Formed over the substrate  200  is a thin-film layer  204 , a primer layer  205 , a chamber layer  206 , and a nozzle layer  208 . The thin-film layer  204  implements thin film thermal resistors  210  and associated electrical circuitry such as drive circuits and addressing circuits (not shown) that operate to eject fluid drops from printhead  114 . During processing of printhead  114 , the removal (e.g., etching) of a portion of thin-film layer  204  creates an ink feed hole (IFH)  212  (shown as a dotted ellipse in  FIG. 3 ) between the substrate  200  and the chamber layer  206 . The IFH  212  allows fluid flow between the substrate and chamber layer by enabling an extension of the slot  202  into the chamber layer  206  from the substrate  200 . Thus, the thin-film layer  204  can also be referred to as the ink feed hole layer  204 . The dotted lines  300  with arrows in  FIG. 3  show the general direction of ink flow through the slot  202  from the substrate  200  and into the chamber layer  206 . In  FIG. 2 , this flow of ink through the slot  202  from the substrate  200  and into the chamber layer  206  would be a flow that proceeds in a direction out of the page, toward the viewer. The flow would then proceed to the left and right between particle tolerant pillars ( 222 ,  224 ), through channel inlets  216  and fluidic channels  218 , and into fluid chambers  220 . 
     In the example implementation shown in  FIGS. 2 and 3 , thermal resistors  210  are formed in the thin-film layer  204  and located in columnar arrays along either side of the slot  202  and edges  214  of the ink feed hole  212 . The thin-film layer  204  comprises a number of different layers (not illustrated individually) that include, for example, an oxide layer, a metal (e.g., tantalum) layer that defines the thermal resistors  210  and conductive traces (not shown), and a passivation layer. A passivation layer can be formed of several materials, such as silicon oxide, silicon carbide, and silicon nitride. 
     The primer layer  205  formed over thin-film layer  204  is typically formed of a photo-definable epoxy such as SU8 epoxy, which is a polymeric material commonly used in the fabrication of microfluidic and MEMS devices. Primer layer  205  can also be made of other materials such as a polyimide, a deposited dielectric material, a plated metal, and so on. The chamber layer  206  formed over thin-film layer  204  and primer layer  205 , includes a number of fluidic features such as channel inlets  216  that lead to fluidic channels  218  and the fluid/ink firing chambers  220 . As shown in  FIGS. 2 and 3 , the fluidic firing chambers  220  are formed around and over corresponding thermal resistors  210  (ejection elements). Like primer layer  205 , the chamber layer  206  is typically formed of SU8 epoxy, but can also be made of other materials such as a polyimide. 
     In some implementations, the chamber layer  206  also includes particle tolerant architectures in the form of particle tolerant pillars ( 222 ,  224 ). On-shelf pillars  222 , formed during the fabrication of chamber layer  206 , are located on a shelf  226  of the chamber layer  206  near the channel inlets  216 . The on-shelf pillars  222  help prevent small particles in the ink from entering the channel inlets  216  and blocking ink flow to chambers  220 . Off-shelf pillars  224 , or hanging pillars  224 , are also formed during the fabrication of chamber layer  206 . The hanging pillars  224  are formed prior to formation of the slot  202 , and they are adhered to the nozzle layer  208 . Thus, when slot  202  is formed, hanging pillars  224  effectively “hang” in place through their adherence to the nozzle layer  208 . Both the on-shelf pillars  222  and hanging pillars  224  help stop small particles from entering the channel inlets  216  and blocking ink flow to chambers  220 . 
     Nozzle layer  208  is formed on the chamber layer  206  and includes nozzles  116  that each correspond with a respective chamber  220  and thermal resistor ejection element  210 . The nozzle layer  208  forms a top over the slot  202  and other fluidic features of the chamber layer  206  (e.g., the channel inlets  216 , fluidic channels  218 , and the fluid/ink firing chambers  220 ). The nozzle layer  208  is typically formed of SU8 epoxy, but it can also be made of other materials such as a polyimide. 
     In addition to the particle tolerant pillars  222 ,  224 , printhead  114  also includes a particle tolerant primer layer extension  228 . The particle tolerant primer layer extension  228  comprises an extension of the primer layer  205  out from between the thin-film layer  204  and chamber layer  206 , and into the area of the slot  202 . In general, the particle tolerant primer layer extension  228  enhances the ability of the printhead  114  to manage small particles within the ink and prevent them from diminishing or blocking ink flow to the chambers  220 . More specifically, however, the particle tolerant primer layer extension  228  prevents longer particles from settling length-wise in the fluidic shelf region  230  located in front of the channel inlets  216  that lead to fluid chambers  220 . In  FIG. 3 , this the fluidic shelf region  230  is labeled with an “X”, and it lies between the on-shelf pillars  222  and the hanging pillars  224 . 
       FIG. 4  shows a plan view of a portion of an example fluid ejection device  114  (i.e., printhead  114 ) illustrating how a particle tolerant primer layer extension  228  prevents a long particle  400  from blocking ink flow to fluid chambers  220 , according to an embodiment of the disclosure.  FIG. 5  shows a side view (view B-B) taken from the example fluid ejection device  114  shown in  FIG. 4 . The printheads  114  in  FIGS. 4 and 5  are the same as or similar to those shown in  FIGS. 2 and 3 , except that they include an illustration of how the particle tolerant primer layer extension  228  functions to prevent long particles  400  from blocking or diminishing ink flow to the printhead ink chambers  220 . 
     Referring to  FIGS. 4 and 5 , long particles  400  within fluid ink can travel through the fluid slot  202  in the general direction  300  of the ink flow. The long particles can travel along the sides of the slot  202  toward the fluidic shelf region  230  ( FIG. 5 ; marked “X”) of the chamber layer  206  near the channel inlets  216  that lead to fluid chambers  220 . If the long particles  400  come to rest, or get lodged in the fluidic shelf region  230 , they can block the flow of ink into the channel inlets  216  that lead to fluid chambers  220 . As is apparent from  FIG. 4 , multiple adjacent channel inlets  216  can be blocked by such long particles  400 . However, as  FIG. 4  also shows, the particle tolerant primer layer extension  228  prevents the long particles  400  from reaching the fluidic shelf region  230 . 
       FIGS. 2-5  show one of various possible designs of a particle tolerant primer layer extension  228 . In particular, the particle tolerant primer layer extension  228  of  FIGS. 2-5  comprises a plurality of finger-like, protrusions that are partially interleaved between the hanging pillars  224 . The interleaving of the protrusions in the particle tolerant primer layer extension  228  with the hanging pillars  224  prevents the long particles  400  from coming to rest or lodging in the fluidic shelf region  230  between the on-shelf pillars  222  and the hanging pillars  224 . However, various other designs of a particle tolerant primer layer extension  228  are possible and are contemplated by this disclosure, that can achieve a similar result of preventing long particles from coming to rest or lodging in the fluidic shelf region  230  between the on-shelf pillars  222  and the hanging pillars  224 . 
       FIGS. 6-8  show plan views of a portion of example fluid ejection devices  114  (i.e., printhead  114 ) with varying designs of particle tolerant primer layer extensions  228 , according to embodiments of the disclosure. As shown in  FIG. 6 , the primer layer  205  can protrude from between the thin-film layer  204  and chamber layer  206  as a particle tolerant primer layer extension  228  that extends all the way across the slot  202 . That is, the particle tolerant primer layer extension  228  spans the entire width of the slot  202  between the columns of fluid drop ejectors located on either side of the slot  202 . In this illustration, the slot  202  extends both above and below the particle tolerant primer layer extension  228 . That is, although the substrate  200  and chamber layer  206  are not specifically shown in  FIG. 6 , the slot  202  still extends through both the substrate  200  and the chamber layer  206 , as in the previous design. However, instead of having a singular large ink feed hole  212  as shown in  FIGS. 2-5 , the  FIG. 6  design comprises multiple ink feed holes  212  formed in the particle tolerant primer layer extension  228  that enable fluid ink to flow through the slot  202  between the substrate and the chamber layer  206 . While the multiple ink feed holes  212  in the  FIG. 6  design are rectangular in shape, other shapes are possible that may provide the same benefits of preventing long particles from coming to rest or lodging in the fluidic shelf region  230  between the on-shelf pillars  222  and the hanging pillars  224 . 
       FIG. 7  shows another example printhead  114  with a different design of a particle tolerant primer layer extension  228  that is similar to the design of  FIG. 6 . Like in  FIG. 6 , the particle tolerant primer layer extension  228  of  FIG. 7  extends all the way across the slot  202 . In addition, instead of having a singular large ink feed hole  212  as shown in  FIGS. 2-5 , the  FIG. 7  design comprises multiple ink feed holes  212  in the particle tolerant primer layer extension  228  that enable fluid ink to flow through the slot  202  between the substrate and the chamber layer  206  (not specifically shown in  FIG. 7 ). The multiple ink feed holes  212  in the particle tolerant primer layer extension  228  of  FIG. 7 , however, are both fewer and larger than the ink feed holes  212  in  FIG. 6 . The larger ink feed holes  212  in  FIG. 7  are circular, but may in other examples be shaped differently to provide the benefits of preventing long particles from coming to rest or lodging in the fluidic shelf region  230  between the on-shelf pillars  222  and the hanging pillars  224 . 
       FIG. 8  shows another example printhead  114  with a different design of a particle tolerant primer layer extension  228  that is similar to the design shown in  FIGS. 2-5 . As in the design shown in  FIGS. 2-5 , the particle tolerant primer layer extension  228  of  FIG. 8  does not extend all the way across the slot  202 , and there is generally, a singular large ink feed hole  212  similar to that of the design in  FIGS. 2-5 . In  FIG. 8 , the particle tolerant primer layer extension  228  comprises a plurality of finger-like, protrusions that are partially interleaved between the hanging pillars  224 . However, the particle tolerant primer layer extension  228  protrusions in the  FIG. 8  design extend into the slot  202  in varying lengths. That is, the protrusions  228  in  FIG. 8  are not the same length as is generally the case with the design shown in  FIGS. 2-5 . However, like the design shown in  FIGS. 2-5 , the particle tolerant primer layer extension  228  protrusions of varying lengths in the  FIG. 8  design are interleaved with the hanging pillars  224  to prevent long particles  400  from coming to rest or lodging in the fluidic shelf region  230  between the on-shelf pillars  222  and the hanging pillars  224 . 
     While various other designs of a particle tolerant primer layer extension  228  are possible and are contemplated by this disclosure, it is noted that different designs may provide varying degrees of robustness associated with the particle tolerant primer layer extension  228  itself. For example, the shorter particle tolerant primer layer extension  228  protrusions shown in  FIGS. 2-5  may be more robust and therefore less prone to damage than the longer particle tolerant primer layer extension  228  protrusions shown in  FIG. 8 . Likewise, the particle tolerant primer layer extension  228  that extend all the way across the slot  202  as shown in  FIGS. 6 and 7 , may be more robust and less prone to damage than the longer particle tolerant primer layer extension  228  protrusions shown in  FIG. 8 . 
       FIG. 9  shows a plan view of a portion of an example fluid ejection device  114  (i.e., printhead  114 ) comprising a recirculation channel and a particle tolerant primer layer extension  228 , according to an embodiment of the disclosure. In each of the printheads  114  discussed above with regard to  FIGS. 2-8 , the general fluidic architecture of the chamber layer  206  comprises a single channel inlet  216  in communication with a single fluidic channel  218  that leads to a fluid chamber  220 . However, the various designs of a particle tolerant primer layer extension  228  are also applicable to printheads  114  having recirculation channels  900  (and other fluidic architectures) that circulate ink through the fluid chamber  220  between two channel inlets  216 . 
     As shown in  FIG. 9 , for example, the chamber layer  206  (not specifically shown) defines a recirculation channel  900  that enables ink circulation through the fluid chamber  220  between two channel inlets  216  that are in fluid communication with the slot  202 . As in the previous examples that each comprise single channel inlets  216 , a particle tolerant primer layer extension  228  employed in the example of  FIG. 9  functions in a similar manner as discussed above to prevent long particles from coming to rest or lodging in the fluidic shelf region  230  between the on-shelf pillars  222  and the hanging pillars  224 . Thus, the particle tolerant primer layer extension  228  prevents the long particles from inhibiting ink flow at both channel inlets  216  associated with the recirculation channels  900  in the example printhead  114  of  FIG. 9 . 
     In addition to preventing particles from lodging in the fluidic shelf region  230  and blocking ink flow to chambers  220 , the particle tolerant primer layer extension  228  also serves to coat the edges of the thin-film layer  204 . As noted above, the processing of the thin-film layer  204  during fabrication of the printhead  114  can leave behind tantalum (Ta) or other metal filaments along the edges  214  ( FIGS. 3, 5 ) of the thin-film layer  204 . The Ta filaments can break off the edges  214  of the thin-film layer  204 , producing both long and short particles that can block the flow of ink. 
       FIGS. 10-13  show several basic processing steps that illustrate how the particle tolerant primer layer extension  228  coats the edges  214  of the thin-film layer  204 , according to embodiments of the disclosure.  FIG. 10  shows a plan view and cross sectional view (across line C-C) of a portion of an example fluid ejection device  114  (i.e., printhead  114 ), according to an embodiment of the disclosure. In an initial processing step, as shown in  FIG. 10 , a thin-film layer  204  is formed on the substrate  200  (e.g., silicon). The thin-film layer  204  typically comprises a number of different layers (not illustrated individually) that include, for example, an oxide layer, a metal (e.g., tantalum) layer that defines the thermal resistors  210  and conductive traces (not shown), and a passivation layer. The thin-film layer  204  can be formed using various microfabrication and integrated circuit fabrication techniques such as electroforming, laser ablation, anisotropic etching, sputtering, spin coating, dry film lamination, dry etching, photolithography, casting, molding, stamping, machining, and the like. After the thin-film layer  204  is formed on substrate  200 , a latent ink feed hole (IFH)  212  is formed by removing an area of the thin-film layer  204 . Removal of an area of the thin-film layer  204  is typically achieved by etching. Etching the thin-film layer  204  results in edges  214  that can have metal filaments (e.g., Ta filaments) that are left by the etching process. These filaments can break off the edges  214  and block the flow of ink to the ink firing chambers  220 . 
       FIG. 11  shows a plan view and cross sectional view (across line D-D) of a portion of an example fluid ejection device  114  (i.e., printhead  114 ), according to an embodiment of the disclosure. In a next processing step, as shown in  FIG. 11 , a primer layer  205  is formed over the thin-film layer  204 . The primer layer  205  can be a photo-imageable epoxy such as SU-8, formed by spin-coating or lamination, for example. The primer layer  205  can be defined to form a particle tolerant primer layer extension  228  as detailed herein above. In addition, the primer layer  205  is formed over the edges of the thin-film layer  204  to coat the edges  214 . The primer layer  205  coating formed over the edges  214  of the thin-film layer  204  holds onto any metal filaments (e.g., Ta filaments) that are left by the etching process, and prevents the filaments from breaking off the edges  214  and blocking the flow of ink to the ink firing chambers  220 . 
       FIG. 12  shows a plan view and cross sectional view (across line E-E) of a portion of an example fluid ejection device  114  (i.e., printhead  114 ), according to an embodiment of the disclosure. In a next processing step, as shown in  FIG. 12 , a chamber layer  206  is formed over the primer layer  205 . The chamber layer  206  can be a photo-imageable epoxy such as SU-8, formed by spin-coating or lamination, for example. The chamber layer  206  can be defined to include a number of fluidic features such as fluid/ink firing chambers  220 , and channel inlets  216  and fluidic channels  218  that lead to the chambers  220 . The fluidic firing chambers  220  are formed around and over corresponding thermal resistors  210  (ejection elements). 
       FIG. 13  shows a plan view and cross sectional view (across line F-F) of a portion of an example fluid ejection device  114  (i.e., printhead  114 ), according to an embodiment of the disclosure. In a next processing step, as shown in  FIG. 13 , a nozzle layer  208  is formed over the chamber layer  206 . The nozzle layer  208  can be a photo-imageable epoxy such as SU-8, formed by spin-coating or lamination, for example. The nozzle layer  208  can be defined to include a number of fluidic features such as nozzles  116 . Each nozzle  116  corresponds with a respective chamber  220  and thermal resistor  210 . 
     While particle tolerant architectures have been described herein as being formed by a primer layer extension  228 , in other implementations, similarly designed particle tolerant architectures (e.g., as shown in  FIGS. 2, 6, 7, 8, 9 ) can be formed by the thin-film layer  204 . That is, the thin-film layer  204  can be patterned to form particle tolerant architectures in designs such as those shown in  FIGS. 2, 6, 7, 8, and 9 . In such implementations, where the thin-film layer  204  forms such particle tolerant architectures, the primer layer extension  228  maintains the purpose of extending over the edges  214  of the thin-film layer  204  to coat the edges  214  and prevent metal filaments (e.g., Ta filaments) from breaking off the edges  214  and blocking the flow of ink to the ink firing chambers  220 .