JP2990719B2 - Thermal head - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a thermal head used in a thermal recording apparatus, and more particularly, to a thin-film thermal head which has a long life and can operate at high speed.

(Prior Art and Problems) In order to extend the service life of the thermal head, a protective film is required. This protective film has abrasion resistance to prevent the heating resistors and electrodes from being worn by contact with thermal paper, etc., and acid resistance to prevent the heating resistors from reacting with external oxygen and deteriorating. Basically, chemical nature is required. In recent years, there has been a demand for high printing quality and high-speed printing by increasing the density of heating resistors, and furthermore, good thermal conductivity for efficiently transferring the heat of the heating resistors to thermal paper at high speed. Crack resistance to prevent the occurrence of cracks due to thermal shock such as temperature drop, high withstand voltage insulation due to high resistance of the heating resistor to save current, non-reactivity with the heating resistor and electrode material, etc. Functions have been required for protective films.

As a protective film satisfying wear resistance and oxidation resistance, a two-layer structure of Ta ₂ O ₅ as a wear resistant material and SiO ₂ as an oxidation resistant material is known. But this is how the process is only a problem that also increases complexity and processing time, SiO ₂
Also had a problem of poor thermal conductivity. As a further protective film that does not complicate the process, SiC in which Si is mixed at 5 to 70% is known. This is an improvement in oxidation resistance by mixing Si with SiC, which has excellent wear resistance and heat conductivity, but when 70% of Si is mixed, high withstand voltage insulation and electrode materials are used. Non-reactivity with Si deteriorates
%, There is a disadvantage that crack resistance due to thermal shock becomes a problem.

(Means for Solving the Problems) The present invention has been made in view of the above-described problems, and is directed to a thin-film thermal head including a heat storage layer, a heating resistor, an electrode, and a protective film formed on an insulating substrate. In the above, the protective film is
By providing a thin-film thermal head characterized by being made of aluminum containing 25 to 45 atomic% of nitrogen, it is intended to provide a high-speed operable thin-film thermal head having a high-density heating resistor. It is.

Aluminum nitride (AlN) is known as a material having excellent thermal conductivity, and aluminum containing 25 to 45 atomic% of nitrogen also has good thermal conductivity. FIG. 1 shows the sheet resistance and Vickers hardness of a nitrogen-containing aluminum film formed by changing the nitrogen content on a glass plate as physical quantities showing wear resistance and insulation resistance as a protective film of a thermal head. Each film was formed by reactive sputtering using aluminum as the target, with a total gas pressure of 5 × 10 ^-3 Torr, RF
It was formed at about 7.5 μm by changing the nitrogen partial pressure under the condition of electric power of 400 W. The sheet resistance increases with increasing nitrogen content, and even at a nitrogen content of 25 atomic%, 10 ⁸ Ω / □
The above values indicate that the thermal head has sufficient insulating properties as a protective film. Further, the hardness of the film shows a sufficient hardness of about 1500 Hv when the nitrogen content is large, but drops sharply to 1000 Hv or less when the nitrogen content is 20 atomic% or less. That is, in order to obtain sufficient wear resistance as a protective film of the thermal head, a nitrogen content of 25 atomic% or more is required.
It causes cracks.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings based on examples.

In FIG. 2 showing an example of a thin film thermal head,
1 is an insulating substrate made of alumina ceramic or the like, 2 is a heat storage layer made of a material having a low thermal conductivity such as glass, and 3 is a contamination prevention layer made of silicon dioxide or the like, which may be omitted as appropriate. 4 is a heating resistor made of a silicide of a high melting point metal such as tantalum, titanium, chromium, etc., 4a is a heating portion thereof, 5 is an electrode layer made of an aluminum alloy or gold, etc., 6 is 25 to 45 atomic% of nitrogen, particularly preferably Is a protective film made of aluminum containing 30 to 40 atomic%.

Example 1 A pollution prevention layer made of silicon dioxide, a Ti-Si-N-based heating resistor layer, and an electrode layer made of an aluminum alloy were sequentially laminated on an alumina ceramic substrate on which a partial glaze of glass was formed as a heat storage layer by a sputtering method. After that, a heating resistor and an electrode pattern were formed by photolithography. On top of this, a thermal head is created by sputtering an aluminum target in a mixed gas atmosphere of argon and nitrogen to protect aluminum containing 45 atomic% of nitrogen except for the electrode connection with the outside to protect aluminum. did.

Example 2 A thermal head was prepared in the same manner as in Example 1 except that aluminum containing 40 atomic% of nitrogen was used as a protective film.

Example 3 A thermal head was prepared in the same manner as in Example 1 except that aluminum containing 30 atomic% of nitrogen was used as a protective film.

Example 4 A thermal head was prepared in the same manner as in Example 1 except that aluminum containing 25 atom% of nitrogen was used as a protective film.

Comparative Example 1 Aluminum containing 50 atomic% of nitrogen (so-called Al
A thermal head was prepared in the same manner as in Example 1 except that N) was used as a protective film.

Comparative Example 2 A thermal head was prepared in the same manner as in Example 1 except that aluminum containing 20 atomic% of nitrogen was used as a protective film.

 Table 1 shows the test results.

(Effect of the Invention) The protective film of the present invention made of aluminum containing 25 to 45 atomic%, particularly 30 to 40 atomic% of nitrogen, has not only excellent wear resistance and oxidation resistance, but also thermal conductivity and resistance to heat. It has excellent cracking properties, insulating properties, and non-reactivity with the electrode layer. By using this protective film, it is possible to obtain a long-life, high-speed thermal head.

[Brief description of the drawings]

FIG. 1 is a graph showing the nitrogen content dependence of the sheet resistance and Vickers hardness of a nitrogen-containing aluminum film, and FIG. 2 is a structural example of a thermal head using the nitrogen-containing aluminum protective film of the present invention. 1 ... insulating substrate, 2 ... heat storage layer, 3 ... pollution prevention layer,
4 ... heating resistor layer, 5 ... electrode layer, 6 ... nitrogen-containing aluminum protective film

Claims (1)

(57) [Claims] 1. A thin-film thermal head comprising a heat storage layer, a heating resistor, an electrode and a protective film formed on an insulating substrate, wherein the protective film is made of aluminum containing 25 to 45 atomic% of nitrogen. A thin film type thermal head characterized by the following.