Patent Publication Number: US-8523324-B2

Title: Liquid discharge head substrate and head unit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid discharge head substrate and a head unit. 
     2. Description of the Related Art 
     A contact pad (a connection terminal) works as an electric contact between a recording apparatus and a head unit capable of being mounted to the recoding apparatus. The contact pad can be touched by a user who has not carried out a static elimination processing when the user attaches/detaches the liquid discharge head. In such a case, a surge voltage by a static electricity discharge enters internal elements of a liquid discharge head from a terminal and can break the internal elements, so that the liquid discharge head is required to have a countermeasure for the static electricity discharge. U.S. Pat. No. 6,945,622 discusses a configuration in which a protection diode is provided as a static electricity protection circuit in an input terminal provided on a liquid discharge head substrate. 
     The liquid discharge head substrate mounted in the liquid discharge head is produced using semiconductor production processing. To cut down on the cost by increasing numbers of products which can be produced from one piece of wafer, downsizing of the head is required, so that reduction of an area for wiring is advancing. Therefore, in the protection diode, the reducing an area of the liquid discharge head has advanced by providing the wiring with a laminated structure. 
     An example of configurations of a circuit of a liquid discharge head substrate and a wiring layer is illustrated in  FIGS. 8A ,  8 B,  8 C, and  8 D. The liquid discharge head has a configuration in which a protection diode is provided in an external terminal as a static electricity protection circuit.  FIG. 8A  illustrates a block diagram of the protection diode. The external terminal  101  electrically connecting to an outside is provided at an end of a first wiring  22  connecting to an inverter circuit  301 . The first wiring  22  is further connected to a second wiring  55  via a first protection diode  103  and a third wiring  66  via a second protection diode  104 . 
       FIG. 8B  is a top view illustrating an example in which the protection diode in the X part illustrated in  FIG. 8A  is downsized by laminating a plurality of wirings and provided. In the first wiring  22 , a first lower conductive layer  118  and a first upper conductive layer  102  are laminated and connected via a through hole  1001  provided in the second insulation layer  115  made of SiO. The first lower conductive layer  118  and the upper conductive layer  102  are made of a conductive material such as aluminum. In this structure, the first lower conductive layer  118  has an equal potential to the first upper conductive layer  102 . A second lower conductive layer  105 , which forms the second wiring  55 , connects to a potential connecting to a large capacity power supply (the potential can be an almost same potential used in a signal input from the terminal  101 : hereinafter referred to as a power supply potential). A third lower conductive layer  106 , which forms the third wiring  66 , is connected to a substrate potential. Further, on a lower side of the second lower conductive layer  105  and the third lower conductive layer  106 , a first insulation layer  114  and a thermally-oxidized layer  113  are provided. The first insulation layer  114  is made of boron phosphorus silicon glass (BPSG), and used as an insulation layer and a heat accumulation layer. The thermally-oxidized layer  113  is formed by oxidizing a substrate  109  made of silicon. The second lower conductive layer  105  and the third lower conductive layer  106  are connected to the first protection diode  103  and the second protection diode  104 , which are formed in the silicon substrate, via a plurality of through holes  1003  provided in the first insulation layer  114 . 
       FIG. 8C  is a cross-sectional view of a line C-C′ of the first protection diode  103  in  FIG. 8B , which is connected to the power supply potential. In a p-type substrate  109 , a n-type well region  110 , a n-type (n+) impurity diffusion region  111 , p-type (p+) impurity diffusion region  112 , and the thermally-oxidized layer  113  are formed. The first insulation layer  114  made of BPSG is formed on the above described layers. The through hole  1003  is formed in the thermally-oxidized layer  113  and the first insulation layer  114 . The impurity diffusion region  112  and the first lower conductive layer  118  are connected to each other, and the impurity diffusion region  111  and the second lower conductive layer  105  are connected to each other respectively, so that the first protection diode  103  is formed. 
       FIG. 8D  is a cross sectional view of a line D-D′ of the second protection diode  104  in  FIG. 8B , which is connected to the substrate potential. In a p-type substrate  109 , a p-type well region  120 , a n-type (+n) impurity diffusion region  111 , a p-type (+p) impurity diffusion region  112 , and the thermally-oxidized layer  113  are formed. The first insulation layer  114  made of BPSG is formed on the above described layers. The through hole  1003  is formed in the thermally-oxidized layer  113  and the first insulation layer  114 . The impurity diffusion region  112  and the third lower conductive layer  106  are connected to each other, and the impurity diffusion region  111  and the first lower conductive layer  118  are connected to each other respectively, so that the second protection diode  104  is formed. 
     With this configuration, when a surge voltage caused by static electricity is applied from the contact pad of the head unit, a surge current flows in the terminal of the liquid discharge head from the contact pad. Further, the surge current flows from the terminal to the upper conductive layer  102 , and flows from the upper conductive layer  102  to the second lower conductive layer  105  through the first protection diode  103  or to the third lower conductive layer  106  through the second protection diode  104 . With the configuration, the surge current caused by the static electricity can be prevented from flowing in an inside of the inverter circuit  301 , so that dielectric breakdown of a switching element can be prevented. 
     In this case, in the protection diode, it is required that insulation between the upper conductive layer  102 , and the second lower conductive layer  105  and the third lower conductive layer  106  is provided by the second insulation layer  115 . More specifically, in an area Y of the second insulation layer  115 , the insulation between the upper conductive layer  102  and the second lower conductive layer  105 , and the insulation between the upper conductive layer  102  and the third lower conductive layer  106  need to be secured. The upper conductive layer  102  has an equal potential to the surge voltage, the second lower conductive layer  105  has the power supply potential and the third lower conductive layer  106  has the substrate potential. 
     However, since the second insulation layer  115  is sandwiched between the upper conductive layer  102 , and the second lower conductive layer  105  or the third lower conductive layer  106 , which have different potentials from each other, dielectric breakdown can arise. Particularly, in a step part (a concavo-convex part) of the through hole  1003  of the lower conductive layer, that is, a thickness of the second insulation layer  115  in the end part of the first insulation layer  114  is thinner than the second insulation layer  115  in a flat part. Thus, the dielectric breakdown of the second insulation layer  115  in the area Y can occur depending on a size of the surge voltage. 
     Particularly, in the liquid discharge head, which discharges a liquid utilizing heat generated by an energy generation element, there is a close relationship between a thickness of the layers of the thermally-oxidized layer  113 , the first insulation layer  114 , and the second insulation layer  115 , and discharge characteristics of the liquid discharge head, such as a heat accumulation property and heat irradiation property. Thus, it is actually difficult to make the second insulation layer  115  thick enough to prevent the dielectric breakdown, when a compatibility with the discharge characteristics of liquid discharge head is considered. 
     SUMMARY OF THE INVENTION 
     The present invention provides a liquid discharge head substrate with high reliability, in which a dielectric breakdown in an inside of an electric circuit is suppressed and a breakdown of the electric circuit caused by a static electricity discharge is suppressed. 
     According to an aspect of the present invention, a liquid discharge head substrate includes an external terminal, a diode, a first conductive layer, a second conductive layer, and a third conductive layer. The external terminal is configured to connect to an external. The first conductive layer is connected to the external terminal for causing a current input from the external terminal to flow, and the diode includes a cathode and an anode. The second conductive layer is connected to the first conductive layer and one electrode of the cathode and the anode, and causes a surge current generated when a surge voltage is applied from the external terminal, to flow from the first conductive layer to the one electrode. The third conductive layer is connected to another electrode of the cathode and the anode, and passes the surge current which flows from the one electrode to the other electrode. The first conductive layer includes a part laminated with the second conductive layer sandwiching an insulation layer and does not include apart laminated with the third conductive layer. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIGS. 1A and 1B  illustrate a perspective view of a liquid discharge apparatus and a liquid discharge head unit which can use an exemplary embodiment of the present invention. 
         FIGS. 2A and 2B  is a perspective view and a cross sectional view of the liquid discharge head which can use the exemplary embodiment of the present invention. 
         FIGS. 3A and 3B  is an top schematic view of the liquid discharge head which can use the exemplary embodiment of the present invention. 
         FIGS. 4A through 4C  illustrate a static electricity protection element. 
         FIGS. 5A through 5C  illustrate a static electricity protection element. 
         FIGS. 6A through 6D  illustrate a static electricity protection element. 
         FIGS. 7A through 7D  are an example of a block diagram of the static electricity protection element which can use the exemplary embodiment of the present invention. 
         FIGS. 8A through 8D  illustrate a conventional static electricity protection element. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
     The liquid discharge head can be equipped in an apparatus such as a printer, a copying machine, a facsimile having a communication system, and a word processor having a printing unit, and further in an industrial recording apparatus complexly combined with various kinds of a processing apparatus. Using the liquid discharge head, the apparatus can record an image on various recording mediums, such as a paper, a thread, a fiber, a cloth, leather, a metal, plastics, a glass, a wood, and ceramics. 
     The meaning of the word “recording” used in the present specification not only applies to images having a denotation such as characters and figures, to the medium to be recorded but also applying images having no denotation such as patterns. 
     Further, the word “ink” should be widely interpreted and means a liquid which is applied to the recording medium and used for forming images, designs, and patterns, processing the recording medium, or a liquid which is subjected to a treatment of the ink or the recording medium. The treatment of the ink or the recording medium refers to, for example, an improvement of fixing by solidification or insolubilization of color materials in the ink applied to the recording medium, an improvement of a recoding quality or a coloring property, and an improvement of durability of recorded image. 
       FIG. 1A  is a schematic view illustrating an example of a liquid discharge apparatus which can be mounted with the liquid discharge head according to the exemplary embodiments of the present invention. As illustrated in  FIG. 1A , a lead screw  5004  rotates coordinating with a positive/negative rotation of a drive motor  5013  via driving force transmission gears  5011  and  5009 . A carriage HC can be mounted with the head unit and has a pin engaging with a spiral groove  5005  of the lead screw  5004 . A head unit can make a reciprocating motion in directions of arrows a and b by rotating the lead screw  5004 . 
     A paper pressing plate  5002  presses a recording sheet P to a platen  5000  over a moving direction of the carriage HC. Photo-sensors  5007  and  5008  are home position detection elements for detecting a lever  5006  of the carriage HC in a detection area and switching a rotation direction of the motor  5013 . A cap  5022  air-tightly covering a front face of the head unit  40  is supported by a supporting member  5016 . Further, a suction member  5015  for sucking an inside of the cap  5022  can perform suction recovery of the head unit  40  via an opening  5023  in the cap  5022 . A cleaning blade  5017  and a member  5019  which moves the cleaning blade  5017  in forward/backward direction are supported by a supporting plate  5018  of an apparatus main body. 
       FIG. 1B  is a perspective view of the head unit  40  including the liquid discharge head  41  detachable to a liquid recording apparatus (a discharge apparatus). The liquid discharge head  41  (hereinafter referred to as a head) connects to the liquid recording apparatus by a flexible film wiring board  43  connecting to a connection terminal  7  and electrically connects to a contact pad  44  having electric continuity. Further, the head  41  is supported by the head unit  40  by being bonded to a supporting substrate. In this exemplary embodiment, as the head unit  40 , the head  41  integrated with an ink tank  42  is illustrated, but a separate-type which can separate the ink tank can be used. 
     By connecting the contact pad  44  to the liquid recording apparatus, a data signal and a voltage for discharging a liquid, are supplied from the liquid recording apparatus to the head  41 . Since such a contact pad  44  is often provided at an outside face of the head unit  40 , a user can touch the contact pad  44  when the user attaches/detaches the head unit  40  to/from the liquid recording apparatus, so that there is a possibility to generate a surge. 
       FIG. 2A  is a perspective view of the liquid discharge head  41  which can use the exemplary embodiment of the present invention. The liquid discharge head  41  according to the exemplary embodiment of the present invention includes a liquid discharge head substrate  50  including an energy generating element  45  and a flow path member  46  contacting the liquid discharge head substrate  50 . In the liquid discharge head substrate  50 , a supply port  49  for supplying a liquid is provided, penetrating the liquid discharge head substrate  50 , and a plurality of energy generating elements  45  are arranged at the both side of the supply port  49  along the supply port  49 . Further, at an end part of the liquid discharge head substrate  50 , a plurality of terminals  101  for supplying electric signals and electric power, which are used for driving the energy generating elements  45 , is provided. 
     The flow path member  46  includes the discharge ports  47 , which can discharge a liquid using the energy generated by the energy generating element  45 , at a position opposite to each energy generating element  45 . The flow path member  46  further includes a concave portion  48   a , which configures a flow path  48  communicating the discharge port  47  with supply port  49 , and contacts the liquid discharge head substrate  50 . 
       FIG. 3A  illustrates a layout of an electric circuit of the liquid discharge head  41 . In areas  91  provided at both sides of supply port  49 , arrays of energy generating elements  45 , a switching element  452  for drive-controlling (control ON/OFF) of the energy generating element  45 , and an AND circuit are provided. In the AND circuit including metal-oxide-semiconductor (MOS) transistors ( 450  and  451 ), a signal from a shift resister  93  and a decoder  94  is input. The shift resistor  93  temporally stores a recording data signal and the decoder  94  sends a block selection signal for selecting a block of the energy generating elements  45 . The AND circuit implements logical sum operation of the recording data signal and the block selection signal, and outputs a signal with which the switching element  452  drive-controls the energy generating elements  45 . In the present exemplary embodiments, the recording data signal used for drive-controlling the energy generating elements  45 , the block selection signal, a clock signal, a latch signal, and a heat-enable signal are referred to as a logic signal. 
     The logic signal input from the terminal  101  (an external terminal) is sent to input circuit  95  which is used as a buffer circuit and includes a plurality of inverter circuits, and further sent to the shift resistor  93  and the decoder  94 . As an input voltage used for inputting the logic signal, comparatively low voltage of about around 3.3 V is used. 
     When the surge voltage of a high voltage caused by a static electricity discharge comes in from the terminal  101  inputting such a logic signal, there is a high possibility of dielectric breakdown of the insulation layer. Therefore, to prevent the internal circuit from the dielectric breakdown by the static electricity discharge, a static electricity protection circuit (a protection diode), which is a feature part of the exemplary embodiment of the present invention, is provided. 
     In addition, it is preferable to provide the static electricity protection circuit because if static electric discharge occurs there is a high possibility of generating the dielectric breakdown in not only in a terminal for the logic signal but also in a terminal for other functional elements which are driven by a relatively low voltage. The terminal for other functional elements is, for example, a terminal of a thermal sensor or a detection terminal. 
       FIG. 2B  illustrates an example of a cross-sectional view of the area  91 , in which the energy generating element  45  and the switching element  452  are provided, in such a liquid discharge head  41 . A silicon substrate  109  containing a p-type conductive material includes a thermally-oxidized layer  113  which is formed by thermally oxidizing a part of the substrate  109 . Further, a first insulation layer  114 , lower conductive layer (a first conductive layer), a second insulation layer  115 , a heating resistance layer  116 , an upper conductive layer (a second conductive layer), and protection layer  117  are laminated and provided in this order. As the lower conductive layer and the upper conductive layer, a conductive material, such as aluminum, can be used. The first insulation layer  114  can be formed using an insulation material containing silicon, such as BPSG (silicon oxide doped by phosphorous and born). The second insulation layer  115  can be formed using an insulation material containing silicon, such as silicon oxide (SiO) and silicon nitride (SiN). Further, the heating resistance layer  116  can be formed using a high electric resistance material, such as TaSiN. 
     A part of the upper conductive layer is partially removed on the heating resistance layer  116 , and used as one pair of discrete wirings  202 . The one pair of the discrete wirings  202  and heating resistance layer  116  are covered with the protection layer  117  and protected from a liquid. A gap part between the one pair of the discrete wirings  202  is used as the energy generating element  45  for discharging the liquid. One of the discrete wirings  202  is used as an electrode  202   a  supplying the power supply potential and the other one is used as an electrode  202   b  connecting to a substrate potential. By applying electrical current to the one pair of the discrete wirings  202 , the energy generating element  45  generates heat energy, and causes the liquid film boiling and generate bubbles. A pressure of these bubbles pushes the liquid out of the discharge port  47 , so that the recording operation is performed. Since cavitation can generate and give a damage to the protection layer  117  when the debubbling occurs, an anti-cavitation layer  128  made of Ta can be formed on the protection layer  117 . Further, in the liquid discharge head  41 , the thermally-oxidized layer  113 , the first insulation layer  114 , and the second insulation layer  115  are provided on the substrate  109 , and heat accumulation properties and heat radiation properties, more specifically, thicknesses of the layers, are adjusted so as to enable a stable discharging operation. 
     Then, a cross-sectional structure part provided by the switching element  452  including a N-MOS transistor  451 , a P-MOS transistor  450  configuring the AND circuit and the N-MOS transistor  451  will be described. In an inside of the substrate  109 , n-type well region  402  and p-type well region  403  are formed by doping an impurity and diffusion, using a conventional ion implantation technology. The P-MOS transistor  450  and the N-MOS transistor  451  are respectively configured with a gate insulation layer  408 , a gate wiring  415  made of polycrystalline silicon (poly-Si), a source region  405  or a drain region  406  which are doped by n+ type impurity or p+ type impurity. Further, the N-MOS transistor which forms the switching element  452  is configured by providing a drain region  411 , a source region  412 , and a gate wiring  413  on the p-type well region  403 . A thermally-oxidized film separation region  453  made of the thermally-oxidized layer  113  is formed between these adjoining MOS transistors so that element separation is performed. 
     A wiring  417  provided in apart of the lower conductive layer (the first conductive layer) connects to the MOS transistor via a through hole (a penetration part) provided in the first insulation layer  114 . Further, the wiring  417  connects to the discrete wiring  202  via a through hole (a penetration part) provided in the second insulation layer  115 . The discrete wiring  202  is positioned in an upper side of the second insulation layer  115  and is apart of the upper conductive layer. 
     In a direction perpendicular to a surface of the substrate  109 , in  FIG. 3B , a common wiring  222  is provided in an upper side of the second insulation layer  115  of the domain  91 . The common wiring  222  connects a terminal  101  to the discrete wirings  202 , which connects to a plurality of the energy generating elements  45 , and connects to the substrate potential, and supplies the power supply potential. As described above, the lower conductive layer and the upper conductive layer configuring the discrete wiring  202  and the common wiring  222  are laminated in the direction perpendicular to the surface of the substrate  109 , so that the area of the liquid discharge head substrate is reduced. 
     With regard to a configuration and an operation of the static electricity protection circuit used in the aforementioned liquid discharge head substrate, a first exemplary embodiment will be described below. In the first exemplary embodiment, an example of a case in which the power supply potential is higher than the substrate potential will be described. 
       FIG. 4A  is a block diagram illustrating a liquid discharge head in which a first protection diode  103  is provided. The first protection diode  103  can pass a surge current, which is generated when a static electricity surge is applied, to a wiring connecting to a potential connected to a large capacity power supply (hereinafter referred to as a power supply potential). In the first exemplary embodiment, the power supply potential is connected to a power supply which can supply an almost the same potential as the potential used for a signal input from the terminal  101 , and can use, for example, the potential of 3.3 V. An anode (one of the electrodes) of the first protection diode  103  is connected to the first wiring  22 , connecting the terminal  101  (an external terminal) which electrically connects with an outside, to an inverter circuit  301  provided in the input circuit  95 . A cathode (the other electrode) of the first protection diode  103  is connected to the second wiring  55  connecting to the power supply potential including the lower conductive layer. 
     With this configuration, even when the surge by the static electricity discharge having a potential higher than the power supply potential is applied from the terminal  101 , the surge current flows from the terminal  101  to the second wiring  55  via the first protection diode  103  (from the anode to the cathode). Therefore, the inverter circuit  301  can be prevented from being broken. 
       FIG. 4B  is atop view of an X part in  FIG. 4A .  FIG. 4C  illustrates a cross-sectional view of an A-A line in  FIG. 4B . On the substrate  109 , the lower conductive layer and the upper conductive layer are laminated and provided sandwiching the second insulation layer  115 . In an inside of the surface of the p-type silicon substrate  109 , the first protection diode  103  including n-type well region  110 , a n-type (n+) impurity diffusion region  111 , and a p-type (p+) impurity diffusion region  112  is provided. Further, the thermally-oxidized layer  113  is provided between the n-type (n+) impurity diffusion region  111  and the p-type (p+) impurity diffusion region  112 , and performs an element separation of the n-type (n+) impurity diffusion region  111  and the p-type (p+) impurity diffusion region  112 . Further, the first insulation layer  114  made of BPSG is formed on the thermally-oxidized layer  113 . 
     In the first insulation layer  114 , a first through hole  1003   b  (a first penetration part) is provided and the p+ impurity diffusion region  112  and the first lower conductive layer  118  (the second conductive layer), which is one part of the lower conductive layer, are connected to each other. Further, in a second through hole  103   a  (a second penetration part) in the first insulation layer  114 , the n+ impurity diffusion region  111  and the second lower conductive layer  105  (the third conductive layer), which is another part of the lower conductive layer, are connected. In this structure, one pair of the lower conductive layers (the second conductive layer and the third conductive layer) are provided so as to respectively connect to the impurity regions of the first protection diode. 
     An upper conductive layer  102  (the first conductive layer) is connected to the terminal  101  electrically connecting to an external. In the second insulation layer  115  made of SiO, a through hole  1001  is provided. The first lower conductive layer  118  and the upper conductive layer  102  are connected via the through hole  1001  so as to be the same potential, and the first wiring  22  is provided. The second lower conductive layer  105  which forms a second wiring  55  is connected to the power supply potential. 
     In the area in which the through hole  1003  is provided, as illustrated in  FIG. 4C , since the through hole  1003  is provided in the thermally-oxidized layer  113  and the first insulation layer  114 , a step height of the second insulation layer  115  is large in comparison with the other areas, so that dielectric breakdown can be generated when a high potential difference is applied. 
     In this configuration, the first lower conductive layer  118  is connected to the upper conductive layer  102  by a through hole  1001  provided in the second insulation layer  115 , and the upper conductive layer  102  and the first lower conductive layer  118  are at the same potential even when the surge is applied. Therefore, although the first lower conductive layer  118  (the second conductive layer) and the upper conductive layer  102  (the first conductive layer) are laminated sandwiching the second insulation layer  115 , there is low possibility of the dielectric breakdown of the second insulation layer  115 . On the other hand, in the second through hole  1003   a , if the upper conductive layer  102  is provided on the second insulation layer  115 , a large potential difference is generated between the upper conductive layer  102  through which the surge voltage flows and the second lower conductive layer  105  which connects to the power supply potential. Therefore, a penetration part  107  in the upper conductive layer  102  is provided on the upper side of the second through hole  1003   a , so that with the structure, the second lower conductive layer  105  (the third conductive layer) and the upper conductive layer  102  (the first conductive layer are in no part laminated sandwiching the second insulation layer  115 . With this structure, a large potential difference is not generated at the area near the second through hole  1003   a , where the thickness of the second insulation layer  115  becomes comparatively thin, so that the dielectric breakdown of the second insulation layer  115  can be prevented. 
     More concretely, in a direction parallel to the surface of the substrate, it is useful to provide a distance Z between the through hole  107  in the upper conductive layer and the end part of the first insulation layer  114  which is at least equal to or more than 2 μm apart. By causing the distance Z to be equal to or more than 2 μm apart, the dielectric breakdown of the second insulation layer  115  at the part of the second through hole  1003   a  can be more certainly prevented. 
     With this structure, the liquid discharge head having high reliability, in which the inverter circuit  301  and the second insulation layer  115  is not dielectric-broken when static electricity discharge is generated, can be provided. 
     Next, a second exemplary embodiment will be described.  FIG. 5A  is a block diagram illustrating a liquid discharge head, in which a second protection diode  104  can pass a surge current to a wiring connecting to the substrate potential when the static electricity surge is applied. A cathode (one of the electrodes) of the second protection diode  104  is connected to the. The first wiring  22  connects the terminal  101  for electrically connecting to the external, to the inverter circuit  301  provided in the input circuit  95 . An anode (the other electrode) of the second protection diode  104  is connected to a third wiring  66  connecting to the substrate potential. 
     With this structure, even when the surge by the static electricity discharge having a lower potential than the substrate potential is applied from the terminal  101 , the surge current flows from the terminal  101  to the third wiring  66  via the second protection diode  104 . More specifically, the surge current flows from the cathode of the second protection diode  104  to the anode, and further flows to the third wiring  66 . Therefore, the dielectric breakdown of the inverter circuit  301  can be prevented. 
       FIG. 5B  is a top view of an X part in  FIG. 5A .  FIG. 5C  is a cross-sectional view of a B-B line in  FIG. 5B . On the substrate  109 , the lower conductive layer and the upper conductive layer are laminated and provided sandwiching the second insulation layer  115 . In an inside of the surface of the p-type silicon substrate  109 , the second protection diode  104  including a p-type well region  120 , a n-type (n+) impurity diffusion region  111 , and a p-type (p+) impurity diffusion region  112  is provided. Further, the thermally-oxidized layer  113  is provided between the n-type (n+) impurity diffusion region  111  and the p-type (p+) impurity diffusion region  112 , and performs the element separation of the n-type (n+) impurity diffusion region  111  and the p-type (p+) impurity diffusion region  112 . Furthermore, on the thermally-oxidized layer  113 , the first insulation layer  114  made of BPSG is provided. 
     In the first insulation layer  114 , a first through hole  1003   b  (a first penetration part) is provided and the n+ impurity diffusion region  111  and the first lower conductive layer  118  (the second conductive layer) which is a part of the lower conductive layer are connected to each other. Further, in the second through hole  1003   a  (a second penetration part) of the first insulation layer  114 , the p+ impurity diffusion region  112  and the second lower conductive layer  106  (the third conductive layer), which is another part of the lower conductive layer, are connected to each other. As described above, one pair of the lower conductive layers (the second conductive layer and the third conductive layer) are provided so as to respectively connect to the impurity diffusion regions of the second protection diode  104 . 
     The upper conductive layer  102  (the first conductive layer) is connected to the terminal  101  electrically connecting to the external. In the second insulation layer  115  made of SiO, the through hole  1001  is provided and the first lower conductive layer  118  and the upper conductive layer  102  are connected via the through hole  1001  so as to be at an equal potential and the first wiring  22  is provided. The second lower conductive layer  106  which forms the third wiring  66  is connected to the substrate potential. 
     In an area in which the through hole  1003  is provided, as illustrated in  FIG. 5C , the through hole is formed in the thermally-oxidized layer  113  and the first insulation layer  114 , a step height of the second insulation layer  115  is larger in comparison with the other areas, and the dielectric breakdown can be generated when a high potential difference is applied. 
     In this structure, the first lower conductive layer  118  is connected to the upper conductive layer  102  by the through hole  1001  provided in the second insulation layer  115 , so that the upper conductive layer  102  and the lower conductive layer  118  are at an equal potential even when the surge is applied. Therefore, although the first lower conductive layer  118  (the second conductive layer) and the upper conductive layer  102  (the first conductive layer) are laminated sandwiching the second insulation layer  115 , there is low possibility of the dielectric breakdown of the second insulation layer  115 . On the other hand, in the second through hole  1003   a , if the upper conductive layer  102  is provided on the second insulation layer  115 , a large potential difference is generated between the upper conductive layer  102  which is at the surge potential and the second lower conductive layer  106  connecting to the power supply potential. Therefore, a penetration part  107  in the upper conductive layer  102  is provided on the upper side of the second through hole  1003   a , so that the second lower conductive layer  106  (the third conductive layer) and the upper conductive layer  102  (the first conductive layer) are in no part laminated sandwiching the second insulation layer  115 . With this structure, a large potential difference is not generated at the part near the second through hole  1003   a  in which the thickness of the second insulation layer  115  becomes thin, so that the dielectric breakdown of the second insulation layer  115  can be prevented. 
     More concretely, in the direction parallel to the surface of the substrate it is useful that a distance Z between the end of the upper conductive layer  102  and the through hole of the first insulation layer  114  is at least equal to or more than 2 μm apart. With the distance Z at least equal to or more than 2 μm, the dielectric breakdown of the second insulation layer  115  at the second through hole  1003   a  part can be prevented. 
     With this structure, a high reliability liquid discharge head can be provided, in which the dielectric breakdown of the inverter circuit  301  and the second insulation layer  115  is not generated when the static electricity discharge occurs. 
     Next, a third exemplary embodiment will be described.  FIG. 6A  is a block diagram of a liquid discharge head including the first protection diode  103  and the second protection diode  104 . The first protection diode  103  described in the first exemplary embodiment can pass the surge current to the power supply potential. The second protection diode  104  described in the second exemplary embodiment can pass the surge current to the substrate potential. 
     The anode of the first protection diode  103  and the cathode of the second protection diode  104  are connected to the first wiring  22  which connects the terminal  101  to the inverter circuit  301 . The first protection diode  103  connects to the power supply potential and the second protection diode  104  connects to the substrate potential. The cathode of the first protection diode  103  is connected to the second wiring  55  of the lower conductive layer, which is connected to the power supply potential. The anode of the second protection diode  104  is connected to the third wiring  66 , which is configured by the lower conductive layer and connected to the substrate potential. 
     With this structure, when the surge by the static electricity discharge having a higher potential than the power supply potential is applied from the terminal  101 , the surge current flows to the second wiring  55  via the first protection diode  103 . Further, when the surge by the static electricity discharge having a lower potential than the substrate potential is applied from the terminal  101 , the surge current flows from the terminal  101  to the third wiring  66  via the second protection diode  104 . Therefore, even when any surges by the static electricity is applied from the terminal  101 , the breakdown of the inverter circuit  301  can be prevented. 
       FIG. 6B  illustrates a top view of a X part in  FIG. 6A .  FIG. 6C  illustrates a cross-sectional view of a A-A line in  FIG. 6B .  FIG. 6D  illustrates a cross-sectional view of a B-B line in  FIG. 6B . The configuration of the first protection diode  103  is same as the first exemplary embodiment, and the configuration of the second protection diode  104  is same as the second exemplary embodiment, so that the description will be omitted. 
     In addition, as illustrated in  FIG. 7A , a resistor  601  is provided between a part, in which the first protection diode  103  and the second protection diode  104  are provided, and the inverter circuit  301 , so that the potential of the surge which is not absorbed by the protection diode can be lowered. As the resistor  601 , a thin film resistor made of polycrystalline silicon or a metal compound, or a diffusion resistor made by doping impurities to a semiconductor can be used. 
     Further, as illustrated in  FIG. 7B  and  FIG. 7C , a plurality of the first protection diodes  103  and the second protection diodes  104  and a plurality of the resistors  601  can be provided. With this structure, the dielectric breakdown by the static electricity discharge can be more certainly prevented. 
     In the exemplary embodiments from the first to the third, the example in which the power supply potential is higher than the substrate potential is used for description. However, when the power supply potential is lower than the substrate potential, as illustrated in  FIG. 7D , the first protection diode  103  is provided on the substrate potential side and the second protection diode  104  is provide on the power supply potential side, so that the same effect can be obtained. In this case, the cathode of the second protection diode  104  connected to the power supply potential and the anode of the first protection diode  103  connected to the substrate potential are connected to the upper conductive layer  102 . The upper conductive layer  102  is connected the terminal  101  and the inverter circuit  301 . With this structure, when the potential of the static electricity discharge is higher than the substrate potential, the surge current flows to the first protection diode  103 . On the other hand, when the potential of the static electricity discharge is lower than the power supply potential, the surge current flows to the second protection diode  104 . With this structure, even when the static electricity discharge occurs, the dielectric breakdown of the inverter circuit  301  can be prevented. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2010-054719 filed Mar. 11, 2010, which is hereby incorporated by reference herein in its entirety.