JPS5946791B2 - thermal head - Google Patents

Description

[Detailed description of the invention] The present invention relates to a thermal head using boride.

A thermal head is a device that records data by installing a plurality of electrical resistance heating elements and an electrical conductor for supplying power to the resistance heating elements on a substrate having electrical insulation properties and a smooth surface, such as glass. Recording is performed by passing a current through an electric conductor through a corresponding resistance heating element to generate heat so that a necessary thermal pattern can be obtained according to the information to be generated, and the resistive heating element is brought into contact with a recording medium.

Conventional resistance heating elements used therein include thin film resistors made of tantalum nitride, nichrome, etc., thick film resistors made of silver-palladium, etc., and semiconductor resistors made of silicon semiconductor. Among these, thermal heads using thin film resistors have characteristics such as better thermal response, superior heat resistance and thermal shock resistance, longer life, and higher reliability than thick film resistors, semiconductor resistors, etc. have. Conventionally, this thin film resistor is
Tantalum nitride resistors are particularly widely used because they have excellent heat resistance, are highly reliable, have a relatively high specific resistance value of 250 to 300 μΩ, and have good manufacturing controllability. However, the sheet resistance of a tantalum nitride thin film resistor is usually around 50Ω/□, and even when it is made especially large for a thermal head, it is around 150Ω/□, and in order to further increase the resistance value, it must be trimmed. However, there are drawbacks such as complicating the manufacturing process and adversely affecting the service life.

As described above, tantalum nitride thin film resistors cannot have a large sheet resistance, so in order to supply enough power to heat the resistor, a large current is inevitably required, and the resistance value of the electrical conductor becomes a problem.

In other words, since the resistance value of the electrical conductor cannot be ignored compared to the resistance value of the thin film resistor, the amount of heat generated by each resistor will differ due to the difference in the distance between each electrical conductor connected to the resistor.
A difference in density occurs in the recorded pattern, resulting in poor recording quality. Furthermore, if the size of the thin film resistor is reduced in order to increase the recording density, the sheet resistance value of the thin film resistor remains unchanged and only the resistance value of the electrical conductor increases, so power consumption in the electrical conductor becomes a problem. If the thickness of the electrical conductor is made extremely large in order to avoid this, major structural problems will occur. In addition, the large current also causes disadvantages such as the need to increase the capacity of the heating power source, switching circuit, etc.
Furthermore, compared to thin film resistors such as nichrome and tungsten, tantalum nitride thin film resistors have superior heat resistance and reliability, but in terms of oxidation resistance, they oxidize rapidly at temperatures above about 3000C, and their resistance value decreases. There is a drawback that the amount increases rapidly and the print density deteriorates. Generally, in order to compensate for this drawback, an oxidation-resistant layer of silicon oxide (SiO2) is provided, and a wear-resistant layer (a tantananoyl oxide of Ta2O5) is provided on top of that for use in thermal heads, which increases the number of steps, increases costs, and increases management costs. Furthermore, when the energizing pulse was shortened to speed up printing, there was a problem that the conductivity of the heat generated by the thin film heating element to the recording medium deteriorated. The resistance heating element for a thermal head described in Japanese Patent No. 52-109947 includes Ti, MO, W, V, and Nb.
, Zr, Ta and other silicides, carbides, borides, nitrides, and low resistance hard heat-resistant materials such as nichrome and cartan; oxides such as SlO2, ZrO2, ThO2, and MgO, glass, and nitrides such as Si3N4 and AIN. It is a mixture of any one of high-resistance elemental elements such as Si or an electrically insulating material that is a mixture thereof. Conventionally, it was thought that in order to increase the resistance value, it was necessary to mix the resistor material with a high-resistance material.

The resistance heating elements for thermal heads described in Japanese Patent Application Laid-open Nos. 52-109947 were also developed based on the above concept. However, when a resistor material and a high-resistance material are mixed, the specific resistance changes greatly due to slight fluctuations in the mixing ratio and mixing state, which poses a major problem in the reproducibility of the resistance value.

An object of the present invention is to provide a thermal head that improves the above points, and is characterized by a thermal head that uses boride as an electrical resistance heating element, and further includes a protective film that covers the heating element. It is a combination of

A detailed description will be given below with reference to the drawings.

FIG. 1 is a sectional view 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 ceramic glass or crystal ceramics. 2 is an electrical resistance heating element made of a boride thin film resistor.

3 is an electric conductor for supplying power to the thin film resistor;
It is made of a good electrical conductor such as aluminum or gold.

Borides used in the thin film resistor include zirconium boride, lanthanum boride, titanium boride, etc., and electrical resistance heating elements are formed on the substrate by sputtering or electron beam evaporation using these materials. be. For example, zirconium boride thin film resistors are made by sputtering electron beam evaporation, ion plating, flash evaporation, CVD methods, etc., but zirconium boride thin film resistors formed by sputtering or electron beam evaporation are
0~5×103μΩ? It is possible to change the specific resistance within the range of 250
~300μΩ? However, it is possible to have a resistance value of more than twice that, making it an extremely good resistor as a thermal head. FIG. 2 is a sectional view of a main part of another example of the shape of the thermal head applied to the present invention. In the figure, parts similar to those shown in FIG. 1 are given the same reference numerals. Reference numeral 4 designates a protective layer for the thin film resistor and electric conductor, for example, magnesium oxide, aluminum oxide, tantalum oxide, etc., which can further extend the life of the thermal head. A plurality of thermal heads having the shapes shown in FIGS. 1 and 2 described above can be arranged side by side and used for facsimile printing, etc. Next, an explanation will be given based on an example.

(Example 1) A sample of zirconium boride, ZrB2, was evaporated at 1200A onto claest ceramics using an electron beam evaporator at a vacuum degree of about 2 x 10-5 mmHg.

The sheet resistance value at this time was 60Ω/mouth. For comparison, tantalum was targeted by high-frequency bipolar reactive sputtering, and the total pressure of argon and nitrogen was 3 x 10-2 Hg, and the partial pressure of nitrogen was 1 x 10-4 m7!
A thermal film with a thickness of 1200A was prepared under LHg conditions. When this thin film was analyzed by X-ray diffraction, it was found to be Ta2N. Also, the sheet resistance value was 20Ω/mouth. For the thermal head created in this way -
The rate of change in resistance (g) when heated at a constant temperature (30'C, 4O'C, 5OO'C) for a long time was measured, and the results are shown in FIG. In the figure, the vertical axis is the resistance change rate, the horizontal axis is the heating time, A1 is zirconium boride at 300°C, A2 is zirconium boride at 400°C, A3 is zirconium boride at 500°C, B1 indicates tantalum nitride at 300°C, and B2 indicates tantalum nitride at 4000C. As is clear from the figure, the resistance value of the thermal head using the zirconium boride thin film resistor according to the present invention hardly changed at 300°C and 400°C.

On the other hand, in the thermal head using tantalum nitride as a comparative example, oxidation progressed considerably over time even at 300° C., and the resistance value changed. When actually used as a thermal head, it generates heat of 300° C. or more, so when a zirconium boride thin film resistor is used in a thermal head, it generates stable heat with a much longer lifespan than tantalum nitride. (Example 2) Thermal heads A and l having the zirconium boride thin film prepared in Example 1, and the thermal heads provided with protective layers of tantalum oxide, aluminum oxide, and magnesium oxide, respectively, by electron beam evaporation Al2, A
13 and Al4 were prepared.

The film thicknesses of these protective layers are a magnesium oxide film of 4μ, an aluminum oxide film of 10μ, and a tantalum oxide film of 6μ.
It was hot. For comparison, a thermal head Bll having a tantalum nitride thin film resistor of Example 1, a thermal head B and 2 in which a tantalum oxide protective layer with a thickness of 6 μm was provided on the thermal head, and a silicon oxide film provided with a 2 μm thick silicon oxide film and 6 on top
Bl3 having a two-layer protective layer provided with a μ-thick tantalum oxide film was prepared.

The results of measuring the change in resistance change rate when a voltage with a pulse width of 6 ms and 50 Hz was repeatedly applied to these prepared thermal heads, and the supplied power was increased by 1 watt/M77 l every 30 minutes (ΔR). R is shown in FIG.

A zirconium boride thin film resistor can supply approximately 1.5 times as much power per unit area as a tantalum nitride thin film resistor. Although improvements can be made with the use of a protective layer, zirconium boride thin film resistors even with a single protective layer are superior to tantalum nitride thin films with two protective layers, and much better than tantalum nitride thin films with a single protective layer. It was excellent. This increase in the maximum power supply means that in the case of constant power driving, deterioration of the 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 approximately 11 to 14 W/M77L is sufficient, so in the case of tantalum nitride thin film resistors, an oxidation-preventing protective layer is essential. On the other hand, in the case of a zirconium boride thin film resistor, it can be printed satisfactorily without the use of an oxidation-resistant protective layer, and it can be seen that the presence of a protective layer further extends the service life.
(Example 3) A thermal head having the same protective layer as that prepared in Example 2 was subjected to an abrasion resistance test at a contact pressure of about 6009/~ with thermal recording paper.

As a result, the wear degree of the protective layer was 0.1μ of magnesium oxide.
/1c1n, aluminum oxide 0.8μ/1CffL,
The tantalum oxide was 0.2μ/1CIn, which was very good. (Example 4) A thermal head using a zirconium boride thin film resistor having the same protective layer as prepared in Example 2 was heated for 6ms15.
As a result of performing the printing test △R 75 million times (the running distance of the recording paper is approximately 10-) at 0Hz 12Watt/MTIL, the resistance change rate (-T) of the resistor was less than 2% in all cases, and the protective layer There was no peeling, and the abrasion did not adversely affect the printing, which was good.

(Example 5) Lanthanum boride LaB6 [manufactured by Research, USA, purity 99.9] hot-pressed at 1300°C on a cleist ceramic substrate that had been thoroughly cleaned in advance.
%], a heating element with a thickness of 700 mm was fabricated using a high frequency two-pole sputter under conditions of a total argon pressure of 5 x 10 -2 T0 rr and a substrate heating temperature of 200°C.

At this time, the specific resistance value is approximately 420μΩ, and the area resistance is approximately 6
It was 0Ω/mouth. After evaporating titanium at 10λ and aluminum at 1.5μm using an electron beam, selective etching was performed to form a thermal line with a resolution of 4 lines/dragon.
was formed. Next, tantalum oxide was deposited on the thermal CLL as a protective layer to a thickness of 6 μm by cage beam evaporation.
Thermal head Cl2 was vapor-deposited, thermal head Cl3 was vapor-deposited aluminum oxide to a thickness of 8 μm, thermal head Cl4 was vapor-deposited magnesium oxide to a thickness of 5 μm, silicon oxide was deposited to a thickness of 1.5 μm, tantalum oxide was deposited to a thickness of 6 μm, and tantalum oxide was deposited to a thickness of 6 μm. Thermal head Cl5 deposited on the layer structure
prepared. For comparison, tantalum was targeted by high-frequency bipolar reactive sputtering, and the total pressure of argon and nitrogen was 8X1072T0rr, and the partial pressure of nitrogen was 1X.
A thermal Dll of a tantalum nitride heating resistor with a thickness of 700λ was fabricated under the condition of 10-4T0rr.

When this thin film was analyzed by X-ray diffraction, it was found to be Ta2N. Further, the specific resistance value was 210 μΩ, and the sheet resistance value at this time was 30 μ/hole.Next, a tantalum oxide protective layer with a thickness of 6 μm was provided by sputtering on the thermal head D12, and a silicon oxide film D and 3 were prepared, each having a two-layer protective layer consisting of a tantalum oxide film with a thickness of 5 μm and a tantalum oxide film with a thickness of 6 μm thereon. For these prepared thermal points, the pulse width is 6 ms,
A repetitive voltage of 50 Hz is applied, and the supplied power is increased to 30 Hz.
FIG. 5 shows the measurement results of the resistance change rate ΔR/R×100 (g) when an acceleration test was performed by increasing the resistance by 1 Watt/Md per minute.

Here, R is the resistance value before the test, and ΔR is the change in resistance value. The lanthanum boride thin film heating resistor Cll produced by sputtering can supply about 1.8 times as much power per unit area as the tantalum nitride thin film heating resistors D and I.

In addition, by providing a protective layer, the power that can be supplied per unit area is greatly improved, but the lanthanum boride thin film heating resistor is made of tantalum oxide Cl2, aluminum oxide C,3 made by electron beam evaporation. Even when only one protective layer of magnesium oxide Cl4 is used, the thermal head D13 of the tantalum nitride thin film heating resistor with two protective layers is almost the same as that of the tantalum nitride thin film heating resistor with one protective layer. It was much better than the thermal head Dl2. Further, the thermal head Cl5, which has a two-layer protective layer of silicon oxide and tantalum oxide on lanthanum boride, 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 approximately 11 to 14 W/Md is sufficient, so in the case of a tantalum nitride thin film heating resistor, a combination of silicon oxide and tantalum oxide, etc. While a two-layer protective layer is essential, in the case of lanthanum boride thin film heating resistors, printing can be achieved with just one protective layer such as tantalum oxide, aluminum oxide, magnesium oxide, etc. It can be seen that the presence of layers further extends the lifespan. (Example 6
) Lanthanum boride LaB6 [purity 99.9, manufactured by U.S. Research Co., Ltd.]
%] powder was pressed at 100 kg/(-!!t or more) to make a tablet, and the tablet was placed on a cleist ceramic substrate that had been thoroughly cleaned in advance at a temperature of 300°C and a vacuum of 5 x 1.
Electron beam deposition was performed to a thickness of 1000 at 0-6T0rr.

This specific resistance value is 900μΩ, and the area resistance is approximately 90Ω/
It was hot in the mouth.

Next, on top of this, 10λ of titanium and 1.5μ of aluminum
After vapor deposition using an electron beam, a pattern with a resolution of 4 lines/Mm was formed by selective etching to form a thermal head Ell. Thermal head El2 has tantalum oxide evaporated to a thickness of 6 μm as a protective film by electron beam evaporation, thermal head El3 has aluminum oxide evaporated to a thickness of 8 μm, and thermal head El has magnesium oxide evaporated to a thickness of 5 μm as a protective film.
4, and silicon oxide 1.5 μm, then tantalum oxide 6
A thermal head El5 deposited in a two-layer structure of .mu.m was prepared and the same test as in Example 5 was conducted. As a result, the power limit value per unit area at which the rate of resistance change rapidly increases is 12.5 W/MilL for each Ell. 17 in El2
．． 5W/Md. El3 has 18.5W/Md. 19W/m for El4! In L and El5, it was 21 W/Md.

The lanthanum boride heating resistor produced by electron beam evaporation in this example was also much better than the tantalum nitride heating resistor.
As is clear from the above explanation, by using a resistor selected from zirconium boride thin film resistors and lanthanum boride thin film resistors as the resistor of the thermal head, the lifespan of the thermal head is longer than that of conventional thermal heads, and the manufacturing process is simplified. It is possible to achieve cost reductions and improve print quality, and the possibility of high-speed thermal recording is also expected.

Furthermore, as is clear from the above description, the thermal head of the present invention does not contain a high-resistance material as a heating resistor. Therefore, there is no need to consider the mixing ratio or mixing state of materials, and a predetermined resistance value can be easily obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of a thermal head showing an embodiment of the present invention, FIG. 3 is a comparison of heat treatment characteristics between a tantalum nitride thin film and a zirconium boride thin film, and FIGS. 4 and 5 are in accordance with the present invention. FIG. 3 is a characteristic diagram shown to explain the effects of the thermal head of the invention. 1...Substrate, 2...Thin film resistor, 3
...Electric conductor, 4...Protective layer.

Claims (1)

[Claims] 1. A thermal head having a substrate, an electric resistance heating element disposed on the substrate, and an electric conductor for supplying power to the heating element, wherein the electric resistance heating element is selected from zirconium boride and lanthanum boride. A thermal head characterized by being