JPS61237661A - Thermal printer head - Google Patents

Abstract

PURPOSE:To obtain a thermal printer head having a protective film excellent in heat resistance and impact resistance by using a mixture of silicon carbide (SiC) and alumina (Al2O3) as a protective film covering the dot-forming portion of a heating resistor and a conductive electrode. CONSTITUTION:In a thermal printer head 1, a heating resistor 3 is formed on a base plate 2 of ceramics, etc., and a common conductor electrode 5 and a separate conductor electrode 6 are formed on the resistor 3, excluding the dot-forming portion 4. A protective film 7 is formed on the resistor 3 and the electrodes 5 and 6. The film 7 is made of a mixture of SiC and Al2O3 by a method in which the base plate 2 with the resistor 3 and the electrodes 5 and 6 is put in an atmosphere of Ar gas and sputtering is made by using a target formed by bonding alumina plate 9 to a silicon carbide plate 8, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a thermal print head, and particularly to a thermal print head having features in a protective film layer.

(b) Conventional technology In general, in a thermal print head, a heating resistor is formed on a substrate such as a ceramic, and a pair of conductive electrodes are laminated on top of the heating resistor, excluding the dot forming part, and then A Stow layer and a protective film layer are formed to cover the dot forming portion of the resistor and the conductive electrode.

TazOs (tantalum pentoxide) has traditionally been widely used as the protective film layer (wear-resistant film) of this type of thermal print head (e.g., JP-A-56-154974, JP-A-57-102373). ). The Ta206 layer was formed by placing the substrate on which the protective film was to be formed in argon gas containing O2 gas, and performing sputtering using Ta2O as a sintering target.

(c) Problems to be solved by the invention Although the Ta2O film mentioned above has the advantage of excellent thermal shock resistance, on the other hand, the film hardness is about HV700, so it is easily scratched in the running direction and the head Acceleratingly shorten the wear life of

(2) In order to prevent the above (2), the film thickness is increased (C1J11 usually about 10 μm), but this deteriorates the thermal response and adversely affects high-speed printing.

There was a drawback.

In view of the above, an object of the present invention is to provide a thermal print head having a protective film having high film hardness and excellent thermal shock resistance.

(d) Means and operation for solving the problems In order to achieve the above object, the thermal print head of the present invention uses silicon carbide (S i C) and alumina as a protective film.
A mixture of Al1ay3) is used.

Silicon carbide has a high film hardness, but the sputtered film has large internal stress and is prone to cracking.
It is difficult to use it alone as a protective film. but,
By mixing alumina with silicon carbide, internal stress is relaxed and crack resistance is improved, resulting in a film with higher hardness and better thermal shock resistance than tantalum pentoxide alone.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a sectional view of a thermal print head showing an embodiment of the present invention. Rad1 to this thermal print
A heating resistor 3 is formed on a substrate 2 made of ceramic or the like, a common conductor electrode 5 and individual conductor electrodes 6 are formed on the upper part of the heating resistor 3 except for the dot forming part 4, and the heating resistor 3 is further formed on the heating resistor 3. A protective film layer 7 is formed on the conductive electrode 5.3 and the conductive electrode 5.6. This protective film layer 7 is a mixture of silicon carbide and alumina.

This protective film layer 7 is made by placing the substrate 2 on which the heating resistor 3 and conductive electrodes 5.6 are formed in an argon gas atmosphere, and pasting an alumina plate 9 on a silicon carbide plate 8 shown in FIG. 2, for example. It is formed by performing sputtering using as a sputtering target. The mixing ratio is determined by the surface area ratio of silicon carbide plate 8 and alumina plate 9.

The relationship between the area ratio (mixing ratio) of alumina to silicon carbide and the film hardness of the protective film layer 7 formed as described above is as shown in FIG. 3. According to this diagram,
When the area ratio of alumina is 30%, the film hardness is about HV1500. As shown in the figure, an alumina mixing ratio of 20% to 40% is practical.

Now, FIG. 4 shows the thermal shock test results of a thermal print head when the protective film layer 7 is mixed and formed to have a hardness of Hv1250. In FIG. 4, the horizontal axis represents the applied power for each dot, and the vertical axis represents the rate of change in resistance value. Curve a in the figure is for the conventional tantalum pentoxide film, and curves b1 and b2 are for the mixed film of silicon carbide and aluminum of this embodiment. According to this figure, compared to curve a, curve b2 has a resistance change rate of +/- up to a higher applied power.
It is within 10%, which shows that the silicon carbide film of this example has better thermal shock resistance (it is less likely to generate cracks). The thermal print head of this embodiment eliminates the need to provide an anti-oxidation film (e.g. SiO□) between the heating resistor and the protective film, which was conventionally provided, and the thickness of the protective film layer can be reduced to half that of the conventional head. 1 or less.

In addition, in the above embodiment, an alumina plate pasted on a silicon carbide plate was used as a sputtering target for forming the protective film layer 7, but instead of this,
A mixed sintered body of silicon carbide and alumina may be used as a sputtering target.

A) Effects of the Invention According to the thermal print head of the present invention, since the hardness of the protective film is increased, scratches in the running direction do not occur, and therefore the life of the thermal print head is extended. Furthermore, since the hardness of the protective film is increased, the film thickness can be reduced, resulting in improved productivity and improved thermal response. Further, since there is no need to provide an anti-oxidation layer, miniaturization and cost reduction can be realized.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a thermal print head showing an embodiment of the present invention, and FIG. 2 is a view showing an example of a sputtering target used when forming a protective film layer of the thermal print head. FIG. 3 is a diagram showing the relationship between the alumina area ratio and film hardness of the protective film layer used in the thermal print head, and FIG. 4 is a diagram showing the thermal shock test results of the thermal print head. 1: Thermal print head, 2: Substrate, 3: Heat generating resistor, 4: Dot part, 5 and 6: Conductor electrode, 7: Protective film layer.

Claims (1)

[Claims] (1) A heating resistor including a dot portion is formed on a substrate, a pair of conductive electrodes is laminated on top of the heating resistor excluding the dot forming portion, and furthermore, at least the dot forming portion and the conductive electrode What is claimed is: 1. A thermal print head comprising: a protective film layer formed over the thermal print head, wherein the protective film layer is formed of a mixture of silicon carbide and alumina.