JPS6032586B2 - thin film thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film thermal head used in various types of heat-sensitive recording.

A thin film thermal head has a plurality of heating resistor films as printing elements provided on an insulating substrate, and usually has a structure in which electricity can be selectively applied.

In this printing method, heat-sensitive recording paper is placed in contact with a thermal head, and a predetermined portion of the heat-sensitive recording paper is heated and colored by selectively energizing the heating resistor film in pulses. In order to perform continuous printing, the heat-sensitive recording paper comes into contact with and slides on the heat-generating resistor film, and for this purpose, a wear-resistant protective film is usually provided on the heat-generating resistor film. Of course, this wear-resistant protective film is required to be sufficiently hard, but it is also possible for the wear-resistant protective film to crack or deteriorate due to thermal stress caused by pulse current application to the heat-generating resistive film. Oxidation of the heating resistor film due to the diffusion of oxygen must also be sufficiently considered. For this reason, it has also been proposed to interpose an oxidation-preventing film between the wear-resistant protective film and the heating resistor film. FIG. 1 shows the main structure of an example of such a thin film thermal head.

Reference numeral 1 denotes an insulating substrate such as glazed alumina, on which a Ta2N film 2 is provided as a heating resistor film, and a Cr-Au film 3 is provided as an electrode film for conducting current to this Ta2N film. On top of that, Si0 is used as an anti-oxidation film.
A Ta2Q film 5 is provided as a wear-resistant protective film with the two films 4 interposed therebetween.

Although Ta2058 is hard, it does not have the function of preventing oxygen diffusion, so the Si02 film 4 is interposed therebetween. However, in such a structure, since the heating resistor film, the anti-oxidation film, and the wear-resistant protective film are each made of different materials, it is difficult to ensure sufficient adhesion strength at each interface.

Therefore, when the heating resistor film and its surroundings are heated by application of a current pulse, stress is concentrated at each interface, resulting in a drawback that peeling or cracking is likely to occur along the interface. Furthermore, hard materials are generally strong against compressive stress and weak against tensile stress. Especially Ta20 obtained by sputtering method
5 membrane has a large tensile stress within the membrane of about 8×1 to 9 d skin e/, which makes it easy to generate cracks. Ta
When the 2Q film is cracked, the Si02 film is also cracked almost simultaneously, and the heating resistor film is rapidly oxidized due to the intrusion of oxygen, making it impossible to record. An object of the present invention is to provide an inexpensive and highly reliable thin film thermal head that eliminates the above-mentioned drawbacks.

In this invention, the wear-resistant protective film is constructed by alternately laminating a plurality of thick insulating layers and hard insulating layers.

In this case, the plurality of hard insulator layers are arranged so that they become thicker as they approach the heating resistor film side, and the hard insulator layers are arranged so that they become thicker as they get closer to the surface. Make sure that the hard insulator layer is on top. The soft insulating layer has the function of relieving stress, and the hard insulating layer has wear resistance. Therefore, according to the present invention, a highly reliable thin film thermal film that can sufficiently withstand the stress during thermal recording can be created by stacking the wear-resistant protective film in such a way that there is no sudden change in the material inside the protective film as described above. You will get the head. FIG. 2 shows the main structure of an embodiment of the present invention.

In the figure, turtle 1 is an insulating substrate such as glazed alumina with a glass layer of about 60 m, on which a Ta-Si02 film 12 with a thickness of 0.4 m is provided as a heating resistor film. Cr-A with a thickness of 0.5 m is used as an electrode film to conduct electricity.
A U film 13 is provided. Then, on top of this, as a wear-resistant protective film, a Ta2Q layer 14,0
. 5 Am thick Sj02 layer 1 5, 0.5 Am thick Ta
A 205 layer 142, a 0.1 rm thick Si02 layer 152, and a 5 m thick Ta2Q layer 143 are sequentially laminated.

Such a protective film is made of, for example, Ta205 target and S
This can be easily obtained by using a two-pole sputtering apparatus in which a j02 target is placed on the cathode in the same sputtering chamber, and by switching the targets and alternately discharging them. According to this example, the top hard Ta205 layer 143 exhibits excellent wear resistance.

In addition, a soft Si02 layer 1 5,,1 as a stress relaxation layer
Since the layers 52 are laminated so that the thickness increases toward the inside, the adhesion between each layer is strong and the occurrence of cracks can be effectively prevented. The improvement in crack resistance is due to the thermal stress generated between the substrate and the wear-resistant protective film due to the soft Si02 layer 16,
, 1 52 and is gradually transmitted to the surface side. In addition, in this embodiment in which the heating resistor film is a Ta-Si02 film, the portion that is in direct contact with it is Ta-Si02 film.
The 2Q film 14 is advantageous in increasing the adhesion force. Moreover, since it is easy to manufacture, it is inexpensive. FIG. 3 shows the results of an energization life test using pulses with an interval of 2 sec and a width of 1.9 h sec and maintaining the temperature at 450 oo.

Characteristic B is obtained from the thin-film thermal head of the above example, and characteristic A is obtained by interposing a Si02 film of 1 m thick as an oxidation prevention film on which a Ta205 film of 5 m thick is interposed.
A thin film thermal head using the same materials, shape, and manufacturing conditions as in the above embodiments can also be obtained, except that the film is provided as a wear-resistant protective film. The slopes of the resistance change rates for characteristics A and B are the same, and this is thought to be due to oxidation of the surface of the heating resistive film due to oxygen diffusion during wear-resistant protection. However, it can be seen that the value of the rate of change of characteristic B is suppressed to be about one order of magnitude smaller than that of characteristic A. Also, characteristic A is 1 e
Although the resistance value shows a rapid increase after passing c, it has been confirmed that this is the result of cracks occurring in the wear-resistant protective film. As explained above, according to the present invention, an inexpensive and highly reliable thin film thermal head is realized by alternately stacking a plurality of sensitive insulator layers and hard insulator layers as wear-resistant protective films. can do.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the main parts of an example of a conventional thin film thermal head, and Figure 2 is a sectional view of the main parts of a thin film thermal head according to an embodiment of the present invention. It is a diagram showing a comparison with a conventional example. 1 1... Insulating substrate, 1 2... Ta-Si02 (
heating resistor film), 13...Cr-Au film (electrode film), 14
, ~143...Ta205 layer (hard insulator layer), 16.
, 152...Si02 layer (soft insulator layer). Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. A thin film thermal head having a heating resistor film and an electrode film for supplying electricity to the heating resistor film on an insulating substrate, and further having a wear-resistant protective film on the surface thereof, wherein the wear-resistant protective film is , Si
A plurality of O_2 layers and Ta_2O_5 layers are alternately stacked such that the SiO_2 layer becomes thicker as it approaches the heating resistor film, and the TaO_5 layer becomes thicker as it approaches the surface, and the top layer is A thin film thermal head characterized in that it has a Ta_2O_5 layer. 2. The thin film thermal head according to claim 1, wherein the heating resistor film is a Ta-SiO_2 film.