Patent Publication Number: US-10315422-B2

Title: Liquid discharging head substrate, liquid discharging head, and liquid discharging apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a liquid discharging head substrate, a liquid discharging head, and a liquid discharging apparatus. 
     Description of the Related Art 
     A liquid discharging apparatus as typified by an ink-jet printer is equipped with a liquid discharging head, and in the liquid discharging head is provided a substrate (liquid discharging head substrate) in which a plurality of discharging elements for performing a liquid discharge are arranged (refer to Japanese Patent Laid-Open No. 2016-087941). In each discharging element, an electrothermal transducer element (heater element), for example, is used. Thermal energy is generated when a driving current is supplied to the respective discharging elements, and liquid is discharged from a nozzle (discharge port) disposed in the liquid discharging head when the liquid to which the thermal energy is applied bubbles. 
     Note that since a relatively large current is supplied to each of the discharging elements in order to perform liquid discharge appropriately, there is the possibility that a voltage drop will occur in a power-supply line that transmits a power-supply voltage that is supplied to each of the discharging elements. For this reason, it is advantageous to reduce an impedance component (parasitic resistance component) of the power-supply line. 
     However, the power-supply voltage is typically supplied to the power-supply line from outside via an electrode pad (power-supply pad) arranged at an end portion of the liquid discharging head substrate. For this reason, a difference in impedance due to the distance from this electrode pad may arise between different portions on the power-supply line. As a result, it is possible that a difference in the values of the power-supply voltage that is supplied (supply voltage) will arise between discharging elements that are provided at different positions. 
     SUMMARY OF THE INVENTION 
     The present invention provides a technique that is advantageous at reducing a difference in values of supply voltage that can occur between discharging elements. 
     One of the aspects of the present invention provides a liquid discharging head substrate in which a plurality of driving elements for respectively driving a plurality of discharging elements for discharging liquid are arranged on a semiconductor substrate, the liquid discharging head substrate comprising a conductive film provided to cover a region in which the plurality of driving elements are arranged in a plan view corresponding to the top surface of the semiconductor substrate, so as to supply a power-supply voltage to the plurality of driving elements, and a power-supply pad provided at an end of the semiconductor substrate in the plan view, and into which the power-supply voltage is inputted from outside, wherein the conductive film has an outer shape that is not linearly symmetrical in relation to a line orthogonal to an edge at which the power-supply pad of the semiconductor substrate is provided in the plan view, and a plurality of openings are disposed in the conductive film, the conductive film has a first portion and a second portion wherein an impedance of the conductive film from the power-supply pad to the second portion is smaller than an impedance of the conductive film from the power-supply pad to the first portion, and the liquid discharging head substrate further comprises a conductive pattern that electrically connects the first portion and the second portion in a layer different to the conductive film. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A ,  FIG. 1B ,  FIG. 1C , and  FIG. 1D  are views for describing an example of a configuration of a liquid discharging apparatus. 
         FIG. 2A ,  FIG. 2B , and  FIG. 2C  are views for describing an example of a structure of a liquid discharging head substrate. 
         FIG. 3  is a view for describing a cross-sectional structure of the liquid discharging head substrate. 
         FIG. 4A  and  FIG. 4B  are views for describing an example of a structure of the liquid discharging head substrate and an example of electrical characteristics thereof. 
         FIG. 5A  and  FIG. 5B  are views for describing an example of a structure of the liquid discharging head substrate and an example of electrical characteristics thereof. 
         FIG. 6  is a view for describing an example of a structure of the liquid discharging head substrate. 
         FIG. 7A  and  FIG. 7B  are views for describing an example of a structure of the liquid discharging head substrate. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, explanation will be given regarding a preferred embodiment of the present invention with reference to the attached drawings. Note that each drawing is given merely with the objective of describing the structure or configuration, and the dimensions of each member shown graphically do not necessarily reflect the actual dimensions. Also, in the drawings, the same reference numerals are given to members that are the same and elements that are the same, and duplicate descriptions of content are omitted below. 
     (Example of Configuration of Liquid Discharging Apparatus) 
       FIG. 1A  exemplifies an internal configuration of a liquid discharging apparatus  900  as typified by an ink-jet printer, a facsimile, a copy machine, or the like. In the present example, the liquid discharging apparatus may also be referred to as a printing apparatus. The liquid discharging apparatus  900  comprises a liquid discharging head  810  that discharges liquid (ink, a print agent in the present example) onto a predetermined medium P (a print medium such as a sheet in the present example). In the present example, the liquid discharging head may be referred to as a printhead. The liquid discharging head  810  is mounted on a carriage  820 , and the carriage  820  may be attached to a lead screw  921  that has a spiral groove  904 . The lead screw  921 , via driving force conveying gears  902  and  903 , can rotate by linking with the rotation of a driving motor  901 . By this, the liquid discharging head  810  can move in the directions of arrow symbols a and b following a guide  919  together with the carriage  820 . 
     The medium P is pressed in a direction of movement of the carriage by a paper pressing plate  905 , and fixed in relation to a platen  906 . The liquid discharging apparatus  900  causes the liquid discharging head  810  to move reciprocally, and performs a liquid discharge (printing in the present example) onto the medium P which has been conveyed onto the platen  906  by a conveying unit (not shown). 
     Also, the liquid discharging apparatus  900 , via photocouplers  907  and  908 , confirms the position of a lever  909  disposed on the carriage  820 , and switches the rotation direction of the driving motor  901 . A support member  910  supports a cap member  911  for covering a nozzle (a liquid discharging port/orifice, or simply a discharge port) of the liquid discharging head  810 . A suction unit  912  performs a recovery process for the liquid discharging head  810  by sucking inside of the cap member  911  via an in-cap opening  913 . A lever  917  is disposed in order to start the recovery process by suction, and moves along with movement of a cam  918  that engages with the carriage  820 , and a driving force from the driving motor  901  is controlled by a known transmitting unit such as a clutch switch or the like. 
     Also, a main body support plate  916  supports a moving member  915  and a cleaning blade  914 , and the moving member  915  causes the cleaning blade  914  to move, and performs a recovery process of the liquid discharging head  810  by wiping. Also, a control unit (not shown) is disposed on the liquid discharging apparatus  900 , and the control unit controls driving of each mechanism described above. 
       FIG. 1B  exemplifies an outer appearance of the liquid discharging head  810 . The liquid discharging head  810  may comprise a head unit  811  that has a plurality of nozzles  800  and a tank (liquid reservoir)  812  that holds liquid to be supplied to the head unit  811 . The tank  812  and the head unit  811  can be separated at the dashed line K, for example, and the tank  812  can be replaced. The liquid discharging head  810  comprises an electrical contact (not shown) for receiving an electrical signal from the carriage  820 , and discharges liquid in accordance with the electrical signal. The tank  812  has a liquid holding member (not shown) of a fibrous form or a porous form, for example, and liquid can be held by the liquid holding member. 
       FIG. 1C  exemplifies an internal configuration of the liquid discharging head  810 . The liquid discharging head  810  comprises a substrate  808 , channel wall members  801  provided on the substrate  808  that form channels  805 , and a top plate  802  which has a liquid supply channel  803 . Also, as a discharging element or a liquid discharging element, heaters  806  (electrothermal transducer element) are arranged to correspond to each of the nozzles  800  on the substrate (liquid discharging head substrate) that the liquid discharging head  810  comprises. Each of the heater  806  generates heat when driven by a driving element disposed to correspond with the heater  806  (a switching element such as a transistor) entering a conductive state. 
     The liquid from the liquid supply channel  803  is stored in a common liquid chamber  804 , and supplied to each of the nozzles  800  via the channels  805 . The liquid supplied to a respective nozzle  800  is discharged from the nozzle  800  in response to the heater  806  corresponding to the nozzle  800  being driven. 
       FIG. 1D  exemplifies a system configuration of the liquid discharging apparatus  900 . The liquid discharging apparatus  900  has an interface  1700 , an MPU  1701 , a ROM  1702 , a RAM  1703 , and a gate array  1704 . An external signal for executing a liquid discharge is inputted from outside to the interface  1700 . The ROM  1702  stores a control program that the MPU  1701  executes. The RAM  1703  saves various signals or data such as the previously described external signal for liquid discharge or data supplied to a liquid discharging head  1708 . The gate array  1704  performs data supply control corresponding to the liquid discharging head  1708 , and performs control of data transfer between the interface  1700 , the MPU  1701 , and the RAM  1703 . 
     The liquid discharging apparatus  900  also has a head driver  1705 , as well as motor drivers  1706  and  1707 , a conveying motor  1709 , and a carrier motor  1710 . The carrier motor  1710  conveys the liquid discharging head  1708 . The conveying motor  1709  conveys the medium P. The head driver  1705  drives the liquid discharging head  1708 . The motor drivers  1706  and  1707  drive the conveying motor  1709  and the carrier motor  1710  respectively. 
     When a driving signal is inputted into the interface  1700 , this driving signal can be converted into data for liquid discharge between the gate array  1704  and the MPU  1701 . In accordance with this data, each mechanism performs a desired operation, and in this way, the liquid discharging head  1708  is driven. 
     First Embodiment 
       FIG. 2A  illustrates a top surface layout of a liquid discharging head substrate  1  according to the first embodiment. The liquid discharging head substrate  1  comprises a semiconductor substrate SUB and a plurality of electrode pads T. The semiconductor substrate SUB, in a plan view corresponding to the top surface (an orthogonal projection in a direction orthogonal to the top surface or a surface parallel thereto may be represented; hereinafter, referred to simply as “plan view”), has edges E 1  and E 2  which oppose each other, and edges E 3  and E 4  which intersect these and oppose each other. 
     In the present embodiment, the semiconductor substrate SUB has a parallelogram shape in the plan view, but the outer shape of the semiconductor substrate SUB may be a quadrangle such as a rectangular shape or a polygon, and limitation is not made to this example. In the present embodiment, an acute angle is formed between the edge E 1  and the edge E 3 , an obtuse angle is formed between the edge E 1  and the edge E 4 , an obtuse angle is formed between the edge E 2  and the edge E 3 , and an acute angle is formed between the edge E 2  and the edge E 4 . 
     In the present embodiment, the plurality of electrode pads T are arranged along the edge E 1  at an end of the semiconductor substrate SUB. The plurality of electrode pads T include power-supply pads T PW1  for receiving a power-supply voltage (voltage V 1 ) from outside. In the present embodiment, two power-supply pads T PW1  are provided at positions closer to the edge E 3  than the edge E 4 . Note that though not illustrated here, the plurality of electrode pads T further include a power-supply pad (power-supply pad T PW2 ) for receiving another power-supply voltage (voltage V 2 ) from outside. 
       FIG. 2B  illustrates a magnification view for a region R illustrated in  FIG. 2A . On the semiconductor substrate SUB, heaters HT corresponding to discharging elements and driving elements DR for driving the heaters HT are respectively provided, and, on the semiconductor substrate SUB, one or more liquid supply ports (openings) OP EQ  for supplying liquid to the heaters HT are disposed. In the present embodiment, two heaters HT and two driving elements DR are provided for one supply port OP EQ , but there is no limitation to this 2:2:1 ratio example. 
     With reference to  FIG. 2A  once again, in the present embodiment, a plurality (16 rows×3 lines) of supply ports OP EQ  are disposed on the semiconductor substrate SUB, and on the substrate SUB, 32 rows×3 lines of heaters HT and driving elements DR are arranged. In the drawing, a line closest to the edge E 1  is referred to as a first line L 1 , the next closest line to the edge E 1  is referred to as a second line L 2 , and the line that is the most separated from the edge E 1  is referred to as a third line L 3 . 
     As illustrated in  FIG. 2C , each heater HT is connected in series to one corresponding driving element DR in the electrical path between the voltages V 1  and V 2 . In the present embodiment, the driving element DR is provided at the voltage V 1  side, and the heater HT is provided at the voltage V 2  side, but these positions may be inverted. Note that the voltage V 1  corresponds to a ground voltage (for example, 0[V]), and the voltage V 2  corresponds to a constant voltage of a positive value (for example, 24[V]). Typically, a high-voltage tolerant transistor such as a DMOS transistor is used for the driving element DR, and the heater HT is driven to cause it to generate heat in accordance with a control signal or a driving signal supplied to its gate. 
     With reference to  FIG. 2A  once again, the liquid discharging head substrate  1  comprises a conductive film M 21  and a conductive pattern M 11 . This is described below with reference to  FIG. 3 . 
       FIG. 3  illustrates a cross-sectional view for the line A-A and a cross-sectional view for the line B-B in relation to  FIG. 2A . The liquid discharging head substrate  1  further comprises a wiring structure ST on the semiconductor substrate SUB on which the driving elements DR are formed. The heater HT is provided on the wiring structure ST. The liquid discharging head substrate  1  comprises a channel wall WP that is provided on the wiring structure ST and forms liquid channels, and a nozzle plate PL provided on the channel wall WP. On the nozzle plate PL, the nozzles NZ are disposed immediately above the heaters HT. 
     In the present embodiment, the wiring structure ST is a multilayer wiring structure formed by alternatingly stacking an interlayer insulation film and a wiring layer. In the present embodiment, there are three wiring layers, and the wiring structure ST includes a wiring layer M 1  which is the closest layer to the semiconductor substrate SUB, a wiring layer M 2  which is the layer above the wiring layer M 1 , and a wiring layer M 3  which is the layer above the wiring layer M 2 . 
     The wiring layer M 3  includes a conductive film M 31  and a connecting portion M 32 . The wiring layer M 2  includes the conductive film M 21  and a connecting portion M 22 . The wiring layer M 1  includes the conductive pattern M 11 , a connecting portion M 12 , a line pattern M 13  for a control signal, and a connecting portion M 14 . 
     The conductive film M 31  is electrically connected to the previously described power-supply pad T PW2  and corresponds to a power-supply voltage node that transmits the voltage V 2 , and is electrically connected to a terminal of a heater HT. This connection between the conductive film M 31  and the heater HT is realized via a plug. The plug is a conductive member that extends vertically with respect to the top surface of the semiconductor substrate SUB, and may be referred to as a contact plug, a via, or the like (same below). Note that this is similar even in a case where this plug and the heater HT are formed to be integrated such as in a case where the plug is formed by a damascene method. 
     The conductive film M 21  corresponds to a power-supply voltage node that is electrically connected to the previously described power-supply pads T PW1  and transmits the voltage V 1 , and the conductive film M 21  is electrically connected to a source terminal of a driving element DR. This connection between the conductive film M 21  and the driving element DR is realized via the connecting portion M 14 , a plug connecting the connecting portion M 14  and the conductive film M 21 , and a plug connecting a source terminal of the driving element DR and the connecting portion M 14 . 
     The line pattern M 13  is electrically connected to the drain electrode G DR  of the driving element DR. This connection is realized via a plug. 
     The other terminal of the heater HT (the terminal on the side opposite to the side that the conductive film M 31  is connected to) and the source terminal of the driving element DR are electrically connected by the connecting portions M 12 , M 22 , and M 32 , and a plurality of plugs (these may be represented collectively as a connecting portion) that connect these. An opening OP 1  for realizing this connection (specifically for passing through the connecting portion M 22 ) is disposed in the conductive film M 21 . In other words, a plurality of openings OP 1  are disposed in the conductive film M 21  at the same pitch as the arrangement pitch of the driving elements DR and the heaters HT. 
     In the present embodiment, in addition to the opening OP 1 , an opening for forming a supply port OP EQ  described previously is also arranged in the conductive film M 21 . Note that, an opening for realizing another connection between the wiring layers M 1  to M 3  may be further arranged as necessary. 
     The previously described supply ports OP EQ , which are for supplying liquid to the heaters, are disposed between the driving elements DR. The supply ports OP EQ  are disposed so as to extend through the semiconductor substrate SUB from its bottom surface side to its top surface side, and communicate with the nozzles NZ disposed in the nozzle plate PL. In a case where the driving element DR enters a conductive state and the heater HT is driven, it causes the liquid above the heater HT to bubble, and the liquid is thereby discharged from the nozzle NZ. 
     Note that on the side surface of the supply port OP EQ , a protective film (not shown) is formed for protecting the wiring structure ST from the liquid. Also, on the top surface of the wiring structure ST and the heater HT, a protective film (not shown) is formed for protecting these from the liquid. 
     As illustrated in the cross-sectional structure for the line B-B, the driving element DR is not arranged in this region, and the connecting portions M 12  and M 14  and the line pattern M 13  for the control signal are not arranged in the wiring layer M 1 . Therefore, in this region, the conductive films M 21  and M 31  are respectively arranged in the wiring layer M 2  and the wiring layer M 3 , and the conductive pattern M 11  which is connected in parallel with the conductive film M 21  is arranged. Though details are described later, the conductive film M 21  includes a portion P 1  which is a part thereof and a portion P 2  which is another part thereof. Also, the conductive pattern M 11  is connected to the portion P 1  of the conductive film M 21  by a plug V 11  at one terminal, and is connected to the portion P 2  of the conductive film M 21  by a plug V 12  at the other terminal. 
     The conductive pattern M 11  has a function for assisting a supply of the voltage V 1  by the conductive film M 21 , and may be referred to as an assisting wiring pattern, an assisting line pattern, or the like. In the present specification, “assisting” indicates an action of ancillarily compensating a predetermined function. Accordingly, in this regard, even if the conductive pattern M 11  hypothetically is not arranged, a voltage supply function of the conductive film M 21  is not lost in the liquid discharging head substrate  1 . In the present embodiment, a connecting portion such as the plug for connecting to the semiconductor substrate SUB (or a circuit or element formed on the semiconductor substrate SUB) is not disposed immediately below the conductive pattern M 11 . In other words, the bottom surface of the conductive pattern M 11  is covered in an interlayer insulation film across the entire region. 
       FIG. 4A  is a simplified depiction of the top surface layout illustrated in  FIG. 2A . The conductive film M 21 , in the plan view, is connected to the two power-supply pads T PW1  provided in the vicinity of the edge E 1 , and extends so as to cover a region in which the plurality of driving elements DR of the lines L 1  to L 3  are provided (so as to cover the entire plurality of driving elements. In this regard, the conductive film M 21  only has the previously described opening OP 1 , and lacks a site of substantial branching (for example, a pattern in a line form or an oblong rectangle shape or a sub-channel). Also, the conductive film M 21  is of a shape in which it overlaps with some but not all of the heaters HT due to the opening OP 1 , and in which it overlaps a part of, but not all of, the driving elements DR. 
     Even with such a structure, a difference in the impedance component according to the distance from the power-supply pads T PW1  may arise between two different portions in the conductive film M 21 . In the present embodiment, since the two power-supply pads T PW1  are close to the edge E 3  side, there is the possibility that a difference in the impedance component will arise on the side of the edge E 4  with respect to a virtual line IL that passes between the two power-supply pads T PW1 and is orthogonal to the edge E 1 . Note that there is a possibility that in the line L 3 , the driving elements DR will all be positioned on the side of the edge E 4  with respect to the virtual line IL, and that the closer they are to the edge E 4  side, the smaller the supplied voltage will be. 
     In the present embodiment, in the conductive film M 21 , the portions in the vicinity of the end on the edge E 4  side of line L 1  and the portions in the vicinity of the end on the side of edge E 4  in the line L 3  are focused on, and these respectively correspond to previously described portions P 1  and P 2 . Here, Z 1  is the impedance from the power-supply pad T PW1  in the conductive film M 21  of the portion P 1 , and Z 2  is the impedance from the power-supply pad T PW1  in the conductive film M 21  of the portion P 2 . The above described impedances are combined impedances in a planar direction of the conductive film M 21 . Also, “in the conductive film M 21 ” means that the conductive pattern M 11  is not considered (in other words, it is assumed that the conductive pattern M 11  is not connected to the conductive film M 21 , or that the state is prior to the conductive pattern M 11  being added). Note that in the present embodiment, since the portion P 1  is further from power-supply pads T PW1  than the portion P 2 , Z 1 &gt;Z 2 . 
     As previously described, the portion P 1  and the portion P 2  are electrically connected by the conductive pattern M 11 . 
     Here, Z 3  is the impedance from one end to the other end of the conductive pattern M 11 . Since the conductive pattern M 11  does not have a width that is as a wide as the conductive film M 21 , typically, Z 3 &lt;Z 1  and Z 3 &lt;Z 2 . 
     In such a case, assuming Z 1 ′ is the actual impedance from the power-supply pads T PW1  of the portion P 1 , and Z 2 ′ is the actual impedance from the power-supply pads T PW1  of the portion P 2 , Z 1 ′ and Z 2 ′ can be expressed as follows. Z 1 ′=(Z 1 ×Z 2 +Z 1 ×Z 3 )/(Z 1 +Z 2 +Z 3 ) and Z 2 ′=(Z 2 ×Z 1 +Z 2 ×Z 3  )/(Z 1 +Z 2 +Z 3 ). Here, “actual” means that the conductive pattern M 11  is considered (in other words, it is the impedance in the structure in which the conductive film M 21  and the conductive pattern M 11  are connected in parallel). 
     Here, assuming ΔZ 1  is the difference in impedance of the portion P 1  before/after adding the conductive pattern M 11 , and ΔZ 2  is the difference in impedance of the portion P 2  before/after adding the conductive pattern M 11 , ΔZ 1  and ΔZ 2  are expressed as follows. 
     
       
         
           
             
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     Here, since Z 1  to Z 3 &gt;0, ΔZ 1 &gt;0, and ΔZ 2 &gt;0. This indicates that by addition of the conductive pattern M 11 , the impedance of both the portions P 1  and P 2  is reduced. 
     Also, because Z 1 &gt;Z 2 , ΔZ 1 &gt;ΔZ 2  holds. This indicates that the change (decrease value) of impedance in relation to the portion P 1  due to addition of the conductive pattern M 11  is larger than the change of impedance in relation to the portion P 2 . Alternatively, it can be said that the conductance applied with respect to the portion P 1  by the conductive pattern M 11  is larger than the conductance applied with respect to the portion P 2 . 
       FIG. 4B  is a plot indicating the influence of a voltage drop before/after adding the conductive pattern M 11 . The abscissa indicates the element number (numbers identifying the 32 individual heaters HT in each row), and these numbers range from 1 to 32 in order from the edge E 3  side to the edge E 4  side (from the right side to the left side in the drawing). The ordinate indicates an amount of voltage drop in the portions corresponding to each element number in the conductive film M 21  normalized by the amount of voltage drop of the number 32 of the line L 3  whose amount of voltage drop is the largest prior to adding the conductive pattern M 11 . In the drawing, plot values for the amount of voltage drop of the portions corresponding to the respective element numbers of the first line L 1  and the third line L 3  in the case where all heaters HT are driven are indicated (values for prior to adding the conductive pattern M 11  are shown graphically as a “×” symbol and values for after adding the conductive pattern M 11  are shown graphically as a “∘” symbol). 
     As can be seen in  FIG. 4B , in the line L 3 , a voltage drop after adding the conductive pattern M 11  is suppressed as compared to prior to adding the conductive pattern M 11 , and in the present embodiment, an effect of suppressing a voltage drop of about 10% for element number 32 occurs. Note that in the line L 1 , as described with reference to ΔZ 1  and ΔZ 2 , the effect on the voltage drop due to the addition of the conductive pattern M 11  is small, and it is particularly small in regions whose element number is particularly small (the regions element numbers 1 to 24). 
     By virtue of the present embodiment, it is possible to make the difference in impedance between two different portions of the conductive film M 21  smaller. Specifically, the conductive film M 21  for supplying the voltage V 1  to the plurality of driving elements DR extends so as to cover the region in which the plurality of driving elements DR is provided (so as to cover all of the plurality of driving elements DR). Furthermore, the conductive pattern M 11  is connected between the aforementioned two portions between which an impedance difference may arise in the conductive film M 21 . Thereby, the voltage drop in the conductive film M 21  is suppressed, and as a result, the difference in the values of supplied voltage (voltage actually supplied which may be smaller than the voltage V 1 ) that may arise between these two portions is reduced, and it is possible to uniformize the distribution of voltage. This is particularly advantageous in increasing the number of heaters HT (increasing the number of driving elements DR). The conductive pattern M 11  extends in a direction parallel to the edge E 1  so as to overlap with all of the driving elements DR of the lines L 1  to L 3 . 
     The conductive film M 21  and the conductive pattern M 11  are respectively provided for the wiring layers M 2  and M 1  of the wiring structure ST. As illustrated in the A-A cross-sectional structure of  FIG. 3 , in the region in which the driving element DR is arranged, the opening OP 1  for realizing a connection between the heater HT and the driving element DR is arranged in the conductive film M 21 . Meanwhile, as illustrated in the B-B cross-sectional structure of  FIG. 3 , in a region in which the driving element DR is not arranged, the opening OP 1  is not disposed in the conductive film M 21 , and accordingly, the rigidity of the substrate  1  is ensured. Also, in the conductive film M 21 , the conductive pattern M 11  is connected in parallel in the wiring layer M 1  of the lower layer, and thereby it is possible to reduce the aforementioned impedance difference and further improve the rigidity of the substrate  1 . 
     Also, with regards to suppressing the voltage drop due to the aforementioned impedance difference and reducing the difference in supplied voltage, the present embodiment is particularly advantageous in not only in a case of increasing the number of driving elements DR but also in a case of increasing the number of these that are simultaneously driven. Accordingly, in a case where the liquid discharging apparatus is a printing apparatus such as a printer (in a case where the liquid discharging head is a printhead), it becomes possible to increase the number of regions that can be printed simultaneously, and it is advantageous in increasing the number of dots formed per unit time (specifically, improve to printing speed). Furthermore, by virtue of the present embodiment, it becomes possible to reduce unnecessary power consumption in conjunction with reducing the impedance in a power-supply voltage node, and this is advantageous with regards to improving the product lifespan. 
     In the present embodiment, the conductive film M 21  through which the voltage V 1  is transmitted is focused on, but the content of the present embodiment can be applied to the conductive film M 31  through which the voltage V 2  is transmitted. That is, the conductive film M 21  and/or M 31  can extend so as to cover a region in which a plurality of driving elements DR are provided in the plan view. Also, in the conductive film M 21  and/or M 31 , an opening (OP 1 ) for realizing an electrical connection between the heater HT and the driving element DR and an opening corresponding to a supply port (OP EQ ) for supplying liquid to the heater HT are formed. In this regard, the conductive film M 21  and/or M 31  can be said to have a lattice shape in the plan view. Also, the outer shape of the conductive film M 21  in the plan view is a parallelogram in the present embodiment, but it may be a quadrangle or a polygonal shape (this is similar for the conductive film M 31 ). 
     Also, in the present embodiment, the conductive film M 31  transmits the voltage V 2 , and the conductive films M 21  and M 11  transmit the voltage V 1  (refer to  FIG. 3 ), but it is possible to make a change as appropriate to arrange these in any wiring layer. For example, configuration may be taken to arrange a conductive film that transmits the voltage V 1  in the wiring layer M 3 , and to arrange a conductive film that transmits the voltage V 2  in the wiring layers M 1  to M 2 . Also, for example, in a case where the wiring structure ST comprises another wiring layer (referred to as wiring layer M 4 ), configuration may be taken to arrange a conductive film that transmits the voltage V 1  (V 2 ) in the wiring layers M 1  to M 3 , and to arrange a conductive film that transmits the voltage V 2  (V 1 ) in the wiring layer M 4 . 
     Also, in the present embodiment, the conductive film M 21  has an outer shape that is not linearly symmetrical with respect to the line L 1  which is orthogonal to the edge E 1 . In the present embodiment, the outer shape of the conductive film M 21  is a parallelogram. For this reason, a difference in impedance between the two portions described above tends to appear. Also, since the outer shape of the conductive film M 21  is not linearly symmetrical, reducing the aforementioned impedance difference by changing the arrangement of the power-supply pads T PW1 , for example, is more difficult than in the case of a linearly symmetrical outer shape. In particular, if the outer shape of the conductive film M 21  is a parallelogram as in the present embodiment, the aforementioned impedance difference may become a significant problem at a corner that is relatively far from the power-supply pads T PW1 , namely the acute angle portion between the edge E 2  and the edge E 4  in the present embodiment. 
     In the present embodiment, two portions whose impedances from the power-supply pad T PW1  in the conductive film M 21  differ are connected by the conductive pattern M 11 . In the present embodiment, a portion P 1  having relatively high impedance (the acute angle portion between the edge E 2  and the edge E 4  in the present embodiment) and a portion P 2  with comparatively lower impedance are connected by the conductive pattern M 11 . Thus, it is possible to concentratedly suppress a reduction of the supplied voltage in the portion P 1  whose impedance is relatively higher. Thus, in the liquid discharging head substrate  1 , it is possible to reduce the difference in supplied voltage that can arise due to the difference in distance from the power-supply pads T PW1 . In the present embodiment, the conductive film M 21  has an outer shape that is not linearly symmetrical, and the aforementioned impedance difference and a difference in supplied voltage associated therewith tends to occur, and therefore it is possible to effectively reduce these differences by virtue of the present embodiment. 
     To summarize, in a case where the outer shape in the plan view of the conductive film M 21  is not linearly symmetrical with respect to the line L 1  which is orthogonal to the edge E 1  at which the power-supply pads T PW1  are provided, and in particular in the case of a parallelogram, a difference in impedance between two portions arises due to distances from the power-supply pads T PW1  differing. In a case in which the outer shape of the conductive film M 21  is a parallelogram, the impedance of the acute angle portion between the edge E 2  and the edge E 4  which is far from the power-supply pads T PW1  is higher than other portions, and this impedance difference becomes more significant than in the case where the shape of the conductive film M 21  is a rectangular shape. Accordingly, by adding the conductive pattern M 11  as an assisting wiring line, the aforementioned impedance difference and the difference in supplied voltage associated therewith are effectively reduced. 
     Note that the conductive pattern M 11  is not in surface contact over the entirety of its top surface with the bottom surface of the conductive film M 21 ; rather, it is connected via the plug V 11  to the portion P 1  of the conductive film M 21  at one end and it is connected via the plug V 12  to the portion P 2  of the conductive film M 21  at the other end. Thereby, it becomes possible to concentratedly impart the effect of lowering the impedance in relation to the portion P 1  whose impedance from the power-supply pad T PW1  is relatively high. 
     In the present embodiment, the above-mentioned conductive pattern M 11 , for assisting the supply of the voltage V 1 , is provided in the wiring layer M 1 . However, as another embodiment, the conductive pattern M 11  may be provided in the wiring layer M 3  which includes the conductive pattern M 31  for supplying the voltage V 2 . That is, by providing the conductive pattern M 11  in a layer (M 1  or M 3 ) different from the layer (M 2 ) which mainly functions to supply the voltage V 1 , the above-mentioned assisting of the supply of the voltage V 1  may be realized correctly, and thereby, it may become possible to avoid or suppress the lowering of the drivability of the driving elements DR. 
     Second Embodiment 
       FIG. 5A  illustrates a top surface layout of a liquid discharging head substrate  2  according to a second embodiment. The present embodiment mainly differs from the previously described first embodiment in that a conductive pattern M 11 ′ which is provided along the edge E 2  is arranged in place of the conductive pattern M 11  provided along the edge E 4 . 
     The conductive pattern M 11 ′ extends from one end of the line L 3  to the other end on the side of the edge E 2  with respect the line L 3  in the conductive film M 21 . The conductive pattern M 11 ′ extends in a direction orthogonal to the edge E 1  so as to overlap with all of the driving elements DR of at least the line L 3 . The conductive pattern M 11 ′, at one end, is connected by the plug V 13  to a portion corresponding to the conductive film M 21 , and, at the other end, is connected by the plug V 14  with a portion corresponding to the conductive film M 21 . 
     As described previously, there will be different portions between which there is a difference in the impedance component in the region on the side of the edge E 4  in relation to the virtual line IL of the conductive film M 21 . For that reason, in the vicinity of the edge E 2  (in particular, in the line L 3 ), a difference in the impedance component may arise depending on which of the edge E 3  and the edge E 4  is closer, and in the present embodiment, the conductive pattern M 11 ′ will be used to make this difference smaller. 
       FIG. 5B  is a plot indicating the influence of a voltage drop before/after adding the conductive pattern M 11 ′, and is similar to  FIG. 4B . As can be seen in  FIG. 5B , in the line L 3 , a voltage drop after adding the conductive pattern M 11 ′ is suppressed as compared to prior to adding the conductive pattern M 11 ′, and in the present embodiment, an effect of suppressing a voltage drop of about 4% for element number  32  occurs. Note that in the present embodiment, the conductive pattern M 11 ′ is not of a shape that reduces the difference in impedance between the lines L 1  to L 3  substantially. For that reason, in the line L 1 , there is substantially no effect on the voltage drop due to addition of the conductive pattern M 11 ′. 
     By the present embodiment, a similar effect to that of the first embodiment can be achieved. That is, the conductive pattern M 11  and/or M 11 ′ may be provided in at least a part of the outer frame portion of the conductive film M 21 . Thereby, it is possible to realize an improvement in the rigidity of the substrate  1  along with a suppression of a voltage drop due to the previously described impedance difference and a reduction in a difference in supplied voltages. 
       FIG. 6  illustrates a top surface layout of the liquid discharging head substrate  2  according to a variation of the embodiment. In the present variation, a pair of elements, where one element is a structure in which groups of the supply port OP EQ , the heater HT, and the driving element DR are arranged, and a plurality of electrode pads T including the power-supply pads T PW1 , as well as a conductive film M 21 , are provided point-symmetrically about the center of the semiconductor substrate SUB. The electrode pad T, the power-supply pad T PW1 , and the conductive film M 21  on the edge E 2  side are respectively distinguished as “the electrode pad T′”, “the power-supply pad T PW1 ′” and “the conductive film M 21 ′”. 
     Also, in the present variation, conductive patterns M 11 A′ and M 11 B′ are arranged in place of the conductive pattern M 11 ′. The conductive pattern M 11 A′ connects a portion on the side of the edge E 4  of the conductive film M 21  (a portion whose impedance is relatively large) and a portion on the side of the edge E 4  of the conductive film M 21 ′ (a portion whose impedance is relatively small). The conductive pattern M 11 B′ connects a portion on the side of the edge E 3  of the conductive film M 21  (a portion whose impedance is relatively large) and a portion on the side of the edge E 3  of the conductive film M 21 ′ (a portion whose impedance is relatively small). In this way, in the configuration in which two or more conductive films M 21  are arranged, the difference in impedance between different portions that may occur between the differing conductive films M 21  and M 21 ′ is reduced by the conductive patterns M 11 A′ and M 11 B′. Note that in the present variation, the conductive patterns M 11 A′ and M 11 B′ may be provided in both the wiring layers M 1  and M 2 . 
     Third Embodiment 
       FIG. 7A  illustrates a top surface layout of a liquid discharging head substrate  3  according to a third embodiment. The present embodiment mainly differs from the previously described first embodiment in that a conductive pattern M 15  is further arranged from the power-supply pads T PW1  to the vicinity of the driving elements DR of the line L 1 . 
     The conductive pattern M 15  is electrically connected to the power-supply pads T PW1  via a connecting portion of another wiring layer and a plug, and extends to the vicinity of the driving element DR on the side of the edge E 3  of the line L 1  in a direction orthogonal to the edge E 1 . Also, the conductive pattern M 15  is connected at that end by a plug with a portion (referred to as portion P 4 ) in the vicinity of the driving element DR on the side of the edge E 3  of the line L 1  in the conductive film M 21 . 
     In  FIG. 7B , the impedance of the conductive film M 21  and the conductive pattern M 15  is illustrated similarly to in  FIG. 4A  in accordance with the top surface layout of the liquid discharging head substrate  3 . Here, similar to Z 1  and Z 2  (refer to the first embodiment), Z 4  is the impedance from the power-supply pad T PW1  in the conductive film M 21  of the portion P 4 . Also, 
     Z 5  is the impedance from one end (the side of the power-supply pads T PW1 ) to the other end (the side of the portion P 4 ) of the conductive pattern M 15 . Here, assuming that Z 4 ′ is the actual impedance of the portion P 4  from power-supply pad T PW1 , Z 4 ′ can be expressed as follows. 
     Specifically, Z 4 ′=Z 4 ×Z 5 /(Z 4 +Z 5 ). Accordingly, 
     assuming that ΔZ 4  is the difference in impedance of the portion P 4  before/after adding the conductive pattern M 15 , 
     ΔZ 4  can be expressed as follows. Specifically, 
     
       
         
           
             
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             = 
             
               
                 
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                   4 
                 
                 - 
                 
                   Z 
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                 Z 
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                           Z 
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                           4 
                         
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                           Z 
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                           5 
                         
                       
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     Here, in order to reduce the impedance effectively in relation to the portion P 1  whose impedance is highest (refer to the first embodiment ( FIG. 2A  to  FIG. 4B )), it is sufficient that ΔZ 1 &gt;ΔZ 4  holds. Accordingly, it can be said that it is sufficient that the following equation, which is based on the equation of ΔZ 4  above and the equation of ΔZ 1  described in the first embodiment, holds. Specifically, it is sufficient that Z 3 &lt;(Z 1 /Z 4 ) 2 ×Z 5 +{(Z 1 /Z 4 )−1}×Z 1 −Z 2  holds. 
     By virtue of the present embodiment, in addition to achieving a similar effect to the first embodiment, it is possible to reduce impedance from the power-supply pads T PW1  to the line L 1  on the edge E 1  side, and there is the additional advantage of suppressing the voltage drop due to the previously described impedance difference and reducing the difference in supplied voltage. 
     (Other) 
     While several preferred embodiments have been exemplified above, the present invention is not limited to these examples, and these may be partially changed without deviating from the gist of the present invention, such as by applying the contents of a portion of one embodiment to another embodiment. Also, the individual terms recited in the present specification are merely used with the objective of describing the present invention, and it goes without saying that the present invention is not limited to the strict meaning of these terms, but includes equivalents thereof. 
     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 such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2017-016975, filed on Feb. 1, 2017, which is hereby incorporated by reference herein in its entirety.