JPH11129516A - Thermal head and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a printing-fail dot due to oxidation of a heating resistor on an under layer and to make a life of a thermal head longer by a method wherein a protection layer of the thermal head is formed by sputtering using a sputtering target of Si3 N4 of a high hardness, added with SiO2 of a low hardness to form a film which is a coloring film having a prescribed Vickers hardness. SOLUTION: There is disclosed a thermal head constituted such that a heat insulation layer 12 is formed on the top of a substrate and heating resistors 13, electrodes 14 are laminated on the top face of the heat insulation layer 12 and a protection layer 16 is applied on the top face thereof. The protection layer 16 is a sputtering film formed by using a sputtering target made of a ceramic sintered body consisting of Si3 N4 , SiO2 and AlN as main components. It is a coloring film having a Vickers hardness of approximately 700-1000 kg/mm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermal head used in a thermal printer and a method of manufacturing the same.
In particular, the present invention relates to a long-life thermal head that prevents the occurrence of local cracks and peeling of a protective layer, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A conventional thermal head structure and a manufacturing method thereof are generally arranged such that a plurality of heating resistors are linearly arranged at an end on a heat-radiating substrate such as alumina or silicon and a desired printing information is obtained. The heat is generated by selectively energizing each heating resistor, and the recording is performed by coloring the heat-sensitive recording paper, or the ink is transferred to plain paper through a thermal transfer ink ribbon to perform dot recording. Things.

FIG. 3 is a sectional view of a main part showing the structure of a conventional thermal head. A heat-transmissive substrate 1 made of ceramic such as alumina is provided at the end of a heat-transmissive substrate 1 made of glass glaze or the like. The layer 2 is formed to a thickness of about 30 μm, and a heating resistor 3 made of Ta ₂ N, Ta—SiO _2, or the like is laminated thereon by sputtering or the like, and a plurality of straight lines are formed by photolithography according to the number of dots. The pattern of the heat generating resistor 3 is formed so as to be arranged in a row.

Electrodes made of Al, Cu, Au, or the like are stacked on the heating resistor 3 by sputtering or the like to supply power energy, and are formed in a desired pattern by a photolithography technique to generate heat. On one side of the resistor 3, a common electrode 4 is formed, and on the other side, an individual electrode 5 for independently supplying current to each heating resistor 3 is formed.

Further, the heating resistor 3 and the electrodes 4,
In order to prevent their oxidation and wear, the surface of
A high-hardness protective layer 6 made of C, sialon, or the like is laminated to a thickness of about 5 μm by sputtering or the like. The protective layer 6 is formed so as to cover all surfaces of the electrodes 4 and 5 except for external connection terminals (not shown).
Finally, the substrate 1 is diced to produce a chip-shaped thermal head. In such a thermal printer using a conventional thermal head, this thermal printer is used.
In a state where the multiple head is pressed through a thermal transfer ink ribbon or in the case of thermal recording paper directly against paper conveyed on a platen, the individual electrodes 5 are selectively energized based on a predetermined print signal. Then, by heating the desired heating resistor 3, the ink on the ink ribbon is melted and transferred onto paper, or the heat-sensitive recording paper is colored to perform desired printing.

[0006]

However, in such a thermal printer, dust is often caught during printing, and the dust forms the protective layer 6 of the thermal head and the platen. Since the protective layer 6 is forcibly passed while being strongly pressed, local cracks and peeling occur in the protective layer 6. That is, the S of the conventional thermal head
The protective layer 6 made of iC or Sialon is a single layer and has good oxygen barrier properties, and generally has a Vickers hardness of about 15
It is a material having a high hardness of 00 to 2000 kg / mm ² , a high Young's modulus, and excellent rigidity. However, the protective layer 6 is used with a very thin film thickness of about 5 μm, and the material hardness of the underlying heating resistor 3 and the heat insulating layer 2 is about 1 μm of that of the protective layer 6.
Since it is as soft as ２〜 to １ ／, if a foreign substance of about 10 μm or more is caught, it cannot withstand deformation and cracks occur,
An obstacle such as local peeling from the interface of the underlying heating resistor 3 occurs, and oxygen in the air enters into the inside. Therefore, the heating resistor 3 is oxidized, the dot resistance increases, and no current flows. As a result, unprintable dots are generated, and the printing life is shortened.

When the pressing pressure (pressing force) between the thermal head and the platen is increased in order to improve the quality of printing on rough paper, when the protective layer 6 is made of a material having a high hardness and a high rigidity, sputtering is performed. As a result of being formed into a film having a large internal stress by the film, and trying to withstand without being deformed against a thermal shock by the heating resistor 3 and a shear stress caused by friction with a printing medium on a platen during printing. In addition, there is a problem that stress separation easily occurs between the protective layer 6 and the heating resistor 3.

As a means for reducing local destruction of the protective layer 6 due to foreign matter being caught during printing, when the protective layer 6 is made of sialon, a large amount of oxygen is intentionally added during sputtering. The applicant of the present application has proposed that a transparent protective layer having a desired hardness can be formed by converting a hard Si—N bond into a soft Si—O bond and having a foreign matter resistance of a desired hardness. In order to obtain a desired hardness by denaturation with oxygen, a large amount of oxygen needs to be added. There was a problem in mass production that it was small. The present invention has been made in view of the above problems, and has as its object to provide a thermal head which prevents local cracking and peeling of a protective film and is easy to manufacture, and a method for manufacturing the same.

[0009]

According to the thermal head of the present invention, a heat insulating layer is formed on an upper surface of a substrate, a heating resistor and an electrode are laminated on the upper surface of the heat insulating layer, and the upper surface is covered with a protective layer. In the thermal head formed as described above, the protective layer is formed of S
A sputtering film using a sputtering target composed of a ceramic sintered body containing i ₃ N ₄ , SiO ₂ and AlN as main components, and having a Vickers hardness of about 700 to 1
It is a colored film of 000 kg / mm ² .
Further, the present invention is characterized in that the composition ratio of SiO _{2 in} the sputtering target is approximately 20 to 50 mol%.

The method of manufacturing a thermal head according to the present invention further comprises a step of forming a heat insulating layer on the upper surface of the substrate, a step of forming a heating resistor on the upper surface of the heat insulating layer, and a step of connecting to the heating resistor. Forming a protective layer covering the surface of the heating resistor and the electrode, the step of forming the protective layer comprises Si ₃ N ₄ and SiO 2. Using a sputtering target composed of a ceramic sintered body containing ₂ and AlN as main components and having a composition ratio of SiO ₂ of about 20 to 50 mol%, sputtering is performed using Ar gas as a sputtering gas to form a colored film. It is characterized by the following. Further, in the present invention, the Ar gas may be an Ar gas and an O ₂ gas.
A mixed gas of a gas and a mixed gas of an Ar gas and a N ₂ gas, wherein the flow rate of the O ₂ gas or the N ₂ gas is approximately 1 to 3% of the total gas flow rate.

As described above, according to the present invention, as a sputtering target material for the protective layer, approximately 2% of Si ₃ N ₄ of high hardness is used.
For the 0-50 mol% of SiO ₂ of low hardness is obtained in advance by adding, Vickers hardness of the protective layer - scan hardness, to approximately 1500 kg / mm ² of conventional sialon, the present invention is substantially 700~1000kg / mm ² Since the protective layer follows deformation even when foreign matter is caught during printing, the occurrence of cracks and peeling can be reduced.

In the protective film of the present invention, nitrogen, which is a light element of a material, is easily exhausted during sputtering, and nitrogen in the deposited film is deficient, and active Si or Al metal is released. Utilizing the nature of sputtering that causes excess metal, it is formed in an insulating colored film that is nitrogen-deficient, so the free metal included in the film increases the toughness and adhesion of the film and protects it. The crack resistance of the layer can be further improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the structure of a thermal head and a method of manufacturing the same according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a main part showing the structure of a thermal head according to the present invention. In the same figure, a heat insulating layer 12 made of glass glaze is formed on the surface of a heat dissipating substrate 11 made of alumina or the like, and a T
Heating resistors 13 made of a-SiO ₂ or the like are stacked and formed in a desired pattern by photolithography. Further, an electrode made of Al, Cu, Au or the like is laminated thereon, and a common electrode 14 is formed on one side of the heating resistor 13 and an individual electrode 15 is formed on the other side.

In order to protect the heating resistor 13 and the electrodes 14 and 15 from oxidation and abrasion, a sputtering target made of Si ₃ N ₄ —SiO ₂ —AlN, which is a feature of the present invention, is used. The thermal head of the present invention is manufactured by laminating a protective layer 16 having a thickness of about 5 μm on a metal-excessive insulating colored film having a desired hardness and a nitrogen deficiency.

Therefore, the Si ₃ N ₄ —SiO _{2 according} to the present invention
-A sputter target material made of AlN has a low hardness of S ₃ N _{4 and} a low hardness of S ₃ N ₄ so as to achieve the object of the present invention.
The composition ratio at which desired crack resistance is exhibited by adding iO ₂ is experimentally determined.

Note that AlN is hardly sinterable Si ₃
The sintering aid serves to increase the sintering density of N ₄ and is added to further enhance the adhesion of the protective layer. For example, Si ₃ N ₄ —SiO ₂ has a target having a low sintered density of about 70% and is a porous material.
When about 10 mol% of AlN is added, a synergistic effect with SiO ₂ occurs, and the sintered density of the target can be made about 90%,
This has the effect of improving the sputtering target life and sputtering stability. The range of the amount of AlN added is considered to be several mol% to 20 mol% in relation to the amount of SiO ₂ . Further, AlN has a property that nitrogen of a light element is deficient due to sputtering of Ar and metal Al is easily released, and the released active Al is Si ₃
This has the effect of increasing the adhesion to the underlying layer such as the heating resistor 13 together with the Si released from N ₄ .

When sputtering is performed using the sputtering target, since a large amount of SiO ₂ is contained in the material in advance, a desired hardness can be stably obtained by sputtering only Ar. However, when using a good sputtering apparatus which has an excellent exhaust capacity and less degassing in the chamber at the time of this sputtering, the amount of the impurity gas (mainly water) taken in during the film formation is reduced. The degree of deficiency of the light element nitrogen in the protective layer used increases.
In some cases, a large amount of free metal such as Si or Al is generated in the film, and the film becomes black, becomes conductive, loses insulation, and cannot be used as a protective layer.

For this reason, according to the present invention, the protective layer is controlled and formed into a nitrogen-deficient metal-excessive colored film as long as the insulating property can be maintained. , A small amount of a reactive gas composed of O ₂ or N _{2 at} a flow rate of about 1 to 3% of the total gas flow rate is added to Ar. That is, O ₂ gas flow rate / (Ar gas flow rate + O ₂ gas flow rate) = 1 to 3%, or N ₂ gas flow rate / (Ar
By performing the reactive sputtering under the condition of (gas flow rate + N ₂ gas flow rate) = 1 to 3%, a protective layer having a substantially brown color can be obtained. In this way, the protective layer formed into a brown film while intentionally maintaining insulation can have excellent toughness and adhesiveness of the film, particularly by releasing metal in the film, and can be used during printing. This has the effect of providing the best crack resistance against foreign matter that gets caught. If the flow rate ratio of the reactive gas is less than 1%, the insulating property of the sputtered film is insufficient. Conversely, if the flow rate ratio is more than 3%, the sputtered film becomes transparent, and the crack resistance is insufficient. No longer available.

[0019]

EXAMPLES Next, the results of experiments on the characteristics of the protective layer of the present invention will be described. As shown in Table 1 below, Si ₃ N ₄ −
Examples and comparative examples in which the composition ratio of a sputter target material composed of SiO ₂ -AlN was changed. Using these sputtered materials, sputtering was performed at a film forming gas pressure of 0.4 Pa and an Ar gas flow rate of 50 SCCM, and 5 μm
Was obtained.

[0020]

[Table 1]

FIG. 2 is a graph showing the results obtained by measuring the foreign matter resistance of the protective layer sputtered using the above target. The horizontal axis represents the amount of added SiO ₂ , and the vertical axis represents the foreign matter resistance. ing. In addition, the test method of the foreign matter resistance is as follows. A thermal head having a protective layer formed thereon is mounted on a printer, the foreign matter bite is caused to travel on a predetermined sandpaper, and the heating resistor is broken due to cracks or wear. It is a comparison of the mileage to get up.

As shown in FIG. 2, the SiO 2 of Examples 1 and 2 was used.
_The longest life is exhibited when the addition amount of ₂ is 30 mol% and 40 mol%, and when the normal traveling distance at this time is 100%, when the addition amount of SiO ₂ of Comparative Example 1 is 10 mol%, the normal traveling distance is obtained. Is about 30%, the foreign matter resistance is insufficient, and a failure mode of cracking or peeling of the protective layer occurs, thereby shortening the service life. Further, the SiO _{2 of} Comparative Example 2 was used.
In the case where the amount of addition is 60 mol%, the normal traveling distance is about 70.
% And the wear resistance is insufficient due to the decrease in hardness of the protective layer.
A failure mode of oxidation and abrasion of the heating resistor occurs, thereby shortening the service life. On the other hand, the SiO 2 of Examples 1 and 4
_When the addition amount of ₂ is 20 mol% and 50 mol%, the normal traveling distance is maintained at 80% or more, and the foreign matter resistance of the protective layer is good. From the above results, it was experimentally obtained that the addition amount of SiO ₂ in the range of 20 to 50 mol% was excellent in foreign matter resistance.

On the other hand, when a conventional thermal head having a high hardness protective film made of sialon or the like is subjected to a similar foreign matter resistance test, a small traveling distance (normal traveling distance is approximately 10
%), A failure occurs. Compared with this, the thermal head using the protective layer of the present invention has about 10 times improvement in foreign matter resistance.

Next, as a result of measuring the Vickers hardness, the protective layer of Example 1 was approximately 1000 kg / mm ² , and the protective layer of Example 4 was approximately 700 kg / mm ² . That is, the addition amount of SiO ₂ is from 20 mol% to 50 mol%.
%, The Vickers hardness is approximately 1000-700.
It can be seen that it changes within the range of kg / mm ² .

From the above results, in the conventional high hardness protective layer made of SiC or Sialon, cracks and peeling occurred immediately when foreign matter was caught, but the Vickers hardness was approximately 700 to 1000 kg / kg. It has been experimentally found that the protective layer having a thickness of ² mm can reduce the occurrence of cracks and peeling even if there is a trace of foreign matter passing therethrough. Further, when a diamond indenter of a Vickers hardness tester was pushed into the heat-generating dot portion of the thermal head at 300 g, cracks and peeling were immediately propagated in the conventional protective layer 6. No defects are observed, crack resistance is improved, and variations in printing life can be reduced.

[0026]

According to the first aspect of the present invention, the protective layer of the thermal head has a low hardness of Si ₃ N _{4 and} a low hardness of Si ₃ N ₄ .
The film is sputtered using a sputtering target to which O ₂ is added, and its Vickers hardness is moderately reduced to a color film of approximately 700 to 1000 kg / mm ^2. Even if
Since a local crack or peeling does not occur in the protective layer, it is possible to prevent the generation of unprintable dots due to oxidation of the underlying heating resistor, and to provide a remarkable effect of extending the life of the thermal head.

According to the invention of claim ₂ , the composition ratio of SiO _{2 in} the sputtering target is approximately 20 to 5
Since it is 0 mol%, the Vickers hardness of the sputtered film forming the protective layer is preferably about 700 to 1000 kg /
It can be easily adjusted to the range of mm ² .

According to the manufacturing method of the third aspect of the present invention, the sputtering target is made of SiO ₂ having a low hardness of about _{2 in} advance.
0 to 50 mol% is added, and the Vickers hardness is preferably about 700 to 10 by sputtering only with Ar gas.
Since a protective layer serving as a colored film of 00 kg / mm ² can be formed, production is extremely simple. Furthermore, SiO
_Since the composition ratio of ₂ is limited to the above range, the active Si or Al metal component is liberated in the sputtered film forming the protective layer, and the film takes on a brown color. Because the toughness and adhesion of the protective layer are improved, even if the pressure contact force of the thermal head is increased, stress peeling between the protective layer and the heating resistor does not occur. It has the effect.

According to the manufacturing method of the present invention, even if a reactive gas consisting of O ₂ gas or N ₂ gas is added in sputtering, the amount of addition is about 1 to 3% of the total gas flow rate. Since the amount is small, the sputtered protective layer can be a colored film (brown film) in which the active Si or Al metal component is liberated while maintaining insulation. Furthermore, even if the target material is inexpensive, and the film is formed using either O ₂ or N _{2 as} the reaction gas, the change in hardness is small and the control is easy, and a single layer is excellent in adhesion, crack resistance, and insulation. There is also an effect that a long life and high print quality thermal head can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing a structure of a thermal head according to the present invention.

FIG. 2 is a graph showing the foreign matter resistance of the protective layer of the present invention with respect to the amount of added SiO ₂ .

FIG. 3 is a sectional view of a main part showing a structure of a conventional thermal head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Substrate 2, 12 Heat insulation layer 3, 13 Heating resistor 4, 14 Common electrode 5, 15 Individual electrode 6, 16 Protective layer

Claims (4)

[Claims] 1. A thermal head in which a heat insulating layer is formed on an upper surface of a substrate, a heating resistor and an electrode are stacked on the upper surface of the heat insulating layer, and the upper surface is covered with a protective layer. A sputtered film using a sputtering target composed of a ceramic sintered body containing Si ₃ N ₄ , SiO ₂ and AlN as main components, characterized in that it is a colored film having a Vickers hardness of approximately 700 to 1000 kg / mm ^2. Thermal head. 2. The thermal head according to claim 1, wherein the composition ratio of SiO _{2 in} the sputtering target is approximately 20 to 50 mol%. Forming a heat insulating layer on the upper surface of the substrate;
Forming a heating resistor on the upper surface of the heat insulating layer, forming an electrode connected to the heating resistor, and forming a protective layer covering the surface of the heating resistor and the electrode. In the method of manufacturing a thermal head, the step of forming the protective layer includes Si ₃ N ₄ , SiO ₂ , AlN
And the composition ratio of the SiO ₂ is approximately 20 to 50 m.
A method for producing a thermal head, comprising: performing sputtering using a sputtering target made of a ceramic sintered body having a concentration of 0.1% by weight and using an Ar gas as a sputtering gas to form a colored film. 4. The sputtering gas is a mixed gas of Ar gas and O ₂ gas or a mixed gas of Ar gas and N ₂ gas, and the flow rate of the O ₂ gas or N ₂ gas is a total gas flow rate. 3. The method according to claim 3, wherein
3. The method for manufacturing a thermal head according to 1.,