Patent Publication Number: US-11020966-B2

Title: Liquid ejection head substrate, method of manufacturing liquid ejection head substrate, and liquid ejection head

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to a liquid ejection head substrate, a method of manufacturing a liquid ejection head substrate, and a liquid ejection head. 
     Description of the Related Art 
     At present, many liquid ejection apparatuses are employed in which a liquid ejection head is mounted. The liquid ejection head ejects a droplet from an ejection opening using bubble generating energy created by film boiling a liquid by applying electricity to a heat generation element and heating the liquid inside a liquid chamber. When printing is performed in such a liquid ejection apparatus, there are cases in which a physical effect, such as an impact caused by cavitation that occurs when liquid bubbling, shrinkage, and debubbling take place in an area on a heat generation element, is exerted in the area on the heat generation element. Furthermore, when the liquid is ejected, since the heat generation element becomes high in temperature, there are cases in which a chemical action, such as a component of the liquid becoming decomposed by heat, becoming attached to a surface of the heat generation element, and solidifying and accumulating on the surface of the heat generation element, occur in a region of the heat generation element. In order to protect the heat generation element from such a physical effect or a chemical action, a protective layer serving as a covering portion that covers the heat generation element is disposed on the heat generation element. 
     The protective layer is typically formed of a metal material such as tantalum or iridium, and is disposed at a position where the protective layer comes in contact with the liquid. Furthermore, in order to achieve insulation between the heat generation element and the protective layer, an insulating layer is disposed between the heat generation element and the protective layer. 
     However, there is a possibility of the function of the insulative layer becoming lost (a chance failure) due to some kind of cause and a connection may be established in which electricity directly flows from the heat generation element or the wiring to the protective layer. When a portion of the electricity supplied to the heat generation element flows to the protective layer, an electrochemical reaction may occur between the protective layer and the liquid and the protective layer may become degenerated or eluted, and the durability of the protective layer may be degraded. Furthermore, in a case in which a plurality of protective layers are electrically connected to each other, the current may flow to a protective layer other than the protective layer in which connection with the heat generation element has been established, and the effect of the degeneration may spread inside the liquid ejection head. 
     Note that Japanese Patent Laid-Open No. 2014-124923 describes a configuration in which a plurality of protective layers are each connected through fuse portions to common wiring that are electrically coupled to the protective layers. In such a configuration, when a current flows into one of the protective layers due to an establishment of a connection described above, the current causes the corresponding fuse portion to be cut; accordingly, electric connection with other protective layers becomes disconnected as well. With the above, the effect of the degeneration of the protective layer can be suppressed from spreading inside the liquid ejection head. 
     SUMMARY OF THE DISCLOSURE 
     A liquid ejection head substrate according to an aspect of the present disclosure includes a base including a surface in which a first heat generation element and a second heat generation element that generate heat to eject liquid are provided, a conductive first covering portion that covers the first heat generation element, a conductive second covering portion that covers the second heat generation element, an insulating layer disposed between the first heat generation element and the first covering portion, and between the second heat generation element and the second covering portion, a fuse portion, first wiring electrically connected to the first covering portion through the fuse portion, the first wiring electrically connecting the first covering portion and the second covering portion to each other, a terminal electrically connected to the first covering portion and the second covering portion through the first wiring, second wiring provided at a position different from that of the first wiring in an orthogonal direction with respect to the surface of the base, and a plurality of electric connection portions provided between the fuse portion and the terminal in a path of current passing through the first wiring, the plurality of electric connection portions connecting the first wiring and the second wiring to each other in parallel. 
     Further features and aspects of the disclosure will become apparent from the following description of example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of an example printing apparatus. 
         FIGS. 2A and 2B  are perspective views of an example printing head. 
         FIG. 3  is a perspective view schematically illustrating an example printing element substrate. 
         FIGS. 4A and 4B  are schematic plan views of an example liquid ejection head substrate. 
         FIGS. 5A and 5B  are cross-sectional views of a portion of the liquid ejection head substrate. 
         FIGS. 6A and 6B  are cross-sectional views of a portion of the printing element substrate. 
       FIGS.  7 A 1  to  7 G 2  are partial cross-sectional views illustrating manufacturing steps of the liquid ejection head substrate. 
         FIGS. 8A and 8B  are schematic plan views of the liquid ejection head substrate. 
         FIG. 9  is a cross-sectional view of a portion of the liquid ejection head substrate. 
         FIG. 10  is a graph illustrating wiring resistance values between a terminal fuse portions. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     If wiring resistance of a piece of common wiring to a fuse portion is high, a value of current flowing through the fuse portion will become small, and it will be difficult to allow the current necessary to disconnect the fuse portion to flow. The above may impair the function of the fuse portion. Particularly, if the length of the liquid ejection head substrate is long and the common wiring extends in a length direction of the substrate, the wiring resistance of the common wiring will tend to become higher. Furthermore, if a width of the liquid ejection head substrate is small, a width of the common wiring will be small as well; accordingly, the resistance of the wiring will tend to be high. Accordingly, depending on the position where the fuse portion is provided, the current value flowing through the fuse portion becomes smaller and the possibility of the fuse portion not becoming disconnected increases. 
     Accordingly, the present disclosure obtains sectility of the fuse portion provided in the liquid ejection head substrate and suppresses spreading of an effect of degeneration of the covering portions when a heat generation element and a covering portions are in communication with each other. 
     According to the present disclosure, the sectility of the fuse portion provided in the liquid ejection head substrate can be obtained and the spreading of the degeneration effect of the covering portions can be suppressed when the heat generation element and the covering portions are in communication with each other. 
     Hereinafter, example embodiments of the present disclosure will be described with reference to the drawings. Note that the following description does not limit the scope of the present disclosure. 
     While an example embodiment is an ink jet printing apparatus (a printing apparatus) configured to circulate liquid, such as ink, between a tank and a liquid ejection apparatus, the example embodiment may have a different configuration. For example, the example embodiment may have a configuration in which the ink inside pressure chambers is made to flow without any circulation of the ink by providing two tanks on an upstream side and a downstream side of the liquid ejection apparatus and having the ink flow from one tank to the other. 
     While an example embodiment is a liquid ejection apparatus having a so-called line head that has a length corresponding to the width of the printed medium, the present disclosure can be applied to a so-called serial-type liquid ejection apparatus that performs printing while scanning the printed medium. The serial-type liquid ejection apparatus may have a configuration in which a single printing element substrate for black ink and a single printing element substrate for chromatic color ink are mounted, for example. Not limited to the above, a short line head that has a length shorter than the width of the printed medium and that includes a plurality of printing element substrates disposed in an ejection opening row direction so as to overlap the ejection openings may be fabricated, and the short line head may be configured to scan the printed medium. 
     Example Ink Jet Printing Apparatus 
     A schematic configuration of a liquid ejection apparatus of an example embodiment, in particular, an ink jet printing apparatus  1000  (hereinafter, also referred to as a printing apparatus) that performs printing by ejecting ink is illustrated in  FIG. 1 . The printing apparatus  1000  includes a conveying unit  101  that conveys a printed medium  102 , and a line type liquid ejection head  103  disposed substantially orthogonal to a conveyance direction of the printed medium. The printing apparatus  1000  is a line type printing apparatus that performs continuous recording in one pass while conveying a plurality of printed mediums  102  continuously or intermittently. The printed medium  102  is not limited to a cut sheet and maybe a continuous roll sheet. The printing apparatus  1000  includes four liquid ejection heads  103  each for a single color corresponding to inks of four colors, namely, CMYK (cyan, magenta, yellow, and black). Furthermore, the printing apparatus  1000  includes caps  1007 . Evaporation of the ink from the ejection openings can be prevented with the caps  1007  covering the ejection opening surface sides of the liquid ejection heads  103  during a non-recording period. 
     Example Printing Head 
     A configuration of a printing head  103  (the liquid ejection head  103 ) according to an example embodiment will be described.  FIGS. 2A and 2B  are perspective views of the liquid ejection head  103  according to the example embodiment. The liquid ejection head  103  is a line type liquid ejection head in which  16  printing element substrates  10 , a single printing element substrate  10  being capable of ejecting ink of a single color, are aligned on a straight line (disposed inline). The liquid ejection heads  103  that eject each of the colors of ink are configured in a similar manner. 
     As illustrated in  FIGS. 2A and 2B , the liquid ejection head  103  includes the printing element substrates  10 , flexible wiring substrates  40 , and electric wiring boards  90  provided with signal input terminals  91  and power supply terminals  92 . The signal input terminals  91  and the power supply terminals  92  are electrically connected to a control unit of the printing apparatus  1000  and supply ejection drive signals and electric power necessary for the ejection to the printing element substrates  10 . By integrating the wiring with the electric circuits in the electric wiring boards  90 , the number of signal input terminals  91  and the number of electric power supply terminals  92  can be less than the number of printing element substrates  10 . With the above, the number of electric connection portions needed to be dismounted can be small when the liquid ejection head  103  is installed in the printing apparatus  1000  or when the liquid ejection head is replaced. Connecting portions  93  provided on both end portions of the liquid ejection head  103  are connected to an ink supply system of the printing apparatus  1000 . Ink is supplied to the liquid ejection head  103  through one of the connecting portions  93  from a supply system of the printing apparatus  1000 , and the ink that has passed inside the liquid ejection head  103  is collected by the supply system of the printing apparatus  1000  through the other connecting portion  93 . As described above, the liquid ejection head  103  is configured so that the ink can be circulated through the path of the printing apparatus  1000  and the path of the liquid ejection head  103 . 
     Example Printing Element Substrate 
       FIG. 3  is a perspective view schematically illustrating a printing element substrate  10  according to an example embodiment of the present disclosure. Note that in the present specification, a surface of the substrate or a layer on the side in which the liquid is ejected is referred to as a surface of the substrate or the layer, and a side of the substrate or a layer on which the liquid is ejected is referred to as an upper side of the substrate or the layer. 
     The printing element substrate  10  includes a substrate  11  (the liquid ejection head substrate) in which liquid supply passages  18  and liquid collection passages  19  are formed, a flow passage forming member  12  formed on a front surface side of the substrate  11 , and a cover plate  20  formed on a back surface side of the substrate  11 . Four lines of ejection opening rows each corresponding to a respective ink color are formed in the flow passage forming member  12  of the printing element substrate  10 . In the substrate  11 , a liquid supply passage  18  is provided on one side of each ejection opening row and a liquid collection passage  19  is provided on the other side of each ejection opening row. Each liquid supply passage  18  and each liquid collection passage  19  are provided so as to extend in the ejection opening row direction. Furthermore, a plurality of supply ports  17   a  in communication with the liquid supply passages  18  are provided in the substrate  11  in the ejection opening row direction, and a plurality of collection ports  17   b  in communication with the liquid collection passages  19  are provided in the substrate  11  in the ejection opening row direction as well. 
     As illustrated in  FIG. 3 , a heat applying portion  31  that forms a bubble in the liquid with thermal energy is disposed at a position corresponding to each ejection opening  13 . The heat applying portions  31  are portions that add heat generated by the heat generation elements  15  ( FIG. 5A ) to the liquid. Note that the heat applying portions  31  are also used as first electrodes  31  described later. 
     Pressure chambers  23  (flow passages) including therein the heat applying portions  31  are sectioned with the flow passage forming member  12 . The heat generation elements  15  corresponding to the heat applying portions  31  are electrically connected to terminals  16 , which electrically couples the heat applying portions  31  to a portion external thereto, with electrical wiring provided in the substrate  11 . Based on pulse signals from the electric wiring boards  90  input through the flexible wiring substrate  40  and the terminals  16 , the heat generation elements  15  generate heat and boils the liquid inside the pressure chambers  23 . With the bubbling force generated by boiling, the liquid is ejected through the ejection openings  13 . 
     Furthermore, the cover plate  20  is provided with openings  21  that are in communication with the liquid supply passage  18  and openings  21  that are in communication with the liquid collection passages. The ink passing through the opening  21 , the liquid supply passage  18 , the supply port  17   a  in that order Is supplied to the pressure chamber  23 . The ink supplied to the pressure chamber  23  is collected through the collection port  17   b , the liquid collection passage  19 , and the opening  21 . 
     First Example Embodiment 
     Example Configuration of Liquid Ejection Head Substrate 
       FIG. 4A  is a schematic plan view of the substrate  11  according to the example embodiment of the present disclosure. Furthermore,  FIG. 4B  is a schematic plan view of an area IVB in  FIG. 4A  indicated by a broken line and is illustrated in an enlarged manner. 
     As illustrated in  FIG. 4B , a protective layer  7  (covering portions) that protects the heat generation elements  15  from cavitation is provided so as to cover the heat generation elements  15 . This protective layer  7  can be formed, for example, as a metal film including tantalum or iridium, or a layered film in which a plurality of the above metal films are layered. A surface of the protective layer  7  is provided so as to be in contact with the liquid inside the pressure chambers  23  and portions of the above protective layer  7  including the surface function as the first electrodes  31  positioned above the heat generation elements  15 . Furthermore, second electrodes  32  corresponding to the first electrodes  31  are disposed inside the pressure chambers  23 , and surfaces of the second electrodes  32  are provided so as to be in contact with the liquid inside the pressure chambers  23 . 
     The present example embodiment is configured so that a voltage can be applied between the first electrodes  31  and the second electrodes  32  through the liquid. With the above, a voltage is applied between the first electrodes  31  and the second electrodes  32  through the liquid, and kogation adhered on the surface of the first electrodes  31  can be eluted into the liquid together with the first electrodes  31 , and charged particles causing kogation can be repelled from the surfaces of the first electrodes  31 . Hereinafter, from the viewpoint of removing kogation and suppressing adhesion of kogation, a description of the present example embodiment will be given with an example in which the portions of the first electrodes  31  and the second electrodes  32  including the surfaces in contact with the liquid are formed of iridium. 
     The first electrodes  31  and the second electrodes  32  are each connected to the corresponding terminal  16  ( FIG. 4A ) through wiring described later, and a voltage is applied between the first electrodes  31  and the second electrodes  32  from a portion external to the substrate  11  through the terminals  16 . 
     As illustrated in  FIG. 4B , the supply ports  17   a  and the collection ports  17   b  are disposed so as to interpose the heat generation elements  15  in between. Furthermore, a pair of supply ports  17   a  and a pair of collection ports  17   b  are disposed for two heat generation elements  15 . A plurality of supply ports  17   a  are provided in the ejection opening row direction (a direction in which the heat generation elements  15  are arranged), and a plurality of collection ports  17   b  are also provided in the ejection opening row direction. 
     The first electrodes  31  are each connected to a piece of individual wiring  33  for the first electrode  31 , which is provided so as to pass through a beam portion between adjacent supply ports  17   a . Furthermore, the plurality of pieces of individual wiring  33  are electrically connected to a piece of common wiring  34  (a first wiring) for the first electrodes  31 . The plurality of second electrodes  32  are electrically connected to a piece of wiring  36  for the second electrodes  32 . 
     As illustrated in  FIG. 4A , the pieces of common wiring  34  and the pieces of wiring  36  extend in the direction in which the ejection opening rows (the rows of heat generation elements  15 ) extend, and a single piece of common wiring  34  and a single piece of wiring  36  are provided for a single row of heat generation elements  15 . The common wiring  34  is provided on a supply port  17   a  side with respect to the row of heat generation elements  15 , and the wiring  36  is provided on a collection port  17   b  side with respect to the row of heat generation elements  15 . The plurality of pieces of common wiring  34  and the plurality of pieces of wiring  36  are disposed on the substrate  11  so as to have a etenidium shape. The plurality of pieces of common wiring  34  are connected to the terminal  16  through a terminal connection wiring  41 , and the plurality of pieces of wiring  36  are connected to the terminal  16  through a terminal connection wiring  42 . Furthermore, the common wiring  34  and the wiring  36  are disposed between the rows of heat generation elements  15 . 
     As illustrated in  FIG. 4B , each common wiring  34  and the corresponding individual wiring  33  are connected with a fuse portion  35  provided in between. In other words, the common wiring  34  is electrically connected to a protective layer  7  (a first covering portion  7   a ) that covers a heat generation element  15  (a first heat generation element  15   a ) and a protective layer  7  (a second covering portion  7   b ) that covers another heat generation element  15  (a second heat generation element  15   b ). The fuse portions  35  are provided in the current paths between the common wiring  34  and the plurality of protective layers  7 . 
     When a chance failure occurs and the heat generation element  15  and the protective layer  7  covering the heat generation element  15  become connected to each other, current flows from the heat generation element  15  to the fuse portion  35  through the protective layer  7 , and the fuse portion  35  becomes disconnected. With the above, by electrically separating the protective layer  7  that has become connected to the heat generation element  15  from the common wiring  34 , spreading of the degeneration of the above protective layer  7  to the protective layers  7  covering other heat generation elements  15  can be suppressed. 
     A width of each fuse portion  35  is narrower than a width of each individual wiring  33  so that when a current flows from a heat generation element  15  to a terminal  16 , the relevant fuse portion  35  is melted. The width of the fuse portion  35  needs to be several micro meters or less in processing dimension, and is preferably 3 μm or less to secure sectility. 
     In the present example embodiment, a single fuse portion  35  is provided for a protective layer  7  that covers two heat generation elements  15 . The manner in which the heat generation elements  15  and the fuse portions  35  are combined may be determined so that when a chance failure occurs in a heat generation element  15 , the other heat generation elements  15  can compensate for the heat generation element  15  in which the chance failure has occurred. 
     However, as described above, there are pieces of common wiring  34  that are disposed between adjacent rows of heat generation elements  15 . Accordingly, when the interval between adjacent rows of heat generation elements  15  is reduced to reduce the size of the substrate  11 , since the width of the common wiring  34  disposed between the rows needs to be reduced as well, the wiring resistance of the common wiring  34  becomes higher. Furthermore, when the number of ejection openings  13  (the heat generation elements  15 ) is large and the ejection opening rows (the rows of heat generation elements) are long, the wiring resistance at the common wiring  34  becomes high in the fuse portion  35 , among from the plurality of fuse portions  35 , in which the distance from the terminal  16  to the fuse portion  35  via the common wiring  34  is long. As described above, when the wiring resistance of the common wiring  34  is high, the current flowing through the fuse portion  35  is small and the fuse portion  35  may not be cut. 
     Accordingly, in the present example embodiment, wiring  37  (second wiring) is provided in a layer different from that of the common wiring  34  (first wiring) in a layered direction, or in a direction orthogonal to the surface of the substrate ( FIG. 4B ). Furthermore, the common wiring  34  and the wiring  37  are electrically connected to each other through a plurality of electric connection portions  39  provided so as to penetrate through an insulating layer  5 . Furthermore, the plurality of electric connection portions  39  are provided between the terminal  16  and the fuse portions  35  and in the path of the current passing through the common wiring  34 , and parallelly connect the common wiring  34  and the wiring  37  to each other. With the above, the wiring resistance in the path of the current between the terminal  16  and the fuse portions  35  is set low ( FIG. 4A  and  FIG. 5B  described later). With the above, a voltage drop in the common wiring  34  is suppressed and a decrease in the amount of current flowing through the fuse portions  35  is suppressed; accordingly, sectility of the fuse portions  35  can be obtained. In other words, when the heat generation element  15  and the protective layer  7  become connected to each other, the current flowing from the heat generation element  15  is allowed to flow through the wiring  37  such that the fuse portion  35  is cut easily. Accordingly, the influence exerted when the heat generation element  15  and the protective layer  7  become connected to each other can be suppressed from spreading to the protective layer  7  covering the other heat generation elements  15 . 
     Note that as illustrated in  FIG. 4A , in the present example embodiment, the electric connection portion  39  connecting the wiring  37  and the common wiring  34  to each other is provided at both end portions of each common wiring  34 . Furthermore, an electric connection portion  39  that connects the terminal connection wiring  41 , which connects the plurality of pieces of common wiring  34  and the terminal  16  to each other, and the pieces of wiring  37  to each other is provided in the vicinity of the terminal  16 . 
     Note that in order to further reduce the wiring resistance in the path of the current between the terminal  16  and the fuse portions  35 , desirably, a sheet resistance of the wiring  37  is set lower than a sheet resistance of the common wiring  34 . For example, it is desirable to provide the wiring  37  using an alloy of aluminum and copper. For example, when an iridium layer is used for the protective layer  7 , a film thickness of the iridium layer is preferably within the range of 30 to 100 nm in order to obtain sufficient durability, and in order to suppress the manufacturing load, a sheet resistance of the common wiring  34  formed to include the iridium layer constituting the protective layer  7  is about several ohms per square. On the other hand, when the wiring  37  is formed using an alloy of aluminum and copper, the sheet resistance is 1 Ω/sq or less with a thickness of 200 nm, for example. Accordingly, by electrically coupling the above two to each other, the effect of suppressing the wiring resistance in the path of the current between the terminal  16  and the fuse portions  35  can be obtained sufficiently. 
     Furthermore, in order to suppress an increase in the size of the substrate  11 , desirably, the common wiring  34  and the wiring  37  are provided so as to overlap each other at least partially when the substrate  11  is viewed in plan view. 
     In the present example embodiment, as illustrated in  FIG. 4A , for example, a length of the terminal connection wiring  41  that connects the common wiring  34 , among the plurality of pieces of connection wiring  34 , that is farthest from the terminal  16  and the terminal  16  to each other is 7 mm, and a width thereof is 70 μm. Furthermore, for example, a length of the common wiring  34  disposed between the rows of heat generation elements 15 is 20 mm, and a width thereof is 200 μm. 
     Subsequently, a layered configuration of the liquid ejection head substrate  11  will he described.  FIG. 5A  is a partial cross-sectional view of the substrate  11  taken along line VA-VA in  FIG. 4A  and is a diagram illustrating the heat generation element  15 , the terminal  16 , and the vicinity of the heat generation element  15  and the terminal  16 .  FIG. 5B  is a partial cross-sectional view of the substrate  11  taken along line VB-VB in  FIG. 4A  and is a cross-sectional view illustrating the electric connection portion  39  that electrically couples the common wiring  34  and the wiring  37  to each other, and the vicinity of the electric connection portion  39 . 
     A base  1  is configured by providing an insulating layer such as SiO (preferably several hundred nanometers thick) on a surface of a silicon substrate provided with a driving element and wiring for the driving element (both not shown). Furthermore, a wiring layer  2  formed of an alloy of aluminum and copper, for example, is provided on a front surface side of the insulating layer. Since the wiring layer  2  constitutes power wiring for driving the heat generation elements  15 , a thickness thereof is preferably 200 to 2000 nm. Herein, the thickness of the wiring layer  2  is 1000 nm, for example. 
     An insulating layer  3  formed of, for example, SiO and with a thickness within the range of 1 to 2 μm. (1.5 μm in the present example embodiment, for example) is desirably provided on the surface of the wiring layer  2 . A thermal resistor layer  14  formed of, for example, TaSiN or the like is provided on a surface of the insulating layer  3 . In the thermal resistor layer  14 , a portion supplied with electric power from the wiring layer  2  functions as the heat generation element  15 . The size of the above heat generation element  15  is, for example, 15 μm by 15 μm. The heat generation element  15  and the wiring layer  2  are electrically connected to each other through plugs  4  that is formed of, for example, tungsten and that is provided in the insulating layer  3 . Note that the base  1  on which the insulating layer  3  is provided, in other words, a member that is a combination of the base  1  and the insulating layer  3  may be referred to as a base. In such a case, the base includes a surface on which the heat generation element  15  is provided. 
     Furthermore, a metal layer is formed on the insulating layer  3  with the thermal resistor layer  14  in between. The wiring layer  37  and a terminal forming layer  16   a  constituting a portion of the terminal  16  for external connection are formed with the metal layer. An aluminum layer formed of an alloy of aluminum and copper, for example, can be used as the metal layer. 
     The insulating layer  5  (200 nm in thickness, for example) formed of SiN, SiC, SiCN or the like is provided so as to cover the heat generation element  15  and the wiring  37 . 
     Furthermore, the protective layer  7  formed of a conductive material and for protecting the heat generation element  15  from cavitation is provided on a front surface side of the insulating layer  5  at a position corresponding to the heat generation element  15 . In the present example embodiment, the protective layer  7  is a layered film in which a tantalum layer and an iridium layer are layered from the insulating layer  5  side. For example, regarding the thickness of the protective layer  7 , the tantalum layer is 30 nm thick and the iridium layer is 70 nm thick. 
     Furthermore, the common wiring  34  is provided above the wiring  37  with the insulating layer  5  in between. In the present example embodiment, in order to suppress the manufacturing load, the common wiring  34  is configured to include at least some of the layers forming the protective layer  7 . In the present example embodiment, the common wiring  34  has a three-layer structure in which a tantalum layer is provided above the iridium layer in addition to the tantalum layer and the iridium layer constituting the protective layer  7 . For example, regarding the thickness of each layer of the common wiring  34  from the insulating layer  5  side, the tantalum layer is 30 nm, the iridium layer is 70 nm, and the tantalum layer is 70 nm. Note that the common wiring  34  may be formed using a material different from that of the protective layer  7  and in a different manufacturing process. 
     Note that as illustrated in  FIG. 5A , desirably; the common wiring  34  is provided so as to cover step portions of the insulating layer  5  formed due to the end portions of the wiring  37 . The reason for the above is that etching residues may be created at the step portions when etching is performed on the common wiring  34  so that the end portions of the common wiring  34  are formed inside the step portions of the insulating layer  5  formed by the end portions of the wiring  37 . 
     Furthermore, an intermediate layer  6  including Si is disposed above the common wiring  34  and the insulating layer  5  in order to obtain adhesion with the flow passage forming member  12 . For example, in the present example embodiment, in order to suppress corrosion caused by liquid, a SiCN film having high resistance to liquid and having a thickness of 150 nm is provided as the intermediate layer  6 . Note that as illustrated in the cross-sectional view in  FIG. 5A , in the area above the heat generation element  15 , the tantalum layer and the intermediate layer  6  are removed so that a through hole is formed in the tantalum layer on the surface layer side and the intermediate layer  6  and so that the iridium layer is exposed. The first electrode  31  is formed with the above iridium layer. Similarly, the second electrode  32  (not shown in the cross-sectional view in  FIG. 5A ) is also formed by the iridium layer exposed with the removal of the tantalum layer on the surface layer side and the intermediate layer. 
     Furthermore, as illustrated in  FIG. 5B , the common wiring  34  and the wiring  37  are connected to each other through the electric connection portion  39 . The above electric connection portion  39  connects the surface of the iridium layer exposed by the removal of the tantalum layer on the surface layer side of the common wiring  34  and the intermediate layer  6 , and the surface of the wiring  37  exposed by the removal of the insulating layer  5  and the intermediate layer  6 . In other words, the electric connection portion  39  is provided so as to connect a surface of the common wiring  34  on a side opposite to the surface opposing the wiring  37 , and the surface of the wiring  37  opposing the common wiring  34 . Furthermore, the electric connection portion  39  is formed of a material that is the same as that of a terminal forming layer  16   b  constituting a portion of the terminal  16  illustrated in  FIG. 5A . For example, the electric connection portion  39  and the terminal forming layer  16   b  are formed as layered films in which a layer formed of gold is provided on the front surface side and in which a TiW layer serving as a barrier metal is provided below the gold layer. Note that while  FIG. 5A  illustrates the terminal  16  electrically connected to the heat generation element  15 , the terminal  16  connected to the common wiring  34  also has a similar layered configuration in which the terminal forming layer  16   a  and the terminal forming layer  16   b  are layered. 
       FIGS. 6A and 6B  illustrate partial cross-sectional views of the printing element substrate  10  corresponding to the partial cross-sectional view of the liquid ejection head substrate  11  in  FIG. 5B . 
     In the present example embodiment, since the electric connection portions  39  are provided on the upper layer side of the substrate  11 , the liquid may contact the electric connection portions  39 . Accordingly, in the example illustrated in  FIG. 6A , the electric connection portion  39  is covered with the flow passage forming member  12  to protect the electric connection portion  39  from the liquid. Note that since it is only sufficient to protect the electric connection portion  39  from the liquid, the flow passage forming member  12  may be configured to cover the electric connection portion  39  so as to be in contact with the electric connection portion  39  or the flow passage forming member  12  may be configured so as to be disposed with a gap with the electric connection portion  39  and cover a portion around the electric connection portion  39 . 
     In the example illustrated in  FIG. 6B , the flow passage thrming member  12  provided around the electric connection portion  39  is provided with a gap with the electric connection portion  39  and, further, an opening is provided above the electric connection portion  39  and partially covers the electric connection portion  39 . In order to prevent peeling between the flow passage forming member  12  and the electric connection portion  39  that includes gold, the flow passage forming member  12  and the electric connection portion  39  are configured so as not to be in direct contact with each other. 
     Note that if the number of electric connection portions  39  is large, the possibility of the liquid contacting the electric connection portions  39  increases. Accordingly, in the present example embodiment, a single electric connection portion  39  is provided above each of the two end portions of the common wiring  34  as described above ( FIG. 4A ). With the above, the wiring resistance of the common wiring  34  can be suppressed while suppressing the possibility of liquid intruding, and the sectility of the fuse portion  35  disposed at a position distanced from the terminal  16  can be obtained. Note that by having at least one of the electric connection portions  39  provided at both end portions of the common wiring  34  have a portion positioned outside the row of heat generation elements  15  in the row direction, the possibility of the liquid invading into the portion around the electric connection portion  39  can be suppressed further. Furthermore, between the electric connection portions  39  provided at both end portions of the common wiring  34 , desirably, at least one of the electric connection portions  39  includes a portion positioned on the outer side in the row direction with respect to the row of the fuse portions  35  provided in the row direction of the heat generation elements  15 . The above is desirable since with the above, the effect of suppressing the resistance of the common wiring  34  obtained by electrically connecting the common wiring  34  and the wiring  37  to each other can be improved. 
     Note that while the planar shape of the substrate  11  (the printing element substrate  10 ) illustrated in  FIG. 4A  is rectangular, the shape of the substrate  11  is not limited to the above shape. The planar shape of the substrate  11  may be, for example, a trapezoid or a parallelogram shape that has no right angles. With such a shape, it will be easier to configure the line type liquid ejection head illustrated in  FIG. 2  having a plurality of printing element substrates  10  arranged on a straight line. 
     Example Method of Manufacturing Liquid Ejection Head Substrate 
     FIGS.  7 A 1  to  7 G 2  are cross-sectional views for illustrating manufacturing steps of the liquid ejection head substrate of the present example embodiment. FIGS.  7 A 1  to  7 G 1  illustrate partial cross-sectional views of the substrate  11  taken along lines VIIA 1 -VIIA 1  to VIIG 1 I-VIIG 1  in  FIG. 4A , and FIGS.  7 A 2  to  7 G 2  illustrate partial cross-sectional views of the substrate  11  taken along lines VIIA 2 -VIIA 2  to VIIG 2 -VIIG 62  in  FIG. 4A . 
     A base  1  provided with an insulating layer such as SiO on a surface of a silicon substrate provided with a driving element and wiring for the driving element (both not shown) is first prepared. Subsequently, a wiring layer  2  formed of an alloy of aluminum and copper, for example, is formed on a front surface side of the insulating layer of the base  1 . Subsequently, an insulating layer  3  formed of, for example, SiO that covers the wiring layer  2  is formed, and a surface of the insulating layer  3  is planarized with a CMP method (FIGS.  7 A 1  and  7 A 2 ). 
     Subsequently, through holes are formed in the insulating layer  3 , tungsten is formed by a CVD method to fill the through holes, for example, and, furthermore, the surface of the insulating layer  3  is planarized by a CMP method to form plugs  4 , Further, a thermal resistor layer  14  formed of, for example, TaSiN and a metal layer formed of an alloy of aluminum and copper, for example, are formed with a sputtering method and pattering is performed. With the above, a terminal thrming layer  16   a  and wiring  37  are formed (FIGS.  7 B 1  and  7 B 2 ). 
     Subsequently, the metal layer on the thermal resistor layer  14  that is to become a heat generation element  15  is partially removed by wet etching to provide the heat generation element  15  (FIG.  7 C 1 ). 
     Subsequently, an insulating layer  5  formed of, for example, SiN is formed so as to cover the heat generation element  15  and the metal layer and, furthermore, a layered film of, for example, a tantalum layer/a iridium layer/a tantalum layer is formed with a sputtering method. The layered film is patterned to form common wiring  34  (FIG.  7 D 1 ), a fuse portion  35 , wiring  36  for a second electrode  32 , and the like. In so doing, in order to provide a connection area between the wiring  37  and an electric connection portion  39  formed in a later step, the common wiring  34  (a layered film) is patterned and a portion thereof is removed to form a through hole  34   a  in the common wiring  34  (FIG.  7 D 2 ). 
     Subsequently, an intermediate layer  6  formed of, for example, SiCN is formed so as to cover the layered film constituting the insulating layer  5  and the common wiring  34  (FIGS.  7 E 1  and  7 E 2 ). 
     Subsequently, first electrodes  31  and second electrodes  32  ( FIG. 4B ) are formed from the layered film. For the above, the intermediate layer  6  and the tantalum layer that is the outermost layer in the layered film, which are formed on the layered film above the portions that are to become the electrodes, are removed by dry etching, and through holes  8  that penetrate the above layers are formed (FIG.  7 F 1 ). With the above, the first electrode  31  positioned above the heat generation element  15  and the second electrode  32  corresponding to the first electrode  31  are formed. In other words, a protective layer  7  in which two layers, namely, the tantalum layer and the iridium layer, are layered on the heat generation element  15  is formed. Furthermore, in the same process as the above, the intermediate layer  6  and the tantalum layer that is the outermost layer in the layered film are removed to provide a connection area between the common wiring  34  and the electric connection portion  39  formed at a later step so that a through hole  9  that penetrates the above layers are formed (FIG.  7 F 2 ). 
     Subsequently, a through hole penetrating the insulating layer  5  and the intermediate layer  6  is provided to expose a surface of the terminal forming layer  16   a ,  1 n the same process as the above, in order to expose a portion of a surface of the wiring  37 , a through hole penetrating the insulating layer  5  and the intermediate layer  6  provided inside the through hole  34   a  (FIG.  7 D 2 ) of the common wiring  34  is formed. Furthermore, for example, as an underlayer, a TiW layer serving as a barrier metal is provided on the terminal forming layer  16   a , and a terminal forming layer  16   b  provided with a gold layer is formed thereon (FIG.  7 G 1 ). With the above, the terminal  16  is formed. Furthermore, in the same process as above, for example, the TiW layer is provided in the underlayer and the electric connection portion  39  in which and the gold layer is provided thereon is formed. A portion of a surface of the exposed wiring  37  is connected to a surface of the iridium layer in the exposed common wiring  34  with the above electrical connection portion  39  (FIG.  7 G 2 ). 
     As described above, in the present example embodiment, the wiring  37  that is connected in parallel to the common wiring  34  between the terminal  16  and the fuse portions  35  is formed in the same step as the step in which the terminal  16  (the terminal forming layer  16   a ) is formed. Furthermore, the electric connection portion  39  that connects the common wiring  34  and the wiring  37  to each other is also formed in the same step as the step forming the terminal  16  (the terminal forming layer  16   b ). With the above, while suppressing the load in the manufacturing steps, the voltage drop in the common wiring  34  can be suppressed and the sectility of the fuse portion  35  can be obtained. 
     Second Example Embodiment 
     A liquid ejection head substrate of the present example embodiment will be described mainly on points different from the example embodiment described above. 
       FIG. 8A  is a schematic plan view of the substrate  11  according to the example embodiment of the present disclosure. Furthermore,  FIG. 8B  is a schematic plan view of an area VIIIB indicated by a broken line in  FIG. 8A  and is illustrated in an enlarged manner. 
       FIG. 9  is a partial cross-sectional view of the substrate  11  taken along line IX-IX in  FIG. 8A , and is a diagram illustrating the electric generating element  15 , the terminal  16 , electric connection portions  49  that electrically connect the common wiring  34  and the wiring  37  to each other, and the vicinity of the above. 
     In the present example embodiment, the configuration of the electric connection portion  49  is different from that of the example embodiment described above, and as illustrated in  FIG. 9 , a through hole  5   a  is provided in the insulating layer  5  between the common wiring  34  and the wiring  37 , and the electric connection portion  49  is formed by directly connecting the common wiring  34  and the wiring  37  to each other. 
     In the present example embodiment, the intermediate layer  6  having a high bondability with the flow passage thrming member  12  is provided on the front surface side of the substrate  11 , and the electric connection portion  39  such as the one in the example embodiment described above is not exposed towards the front surface side of the substrate  11 ; accordingly, adhesion between the flow passage forming member  12  and the substrate  11  can be obtained. Accordingly, as illustrated in  FIG. 8B , a single electric connection portion  49  corresponding to a single fuse portion  35  can also be provided. With the above, while further suppressing the voltage drop in the common wiring  34 , the sectility of the fuse portion  35  can be improved further. 
     In the present example embodiment, a through hole  5   a  is formed in the insulating layer  5  after forming the insulating layer  5 . In a state in which the through hole  5   a  is provided, a portion of a surface of the wiring  37  is exposed from an opening of the through hole  5   a  and an insulating film may be formed on the surface. In order to sufficiently establish an electrical connection between the common wiring  34  and the wiring  37 , after forming the through hole  5   a  and before the layer constituting the common wiring  34  is formed, desirably, reverse sputtering is performed and the insulating film on the surface is removed. Note that the insulating layer  5  on the heat generation element  15  may be scraped off as well with the reverse sputtering step. Accordingly, in order to obtain the insulation properties between the heat generation element  15  and the protective layer  7 , the configuration of the present example embodiment can be said to be effective when the insulating layer  5  is thick. 
     Wiring Resistance to Fuse Portion in Example Embodiments and in Comparative Example 
       FIG. 10  is a graph illustrating wiring resistance values between the terminal  16  and the fuse portions  35  in the example embodiments described above and in the comparative example. Note that unlike the example embodiments described above, the comparative example is not provided with the wiring  37 , and the portion between the terminal  16  and the fuse portions  35  is connected with the common wiring  34  and the terminal connection wiring  41 .  FIG. 10  illustrates the wiring resistance values from the terminal  16  to each of the fuse portions  35  in the row of heat generation element  15  disposed at a position that is farthest from the terminal  16  in the +X direction ( FIGS. 4A and 8A ). Furthermore, the axis of abscissas in  FIG. 10  indicates the position of each fused portion  35  in the +Y direction ( FIGS. 4A and 8A ), and the distance from the terminal  16  to the fuse portion  35  passing through the common wiring  34  increases towards the right side of the graph. 
     Note that the sheet resistance of the common wiring  34  is 1.6 Ω/sq, and compared to the sheet resistance of the common wiring  34 , the sheet resistance of the wiring  37  is significantly low at 0.1 Ω/sq. 
     The first and second example embodiments are provided with electric connection portions  39  and electric connection portions  49  ( FIGS. 4A and 8A ) that connect the pieces of wiring  37  to the vicinity of the terminal  16 . Accordingly, the wiring resistance value from the terminal  16  is, compared with that of the comparative example, low in either of the fuse portions  35 . Furthermore, in the first example embodiment, since the electric connection portions  39  that connect the wiring  37  and the common wiring  34  to each other are provided at the two end portions of the common wiring  34 , the resistance values from the terminal  16  to the fuse portions  35  positioned in the vicinities of the electric connection portions  39  are low. In the second example embodiment, since the electric connection portions  49  are provided so as to correspond to the fused portions  35 , the wiring resistance from the terminal  16  to the fuse portions  35  is even lower than that in the first example embodiment. As described above, since the present example embodiments are capable of suppressing the wiring resistance to the fuse portions  35 , the sectility of the fuse portions  35  can be obtained. 
     While the disclosure has been described with reference to example embodiments, it is to be understood that the invention is not limited to the disclosed example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2018-087531 filed Apr. 27, 2018, and No. 2019-042261 filed Mar. 8, 2019, which are hereby incorporated by reference herein in their entirety.