Patent Publication Number: US-9849672-B2

Title: Fluid ejection apparatus including a parasitic resistor

Description:
BACKGROUND 
     Inkjet technology is widely used for precisely and rapidly dispensing small quantities of fluid. Inkjet printheads eject drops of fluid, such as, for example, ink, from a nozzle by creating a short pulse of increased pressure within a firing chamber. During printing, this ejection operation can repeat thousands of time per second. One way to create pressure in the firing chamber is by heating the fluid in the firing chamber. A thermal inkjet (TIJ) device may include a heating element, such as, for example, a firing resistor, in the firing chamber. To eject a drop of the fluid, an electrical current may be passed through the heating element, and as the heating element generates heat, a portion of the fluid within the firing chamber may be vaporized. The vapor may rapidly expand, forcing a drop of fluid out of the firing chamber and through the nozzle. The electrical current across the heating element may then be turned off, allowing the heating element to cool. As the vapor bubble rapidly collapses, more fluid my be drawn into the firing chamber. 
    
    
     
       BRIEF DESCRIPTION Of THE DRAWINGS 
       The detailed descriptive section references the drawings, wherein: 
         FIG. 1  is a block diagram of an example of a fluid ejection system suitable for incorporating a parasitic resistor to add a parasitic resistance to a firing resistor; 
         FIG. 2  is a perspective view of an example fluid ejection cartridge suitable for incorporating a parasitic resistor to add a parasitic resistance to a firing resistor; 
         FIG. 3  is a circuit diagram for an example fluid ejection apparatus including a parasitic resistor; 
         FIG. 4-6  are sectional views of example fluid ejection apparatuses including a parasitic resistor; 
         FIG. 7  is a flow diagram illustrating an example of a method for making a fluid ejection apparatus; and 
         FIG. 8  is a flow diagram illustrating another example of a method for making a fluid ejection apparatus; 
     
    
    
     all in which various embodiments may be implemented. 
     Examples are shown in the drawings and described in detail below. The drawings are not necessarily to scale, and various features and views of the drawings may be shown exaggerated in scale or in schematic for clarity and/or conciseness. The same part numbers may designate the same or similar parts throughout the drawings. 
     DETAILED DESCRIPTION 
     There remains continued interest in increasing print speeds, print quality, and printing versatility. Among the solutions to increasing print speeds is increased printhead swath, but this solution may pose a cost challenge for printheads using an increased printhead silicon area to achieve the increased printhead swath. A solution to high-quality, versatile printing may include dual drop weight configurations including individual fluid chambers and associated nozzles having different drop volumes. For example, a printhead may include some fluid chamber/nozzle sets designed to eject drops having a smaller size than other ones of the fluid chamber/nozzle sets. While this configuration may allow for different drop characteristics for large and small drops from a single inkjet printhead, the print speed and nozzle density may be reduced given the nozzle redundancy. 
     Described herein are various implementations of a fluid ejection apparatus including a first firing resistor and a second firing resistor to selectively cause fluid to be ejected through a single nozzle, and a parasitic resistor arranged to add a parasitic resistance to the first firing resistor. In various implementations, the first firing resistor may produce a fluid drop having a first size and the second firing resistor may produce a fluid drop having a second size larger than the first size. In various ones of these implementations, the fluid ejection apparatus may include a single firing line arranged to provide a same firing voltage to the first firing resistor and the second firing resistor, and the parasitic resistor may operate to control an amount of energy, and associated stress, across the first firing resistor, which may increase the life of the first firing resistor as compared to apparatuses not including the parasitic resistor. 
     Turning now to  FIG. 1 , illustrated is a block diagram of an example fluid ejection system  100  suitable for incorporating a parasitic resistor as disclosed herein. In various implementations, the fluid ejection system  100  may comprise a thermal inkjet printer or printing system. The fluid ejection system  100  may include a printhead assembly  102 , a fluid supply assembly  104 , a mounting assembly  106 , a media transport assembly  108 , an electronic controller  110 , and at least one power supply  112  to provide power to the various electrical components of fluid ejection system  100 . 
     The printhead assembly  102  may include at least one printhead  114 . The printhead  114  may include one or more printhead dies to supply a fluid, such as ink, for example, to a plurality of nozzles  116 . At least one of the printhead dies may include a first firing resistor  122   a  and a second firing resistor  122   b  to selectively cause fluid to be ejected through a single one of the nozzles  116 , and a parasitic resistor  123  arranged to add a parasitic resistance to the first firing resistor  122   a , as described more fully herein. 
     The plurality of nozzles  116  may eject ejects drops of the fluid toward a print media  118  so as to print onto the print media  118 . The print media  118  may be any type of suitable sheet or roll material, such as, for example, paper, card stock, transparencies, polyester, plywood, foam board, fabric, canvas, and the like. The nozzles  116  may be arranged in one or more columns or arrays such that properly sequenced ejection of fluid from nozzles  116  may cause characters, symbols, and/or other graphics or images to be printed on the print media  118  as the printhead assembly  102  and print media  118  are moved relative to each other. 
     The fluid supply assembly  104  may supply fluid to the printhead assembly  102  and may include a reservoir  120  for storing the fluid. In general, fluid may flow from the reservoir  120  to the printhead assembly  102 , and the fluid supply assembly  104  and the printhead assembly  102  may form a one-way fluid delivery system or a recirculating fluid delivery system. In a one-way fluid delivery system, substantially all of the fluid supplied to the printhead assembly  102  may be consumed during printing. In a recirculating fluid delivery system, however, only a portion of the fluid supplied to the printhead assembly  102  may be consumed during printing. Fluid not consumed during printing may be returned to the fluid supply assembly  104 . The reservoir  120  of the fluid supply assembly  104  may be removed, replaced, and/or refilled. 
     The mounting assembly  106  may position the printhead assembly  102  relative to the media transport assembly  108 , and the media transport assembly  108  may position the print media  118  relative to the printhead assembly  102 . In this configuration, a print zone  124  may be defined adjacent to the nozzles  116  in an area between the printhead assembly  102  and print media  118 . In some implementations, the printhead assembly  102  is a scanning type printhead assembly. As such, the mounting assembly  106  may include a carriage for moving the printhead assembly  102  relative to the media transport assembly  108  to scan the print media  118 . In other implementations, the printhead assembly  102  is a non-scanning type printhead assembly. As such, the mounting assembly  106  may fix the printhead assembly  102  at a prescribed position relative to the media transport assembly  108 . Thus, the media transport assembly  108  may position the print media  118  relative to the printhead assembly  102 . 
     The electronic controller  110  may include a processor  138 , memory  140 , firmware, software, and other electronics for communicating with and controlling the printhead assembly  102 , mounting assembly  106 , and media transport assembly  108 . Memory  140  may include both volatile (e.g., RAM) and nonvolatile (e.g., ROM, hard disk, floppy disk, CD-ROM, etc.) memory components comprising computer/processor-readable media that provide for the storage of computer/processor-executable coded instructions, data structures, program modules, and other data for the printing system  100 . The electronic controller  110  may receive data  130  from a host system, such as a computer, and temporarily store the data  130  in memory  140 . Typically, the data  130  may be sent to the printing system  100  along an electronic infrared, optical, or other information transfer path. The data  130  may represent, for example, a document and/or file to be printed. As such, the data  130  may form a print job for the printing system  100  and may include one or more print job commands and/or command parameters. 
     In various implementations, the electronic controller  110  may control the printhead assembly  102  for ejection of fluid drops  117  from the nozzles  116 . Thus, the electronic controller  110  may define a pattern of ejected fluid drops  117  that form characters, symbols, and/or other graphics or images on the print media  118 . The pattern of ejected fluid drops  117  may be determined by the print job commands and/or command parameters from the data  130 . 
     In various implementations, the printing system  100  is a drop-on-demand thermal inkjet printing system with a thermal inkjet (TIJ) printhead  114  suitable for implementing a printhead die  114  such that the firing resistors  122   a/b  thermally eject the fluid from the fluid chamber of the fluid ejection apparatus  100  through the respective nozzle  116 . In some implementations, the printhead assembly  102  may include a single TIJ printhead  114 . In other implementations, the printhead assembly  102  may include a wide array of TIJ printheads  114 . 
     In various implementations, the printhead assembly  102 , fluid supply assembly  104 , and reservoir  120  may be housed together in a replaceable device such as an integrated printhead cartridge.  FIG. 2  is a perspective view of an example inkjet cartridge  200  that may include the printhead assembly  102 , ink supply assembly  104 , and reservoir  120 , according to an implementation of the disclosure. 
     In addition to one or more printheads  114 , inkjet cartridge  200  may include electrical contacts  205  and an ink (or other fluid) supply chamber  207 . In some implementations, the cartridge  200  may have a supply chamber  207  that stores one color of ink, and in other implementations it may have a number of chambers  207  that each store a different color of ink. The electrical contacts  205  may carry electrical signals to and from a controller (such as, e.g., the electrical controller  110  described herein with reference to  FIG. 1 ) and power (from the power supply  112  described herein with reference to  FIG. 1 ) to cause the ejection of ink drops through the nozzles  216 . 
       FIG. 3  illustrates an example of a circuit diagram for a portion of an example fluid ejection apparatus including a first firing resistor  122   a  and a second firing resistor  122   b  to selectively cause fluid to be ejected through a single nozzle  116  (depicted by hashed lines for discussion purposes), and a parasitic resistor  123  arranged to add a parasitic resistance to the first firing resistor  122   a  to control an amount of energy across the first firing resistor  122   a.    
     As illustrated, the first firing resistor  122   a  and the second firing resistor  122   b  are arranged to receive the same firing voltage and the same firing pulse from the firing line  142 . Select circuitry  144 , which may operate by direct addressing, matrix addressing, or smart drive chip, may facilitate, at least in part, ejection of the fluid by the first firing resistor  122   a  and/or the second firing resistor  122   b , by selectively opening or closing drive transistors  146   a ,  146   b  coupled between the selected resistor  122   a ,  122   b , respectively, and ground, thereby allowing current to flow across the selected resistor. For example, the select circuitry  144  may select the first firing resistor  122   a  to fire, the second firing resistor  122   b  to fire, or both the first firing resistor  122   a  and the second firing resistor  122   b  to fire. Selection of which resistor to fire by the select circuitry  144  may be carried out by a processor (such as, e.g., the processor  138  described herein with reference to  FIG. 1  or another processor of the fluid ejection device or system, or another controlling device, or a combination thereof). 
     In various implementations, the first firing resistor  122   a  and the second firing resistor  122   b  may have different resistances. For at least some of these implementations, the resistors  122   a ,  122   b  may be configured with differing resistances in order to produce fluid drops of differing sizes. For example, the first firing resistor  122   a  may be a low drop-weight resistor and the second firing resistor  122   b  may be a high drop-weight resistor, with the second firing resistor  122   b  having a resistance greater than a resistance of the first firing resistor  122   a  such that the second firing resistor  122   b  is to produce a fluid drop having a size larger than a fluid drop produced by the first firing resistor  122   a . In various implementations, the differing resistances may be achieved by forming the first firing resistor  122   a  with an area/size greater than the area/size of the second firing resistors  122   b.    
     In various implementations, producing fluid drops of differing sizes may allow the fluid ejection apparatus to produce images across a wider range of resolution, saturation, or speed, or a combination thereof. For example, printing using the low drop-weight first firing resistor  122   a  may produce smaller fluid drops to print with higher resolution, while printing using both the low drop-weight first firing resistor  122   a  and the high drop-weight first firing resistor  122   b  may eject a larger amount of fluid for higher speed printing or higher color saturation. 
     In the configuration shown in  FIG. 3  in which the first firing resistor  122   a  and second firing resistor  122   b  are arranged to receive a firing pulse from the same firing line  142  at the same time when both the first firing resistor  122   a  and second firing resistor  122   b  are selected to fire by the select circuitry  144 , the energy stress and power density to the smaller first firing resistor  122   a  may be higher than that of the second firing resistor  122   b  under the same firing pulse width and applied voltage. In some cases, this increases energy stress may result in earlier failure of the first firing resistor  122   a . The energy, E, delivered to each of the resistors  122   a ,  122   b  is generally governed by the following equation: 
                   E   =       ⁢     P   *   PW                 =       ⁢         V   2       R   bb       *   PW                 =       ⁢         V   2         R   122     +     R   parasitic         *   PW                 
where P is power, PW is pulse width, V is voltage across the resistor, R bb  is bulk resistance, R 122  is the resistance of the resistor  122   a  or  122   b , and R parasitic  is the parasitic resistance of resistor  122   a  or  122   b . As such, introducing a parasitic resistance in the electrical path of the smaller first firing resistor  122   a  may reduce the energy delivered to the first firing resistor  122   a  when both the first firing resistor  122   a  and the second firing resistor  122   b  are fired simultaneously. The reduced energy may result in an increased life of the first firing resistor  122   a  than that experienced for configurations without the added parasitic resistance.
 
     To increase the parasitic resistance of the first firing resistor  122   a  to control the energy delivered to the first firing resistor  122   a  when both the first firing resistor  122   a  and the second firing resistor  122   b  are fired simultaneously, the parasitic resistor  123  may be arranged in the electrical path of the first firing resistor  122   a . In some of these implementations, the parasitic resistor  123  may have a resistance to reduce or eliminate R-life failure of the first firing resistor  122   a . In some implementations, the parasitic resistor  123  may have a resistance smaller than the resistance of the first firing resistor  122   a . For example, the parasitic resistor  123  may have a resistance about half that of the first firing resistor  122   a . In some implementations, the first firing resistor  122   a  may have a resistance of about 100Ω and the parasitic resistor  123  may have a resistance of about 50Ω. In other implementations, the first firing resistor  122   a  and the parasitic resistor  123  may be configured with other resistances and other resistance ratios. 
       FIGS. 4-6  depict sectional diagrams of several examples of fluid ejection apparatuses including a first firing resistor and a second firing resistor to selectively cause fluid to be ejected through a single nozzle, and a parasitic resistor arranged to add a parasitic resistance to the first firing resistor as described herein. 
     Turning now to  FIG. 4 , the fluid ejection apparatus  400  may include a substrate  450 , a thin-film stack  452 , and a fluid chamber  454  formed on the thin-film stack  452 . The fluid chamber  454  may be formed within a barrier layer  456  and a nozzle plate layer  458 , each deposited on the thin-film stack  452 . The fluid chamber  454  may be fluidically coupled to a nozzle  416 . The fluid chamber  454  may be configured to hold fluid (e.g., ink), which can be ejected from the nozzle  416 . 
     The substrate  450  may be a semiconductor substrate having doped regions, such as a doped region  460  and a doped region  462 , and the thin-film stack  452  may be formed over the substrate  450 . The thin-film stack  452  may include an oxide layer  464 , a polysilicon layer  466  on the oxide layer  464 , an insulating layer  468  over the patterned oxide layer  464  and polysilicon layer  466 , a conductive layer  470  over the insulating layer  468 , and insulating layer  472 . The thin-film stack  452  may include multiple layers deposited on the substrate  450  in a pattern. The layers in the thin-film stack  452  can be deposited and patterned using known semiconductor deposition and processing techniques. It is to be understood that  FIG. 4  shows the thin-film stack  452  in a simplified manner and may omit topology details, such as the varying heights and thicknesses of the layers as they are deposited over the substrate  452 . 
     A portion of the oxide layer  464  may form a gate oxide layer and a portion of the polysilicon layer  466  may form a gate of a drive transistor  446   a . The doped regions  460  and  462  may form a source and drain of the drive transistor  446   a . Other portions of the oxide layer  464  and the polysilicon layer  466  may form the parasitic resistor  423 . Although the parasitic resistor  423  could be formed using a different material or materials, either on the substrate  450 , s shown, or on another layer, forming the parasitic resistor  423  using the same polysilicon layer  466  used for forming the driver transistor  446   a  may have some benefits. Polysilicon may have a high sheet resistivity of about 28-30 Ω/sq and the process for forming the drive transistor  446   a , or any other transistor on the substrate  450  during the same operation, generally has tight process controls for thickness, critical dimension (CD), and resistivity, and so forming the parasitic resistor  423  during the same operation may facilitate forming the parasitic resistor  423  with the desired resistance and footprint with tight process control. In addition, forming the parasitic resistor  423  under the dielectric layer  428  may result in the layers of the parasitic resistor  423  having less thermal impact and smaller surface adhesion impact on the barrier layer  456  in the downstream process operations than if the parasitic resistor  423  were located elsewhere. Furthermore, forming the parasitic resistor  423  of polysilicon may allow the parasitic resistor  423  to experience less leakage current, with the capability to carry enough current density during nozzle firing, than might be achieved if the parasitic resistor  423  were formed of another material. 
     The insulating layers  468 ,  472  may comprise any type of insulating layer, such as silicon oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), undoped silicate glass (USG), silicon carbide (SiC), silicon nitride (SiN), tetraethyl orthosilicate (TEOS), or the like, or combinations thereof. The insulating layers  468 ,  472  may comprise the same or different materials. 
     The conductive layer  470  may comprise any type of conductive layer or layers, such as tantalum (Ta), aluminum (Al), copper (Cu), tungsten (W), gold (Au), silicon (Si), or the like, or combinations thereof (e.g., Ta and Au), including alloys or combinations thereof (e.g., TaAl, AlCu, WSiN, AlCuSi, etc.). For example, conductive layers  482  and  484  are shown, and in some examples, the first conductive layer  482  may comprise WSiN and the second conductive layer  484  may comprise AlCu. In another example, the first conductive layer  482  may comprise TaAl and the second conductive layer  484  may comprise AlCu. Other combinations may be possible within the scope of the present disclosure. 
     In various implementations, the conductive layers  482 ,  484  may have different sheet resistances. For example, the conductive layer  482  may have a higher sheet resistance than the conductive layer  484  such that, where the conductive layer  484  is present, the majority of the current goes through the conductive layer  484 . Thus, the conductive layer  484  may act as a conducting line and may be used to route signals, and the conductive layer  482  may act as a resistive line and may be used as a resistor. A portion of the conductive layer  482  may be exposed at the surface facing the fluid chamber  454 , as shown, which may provide of surface of the first firing resistor  422   a.    
     Conductive paths  476 ,  478 ,  480  may be formed in the insulating layer  468  to electrically couple the doped region  460  to the metal layer  470 , the doped region  462  to the first resistor  422   a , and the parasitic resistor  423  to the first resistor  422   a , respectively, as shown. 
     Although the second firing resistor (see, e.g., second firing resistor  122   b  described herein with reference to  FIG. 3 ) is not explicitly illustrated in  FIG. 4 , the second firing resistor may be formed on the insulating layer  468  when the first firing resistor  422   a  is formed and may have a configuration similar to that of the first firing resistor  422   a  shown in  FIG. 4  with differences to account for the differing resistance values. In other words, the first firing resistor  422   a  illustrated in  FIG. 4  may look virtually identical to the second firing resistor except that the second firing resistor may have a larger area and would not be electrically coupled to the parasitic resistor  423  by the conductive path  480 . 
     The conductive layer  474  may comprise any type of conductive layer or layers, similar to the conductive layer  470 , such as, for example, Ta, Al, Cu, W, Au, Si, or the like, or combinations thereof (e.g., Ta and Au), including alloys or combinations thereof (e.g., TaAl, AlCu, WSiN, AlCuSi, etc.). As shown, for example, the conductive layer  474  may include a conductive layer  488  and a conductive layer  490 . The conductive layer  490  may be used to provide a bond pad  492  for receiving electrical signals from an external source (not shown). 
     It is to be understood that the layers of the thin-film stack  452  may not be shown to scale. The layers may have various thicknesses depending on particular device configuration and processes used. In an example, the oxide layer  464  may have a thickness on the order of 750 Angstroms (A); the polysilicon layer  466  on the order of 3600 A; the dielectric layer  468  on the order of 13000 A; the metal layer  470  on the order of 5000 A; the dielectric layer  472  on the order of 3850 A; and the metal layer  474  on the order of 4600 A. These thicknesses are merely examples and other configurations may be possible. 
     Additionally, the particular configuration of layers in the thin-film stack  452  is also provided by way of example. It is to be understood that additional dielectric and/or metal layers may be provided in different configurations.  FIGS. 5 and 6  illustrate examples of such variations.  FIGS. 5 and 6  illustrate fluid ejection apparatuses  500  and  600 , respectively, that include similar elements as those described herein with reference to  FIG. 4  and these similar elements in  FIGS. 5 and 6  are not described again to avoid redundancy and for ease of explanation. Similar elements are indicated using the same reference numbers used in  FIG. 4 . 
     As shown in  FIG. 5 , the fluid ejection apparatus  500  includes another conductive layer  594  and another insulating layer  596  between the drive transistor  446   a /parasitic resistor  423  layer and the conductive layer  470 . The conductive layer  594  may comprise any type of conductive layer or layers, similar to the conductive layers  470 ,  474 . As shown, for example, the conductive layer  594  may include a conductive layer  597  and a conductive layer  598 . In other implementations, the conductive layer  594  may be omitted. The fluid ejection apparatus  500  may include conductive paths  576 ,  578 ,  580  to electrically couple, at least in part, the doped region  460  to the metal layer  470 , the doped region  462  to the first resistor  422   a , and the parasitic resistor  423  to the first resistor  422   a , respectively, as shown. 
       FIG. 6  illustrates another example of a fluid ejection apparatus  600 . As shown, the fluid ejection apparatus  600  includes the conductive layers  594  and another insulating layer  506  between the drive transistor  446   a /parasitic resistor  423  layer and the conductive layer  470 . As shown, however, the conductive layer  594  forms a second resistor  622   b . The second resistor  622   b  may be stacked over the first resistor  422   a , may overlap the first resistor  422   a , or may be offset from the first resistor  422   a  such that there is no overlap. In the illustrated example, the second resistor  422   b  is not stacked directly over the  422   a  (and thus is shown by hashed lines). The conductive paths  576 ,  580  may electrically couple, at least in part, the doped region  460  to the metal layer  470 , the doped region  462  to the first resistor  422   a , and the parasitic resistor  423  to the first resistor  422   a , respectively, as shown. The conductive path  578  may electrically couple the second resistor  422   b  to another doped region of another drive transistor (not illustrated). 
       FIGS. 7 and 8  are flow diagrams illustrating example methods  700  and  800 , respectively, for making a fluid ejection apparatus including a first firing resistor and a second firing resistor to selectively cause fluid to be ejected through a single nozzle, and a parasitic resistor arranged to add a parasitic resistance to the first firing resistor. The methods may be associated with the various implementations described herein, and details of the operations shown in the methods  700 ,  800  may be found in the related discussion of such implementations. It is noted that various operations discussed and/or illustrated may be generally referred to as multiple discrete operations in turn to help in understanding various implementations. Some implementations may include more or fewer operations than my be described. 
     Turning now to  FIG. 7 , the method  700  may begin or proceed with forming a parasitic resistor over a substrate at block  701 . The parasitic resistor may be formed directly on the substrate or on an intervening layer between the substrate and the parasitic resistor. The parasitic resistor may comprise at least a polysilicon layer. As described herein, the parasitic resistor may be formed during a same operation as forming one or more drive transistors. 
     The method  700  may proceed to block  703  with forming a first firing resistor and a second firing resistor over the substrate such that the parasitic resistor is electrically coupled to the first firing resistor to add a parasitic resistance to the first firing resistor. The firing resistors may be formed such that the parasitic resistor and/or drive transistor, and one more insulating layers, are between the firing resistors and the substrate. In various implementations, the substrate may comprise a semiconductor substrate and the method  700  may include doping the substrate, prior to forming the firing resistors, to form doped regions that provide source and drain regions of the drive transistor. 
     The method  700  may proceed to block  705  with forming a fluid chamber over the firing resistors, and then forming a nozzle fluidically coupled to the fluid chamber at block  707 . The fluid chamber may be defined, at least in part, by a barrier layer and a nozzle plate layer. The nozzle may be formed in the nozzle plate layer. 
     Turning now to  FIG. 8 , the method  800  may begin or proceed with forming a parasitic resistor and at least one drive transistor over a substrate at block  809 . The parasitic resistor and the drive transistor may be formed directly on the substrate or on an intervening layer between the substrate and the parasitic resistor/drive transistor. In various implementations, the substrate may comprise a semiconductor substrate and the method  700  may include doping the substrate, prior to forming the firing resistors, to form doped regions that provide source and drain regions of the drive transistor. The parasitic resistor and drive transistor may comprise similar layer stacks include at least a polysilicon layer. In many implementations, forming the parasitic resistor and drive transistor may comprise forming an oxide layer over the substrate, forming a polysilicon layer over the oxide layer, etching the stack (oxide layer/polysilicon layer), and doping the polysilicon layer. 
     The method  800  may proceed to block  811  with forming at least one insulating layer over the parasitic resistor and drive transistor, and then to block  813  with forming, in the at least one insulating layer, a first conductive path electrically coupled to the drive transistor and a second conductive path electrically coupled to the parasitic resistor. 
     The method  800  may proceed to block  815  with forming a first firing resistor and a second firing resistor over the substrate such that the parasitic resistor is electrically coupled to the first firing resistor to add a parasitic resistance to the first firing resistor. In various implementations, forming the first firing resistor may comprise forming the first firing resistor over the at least one insulating layer such that the first firing resistor is electrically coupled to the first conductive path and the second conductive path. In this configuration, the first firing resistor may be electrically coupled to the parasitic resistor and the drive transistor. 
     The method  800  may proceed to block  817  with forming a fluid chamber over the firing resistors, and then forming a nozzle fluidically coupled to the fluid chamber at block  819 . The fluid chamber may be defined, at least in part, by a barrier layer and a nozzle plate layer. The nozzle may be formed in the nozzle plate layer. 
     Although certain implementations have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the implementations shown and described without departing from the scope of this disclosure. Those with skill in the art will readily appreciate that implementations may be implemented in a wide variety of ways. This application is intended to cover any adaptations or variations of the implementations discussed herein. It is manifestly intended, therefore, that implementations be limited only by the claims and the equivalents thereof.