Patent Application
20080012906
These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.
The inkjet image forming apparatus may include an array type inkjet print head cartridge 252 which is fixed in the inkjet image forming apparatus and includes a plurality of inkjet printheads 260 (see
Referring to
For example, in order to print a color image, four kinds of nozzle rows 161C, 161M, 161Y, and 161K may be provided in each of the inkjet printheads 260 so that cyan (C), magenta (M), yellow (Y), and black (K) colored ink can be respectively ejected. The inkjet printheads 260 that can print a color image may include a plurality of ink tanks (not illustrated) that respectively store cyan, magenta, yellow, or black colored ink in the main body 255. The ink channel unit 256 forms an ink path from the ink tanks to rear surfaces of the inkjet printheads 260. The ink channel unit 256 can be formed, for example, by injection molding a liquid crystal polymer (LCP) to ensure thermal stability, durability, and productivity. The inkjet printheads 260 are connected to a control unit (not illustrated) of the inkjet image forming apparatus through flexible printed circuits 270 to receive driving signals and power to eject the ink.
The inkjet printheads 260 are separated a predetermined distance from each other in the primary and secondary ejection directions and may be disposed in a zigzag pattern. Although it is not illustrated, one or multiple inkjet printheads 260 can be arranged in a straight line pattern along the y-axis of the nozzle part 257 to a length corresponding to at least the width of the printing medium P. That is, the inkjet printheads 260 according to an embodiment of the present general inventive concept are not affected by the form of the arrangement pattern, and can be mounted to any type of inkjet image forming apparatus including a shuttle type inkjet image forming apparatus and an array type inkjet image forming apparatus.
As illustrated in
As illustrated in
A vertical structure of each of the inkjet printheads 260 will now be described with reference to
An insulating layer 112 may be formed on an upper surface of the substrate 111 to thermally and electrically insulate the heater 113 from the substrate 111. The insulating layer 112 can be formed of silicon oxide.
The heater 113 may be formed on an upper surface of the insulating layer 112 in a predetermined form to generate bubbles in the ink by heating the ink in the ink chamber 122. In the present embodiment, a heat generation part of the heater 113a is formed to directly contact the ink in the ink chamber 122. The heater 113 is formed of an alloy of Platinum and Ruthenium (Pt—Ru) or an alloy of Platinum, Iridium, and X (Pt—Ir—X) (wherein X is one of Tantalum (Ta), Tungsten (W), Chromium (Cr), Aluminium (Al), and Oxygen (O)). The heater 113 can be formed by patterning a thin film of Pt—Ru alloy or a Pt—Ir—X alloy deposited on the insulating layer 112 by sputtering. According to the present embodiment of the present general inventive concept, the heater 113 can be formed to a thickness of 500 to 3000 Å. In the present embodiment, an input energy applied to the heater 113 through the electrode 114 which will be described later may be 1.0 μJ or less. The heater 113 may have a lifespan of one hundred million pulses or more.
The electrode 114, which is electrically connected to the heater 113 to apply a current to the heater 113, is formed on upper side surfaces of the heater 113. The electrode 114 can be formed of a metal having high electric conductivity, such as aluminum. The electrode 114 can be formed on the heater 113 so that a heat generation part of the heater 113a, that is, an area of the heater 113 exposed to the ink chamber 122 between the upper side surfaces of the heater 113 on which the electrode 114 is formed, can be approximately 650 μm2 or less. A passivation layer 115 covering the electrode 114 can be further formed on the substrate 111 to protect the electrode 114 from being corroded by ink. The passivation layer 115 may be formed of a silicon nitride SiNx.
The chamber layer 120 in which the ink chamber 122 to store the ink to be ejected is stacked above the substrate 111 on which the heater 113, the electrode 114, and the passivation layer 115 may be formed. The chamber layer 120 can be formed of a polymer. The ink chamber 122 is located above the heat generation part 113a. Accordingly, the heat generation part 113a is located on a bottom surface of the ink chamber 122, and directly contacts the ink in the ink chamber 122.
The nozzle layer 130 having the nozzle 132 through which ink in the ink chamber 122 is ejected is stacked on an upper part of the chamber layer 120. The nozzle layer 130 can be formed of a polymer. The nozzle 132 can be disposed at a position corresponding to the center of the ink chamber 122. While in the present embodiment the heater 113 is applied to a top-shooting type inkjet printhead 260, the present general inventive concept is not limited thereto, and the heater 113 according to an embodiment of the present general inventive concept can be applied to any type of inkjet printhead, such as a side-shooting type inkjet printhead or a back-shooting type inkjet printhead.
As described above, the inkjet printhead 260 according to the current embodiment of the present general inventive concept has a structure in which the heat generation part 113a directly contacts the ink in the ink chamber 122. In this case, a material to form the heater 113 must have electrical, chemical, and mechanical stability with respect to the ink. More specifically, the resistance of the heater 113 must not be rapidly changed by oxidation, the heater 113 must not be corroded by ink, and the heater 113 must resist a cavitation force generated when the bubbles disappears.
According to the present general inventive concept, various tests and simulations show that a material selected from a noble metal group having high electrical, chemical, and mechanical stability with respect to ink is an alloy of Pt—Ru or an alloy of Pt—Ir—X. Here, X may be at least one material selected from the group consisting of Ta, W, Cr, Al, and O. The Pt—Ru thin film or the Pt—Ir—X thin film may be formed by a co-sputtering process in which more than two materials are deposited together on the substrate 111 placed in a deposition chamber.
An adhesiveness between the insulating layer 112 formed of silicon oxide SiO2 and the heater 113 can be a problem. Therefore, according to an embodiment of the present general inventive concept, the inkjet printhead 260 can further include an adhesive layer between the insulating layer 112 and the heater 113 to increase the adhesiveness between the insulating layer 112 and the heater 113. As an example, the adhesive layer can be formed of Ta, and the adhesiveness may be increased by depositing a Ta layer having a thickness of 10 nm on the substrate 111 and the insulating layer 112 prior to forming the heater 113.
The heater 113 is required to have a high resistivity so that a large amount of heat can be generated even with a small amount of energy input. Also, to control the heater 113 at a uniform temperature despite a component change or a high frequency driving of the heater 113, it is required that the resistivity of the heater 113 remain uniform even though the composition percentage of Ru may change in a deposition process. Referring to
For convenience of explanation and calculation, it is assumed that the TCR is 1000 PPM/° C. and the resistance of the heater 113 at 0° C. is 1 kΩ. In this case, the resistance of the heater 113 at 0° C. is 1.001 kΩ and at 500° C. is 1.5 kΩ. Accordingly, the heater 113 is required to have a low TCR due to the characteristics of the heater 113 that is repeatedly heated to 500° C. and cooled. Also, to control the heater 113 at a uniform temperature despite a component change or the high frequency driving of the heater 113, it is required that the TCR of the heater 113 remain uniform even though the composition percentage of Ru may change in the deposition process.
Referring to
From the above test results, electrical, chemical, and mechanical characteristics of the heater 113 formed of an alloy of Pt—Ru are evaluated as follows.
First, a reactivity test of the heater 113 with ink was performed. A shape of the heater 113 was observed after the heater 113 was driven for eight weeks using ten kinds of inks at a temperature of 60° C. However, no reaction between the heater 113 and the ink was observed and a delamination of the heater 113 did not occur.
The resistance of the heater 113 can vary in an inkjet printhead manufacturing process. More specifically, in a process of forming the electrode 114 using Al after the heater 113 is deposited, the heater 113 can be exposed to an etchant in a process of etching the Al, and in a process of removing a photoresist in a patterning process of the heater 113, the heater 113 can be exposed to oxygen plasma.
The sheet resistance of the heater 113 measured right after the heater 113 was deposited was 7.56 kΩ/□, the sheet resistance measured after the process of etching Al was 7.56 kΩ/□, and the sheet resistance measured after the process of removing the photoresist was 5.57 kΩ/□. That is, the heater 113 formed of an alloy of Pt—Ru showed almost no resistance change with respect to the atmospheric conditions in which the inkjet printhead 260 was manufactured.
The heater 113 must also have an electrical strength of approximately 1.5 GW/m2 or more so that the heater 113 cannot be damaged when the heater 113 is repeatedly heated to generate bubbles in the ink. In the inkjet printhead 260 according to an embodiment of the present general inventive concept, when the heat generation part 113a of the heater 113 formed of an alloy of Pt—Ru is formed to have an area of 22 μm×29 μm, that is 638 μm2, the heater 113 has an electrical strength of approximately 3 GW/m2 in an air atmosphere. That is, since the heater 113 formed of an alloy of Pt—Ru has an electrical strength twice that of the required electrical strength, the heater 113 according to an embodiment of the present general inventive concept has a sufficient electrical strength margin, and thus, has a high electrical stability.
Also, in the inkjet printhead 260 according to an embodiment of the present general inventive concept, since the heater 113 is directly exposed to ink, the heater 113 must have a sufficient mechanical strength with respect to a cavitation force generated when the bubbles disappear. Also, since the heater 113 directly contacts ink, there must be no electrochemical reaction between the heater 113 and the ink. A bubble test of the heater 113 which is formed of an alloy of Pt—Ru and has a heat generation part area 113a of 22 μm×29 μm was carried out using a commercially available ink. As a result of the test, the energy required to be input to the heater 113 to form stable bubbles was approximately 0.51 μJ. This energy is much lower than the energy (1.2 μJ) input to a heater formed of Ta (with a heat generation part area of 22 μm×22 μm) of a conventional inkjet printhead in which a passivation layer formed of silicon nitride SiNx having a thickness of 6000 Å and an anti-cavitation layer having a thickness of 3000 Å were formed on the heater and also covered the heat generation part area. That is, since the heater 113 according to the present general inventive concept directly contacts the ink, the energy input to the heater 113 required to generate stable bubbles can be reduced to less than 50% of that of the conventional inkjet printhead.
Also, when the above energy is continuously applied to the heater 113 formed of an alloy of Pt—Ru, the heater 113 shows a lifespan of approximately one hundred million pulses or more. A lifespan of one hundred million pulses indicates that the heater 113 has a high mechanical, electrical, and chemical stability.
The characteristics of the heater 113 according to an embodiment of the present general inventive concept, when the heater 113 is formed of an alloy of Pt—Ir—X will now be described with reference to
In
As described above, the heater 113 of the inkjet printhead 260 is required to have a high resistivity and a low TCR. As the composition percentage of Ta increases in the heater 113, the resistivity increases but the TCR decreases. The resistivity of the heater 113 does not change in spite of annealing. These results show that an inkjet printhead that is repeatedly heated to 500° C. and cooled has a high thermal stability.
Accordingly, an example of an embodiment of the present general inventive concept is a heater 113 formed of an alloy of Pt—Ir—X, where Pt and Ir have substantially the same composition percentage, X is Ta, and Ta has a composition percentage of between about 0% to about 30% with respect to the total composition of the alloy of Pt, Ir, and Ta.
In
Referring to
Sheet resistances, input energies, and life spans of two kinds of heaters 113, that is, heaters formed of an alloy of Pt—Ir—Ta and an alloy of Pt—Ir—O, having composition ratios of, for example, 35, 35, and 30 and 30, 30, and 40 respectively, were measured. The areas of the heat generation parts 113a and the thicknesses of the heaters 113 for these two heaters after patterning were 22 μm×29 μm (638 μm2) and 1000 Å, respectively.
A sheet resistance of 18.74 Ω/□, an input energy of 0.61 μJ, an electrical strength of 2.61 GW/m2, and a life span of 2.0×108 were measured with respect to the heater 113 formed of Pt0.35—Ir0.35—Ta0.30, and no abnormality was observed in the heater 113. A sheet resistance of 24.14 Ω/□, an input energy of 0.70 μJ, an electrical strength of 3.20 GW/m2, and a life span of 2.3×107 were measured with respect to the heater 113 formed of Pt0.30—Ir0.30—O0.40, and no abnormality was observed in the heater 113.
If a heater 113 has a heat generation part area of 22 μm×29 μm (638 μm2) and a thickness of 1000 Å, the heater 113 must have an electrical strength of approximately 1.5 GW/m2 or more so that the heater 113 cannot be damaged when bubbles are formed in the ink by the heater 113. Since the heater 113 formed of an alloy of Pt—Ir—X has the electrical strength twice that of the required electrical strength, the heater 113 according to the current embodiment of the present general inventive concept has a sufficient electrical strength margin, and thus, has high electrical stability.
From the test results, energies inputted to the heaters 113 formed of Pt0.35—Ir0.35—Ta0.30 and Pt0.30—Ir0.30—O0.40 respectively to generate stable bubbles in the ink were 0.61 μJ and 0.7 μJ respectively. This level of energy input to the heaters 113 is very small when compared to the energy (1.2 μJ) inputted to a heater formed of TaN (having a heat generation part area of 22 μm×22 μm) of a conventional inkjet printhead in which a passivation layer formed of silicon nitride SiNx having a thickness of 6000 Å and an anti-cavitation layer having a thickness of 3000 Å were formed on the heater 113. That is, since the heaters 113 according to the present general inventive concept formed of Pt—Ir—Ta or Pt—Ir—O directly contact the ink, the energy input to the heaters 113 required to generate stable bubbles can be reduced to less than 50% of that of the conventional inkjet printhead.
Also, when the above energy is continuously applied to the heater 113 formed of an alloy of Pt—Ir—X, the heater 113 shows a lifespan of approximately a few tens of millions to a few hundreds of millions of pulses or more. The long lifespan of the heater 113 indicates that the heater 113 has high mechanical, electrical, and chemical stability.
While in the paragraphs above, heaters formed of an alloy of Pt—Ir—X where X is either Ta or O have been described, X can be one of a group of Ta, W, Cr, Al, and O, for which similar sheet resistance, input energy of 0.61, electrical strength, and mechanical, electrical, and chemical stability cab be expected when X is also W, Cr, and Al.
As described above, an inkjet printhead according to the present general inventive concept and an inkjet image forming apparatus including the inkjet printhead can reduce energy input to a heater required to eject ink, can increase the mechanical, electrical, and chemical stability of the heater, can reduce power required to instantaneously eject ink, can prevent the degradation of characteristics of ink due to accumulation of heat and can increase integration density of nozzles. In particular, the inkjet printhead according to an embodiment of the present general inventive concept is suitable as both an array type printing inkjet printhead and a line type printing inkjet printhead that have problems of power capacity due to high-speed printing using several tens of thousands of nozzles and of heat accumulation.
Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-64858 | Jul 2006 | KR | national |
