JP3461246B2 - Heating element substrate for inkjet recording head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element substrate used for a bubble jet recording head, and more particularly to a heating element substrate which is excellent in durability and mass productivity and is particularly suitable for a long head such as a full line head.

[0002]

2. Description of the Related Art The bubble jet method is capable of high-speed and high-density printing and is suitable for colorization and compactness.
In recent years, it has attracted attention. FIG. 1 shows the configuration in the vicinity of the discharge portion of a conventional typical bubble jet head. In FIG. 1, 1 is a support. The support not only structurally supports the heating element, but also diffuses excess heat generated by the heating element so that the vicinity of the heating section quickly returns to a certain temperature or less after the application of the pulses for foaming and discharging. Must be
High thermal conductivity is required. Further, the smoothness of the heat generating portion is important in order to generate uniform and high-energy-density foaming in the heat generating portion for stable ink ejection, and for that purpose, the smoothness of the surface of the support is also important. . Further, the planarity of the support is also an important factor for forming a fine pattern on the heating element, electrodes, nozzles, and the like. Usually Si
Wafers are often used.

In FIG. 1, reference numeral 2 is a heat storage layer. This portion suppresses the heat generated by the heating resistor during the pulse application from escaping to the support, and plays a role of efficiently acting on the ink. Therefore, it is required to have low thermal conductivity as opposed to the support. Furthermore, since it is in direct contact with the heating resistor, it must have heat resistance and insulation to prevent electrical continuity between individual resistors and electrodes. Usually, it is an inorganic insulating material, especially silicon oxide with low thermal conductivity. Is used.

In FIG. 1, reference numeral 3 is a heating resistor layer (heating resistor). An electric pulse is applied to the heating resistance layer 3 between the electrodes through a common electrode 4 and an individual electrode 4'which are electrically connected to a driving circuit, a power source, etc. (both not shown), and heat required for ink bubbling is generated. . Heat-generating resistors are required to have heat resistance, moderately large specific resistance, and resistance stability.
B2, TaAl, etc. are used. The electrodes 4, 4'usually use Al, Au or the like having a small specific resistance.

Reference numeral 5 in FIG. 1 denotes a protective layer, which shields the electrodes and the heating resistor from the ink, prevents insulation of the conductive ink and electrochemical damage, and also serves as an oxidation preventing layer of the heating resistor. Play a role of. The protective layer is required to have heat resistance, insulation, etc., and silicon oxide,
Silicon nitride or the like is used.

Reference numeral 6 in FIG. 1 is an anti-cavitation layer. It works to protect the heat-generating resistor from cavitation damage that occurs when ink is defoamed. Usually, a metal having a high resistance to cavitation erosion such as Ta is used. Since it comes into contact with the ink at a high temperature, some chemical stability is also required. Further, in order to prevent electrode damage due to pinholes 5 and 6, a protective film (organic protective film or the like) may be formed on the portion excluding the heat generating portion by a coating method. A bubble jet head 10 is provided with a liquid flow path 8 communicating with a recording liquid supply port (not shown) and corresponding to each heating element, and a discharge port 9 on a heating element substrate 7 composed of 1 to 6 etc. Is completed.

The structure of the heating element substrate in the vicinity of the discharge portion is similar to that of a conventional so-called thermal head. However, the point of direct contact with liquid, the point of being exposed to mechanical shock (cavitation erosion) due to repeated foaming and defoaming of ink, and the temperature rise and fall of several 100 to 1000 ° C in a short time of up to several microseconds. The thermal and chemical properties required for exposure to are more severe than those of thermal heads.

The bubble jet head having the above-described structure is manufactured by using a fine pattern forming technique such as photolithography, so that the head has high density (several tens of nozzles / mm) and high integration (several hundreds). nozzle/
Head) is easy and therefore very high quality recording is possible, and the ejection frequency of ink droplets is significantly higher than that of a thermal head (for example, several to several).
Since it is several tens of kHz, it is possible to record at a considerably high speed.
Color compatibility is easy, the head is compact, and the running cost is low. It has many excellent characteristics.

[0009]

As described above, the bubble jet head still has excellent characteristics as described above, but the recording speed is further increased with the improvement of the processing capacity of the computer and the increase of the information amount. Has been desired. Moreover, the increase in recording density makes the speedup even more severe. One of the simplest methods for speeding up recording is to increase the number of nozzles in the head. However, if the number of nozzles of the conventional head is increased and the head is made longer, the following various problems occur.

First, as described above, the conventional support is S
i-wafers have been used. Si wafers are easily available and have high heat resistance and thermal conductivity. High surface smoothness and flatness. The film forming and patterning apparatus and the like which have been conventionally used in semiconductor processes can be used as they are. Further, although it is a base material having many advantages such as a driving IC can be formed in a supporting base,
It has the disadvantage that a long head of 1 chip cannot be obtained.
For 8-inch wafers that are currently generally available, A4
A full line head with a width cannot be obtained with one chip. Although it is possible to obtain one chip by using a larger wafer, a device corresponding to such a wafer is not commonly used at present, and the number of wafers to be obtained is small, and the cost is significantly increased. Therefore, in order to obtain a long head using a Si wafer, it is necessary to configure one head with a plurality of chips (supports) or one line with a plurality of heads. Or, it is not easy to align the head. As the recording density increases and higher quality recording is demanded, the difficulty of this alignment rapidly increases. Therefore, in order to produce a long bubble jet head, a long support instead of a Si wafer is desired.

It is necessary to form a heat storage layer made of a substance having a low thermal conductivity as shown in 2 of FIG. 1 on the support by some method. When a Si wafer is used as a support, the surface of the wafer itself is denatured and thermally oxidized Si.
Although the O2 film can be used as the heat storage layer, when another support is used, a material having insulating properties, heat resistance, and low thermal conductivity, such as silicon oxide, is formed by a method such as sputtering or CVD. It is necessary to form a film on it. Generally, silicon oxide or the like formed by physical vapor deposition, chemical vapor deposition, coating baking, etc. is inferior in film quality such as chemical stability to thermally oxidized SiO2.

The inventors have found that the difference in the film quality of the heat storage layer is
It was sometimes found that the durability of the heating resistor of the bubble jet is greatly affected. When the film quality of the heat storage layer is poor, the resistance value of the heating resistor changes greatly when the head is driven,
It may break early. It is necessary to form a heat storage layer having a film quality as good as possible. On the other hand, the heat storage layer of the bubble jet head for efficient ejection generally requires a thickness of 1.5 to 2 μm or more when silicon oxide or the like is used as its material, although it depends on the driving pulse width. However, at this thickness, the stress of the film has a great influence on the support. For example, if the stress of the film is too large, the support may warp, or the film may peel off without being able to withstand the stress, both of which are serious problems in the manufacturing process.

Therefore, it is necessary to control not only the film quality as the heat storage layer but also the film stress. As the head becomes longer and the corresponding support becomes larger, the importance of film stress control also increases. Generally sputtering or CV
D The film quality of the film obtained by the other method can be improved by increasing the substrate temperature during film formation or forming the film while applying an impact with ions or the like. However, for example, when a film is formed by raising the substrate temperature, a large internal stress is generated when the temperature is returned to room temperature due to a difference in thermal expansion coefficient between the support and the film material, and the support is warped. Occurs. Thus, it is often very difficult to keep the film quality and the film stress appropriately.

Next, the conventional bubble jet head is
As shown in FIG. 1, a protective film made of silicon oxide, silicon nitride, or the like is also provided on the heating element and the electrodes. With such a type of bubble jet head, it is very difficult to completely prevent the occurrence of defects that occur during the formation of the protective film, which is a major factor in reducing the yield during mass production.
This problem becomes more serious as the head becomes longer and the area increases. Further, since the heating resistor heats the ink through the protective film, the thicker the protective film is, the more the power consumption required for ejection increases, and the temperature change of the entire head during driving increases. The change in the temperature of the head leads to a change in the volume of the ejected droplets, which causes density unevenness in the image. Also,
If the drive frequency is increased to support faster recording,
The power consumption in the head is further increased, and the uneven density of the image due to the temperature change becomes more remarkable. This is against the demand for higher image quality of recorded images and is a problem to be solved. JP-A-59-143650 and JP-A-60-109850 describe that the surface layers of the heat-generating resistor and the electrode itself are altered to be inorganic-insulated to form a protective layer. This method is a very excellent method in which it is possible to form a thin protective film without defects, the treatment of a large area is easy, and the process is simple. The inventors of the present invention have previously used T as a heating resistor.
It was found that this method can be utilized more effectively by using an a-Al alloy.

On the other hand, the inventors have found that the problem of the heat storage layer film quality described above becomes more remarkable in the durability of the bubble jet heating element substrate produced by this method.
That is, in the conventional type of bubble jet heating element substrate which does not have a thick protective film such as silicon oxide or silicon nitride but has a thin protective film which is a modification of the heating element or the electrode itself, the quality of the heat storage layer film is good or bad. However, since it is reflected more directly on the durability of the heat generating resistor, the demand for the quality of the heat storage layer film becomes more severe. This is a major obstacle in a long head in which thermally oxidized SiO2 having a good film quality cannot be used as a heat storage layer.

Therefore, the present invention solves the above-mentioned problems in the prior art, and is suitable for a long head capable of high-definition and high-speed recording, and a heating element substrate for a bubble jet head which is excellent in productivity and reliability. It is intended to be provided.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides heat generation by generating heat energy by energization.
Body and a silicon oxide film formed by deposition on a metal support
And forming the heating element provided in the heating portion of the heating element
And an insulating protective layer formed by modifying the material itself,
In a heating element substrate of an inkjet head that foams and ejects ink using the thermal energy, the heating element
A silicon nitride film is formed between the silicon oxide film and the silicon oxide film.
It is configured to. And in the present invention
May form a protective film such as an organic resin on a portion of the heating element other than the heating portion. In the present invention, the
Silicon nitride preferably has a thickness of 0.2 to 1 μm.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The above-mentioned object of the present invention is to directly contact the heat storage layer provided on the support with the heat-generating resistor or the ink as described above, and to chemically, thermally stabilize, insulate and generate heat. This is achieved by forming a plurality of layers including an upper layer formed of a material that places importance on the adhesiveness with the resistor, and a lower layer that has a small thermal conductivity and film stress and is mainly responsible for the heat storage effect. The upper layer may have a thickness such that chemical, thermal stability, insulation, and adhesion are effective, and is usually 0.2 μm.
It is enough if there is more than a certain degree. Therefore, a material having a large film stress can be used. The shortage as the heat storage effect is taken up by the lower layer having a small film stress. Membrane stress for the upper layer,
Since the constraint of chemical and thermal stability can be relaxed for the lower layer, the degree of freedom in selecting the material is widened, and the realistic material can be selected.

The present invention will now be described in more detail by the preferred embodiments. FIG. 2 is an example of a preferred embodiment of the present invention. As the support 1 used for the bubble jet heating element substrate of the present invention, any support may be used as long as it satisfies the above-mentioned characteristics required for the support, but a long one-chip head can be obtained. Examples of materials that can be made large include various metal substrates such as aluminum from the viewpoints of thermal conductivity, processability, cost, and the like. Since the alumina substrate used as the support for the thermal head is a sintered body, it has many recesses in which particles are missing during polishing, and thus is not suitable as a support for a bubble jet head. Further, the glass substrate used for the liquid crystal display is not suitable for a bubble jet head driven at high speed because of its low thermal conductivity.

Next, the heat storage layer 2, which is the most significant feature of the present invention, is formed by a plurality of layers separated as described above. As the lower layer 2a formed on the support side, it is important that the thermal conductivity and the film stress are small, and further, heat resistance to some extent is required. As a preferable material, silicon oxide formed by sputtering or plasma CVD can be used. Since the requirements for film quality such as chemical and thermal stability are not so strict, the substrate temperature during film formation can be kept low. As described above, if the substrate temperature during film formation is increased, large stress is generated due to the difference in thermal expansion coefficient between the support and the film when the temperature is returned to room temperature, and the support is warped, which is not desirable. If the upper layer 2b is not provided and only the material of the lower layer 2a is used to form the entire heat storage layer, the film quality is not sufficient and the durability of the heating resistor deteriorates.

The upper layer 2b of the heat storage layer in the present invention is a layer of a portion of the heat storage layer composed of a plurality of layers which is in direct contact with a heating resistor or a recording material such as ink. The properties required of the upper layer 2b are chemical and thermal stability at high temperature,
Insulation and adhesion to the heating resistor are important. The thickness may be such that these characteristics are effective, and normally a thickness of about 0.2 μm or more is sufficient, so the film stress may be a little high. Further, since the heat storage effect can be taken over by the lower layer 2a, the thermal conductivity does not have to be as low as that of the lower layer. However, also in this case, it is not preferable to increase the substrate temperature during film formation. This is because even if the lower layer is formed at a low temperature, if the temperature is again raised to a high temperature, the stress is relaxed at a high temperature, and when the temperature is returned to room temperature, the stress due to the thermal expansion coefficient becomes large even in the lower layer 2a. This is because the warp and the like will occur. As the upper layer 2b that satisfies the above characteristics at a low substrate temperature during film formation, a silicon nitride film formed by sputtering or plasma CVD can be cited as a preferable material. Although the silicon nitride film has excellent characteristics such as chemical and thermal stability at high temperatures as described above, insulation, and adhesion with a heating resistor, it generally has internal stress of the film as compared with silicon oxide. When the heat storage layer 2 which has a large thickness and requires a thickness of 2 μm or more is formed entirely by itself, problems such as warpage of the support occur. In addition, the thermal conductivity is higher than that of silicon oxide, and the energy efficiency of ejection is reduced. In order to avoid such a problem, it is desirable to suppress the thickness of the silicon nitride film to 1 μm or less at the maximum.

The heat generating resistor 3 and the electrode 4 formed on the heat storage layer 2 formed as described above are capable of forming the insulating protective layer 12 by modifying the surface thereof by a method such as anodic oxidation later. Is desirable. By selecting such a heating resistor or electrode material, the above-mentioned Japanese Patent Laid-Open No.
This is because it is possible to employ a manufacturing method suitable for a long head, which has high thermal efficiency, has few defects, and has a simple process as described in JP-A-9-143650 and JP-A-60-109850. The heat storage layer 2 of the present invention exerts a particularly great effect on a bubble jet heating element substrate produced by such a manufacturing method. Particularly preferable as such a heat generating resistor is a heat generating resistor made of a Ta-Al alloy, and an electrode having Al as a main component. Such heating resistors and electrodes can be formed by a known method such as sputtering or vapor deposition, and can also be patterned by a known method such as photolithography.

As a method for modifying the surface of the heating resistor and the electrode to form the insulating protective layer 5, an anodic oxidation method in an electrolyte solution can be mentioned. The device is simple and suitable for large format processing. Further, forming the coating type protective film 11 of an organic resin or the like on a portion other than the heat generating portion is useful for improving reliability and handling property during the process. In this way, the bubble jet heating element substrate 7 of the present invention is completed.

On the bubble jet heating element substrate 7 obtained as described above, for example, JP-A-62-253457.
The bubble jet head can be manufactured by forming the liquid flow path 8, the discharge port 9 and the like by a known method such as the method described in Japanese Patent Publication No. An ink supply system and a driving device (both not shown) are further connected to the bubble jet head to complete the bubble jet recording device.

[0025]

The present invention will be described in more detail below with reference to examples. [Example 1] In Example 1, the bubble jet head of the present invention was prepared as follows. As the support, an Al substrate (5386 material, size 330 × 150 × 2 mm) manufactured by Shinko North Co., Ltd., the surface of which was mirror-polished, was used. First, as a lower layer of the heat storage layer by RF sputtering on the polished surface. A silicon oxide film was formed to have a thickness of about 2.2 μm, and subsequently, an upper silicon nitride film was formed to a thickness of about 0.3 μm. Further on, this time Ta
T by DC sputtering of composite target of Al and Al
An exothermic resistor layer of an a-Al alloy was formed to a thickness of about 0.25 μm, and subsequently Al to be an electrode was formed to a thickness of about 1 μm also by DC sputtering. Then, the electrodes are patterned first by photolithography and RIE (reactive ion etching), and then the heating resistors are patterned, so that the size of the heating portion is reduced to 20.
× 100μm, pitch 63.5μm pattern A4
It was formed (about 3300 segments) over the width (210 mm).

Then, a mask of photoresist is formed on a portion such as an electrical contact where an oxide film is not desired to be formed by a photolithography technique, and then anodization treatment is performed in an ammonium tartrate aqueous solution with the platinum electrodes facing each other. An insulating protective layer was formed on the surfaces of the electrodes and the heating resistor. Anodization starts with 10 mA / cm ²
When the constant current and voltage reached 100 V, the voltage was changed to the constant voltage and held for 10 minutes. The thickness of the insulating protective layer is about 0.
It is considered to be about 15 μm.

After the anodic oxidation treatment, a resin (Photoneis UR-3100 manufactured by Toray Industries, Inc.) which can be patterned by photolithography is used to form an organic protective layer of about 2 μm except for the heat generating portion and the external electrical connection points. To form a bubble jet heating element substrate. A liquid flow path, a discharge port, a common liquid chamber, etc. are formed on this heating element substrate in accordance with the method described in Japanese Patent Laid-Open No. 253457/1987, and the A4 width has a structure as shown in FIG. I got a recordable bubble jet line head.

The bubble jet head thus prepared was evaluated as follows. a) CST (Constant Stress Test) The ink of the following composition is supplied to the liquid path of the manufactured head, and an external drive circuit is connected, and the width is 10 μs.
While applying the rectangular pulse voltage of ec, the voltage was gradually increased to obtain the voltage (ejection threshold voltage Vth) when the ink starts to be ejected from the ejection port. Next, the ink is removed from the head and a voltage pulse of 1.25 Vth is applied at 2 KHz.
The frequency was applied to measure the resistance change of the heating resistor. Ink composition Water 77 parts Diethylene glycol 20 parts Black dye (CI Food Black 2) 3 parts pH adjuster (CH3COONa) 0.1 parts or less b) Discharge durability test The same Vth as in a) was measured with another head prepared. Then, a voltage pulse of 1.2 Vth is applied to the A4 sheet 1
Ink droplets equivalent to recording for ten thousand sheets were ejected. Before and after this ejection (initial and after ejection of 10,000 sheets), this head is mounted on another recording device to record characters and the like,
The obtained recorded matter was visually evaluated.

(Comparative Example 1) As Comparative Example 1, Example 1 was repeated except that the heat storage layer was formed of only one silicon oxide layer, which is the same as the lower layer of the heat storage layer of Example 1, and the thickness thereof was about 2.5 μm. A heating element substrate for a bubble jet and a bubble jet head were prepared in the same manner as in, and the same evaluation was performed.

Comparative Example 2 In Comparative Example 2, the heat storage layer was formed by only one layer of silicon nitride, which is the upper layer of the heat storage layer of Example 1, and the thickness thereof was set to about 2.5 μm. The Al substrate was largely warped after the film formation, and the subsequent steps could not be performed.

FIG. 3 shows the CST results of the examples and comparative examples. In the embodiment in which the heat storage layer is formed of two layers and silicon nitride excellent in thermal stability is used as the upper layer, the resistance change of the heating resistor is small and the durability against the heat cycle during driving is excellent. Recognize. Table 1 shows the results of the discharge durability test. As is clear from the table, both initially show good recording characteristics, but after the ejection endurance test, the heads of the examples of Comparative Examples still show good recording characteristics. A break has occurred and normal recording cannot be obtained. This is probably due to the difference in chemical and thermal stability between the heat-generating resistor of the heat storage layer and the part in contact with the ink.

[0032]

[Table 1] Here, the symbols indicate the following evaluations. ○ When good recording is obtained × A state where there are nozzles that do not eject and defects such as white streaks appear × × There are many nozzles that do not eject and the image is faint

[0033]

As described above, according to the present invention, the heat storage layer is formed by the upper layer having excellent chemical, thermal stability and adhesiveness and the lower layer having small film stress and thermal conductivity. The heating resistor has excellent durability and does not cause process problems such as substrate warpage or film peeling.
It is possible to obtain a heat generating resistor for bubble gent suitable for a long head and having excellent productivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram in the vicinity of a discharge part of a conventional typical bubble jet head.

FIG. 2 is a configuration diagram in the vicinity of a discharge portion of a bubble jet head of the present invention.

FIG. 3 is a diagram showing CST results of Examples and Comparative Examples.

[Explanation of symbols]

1: Support 2: Heat storage layer 3: Heating resistance layer 4, 4 ': electrode 5: Protective layer 6: Anti-cavitation layer 7: Heating element substrate 8: Liquid flow path 9: Discharge port 10: Bubble jet head 11: Protective film

Claims (3)

(57) [Claims] 1. Heat generated by generating heat energy when energized
Body and a silicon oxide film formed by deposition on a metal support
And forming the heating element provided in the heating portion of the heating element
And an insulating protective layer formed by modifying the material itself,
In a heating element substrate of an inkjet head that foams and ejects ink using the thermal energy, the heating element
A silicon nitride film is formed between the silicon oxide film and the silicon oxide film.
Heating element substrate of the ink jet head, characterized in that that. 2. A portion other than the heating portion of the heating element, the heating element substrate according to claim 1, characterized in that the organic resin protective film is formed. 3. The silicon nitride has a film thickness of 0.2 to 1 μm.
The heating element substrate according to claim 1 , wherein the heating element substrate is m.