Thermal head

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a thermal head used in an inkjet printer, a thermal transfer printer, or a thermal printer.

【0002】

[Previous technology]

Conventionally, this type of thermal head has been disclosed in Japanese Patent Application Laid-Open No. 61-260604, and the structure of the thermal head and a cross-sectional view of a roller are shown in FIG.

【0003】

In FIG. 5, in this thermal head, a resistor 32 is formed on the substrate 31, and a conductor 34 is formed on the resistor 32 in addition to the portion serving as the heat generating portion 33. Further, the surface of the resistor 32 at the heat generating portion 33 is covered with the anodic oxide film 35, and the anodic oxide film 35 and the conductor 34 are further covered with the protective layer 36. The thermal paper 37 is pressed against the protective layer 36 on the heat generating portion 33 by the rubber roller 38 and recorded.

【0004】

In a thermal head having such a structure, when the conductor 34 is energized, the resistor 32 at the heat generating portion 33 is heated and dots are printed on the thermal paper.

【0005】

Further, another conventional thermal head is disclosed in Japanese Patent Application Laid-Open No. 60-109850, and a cross-sectional view of the structure of the thermal head is shown in FIG.

【0006】

In FIG. 6, the thermal head forms a heat insulating layer 42, a resistor 43 and a conductor 44 on a silicon substrate 41, removes the conductor 44 above the portion that becomes the heat generating portion 45, and removes the resistor 43 and the conductor 44. , 44'is anodized to form tantalum pentoxide 46 and aluminum oxide 47, 47'on the surface. Further, a barrier 49,49'and an orifice plate 50,50'are adhered onto the thermal head via an adhesive layer 48,48'.

【0007】

In a thermal head having such a structure, when conductors 44 and 44'are energized, the resistor 43 at the heat generating portion 45 heats up, the ink on the thermal head (not shown) boils, and the ink comes from the orifice 51. It is ejected and dots are printed on the printing paper (not shown).

【0008】

[Problems to be Solved by the Invention]

In the thermal head described in JP-A-61-260604, the resistor 32, the conductor 34, and the protective layer 36 are formed by sputtering, so that the sputtering process is required three times. This sputtering process has a problem that the cost is high because the equipment and the target for sputtering are expensive.

【0009】

Further, although the thermal head used in the thermal printer has been described as an example, the thermal head of the inkjet printer has the same structure. For inkjet printers, the thermal head is placed in an ink atmosphere. Aluminum, copper, or the like is used for the conductor 34, which corrodes when in contact with ink. Therefore, the protective layer 36 needs to prevent the infiltration of ink. Although the protective layer 36 is formed by sputtering, the sputtering film is microscopically porous, and it is necessary to increase the film thickness in order to use the sputtering film as the protective layer. Therefore, since the conventional thermal head has a thick protective layer, the heat capacity of the protective layer portion is large, the thermal responsiveness is poor, the printing speed cannot be increased, and the input power must be increased. There was a problem that the power consumption was large.

【0010】

For example, in the case of a thermal head having the above structure, in order to eliminate the influence of pinholes in the protective layer, a protective layer with a thickness of 1.5 μm is required, and at this time, silicon with a thermal oxide film of 1.35 μm as a substrate. When a wafer was used and silicon nitride was used as the protective layer, the thermal response was about 10 kHz, and the input power to the heat generating part required 1000 W / mm2 to generate bubbles.

【0011】

Further, in the thermal head described in Japanese Patent Application Laid-Open No. 60-109850, the sputtering process is performed twice for the resistor 43 and the conductor 44, and the cost is low, but there are the following problems. That is, the surface of the thermal head is covered with tantalum pentoxide 46 and aluminum oxide 47,47', but since they are different substances and do not chemically bond with each other, microslits occur at the boundaries B and B'of the two. It is easy, and since thermal stress is generated at the boundary when the thermal head is driven, ink infiltrates from the boundary and the boundary is destroyed, and the durability is short.

【0012】

Further, since the resistor 43 and the conductors 44, 44'are different substances, the optimum anodizing conditions are different for each, but in the case of this thermal head, anodizing is performed at the same time, so that the optimum anodic oxide film can be formed for both. There was a problem that it was difficult. For example, in the case of a thermal head having this structure, the durability was about 106 pulses, and the fracture occurred at the boundary between the two, B and B'.

【0013】

Therefore, the present invention solves such a problem, and an object of the present invention is to provide a thermal head capable of improving the durability of the thermal head, low cost, low power consumption, and high-speed printing. And.

【0014】

[Means for solving problems]

In order to achieve the above object, the thermal head of the present invention continuously connects a heat generating portion defined in a predetermined region on the insulating substrate, a conductor formed on the substrate with the heat generating portion interposed therebetween, and the heat generating portion and the conductor. The surface covering the surface is composed of an anodized resistor.

【0015】

[Example]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a thermal head showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view of XX'of the thermal head of FIG.

【0016】

In the figure, 0.5 μm of aluminum is formed by sputtering as a conductor 3 on a silicon substrate 1 having a thermal oxide film having a film thickness of 1.35 μm on the surface, and the portion that becomes the heat generating portion 2 and the adjacent conductor are formed by a photolithography process. The part between them is removed to form conductors 3, 3 ́, and a conductor pattern like the area surrounded by the broken line in Fig. 1 is formed.

【0017】

Then, 0.25 μm of tantalum having a volume resistivity of a certain size as a resistor 4 and having excellent heat resistance is formed on the conductor 3 by sputtering. The resistor 4 is formed by removing the portion between the resistor 4 and the adjacent resistor by a photolithography process so as to continuously cover the conductors 3, 3 ́ and the heat generating portion 2, and the region surrounded by the solid line in FIG. Form a resistor pattern like this.

【0018】

Next, when 147 V is applied to the surface of the resistor 4 as an anode in a 0.1% aqueous phosphoric acid solution and the surface of the resistor 4 is anodized, an anodic oxide film 5 of tantalum pentoxide is formed as a protective layer by 0.3 μm. At this time, the thickness of the resistor 4 that has not been anodized is 0.1 μm.

【0019】

In a thermal head having such a structure, when a voltage is applied to the conductors 3, 3 ́, a current flows through the conductors 3, 3 ́ and the resistor 4, and the heat generating portion 2 has no conductor and only the resistor has a high resistance value. Because of this, heat is generated in the heat generating section 2, and the ink (not shown) on the thermal head is heated and boils, which causes bubbles to be generated and the ink to be ejected onto the printing paper (not shown). Print.

【0020】

Here, in the embodiment of the present invention, the sputtering process is performed twice for the conductor 3 and the resistor 4, which is inexpensive. In addition, the input power to the heat generating unit 2 required to generate bubbles is 650 W / mm2, which is low power consumption.

【0021】

Furthermore, the anodized film 5 of the resistor tantalum is stoichiometrically made of tantalum pentoxide (Ta2O5) and is extremely dense, so the film thickness of the resistor 4 that has not been anodized is 0.1 μm or more. All you need is it, and it can be made very thin. As a result, it can be driven at a high speed of 20 kHz or more.

【0022】

Further, since the material to be anodized is only tantalum, which is a resistor material, it can be carried out under the optimum conditions suitable for this, and the conductors 3, 3 ́ and the heat generating portion 2 have a resistance whose surface is anodized. Durability is improved because it is continuously covered with the body and there are no discontinuities. In the case of this example, a thermal head having a durability of about 107 pulses was obtained. This is about 10 times more durable than conventional thermal heads.

【0023】

In this embodiment, the case of aluminum as the conductor material has been described, but the same effect can be obtained with other materials such as copper, aluminum-copper, and aluminum-silicon. Further, although tantalum is used as the resistor material, the same effect can be obtained by using a material such as tantalum-aluminum, tantalum nitride, titanium, niobium or a compound containing these.

【0024】

It is better to incline the end of the conductor as shown in FIG. 2, which is possible by controlling the processing time and the adhesive force between the resist agent and the conductor during the photolithography process of the conductor.

【0025】

Further, as another embodiment of the thermal head of the present invention, as shown in FIGS. 3 and 4, when a pulse of 107 or more is applied on the anodized film 5 of the thermal head of FIG. 1 described above, heat is generated by cavitation. A cavitation resistant layer 6 is provided to prevent the portion 2 from being destroyed.

【0026】

The cavitation-resistant layer 6 is formed by sputtering tantalum so as to cover the entire surface of the heat generating portion 2 and the anodized film 5. In this embodiment, tantalum was used as the material constituting the cavitation resistant layer 6, but the same effect can be obtained by using titanium. Further, since the cavitation-resistant layer 6 is formed on an anodized film which is an insulator and electrical short-circuits between conductors do not occur, pattern formation after sputtering becomes unnecessary. As a result, the thermal head can be manufactured at low cost.

【0027】

In this example, as a result of applying tantalum as the cavitation resistant layer 6, the durability of the thermal head with respect to the film thickness of tantalum is the same as that of the above-mentioned example when the film thickness of tantalum is 0.2 to 0.8 μm. Compared to that, it improved more than 5 times.

【0028】

However, if the film thickness of the tantalum is made too thick, the film stress increases, which causes a decrease in the adhesive force of the cavitation resistant layer 6 to the substrate and also increases the cost. Therefore, the cost and durability of the thermal head are increased. The optimum tantalum film thickness was 0.5 μm, and the durability of the thermal head at that time was 108 pulses, which was 100 times higher than that of the conventional thermal head and 10 times higher than that of the above embodiment.

【0029】

Further, although the thermal head of the present invention has been described for an inkjet printer, it can be sufficiently applied to a thermal transfer printer and a thermal printer.

【0030】

[Effect of the invention]

As described above, in the present invention, the heat generating portion defined in the predetermined region on the substrate, the conductor formed on the substrate with the heat generating portion interposed therebetween, and the surface that continuously covers the heat generating portion and the conductor. Since the anodized resistor is provided, the durability of the thermal head can be improved, and high-speed printing can be performed at low cost and low power consumption.

【0031】

Further, by providing the cavitation resistant layer on the anodized film, the durability of the thermal head can be further improved.

[Simple explanation of drawings]

[Figure 1]

It is a top view of the thermal head which shows one Example of this invention.

[Figure 2]

It is XX'cross-sectional view of the thermal head of FIG.

[Fig. 3]

It is a top view of the thermal head which shows the other embodiment of this invention.

[Fig. 4]

It is YY'cross-sectional view of the thermal head of FIG.

[Fig. 5]

It is a cross-sectional view of the structure of a conventional thermal head and a roller.

[Fig. 6]

It is sectional drawing of another conventional thermal head.

[Explanation of symbols]

1 Silicon substrate 2 Heat generating part 3,3'conductor 4 resistor 5 Anodized film 6 Cavitation resistant layer