JP2001026130A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance power resistance by providing a supporting basic body formed of inorganic insulating layer formed on one major surface of a metallic base body, a plurality of heating resistors formed on the inorganic insulating layer, an electrode pattern connected with the heating resistors thereby eliminating variation in the resistance of the heating resistors at the time of high working temperature. SOLUTION: An SiON layer 2 is formed on a basic body 1 and a heating resistor 3 is formed on the layer 2 while being exposed partially such that an electrode 4 supplying power to the heating resistor 3 serves as a heat generating part. Furthermore, an SiON layer 5 is provided to cover the heat generating part thus completing a thermal head. More specifically, a basic body 1 of SUS of about 0.5 mm thick is cut into specified dimensions and subjected to degreasing and then an SiON layer 2 is formed on the basic body 1 by sputtering. Subsequently, a heating resistor 3 of TaSiO of about 0.1 μm is formed on the SiON layer 2 by sputtering and annealed at 750-950 deg.C in vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used for a video printer, a card printer, a plate making machine, a facsimile, and the like.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for miniaturization and high-speed printing in thermal recording devices of various type A devices. Demands are becoming more demanding.

That is, if the shape of the heating resistor in the thermal print head is reduced in order to cope with the fine printing of the thermal recording apparatus, the heat load per unit area of the heating resistor increases, The heating temperature of the heating resistor rises. Therefore, the resistance value of the heating resistor changes within a short period of time, and the thermal print head cannot be used.

Further, when a high-power pulse is applied to the heating resistor of the thermal print head in order to cope with the high-speed printing of the thermal recording apparatus, the heating temperature of the heating resistor rises and the heating resistor increases. As in the case where the shape of the body is miniaturized, the resistance value of the heating resistor changes within a short period of time and becomes unusable.

Therefore, in order to realize finer printing and higher speed printing in a thermal recording apparatus of various #A devices,
It is indispensable to apply a heating resistor excellent in heat resistance, which does not change its resistance value characteristics even at a high temperature, as a heating resistor of a thermal print head.

As one of the major factors causing such a change in the resistance value of the heat generating resistor, conventionally, between the alumina substrate and the heat generating resistor layer, the main purpose is to improve the surface smoothness and the heat storage property. Diffusion of oxygen or other components between the glaze glass layer and the heat generating resistor.

Accordingly, a method has been proposed in which a barrier layer is interposed between the heating resistor and the glaze glass layer.
However, according to this method, the manufacturing process becomes complicated and the cost increases.

As a method other than providing a barrier layer under a heating resistor, a supporting substrate having a glass glaze layer in a reducing gas atmosphere, a nitriding gas atmosphere, an inert gas atmosphere, or a vacuum is used. Is fired in a temperature range not lower than the glass transition point of the glass glaze layer. According to this method, the oxygen content of the glass glaze layer at least near the interface in contact with the heating resistor is equal to or lower than the oxygen content of the heating resistor. However, there are the following problems.

That is, in a method of firing a supporting substrate having a glass glaze layer in a temperature range not lower than the glass transition point of the glass glaze layer, the reproducibility of the firing effect is poor, especially at a mass production level, and individual glass glaze layers may not be reproducible. It turned out that the variation was large. This is because it is difficult to heat-treat (fire) all the batches and lots of the supporting substrate having the glass glaze layer in a strictly identical atmosphere, particularly in a gas atmosphere. This is because it is difficult to precisely adjust the flow rate, temperature, and the like. Further, even with the same type of supporting substrate, subtle variations occur in the composition and thermophysical properties of the glass glaze layer, and these subtle variations produce large differences in device characteristics due to heat treatment.

FIG. 4 is a schematic sectional view showing the vicinity of a heating resistor of a conventional thermal head. A glaze layer 7 serving as a heat insulating layer and a smoothing layer is provided on a support base 6 of alumina ceramic,
Further, the electrode wiring 4 is formed in a portion other than the heat generating portion 3 of the heat generating resistor, and the protective layer 5 is formed so as to cover at least the heat generating portion 3 of the heat generating resistor.

The thermal head having such a conventional structure cannot sufficiently secure the power resistance especially for a plate making machine. The power resistance refers to, for example, “a resistance change rate of a heating resistor is 10% when a pulse of several W / dot is applied 3 × 10 ⁷ times in the same resistor shape, the same pulse width and the same pulse period. The concept is defined by The cause of insufficient power resistance is melting of the glaze. Ba, Ca, Sr, and S have the highest heat resistance among glazes currently in practical use.
Glass transition point of 750 containing i and O as main components
° C and a softening point of 950 ° C. The upper limit of the softening point of the glaze is 900 to 950 ° C. on the assumption that the smoothness is not impaired even if the composition and the manufacturing conditions are improved. However, the peak temperature at the center of the heating element may exceed the glass transition point of the glaze (upper limit of 750 ° C.) and approach the softening point depending on the type and driving conditions. When the thermal head is driven in such a situation, the mutual diffusion of the glaze and the heating resistor component is promoted, and the product resistance value continues to increase. I will not stand it.

Further, since the glaze has poor heat resistance,
Since the annealing temperature cannot be set higher than the temperature at the time of driving the thermal head, the resistance value decreases at the time of driving the thermal head, particularly at the initial stage. In general, when the resistance value decreases, the current increases accordingly, the resistance value further decreases, and the current further increases. This vicious cycle is repeated, and the thermal head is destroyed early.

Further, since the alumina ceramic substrate has a low thermal diffusivity, when the thermal head is turned on / off at a high speed, the substrate accumulates heat and it is difficult to control the heat generation temperature.

[0014]

As described above, in the conventional thermal head, the requirement for heat resistance of the heating resistor becomes strict, and if the conventional glaze is used,
Even if the material having the highest heat resistance among the glaze materials is used, there is a problem that the material is melted. In addition, since the annealing temperature of the glaze, which is inferior in heat resistance, cannot be higher than the temperature at the time of driving the thermal head, the resistance value decreases in the initial stage of driving the thermal head, and the current increases accordingly. The situation was repeated, and there was a problem that the thermal head was destroyed at an early stage.

Therefore, the present invention provides a method for improving the resistance of a heating resistor when used at a high temperature, substantially eliminating the change in the resistance value, improving the power resistance, realizing finer and faster printing, and improving the productivity. Moreover, it is an object of the present invention to provide an inexpensive thermal head having excellent heat resistance.

A thermal head according to the present invention comprises a supporting base comprising a metal base and an inorganic insulating layer formed on one main surface of the metal base; and a plurality of bases formed on the inorganic insulating layer. It is characterized by comprising a heating resistor, an electrode pattern connected to the heating resistor, and a protective layer provided so as to cover a heating portion of the heating resistor.

In the thermal head of the present invention, the inorganic insulating layer is made of a material containing silicon and oxygen as main components or a material containing silicon, oxygen and nitrogen as main components.

Further, in the thermal head of the present invention,
The protective layer is made of an inorganic insulating material, and is particularly made of a material mainly containing silicon and oxygen or a material mainly containing silicon, oxygen and nitrogen.

In the present invention, as the inorganic insulating layer, S
iO ₂ or _SiO x _{N y,} etc. However, SiON is preferable to increase the stability of the resistance value. From the viewpoint of simplifying the manufacturing process, both the inorganic insulating layer and the protective layer are made of S
It is preferable to configure with iON.

Further, in the thermal head of the present invention,
The thickness of the inorganic insulating layer is 10 to 70 μm, preferably 20 to 70 μm.
５０50 μm. When the thickness is less than 10 μm, the heat storage property is insufficient, that is, the heat radiation property is too high, and it is difficult to raise the temperature. If it exceeds 70 μm, not only the heat storage property becomes excessive, but also the layer formation becomes difficult.

Here, the change of the resistance value of the heating resistor and its influence will be described in detail.

The change in the resistance value of the heating resistor can be divided into two modes, a falling mode and a rising mode.

The reason why the resistance value of the heating resistor shows a decrease is that imperfections in the structure of the heating resistor due to lattice defects and the like are gradually removed by the heat generated at the time of driving the thermal print head, and the electrical conductivity is reduced. It is presumed that this is because the mobility of the carrier that controls the sex is improved.

The decrease in the resistance value of the heating resistor can be prevented by subjecting the heating resistor to a heat treatment at least at a temperature higher than the temperature of the environment in which the thermal printhead is used. As a method, after commercializing a thermal print head, a method of applying a pulse to the heating resistor with a power larger than that used as a product and electrically aging the heating resistor, in order to obtain a higher effect There is a method of thermally annealing the heating resistor in a vacuum after forming the heating resistor, or a method of annealing the heating resistor by laser irradiation.

In particular, according to the method of annealing these heat generating resistors, it is possible to completely eliminate the above-described mode of decreasing the resistance value of the heat generating resistor, and the power resistance is equal to 1.3 of the electric aging method. It improves twice as much. In the electric aging method, the temperature of the heating resistor for stabilizing the resistance value of the heating resistor is limited compared to the annealing method because the characteristic of energizing the commercialized thermal print head is higher than that of the annealing method. If the heat generation temperature is high, the material of the conductive layer or the material component of the protective layer diffuses and penetrates into the heat generating resistor, and the protective layer cracks due to the difference in thermal expansion coefficient.

On the other hand, the increase in the resistance value of the heating resistor is caused by the fact that O contained in the components of the upper and lower layers such as the glaze glass layer diffuses into the heating resistor, thereby causing oxidation of the heating resistor. It is thought that it is to be done.

Further, by using an inorganic insulating layer of SiON or the like instead of the glaze layer, it is possible to prevent an increase in resistance value due to component diffusion between the heating resistor and the underlying layer and a breakage of the thermal head due to melting of the underlying layer. Becomes possible. Also, S
Because iON has better heat resistance than glaze,
The annealing temperature in the step of thermally stabilizing the heating resistor can be increased. As described above, the softening point of the glaze is at most 950 ° C.,
iON has a remarkably high melting point of 1500 to 1800 ° C. That is, since the annealing process can be performed at a temperature higher than the temperature at the time of driving the thermal head, it is possible to prevent the resistance value from decreasing at the initial stage of driving the thermal head, and the life of the thermal head is prolonged.

Further, according to the present invention, the use of a metal substrate such as SUS made of stainless steel in place of the alumina ceramic substrate increases the thermal diffusivity, improves not only the control of the heat generation temperature, but also the material. Costs can be significantly reduced.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the following embodiments.

FIG. 1 is a sectional view of a thermal head according to the present invention. A SiON layer 2 is formed on a base 1, a heating resistor 3 is further formed thereon, and a part of the heating resistor 3 is formed such that an electrode 4 for supplying power to the heating resistor 3 serves as a heating portion. Are formed to be exposed. The SiON layer 5 is formed so as to cover at least the heat generating portion.

The manufacturing process of the thermal head will be described below.

For example, a substrate 1 made of SUS having a thickness of 0.5 mm or an Fe (16%)-Cr alloy having a thickness of 0.7 mm
Is cut to a predetermined size and subjected to degreasing and washing.

Next, a sputtering method such as high-frequency sputtering or magnetron sputtering or CVD (Chemical Vapor Dep.
An SiON layer 2 is formed on the substrate 1 to a thickness of 40 μm by using an osition method. In the case of the sputtering method, S
Ar, O ₂ , and N ₂ gases are introduced using an i target, and a film is formed by reactive sputtering. Further, an SiON target may be used.

Thereafter, a heating resistor 3 made of TaSiO or the like is formed on the SiON layer 2 by sputtering or another known method to a thickness of about 0.1 μm, and the heating resistor 3 is formed in a vacuum (10 ⁻⁵ P
a) Annealing is performed at 750 to 950 ° C. This annealing treatment is performed to reduce defects on the surface of the heat-generating resistor film immediately after formation and to improve thermal stability. It is desirable that the annealing temperature is higher than at least the maximum heat generation temperature when the thermal head is driven.

The subsequent steps are basically the same as the conventional thermal head.

That is, after a film of Al, an Al alloy, or the like to be the electrode 4 is formed on the heating resistor 3 by a sputtering method or the like.
A photo-engraving method is used to form a heating resistor array and pattern individual electrodes and common electrodes.

Next, in order to provide a function of oxidation resistance and abrasion resistance so as to cover at least the heat generating portion, a protective layer 5 made of SiON is formed to a thickness of 5 μm by sputtering or the like.
Is formed with a thickness of

Thereafter, a heat sink and a PCB (Print Circ
uit Board) The thermal head is completed through processes such as sticking to the board and IC mounting.

The performance of the thermal head of the present invention and the performance of the conventional thermal head were compared as follows.

FIG. 2 shows the rate of change of the sheet resistance value when the annealing temperature is changed. As a conventional thermal head, a thermal head having a 0.7 μm-thick alumina ceramic substrate and a 40 μm-thick glaze layer formed thereon was used.
As this glaze layer, one having a softening point of 950 ° C. containing Ba, Sr and Ca was used.

As is clear from the graph of FIG. 2, when the annealing temperature is 750.degree. C., the slope of the resistance value change rate curve changes from negative to positive, and further, the value of the change rate becomes positive between 850 and 900.degree. It rises functionally.

Whether the rate of change is positive or negative depends on whether the resistance value is increased due to oxidation of the resistor film due to diffusion of oxygen from the glaze layer or the resistance value is decreased due to reduction of defects in the resistor film. Decided. In a thermal head in which the slope of the resistance value change rate curve changes from negative to positive, the density unevenness during driving becomes so large that it cannot be ignored.If the value of the resistance value change rate becomes positive, the smoothness of the glaze surface increases. Is lost and the original glaze function is lost. For the reasons described above, the upper limit temperature of annealing must be limited to 750 ° C.

On the other hand, it has been confirmed that the resistance change rate curve of the thermal head of the present invention maintains a negative slope at least up to the annealing temperature of 950 ° C. Also,
There was no increase in the variation of the resistance value and no loss in the surface smoothness.

FIG. 3 shows the relationship between the applied pulse and the rate of change in resistance when the annealing temperature is changed. The pulse period is 2.
05 ms, pulse width 0.44 ms, power 0.90
W / dot.

When the annealing temperature is 700 ° C., the reduction of the defect of the resistor film is insufficient, and the rate of change of the resistance value of both the thermal head of the present invention and the conventional thermal head is −10 at the pulse number of 1 × 10 ^5. About 5%, the value greatly increases with the number of applied pulses of 3 × 10 ^5.
It was 6.0%, which exceeded + 10% in the conventional thermal head. In particular, in the conventional thermal head, the glaze immediately below the heat-generating portion of the resistor melts to form voids.

When the annealing temperature is 800 ° C., the rate of change in the resistance value of both the thermal head of the present invention and the conventional thermal head is a negative value when the number of applied pulses is 1 × 10 ⁵ , and gradually increases as the number of applied pulses increases. . With the number of applied pulses of 1 × 10 ^8, the resistance change rate of the conventional thermal head is 9.1%, whereas that of the thermal head of the present invention is as low as 2.8%. It can be seen that the thermal head has better stability.

When the annealing temperature is 950 ° C., the thermal head of the present invention exhibits extremely stable characteristics,
Even a pulse number of 10 ⁸ is only 0.4%. On the other hand, in the conventional thermal head at 950 ° C., the smoothness of the glaze surface is impaired and the original glaze function is lost, so that a normal thermal head cannot be manufactured.

[0047]

In the thermal head of the present invention, since no glaze is used, there is no restriction due to the thermal properties of the glaze, and the heating resistor film is annealed at a high temperature which could not be applied to the glaze. The resistance of the heat-generating resistor does not drop significantly even during driving when a pulse is applied, and it has excellent heat resistance and power resistance, prolongs the service life, and consequently makes the printing finer and faster. Can be realized. Further, in the thermal head of the present invention, a metal substrate can be used as the base instead of the conventional ceramic substrate, so that not only can the thermal head be manufactured at low cost, but also the metal substrate itself can be used for the common electrode. It can also be bent, which greatly contributes to downsizing of the thermal head.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic cross-sectional view of the vicinity of a heating resistor of a thermal head according to the present invention.

FIG. 2 is a graph showing a relationship between an annealing temperature of a heating resistor film and a rate of change in resistance value.

FIG. 3 is a graph showing a relationship between an applied pulse and a resistance value change rate when an annealing temperature is changed.

FIG. 4 is an enlarged schematic cross-sectional view of the vicinity of a heating resistor of a conventional thermal head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Inorganic metal layer, 3 ... Heating resistor, 4 ... Electrode, 5 ... Protective layer, 6 ... Glaze layer

Claims (7)

[Claims] 1. A support base comprising a metal base and an inorganic insulating layer formed on one main surface of the metal base, a plurality of heating resistors formed on the inorganic insulating layer, and the heating resistor And a protective layer provided so as to cover a heat-generating portion of the heat-generating resistor. 2. The thermal head according to claim 1, wherein the inorganic insulating layer is made of a material containing silicon and oxygen as main components. 3. The thermal head according to claim 1, wherein said inorganic insulating layer is made of a material containing silicon, oxygen and nitrogen as main components. 4. The thermal head according to claim 1, wherein said protective layer is made of an inorganic insulating material. 5. The thermal head according to claim 4, wherein the protective layer is made of a material containing silicon and oxygen as main components. 6. The thermal head according to claim 4, wherein said protective layer is made of a material containing silicon, oxygen and nitrogen as main components. 7. The inorganic insulating layer has a thickness of 10 to 70 μm.
2. The thermal head according to claim 1, wherein m.