JP3778488B2 - Heat generating resistor for ink jet recording head, ink jet recording head, and recording apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heating resistor for an ink jet recording head, an ink jet recording head, and a recording apparatus that use thermal energy to fly ink droplets toward a recording medium.
[0002]
[Prior art]
An ink jet recording apparatus of a type in which a part of ink is rapidly vaporized by pulse heating and an ink droplet is ejected from the orifice by the expansion force is disclosed in JP-A-48-9622, JP-A-54-51837, etc. It is disclosed.
[0003]
The simplest method of this pulse heating is to apply a pulse current to the heating resistor, and the specific method is announced on page 58 of Nikkei Mechanical December 28, 1992 and Hewlett-Packard-Journal, Aug.1988. Has been. The basic structure common to these conventional heating resistors is that a thin film resistor and a thin film conductor are covered with an antioxidant layer, and an anti-cavitation layer is formed on the anti-oxidation layer for the purpose of preventing cavitation destruction of 1-2. It was to coat the layers.
[0004]
In order to drastically simplify the complex multilayer structure, as described in Japanese Patent Application Laid-Open No. 06-71888 filed earlier by the present applicant, a heating resistor that eliminates the need for the antioxidant layer and the anti-cavitation layer is provided. There is a method of printing using the body. In this case, since the thin film resistor is in direct contact with the ink, the rapid nucleate boiling of the ink due to pulse heating and the resulting ink ejection characteristics are greatly improved, greatly improving thermal efficiency and increasing the ejection frequency. I was able to plan. The biggest reason for realizing such breakthrough performance is only Cr-Si-SiO or Ta-Si-SiO alloy thin film resistors and Ni thin film conductors with excellent pulse resistance, oxidation resistance, and electrolytic corrosion resistance. This is because a heating resistor composed of the above is used and no protective layer is required.
[0005]
In this way, since it is possible to eject ink with much smaller input energy than in the prior art, even if this heating resistor is formed close to the device region on the driving LSI chip, it is no longer LSI. A monolithic LSI head having a very simple configuration can be realized without heating the device and causing a temperature rise. This is as described in Japanese Patent Application No. 04-347150 and Japanese Patent Application No. 05-90123 filed earlier by the present applicant. This new technology enables on-demand inkjet printheads with many ink jet nozzles to be densely and two-dimensionally integrated to produce a full-color inkjet printer capable of high-speed printing. I was able to.
[0006]
Further, if an excellent foam extinction characteristic (Japanese Patent Application No. 05-272451) of a thin film heating resistor that does not require a protective layer is used, a thermal system that ejects ink droplets in a direction perpendicular to or substantially perpendicular to the surface of the heating resistor. In the ink jet print head, the crosstalk can be greatly reduced by a new driving method, and it is possible to make the head free from the occurrence of sub-drop and the print density change (Japanese Patent Application Nos. 06-21060 and 06). -49202, Japanese Patent Application No. 06-156949).
[0007]
In addition, a method of manufacturing a large-scale highly integrated print head having such characteristics has been devised with a high yield (see Japanese Patent Application No. 06-201985).
[0008]
[Problems to be solved by the invention]
When full-color printing was performed by filling this large-scale highly integrated print head with various water-based inks, it was found that a head having a design life shorter than the design life appeared. Therefore, a detailed study was conducted, and it was found that the ink of the head that had no problem in life was a neutral water-based ink having a relatively large specific resistance, and the ink of the head that had a design life of less than 10 had a specific resistance. It was found to be as small as ² to 10 ³ Ωcm and non-neutral with PH = 8 to 9.
[0009]
An object of the present invention is to provide a heating resistance for an ink jet recording head, which has no problem in life even for non-neutral aqueous ink having a small specific resistance, and is equivalent to a heating resistor having no protective layer in terms of heating and foaming characteristics. It is an object to provide an ink jet recording head and a recording apparatus using the same.
[0010]
[Means for Solving the Problems]
The object is composed of a Ta—Si—SiO alloy thin film resistor formed on a Si substrate and a thin film conductor partially formed on the Ta—Si—SiO alloy thin film resistor. For an ink jet recording head, the SiO alloy thin film resistor has an electrically insulating film formed by thermally oxidizing the surface of the Ta-Si-SiO alloy thin film resistor on which the thin film conductor is not formed. Ink jetting characterized in that the resistance value of the Ta-Si-SiO alloy thin film resistor on which the electrically insulating film is formed does not change even if it is heated to 350 degrees by pulse heating. This is achieved by the heating resistor for the recording head .
[0012]
In this case, the electrically insulating film is preferably a homogeneous film having no pinholes.
Further, the object is to provide a plurality of heating resistors for the ink jet recording head,
A plurality of ejection nozzles that eject ink droplets in a direction perpendicular to or substantially perpendicular to the heating resistor;
A plurality of individual ink passages provided on the Si substrate corresponding to each of the plurality of discharge nozzles;
This is achieved by an ink jet recording head comprising a common ink passage provided on the Si substrate communicating with the plurality of individual ink passages.
[0013]
In that case, the thin film conductor has an individual thin film conductor connected to each of the Ta-Si-SiO alloy thin film resistor,
It is preferable that all of the individual thin film conductors and a part of the heating resistor are covered with a heat-resistant resin partition which forms the individual ink passages.
[0014]
In that case, it is preferable that the said heat resistant resin is a polyimide.
The thin film conductor is preferably a Ni metal thin film conductor.
[0015]
The present invention also provides a recording apparatus comprising the ink jet recording head.
[0016]
As described above, the thin film resistor coated with a thin and homogeneous thermally oxidized electrical insulating film no longer comes into direct contact with the electrolyte ink, and therefore does not cause the problem of shortening the life due to electrolytic corrosion. . Furthermore, even if there is a thin insulator layer on top of this, the thickness is very thin, equivalent to the resistor film thickness, so the heating efficiency to the ink is almost the same as in the case without the insulator layer, which is the same as before. Performance is obtained and reliability is further increased.
[0017]
However, if these thin insulator layers are destroyed, there is a possibility that electrolytic corrosion may occur. Therefore, it is important to completely prevent the insulator layers from being destroyed. For this purpose, the shock wave generated when the bubble disappears must not be caused.
[0018]
Therefore, the applicant of the present invention, as a method of preventing the shock wave, “whether the height of the individual ink passage is 30 μm or less and the vertical projection image on the surface of the heating resistor at the bottom of the discharge nozzle overlaps the heating resistor within ± 5 μm. It has been found that the head structure is smaller than that, and preferably the nozzle depth is less than 80 μm ”. It was also confirmed experimentally that by using such a structure, the generated bubbles continued to grow to a place connected to the outside air (discharge port), and the phenomenon that the bubbles collapsed no longer occurred.
[0019]
On the other hand, covering the individual thin film conductor including a part of the heater with a resin partition such as polyimide having a thermal decomposition starting temperature of 400 ° C. or higher is a high (or low) potential with respect to the electrolyte ink at the same potential as the common thin film conductor. This is because the possibility that the individual thin-film conductor is electrically eroded is completely zeroed by embedding the individual thin-film conductor in the resin. The required heating temperature of the heater is about 310 ° C. at which fluctuation nucleate boiling occurs, and it is easy to control the heating temperature of the heater within the range of 340 ± 30 ° C. even considering variations in the heater and drive circuit. is there. That is, the maximum temperature of the heater portion close to the individual thin film conductor covered by the heat resistant resin is 360 to 370 ° C., and the accumulated time for heating to the temperature close to this maximum temperature is about 0.2 μs × 100 million pulses = 20 seconds. It is a short time. That is, it can be understood that as long as a resin having a thermal decomposition start temperature of 400 ° C. or higher such as polyimide is used, no problem occurs in the life and reliability of the head having this configuration. Data on these will be described in the examples.
[0020]
The reason why it is not necessary to coat the same resin on the common thin film conductor is that the conductor and the ink are kept at the same potential, so that simple corrosion does not occur in the Ni thin film metal.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments will be described with reference to the drawings.
[0022]
FIG. 1 is an enlarged cross-sectional view of the vicinity of an ink discharge nozzle of an ink jet recording head which is an example of the ink jet recording head of the present invention, and FIG. 2 is a cross-sectional view including the periphery thereof. A SiO ₂ heat insulating layer 17 having a thickness of 1 to ₂ μm is provided on the silicon substrate 1, and a Ta—Si—SiO alloy thin film resistor 3 having a thickness of about 0.2 μm and excellent in pulse resistance and oxidation resistance is provided thereon. The individual Ni metal thin film conductor 4 and the common Ni metal thin film conductor 5 having a thickness of about 1 μm are formed by sputtering and photoetching as described in Japanese Patent Application Laid-Open No. 06-71888 filed earlier by the present applicant. is there.
[0023]
First, the high-temperature thermal oxidation characteristics of a Ta—Si—SiO alloy thin film resistor (hereinafter referred to as a resistor) will be described. The resistance value R when this resistor was left in the atmosphere at 500 ° C. was measured, and its reciprocal Ro / R is shown in FIG. Here, Ro is a resistance value before the heat treatment. It has been confirmed that the surfaces of the resistors subjected to the thermal oxidation treatment are all changed into electrical insulators (oxides). In FIG. 5, the fact that Ro / R decreases linearly indicates that the rate of change to the insulating oxide by the thermal oxidation treatment (oxidation depth from the surface) is proportional to the heat treatment time. ing.
[0024]
On the other hand, it has been confirmed that the resistance value of the resistor oxidized at 500 ° C. does not change when left in the atmosphere at 350 ° C., and this resistor is pulse-heated at around 350 ° C. in this state. However, it has been confirmed by an application test of 100 million pulses or more that the resistance value does not change at all.
[0025]
Furthermore, an electric corrosion test was conducted at a potential gradient of 30 V / 50 μm by applying a resistor having a thickness of about 1000 mm to the electrolyte ink having a pH of 8 to 9 to this insulating oxide film. No change was observed. This indicates that an insulating film having no defects such as pinholes is formed even though it is a very thin film of 1000 mm (0.1 μm). It can be seen that it has the characteristics of being unobtainable and homogeneous.
[0026]
By this thermal oxidation treatment, a metal thin film conductor such as Ni is oxidized, or Japanese Patent Application Nos. 04-347150, 05-90123, and 06-201985 filed earlier by the present applicant. When heat treatment at 400 ° C. or higher is difficult as in the monolithic LSI head described in No. 1, thermal oxidation treatment is performed by pulsing the alloy thin film resistor and pulse-heating only the resistor to about 550 to 600 ° C. There is a need. In this case, it is effective for the thermal oxidation treatment to make the heating pulse width as long as about 1 ms with a long high temperature holding time, and this can be easily performed by driving from the outside. That is, since the heat treatment is performed with a pulse width that is 10 ³ times longer than the pulse width of 1 to 2 μs during actual driving, the rating of the driving LSI is maintained even if the heat treatment temperature is 200 to 250 ° C. higher than that during actual driving. It is far below electricity and no problem. Further, the Si substrate temperature during the pulse heat treatment may be heated to about 100 ° C.
[0027]
Although the resistance value of the thin film resistor is increased by 30 to 40% by the heat treatment, the resistance value can be measured and inspected at the same time particularly during the pulse heat treatment process. Therefore, the resistance values of all the resistors were monitored during the pulse heat treatment, and the resistance values were adjusted to within ± 1%. This makes it possible to align the resistance value of the resistor array, which has had a variation of about ± 5% in the past, and eliminates unnecessary heating by uniformly aligning the ink heating temperature during actual driving, resulting in ink scooping, It has become possible to make a significant contribution to improving the reliability of the head, such as the life of the resistor.
[0028]
Further, the partition wall 8 and the orifice plate 11 are formed by the method described in Japanese Patent Application No. 06-201985 filed earlier by the present applicant. As shown in FIG. A part of the body 3 is covered with a partition wall 8. The heating resistor 3 may be covered from 5 to 8 [mu] m from the end of the individual electrode 4, and the decrease in thermal efficiency due to this is only about 10 to 15%.
As described above, the maximum temperature of the heating resistor is 360 to 370 ° C. or lower, and the life of the heat generating resistor is not limited as long as a heat resistant resin having a thermal decomposition starting temperature of 400 ° C. or higher such as polyimide is used as the constituent material of the partition wall 8. I will show later that it does not matter.
[0029]
On the other hand, when a photosensitive resist material having low heat resistance used in the prior art is used for this partition wall, it has been confirmed that breakage due to electrolytic corrosion occurs when discharging about 10 million dots. By using such a heat resistant resin as the partition wall material, there is no problem in reliability even if the heating resistor 3 and the partition wall 8 overlap in the width direction of the individual ink passages 9. A good result is given that a margin is given to the alignment accuracy (alignment accuracy).
[0030]
As shown in FIGS. 1 and 2, the ink discharge nozzle 12 opened in the orifice plate 11 by dry etching has a straight cylindrical shape, and in some cases, the Japanese Patent Application previously filed by the present applicant. As described in Japanese Patent Laid-Open No. 05-318272, the vertical projection image of the bottom surface of the heating resistor 3 overlaps the heating resistor 3 within ± 5 μm or smaller, and the height of the partition 8 is 30 μm or less. In this embodiment, it is 25 μm, the heater is 50 μm square, and the nozzle diameter is 50 μmφ.
[0031]
The orifice plate 11 uses the same polyimide 50 μm thick film as the partition wall. When the stroboscopic observation is performed by filling pure water into the orifice plate 11, the polyimide is almost transparent. The state of discharge can be seen. When the energization pulse width is 2 μs, this observation result after the energization is started is shown in FIG.
[0032]
That is, the water in the nozzle starts to be ejected at a speed of 12 to 15 m / s about 2-3 μs after the start of energization, but the water in the ink passage 9 hardly moves. However, the internal pressure of the bubble 16 at this time is almost zero. The tail of the water discharged at 6 μS after the start of energization has come close to the outlet of the nozzle 12, and the water in one ink passage 8 has started to move toward the heating resistor 3 due to a pressure difference of 1 atm. However, at 9 μS after the start of energization, the nozzle 12 is already at atmospheric pressure, and the movement of water in the ink passage 9 becomes slow because the pressure difference becomes zero. Then, it took about 70 μs to fill the nozzle 12 again with water. As is clear from the observation result of the discharge process, the phenomenon of the disappearance of the vacuum bubble does not occur, and therefore the shock wave peculiar to cavitation does not occur.
[0033]
On the other hand, in the case of FIG. 3B in which the nozzle bottom is greatly expanded, the water to be discharged is completely connected to the water in the ink passage 9, and the vacuum bubble disappears after about 9 μS and generates a shock wave at that time. Although this shock wave is not strong enough to cause a rebound phenomenon (re-foaming), it applies a local impact force to the center of the heater, and in some cases destroys the heater (Hewlett-Packard Journal, Feb. 1994, p. 41).
[0034]
In the life test in which the electrolyte ink is filled, there is no problem in ejecting ink of 100 million pulses or more in FIG. 3A, and in FIG. 3B, there is a large variation in the range from 1 million pulses to 10 million pulses. The difference was clear. The presence or absence of the impact force could be directly verified by an AE sensor (acoustic detector) attached to the back surface of the head substrate. That is, in the open boiling, the impact force detected at the time of bubble generation and disappearance is as small as 1/10 or less in the head of the present invention, and is observed when the bubble disappears. The impact force to be detected cannot be detected at all. This indicates that the phenomenon of the disappearance of the bubble itself disappears as described above.
[0035]
In the case of another resistor material which is easy to generate defects such as pinholes although an insulating oxide film is formed, an insulator layer 7 having a thickness similar to that of the heating resistor film is formed on the entire surface of the heater. It was confirmed that it was effective when coated on (see FIG. 4). As the thin insulator layer 7, SiO ₂ layer by RF sputtering, Ta ₂ O ₅ layer, Si ₃ N ₄ layers, Si ₃ N ₄ layer by plasma CVD method, or Zorugeruko - Al ₂ O ₃ layer by preparative method Any insulator having good adhesion and covering properties, such as an SOG film often used in a semiconductor process, can be used. Even in this case, the applied power necessary for fluctuation nucleate boiling may be about 1.5 times that in the case of a bare heater when the pulse width is 2 μS, which is that of the prior art having a thick two-layer protective layer. It will be understood that the thermal efficiency is 1/7 to 1/10 of the applied energy in the case of a heater. With this excellent thermal efficiency, the drive circuit can be integrated at a high density on the same Si substrate as the head, and a high-speed full-color ink jet printer can be made with the highly integrated head produced by this. This is as described in Japanese Patent Application No. 06-201985 and other applications.
[0036]
If the thickness of the orifice plate 11 is 80 μm or more, the replenishing ink may be completely restored onto the heating resistor before the ejected ink is detached from the nozzle. In this case, it has been confirmed that a shock wave of cavitation is generated and the life of the heating resistor is shortened, which is a restriction on the design of the head.
[0037]
【The invention's effect】
According to the present invention, the heating resistor is isolated from the electrolyte ink by a very thin thermal oxide layer or further a thin insulating layer thereon, all the individual electrodes are isolated from the electrolyte ink by a heat-resistant partition wall, and the core is separated. By adopting a nozzle structure that does not extinguish bubbles generated by boiling, the thin insulating layer can be protected from cavitation destruction, and these can completely prevent heater corrosion due to almost no decrease in heating efficiency. did it. This indicates that a highly integrated head with high reliability can be manufactured, and that a high-speed full-color ink jet printer can be constructed even if electrolyte ink is used.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view of an ink discharge nozzle of an ink jet recording head which is an example of an ink jet recording head of the present invention.
FIGS. 2A and 2B are cross-sectional views including the peripheral portion of the nozzle shown in FIG.
FIGS. 3A and 3B are the results of observing the movement of bubbles and water droplets due to the difference in nozzle structure. FIGS.
4 is an enlarged cross-sectional view of an ink discharge nozzle in which the heating resistor shown in FIG. 1 is coated with an insulating layer having a thickness similar to that of a thin film resistor.
FIG. 5 is a graph showing a change in resistance of a Ta—Si—SiO alloy thin film resistor in the atmosphere at 500 ° C.
[Explanation of symbols]
1, silicon substrate 2, driving LSI device region 3, thin film heating resistor 4, individual thin film conductor 5, common thin film conductor (ground)
6, through-hole connection portion 7, insulator layer 8, partition wall 9, individual ink passage 10, common ink passage 11, orifice plate 12, ink discharge nozzle 13, discharge ink 14, ink groove 15, ink meniscus 16, bubble 17 Insulation layer

Claims (4)

A Ta-Si-SiO alloy thin film resistor formed on a Si substrate and a thin film conductor partially formed on the Ta-Si-SiO alloy thin film resistor, the Ta-Si-SiO alloy thin film resistor A heating resistor for an ink jet recording head, wherein the body has an electrically insulating coating formed on the surface of the Ta-Si-SiO alloy thin film resistor on which the thin film conductor is not formed by thermally oxidizing the surface of the resistor. There,
The heating resistor for an ink jet recording head, wherein the Ta—Si—SiO alloy thin film resistor having the electrically insulating film formed thereon does not change in resistance even when heated to 350 degrees by pulse heating. The heating resistor for an ink jet recording head according to claim 1 , wherein the electrically insulating film is a homogeneous film having no pinholes. A plurality of heating resistors for ink jet recording heads according to claim 1 or 2 ,
A plurality of ejection nozzles that eject ink droplets in a direction perpendicular to or substantially perpendicular to the heating resistor;
A plurality of individual ink passages provided on the Si substrate corresponding to each of the plurality of discharge nozzles;
An ink jet recording head comprising: a common ink passage provided on the Si substrate communicating with the plurality of individual ink passages. A recording apparatus comprising the ink jet recording head according to claim 3 .

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