JPS6119438B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal head in which the heating resistor is made of two or more metal borides. A thermal head used for thermal print recording has a plurality of heat generating resistors on a substrate with electrical insulation and a smooth surface, such as glass, and an electric conductor for supplying power to the heat generating resistors. established,
Recording is performed by passing a current through a corresponding heating resistor through an electric conductor to generate heat so as to obtain a necessary thermal pattern according to the information to be recorded, and bringing the resistor into contact with a recording medium. Heat generating resistors used therein include conventional thin film heat generating resistors such as tantalum nitride and nichrome, thick film heat generating resistors using silver-palladium, etc., and semiconductor heat generating resistors using silicon semiconductor. Among these, thermal heads using thin film heating resistors have better thermal response, superior heat resistance and thermal shock resistance, longer lifespan, and higher reliability than thick film heating resistors, semiconductor heating resistors, etc. It has the following characteristics. Conventionally, tantalum nitride has been used as a thin film heating resistor because it has relatively excellent heat resistance, high reliability, and has a specific resistance value of 250 to 300μ.
Because it has a relatively high value of Ωcm and has good manufacturing controllability,
Especially often used. However, tantalum nitride is rapidly oxidized when exposed to high temperatures of approximately 300° C. or higher, resulting in a rapid increase in its resistance value, which has the disadvantage of deteriorating print density when printing on recording paper. Generally, to compensate for this drawback, an oxidation-resistant protective layer of silicon oxide (SiO ₂ ) is provided, and then a wear-resistant layer of tantalum oxide (Ta ₂ O ₅ ) is provided on top of the layer for use as a thermal head. When the head was driven for a long time, the change in resistance was not small and was still not completely satisfactory. In particular, as the demand for high-speed thermal heads has increased in recent years, it is necessary to shorten the energizing pulse width of the head to color the thermal paper, which means that the electric power is increased compared to before, and the heating resistor becomes even hotter. lifespan becomes shorter. Therefore, there is a demand for a heating resistor with even higher heat resistance. The present invention aims to improve the above points and provide a thermal head having a thin film heating resistor that is resistant to oxidation and has a stable resistance value.The present invention is characterized by having two or more types of thin film heating resistors. The present invention provides a thermal head using metal boride, a combination with a protective film covering the heating element, and a method for manufacturing the thin film heating resistor. In this heating resistor, two or more types of metal borides are mixed on an atomic scale. A detailed description will be given below with reference to the drawings. FIG. 1 is a sectional view of a main part of an example of the shape of a thermal head applied to the present invention. Reference numeral 1 in the figure is a substrate made of an electrically insulating material such as ceramics, glass, or glazed ceramics. 2 is a thin film heating resistor made of two or more metal borides. Here, two or more metal borides include zirconium boride, hafnium boride, lanthanum boride, chromium boride, titanium boride, tantalum boride, niobium boride, tungsten boride, molybdenum boride, and boride. It contains two or more metal borides selected from vanadium chloride. Reference numeral 3 denotes an electric conductor for supplying power to the thin film heating resistor, which is made of a good electric conductor such as aluminum or gold. Further, 4 is a protective layer for the thin film heat generating resistor and electric conductor, for example, silicon oxide, magnesium oxide, aluminum oxide, tantalum oxide, etc. produced by electron beam evaporation, sputtering, etc., or a multilayer structure using a combination of these is used. This makes it possible to further extend the life of the thermal head. The thin film heating resistor of the present invention can be manufactured by either electron beam evaporation method or sputtering method.
Manufacturing using the electron beam evaporation method involves uniformly mixing two or more types of metal boride powders in the required composition ratio.
Tablets can be made by pressing at a pressure of 100 Kg/cm ² or more, and then vapor-deposited on a substrate that has been kept at a constant temperature in a high vacuum of 1 x 10 ^-4 Torr or more. On the other hand, when manufacturing by the sputtering method, for example, the target can be prepared by mixing metal boride powder at a certain composition ratio on a quartz dish or the like, or in a pressed state. It is easier to control sputtering by using a sintered target using the vacuum hot press described above. Alternatively, another metal boride may be placed partially on the surface of the metal boride disk, and the composition ratio may be used as a target based on the surface area ratio. In either case, 1×10 ^-3 Torr ~ 5×10 ^-1 Torr
This is preferably carried out in an argon atmosphere of
1×10 ^-2 Torr to 1×10 ^-1 Torr is preferable. In addition, heating the substrate to 200°C to 500°C during sputtering or electron beam evaporation improves the adhesion of the metal boride to the substrate, and also has an effect on the stability of the film. . Furthermore, after sputtering or electron beam evaporation, heat treatment is performed at a temperature of 200°C to 650°C in vacuum, air, or an atmosphere of argon gas, etc., so that the resistance value can be controlled to the required value. It also increases stability when used as a thermal head, which has an effect on longevity. The heat treatment temperature is
At temperatures below 200℃, the change in resistance value is very small, so a long heat treatment time is required.On the other hand, at temperatures above 650℃, the resistance value changes rapidly, and substrates such as glass become unusable. Due to usage restrictions or control difficulties, the heat treatment temperature is 200℃.
℃~650℃ is desirable. The heating resistor made of two or more metal borides thus obtained contains oxygen, nitrogen, and carbon as impurities, but this thermal head is stable and resistant to oxidation, compared to conventional thermal head using tantalum nitride. While the maximum power usage limit for heads was 17 to 18W/ ^mm2 , the maximum
It can also be used for power supply of 25 to 25.5W/ ^mm2 . This is also suitable for a thermal head for high-speed printing, in which a large amount of power is applied to the heating resistor to raise the temperature to a high temperature. Furthermore, the specific resistance value of the thin film resistor made of these two or more metal borides is 80μΩcm ~ 5×
You can choose from a wide range of 10 ³ μΩcm, so if you set a high resistance value, you will need less current to generate heat, and the electrodes can be made thinner, which simplifies the manufacturing process and reduces unevenness. It also becomes more resistant to wear. Further, the amount of heat generated by the thin film heating resistor due to the influence of the resistance of the electrode portion can be ignored. Next, it will be explained based on an example. (Example 1) A composition of ZrB ₂ (50 wt%) - HfB ₂ (50 wt%) was hot-pressed at 1300°C on a glazed ceramic substrate that had been thoroughly cleaned in advance, and a total pressure of 5 argon was applied using a high-frequency bipolar sputter. Under conditions of ×10 ^-2 Torr and substrate heating degree of 200℃
A heating element with a thickness of 700 Å was fabricated. This specific resistance value is approximately 420μΩcm, and the area resistance at this time is approximately 600Ω/
It was □. After evaporating titanium and 10 Å aluminum using a 1.5 μm electron beam, selective etching was performed to create a thermal head with a resolution of 4 lines/mm.
Formed A ₁₁ . Next, a thermal head A ₁₂ was formed by depositing tantalum oxide to a thickness of 6 μm as a protective layer on the thermal head A ₁₁ by electron beam evaporation, a thermal head A ₁₃ was formed by depositing aluminum oxide to a thickness of 8 μm, and a thermal head was deposited with magnesium oxide to a thickness of 5 μm.
A ₁₄ and a thermal head A ₁₅ were prepared in which silicon oxide was deposited to a thickness of 1.5 μm and tantalum oxide was deposited in a two-layer structure with a thickness of 6 μm. For comparison, tantalum was targeted by high-frequency bipolar reactive sputtering, with a total pressure of argon and nitrogen of 8 × 10 ^-2 Torr, and a partial pressure of nitrogen of 1
A thermal head _B11 of a tantalum nitride heating resistor with a thickness of 700 Å was fabricated under the conditions of ×10 ^-4 Torr. When this thin film was analyzed by X-ray diffraction, it was found to be Ta ₂ N. Further, the specific resistance value was approximately 245 μΩcm, and the area resistance value at this time was approximately 35Ω/□. Next, the thermal head B ₁₁ is coated with a thickness of 6 μm by sputtering.
B ₁₂ with a thick tantalum oxide protective layer and a 1.5 μm thick silicon oxide film with a 6 μm thick layer on top.
A sample _B13 having a two-layer protective layer provided with a thick tantalum oxide film was prepared. For these thermal heads prepared,
Here are the measurement results of the resistance change rate △R/R×100 (%) when performing an accelerated test by applying a repeated voltage with a pulse width of 6ms and 50Hz and increasing the supplied power by 1Watt/ ^mm2 every 30 minutes. Shown in Figure 2. Here, R is the resistance value before the test, and ΔR is the change in resistance value. The thin film heating resistor A ₁₁ made of a mixture of zirconium boride and hafnium boride produced by sputtering can supply approximately 1.8 times more power per unit area than the tantalum nitride thin film heating resistor B ₁₁ . In addition, by providing a protective layer, the power that can be supplied per unit area is greatly improved, but thin film heating resistors made of a mixture of zirconium boride and haffnium boride are made of tantalum oxide made by electron beam evaporation. Even when only one protective layer of aluminum oxide (A ₁₂ ), aluminum oxide (A ₁₃ ), or magnesium oxide (A ₁₄ ) is used, the thermal head B ₁₃ is superior to the tantalum nitride thin film heating resistor thermal head B 13 with two protective layers. This was much better than the thermal head _B12 , which is a tantalum nitride thin film heating resistor with one protective layer. In addition, a thermal head with a two-layer protective layer of silicon oxide and tantalum oxide on tantalum boride
The A ₁₅ has been further improved. This increase in the maximum power supply means that in the case of constant power driving, deterioration of the heating resistor due to heat generation phenomenon is reduced. Normally, the power supplied when transmitting thermal energy to thermal recording paper varies depending on the contact pressure, but is approximately 11~
14W/mm ² is sufficient, so in the case of tantalum nitride thin film heating resistors, a two-layer protective layer such as a combination of silicon oxide and tantalum oxide is essential, whereas zirconium boride and boron In the case of a thin film heating resistor containing hafnium, printing can be achieved with just one protective layer such as tantalum oxide, aluminum oxide, magnesium oxide, etc., and it can be seen that the life of the resistor can be further extended by having two protective layers. (Example 2) 100% of powder was prepared by thoroughly mixing zirconium boride ZrB ₂ (70 wt%) and titanium boride TiB ₂ (30 wt%).
A tablet pressed at Kg/cm ² or more was prepared and placed on a glazed ceramic substrate that had been thoroughly cleaned beforehand at a temperature of 300℃ and a vacuum of 5×10 ^-6 Torr.
Electron beam deposition was performed to a thickness of 1000 Å. This specific resistance value is approximately 800 μΩcm, and the area resistance at this time is approximately 80
It was Ω/□. Next, on top of this, 10Å of titanium and aluminum
After vapor deposition using a 1.5 μm electron beam, a pattern with a resolution of 4 lines/mm was formed by selective etching to form a thermal head _C11 . Protective layers were formed on this thermal head C ₁₁ by sputtering: a thermal head C ₁₂ of tantalum oxide 6 μm, a thermal head C ₁₃ of aluminum oxide 8 μm, a thermal head C ₁₄ of magnesium oxide 5 μm, a silicon oxide 1.5 μm, and then tantalum oxide 1.5 μm. A thermal head _C15 having a two-layer structure of 6 μm was prepared. These thermal heads were subjected to the same test as in Example 1, and the rate of change in resistance was measured. As a result, the power limits per unit area at which the resistance change rate increases rapidly are 13 W/mm ² for C ₁₁ , 18.5 W/mm 2 for C ₁₂ , 18.5 W/mm ² for C ₁₃ , and 18.5 W/mm ² for C ₁₄ , respectively.
It was 18.5W/mm ² , and 20W/mm ² for C ₁₅ . (Example 3) As metal borides, zirconium boride (ZrB ₂ ), hafnium boride (HfB ₂ ), titanium boride (TiB ₂ ), chromium boride (CrB ₂ ), niobium boride (NbB ₂ ), Select the composition shown in Table 1 from vanadium boride (VB ₂ ), molybdenum boride (MoB), tungsten boride (WB), tantalum boride (TaB ₂ ), and lanthanum boride (LaB ₂ ), A uniform mixture of these metal boride powders was placed on a 5-inch diameter quartz dish and used as a target. Using these targets, sputtering was performed under the same conditions as in Example 1 to produce a heating element with a film thickness of 1000 Å. On top of this, 30Å of titanium and approximately 1.5Å of aluminum
After evaporation with a μm electron beam, a thermal head with a resolution of 4 lines/mm was formed by selective etching. Furthermore, silicon oxide was applied to the thermal head as a protective layer to a thickness of approximately 1.5 μm by sputtering.
Next, a thermal head was prepared in which tantalum oxide was deposited in a two-layer structure with a thickness of 6 μm. The same test as in Example 1 was conducted on the thermal head without a protective film and the thermal head with a protective film, and the rate of change in resistance was measured.

【table】

【table】

[Table] Table 2 shows the power limit values per unit area at which the rate of resistance change rapidly increases at this time. As is clear from Table 2, much better results were obtained than the thermal head using tantalum nitride in the comparative example. (Example 4) Hafnium boride (80 wt.
A sufficiently mixed powder of lanthanum boride (20wt%) and lanthanum boride (20wt%) was placed as a target. A thoroughly cleaned glazed ceramic substrate was subjected to high-frequency bipolar sputtering at a heating temperature of 200° C. and an argon partial pressure of 5×10 ⁻² Torr. Reduce spatter rate to 100Å/
After sputtering at min for 10 minutes, a thin film heating resistor of about 400Ω/□ was obtained. Titanium on top of this
After depositing 100 Å gold with a 1 μm electron beam, a thermal head pattern with a resolution of 4 lines/mm was formed by selective etching. Next, when heat treated in air at 550°C for 10 hours, the resistance value of the heating resistor increased from 40Ω/□ to 75Ω/□. Tantalum oxide (Ta ₂ O ₅ ) is used as a protective film on this heating resistor.
sputtered to a thickness of 6 μm and attached to a thermal head.
Got _D12 . For comparison, a thermal head _D11 obtained by removing the heat treatment from the above process was also prepared. 6ms at 50Hz for these thermal heads,
Figure 3 shows the resistance change rate measurement results when a 1 Watt/mm ² square wave was continuously applied. The resistance change rate of _D11 was 10% or more after 5×10 ⁸ pulses were applied, whereas it was 8% for _D12 , and the resistance change was reduced and stabilized by heat treatment. (Example 5) When the heat treatment in Example 4 was changed to 650°C in Ar for 2 hours, the resistance changed from 40Ω/□ to 38Ω/□. Here, tantalum oxide (Ta ₂ O ₅ ) is used as a protective film.
A thermal head _D13 was obtained by sputtering 6 μm. Here, the same durability test as in Example 4 was conducted. The results are shown in FIG. 3, and the results were better than those of Example 4, and the resistance change rate was about 3% even when 5×10 ⁸ pulses were applied.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of an example of the shape of a thermal head according to the present invention. FIGS. 2 and 3 are characteristic diagrams showing the effects of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Thin film heating resistor, 3... Electric conductor, 4... Protective layer.

Claims (1)

[Scope of Claims] 1. A thermal head having a substrate, a heating resistor formed on the substrate, and an electric conductor for supplying power to the heating resistor, wherein the heating resistor is made of zirconium boride, Hafnium, lanthanum boride, titanium boride, tantalum boride, niobium boride, tungsten boride, molybdenum boride, chromium boride,
A thermal head comprising two or more metal borides selected from vanadium boride. 2. The thermal head according to claim 1, wherein the heating resistor is covered with a silicon oxide thin film. 3. The thermal head according to claim 1 or 2, which has a tantalum oxide protective film. 4. The thermal head according to claim 1 or 2, which has a protective film of aluminum oxide. 5. The thermal head according to claim 1 or 2, which has a protective film of magnesium oxide.