JPS6139195B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal printing head for thermal printing on thermal recording media.

A thermal printing head has a structure in which a plurality of heating resistors are arranged as printing elements on a substrate so as to be selectively energized. By arranging and selectively energizing the heat generating resistors, a portion of the thermosensitive recording medium corresponding to the selected heat generating resistor is heated and a coloring reaction is caused. Therefore, since the head and the thermal recording medium are in constant contact with each other, there is less noise during printing, and there are fewer mechanically moving parts, making maintenance easier. Since the heat-sensitive recording medium comes into contact with and slides on the head surface, the contact surface of the heat-sensitive printing head with the recording medium is required to have excellent abrasion resistance.

Conventionally used thermal printing heads have been designed to improve abrasion resistance by providing a surface protective layer of tantalum oxide, silicon carbide, etc. on the metal electrodes and heating element, but the abrasion resistance is not sufficient. As a result, a thick surface protective layer is required, and as a result, the distance between the heating resistor and the heat-sensitive recording medium increases, which adversely affects print quality and other aspects.

The present invention focuses on the high hardness of boron phosphide compound semiconductors, and aims to provide a new thermal printing head that uses boron phosphide compound semiconductors as a surface protective film and is capable of high-resolution, high-speed printing. do.

The present invention will be described in detail below using Examples.

[Example 1] FIG. 1 is a perspective view of the main parts of a thermal printing head in Example 1, and FIG. 2 is a sectional view for explaining the manufacturing process. In the figure, 1 is a sapphire substrate, 2 and 4 are titanium films, 3 is a molybdenum film, and 5 is a boron phosphide compound semiconductor thin film. The thermal printing head shown in FIG. 1 has two metal electrodes made of titanium films 2 and 4 and a molybdenum film 3 formed on a sapphire substrate 1, and boron phosphide between and on the metal electrodes. A compound semiconductor thin film 5 is disposed so that the space between the metal electrodes functions as a heating element and a surface protection film, and the area above the metal electrodes functions as a surface protection film. In general, materials that can be used as heating resistors in thermal printing heads have a specific resistance of 10 ^-4 to ^{10 -2} Ωcm, and these are semiconductors. For example, TaN, Ti-SiO ₂ , Ta
-SiO _2, etc., and these are semiconductors that exhibit the above specific resistance. boron phosphide compound semiconductor,
It's the same.

When adopting the structure shown in FIG. 1, the boron phosphide compound semiconductor thin film 5 functions as a heating element between the metal electrodes, and a portion close to the surface of the heating element (on the opposite side of the sapphire substrate 1) functions as a surface protective film. However, one material can perform both functions.

In other words, since current flows through the shortest distance between the metal electrodes, it functions as a heating element, and since no current flows on the surface, it functions as a surface protective film.

Boron phosphide compound semiconductors are not only hard materials, but also have excellent crack resistance.
〓Ta ₂ O ₅ > SiC > Superior to Si ₃ N ₄ and also in terms of wear resistance
BP〓SiC≫Si ₃ N ₄ > Ta ₂ O ₅ , making it ideal as a thermal printing head.

Next, the manufacturing process of the thermal printing head shown in FIG. 1 will be explained with reference to FIG. First, a titanium film 2 is deposited on a sapphire substrate 1, a molybdenum film 3 is deposited on the titanium film 2, and a titanium film 4 is deposited on the molybdenum film 3 by continuous sputtering. The first layer titanium film 2 has a thickness of about 1000 Å to improve adhesion to the sapphire substrate, the second layer molybdenum film 3 has a thickness of 1 to 2 μm, and the third layer titanium film 4 is made of a boron phosphide compound. It is a growth base for the semiconductor 5 and is for making ohmic contact, and is formed to a thickness of 1000 Å (FIG. 2a). The above three-layer metal film is patterned all at once by plasma etching.
form metal electrodes. In the metal electrode, the molybdenum film 3 mainly functions as a conductive path (the second
Figure b). A boron phosphide compound semiconductor 5 is grown on a metal electrode consisting of a sapphire substrate 1, titanium films 2 and 4, and a molybdenum film 5 and patterned into a predetermined shape, and the boron phosphide compound semiconductor 5 between the metal electrodes is used as a heating resistor. If the boron phosphide compound semiconductor 5 on the metal electrode is used as a surface protective film, the thermal printing head of the present invention shown in FIG. 1 can be obtained.

The present invention can be implemented not only in this embodiment but also in cases where other resistors are used as heating elements.

[Embodiment 2] FIG. 3 is a perspective view of a main part showing another embodiment of the present invention, and FIG. 4 is a sectional view for explaining the manufacturing process.

In FIG. 3, 6 is a glazed ceramic substrate, 7 is a polycrystalline silicon film, 2 is a titanium film, and 3 is a glazed ceramic substrate.
8 is a molybdenum film, and 8 is a surface protection film. As the surface protective film, a comparison will be made between the properties of a boron phosphide compound semiconductor, tantalum pentoxide, silicon carbide, and silicon nitride, and the structure of Example 1.

The manufacturing process of the thermal printing head shown in FIG. 3 will be explained with reference to FIG. First, a polycrystalline silicon film 7 is formed on a glazed ceramic substrate 6 by vapor phase growth, a titanium film 2 is formed on the polycrystalline silicon film 7, and a molybdenum film 3 is formed on the titanium film 2 by continuous sputtering. The first layer of polycrystalline silicon film is a heating element and has a thickness of about 3000 Å.The second layer of titanium film is for improving the adhesion of the molybdenum film to the polycrystalline silicon film and is about 1000 Å thick. The molybdenum film is an electrode and has a thickness of 2μ. (FIG. 4a) Of the three-layer film, the two-layer film of the titanium film 2 and the molybdenum film 3 are etched by sputter etching or chemical etching to expose the heat generating portion 9. Furthermore, the three-layer film of the polycrystalline silicon film 7, titanium film 2, and molybdenum film 3 is etched in stripes by plasma etching or chemical etching to form heat generating parts and electrode parts. (4th
Figure b) A boron phosphide compound semiconductor is grown on the above three-layer film by vapor phase growth, a boron phosphide compound semiconductor is grown by sputtering, tantalum pentoxide or silicon carbide is grown by sputtering, and silicon titanium is grown by plasma vapor deposition. are each formed as a surface protective film. In the case of a boron phosphide compound, the thickness is approximately 3 μm, and in the case of tantalum pentoxide, silicon carbide, and silicon titanide, the thickness is each approximately 10 μm.
(FIG. 4c) Through the above steps, a thermal printing head having the structure shown in FIG. 3 is produced.

Through the above steps, thermal printing heads with different surface protection film materials and thermal printing heads having the structure of Example 1 were prepared, and the characteristics described below were compared. The thermal printing heads used in the experiment were all 8 heads/mm, A4 size, and had the same shape. The applied power is standardized by this dot size.

(i) Thermal response characteristics Figure 5 shows a graph of the thermal response of the surface of the surface protective film, that is, the part that slides on the thermal paper. The temperature rise at the same applied power (1.1w/dot) is compared for each surface protective layer. with graph
BP-1 is the structure of Example 1, BP-2 is the structure of Example 2
This is the case for the structure of This shows that the thermal response of the boron phosphide compound semiconductor is superior to other surface protective films. This is due to the fact that the boron phosphide compound semiconductor has a thin thickness of 3 μm. Furthermore, in the case of the structure of Example 1,
Since the heating element is directly exposed to the surface, the thermal response characteristics are even better.

(ii) About crack resistance Figure 6 shows a graph of crack resistance. In other words, the applied power should be changed from 1.0w/dot to 1.6w/dot.
The crack resistance was compared based on the number of pulses required to generate a crack in the surface protective film at each applied power. This shows that the crack resistance of the boron phosphide compound semiconductor is superior to other surface protective films. This is thought to be due to the thin thickness of the boron phosphide compound semiconductor and the fact that the film was grown at a high temperature, resulting in small thermal strain during operation.

(iii) Regarding wear resistance Figure 7 shows a graph of wear resistance. That is, a tape coated with an abrasive was pressed against the thermal printing head of each surface protective film at a pressure of 10 g/mm ² .
This is a type of accelerated test in which the wear depth of the surface protective film was measured by sliding at a running speed of 1 mm/sec. This shows that the boron phosphide compound semiconductor has excellent wear resistance.

Note that when silicon carbide is used as a surface protective film, if the thickness is set to approximately 3 μm as in the case of boron phosphide compound semiconductors, cracks will occur at the step between the end of the heat generating part and the electrode, making it difficult to use as a practical device. It cannot be used, and the thickness of the surface protective film must be approximately 10 μm or more.

The thermal printing head of the present invention obtained as described above has the advantage that the surface protective film can be made thinner than conventional printing heads, and as a result, the thermal response characteristics are faster and high-speed printing is possible. Summer.

In addition, if the protective film is thick, the temperature of the heating element must be raised due to heat diffusion and heat loss in the protective film, which may shorten the life of the heating element or cause damage to the heating element protective film due to thermal distortion. Furthermore, a reduction in printing resolution, etc. occurs. In contrast, in the present invention, these drawbacks can be eliminated because the protective film is thin.

Further, boron phosphide compound semiconductors are extremely useful as heating elements because the resistance value can be easily adjusted.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part of an embodiment of a thermal printing head according to the present invention, and FIG. 2 is a sectional view for explaining the manufacturing process thereof. FIG. 3 is a perspective view of a main part of another embodiment of the present invention, and FIG. 4 is an explanatory diagram of its manufacturing process. Figures 5 to 7 are
3 is a graph showing specific effects of the present invention. 1...Saphire substrate, 2,4...Titanium film,
3... Molybdenum film, 5... Boron phosphide compound semiconductor thin film.

Claims (1)

[Claims] 1. In a thermal printing head in which a plurality of heat generating resistors are selectively arranged on a substrate and metal electrodes are connected to each of the heat generating resistors, a boron phosphide compound is placed on the heat generating resistors and the metal electrodes. A thermal printing head characterized by being provided with a surface protective layer whose main component is a semiconductor.