Patent Publication Number: US-11390076-B2

Title: Fluid feed path wettability coating

Description:
RELATED APPLICATIONS 
     This patent arises from a U.S. national stage of International Patent Application Serial No. PCT/US19/16850, having a filing date of Feb. 6, 2019, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Fluid ejection devices in printers provide drop-on-demand ejection of fluid droplets. Printers may include 2D and 3D printers or any other fluid ejection application for example in the field of pharmaceutics, forensics, and/or laboratories. Suitable fluids for 2D and 3D printing applications may include inks, agents. 
     In general, printers print images or objects by ejecting droplets through a plurality of nozzles onto a print medium, such as a sheet of paper or (layers of) build material. The nozzles are arranged in an array, such that properly sequenced ejection of droplets from the nozzles causes patterns to be printed on the print medium as the printhead and the print medium move relative to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram an example printing system that can include an example pen assembly in accordance with teachings of this disclosure. 
         FIG. 2  is a schematic partial, cross-sectional view of an example printhead that can implement the example pen assembly of  FIG. 1 . 
         FIG. 3  is an enlarged view of the encircled portion of the example printhead of  FIG. 2 . 
         FIG. 4  is a side cross-sectional view of an example panel that includes an example plurality of printheads disclosed herein shown in a first manufacturing state. 
         FIG. 5  is a side cross-sectional view of the example panel of  FIG. 4  shown in a second manufacturing state. 
         FIG. 6  is a schematic partial, cross-sectional view of another example printhead disclosed herein. 
         FIG. 7  is a side cross-sectional view of another example panel that includes another example plurality of printheads disclosed herein shown in a first manufacturing state. 
         FIG. 8  is a side cross-sectional view of the example panel of  FIG. 7  shown in a second manufacturing state. 
         FIG. 9  is a schematic partial, cross-sectional view of another example printhead disclosed herein. 
         FIG. 10A  is an enlarged view of the encircled portion of example printhead of  FIG. 9 . 
         FIGS. 10B-10C  are enlarged views of example multilayer coatings that can implement the example printhead of  FIG. 9 . 
         FIG. 11  is a side cross-sectional view of another example panel having another example plurality of printheads disclosed herein. 
         FIG. 12  is a side cross-sectional view of another example panel having yet another example plurality of printheads disclosed herein. 
         FIG. 13  is a block diagram of an example processing platform structured to execute instructions to implement the example printing system of  FIG. 1 . 
     
    
    
     The figures are not to scale. Instead, the thickness of the layers or regions may be enlarged in the drawings. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. Although the figures show layers and regions with clean lines and boundaries, some or all of these lines and/or boundaries may be idealized. In reality, the boundaries and/or lines may be unobservable, blended, and/or irregular. 
     DETAILED DESCRIPTION 
     Certain examples are shown in the identified figures and disclosed in detail herein. Although the following discloses example methods and apparatus, it should be noted that such methods and apparatus are merely illustrative and should not be considered as limiting the scope of this disclosure. 
     As used herein, directional terms, such as “upper,” “lower,” “top,” “bottom,” “front,” “back,” “leading,” “trailing,” “left,” “right,” etc. are used with reference to the orientation of the figures being described. Because components of various examples disclosed herein can be positioned in a number of different orientations, the directional terminology is used for illustrative purposes and is not intended to be limiting. Descriptors “first,” “second,” “third,” etc. are used herein when identifying multiple elements or components which may be referred to separately. Unless otherwise specified or understood based on their context of use, such descriptors are not intended to impute any meaning of priority or ordering in time but merely as labels for referring to multiple elements or components separately for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for ease of referencing multiple elements or components. 
     Printing systems feed printing fluid (e.g., ink) through a printhead to a firing port. While the printing fluid is fed through the printhead, such as through a channel that extends through a substrate, the printing fluid contacts walls of the substrate defining the channel. For example, printheads, pens, and/or other ink dispensing apparatus include chambers that receive printing fluid via a fluid feed path (e.g., an ink feed path) and dispense the printing fluid from a firing chamber via a nozzle. The components defining the fluid feed path, the nozzle, and the firing chamber are often formed of semiconductor material(s). 
     To protect a substrate from the printing fluid, some substrates employ a protective coating. For example, printing fluid including a pigmented ink having charged dispersants can etch surfaces (e.g., walls of a channel) of the substrate (e.g., a silicon substrate) such that the substrate leaches into the pigmented ink. Presence of substrate particles or material in the printing fluid can cause a blockage or partial blockage of a firing port of a printhead. To reduce such blockage or partial blockage of the firing port to improve the print quality of the printing device, some substrates employ a protective coating to protect the substrate material from printing fluid (e.g., ink attack). For example, some printhead apparatus employ an ink feed path coated with hafnium oxide to protect a substrate (e.g., a silicon (Si) substrate) from ink attack. However, application of the hafnium oxide coating is relatively a slow process. The greater a thickness of the protective layer, the longer the manufacturing time to apply the protective material. 
     To improve performance (e.g., higher refill speed) and/or significantly reduce bubble trapping, example pens or fluid ejection devices (e.g., a thermal-ink-jet (TIJ) pen or a cartridge) disclosed herein include fluid feed paths having enhanced wettability characteristics. To enhance wettability characteristics of a fluid feed path, example fluid feed paths of fluid ejection devices disclosed herein employ a wettability enhancement coating. In some examples, the wettability enhancement coating is applied along an entire length of a fluid feed path between a fluid source (e.g., a reservoir, an ink reservoir, a dispenser, a pipette, a continuous fluid source) and a nozzle of a printhead. In some examples, the wettability enhancement coating is applied along a portion (i.e., a partial length) of a fluid feed path between a fluid reservoir (e.g., an ink reservoir) and a nozzle of a printhead. 
     In some examples, a fluid feed path disclosed herein can be defined by a die or substrate made from different materials (e.g., silicon (Si), Epoxy Mold Compound (EMC), photoresist (SU8), etc.) that may have different and/or inferior wettability characteristics compared to the wettability enhancement coating disclosed herein. For example, example substrates or dies disclosed herein include a fluid feed path defined by a slot in a carrier, a fluid feed hole coupling the slot to a firing chamber, and a nozzle to expel ink from the firing chamber. For example, the slot can be defined by a carrier of molded compound such as EMC material. An array of fluid feed holes can be formed in a substrate, for example of Si material. The firing chamber and nozzle can be formed by a thin film layers, for example including SU8 material. All three materials possess different wettability characteristics. The example wettability enhancing coating disclosed herein harmonizes or provides homogenous or identical wettability characteristics of the substrate to improve pen performance. As used herein, to “harmonize or provide homogenous or identical wettability characteristics” means to make wettability characteristics of two or more different materials uniform (e.g., identical or normalized) and/or substantially identical (e.g., within a 5 percent tolerance). For example, a coating (e.g., a same or identical coating) can be provided to channels, paths, holes or slots of an over molded compound composed of a first material having a first wettability characteristic and a die composed of a second material having a second wettability characteristic different than the first wettability characteristic. In some examples, the die can include a third material having a third wettability characteristic. Thus, an example coating disclosed herein harmonizes (e.g., makes identical or near identical) the wettability characteristics of two or more materials defining a fluid flow path of a fluid ejection device. To harmonize the wettability characteristic of the fluid feed path formed of two or more different materials example printheads, substrates (e.g., over molded compound, dies, etc.) and/or fluid ejection devices disclosed herein employ a hafnium oxide coating formed along the fluid feed path. The wettability enhancement coating provides the fluid feed path with a uniform wettability characteristic that improves printing fluid flow, thereby improving pen performance. 
     Additionally, some advantages of using hafnium oxide coating for wettability instead of a protective coating for protecting the surfaces enables a smaller amount of hafnium oxide (e.g., an application of the hafnium oxide coating with a thinner thickness). For example, application of the hafnium oxide coating is relatively a slow process. For instance, hafnium oxide coating is applied to substrates using Atomic Layer Deposition (ALD), which is a thin film growth technique in which a substrate is exposed to alternate pulses of source precursors, with intermediate purge steps including an inert gas to evacuate any remaining precursor after reaction with the substrate surface. Thus, the thicker the layer, the longer the manufacturing time. 
     In some examples, a multilayer coating including a wettability enhancement layer and a protective layer can be applied to a substrate. In this manner, the protective layer prevents printing fluid from etching or damaging the substrate, while the wettability enhancement layer improves wettability characteristics of the substrate. For example, hafnium oxide can be employed to enhance wettability characteristics of the substrate and a different material coating (ALD Al 2 O 3 , ALD SiO 2 , ALD Ta) can be employed to provide a protective coating to the substrate (EMC, Si, SU8). This enables a much thinner application of the hafnium oxide because the hafnium oxide is used to improve and harmonize wettability, not as a protective layer. The thickness of the hafnium oxide coating can be reduced from 200 Angstrom (e.g., when used as a protective layer) to between approximately 10 Angstrom and 50 Angstrom, significantly improving manufacturing time. 
     Examples disclosed herein can be used with printing systems or fluid ejection devices including, but not limited to, 2D printers, 3D printers and/or any other fluid ejection devices or applications for example in the field of pharmaceutics, forensics, laboratories and/or any other applications. Suitable fluids for 2D and 3D printing applications may include inks, agents and/or any there printing fluids. 
       FIG. 1  illustrates an example printing system  100  having an example pen assembly  102  (e.g., a cartridge or an inkjet pen) in accordance with teachings disclosed herein. The printing system  100  of the illustrated example is a drop-on-demand thermal bubble inkjet printing system. However, the examples disclosed herein can implement any other printing system, fluid deliver device(s) (e.g., valves, etc.) and/or any other fluid delivery system(s). The printing system  100  includes the pen assembly  102 , a fluid supply assembly  104 , a mounting assembly  106 , a media transport assembly  108 , an electronic controller  110 , and a power supply or power supplies  112  that provide power to the various electrical components of the printing system  100 . 
     The pen assembly  102  includes a fluid ejection device or printhead  114  that is fluidically connected to a printing fluid source  120  (e.g., a reservoir, a dispenser, a pipette, a continuous fluid source, etc.) of the fluid supply assembly  104  so as to receive printing fluid therefrom. As used herein, the term “printing fluid” refers to any fluid used in a printing process, including but not limited to inks, preconditioners, fixers, etc. The printhead  114  includes a plurality of fluid ejection devices  116  (e.g., nozzles) to eject printing fluid drops  122  onto a print medium  118 , such as paper, card stock, transparencies, Mylar, and/or other media, positioned adjacent to the printhead  114 . The fluid ejection devices  116  may be configured to eject printing fluid in any suitable manner. Examples include, but are not limited to, thermal fluid ejection mechanisms, piezoelectric fluid ejection mechanisms, etc. In some examples, the printhead  114  is arranged in column(s) or array(s) such that properly sequenced ejection of printing fluid (e.g., ink) from the fluid ejection devices  116  causes characters, symbols, and/or other graphics or images to be printed onto print medium  118  as the pen assembly  102  and the print medium  118  are moved relative to each other. 
     The fluid supply assembly  104  supplies printing fluid to the pen assembly  102 . The printing fluid flows from the fluid source  120  to the pen assembly  102 . The fluid supply assembly  104  and pen assembly  102  can form a one-way fluid delivery system or a recirculating fluid delivery system. In a one-way fluid delivery system, substantially all of the printing fluid supplied to pen assembly  102  is consumed during printing. In a recirculating fluid delivery system, however, only a portion of the printing fluid supplied to the pen assembly  102  is consumed during printing. Any printing fluid not consumed during printing is returned to the fluid supply assembly  104 . 
     The fluid source  120  provides a supply of printing fluid and can have either an on-axis configuration or an off-axis configuration. In an on-axis configuration, the fluid source  120  is wholly contained onboard the pen assembly  102 . For example, printhead  114  and the fluid supply assembly  104  are housed together in the pen assembly  102 . With an off-axis configuration, the fluid supply assembly  104  is separate from the pen assembly  102  and supplies the printing fluid to pen assembly  102  through an interface connection, such as a supply tube or other conduit. For example, a relatively small reservoir located onboard the pen assembly  102  is fluidly coupled to an off-board reservoir (e.g., the fluid source  120 ). The onboard fluid reservoir is in fluid communication with the printhead  114 . In either example, the fluid source  120  of the fluid supply assembly  104  may be removed, replaced, and/or refilled. 
     The mounting assembly  106  is configured to move the pen assembly  102  and the printhead  114  relative to the print medium  118 . In one example, the mounting assembly  106  is a scanning carriage that traverses the printhead  114  back-and-forth across the print medium  118 . The media transport assembly  108  is positioned relative to the mounting assembly  106  so as to define a print zone adjacent to the printhead  114 . The media transport assembly  108  moves the print medium  118  through the print zone so that the printing fluid drops  122  ejected by the printhead  114  are directed onto the print medium  118 . 
     The electronic controller  110  (e.g., a printer controller) includes a processor, firmware, and other printer electronics for communicating with and controlling the pen assembly  102 , the mounting assembly  106 , and the media transport assembly  108 . The electronic controller  110  receives data  124  from a host system, such as a computer, and includes memory for temporarily storing data  124 . In some examples, the data  124  is sent to the printing system  100  along an electronic, infrared, optical, or other information transfer path. The data represents, for example, a document and/or file to be printed. As such, the data  124  forms a print job for the printing system  100  and includes print job command(s) and/or command parameter(s). In response to the data, the electronic controller  110  provides control of the fluid ejection devices  116 , including timing control for ejection of the printing fluid. The electronic controller  110  also controls the mounting assembly  106  and the media transport assembly  108  to provide the desired relative positioning of the printhead  114  and the print medium  118 . Thus, the electronic controller  110  defines a pattern of the printing fluid drops  122  to be ejected from the printhead  114  that form characters, symbols, and/or other graphics or images on print medium  118 . 
     While an example manner of implementing the printing system  100  is illustrated in  FIG. 1 , the elements, processes, and/or devices illustrated in  FIG. 1  may be combined, divided, re-arranged, omitted, eliminated, and/or implemented in any other way. Further, the example pen assembly  102 , the example fluid supply assembly  104 , the example mounting assembly  106 , the example media transport assembly  108 , and the example electronic controller  110  and/or, more generally, the example printing system  100  of  FIG. 1  may be implemented by hardware, software (machine readable instructions), firmware and/or any combination of hardware, software and/or firmware. Thus, for example, any of the example pen assembly  102 , the example fluid supply assembly  104 , the example mounting assembly  106 , the example media transport assembly  108 , and the example electronic controller  110  and/or, more generally, the example printing system  100  of  FIG. 1  could be implemented by analog or digital circuit(s), logic circuit(s), programmable processor(s), programmable controller(s), graphics processing unit(s) (GPU(s)), digital signal processor(s) (DSP(s)), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example pen assembly  102 , the example fluid supply assembly  104 , the example mounting assembly  106 , the example media transport assembly  108 , and the example electronic controller  110  and/or, more generally, the example printing system  100  of  FIG. 1  is/are hereby expressly defined to include a non-transitory computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. including the software and/or firmware. Further still, the example printing system  100  of  FIG. 1  may include element(s), process(es) and/or device(s) in addition to, or instead of, those illustrated in  FIG. 1 , and/or may include more than one of any or all of the illustrated elements, processes and devices. As used herein, the phrase “in communication,” including variations thereof, encompasses direct communication and/or indirect communication through intermediary component(s), and does not require direct physical (e.g., wired) communication and/or constant communication, but rather additionally includes selective communication at periodic intervals, scheduled intervals, aperiodic intervals, and/or one-time events. 
       FIG. 2  is a side cross-sectional view of an example printhead  200  having a wettability enhancing coating  202  in accordance with teachings of this disclosure. The printhead  200  of the illustrated example can implement the printhead  114  and/or the pen assembly  102  of  FIG. 1 . The printhead  200  of the illustrated includes a substrate  204  (e.g., a substrate assembly) that defines a fluid feed path  206 . In particular, the fluid feed path  206  is formed through the substrate  204 . The fluid feed path  206  and/or the printhead  200  of the illustrated example includes a slot  208 , a fluid feed hole  210 , a firing chamber  212 , and a nozzle  214 . The slot  208  fluidically couples the fluid feed hole  210  to a fluid reservoir (e.g., the fluid source  120  of  FIG. 1 ), and the fluid feed hole  210  fluidically couples the slot  208  and the firing chamber  212 . The nozzle  214  is fluidically coupled to the firing chamber  212 . A firing resistor  218  is formed in the firing chamber  212  and is connected to an electrical pad of a printed circuit board (PCB) via a lead. To print an image on a sheet of print media (e.g., the print medium  118 ), printing fluid flows from a fluid reservoir (e.g., the fluid source  120 ), through the slot  208 , through the fluid feed hole  210 , through the firing chamber  212  and exits through the nozzle  214 . For example, in operation, an electrical signal is provided to the firing resistor  218  in the firing chamber  212  via the electronic controller  110 , which provides heat to vaporize a portion of the printing fluid and form a bubble within the firing chamber  212 . The bubble propels a print fluid drop (e.g., the printing fluid drops  122  of  FIG. 1 ) through the nozzle  214  onto the print medium  118 . The firing chamber  212  is then refilled by capillary action. In some examples, the PCB and/or the firing resistor  218  can be connected to a power source (e.g., the power source  112  of  FIG. 1 ) and a controller (e.g., the electronic controller  110  of  FIG. 1 ) such that the firing resistor  218  can be activated upon demand to cause ejection of a fluid droplet (e.g., the printing fluid drops  122  of  FIG. 1 ) from the nozzle  214  and onto the print medium  118 . 
     The printhead  200  of the illustrated example can be composed of different material(s). The printhead  200  of the illustrated example is a printhead die  220  composed of a support substrate  222  and a thin film layer  224  (e.g., a negative photoresist layer) In the illustrated example, the printed  200  includes a moldable carrier  226 . However, in some examples, the printhead  200  does not include the moldable carrier  226 . The support substrate  222  can be silicon (Si), glass, and/or any other substrate. The thin film layer  224  can include a negative photoresist layer or an epoxy-based negative photoresist material such as, for example, SU-8. The moldable carrier  226  can include, for example, an epoxy mold compound (EMC) including, but not limited to, at least one epoxide functional group, a self-cross linking epoxy, a polyepoxide that uses a co-reactant to cure the polyepoxide, a thermosetting polymer, and/or any other suitable material(s). 
     The printhead die  220  of the illustrated example includes a silicon (Si) substrate  222   a , an SU-8 layer  224   a , and an EMC substrate  226   a . The EMC substrate  226   a  is overmolded with the silicon substrate  222   a  and the SU-8 layer  224   a . Specifically, the fluid feed path  206  of the illustrated example is formed by the EMC substrate  226   a , the silicon substrate  222   a , and the SU-8 layer  224   a . In particular, the EMC substrate  226   a  defines the slot  208 , the silicon substrate  222   a  defines the fluid feed hole  210 , and the SU-8 layer  224   a  defines the firing chamber  212  and the nozzle  214 . Thus, the fluid feed path  206  is composed of various different materials (e.g., Si, SU-8, and EMC). In some examples, the printhead  200  can be configured without the moldable carrier  226   
     The example printhead  200  has a hydrophobic top orifice to prevent fluid puddle (e.g., ink puddle) and a hydrophilic fluid feed path to improve fluid refill and minimize bubble trapping. However, each of the different materials (the silicon substrate  222   a , the SU-8 layer  224   a , the EMC substrate  226   a ) has a different water contact angle, resulting in a fluid feed path  206  having different wettability characteristics. For example, the EMC substrate  226   a  has a contact angle of approximately 76 degrees (76°), the Si substrate  222   a  has a contact angle of approximately 25 degrees (25°), and the SU-8 layer  224   a  has a contact angle of approximately 62 degrees (62°). Further, substrate material(s) having a relatively high contact angle provide reduced wettability characteristic(s) that can affect print head performance. As a result, a frictional force on the surface of the walls defining the fluid feed path  206  can imped sufficient fluid flow through the fluid feed path  206  (i.e., along the slot  208 , the fluid feed hole  210 , the firing chamber  212  and/or the nozzle  214 ). The greater the water contact angle, the greater a friction force the material (e.g., the Si material, the SU-8 material, the EMC material) imparts to the printing fluid, thereby causing a slower moving printing fluid through the fluid feed path  206 . In other words, the smaller the water contact angle, the greater the wettability characteristic. A greater wettability characteristic of the fluid feed path  206  improves operating performance of the printhead  200 . For example, a greater wettability characteristic (e.g., a smaller water contact angle) increases a refill speed of the printing fluid in the firing chamber  212  and minimizes bubble trapping at the nozzle  214 , the fluid feed hole  210 , and/or the slot  208 . 
     To harmonize and enhance the wettability characteristics of the fluid feed path  206 , the printhead  200  of the illustrated example employs a wettability enhancement coating  202 . The wettability enhancement coating  202  of the illustrated example is applied on the fluid feed path  206  from a fluid reservoir (e.g., the fluid source  120  of  FIG. 1 ) to the nozzle  214 . Specifically, the wettability enhancement coating  202  is provided on exposed walls or surfaces  228  of the substrate  204  and/or the printhead die  220  defining the fluid feed path  206 . For example, the wettability enhancement coating  202  is provided on the EMC substrate  226   a  defining the slot  208 , the silicon substrate  222   a  defining the fluid feed hole  210 , and the SU-8 layer  224   a  defining the firing chamber  212  and the nozzle  214 . Thus, surfaces  228  defining the slot  208 , the fluid feed hole  210 , the firing chamber  212 , and the nozzle  214  include the wettability enhancing coating  202 . The wettability enhancement coating  202  of the illustrated example is provided along an entire length of the fluid feed path  206  between the fluid source  120  ( FIG. 1 ) and the nozzle  214 . In some examples, however, the wettability enhancement coating  202  is provided on a portion of the fluid feed path  206  between the fluid source  120  and the nozzle  214 . Additionally, to prevent fluid puddle at the nozzle  214  and, thus, improve ejection efficiency of the printing fluid from the nozzle  214 , a top or outer surface  230  (e.g., an outer surface) of the SU-8 layer  224   a  does not include the wettability enhancement coating  202 . Thus, the outer surface  230  defining the nozzle  214  has a hydrophobic characteristic. 
     The wettability enhancement coating  202  of the illustrated example harmonizes (e.g., makes uniform) the wettability characteristics of the fluid feed path  206 . For example, the wettability enhancement coating  202  provides a uniform water contact angle along the fluid feed path  206  of the printhead die  220 . The wettability enhancement coating  202  of the illustrated example significantly improves wettability characteristics of the printhead  200  regardless of the various materials defining the fluid feed path  206 . For example, the wettability enhancement coating  202  provides a uniform water contact angle despite the EMC substrate  226   a , the silicon substrate  222   a , and the SU-8 layer  224   a  having different water contact angles. Thus, the wettability enhancement coating  202  harmonizes or makes uniform the surface wetting of various components of the fluid feed path of the printhead  200 . 
     The wettability enhancement coating  202  of the illustrated example is hafnium oxide (HfO 2 ). For example, hafnium oxide has a water contact angle of approximately twelve degrees (12°). Thus, the fluid feed path  206  of the illustrated example has a water contact angle of approximately 12 degrees between the fluid source  120  and the nozzle  214 . In contrast, as noted above, the water contact angle of EMC is approximately 76 degrees, the water contact angle of Si is approximately 25 degrees, and the water contact angle of SU-8 is approximately 62 degrees. 
       FIG. 3  is an enlarged view of the encircled portion of the printhead  200  of  FIG. 2 . The wettability enhancement coating  202  has a thickness  302 . For example, the thickness of the wettability enhancement coating is approximately between 10 Angstroms and 100 Angstroms. As noted above, when the wettability enhancement coating  202  is employed as a protective coating, the thickness  302  is significantly greater than 100 Angstroms. For example, the wettability enhancement coating  202  could have a thickness greater than 250 Angstroms when used as a protective coating. Also, in some instances (e.g., when the wettability enhancement coating  202  is composed of hafnium oxide), application of the wettability enhancement coating  202  having a thickness greater than 100 Angstroms significantly increases manufacturing time, thereby decreasing manufacturing efficiency. 
       FIG. 4  is a side cross-sectional view of a wafer or panel  400  having a plurality of printhead dies  402  disclosed herein shown in a first manufacturing stage. As shown in  FIG. 4 , the printhead dies  402  can implement the printhead  200  of  FIG. 2  and/or the printhead  114  of  FIG. 1 . Although a “panel” is sometimes used to denote a rectangular substrate while a “wafer” is used to denote a circular substrate, a “panel” or “wafer” as used in this document includes any shape substrate. The printhead dies  402  are supported on and/or coupled to a carrier  404  via a thermal release tape  406  (e.g., adhesive). For example, the printhead dies of  FIG. 4  include a support substrate  422  (e.g., a glass substrate, the silicon substrate  222   a , etc.) and a negative photoresist layer  424  (e.g., the SU-8 layer  224   a ) layered on the support substrate  422 . The support substrate  422  defines fluid feed holes  410  (e.g., the fluid feed hole  210 ), and the negative photoresist layer  424  defines firing chambers  412  (e.g., the firing chamber  212 ) and nozzles  414  (e.g., the nozzle  214 ) of the printhead dies  402 . In some examples, a number of rows of nozzles  414  and their respective corresponding circuitry and resistive heating elements may be included within the printhead dies  402 . Thus, a single row of nozzles and their respective corresponding circuitry and resistive heating elements define respective ones of the printhead dies  402 . The printhead dies  402  may include a connection pad or multiple connection pads  405  to electrically couple the printhead dies  402  to a controller of a printing system (e.g., the printing system  100 ). The printhead dies  402  can be coupled to a printed circuit board (PCB). 
     The printhead dies  402  are manufactured from selected combinations of thin film layers of material that are deposited or grown on substrates using processes adapted from semiconductor component fabrication and microelectrical mechanical systems (MEMS) manufacturing technique(s) or processes. For example, each of the negative photoresist layer  424  and/or the support substrate  422  can be manufactured or formed via photolithography, etching, and/or any other suitable processes. The support substrate  422  can be etched to form the fluid feed holes  410 . To form the firing chambers  412  and the nozzles  414 , portions of the negative photoresist layer  424  that are exposed to ultra-violet (UV) radiation become cross-linked, while the remainder of the film or layer remains soluble and can be washed away during development. The negative photoresist layer  424  is coupled to the support substrate  422  such that the fluid feed holes  410  are fluidically coupled to the firing chambers  412  and the nozzles  414 . The negative photoresist layer  424  and the support substrate  422  surround or encase connection pads  405 , or other electrical connections, and a wafer thinning process is employed to reduce a thickness  403  of the support substrate  422  to a target thickness. For example, the support substrate  422  can have a thickness  403  of approximately 650 micrometers. Wafer thinning is the process of removing material from the backside of a wafer to a desired final target thickness. Two example methods of wafer thinning include grind and chemical-mechanical planarization (CMP) 
       FIG. 5  is a side cross-sectional view of the example panel  400  of  FIG. 4  shown in a second manufacturing stage. Specifically, the panel  400  of  FIG. 5  includes a moldable substrate  526  (e.g., the moldable carrier  226  or the EMC substrate  226   a ) and the wettability enhancement coating  202 . The moldable substrate  526  defines slots  508  (e.g., the slot  208 ) of the printhead dies  402  that are fluidically coupled to the fluid feed holes  410 . The panel  400  of  FIG. 5  illustrates the support substrate  422  and the negative photoresist layer  424  over-molded with moldable substrate  526 . After the moldable substrate  526  is overmolded with the support substrate  422  and the negative photoresist layer  424 , the wettability enhancement coating  202  is applied to the printhead dies  402 . For example, the wettability enhancement coating  202  can be applied after wafer thinning process and/or molding of the moldable substrate  526 , but prior to release for electric pad (e.g., a gold (Au) pad) protection. As noted above, the wettability enhancement coating  202  is applied via the ALD manufacturing process. 
     The wettability enhancement coating  202  is applied on an entire length of a fluid feed path  506  between a reservoir (e.g., the fluid source  120 ) and the nozzles  414 . For example, the wettability enhancement coating  202  is applied to the fluid feed path  506  defined by the slots  508 , the fluid feed holes  410 , the firing chambers  412  and the nozzles  414 . Specifically, the wettability enhancement coating  202  is applied to surfaces of the support substrate  422  defining the fluid feed holes  410 , surfaces of the negative photoresist layer  424  defining the firing chambers  412  and the nozzles  414 , and surfaces of the moldable substrate  526  defining the slots  508 . Thus, in this example, the wettability enhancement coating  202  is provided everywhere in the fluid feed path  506  including exposed silicon backside die surfaces  503  and the slots  508 . Each of the printhead dies  402  on the panel  400  can be processed to produce a single printhead (e.g., the printhead  200  or the printhead  114 ). For example, after fabrication, the printhead dies  402  can be separated and incorporated into print cartridges or carriers (e.g., the pen assembly  102  of  FIG. 1 ) that connect the printhead with a fluid supply (e.g., the fluid source  120 ). 
       FIGS. 6-14  illustrate additional example printheads or printhead dies  600 ,  702 ,  900 ,  1102 , and  1202  disclosed herein. Those components of the example printheads or printhead dies  600 ,  702 ,  900 ,  1102 , and  1202  that are substantially similar or identical to the components of the example printheads  200  and  402  disclosed above in connection with  FIGS. 1-5  and that have functions substantially similar or identical to the functions of those components will not be described in detail again below. Instead, the interested reader is referred to the above corresponding descriptions. To facilitate this process, similar reference numbers will be used for like structures. 
       FIG. 6  illustrates a printhead  600  that includes a fluid feed path  606  that is substantially similar to the fluid feed path  206  of  FIG. 2 . However, the fluid feed path  606  includes a wettability enhancement coating  202  on a first portion  606   a  of the fluid feed path  606 , and the fluid feed path  606  does not include the wettability enhancement coating  202  on a second portion  606   b  of the fluid feed path  606 . For example, the wettability enhancement coating  202  is provided on surfaces  228  defining a fluid feed hole  210  (e.g., defined by the support substrate  222 ), a firing chamber  212 , and a nozzle  214  (e.g., defined by the thin film layer  224 ). Thus, surfaces  228  (e.g., the EMC substrate  226   a ) defining the slot  208  do not include the wettability enhancement coating  202 . In other words, the wettability enhancement coating  202  of the illustrated example is applied only on the support substrate  222  and the thin film layer  224 , and the wettability enhancement coating  202  is not applied on the moldable carrier  226 . In some examples, the moldable substrate is not provided and/or the slot  208  is defined by the support substrate  222 . 
       FIG. 7  is a side cross-sectional view of a panel  700  disclosed herein including a plurality of printhead dies  702  disclosed herein. The printhead dies  702  can implement the printhead  600  of  FIG. 6 . The printhead dies  702  are supported on a carrier  404 . In this example, the printhead dies  702  are attached to the carrier  404  via a thermal release tape  406  (e.g., adhesive). The printhead dies  702  are substantially similar to the printhead dies  402  of  FIGS. 4 and 5 . For example, the negative photoresist layer  424  and the support substrate  422  define or form the fluid feed holes  410 , the firing chambers  412 , and the nozzles  414 . However, a wettability enhancement coating  202  is applied to a first portion  706   a  (e.g., a partial portion) of a fluid feed path  706 . Thus, the wettability enhancement coating  202  is applied on a backside surface  705  of the support substrate  222 , the fluid feed hole  410  of the support substrate  222 , and surfaces defining of the firing chambers  412  and the nozzles  414 . After formation of the support substrates  422  and the negative photoresist layers  424  of the printhead dies  702  via semiconductor manufacturing technique(s) and process(es), the wettability enhancement coating  202  is applied via the ALD process. In the illustrated example, the wettability enhancement coating  202  is applied after wafer thinning. 
       FIG. 8  is a side cross-sectional view of the example panel  700  of  FIG. 7 . After the wettability enhancement coating  202  is applied to the support substrate  422  and the negative photoresist layer  424 , the moldable substrate  526  is overmolded with the support substrate  422  and the negative photoresist layer  424 . The wettability enhancement coating  202  is not provided on surfaces of the moldable substrate  526  defining a slot  808  fluidically coupled to the fluid feed holes  410 . In the illustrated example, the wettability enhancement coating  202  is applied prior to overholding the support substrate  422  and the negative photoresist layer  424  with the moldable substrate  526 . Thus, a second portion  806   a  of the fluid feed path  706  is not coated with the wettability enhancement coating  202 . 
       FIG. 9  illustrates another example printhead  900  disclosed herein. The example printhead  900  can implement the example printhead  114  of  FIG. 1 . The printhead  900  includes a multilayer coating  902  (e.g., a film stack). The printhead  900  includes a printhead die  920  defining a fluid feed path  206  that includes a slot  208 , a fluid feed hole  210 , a firing chamber  212 , and a nozzle  214 . For example, a support substrate  222  (e.g., silicon substrate  222   a ), a thin film layer  224  (e.g., a negative photoresist layer, an SU-8 layer  224   a ), and a moldable carrier  226  (e.g., an EMC substrate  226   a ) define the printhead die  920 . 
     The multilayer coating  902  of the illustrated example includes a protective coating  904  and a wettability enhancement coating  202 . Specifically, the multilayer coating  902  can be applied on surfaces  228  of the printhead die  920  defining the fluid feed path  206 . In the illustrated example, the multilayer coating  902  is formed along an entire length of the fluid feed path  206  between a fluid source  120  and the nozzle  214 . Thus, the multilayer coating  902  is applied to surfaces defining the slot  208 , the fluid feed hole  210 , the firing chamber  212 , and the nozzle  214 . However, in some examples, the multilayer coating  902  can be formed on a portion (e.g., the first portion  606   a ,  706   a ) of a fluid feed path (e.g., the fluid feed path  606 ,  706 ) between the fluid source  120  and the nozzle  214 . For example, the multilayer coating  902  can be applied on surfaces defining the fluid feed hole  210 , the firing chamber  212 , and the nozzle  214 . In other words, surfaces defining the slot  208  do not include the multilayer coating  902 . The protective coating  904  is positioned between materials defining the printhead die  920  (e.g., the support substrate  222 , the negative photoresist layer  224 , the moldable carrier  226 ) and the wettability enhancement coating  202 . In some examples, the protective coating  904  can be composed of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ), tantalum. silicon carbide, and/or any other printing fluid impervious material(s). 
     The protective coating  904  provide a printing fluid impervious layer that protects the printhead die from printing fluid attack (e.g., etching). For example, the printing fluid can be a pigmented ink. The use of pigmented inks often provides greater color gamut, high fad resistance, better water-fastness, shorter dry time, and great media compatibility when compared to dye-based inks. However, pigmented inks include charged dispersants and pigment particles or high pH solvent that may etch the materials of the printhead  900  (e.g., the silicon, the SU-8, the EMC, etc.). The multilayer coating  902  via the protective coating  904  prevents the printing fluid from etching materials of the printhead die  920  (e.g., the silicon substrate  222   a ). In other words, the wettability enhancement coating  202  does not provide protection to ink attack but improves or enhances wettability characteristics. The protective coating  904  enables the wettability enhancement coating  202  to have a thickness  1002  that is less than 100 Angstroms. 
       FIG. 10A  is an enlarged view of the encircled portion of the multilayer coating  902  of  FIG. 9 . The protective coating  904  of the printhead die  920  of  FIG. 10A  is aluminum oxide (Al 2 O 3 ), and the wettability enhancement coating  202  is hafnium oxide. In some examples, the protective coating  904  has a thickness  1002  of approximately 0.3 micrometers, and the wettability enhancement coating  202  has a thickness  1004  of approximately 50 Angstroms. Both the protective coating  904  and the wettability enhancement coating  202  are provided on the printhead die via the ALD process. 
     As noted above, when the wettability enhancement coating  202  is composed of hafnium oxide and is employed as a protective coating, the thickness  1004  is significantly greater than 100 Angstroms (e.g., greater than 250 Angstroms), but this significantly increases manufacturing time and/or decreases manufacturing efficiency. In the illustrated example, the protective coating  904  enables a relatively small amount of hafnium oxide (e.g., less than 100 Angstrom) to be applied as the wettability enhancement coating  202 , which provides enhanced wettability characteristics and also improves manufacturing efficiency. 
       FIG. 10B  illustrates another example multilayer coating  1002   b  that can implement the printhead  900  of  FIG. 9 . The multilayer coating  1002   b  includes a protective coating  1006  and a wettability enhancement coating  202 . In this example, the protective coating  1006  is silicon dioxide, and the wettability enhancement coating  202  is hafnium oxide. In some examples, the protective coating  1006  of  FIG. 3C  has a thickness  1008  of approximately 0.2 micrometers, and the wettability enhancement coating  202  has a thickness  1010  of approximately 100 angstroms. The silicon dioxide can be provided on a printhead die (e.g., the printhead die  220 ,  920 , etc.) via plasma enhanced chemical vapor deposition (PECVD), inductively coupled plasma chemical vapor deposition (ICP CVD), microwave plasma assisted chemical vapor deposition (CVD), and/or any other manufacturing process(es). The wettability enhancement coating  202  is provided via the ALD process. 
       FIG. 10C  illustrates another example multilayer coating  1002   c  that can implement the printhead  900  of  FIG. 9 . In this example, the multilayer coating  1002   c  includes a protective coating  1012  composed of Tantalum (Ta), and a wettability enhancement coating  202  composed of hafnium oxide. In some examples, the protective coating  1012  has a thickness  1014  of approximately 0.5 micrometers, and the wettability enhancement coating  202  has a thickness  1016  of approximately 20 Angstroms. 
       FIG. 11  is a side cross-sectional view of a panel  1100  disclosed herein including a plurality of printhead dies  1102  disclosed herein. The printhead dies  1102  are substantially similar to the printhead dies  402  of  FIGS. 4 and 5 . However, the printhead dies  1102  include the multilayer coating  902 . The multilayer coating  902  is applied to the fluid feed path  506  including the slots  508 , the fluid feed holes  410 , the firing chambers  412 , and the nozzles  414  (e.g., an entire length of the fluid feed path  506  between the fluid source  120  and the nozzles  414 ). The multilayer coating  902  is applied after molding the moldable carrier  226 . 
       FIG. 12  is a side cross-sectional view of a panel  1200  disclosed herein including a plurality of printhead dies  1202  disclosed herein. The printhead dies  1202  are substantially similar to the printhead dies  702  of  FIGS. 7 and 8 . However, the printhead dies  1202  include the multilayer coating  902 . Specifically, the multilayer coating  902  is applied to a first portion  706   a  of a fluid feed path  706  and is not applied to a second portion  806   a  (e.g., the slot  808 ) of the fluid feed path  706 . Thus, the multilayer coating  902  is applied to surfaces defining the fluid feed holes  410 , the firing chambers  412 , and the nozzles  414 . However, the multilayer coating  902  is not applied to surfaces defining the slot  808 . In this example, the multilayer coating  902  is applied after wafer thinning and prior to molding the moldable substrate  526 . 
       FIG. 13  is a block diagram of an example processor platform  1300  structured to execute the instructions to implement the example pen assembly  102 , the example fluid supply assembly  104 , the example mounting assembly  106 , the example media transport assembly  108 , and the example electronic controller  110  and/or, more generally, the example printing system  100  of  FIG. 1 . The processor platform  1300  can be, for example, a server, a personal computer, a workstation, a self-learning machine (e.g., a neural network), a mobile device (e.g., a cell phone, a smart phone, a tablet), a personal digital assistant (PDA), an Internet appliance, or any other type of computing device. 
     The processor platform  1300  of the illustrated example includes a processor  1312 . The processor  1312  of the illustrated example is hardware. For example, the processor  1312  can be implemented by integrated circuit(s), logic circuit(s), microprocessor(s), GPU(s), DSP(s), or controller(s) from any desired family or manufacturer. The hardware processor may be a semiconductor based (e.g., silicon based) device. In this example, the processor implements aspect(s) of the example pen assembly  102 , the example fluid supply assembly  104 , the example mounting assembly  106 , the example media transport assembly  108 , and the example electronic controller  110  and/or, more generally, the example printing system  100  of  FIG. 1 . 
     The processor  1312  of the illustrated example includes a local memory  1313  (e.g., a cache). The processor  1312  of the illustrated example is in communication with a main memory including a volatile memory  1314  and a non-volatile memory  1316  via a bus  1318 . The volatile memory  1314  may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS® Dynamic Random Access Memory (RDRAM®), and/or any other type of random access memory device. The non-volatile memory  1316  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1314 ,  1316  is controlled by a memory controller. 
     The processor platform  1300  of the illustrated example also includes an interface circuit  1320 . The interface circuit  1320  may be implemented by any type of interface standard, such as an Ethernet interface, a universal serial bus (USB), a Bluetooth® interface, a near field communication (NFC) interface, and/or a PCI express interface. 
     In the illustrated example, input device(s)  1322  are connected to the interface circuit  1320 . The input device(s)  1322  perm it(s) a user to enter data and/or commands into the processor  1312 . The input device(s) can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, isopoint, and/or a voice recognition system. 
     Output device(s)  1324  are also connected to the interface circuit  1320  of the illustrated example. The output devices  1324  can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display (LCD), a cathode ray tube display (CRT), an in-place switching (IPS) display, a touchscreen, etc.), a tactile output device, a printer, and/or speaker. The interface circuit  1320  of the illustrated example, thus, includes a graphics driver card, a graphics driver chip and/or a graphics driver processor. 
     The interface circuit  1320  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem, a residential gateway, a wireless access point, and/or a network interface to facilitate exchange of data with external machines (e.g., computing devices of any kind) via a network  1326 . The communication can be via, for example, an Ethernet connection, a digital subscriber line (DSL) connection, a telephone line connection, a coaxial cable system, a satellite system, a line-of-site wireless system, a cellular telephone system, etc. 
     The processor platform  1300  of the illustrated example also includes mass storage device(s)  1328  for storing software (e.g., machine readable instructions) and/or data. Examples of such mass storage devices  1328  include floppy disk drives, hard drive disks, compact disk drives, Blu-ray disk drives, redundant array of independent disks (RAID) systems, and digital versatile disk (DVD) drives. 
     The machine executable instructions  1332  may be stored in the mass storage device  1328 , in the volatile memory  1314 , in the non-volatile memory  1316 , and/or on a removable non-transitory computer readable storage medium such as a CD or DVD. 
     The example methods, apparatus, systems, and articles of manufacture disclosed herein provide enhanced wettability characteristics for printheads and/or other fluid delivery systems to improve fluid delivery performance by reducing surface frictions of surfaces defining the fluid flow paths. In some examples, a fluid flow path is coated with hafnium oxide to enhance and harmonize wettability characteristics of the fluid flow path. To protect against ink attach or etching, fluid flow paths can be coated with a multilayer coating that includes a first coating to provide a protective barrier or layer composed of an ink impervious material and a second coating to enhance wettability characteristics. 
     At least some of the aforementioned examples include at least one feature and/or benefit including, but not limited to, the following: 
     In some examples, a printhead includes a nozzle to expel fluid therefrom, and a fluid feed path to fluidly couple a fluid source and the nozzle. Fluid feed path walls are composed of a first material having a first wettability characteristic and a second material having a second wettability characteristic. The second wettability characteristic differs from the first wettability characteristic. A coating is formed on at least a portion of the fluid feed path walls defined by the first material and the second material. The coating is to harmonize the first wettability characteristic and the second wettability characteristic. 
     In some examples, the fluid feed path includes a slot to receive fluid from the fluid source, and a fluid feed hole to enable fluid flow from the slot to a firing chamber upstream from the nozzle. 
     In some examples, the printhead includes a molded compound and a die, wherein the fluid feed path is formed through the compound and die, the molded compound including the first material and the die includes the second material 
     In some examples, the coating is positioned on at least portions of the molded compound and the die defining the fluid feed path. 
     In some examples, the wettability coating includes hafnium oxide. 
     In some examples, wherein the coating includes a multilayer coating including a first layer composed of a third material to harmonize the first wettability characteristic and the second wettability characteristic, and a fourth material to protect the at least one of the first material or the second material. 
     In some examples, the first layer has a first thickness and the second layer has a second thickness, the second thickness being at least three times greater than the first thickness. 
     In some examples, the first thickness is between approximately 20 Angstroms and 100 Angstroms and the second thickness is between approximately 0.2 micrometers and 0.5 micrometers. 
     In some examples, the first layer includes hafnium oxide and the second layer includes an ink impervious material. 
     In some examples, the second layer includes at least one of aluminum oxide, silicon dioxide, or tantalum. 
     In some examples, the first material or the second material includes at least one of silicon, SU-8, or Epoxy Molding Compound (EMC). 
     In some examples, a fluid ejection device includes a substrate defining an ink feed path and a protective coating provided on the substrate defining the ink feed path to protect the ink feed path from ink attack. The protective coating having a first thickness. A hafnium oxide coating is provided on the protective coating along the ink feed path to change a wettability characteristic of the ink feed path. The hafnium oxide coating has a second thickness that is less than the first thickness. 
     In some examples, the protective coating includes at least one of aluminum oxide, silicon dioxide or tantalum. 
     In some examples, the protective coating is provided between the substrate and the hafnium oxide coating. 
     In some examples, the first thickness is approximately between 150 and 250 Angstrom, and the second thickness is approximately 50 Angstrom. 
     In some examples, a printhead includes a substrate defining a nozzle to expel fluid therefrom, and a fluid feed path to fluidly couple a fluid reservoir and the nozzle. A wettability coating is formed on at least a portion of the fluid feed path. The wettability coating is less than 100 Angstrom. 
     In some examples, the substrate includes a first layer composed of SU-8 defining a firing chamber fluidically coupling the nozzle and the fluid feed path, a second layer composed of silicon defining a fluid feedhole to fluidically couple a slot in fluid communication with the reservoir and the firing chamber, and a third layer composed of Epoxy Molding Compound (EMC) defining the slot. 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent.