CA1225274A

CA1225274A - Thermal printing head and method of fabricating the same

Info

Publication number: CA1225274A
Application number: CA000449761A
Authority: CA
Inventors: Haruo Sorimachi; Kiyoshi Satoh; Takumi Suzuki
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 1983-03-17
Filing date: 1984-03-16
Publication date: 1987-08-11
Also published as: KR860000599B1; EP0119811B1; DE3464225D1; EP0119811A2; KR840007989A; US4595823A; JPS59169871A; EP0119811A3

Abstract

ABSTRACT
It has been found that the origin of crack(s) in the Ta2O5 anti-abrasion layer of a thermal printing head results from the crystallization of Ta2O5 in the layer, and that the crystallization can be suppressed by an addition of SiO2 to the layer. Thus, the anti-abrasion layer is kept from the crack(s) even under the high speed printing conditions using pulse width of 1 ms or less, and also under high colour density printing requiring input power density like 50 mj/mm2. Also, the thermal wearing life of the printing head can be extended to more than 10 folds of a conventional thermal printing head employing pure Ta2O5 anti-abrasion layer. The thermal printing head is subject to an appropriate annealing to stabilize the resistivity of the heat elements. The anti-abrasion layer is provided in a uniform mixture of Ta2O5 and SiO2 throughout the layer by sputtering a target composed of a mixture containing tantalum and silicon ingredients.

Description

This invention relates to thermal printing head for a thermal printer, particularly to its anti-abrasion layer usually formed as the uppermost layer for protecting heat elements and electrodes from abrasion wearing by contact of printing papers or ink ribbons. More specifically, this invention relates to improvement in the anti-abrasion layer adaptable for high speed printing, and to a process for producing such anti-abrasion layer.
As a non-impact printer, thermal printers have features of silent, relatively high speed and high dot density printing operation. It also permits to provide compact and low cost design compared with other non-impact printers employing laser or ink jet technologies.
Figure 1 is a schematic diagram for explaining general operation principle of thermal printers, Figure 2 is a cross sectional view of a thermal printing head of Figure 1, Figure 3 is an enlarged perspective view illustrating arrayed heat elements and conductors, Figure 4 is a cross sectional view taken prom the line IV-IV of Figure 3, Figure 5 is a schematic diagram illustrating a typical crack developed in an anti-abrasion layer, Figure 6 is a graph of experimental results showing relation between the peak temperature of the heat elements and the width of a pulsive electric current supplied to the heat elements, ~2~'7~

Figures I and I are example of X-ray spectra taken for a Tao layer formed by sputtering, Figures I and I are X-ray spectra taken for an Tush anti-abrasion layer formed by sputtering a target composed of 80 mow per cent Tao and 20 mow per cent Sue, Figure 9 is a graph of experimental results showing relation between the content of Sue in the Tush anti-abrasion layer and the threshold electric power to the heat elements to originate the crystallization in the anti-abrasion layer.
Figure 10 is a graph of experimental results showing change of abrasion wearing life of the Tush layer as a function of Sue con-tent in the layer, Figure 11 is a graphical view presenting the resistivity changes of heat elements with operation cycles in several thermal printing heads whose Sue content in anti-abrasion layer differs from one another. Through these figures, like reference numerals designate like or corresponding parts of precedent figures.
Referring to Figure 1, letters or graphic patterns are formed of black or color dots developed on a thermosensitive paper or a ordinary paper. When a printing paper 1 is fed between thermal printing head 2 and platen 3, fine heat elements disposed on the substrate 5 in a line are selectively supplied with electric current which is usually in the form of pulsed signals, and heats the paper 1 or ink ribbon (not shown).
As a result, a number of specified fine black or color dots SLY

in a line are generated on the paper 1. Thus, letters (A and B in Figure 1) or graphic patterns are completed when the paper is fed for a specified number of the lines.
Figure 2 presents a cross sectional view of a thermal printing head, comprising an insulating substrate 5 such as alumina (AYE) ceramics, a glaze layer 6 for preventing heat loss through the substrate 5, a heat element layer 7 formed on the glaze layer 6, usually in the Norm of thin film of such material as a tantalum nitride (Tarn), conductors 8, 9 and 9' formed on the heat element layer 7, except the specified portions (designated by R and R' in Figure 2), in order to supply the portions with electric power, an anti-oxidation layer 10 for protecting heat element layer 7 from oxidation, and an anti-abrasion layer 11 for protecting the heat element 4 and conductors 8 and 9 from abrasion wearing caused by friction of printing papers or an ink ribbon (thermal transfer ink ribbon).
Electrodes 12 are transversely formed on the conductor 8 with interposition of insulating layer 13 in between, and each specified one of the electrode 12 is connected to corresponding one of conductors 8 via a through-hole. As a gate means for the electric current supplied to the heat element 4 (the portion R), a diode 14, for example, is provided between electrode 9 and 9'.
Figure 3 is an enlarged perspective view illustrating heat elements (namely a portion for responsible for generating heat), 4 and conductors 8 and 9, which are disposed side by side in a row on a substrate (not shown).

I do Figure 4 is a cross sectional view of the portion taken along the line X-Y in Figure 3. As shown in Figure 4, the surface of anti-abrasion layer 11 is always subject to friction of a printing paper 1 during the paper is fed, and thus causing abrasion wearing. As the anti-abrasion layer, tantalum pentaoxide Tao), is preferably used because of its excellent abrasion resistance and adherence to other materials composing the printing head. However, Tao is insufficient to protect the heat elements from oxidation by atmospheric air during operations. Therefore, it is necessary to provide an anti-oxidation layer 10, composed of Sue, for example, between the heat elements 4 and the anti-abrasion layer 11, when the heat elements 4 are composed of a material such as Tarn, for example, whose oxidation resistance is relatively low.
In recent requirement of high speed operation for thermal printers, it is needed to energize the heat elements with narrower width electric pulses as 1 millisecond (my), compared with 2 to 3 my in conventional thermal printers.
And such high speed operation frequently causes cracks in the anti-abrasion layer. The crack usually extends to reach the surface of the heat elements, even through the anti-oxidation layer when being provided on the heat elements, and let the heat elements be exposed to the air. As a result, the heat elements are oxidized while they are heated, and the operational life of a thermal printing head is shortened than the expected life. The life of a thermal printing head, which is determined by such crack(s), is occasionally as short as one hundredth of that by abrasion wearing.
In the prior art thermal printer technology, occur-fence of the crack(s) in the anti-abrasion layer is ascribed to the stress caused by thermal shock when pulsive electric power is input to the heat elements. Therefore, improvements for preventing the crack(s) has been focused on providing an anti-abrasion layer which can relax such stress. Some proposed techniques are disclosed in Japanese patent applications;
Tokukai-Shou 56-154072 to 56-154075, all published November 28, 1981. Concept through these disclosures is to form the anti-abrasion layer whose chemical composition is not non-uniform along its thickness. For instance, when an anti-abrasion layer is formed of Tao and Sue, Tao, that is a hard component, is richer in near surface region, while Sue, that is a soft come potent, is richer in near underplayer region. And further, such composition change is given in a continuous layer or as disco-tenuous multiple layers each of which differs in the composition.
It should be noted that in the thermal printing head of the above disclosure, the anti-oxidation layer is omitted and the anti-abrasion layer composed of Tao layer containing Sue is responsible for acting as anti-oxidation layer. This is the fundamental discrepancy between above disclosure and understanding of the necessity of the anti-oxidation layer as mentioned before.

5~g Though the above disclosure claims need for no anti-oxidation layer between the heat element and the anti-abrasion layer, above mentioned techniques require complicated process control and a special apparatus for fabricating such anti-abrasion layer, and thus, lead to difficulty of providing low cost thermal printing heads.
According to the investigation by the present inventors, it has been found that the crack(s) in an antiabortion layer composed of Tao is resulted from the crystallization of Tao in the layer, and the crystallization is accelerated under the high speed operation conditions. It is also found that, only when the anti-abrasion layer is free from crack(s), the heat elements can be subject to a necessary annealing to stabilize their resistivity. Therefore, the present invention is based upon a concept to prevent the crystallization in the anti-abrasion layer which may be a uniform single layer.
It is therefore desired to provide a low cost thermal printing head applicable to high speed printing and having long operational life, and it is also desired to provide a method for fabricating a thermal printing head having an anti-abrasion layer which is hard to crystallize even under high speed operation conditions and also having heat elements stabilized of their resistivity.
Accordingly, the present invention provides a thermal printing head comprising: a substrate of insulating materials;
a plurality of heat elements disposed on said substrate in ~5Z'7'~

order to generate color dots constituting printed patterns;
a plurality of conductors for connecting said heat elements to an electric power source through respective gate means to supplying electric power to said heat elements selectively;
an anti-oxidation layer covering said heat elements and conductors in order to protect them from oxidation, and an anti-abrasion layer formed on said anti-oxidation layer in order to protect the anti-oxidation layer, the heat elements and -the conductors from abrasion wearing, said anti-abrasion layer being composed of a uniform mixture including tantalum pentaoxide (Tao) as the principal component and silicon dioxide (Sue) as a sub-component.
The present invention also provides a method of manufacturing a thermal printing head having at least a plurality of heat elements formed on a insulating substrate in order to generate color dots constituting printed patterns, a plurality of conductors for connecting said heat elements to an electric power source through respective gate means to supply electric power selectively to said heat elements, an anti-oxidation layer covering said heat elements and conductors in order to protect them from oxidation, and an anti-abrasion layer composed of a uniform mixture including tantalum pentaoxide (Tao) as the principal component and silicon dioxide (Sue) as a sub-component, and formed on said heat elements and conductors in order -to protect them from abrasion wearing, which method comprises a step of: fabricating said anti-abrasion layer by sputtering a target composed of a mixture containing tantalum principal ingredient and silicon sub-ingredient.
In the thermal printing head of the present invention, an anti-oxidation layer is introduced like an ordinary ones.
As the materials for the anti-oxidation layer, various compound including silicon nitride Sweeney), silicon oxynitride, silicon dioxide (Sue), alumina (AYE), and borosilicate glass layer may be employed, and the first three members, particularly silicon dioxide, have been confirmed to be preferred for practical use.
It is found by the inventors that the origin of the crack(s) in a Tao anti-abrasion layer of a thermal printing head is due to the crystal growth of Tao in the layer. Figure 5 is a schematic diagram illustrating optical microscopic view of a typical crack 15 and a opaque region 16, both observed in a Tao anti-abrasion layer on a heat element portion.
It is necessary to input a specified energy to heat elements in order -to generate printed dots having specific color density. This means that the narrower the width of a pulsive electric current, the higher the peak temperature of the heat elements. Figure 6 is a graphical view showing relation between the peak temperature of the heat element and the width of pulsive electric current supplied to the heat elements at constant power input, 40 milli-joules/pulse/mm2 (this unit will be indicated by mj/mm2 hereinafter) and repetition period of 10 milliseconds (my). The crack(s) 15 occurs in I

the region where the pulse width is less than 1 my, and is always accompanied by the opaque region 16 shown in Figure 5. Observe anion on the opaque region 16 by a polarization microscope indicated existence of crystals in the region. These facts suggest that the crack(s) results from crystallization of the Tao anti-abrasion layer, and it was found that the crystal-ligation is accelerated in the temperature range higher than 600C.
Figures I and I are X-ray spectra of an Tao layer formed by use of sputtering method, wherein I for the layer as sputtered and I for that being subject to a heat treatment at 700C for 10 hours. The peaks in Figure I
correspond to (001), (100), and (101) planes of Tao crystals, respectively. This X-ray diffraction analysis reveals that as-sputtered Tao layer is almost amorphous and it has been crystallized at 700C.
It is not impossible to conceive that if crystal grains grow in the anti-abrasion layer, the tear strength of the layer is reduced, and a crack originates at a weakest grain boundary, when the layer is subject to tensile stress. Such tensile stress may be caused by difference of thermal expansions between the anti-abrasion layer and its underplayers (vainly the glaze layer), when the heat elements generate heat. Then the crack would extend to across the entire layer.
According to this assumption, it follows that such crack is hard to originate thermally in the anti-oxidation layer composed of Sue film which is thermally stable to keep amorphous ,, - 9 -r it t 7 state. However, a crack originated in the Tao anti-abrasion layer spreads further into the Sue anti-oxidation layer, and finally reaches to the surface of the heat elements. Therefore, once a crack originates in the anti-abrasion layer, the anti-oxidation layer is made ineffective for protecting heat elements from oxidation. In other words, if the anti-abrasion layer is prevented from the crystallization, and thus from cracks, the heat elements can be kept free from oxidation.
From this point of view, the present invention is intended to provide an anti-abrasion layer prevented from the crystallization originated by the heat generated from heat elements, even at high speed operation conditions that means a high peak temperature operation.
The present invention is based on the idea that the crystallization must be suppressed by addition of a sub component to the Tao anti-abrasion layer, and Sue is selected as the sub component. Sue is expected to be effective for this purpose because of its stable amorphous state against heat treatment and strong adherence to the underplayer, Sue anti-oxidation layer.
Therefore, it is obvious that a portion of the Sue can be replaced by other one or more of sub components which are also effective for suppressing the crystallization in the Tao anti-abrasion layer.
A preliminary crystallization examination was con-dueled on five kinds of specimens, each of which had a multi-layer structure similar to that in an actual thermal printing head, but conductor layer for it was eliminated. Namely, the following layers were formed one after another on a glazed alumina substrates by use of sputtering method: a 500 A thickness tantalum nitride (Tarn) layer, a 1 micro-meter thickness Sue layer, a 4 micro-meter thickness Tush mixture layer.
Content of Sue in the Tush layer was altered for each containing 5, 10, 20, 30, and I mow per cent, respectively.
Then the specimens were subject to a heat treatment at -temperatures of 600, 650, 700, 750, and 800C for 10 hours each.
According to X-ray analyses on the specimens, no crystallization of Tao was observed in the Tush layers containing Sue more than 20 mow per cent, after the heat treatment up to 800C, and also in the layer containing 5 and 10 mow per cent Sue up to 700C. Under this temperature, no crack was created in the layers.
However, when heated at a temperature above 700C, the layers of the latter case showed existence of Tao crystal.
Figures I and I are X-ray spectra of a Tao-Sue mixture layer containing 20 mow per cent of Sue, the layer formed by the sputtering method as described above, wherein I
for the layer as sputtered and I for that being subject to a heat treatment at 700C for 10 hours. By comparing Figures 8 with Figures 7, crystallization of Tao, represented by peaks corresponding to the planes (001), (100) and (101), is substantially suppressed by the addition of Sue.
According to the results of the preliminary export-mint, three kinds of -thermal printing heads having a same I

structure as shown in Figure 2 were fabricated. Of these print-in heads, the anti-abrasion layer was composed of a uniform mixture of Tao and Sue, but the content of the Sue in the layer is different among the three.
The outline of the fabrication process is as follows:
1) A 500 A thickness tantalum nitride Tony) heat element layer was formed on a glazed alumina substrate by use of sputter-in method.

2) A conductor layer comprising three layers of 500 A Nick, O O
3500 A A and 300 A Or was formed subsequently on the Tarn layer by use of vacuum evaporation method.

3) The Tarn heat element layer and the conductor layer was etched to form stripes with width of 0.1 millimeters by use of conventional photo lithographic method.

4) Each of the conductor layer stripes was etched off of its portion on a specified area of each Tarn layer stripe by use of conventional photo lithographic method, wherein the area was to be used as a heat element. Thus, heat elements and their lead conductors were completed.

5) A 1 micro-meter thickness Sue anti-oxidation layer was formed on the exposed Tarn layer stripes (heat elements) by use of mask sputtering method.

6) A 4 micro-meter thickness Tush anti-abrasion layer was formed on the Sue anti oxidation layer by use of mask sputtering method. In this experiment, three different sputter-in targets composed of a mixture of Tao and Sue were employed 5~'2'7~

to obtain Tush anti-abrasion layers different in Sue con-tent. The content of the Sue among the targets were 0, lo 20, and 30 mow per cent, respectively.
Then, each of these four kinds of thermal printing head was operated under the supply of a pulsive electric current of various power densities (in mj/mm2), and investigated of the threshold power density to originate the crystallization in its anti-abrasion layer. The width and repetition period of the electric pulses were l my and lo my, respectively The input power density was increased from 35 mj/mm2 step by step and duration time at each power density was lxlO8 pulses equivalent to l.67x104 minutes).
Figure 9 is a graph showing relation between the content of Sue in the Tush anti-abrasion layer and threshold power input to the heat elements to originate the crystallization in the anti-abrasion layer. By interpolating the curve of Figure 9, it will be seen that Sue of 5 to lo mow per cent in the anti-abrasion layer is also effective to suppress the crystallization to be caused by power input approximately 40 mj/mm in pure Tao layer. Figure 9 also shows that the Tao-Sue anti-abrasion layer containing 20 mow per cent Sue does not crystallize by the input power up to about 50 mj/mm2 (pulse width 1 my).
By referring back to Figure 6, the 50 mj/mm2 input power will result in peak temperature of 750C of heat elements, because it can be assumed -that the peak temperature of the heat elements is proportional to the input power. Therefore, the Tush antiabortion layer containing 20 mow per cent Sue is applicable to higher density printing requiring input power up to approximately 50 mj/mm2 (pulse width 1 my), and also to high speed printing operation with pulse width more than approxi-mutely 0.6 my (input power density 40 m~/mm2). Even when the content of Sue is little as 5 mow per cent, the anti-abrasion layer is still tolerable for the high speed operation with pulses width around 1 my.
For the purpose of preventing crack(s) in the anti-abrasion layer, it is preferred to increase the content of Sue in a Tush anti-abrasion layer, however, it is anticipated that the increase of the Sue probably impairs anti-abrasion wearing property of the layer.
Figure 10 is a graph showing change of abrasion wear-in life of the Tush layer as a function of Sue content in the layer. The abrasion wearing life is defined in terms of the relative total length of printing papers necessary to wear out each Tush anti-abrasion layer to the total length of papers necessary to wear out same thickness pure Tao anti-abrasion layer. The abrasion wearing life of the pure Tao layer is about 30 kilo-meters (km) per micrometer thickness.
As shown in Figure 10, the abrasion wearing life is decreased with the increase of Sue content, but the decrease is confined in the degree less than 20 per cent, if the Sue content is kept less than 30 mow per cent. Though approximately 30 per ~Z~'7J~L

cent decrease of the abrasion wearing life is observed on the Sue content of 40 mow per cent, it can be said that the rest 70 per cent of the abrasion wearing life is practically still enough large when considering the thermal wearing life of a pure Tao anti-abrasion layer.
According to the above embodiment, it can be concluded that the addition of Sue to Tao anti-abrasion layer is in the range from 5 to 40 mow per cent, preferably from 10 to 30 mow per cent.
In the thermal printing head having heat elements composed of resistive materials such as Tarn, the resistivity of the heat elements is usually decreased with the increase of operational time. However, when the conventional thermal print-in head is operated under the supply of narrow width pulsive electric current such as 1 my, the resistivity of the heat elements abruptly increases and the head becomes inoperable within a relatively short operation period. This is, as mentioned earlier, due to the oxidation of the heat elements, which takes place when crack(s) originates in the anti-abrasion layer. On the contrary, when the anti-abrasion layer is prevented from the crack(s), such abrupt resistivity increase does not appear in an extended operation period and the resistivity rather tends to a minimum.
Figure 11 is a graph presenting the resistivity changes in some thermal printing heads with operation period.
The anti-abrasion layers of the printing heads were formed by I

sputtering targets composed of a mixture of Tao and Sue, the mixtures being different in Sue content from one another. In the figure, ordinate represents the relative resistivity change of the heat elements to its initial values in percentage, while abscissa represents operational time in terms of the number of electric pulses supplied to the heat elements. The power density, width, and repetition period of the electric pulses were 40 mj/mm2, 1 my, and 10 my, respectively. The curve A is for the printing head whose Sue content in the anti-abrasion layer is 0 (pure Tao anti-abrasion layer). The curves B, C, and D correspond to the resistivity changes in the printing heads whose Sue con-tents are 10, 20, and 30 mow per cent, respectively.
As shown by the curve A, steep increase of the resistivity is observed after the supply of 107 pulses, equiva-lent to the operation period of about 30 hours. In other words, if printing is carried out in the density of 4 dots/mm (100 dots/inch) in the feeding direction, the printing head causes such thermal wearing after when the papers of 2.5 km (2.7x103 yards) in total length are fed. As mentioned before, abrasion wearing life of pure Tao anti-abrasion layer is about 30 km per micro-meter thickness (in actual thermal printing head, the thickness of the anti-abrasion layer is used to be few micro-meters), therefore the thermal wearing life of the pure Tao anti-abrasion layer is less than few tenth of the abrasion wear-in fife.
If Sue is added to a Tao anti-abrasion layer, the I

crack(s) in the layer is suppressed, and the oxidation of the heat elements is prevented. As a result, the thermal wearing life of a thermal printing head at the high speed operation conditions is extended to more than 10 folds to be comparable to the abrasion wearing life, as shown by the curves B, C, and D.
The resistivity of each of the curves B, C, and D tend to approach to a minimum after supplied with about 107 pulses. This phenomenon is considered to mean that the heat element layer composed of a semi conductive material such as Tarn is annealed by the supply of the electric current and removed its inherent defects and strains, and thus stabilized. In this sense, the present invention can not only improve the operational life of a thermal printing head but also provide stable resistivity characteristics for a thermal printing head.
It is difficult to define the annealing conditions of the heat elements in general, since the speed and amount of the resistivity change differ according to -the material and the fabrication process of the heat element. However, for the Tarn heat elements employed in this embodiment, of which the resistivity decrease saturates at about 12 per cent within relatively short period as shown in Figure 11, it is possible to set a standard as follows: the annealing should be performed so as to cause the resistivity decrease of 8 to 10 per cent of its initial value, and the electric current supplied there should be in the range from 30 to 50 mj/mm2.

I ox The present invention has been described with no-spent to preferred embodiments thereof, but it will be recognized that modifications and variations may be affected within the spirit and scope of the invention. For example, it is obvious to those skilled in the art that a part of the Sue in the Tao-Sue anti-abrasion layer is replaced by another component such as silicon monoxide (So) or silicon nitride (Sweeney) to suppress the crystallization of Tao in the layer, and also, the source of tantalum and/or silicon in the target for forming Tao Sue anti-abrasion layer is not limited to be in oxide state, but may be in metallic state which is sputtered in an oxidizing atmosphere to form a mixture of Tao and Sue.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A thermal printing head comprising:
a substrate of insulating materials;
a plurality of heat elements disposed on said substrate in order to generate color dots constituting printed patterns;
a plurality of conductors for connecting said heat elements to an electric power source through respective gate means to supplying electric power to said heat elements selectively;
an anti-oxidation layer covering said heat elements and conductors in order to protect them from oxidation; and an anti-abrasion layer formed on said anti-oxidation layer in order to protect the anti-oxidation layer, the heat elements and the conductors from abrasion wearing, said anti-abrasion layer being composed of a uniform mixture including tantalum pentaoxide (Ta2O5) as the principal component and silicon dioxide (SiO2) as a sub-component.

2. A thermal printing head in claim 1, wherein said anti-oxidation layer is composed of silicon dioxide (SiO2), silicon oxynitride, or silicon nitride (Si3N4).

3. A thermal printing head in claim 2, wherein the content of Ta2O5 in said anti-abrasion layer is more than sixty per cent in mol ratio.

4. A thermal printing head in claim 1, 2 or 3 wherein the content of SiO2 in said anti-abrasion layer is less than forty per cent in mol ratio.

5. A thermal printing head in claim 1, 2 or 3, wherein the content of SiO2 in said anti-abrasion layer is in a range from ten through thirty per cent in mol ratio.

6. A method of manufacturing a thermal printing head having at least a plurality of heat elements formed on a insulating substrate in order to generate color dots constituting printed patterns, a plurality of conductors for connecting said heat elements to an electric power source through respective gate means to supply electric power selectively to said heat elements, an anti-oxidation layer covering said heat elements and conductors in order to protect them from oxidation, and an anti-abrasion layer composed of a uniform mixture including tantalum pentaoxide (Ta2O5) as the principal component and silicon dioxide (SiO2) as a sub-component, and formed on said heat elements and conductors in order to protect them from abrasion wearing, which method comprises a step of:
fabricating said anti-abrasion layer by sputtering a target composed of a mixture containing tantalum principal ingredient and silicon sub-ingredient.

7. A method of manufacturing a thermal printing head in claim 6, further comprising a step of:

an annealing of said heat elements by supplying them with an electric current of less than the amount causing recrystallization of said anti-abrasion layer.

8. A method of manufacturing a thermal printing head in claim 6, wherein the content of tantalum ingredient in said target being more than sixty per cent in mol ratio as converted into Ta2O5.

9. A method of manufacturing a thermal printing head in claim 6, wherein the content of silicon ingredient in said target is less than forty per cent in mol ratio as converted into SiO2.

10. A method of manufacturing a thermal printing head in claim 6, wherein the content of silicon ingredient in said target is in a range from ten through thirty per cent in mol ratio as converted into SiO2.

11. A method of manufacturing a thermal printing head in claim 6, wherein said target contains Ta2O5 as the tantalum principal ingredient.

12. A method of manufacturing a thermal printing head in claim 6, wherein said target contains SiO2 as the silicon sub-ingredient.

13. A method of manufacturing a thermal printing head in claim 7, wherein said annealing is performed by supplying pulsed electric current.

14. A method of manufacturing a thermal printing head in claim 7, wherein the heat elements are composed of a tantalum nitride, and said annealing is continued until the resistance of each said heat elements decreases a value in a range eight through ten per cent of its initial value.

15. A method of manufacturing a thermal printing head in claim 13, wherein the heat elements are composed of a tantalum nitride, and the amount of said pulsed electric current is such that it generates heat in a range 30 through 50 milli-joule/pulse/mm2 at each said heat element under a duty factor less than 0.5.