JPH0557938A - Manufacture of thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head wherein print life and yield in manufacturing can be bettered and print quality can be improved. CONSTITUTION:A glazed layer 23, a heat generating resistor layer 24, electrode layers 25, 26 and a protective layer 28 are formed on an insulating substrate 22 in above-mentioned order. At this time, the protective layer 28 is made to have three layers whose sputtering pressures are varied by sputtering, with a material having high hardness and electric insulating property as a target. In the three layers, a lower layer 29 is formed by sputtering gas pressure of 1-3mTorr, a middle layer 30 is formed by sputtering gas pressure of 20-3mTorr, and an upper layer 31 is formed by sputtering gas pressure of 1-3mTorr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head, and more particularly to a thermal head having an improved printing life.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view of a typical conventional thermal head 1. In the thermal head 1, a glaze layer 3 made of glass is formed on an insulating substrate 2 made of alumina ceramics or the like, and a tantalum nitride Ta ₃ N ₄ film is formed thereon by a thin film technique such as sputtering to form a heating resistor layer. 4 is formed. On the heating resistor layer 4, a metal such as aluminum is formed by sputtering or the like, and etching is performed to form a common electrode 5 and an individual electrode 6,
For example, a plurality of heating elements 7 are formed with a density of 8 dots / mm. Such an insulating substrate 2 is made of tantalum pentoxide T
It is covered with a protective film 8 made of a ₂ O ₅ or the like. Such a thermal head 1 presses the thermal recording paper 10 with the platen roller 9 to perform thermal printing.

In such a conventional thermal head 1, after the heating resistor layer 4 and the electrodes 5 and 6 are formed, SiON or the like is 5 mtorr by a sputtering technique.
The protective film 8 is formed to have a layer thickness t1 (about 4 to 7 μm) in an argon Ar gas atmosphere containing approximately oxygen gas O ₂ .

Since the protective film 8 made of SiON thus formed has a micro Vickers hardness of about 1300 to 1700 kg / mm ² , the protective film 8 and the platen roller 9 are pressed against each other during printing. When a foreign matter from the outside is caught between the heat-sensitive recording paper 10 and the heat-sensitive recording paper 10, the cracks are easily formed in the protective film 8 and the electrodes 5 and 6 and the heating resistor layer 4 are formed due to the intrusion of moisture from the outside. Corrosion causes problems such as defective operation and shortened life.

Further, as the protective film 8, silicon nitride SiN is used.
When formed by sputtering, the Vickers hardness is 2000 to 3 under a normal gas pressure of 5 mtorr.
It is formed at 000 kg / mm ^2, and the hardness is improved as compared with the case of SiON, while the internal stress in the protective film 8 is increased by about 5 to 10 times as compared with the case of SiON. Alternatively, its resistance to heat stress during use decreases. Moreover, in this example, the interlayer adhesion between the electrodes 5, 6 and the heating resistor layer 4 is lower than that of SiON, and there is a problem in that the manufacturing yield and reliability are reduced.

[0006]

In order to solve such a problem, as shown in FIG. 6, the protective film 8 has a two-layer structure of a lower layer 8a and an upper layer 8b, and the lower layer 8a is made of SiO 2.
An example of a manufacturing method in which a film is formed from N and an upper layer 8b is formed from SiN is proposed in JP-A-61-158475.

In this conventional example, although an improvement in internal stress was observed as compared with the first conventional example, it was formed when a film was formed by sputtering in a normal film forming atmosphere at about 5 mtorr. Since the Vickers hardness of the protective film 8 is about 2000 kg / mm ² , the crack resistance as described above is slightly improved as compared with the first conventional example, and depending on the hardness and size of the foreign matter, the crack may still occur. Has a problem that causes

It is generally known that a thin film formed by sputtering increases the energy of sputtered particles generated from a target as the film forming atmosphere is made lower in pressure, and a dense and hard film can be obtained. On the other hand, it is known that the internal stress of the formed film rapidly increases as the sputtering pressure decreases. This state is shown by line L1 in FIG. Therefore, usually
It is known that film formation is not performed at a relatively low pressure.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above technical problems, to provide a thermal head which can improve the printing life and the manufacturing yield and can improve the printing quality.

[0010]

According to the present invention, in a method of manufacturing a thermal head in which a glaze layer, a heating resistor layer, an electrode layer and a protective layer are sequentially formed on an insulating substrate, the protective layer is mainly composed of silicon nitride. A step of forming a three-layer structure in which the sputtering pressure is changed by sputtering the material for forming a lower layer with a sputtering gas pressure of 1 to 3 mtorr, and an intermediate layer of 20 to 30 mto.
It is formed with a sputtering gas pressure of rr, and as an upper layer,
A method of manufacturing a thermal head, comprising a step of forming at a sputtering gas pressure of 1 to 3 mtorr.

Further, according to the present invention, there is provided a method of manufacturing a thermal head, characterized in that, in forming at least one of the lower layer and the intermediate layer, a SiON film is formed by sputtering using a gas containing oxygen gas O _2. is there.

[0012]

In the method of manufacturing the thermal head according to the present invention,
A glaze layer, a heating resistor layer, an electrode layer, and a protective layer are sequentially formed on an insulating substrate in this order, and then the protective layer is a target with a material having high hardness and electrical insulation, and sputtering pressure is applied by sputtering. Is formed to have a three-layer structure. Of the three layers, the lower layer is 1-3 mtorr
Formed with a sputtering gas pressure of
Formed at a sputtering gas pressure of ~ 30 mtorr,
The upper layer is formed with a sputtering gas pressure of 1 to 3 mtorr.

Therefore, by forming the lower layer by low-pressure sputtering, it is possible to increase the incident energy of the sputtered particles flying from the target to the surfaces of the heating resistor layer and the electrode layer, and to activate the surface and the electrode. Adhesion of the protective layer to the surfaces of the heating resistor layer and the electrode layer can be significantly improved by the effect of implanting particles into the layer and the heating resistor layer.

By using low pressure sputtering for the upper layer, the upper layer has high hardness and crack resistance is improved.
By using high-pressure sputtering for the intermediate layer, a layer having almost no stress in the film can be formed, and the stress of the entire protective layer can be reduced.

This effect is further improved by using at least one of the lower layer and the intermediate layer of SiON to further increase the interlayer adhesion.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a thermal head 2 according to an embodiment of the present invention.
It is sectional drawing of 1. In the thermal head 21, a glaze layer 23 made of glass is formed on an insulating substrate 22 made of alumina ceramics or the like, and tantalum nitride Ta ₃ N ₄ is formed thereon by a thin film technique such as sputtering to form a heating resistor layer. 24 is formed. On the heating resistor layer 24,
A metal such as aluminum is formed into a film by sputtering or the like, and etching is performed to form a common electrode 25 and an individual electrode 2.
6 are formed, and a plurality of heating elements 27 are formed with a density of 8 dots / mm, for example. On the surfaces of the heating resistor layer 22 and the electrodes 25 and 26, there are a lower layer 29 and an intermediate layer 3 which will be described later.
A protective layer 28 having a three-layer structure including 0 and the upper layer 31 is formed. Such a thermal head 21 presses the thermal recording paper 33 with the platen roller 31 to perform thermal printing.

According to the present invention, when the sputtering gas pressure is lowered during sputtering, the frequency with which implant particles flying from the target collide with gas molecules in the course of movement along the way is suppressed, and as a result, the implant particles are targeted for implantation. The kinetic energy in the reached state can be remarkably increased as compared with the conventional one, whereby the molecular density of the obtained film can be improved, and therefore the hardness of the film can be remarkably improved. It is based on knowledge. Moreover, as will be described later, the protective film 18 has a three-layer structure, the lower layer 29 and the upper layer 31 have high hardness as described above, and the middle layer 30 is formed with a relatively high gas pressure, so that a layer having little film stress It is intended to reduce the stress of the protective film 28 formed as a whole.

FIG. 3 shows a thermal head 21 according to this embodiment.
FIG. 4 is a process diagram for explaining the manufacturing process of FIG. 4, and FIG. 4 is a time chart showing changes in the argon gas pressure during sputtering used in this manufacturing process. In step a1,
A glass layer is formed on the entire surface of the insulating substrate 22 by a thick film technique such as screen printing, and is baked to obtain a glaze layer 23. In step a2, as described above on the glaze layer 23,
The heating resistor layer 24 is formed by a thin film technique such as sputtering. In step a3, a metal layer made of aluminum is formed on the heating resistor layer 24 by sputtering, and patterned so that the common electrode 25 and the individual electrode 26 are obtained.

In step a4, the wiring board 2 in this manufacturing stage is used.
2 is stored in the sputtering apparatus, and oxygen gas O ₂ is added to 5
Gas pressure P1 shown in FIG. 4 for argon Ar gas containing 100%
In an atmosphere of (1 mtorr as an example), sputtering is performed using a target containing SiN as a main component between times T0 and T1 to form a film having a film thickness t1 (0.1 μm as an example), and the lower layer 29 is formed. obtain. In step a5, the lower layer 29
The same composition of the sputtering gas as that at the time of film formation was used, and the gas pressure was changed from P1 to P2 between times T1 and T2.
(30 mtorr as an example).

In step a6, sputtering is performed using the same target, and the film pressure t2 (for example, 2 to 3 μm) is used.
The film is formed to about m) to obtain the middle layer 30. In step a7, the sputtering gas is an argon Ar gas atmosphere, and the gas pressure P2 is switched to the gas pressure P3 (for example, 1 mtorr) at times T3 to T4 to form a film. In step a8, the film is formed to a film thickness t3 (for example, 2 to 3 μm) to form the upper layer 31. In this way, the protective film 28 including the lower layer 29, the middle layer 30, and the upper layer 31 is formed.

Silicon nitride S thus formed
The upper layer 31 made of iN has a Vickers hardness of 250.
It is 0 to 3000 kg / mm ^2, which is a film excellent in crack resistance as compared with the conventional example.

The inventor of the present invention conducted a printing test of the thermal head 21 thus prepared using hard paper under a high load condition. The conventional SiON or SiON shown in FIGS. The generation of cracks seen in the protective film 8 made of SiN did not occur, and good results were obtained.

In the method of manufacturing the thermal head according to the present embodiment, the lower layer 29 is formed by low-pressure sputtering, so that the sputtering particles flying from the target are incident on the surfaces of the heating resistor layer 24 and the electrode layers 25 and 26. The energy can be increased, and the surface of the heating resistor layer 24 and the electrode layers 25 and 26 of the protective layer 28 is activated by the activation of the surface and the effect of implanting particles into the electrode layers 25 and 26 and the heating resistor layer 24. It is possible to significantly improve the adhesion to.

By using low pressure sputtering for the upper layer 31, the upper layer 31 has high hardness and crack resistance is improved. By using high-pressure sputtering for the intermediate layer 30, a layer having almost no stress in the film can be formed, and the stress of the entire protective layer 28 can be reduced.

In the above-described embodiment, the lower layer 29 and the middle layer 30 are made of SiON, and the upper layer 31 is made of SiN. However, as another embodiment of the present invention, all the layers 29 to 31 are made of SiN. You can

The protective film 28 used in each of the above embodiments
The SiON or SiN forming the may contain aluminum Al of, for example, about several mol to 20 mol%.

Further, between the lower layer 29 and the middle layer 30, or between the middle layer 30 and the upper layer 31, oxygen O in argon Ar gas is introduced.
The concentration of ₂ may be changed with time to provide a gradient layer of oxygen. Further, the atmosphere gas may contain nitrogen gas N ₂ or a nitrogen-based gas such as N ₂ O or NO.

[0028]

As described above, according to the present invention, the glaze layer, the heating resistor layer, the electrode layer and the protective layer are sequentially formed on the insulating substrate in this order, and then the protective layer is formed with high hardness. A three-layer structure is formed by changing the sputtering pressure by sputtering using a target having an electrically insulating material as a target. Of the three layers, the lower layer is formed with a sputtering gas pressure of 1 to 3 mtorr, and the middle layer is 20 to 30 m.
It is formed at a sputtering gas pressure of torr and the upper layer is formed at a sputtering gas pressure of 1 to 3 mtorr.

Therefore, by forming the lower layer by low-pressure sputtering, it is possible to increase the incident energy of the sputtered particles flying from the target to the surface of the heating resistor layer and the electrode layer, and to activate the surface and the electrode. Adhesion of the protective layer to the surfaces of the heating resistor layer and the electrode layer can be significantly improved by the effect of implanting particles into the layer and the heating resistor layer.

By using low pressure sputtering for the upper layer, the upper layer has high hardness and crack resistance is improved.
By using high-pressure sputtering for the intermediate layer, a layer having almost no stress in the film can be formed, and the stress of the entire protective layer can be reduced.

Further, this effect is improved by further increasing the interlayer adhesion by using at least one of the lower layer and the intermediate layer of SiON.

[Brief description of drawings]

FIG. 1 is a sectional view of a thermal head 21 according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between sputtering gas pressure and internal stress for explaining the present invention.

FIG. 3 is a process drawing for explaining the manufacturing process of this embodiment.

FIG. 4 is a time chart showing changes in sputtering gas pressure in the present manufacturing process.

FIG. 5 is a sectional view of a thermal head 1 of a first conventional example.

FIG. 6 is a sectional view of a second conventional thermal head 1a.

[Explanation of symbols]

 21 Thermal Head 22 Insulating Substrate 23 Glaze Layer 24 Heating Resistor Layer 25 Common Electrode 26 Individual Electrode 27 Heating Element 28 Protective Layer 29 Lower Layer 30 Middle Layer 31 Upper Layer

Claims (2)

[Claims] 1. A method of manufacturing a thermal head in which a glaze layer, a heating resistor layer, an electrode layer, and a protective layer are sequentially formed on an insulating substrate, wherein the protective layer is a sputtering targeting a material containing silicon nitride as a main component. And a step of forming the following three-layer structure in which the sputtering pressure is changed by the method of manufacturing a thermal head. As the lower layer, 1-3
It is formed at a sputtering gas pressure of mtorr. The middle layer is formed with a sputtering gas pressure of 20 to 30 mtorr. The upper layer is formed with a sputtering gas pressure of 1 to 3 mtorr. 2. The method of manufacturing a thermal head according to claim 1, wherein at least one of the lower layer and the intermediate layer is formed as a SiON film by sputtering using a gas containing oxygen gas O _2. ..