JPS6156111B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thin film type thermal head in which a heating resistor and a layer for preventing deterioration of the heating resistor are provided on an insulating substrate. The thermal head used in the thermal printing method has a plurality of dot-shaped heating resistors formed on an electrically insulated flat substrate such as glazed ceramic, and when used, the thermal head is used to record information. Accordingly, printing is performed by passing a current through an electric conductor (electrode) to a necessary heat-generating resistor to generate heat, and bringing this into contact with heat-sensitive recording paper. There are various types of heating resistors, such as thin-film type, thick-film type, and semiconductor type. Among these, thin-film type heating resistors generally improve the responsiveness of the thermal head, consume less power, and It is said to be particularly useful because it has advantages such as excellent heat resistance, long life, and excellent reliability. Tantalum nitride (Ta ₂ N), nichrome, etc. are known as thin-film resistance heating elements, but the former is particularly widely used due to its heat resistance, reliability, high specific resistance, and ease of manufacturing. has been done. Even with this widely used tantalum nitride thin film, under harsh usage conditions where room temperature and high temperature are repeated, tantalum nitride deteriorates in a relatively short period of time due to thermal shock and resists resistance. As the value increases, it is inevitable that the printing performance of the thermal head on heat-sensitive recording paper will deteriorate. For this reason, a thermal deterioration prevention protective layer made of SiO ₂ or the like is usually provided on the resistance heating element made of a tantalum nitride thin film, and if necessary, a wear-resistant layer made of Ta ₂ O ₅ or the like is further provided above it to form a thermal head. I am using it. However, even in a thin film type thermal head having such a structure, the change in resistance during long-term use cannot be said to be satisfactory. In particular, in recent years, in response to the demand for high-speed drive of thermal heads, printing is being performed at high temperatures using large currents in order to shorten the energizing pulse and achieve good color development. However, in this case, the thermal shock to which the heating resistor is subjected becomes even greater, and the large difference in thermal expansion coefficient between Ta ₂ N, which is the heating resistor, and SiO ₂ , which is the protective layer to prevent thermal deterioration, causes A large thermal strain will be generated at the interface, and as a result, the two will separate, accelerating deterioration of the heating resistor, and increasing the resistance value cannot be prevented. Therefore, the inventors of the present invention have conducted various studies to solve the above-mentioned problems of thin film thermal heads using tantalum nitride as a heating resistor, and found that TaNx
When tantalum nitride expressed by (however 0.4≦x≦0.7) is used as a heating resistor and tantalum nitride expressed by TaNy (however 1.0≦y≦2.0) is used as a protective layer to prevent thermal deterioration, the interface between the two It has been found that a thin-film thermal head can be obtained in which substantially no thermal strain occurs, and therefore the heat generating resistor is less likely to deteriorate due to peeling off even in high temperature conditions due to use of a large current. The present invention was completed based on such new knowledge. Figure 1 shows the partial pressure of nitrogen gas, which is a reaction gas, when forming a tantalum nitride thin film on an insulating substrate by the reactive sputtering method, the specific resistance (ρ: curve), and the temperature coefficient of resistance (TCR: 12 is a graph illustrating an example of the relationship between In this case, the nitrogen gas partial pressure is 1.0×10 ^-5 ~ 4.0
×10 ^-5 Torr nitrogen-argon mixed gas (1.5
When a tantalum nitride thin film is formed by a reactive sputtering method using tantalum as ^a target in
It corresponds to TaNx (0.4≦x≦0.7). This thin film has ρ = about 250μΩcm, TCR =
Oppm/deq or so, and has excellent characteristics as a heating resistor. When a tantalum nitride thin film is formed by increasing the nitrogen partial pressure in a nitrogen-argon mixed gas (1.5×10 ^-3 Torr), the nitrogen content in the thin film increases, and as a result, the specific resistance increases and the resistance decreases. The temperature coefficient increases on the negative side. When the nitrogen partial pressure in the mixed gas exceeds 1.0×10 ⁻⁴ Torr, the composition of the tantalum nitride crystal becomes equivalent to TaNy (1.0≦y≦2.0). In this thin film, ρ=600 μΩcm or more and TCR=−1000 ppm/deq or less, making it substantially difficult for current to flow. Therefore, on an insulator substrate
When forming a first tantalum nitride thin film of TaNx (however, 0.4≦x≦0.7) and a second tantalum nitride thin film of TaNy (however, 1.0≦y≦2.0), the first tantalum nitride thin film is a resistance heating element. As a result, the second tantalum nitride thin film functions as a protective layer for preventing thermal deterioration of the resistance heating element. FIGS. 2 and 3 show a conventional thin film thermal head and a thin film thermal head of the present invention in comparison. The second section provides an overview of a known thin-film thermal head.
In the figure, a substrate 1 such as glass or glazed ceramic has an electrode 3 such as an Au/Cr double layer film,
A heating resistor 5 such as a Ta ₂ N thin film, a protective layer 7 for preventing deterioration of the heating resistor 7 such as SiO ₂ , and an abrasion resistant layer 9 such as Ta ₂ O ₅ are sequentially provided. On the other hand, in FIG. 3 showing the thin film type thermal head of the present invention, the electrode 13
on the substrate 11 with a thickness of about 500 to 2000 Å.
A heating resistor 15 having a composition of TaNx (x is as described above), a heating resistor deterioration prevention protective layer 17 having a thickness of approximately 5000 Å to 1.5 μm and having a composition of TaNy (y is as described above), and TiN, Ta as necessary. ₂ Wear-resistant layer 1 such as O ₅
9 is provided. As described above, according to the thin film type thermal head of the present invention in which the heating resistor 15 and the heating resistor deterioration prevention protective layer 17 are composed of specific tantalum nitrides that are similar in composition but different from each other, the following can be achieved. The effect is produced. (i) Since the difference in coefficient of thermal expansion between the heating resistor and the protective layer is small, concentration of thermal strain at the interface between the two can be largely alleviated. (ii) Tantalum nitride has better thermal conductivity than SiO ₂ , so the heat generated in the heating resistor reaches the surface more quickly. Therefore, the thermal head has excellent responsiveness. (iii) In the protective layer, the crystal grain size decreases as the nitrogen content increases;
When further forming a wear-resistant layer of Ta ₂ O ₅ , TiN, etc., a mixed layer of both is likely to be formed at the interface. Therefore, the protective layer and the wear-resistant layer have good compatibility, and both layers adhere strongly to each other, so that concentration of thermal strain is alleviated and thermal shock resistance is improved. The thin film type thermal head of the present invention is usually manufactured as follows. With a known electrode member such as an Au/Cr double-layer film provided on a known insulating substrate such as glazed ceramic, reactive sputtering was performed using tantalum as a target in a nitrogen-argon mixed gas atmosphere according to a conventional method. Then, a tantalum nitride thin film is formed as a heating resistor. The pressure of nitrogen-argon mixed gas is usually 6.0×10 ^-4 ~
About 6.0×10 ^-3 Torr, more preferably 1.0×
It is best to set it at about 10 ^-3 to 2.0×10 ^-3 Torr. Further, the partial pressure of nitrogen is usually about 1.0 x 10 ^-5 to 4.0 x 10 ^-5 Torr, preferably about 1.5 x 10 ^-5 to 2.5 x 10 ^{-5 Torr} . Next, the partial pressure of nitrogen in the nitrogen-argon mixed gas is increased and the same reaction sputtering as above is performed to protect the composition of TaNy (y is the same as above) on the heating resistor of TaNx (x is the same as above). Form a layer. The pressure of the nitrogen-argon mixed gas during the formation of this protective layer is the same as above, but the partial pressure of nitrogen is usually about 1.0×10 ^-4 to 6.0×10 ^-3 Torr,
Preferably, it is about 2.0×10 ⁻⁴ to 1.5×10 ⁻³ Torr. In the present invention, it is not necessary that the heating resistor and its protective layer have the same composition as a whole. For example, the nitrogen content in the heating resistor may be increased gradually or discontinuously from the bottom to the top within the composition range of TaNx (x is the same as above), or TaNy (y is the same as above). The nitrogen content in the protective layer may be increased continuously or discontinuously from the bottom to the top within the same composition range. When manufacturing such a thin film type thermal head, the nitrogen partial pressure in the nitrogen-argon mixed gas may be increased as necessary. Example 1 Using a plasma sputtering device, nitrogen gas partial pressure
Approximately 1000 Å of TaNx was deposited on a 0.3 mm thick glass substrate by reactive sputtering in a nitrogen-argon mixed gas atmosphere (1.5 x ^{10 -3} Torr) of 2.0 x 10 -5 Torr.
A tantalum nitride thin film heating resistor having a crystal structure mainly having (x=about 0.5) is formed. Next, a tantalum nitride protective layer mainly made of TaNy (y=about 1) with a thickness of about 1000 Å was formed at a nitrogen partial pressure of 2.0×10 ^-4 Torr.
Furthermore, in a nitrogen gas atmosphere (1.5×10 ^-3 Torr)
A tantalum nitride protective layer consisting mainly of TaNy (y=about 2) of 8000 Å is formed. Sample obtained as above (referred to as T-1)
Apply pulse power of 60Hz, 5msec to , every 30 minutes.
The power was increased by 0.5 W/mm ² and the rate of change in resistance of the heating resistor was investigated. The results are shown in FIG. Comparative Example 1 After forming a tantalum nitride thin film heating resistor having a composition of TaNx (x = approximately 0.5) and having a thickness of approximately 1000 Å on a glass substrate having a thickness of 0.3 mm in the same manner as in Example 1,
A protective layer made of SiO ₂ with a thickness of about 9000 Å is formed thereon to obtain a sample (designated S-1). The rate of change in resistance of the heating resistor when pulsed power was applied in the same manner as in Example 1 is as shown in FIG. As is clear from FIG. 4, the thin film type thermal head of the present invention has significantly excellent thermal shock resistance because there is less concentration of thermal strain. Example 2 Ta ₂ N with a thickness of 0.1 μm on a glass substrate with a thickness of 0.3 mm
A heating resistor consisting of a heating resistor, a protective layer for preventing deterioration of the heating resistor consisting of TaN with a thickness of 0.5 μm, and a protective layer for preventing deterioration of the heating resistor made of TaN with a thickness of 3 μm.
Wear-resistant layers made of TiN were sequentially formed to produce a thin film type thermal head element according to the present invention. After conducting an accelerated thermal deterioration test by applying a power of 15 W/mm ² for 24 hours to the thus obtained device using pulses of 60 Hz and 5 msec, the rate of change in resistance of the heating resistor was examined. Table 1 shows the results for five devices. Comparative Example 2 0.3 μm thick Ta on a 0.3 mm thick glass substrate
Heat generating resistor made of SiO ₂ , heating resistor deterioration prevention protective layer made of SiO ₂ with a thickness of 0.5 μm, and a thickness of 3 μm
A wear-resistant layer made of TaN--Au (Au content: 3% by weight) was sequentially formed to obtain a thin film type thermal head element according to Japanese Patent Application Laid-open No. 82677/1983. Table 1 shows the results of an accelerated thermal deterioration test conducted in the same manner as in Example 2.

[Table] As is clear from the results shown in Table 1, Example 2
In the thin film thermal head element according to
%, whereas in the thin film thermal head element according to Comparative Example 2, the resistance change rate reached 10% or more.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between nitrogen gas partial pressure during formation of a tantalum nitride thin film, resistivity and temperature coefficient of resistance of the thin film, and FIG. 2 is a cross-sectional view showing an outline of a known thin film type thermal head. FIG. 3 is a sectional view showing an outline of the thin film type thermal head of the present invention, and FIG. 4 is a graph showing the resistance change rate of the heating resistor of the thin film type thermal head obtained in Example 1 and Comparative Example 1. It is. 1, 11... Insulator substrate, 3, 13... Electrode,
5, 15... Heat generating resistor, 7, 17... Protective layer,
9,19...wear-resistant layer.

Claims (1)

[Claims] 1 In a thin film thermal head in which a heating resistor and a protective layer for preventing deterioration of the heating resistor are provided on an insulating substrate, the heating resistor is TaNx (however, 0.4≦×≦0.7).
The protective layer for preventing deterioration of the heating resistor is formed of tantalum nitride shown by TaNv (however, 1.0≦y≦
2.0) A thin film type thermal head characterized by being formed from tantalum nitride.