Patent Publication Number: US-7896475-B2

Title: Element substrate, printhead, and head cartridge

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an element substrate for an inkjet printhead, a printhead using the element substrate, and a head cartridge having the printhead. 
     2. Description of the Related Art 
     The electrothermal transducers (heaters) of a printhead mounted in an inkjet printing apparatus, and their driving circuit and wiring pattern are generally formed on a single substrate using a semiconductor process technique. A known example of the printhead having this arrangement is one disclosed in U.S. Pat. No. 7,216,960. 
       FIGS. 18 and 19  are schematic views showing an example of a conventional element substrate for an inkjet printhead. 
       FIGS. 18 and 19  characteristically show the same part of the element substrate.  FIG. 18  mainly shows a heater driving power supply wiring pattern and ground wiring pattern.  FIG. 19  mainly shows a heater driver, logic wiring pattern, and logic circuit below these wiring patterns. 
     The arrangement of respective components will be explained first with reference to  FIG. 19 . An ink supply port  604  is formed at the center of the element substrate, and heater arrays  807  are arranged on the two sides of the ink supply port  604 . Ink channels, and orifices for discharging ink are formed in the element substrate in correspondence with respective heaters, and ink is supplied to them via the ink supply port  604 . A driver array  901  is arranged on the outer side of each heater array  807 . A logic circuit wiring pattern and logic circuit  106  are arranged on the outer side of each driver array  901 . Connection terminals  905  are arranged near each short side of the element substrate. A shift register (S/R)  903 , a decoder  904 , a temperature sensor (not shown), and the like are interposed between the connection terminals  905  and the ink supply port  604 . 
     In  FIG. 18 , a heater driving power supply wiring pattern  803  is arranged above each driver array  901 . A ground wiring pattern  804  is arranged above each logic circuit  106 . These wiring patterns are connected to the outside via heater driving connection terminals  801  and ground connection terminals  802 , respectively. 
     Heaters in the heater array are driven by a so-called time division driving method of shifting the driving timing for each block of simultaneously drivable heaters. 
     In order to make the wiring resistances of arrayed heaters almost equal to each other, the power supply wiring pattern is divided for each driving group of heaters not driven simultaneously. The respective wiring patterns have different widths in accordance with the distance from the connection terminal, so as to make resistance values almost equal to each other. For example, a wiring pattern having a longer distance and larger wiring length has a larger width. In each driving group, the number of simultaneously driven heaters is one, so the voltage drop by the wiring resistance is almost equal between heaters. 
     In  FIG. 19 , the connection terminals  905  are arranged near the two short sides of the element substrate. This is because the wiring width becomes excessively large if the connection terminals  905  are arranged on only one short side of the element substrate and the wiring pattern extends up to the other short side. As shown in  FIG. 18 , the power supply wiring patterns are symmetrical in the longitudinal direction on the sheet surface of  FIG. 18 . That is, the heater driving connection terminals  801  and ground connection terminals  802  are necessary on the two short sides. 
     Terminals other than the heater driving connection terminal  801  and ground connection terminal  802  are used as a heater driving enable terminal, data input terminal, latch terminal, clock terminal, logic power supply terminal, temperature sensor terminal, rank measurement terminal, and the like. 
     These days, inkjet printing apparatuses are demanded for higher printing resolutions and higher printing speeds. The element substrate for an inkjet printhead needs to be elongated to cope with a higher-density arrangement of heaters and logic circuits, a larger number of orifice arrays corresponding to a larger number of ink colors, and a larger number of heaters. As a result, the area of the element substrate increases, raising the cost. 
       FIG. 5  is a plan view of an example of the element substrate of an inkjet printhead. As represented by an orifice portion  501  in  FIG. 5 , a plurality of types of orifices having different orifice diameters and the like are arranged so that ink of the same color can be discharged by different discharge amounts. Known examples of the printhead having this arrangement are ones disclosed in U.S. Pat. No. 6,137,502 and Japanese Patent Laid-Open No. 2007-144711 (WO2007/061138). 
     Referring to  FIG. 6  which is an enlarged view of the orifice portion  501 , orifices  602  of array A have a discharge amount of 2 pl and an array density of 600 dpi. Orifices  601  of array B have a discharge amount of 2 pl and an array density of 600 dpi. Orifices  603  of array C have a discharge amount of 1 pl and an array density of 600 dpi. Arrays B and C are positioned on the same side of an ink supply port  604 , and orifices are staggered. The orifices of arrays B and C are arrayed at an array density of 1,200 dpi, which is substantially double that of array A. In other words, orifices are formed at an array density of 600 dpi on one side of the ink supply port  604 , and those are formed at an array density of 1,200 display on the other side. 
       FIG. 10  is a view schematically showing the element substrate of the orifice portion  501  in  FIG. 5 . As shown in  FIG. 10 , heaters  104  corresponding to the orifices  602  of array A are arranged on one side of the ink supply port  604 , whereas heaters  103  corresponding to the orifices  601  of array B and heaters  105  corresponding to the orifices  603  of array C are arranged on the other side. A driver  101  corresponds to each heater  103 , a driver  102  corresponds to each heater  104 , and a driver  107  corresponds to each heater  105 . Reference numeral  106  denotes each logic circuit. In the array of the drivers  102 , the drivers are arrayed at an array density of 600 dpi. In the array of the drivers  101  and  107 , the drivers are arrayed at an array density of 1,200 dpi. 
     Problems will be described, which arise when a plurality of orifice arrays having the same discharge amount exist on a single element substrate, and the drivers of respective driver arrays are formed at different array densities in the respective driver arrays corresponding to the respective orifice arrays. The following description assumes that the driver is a transistor. 
       FIG. 11  shows the arrangement of the heater driving power supply wiring patterns  803  and ground wiring patterns  804  which are superposed on the circuit shown in  FIG. 10  via an insulating film. 
     The heaters  103  and  104  discharge ink droplets in the same discharge amount of 2 pl. To make discharge characteristics such as the discharge amount and discharge speed equal to each other, driving conditions are desirably made equal. That is, the heaters  103  and  104  are desirably driven with the same pulse using the same heat enable signal which defines the period during which the heater is driven. 
     The number of heat enable signal terminals is desirably small in order to downsize the element substrate. A small number of heat enable signals is advantageous even in cost because the printing apparatus main body need not have many pulse tables. 
     To make discharge characteristics such as the discharge amount and discharge speed equal to each other, and share the heat enable signal, it is desirable to make the size equal between heaters and make the ON resistance and wiring resistance equal between drivers. In  FIG. 10 , the drivers  101  and  102  have the same width in the driver array direction and the same length L 1  in a direction perpendicular the driver array direction, and have the same size. Thus, the drivers  101  and  102  have the same ON resistance, and the heater driving power supply wiring pattern  803  and ground wiring pattern  804  in  FIG. 11  have the same sizes and wiring resistances for both the heaters  103  and  104 . In this case, the heaters  103  and  104  can be driven by the same heat enable signal, and attain the same discharge characteristics. 
     However, as is apparent from the drivers  102  in  FIG. 10 , they are arranged in accordance with a 1,200-dpi heater array though they are originally arrayed at 600 dpi. A gap is generated between adjacent drivers, resulting in poor arrangement efficiency, that is, an unnecessarily large chip size. 
       FIGS. 12 and 13  are schematic views, similar to  FIGS. 10 and 11 , and show an example of improving the driver arrangement efficiency. 
     The drivers  102  are arrayed at 600 dpi, similar to  FIG. 10 . In order to make the ON resistance of the drivers  102  equal to that of the drivers  101  arrayed at 1,200 dpi, the length of the driver  102  in a direction perpendicular to the heater array direction is halved while the area of the driver  102  is kept constant, preventing generation of an unnecessary space. 
     In this case, as shown in  FIG. 13 , each driver needs to be connected on the outer side to the ground wiring pattern  804 . The wiring width of the heater driving power supply wiring pattern  803  is narrowed in accordance with the driver  102 . Although the area above the drivers  101  and  107  is sufficiently large, the wiring width is narrowed to set the wiring resistance of the driver  101  equal to that of the driver  102  and make discharge characteristics equal to each other. 
     In this case, the driver arrangement efficiency can be increased to downsize the element substrate, but the wiring resistance rises, decreasing the electrical efficiency. 
     As described above, when a plurality of orifice arrays having the same discharge amount exist on a single element substrate, and transistors which form respective driver arrays are formed at different array densities, it is difficult to achieve both a small-size element substrate and high electrical efficiency. 
     SUMMARY OF THE INVENTION 
     The present invention can provide an element substrate capable of achieving both a small-size element substrate and high electrical efficiency when a plurality of orifice arrays having the same discharge amount exist on a single element substrate, and transistors which form respective driver arrays are formed at different array densities. 
     An element substrate according to the present invention comprises a first printing element array and a second printing element array each formed of a plurality of printing elements for discharging a liquid by substantially the same liquid discharge amount; a third printing element array formed of printing elements which discharge the liquid by a discharge amount different from the discharge amount of the printing elements of the first and second printing element arrays and are staggered from the printing elements of the second printing element array; a first driver array formed of a plurality of driving elements arranged near the first printing element array, a second driver array formed of a plurality of driving elements arranged near the second printing element array, and a third driver array formed of a plurality of driving elements arranged near the third printing element array, the second driver array and the third driver array forming a single array; a first power supply wiring pattern arranged at a position where the first power supply wiring pattern overlaps an area where the first driver array is arranged, and in a different layer; and a second power supply wiring pattern arranged in the layer and at a position where the second power supply wiring pattern overlaps an area where the second driver array and the third driver array are arranged, wherein an array density of the driving elements of the first driver array is lower than an array density of the driving elements of the single array formed from the second driver array and the third driver array, an area of each of the driving elements of the first driver array is larger than an area of each of the driving elements of the second driver array and is larger than an area of each of the driving elements of the third driver array, and a wiring width of the first power supply wiring pattern in a direction perpendicular to the printing element arrays is smaller than a wiring width of the second power supply wiring pattern. 
     The present invention provides a printhead and head cartridge having the element substrate. 
     According to the present invention, the area of drivers arrayed at low density is set larger than that of drivers arrayed at high density. The ON resistance of the drivers arrayed at low density becomes lower than that of the drivers arrayed at high density. To make driving conditions equal between the array of orifices corresponding to the drivers arrayed at low density and that of orifices corresponding to the drivers arrayed at high density, the wiring resistance of the drivers arrayed at low density is set higher than that of the drivers arrayed at high density. That is, the heater driving power supply wiring pattern of the drivers arrayed at low density can be narrowed. The element substrate can be efficiently downsized without decreasing the electrical efficiency. 
     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 view showing the heater, driver, and logic circuit of an element substrate according to the present invention; 
         FIG. 2  is a view showing the power supply wiring pattern and the like of the element substrate according to the present invention; 
         FIG. 3  is a schematic view obtained by superposing  FIGS. 1 and 2 ; 
         FIG. 4  is a view showing a state in which the element substrate according to the present invention is mounted on a TAB tape; 
         FIG. 5  is an enlarged view of the element substrate; 
         FIG. 6  is an enlarged view of an orifice portion; 
         FIG. 7  is a view showing an entire printhead; 
         FIG. 8  is a schematic view of an inkjet printing apparatus; 
         FIG. 9  is a block diagram showing the control arrangement of the inkjet printing apparatus; 
         FIG. 10  is a view showing the heater, driver, and logic circuit of a conventional element substrate; 
         FIG. 11  is a view showing the power supply wiring pattern and the like of the conventional element substrate; 
         FIG. 12  is a view showing the heater, driver, and logic circuit of a conventional element substrate; 
         FIG. 13  is a view showing the power supply wiring pattern and the like of the conventional element substrate; 
         FIG. 14  is an enlarged view of an orifice portion; 
         FIG. 15  is an enlarged view of an orifice portion; 
         FIG. 16  is a view showing the heater, driver, and logic circuit of an element substrate according to the present invention; 
         FIG. 17  is a view showing the heater, driver, and logic circuit of an element substrate according to the present invention; 
         FIG. 18  is a view showing the power supply wiring pattern and the like of a conventional element substrate; and 
         FIG. 19  is a view showing the heater, driver, and logic circuit of the conventional element substrate. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The same reference numerals denote the same parts, and a description thereof will not be repeated. 
     In this specification, the term “printing” (to be also referred to as “print” hereinafter) not only includes 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 perceptible by humans. 
     Also, the term “print medium” not only includes paper used in general printing apparatuses, but also broadly includes materials capable of accepting ink, such as cloth, a plastic film, a metal plate, glass, ceramics, wood, and leather. 
     The term “ink” should be extensively interpreted similar to the definition of “print” described above. “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. Ink processing includes solidification or insolubilization of a coloring agent in ink applied to the print medium. 
     The term “element substrate” in the description means not a simple substrate made of a silicon semiconductor, but a substrate having elements, wiring patterns, and the like. 
     The expression “on an element substrate” includes not only “on the surface of an element substrate”, but also “inside of an element substrate near its surface”. The term “built-in” in the present invention means not “simply arrange separate elements on a substrate”, but “integrally form and manufacture elements on an element substrate by a semiconductor circuit manufacturing process or the like”. 
     The schematic structure of an inkjet printing apparatus will be explained. 
       FIG. 8  is a perspective view of the schematic outer appearance of an inkjet printing apparatus to which the present invention is applicable. In  FIG. 8 , a carriage HC supports an integral head cartridge incorporating a printhead  1708  and an ink tank IT (liquid container) which contains ink. The carriage HC reciprocates in directions indicated by arrows a and b. During reciprocation, the printhead discharges ink to print. 
     A control arrangement for executing printing control of the inkjet printing apparatus will be explained with reference to the block diagram of  FIG. 9 . In  FIG. 9  showing a control circuit, an interface  1700  receives a print signal from a host computer or the like. Reference numeral  1701  denotes an MPU. A ROM  1702  stores control programs to be executed by the MPU  1701 . A DRAM  1703  saves various data (e.g., the print signal, and print data supplied to a printhead  1708 ). A gate array (G.A.)  1704  controls supply of print data to the printhead  1708 , and also controls data transfer between the interface  1700 , the MPU  1701 , and the DRAM  1703 . A carrier motor  1710  conveys the printhead. A conveyance motor  1709  conveys a print medium. A motor driver  1706  drives the conveyance motor  1709 . A motor driver  1707  drives the carrier motor  1710 . Reference numeral  1708  denotes the printhead; and  403 , an element substrate for the printhead. 
     The operation of the control arrangement will be described. When a print signal is input to the interface  1700 , it is converted into print data between the gate array  1704  and the MPU  1701 . Then, the motor drivers  1706  and  1707  are driven, and the printhead  1708  and the element substrate  403  are driven in accordance with print data, executing printing. 
     The printhead will be described. 
       FIG. 4  is a view showing a state in which the element substrate  403  having a plurality of heaters is mounted on a TAB tape  401 . Contact terminals  402  are arranged on one end of the TAB tape  401  to connect the TAB tape  401  to the inkjet printing apparatus main body. The element substrate  403  is connected on the other end via inner leads. 
       FIG. 5  is an enlarged view of a portion  404  in  FIG. 4 . Inner leads  503  and  504  project from the device holes of the TAB tape  401 . The inner leads  503  and  504  are electrically connected to connection terminals by gang bonding. 
       FIG. 7  shows the completed form of the printhead. The TAB tape  401  in  FIG. 4  is joined to the ink tank IT. The inner leads projecting from the device holes are sealed with a sealing material  702 . The TAB tape  401  is bent to fix the contact terminals  402  tightly to the wall surface of the ink tank IT. The element substrate serves as the upper side in  FIG. 7 , but as the lower side when mounted in the inkjet printing apparatus. 
     First Embodiment 
     An element substrate and printhead according to the first embodiment will be described with reference to  FIGS. 1 to 3 . 
       FIG. 1  is a schematic view showing heaters  103 ,  104 , and  105 , drivers  101 ,  102 , and  107 , and logic circuits  106  of the element substrate according to the first embodiment. 
     An ink supply port  604  is formed at the center of the element substrate. The array of the heaters  104  and the array of the drivers  102  are arranged close to each other on one side of the ink supply port  604 , whereas the arrays of the heaters  103  and  105  and the arrays of the drivers  101  and  107  are arranged close to each other on the other side. Each driver is a transistor serving as a kind of driving element. In each heater array,  512  heaters are arrayed at an array density (pitch) of 600 dpi. The heaters  103  and  105  are staggered. In the array of the drivers  102  corresponding to the heaters  104 ,  512  drivers are arrayed at a pitch of 600 dpi. In the array of the drivers  101  corresponding to the heaters  103  and the drivers  107  corresponding to the heaters  105 , 1,024 drivers are arrayed at a pitch of 1,200 dpi. 
     The heaters  103  and  104  have the same area and shape in order to discharge ink by the same ink discharge amount (liquid discharge amount). 
       FIG. 6  shows orifices (printing elements) corresponding to the respective heater arrays shown in  FIG. 1 . The heater  103  corresponds to an orifice  601 , and the heater  104  corresponds to an orifice  602 . The discharge amount from each orifice is 2 pl. The heater  105  corresponds to an orifice  603 , and the discharge amount is 1 pl. The array of the orifices  602  serves as the first orifice array (first printing element array), that of the orifices  601  serves as the second orifice array (second printing element array), and that of the orifices  603  serves as the third orifice array (third printing element array). The array of the drivers  102  serves as the first driver array, and that of the drivers  101  and  107  serves as the second driver array. 
       FIG. 2  is a schematic view showing the power supply wiring patterns and the like of the element substrate according to the first embodiment. 
       FIG. 3  is a schematic view obtained by superposing the power supply wiring patterns in  FIG. 2  on the drivers and logic circuits in  FIG. 1 . Heater driving power supply wiring patterns  803   a  and  803   b  are arranged on the array of the drivers  102  and that of the drivers  101  and  107 , respectively. Ground wiring patterns  804  are arranged on the logic circuits  106 . The element substrate according to the present invention has this multilayered structure. The heater driving power supply wiring pattern  803   a  serves as the first power supply wiring pattern, and the heater driving power supply wiring pattern  803   b  serves as the second power supply wiring pattern. The first power supply wiring pattern is arranged at a position where it overlaps an area where the first driver array is arranged, and in a different layer. The second power supply wiring pattern is arranged in this layer and at a position where it overlaps an area where the second and third driver arrays are arranged. 
     In  FIG. 1 , the drivers  101  and  102  drive heaters having the same discharge amount of 2 pl, so their areas should be originally made equal to have the same ON resistance. In the first embodiment, however, letting S 1  be the area of the driver  101  and S 2  be that of the driver  102 , S 2 &gt;S 1 . That is, the area of the driver  102  is set larger than that of the driver  101 . The array density of the first driver array is lower than that of the array of the drivers  101  and  107 . In the first embodiment, the drivers  101  and  107  are arrayed at 1,200 dpi, and the drivers  102  are arrayed at 600 dpi. Thus, sizes L 1  and L 2  of the drivers  101  and  102  in a direction perpendicular to the heater array direction satisfy L 2 &gt;L 1 /2. 
     As a result, an ON resistance R 102  of the driver  102  becomes lower than an ON resistance R 101  of the driver  101 . To make driving conditions equal to each other, the wiring resistance of the driver  102  needs to be set higher than that of the driver  101 . In  FIG. 2 , the heater driving power supply wiring pattern  803   a  above the driver  102  is narrower (in a direction perpendicular to the printing element array) than the heater driving power supply wiring pattern  803   b  above the drivers  101  and  107 . Wiring resistances R 803   a  and R 803   b  corresponding to the respective heater driving power supply wiring patterns satisfy a relation:
 
 R 102 +R 803 a=R 101 +R 803 b  
 
     Concrete numerical values in the first embodiment are L 1 =200 μm, L 2 =120 μm, R 101 =40Ω, R 102 =33.3Ω, and R 803   b =10Ω. Since the ON resistances of the drivers  102  and  101  are different by 6.7Ω, R 803   a =16.7Ω is set to satisfy the above relation. 
     Assuming that L 1  is almost equal to the wiring width of the heater driving power supply wiring pattern  803   b,  the entire wiring width of the heater driving power supply wiring pattern  803   b  is set to 200 μm. The wiring width of the heater driving power supply wiring pattern  803   a  is calculated from these values, obtaining 200 μm×16.7Ω/10Ω=120 μm, which is almost equal to the width L 2 . The area above the drivers can be efficiently used as a wiring area. 
     This arrangement of the element substrate makes it possible to drive the heaters  103  and  104  having the same discharge amount under the same driving conditions. 
     Compared to a prior art shown in  FIG. 10 , the drivers  102  arrayed at 600 dpi can be downsized. 
     Compared to a prior art shown in  FIGS. 12 and 13 , the size of a conventional driver  102  is smaller. However, the sum of the wiring resistance and ON resistance can be suppressed smaller than the conventional one, achieving high electrical efficiency. 
     Second Embodiment 
     An element substrate and printhead according to the second embodiment will be described with reference to  FIGS. 14 to 17 . 
       FIG. 14  is an enlarged view of an orifice portion  501  in  FIG. 5 , that is, orifice arrays for discharging cyan ink.  FIG. 15  is an enlarged view of an orifice portion  502  in  FIG. 5 , that is, orifice arrays for discharging yellow ink. 
     The ink droplet discharge amount from each orifice in the second embodiment is different from that in the first embodiment. In  FIG. 14 , an orifice  612  discharges a 5-pl ink droplet, an orifice  611  discharges a 2-pl ink droplet, and an orifice  613  discharges a 1-pl ink droplet. A heater  114  corresponds to the orifice  612 , a heater  113  corresponds to the orifice  611 , and a heater  115  corresponds to the orifice  613 . In  FIG. 15 , an orifice  622  discharges a 5-pl ink droplet, and an orifice  621  discharges a 2-pl ink droplet. A heater  124  corresponds to the orifice  622 , and a heater  123  corresponds to the orifice  621 . 
     Array A shown in  FIG. 14  and array B shown in  FIG. 15  discharge inks by the same volume though the ink color is different. It is desirable to make driving conditions equal to each other, similar to the first embodiment. 
       FIG. 16  is a view showing drivers and logic circuits corresponding to  FIG. 14 .  FIG. 17  is a view showing drivers and logic circuits corresponding to  FIG. 15 . 
     The heaters  113  and  123  for discharging ink droplets of the same 2-pl discharge amount are equal in size to the heaters  103  and  104  used in the first embodiment. A driver  111  corresponding to the heater  113  is equal in size to the driver  101  corresponding to the heater  103  used in the first embodiment. A driver  122  corresponding to the heater  123  is equal in size to the driver  102  corresponding to the heater  104  used in the first embodiment. Although not shown, the power supply wiring pattern of each heater in the second embodiment is also equal in size to that of a corresponding heater in the first embodiment. This arrangement allows driving the heaters  113  and  123  having the same discharge amount under the same driving conditions. 
     The array of the orifices  621  serves as the first orifice array, that of the orifices  611  serves as the second orifice array, and that of the orifice  613  serves as the third orifice array. The array of the driver  122  serves as the first driver array, and that of the drivers  111  and drivers corresponding to the heaters  115  serves as the second driver array. 
     Similar to the first embodiment, the second embodiment can also increase the electrical efficiency by suppressing the sum of the wiring resistance and ON resistance small while downsizing the driver. In the first and the second embodiment, the first power supply wiring pattern and the second power supply wiring pattern may be arranged in the same layer. 
     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. 2007-276756, filed Oct. 24, 2007, which is hereby incorporated by reference herein in its entirety.