Patent Publication Number: US-10322581-B2

Title: Element substrate and printhead

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an element substrate and a printhead, and particularly to, for example, a printhead that incorporates an element substrate with a temperature detection element which detects an ink discharge status. 
     Description of the Related Art 
     In a printing apparatus using an inkjet printhead (to be referred to as a printhead hereinafter), a foreign substance may clog an ink orifice (to be referred to as an orifice hereinafter), or a bubble entering into an ink supply channel may clog the supply channel. If this occurs, an ink discharge failure (to be referred to as a discharge failure) from the printhead is caused. In particular, a printing apparatus that prints by using a full-line printhead which supports the full width of a print medium and includes a number of orifices arranged in a line can print at high speed, and thus a process for the discharge failure also needs to be performed at high speed. More specifically, in the printing apparatus that uses the full-line printhead, it is very important that an orifice (discharge nozzle) which causes the discharge failure is specified at high speed, and complimentary printing and an ink discharge recovery operation are performed. 
     Conventionally, various techniques to solve such a discharge failure have been proposed. 
     Japanese Patent Laid-Open No. 2007-290361 discloses an element substrate on which a plurality of heaters which generate heat energy for discharging ink from orifices are formed on a silicon (Si) base, and a temperature detection element of a thin film is formed via an interlayer insulation film immediately below each heater. According to Japanese Patent Laid-Open No. 2007-290361, a temperature detection circuit detects temperature information from the respective temperature detection elements and determines, by a difference between a temperature change by a discharge failure and a temperature change when ink is discharged normally, whether ink discharge is normal or suffers from the discharge failure. 
     The temperature detection elements described in Japanese Patent Laid-Open No. 2007-290361 adopt an arrangement for detecting a small temperature change precisely.  FIG. 12  is a layout diagram showing the positional relationship between conventional heaters and temperature detection elements. As shown in  FIG. 12 , each temperature detection element  3  is folded a plurality of times and arranged immediately below a corresponding one of heaters  5 , setting a resistance value high. In this arrangement, in order to increase the resistance value of each temperature detection element  3 , it is effective to make, thin and long, the line width of the temperature detection element arranged immediately below the corresponding one of the heaters  5 . 
     However, an area occupied by each heater is restricted, and the size of a corresponding one of the temperature detection elements that can be arranged under that restriction is restricted, as a matter of course. It is therefore difficult to further increase the resistance value of each temperature detection element  3  in order to improve the sensitivity of the temperature detection element  3 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is conceived as a response to the above-described disadvantages of the conventional art. 
     For example, an element substrate according to this invention provides a temperature detection element capable of detecting a heater temperature at higher accuracy, and detecting a nozzle that causes a discharge failure at high speed and high accuracy. 
     According to one aspect of the present invention, there is provided a multilayer structured element substrate comprising: a heater; and a temperature detection element formed by series-connecting a first wiring below a position where the heater is provided, a second wiring below the first wiring, and a first conductive via configured to connect the first wiring and the second wiring. 
     According to another aspect of the present invention, there is provided a multilayer structured element substrate comprising: a heater; and a temperature detection element formed by series-connecting a wiring below a position where the heater is provided, and a conductive via configured to connect the heater and the wiring. 
     According to still another aspect of the present invention, there is provided a printhead which uses the element substrate of the above-described arrangement to discharge ink by giving heat energy to ink by the heater. 
     The invention is particularly advantageous since a temperature detection element having high sensitivity to a temperature change can be included, making it possible to detect a heater temperature at high speed and high accuracy. 
     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. 1  is a perspective view for explaining the structure of a printing apparatus which includes a full-line printhead according to an exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram showing the control arrangement of the printing apparatus shown in  FIG. 1 . 
         FIGS. 3A and 3B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the first embodiment of the present invention. 
         FIG. 4  is a diagram showing equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 3A and 3B . 
         FIGS. 5A and 5B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the second embodiment of the present invention. 
         FIGS. 6A and 6B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the third embodiment of the present invention. 
         FIGS. 7A and 7B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the fourth embodiment of the present invention. 
         FIGS. 8A and 8B  are diagrams each showing equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 7A and 7B . 
         FIGS. 9A and 9B  are diagrams each showing another arrangement of equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 7A and 7B . 
         FIGS. 10A and 10B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the fifth embodiment of the present invention. 
         FIGS. 11A and 11B  are diagrams each showing equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 10A and 10B . 
         FIG. 12  is a layout diagram showing a conventional element substrate. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     In this specification, the terms “print” and “printing” not only include the formation of significant information such as characters and graphics, but also broadly includes the formation of images, figures, patterns, and the like on a print medium, or the processing of the medium, regardless of whether they are significant or insignificant and whether they are so visualized as to be visually perceivable by humans. 
     Also, the term “print medium (or sheet)” not only includes a paper sheet used in common printing apparatuses, but also broadly includes materials, such as cloth, a plastic film, a metal plate, glass, ceramics, wood, and leather, capable of accepting ink. 
     Furthermore, the term “ink” (to be also referred to as a “liquid” hereinafter) should be extensively interpreted similarly to the definition of “print” described above. That is, “ink” includes a liquid which, when applied onto a print medium, can form images, figures, patterns, and the like, can process the print medium, and can process ink. The process of ink includes, for example, solidifying or insolubilizing a coloring agent contained in ink applied to the print medium. 
     Further, a “nozzle” generically means an ink orifice or a liquid channel communicating with it, and an element for generating energy used to discharge ink, unless otherwise specified. 
     A printhead substrate (head substrate) used below means not merely a base made of a silicon semiconductor, but an arrangement in which elements, wirings, and the like are arranged. 
     Further, “on the substrate” means not merely “on an element substrate”, but even “the surface of the element substrate” and “inside the element substrate near the surface”. In the present invention, “built-in” means not merely arranging respective elements as separate members on the base surface, but integrally forming and manufacturing respective elements on an element substrate by a semiconductor circuit manufacturing process or the like. 
     &lt;Printing Apparatus Integrating Full-Line Printhead ( FIG. 1 )&gt; 
       FIG. 1  is a perspective view for explaining the structure of a printing apparatus  1  which includes full-line inkjet printheads (to be referred to as printheads hereinafter)  11 K,  11 C,  11 M, and  11 Y and a recovery unit configured to guarantee ink discharge that is always stable. 
     In the printing apparatus  1 , a printing paper sheet  15  is supplied from a feeder unit  17  to a print position by these printheads and conveyed by a conveyance unit  16  included in a housing  18  of the printing apparatus. 
     In printing an image on the printing paper sheet  15 , black (K) ink is discharged from the printhead  11 K when the reference position of the printing paper sheet  15  reaches under the printhead  11 K which discharges the black ink while conveying the printing paper sheet  15 . Similarly, when the printing paper sheet  15  reaches respective reference positions in the order of the printhead  11 C which discharges cyan (C) ink, the printhead  11 M which discharges magenta (M) ink, and the printhead  11 Y which discharges yellow (Y) ink, a color image is formed by discharging the inks of the respective colors. The printing paper sheet  15  on which the image is thus printed is discharged to and stacked on a stacker tray  20 . 
     The printing apparatus  1  further includes the conveyance unit  16 , and ink cartridges (not shown) configured to supply the inks to the printheads  11 K,  11 C,  11 M, and  11 Y and replaceable for each ink. The printing apparatus  1  still further includes, for example, a pump unit (not shown) for a recovery operation and ink supply to the printheads  11 K,  11 C,  11 M, and  11 Y, and a control board (not shown) which controls the entire printing apparatus  1 . A front door  19  is an opening/closing door for replacing the ink cartridge. 
     Printheads  11  of this embodiment adopt an inkjet method of discharging the ink by utilizing heat energy. Therefore, the printheads  11  include electrothermal transducers (heaters). Each of these electrothermal transducers is provided in correspondence with a corresponding one of orifices. A pulse voltage is applied to each of the corresponding electrothermal transducers in accordance with a print signal, discharging ink from the corresponding one of the orifices. Note that the printing apparatus is not limited to a printing apparatus which uses a full-line printhead having a printing width corresponding to the width of the print medium described above. The present invention is also applicable to, for example, a so-called serial type printing apparatus which integrates, in a carriage, a printhead with orifices arrayed in the conveyance direction of a print medium and prints by discharging ink to the print medium while reciprocally scanning the carriage. 
     &lt;Description of Control Arrangement ( FIG. 2 )&gt; 
     A control arrangement for performing the print control of the printing apparatus described with reference to  FIG. 1  will now be described. 
       FIG. 2  is a block diagram showing the arrangement of a control circuit of the printing apparatus. In  FIG. 2 , an interface  1700  inputs print data, reference numeral  1701  denotes an MPU, a ROM  1702  stores control programs executed by the MPU  1701 , and a DRAM  1703  saves print data and data such as a print signal supplied to each printhead. A gate array (G.A.)  1704  performs the supply control of the print signal to each printhead, and also performs data transfer control among the interface  1700 , the MPU  1701 , and the DRAM  1703 . A controller  600  includes the MPU  1701 , the ROM  1702 , the DRAM  1703 , and the gate array  1704 . A carriage motor  1710  is configured to convey the printheads  11  ( 11 K,  11 C,  11 M, and  11 Y). A conveyance motor  1709  is configured to convey printing paper. A head driver  1705  drives the printheads. Motor drivers  1706  and  1707  are motor drivers configured to drive the conveyance motor  1709  and the carriage motor  1710 , respectively. 
     In the operation of the above-described control arrangement, when print data enters the interface  1700 , the print data is converted into a print signal between the gate array  1704  and the MPU  1701 . Then, the motor drivers  1706  and  1707  are driven, and the printheads are driven in accordance with the print data transmitted to the head driver  1705  to print. Information on a transfer error (to be described later) obtained in the printheads is fed back to the MPU  1701  via the head driver  1705  and reflected on the print control. 
     Some embodiments will now be described regarding an element substrate which is integrated in the printheads mounted on the printing apparatus of the above-described arrangement. 
     [First Embodiment] 
       FIGS. 3A and 3B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the first embodiment of the present invention.  FIGS. 3A and 3B  show some of a plurality of heaters formed on the element substrate (head substrate). A semiconductor substrate of silicon (Si) or the like is used for an element substrate  101 .  FIG. 3A  is a plan view showing the heater and the temperature detection element arranged immediately below the heater.  FIG. 3B  is a sectional view taken along a chain line A-A′ in  FIG. 3A . Note that only one heater is illustrated here. On the element substrate  101 , however, the plurality of heaters are integrated in correspondence with a plurality of nozzles which are provided in a printhead and discharge ink. 
     As shown in  FIG. 3A , wirings  108  are connected to the two ends of a heater  102 . As shown in  FIG. 3B , a protection film  104  is formed on the heater  102 . A wiring  105  and wirings  106  are further arranged on an interlayer insulation film  103  below the heater  102 . The wiring  105  and the wirings  106  are connected via conductive via  107 . As described above, the element substrate  101  has a multilayer structure in which various constituent elements are formed in the different layers, and conductive via which connects the constituent elements formed in the different layers are formed among the layers, as needed. 
     The temperature detection element is made of these three constituent elements of the wiring  105 , the wirings  106 , and conductive via  107  that are series-connected. For example, a low-resistance wiring material such as aluminium (Al), AlCu, AlSi, Cu, or the like is used for the wirings  105  and  106 . For example, tungsten (W) is used as the conductive via  107 . 
     The wiring  105  and the wirings  106  are connected via a plurality of conductive via  107 . 
     A temperature immediately below the heater is detected as follows. 
     As shown in  FIG. 3A , a voltage is applied to the two ends of the heater  102  from the wirings  108  connected to the heater  102 . The heater  102  generates heat upon electric current supply when the voltage is applied. The heat is transferred to ink on the protection film  104  on the heater  102  or ink on a metal film (not shown) in a case where the metal film is formed on the protection film  104 , and the ink is discharged by foaming the ink. A change in temperature at this time is detected by monitoring a change in value of a resistance formed by series-connecting the conductive via  107 , wirings  106 , and wiring  105  provided immediately below the heater  102 . 
       FIG. 4  is a diagram showing equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 3A and 3B . 
     A power supply  203  and a transistor  202  are connected to the two ends of a heater  201  shown in  FIG. 4 . The transistor  202  is turned on/off in accordance with a control signal applied to its gate, and electric current supply to the heater  201  is controlled. The heater  201  generates heat when a voltage is applied to the heater  201 . The heat of the heater  201  is transferred to ink, and a temperature change at this time is detected by a temperature detection element (resistance)  204 . Note that the resistance  204  indicates the series resistance of the temperature detection element made of the conductive via  107 , and the wirings  105  and  106  shown in  FIGS. 3A and 3B . 
     The heater  201  is heated upon electric current supply when the voltage is applied to the heater  201 . A constant electric current source  205  through which a constant electric current flows is connected to one end of the resistance  204  shown in  FIG. 4 , and the other end of the resistance  204  is connected to ground. Then, a voltage detection circuit  206  which detects a voltage at the two ends of the resistance  204  is connected. In this arrangement, the constant electric current is supplied to the resistance  204  from the constant electric current source  205 . Accordingly, the voltage detection circuit  206  connected to the two ends of the resistance  204  measures a voltage generated at the two ends of the resistance  204 , reading the resistance value of the resistance  204 . This measured voltage value is output outside the element substrate (printhead), allowing, for example, an MPU  1701  of a controller  600  shown in  FIG. 2  to calculate the resistance value of the resistance  204 . 
     For example, if tungsten is used as the conductive via, and aluminium is used as the wirings, the respective resistivities of the resistance  204  are about 5.5×10 −10  Ω·m and about 2.7×10 −10  Ω·m. The respective temperature coefficients are about 3,800 ppm and about 4,400 ppm. For example, as compared with a case in which a temperature detection element is formed by an aluminium wiring alone in the same area, an electric current can flow in a wiring interlayer direction, making it possible to increase the resistance value by the resistivity of each conductive via. The resistivity and temperature coefficient of tungsten are higher than those of aluminium, making it possible to increase the absolute value and temperature change rate of the resistance value. 
     Therefore, according to the above-described embodiment, it becomes possible, by forming the temperature detection element across a plurality of layers in the element substrate, to detect the temperature at high accuracy while suppressing an increase in size of the temperature detection element. Furthermore, the conductive via among the layers are desirably formed by a substance such as tungsten or the like having higher resistivity and temperature coefficient than the wiring formed in each layer. This is because it becomes possible to increase detection sensitivity to the temperature change and to detect a heater temperature at higher accuracy. 
     [Second Embodiment] 
       FIGS. 5A and 5B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the second embodiment of the present invention. Note that as in  FIGS. 3A and 3B ,  FIG. 5A  is also a plan view showing the heater and the temperature detection element arranged immediately below the heater, and  FIG. 5B  is also a sectional view taken along a chain line A-A′ in  FIG. 5A . In  FIGS. 5A and 5B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIGS. 3A and 3B , and a description thereof will be omitted. 
     Only the characteristic arrangement of the second embodiment will be described below. 
     As seen by comparing  FIGS. 5A and 5B  with  FIGS. 3A and 3B , in this embodiment, the number of conductive via  107  immediately below a heater  102  is increased as compared with the first embodiment. This increase is implemented by forming a series resistance formed by the conductive via  107 , wiring  105 , and wirings  106  so as to meander under the heater  102  in an area occupied by the heater  102 . 
     Therefore, according to the above-described embodiment, it becomes possible to increase the resistance value of the temperature detection element as compared with the first embodiment and with that increase, it becomes possible to further increase detection sensitivity to a temperature change. 
     Note that temperature detection according to this embodiment can be performed in the same manner by the same method as that described with reference to  FIG. 4  in the first embodiment. 
     [Third Embodiment] 
       FIGS. 6A and 6B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the third embodiment of the present invention. Note that as in  FIGS. 3A and 3B ,  FIG. 6A  is also a plan view showing the heater and the temperature detection element arranged immediately below the heater, and  FIG. 6B  is also a sectional view taken along a chain line A-A′ in  FIG. 6A . In  FIGS. 6A and 6B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIGS. 3A and 3B , and a description thereof will be omitted. 
     Only the characteristic arrangement of the third embodiment will be described below. 
     As seen by comparing  FIGS. 6A and 6B  with  FIGS. 3A and 3B , in this embodiment, one wiring layer is added as compared with the first embodiment. As shown in  FIG. 6B , in addition to connecting wiring  105  and wirings  106  by conductive via  107  as in the first embodiment, the wirings  106  and wirings  109  are connected by conductive via  107 ′. As described above, the wirings  109  and the conductive via  107 ′ are added to the first embodiment. 
     Therefore, according to the above-described embodiment, it becomes possible, by adding the wirings and conductive via that form the temperature detection element, to increase a series-connected resistance as compared with the first embodiment even though an area occupied in a plane is the same. This makes it possible, by increasing the resistance value of the temperature detection element, to increase detection sensitivity to a temperature change. 
     Note that temperature detection according to this embodiment can be performed in the same manner by the same method as that described with reference to  FIG. 4  in the first embodiment. 
     [Fourth Embodiment] 
       FIGS. 7A and 7B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the fourth embodiment of the present invention. Note that as in  FIGS. 3A and 3B ,  FIG. 7A  is also a plan view showing the heater and the temperature detection element arranged immediately below the heater, and  FIG. 7B  is also a sectional view taken along a chain line A-A′ in  FIG. 7A . In  FIGS. 7A and 7B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIGS. 3A and 3B , and a description thereof will be omitted. 
     Only the characteristic arrangement of the fourth embodiment will be described below. 
     As seen by comparing  FIG. 7B  with  FIG. 3B , in particular, a conductive via  110  connects a heater  102  and a wiring  105  in this embodiment. 
     In this embodiment, the conductive via  110  is used as the temperature detection element, and the heater  102  is used for electric current supply to the temperature detection element and wiring to detect a voltage. 
       FIGS. 8A and 8B  are diagrams each showing equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 7A and 7B . In this embodiment, the heater  102  is used as a part of the temperature detection element, making it impossible to perform heater driving and temperature detection simultaneously. As shown by these equivalent circuits, heater driving and temperature detection are performed by switching between them with switches. 
       FIG. 8A  shows a circuit arrangement in an operation mode in which heater driving is performed.  FIG. 8B  shows a circuit arrangement in an operation mode in which temperature detection is performed. Note that in  FIGS. 8A and 8B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIG. 4 , and a description thereof will be omitted. 
     As shown in  FIGS. 8A and 8B , heaters  201   a  and  201   b  form one heater, and the node of the conductive via  110  in  FIGS. 7A and 7B  indicates the node between the heater  201   a  and the heater  201   b . A power supply  203  is connected to one end of the heater  201   a  via a switch  601 . One end of the heater  201   b  is connected to ground via a transistor  202  which controls driving of the heater. One end of the conductive via  110  is connected to the node between the heaters  201   a  and  201   b  (as for the entire heater, a midpoint thereof). The other end of the conductive via  110  is connected to ground via one end of a voltage detection circuit  206  and a switch  604 . The other end of the voltage detection circuit  206  is connected to the node between the heater  201   b  and the transistor  202  via a switch  603 . A constant electric current source  205  is connected to the node between the heater  201   a  and the switch  601  via a switch  602 . 
     An operation at the time of heater driving will be described here with reference to  FIG. 8A . 
     At the time of the operation mode in which heater driving is performed, the switch  601  is closed, and the switches  602 ,  603 , and  604  are opened. On the other hand, the transistor  202  is ON/OFF-controlled, by a control signal, to supply an electric current to the heaters  201   a  and  201   b . Since the switches  602 ,  603 , and  604  are opened, the voltage detection circuit  206  and the constant electric current source  205  for temperature detection are not connected to the temperature detection element (heaters  201   a  and  201   b ). 
     A temperature detection operation will now be described with reference to  FIG. 8B . 
     At the time of the operation mode in which temperature detection is performed, the switch  601  is opened, and the switches  602 ,  603 , and  604  are closed. On the other hand, the transistor  202  is turned off by a control signal. At this time, an electric current flows from the constant electric current source  205  to ground via the heater  201 , the conductive via  110 , and the switch  604  as indicated by a solid arrow. The voltage detection circuit  206  is connected to the heater  201   b  via the conductive via  110  and the switch  603  to measure a potential difference between the two ends of the voltage detection circuit  206 . Since the electric current flows as indicated by the solid arrow, the electric current from the constant electric current source  205  does not flow through the switch  603  and the heater  201   b  connected to the voltage detection circuit  206 . Since no potential difference occurs between the two ends of the heater  201   b  and switch  603  that are series-connected, only the potential difference of the conductive via  110  is measured at the two ends of the voltage detection circuit  206 . 
     As compared with the first to third embodiments, for this embodiment, the conductive via  110  of the temperature detection element is connected to the heater, making it possible to detect a temperature change immediately above the heater with high sensitivity. 
     Only the resistance value of the conductive via  110  is detected, making it possible to detect a temperature change in a planar small region for one conductive via indicated in the conductive via  110  of  FIG. 7A  and to increase detection sensitivity to a temperature change in central portion of the heater. 
       FIGS. 9A and 9B  are diagrams each showing equivalent circuits with another arrangement of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 7A and 7B . Note that in  FIGS. 9A and 9B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIG. 4 , and  FIGS. 8A and 8B , and a description thereof will be omitted. 
     As compared with the arrangement of the equivalent circuits shown in each of  FIGS. 8A and 8B , in the circuit arrangement shown in each of  FIGS. 9A and 9B , the transistor  202  which supplies an electric current to the heater is connected to a high voltage side. As in  FIGS. 8A and 8B ,  FIG. 9A  shows the circuit arrangement in an operation mode in which heater driving is performed, and  FIG. 9B  shows the circuit arrangement in an operation mode in which temperature detection is performed. In each of these arrangements, one end of a conductive via  110  is connected to the midpoint of the heater  102 , as also indicated from  FIGS. 7A and 7B . 
     In each of these arrangements, the switch  601  for shutting down power from the power supply  203  to the heater needed in the circuit arrangement shown in each of  FIGS. 8A and 8B  becomes unnecessary when temperature detection is performed. However, the operation is performed in the same manner as in  FIGS. 8A and 8B . 
     When heater driving is performed, a voltage drop by the resistance of the switch  601  series-connected to the heater occurs in  FIGS. 8A and 8B . However, a voltage drop by the resistance of the switch  601  does not occur in the circuit arrangement shown in each of  FIGS. 9A and 9B , making it possible to supply energy to the heater efficiently. In addition, as the switch  601  can be omitted, a layout area can be reduced accordingly. As a result, it is possible to lower the cost of the element substrate. 
     Note that it is possible to control ON/OFF of the switches shown in  FIGS. 8A to 9B  by, for example, switching signals (not shown) from an MPU  1701  of a controller  600  shown in  FIG. 2 . In order to reduce the number of switching signals, it is also possible to adopt a circuit arrangement in which switching is performed in synchronization with ON/OFF of a control signal applied to the gate of the transistor  202 . In either case, an arrangement suffices in which the electric current from the constant electric current source  205  flows through the conductive via  110  and the heater in a mode in which temperature detection is performed, and the electric current from the power supply  203  flows through the heater in a mode in which heater driving is performed. 
     [Fifth Embodiment] 
       FIGS. 10A and 10B  are views showing the positional relationship between a heater and a temperature detection element formed on an element substrate (head substrate) according to the fifth embodiment of the present invention. Note that as in  FIGS. 3A and 3B ,  FIG. 10A  is also a plan view showing the heater and the temperature detection element arranged immediately below the heater, and  FIG. 10B  is also a sectional view taken along a chain line A-A′ in  FIG. 10A . In  FIGS. 10A and 10B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIGS. 3A and 3B , and a description thereof will be omitted. 
     Only the characteristic arrangement of the fifth embodiment will be described below. 
     In this embodiment, the heater is used as a part of the temperature detection element, as in the fourth embodiment. As shown in  FIG. 10B , conductive via  111  and  112  are connected between a heater  102  and wirings  105 . In this embodiment, as compared with the first embodiment, the heater is used as a part of a wiring layer used for the temperature detection element, as in the fourth embodiment. 
     Therefore, the temperature detection element according to this embodiment is made of, for example, a resistance formed by the wirings  105 , conductive via  111 , the heater  102 , and conductive via  112  that are series-connected. Then, also in this embodiment, temperature detection is performed by a temperature change in resistance value of a series-connected combined resistance, as in the first embodiment. 
       FIGS. 11A and 11B  are diagrams each showing equivalent circuits of a temperature detection circuit using the temperature detection element and a driving circuit of the heater described with reference to  FIGS. 10A and 10B . In this embodiment, the heater  102  is used as the part of the temperature detection element, making it impossible to perform heater driving and temperature detection simultaneously. As shown by these equivalent circuits, heater driving and temperature detection are performed by switching between them with switches. 
       FIG. 11A  shows a circuit arrangement in an operation mode in which heater driving is performed.  FIG. 11B  shows a circuit arrangement in an operation mode in which temperature detection is performed. Note that in  FIGS. 11A and 11B , the same reference numerals denote the same constituent elements that have already been described with reference to  FIG. 4 , and  FIGS. 8A and 8B , and a description thereof will be omitted. 
     An operation at the time of heater driving will be described here with reference to  FIG. 11A . 
     At the time of heater driving, switches  604  and  605  are opened. The transistor  202  is ON/OFF-controlled, by a control signal, to supply an electric current to the heater. At this time, since the switches  604  and  605  are opened, a constant electric current source  205  for temperature detection is not connected to the temperature detection element. 
     The operation of temperature detection will now be described with reference to  FIG. 11B . 
     At the time of temperature detection, the switches  604  and  605  are closed. The transistor  202  is turned off by a control signal. On the other hand, an electric current flows from the constant electric current source  205  to ground via the switch  604 , the conductive via  111 , a heater  201   b , the conductive via  112 , and the switch  605  as indicated by a solid arrow. A voltage detection circuit  206  measures a potential difference between the two ends of the conductive via  111 , the heater  201   b , and the conductive via  112  that are series-connected. In this manner, temperature detection is performed by detecting a temperature change in resistance value of the temperature detection element formed by the conductive via  111 , the heater  201   b , and the conductive via  112  that are series-connected. 
     For this embodiment, the arrangement is capable of detecting the temperature change above the heater more easily than the arrangement according to the first embodiment. This makes it possible to increase detection sensitivity to the temperature change of the temperature detection element. 
     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. 2016-155864, filed Aug. 8, 2016, which is hereby incorporated by reference herein in its entirety.