Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Patent
1996-07-15
1999-08-17
Tran, Huan
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
347203, B41J 2335
Patent
active
059401109
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal head which is used in heat sensitive recording of facsimile, printer or the like and a method for manufacturing the same.
BACKGROUND TECHNIQUES
Conventionally, as illustrated in FIGS. 10(a) and 10(b), a glaze layer 2 is provided as a heat accumulation layer on an insulative substrate 1 such as that made of ceramic material. Then, film formations are performed by sputtering or deposition from a heat generating resistor material such as that of Ta system, silicide system, Ni--Cr system or the like and an electrode material such as that of Al, Cr--Cu or Au, whereupon a heat generating resistor 3 and wiring electrodes 12 composed of a common electrode and individual electrodes are formed through performance of patterning in the photolithographing step. Thereafter, in order to prevent oxidation of and provide wear resistance with respect to the heat generating resistor 3, a protective film 9 such as that made of SiO.sub.2, Ta.sub.2 O.sub.5, SiAlON, Si.sub.3 N.sub.4 or SiC is formed by sputtering, ion plating or CVD (Chemical Vapor Deposition) to thereby manufacture a thermal head.
However, in the conventional method for manufacturing a thermal head, since the sectional configuration of a peripheral edge portion of each of the wiring electrodes 12 composed of a common electrode and individual electrodes is almost orthogonal, similar difference in level occurs also in the surface of the protective film 9. In addition, due to a difference in growth process between a protective film for the heat generating resistor 3 and that for the wiring electrode 12 when this protective film is formed, a fault 10 at which the film continuity as viewed in the plane direction is discontinued occurs in the protective film layer.
For this reason, the thermal head that had been manufactured by the above-mentioned manufacturing method had its resistance value increased early in its use, with the result that when printing was performed using this thermal head, such increase in resistance value became a cause of dotting failures, which resulted in that the printing run service life of the thermal head became shorter. Also, it is considered that during printing run, ions in the thermosensible paper, moisture, Na.sup.+ ion and Cl.sup.- ion in the atmosphere, and the like enter into the thermal head due to the faults 10 of the protective film thereof, with the result that there was the problem that the heat generating resistor 3 and wiring electrodes 12 were corroded and as a result the thermal head had inferior corrosion resistance.
As conventional examples of solving the above-mentioned problems, a manufacturing method wherein a forward end portion of each wiring electrode 12 connected to a heat generating resistor 3 is tapered to thereby decrease the fault and level difference of the protective film (e.g., Published Unexamined Japanese Patent Application No. S-56-129184), a manufacturing method wherein a photo-step and etching step are performed twice or so with respect to a forward end portion of each wiring electrode 12 connected to a heat generating resistor 3 to thereby form this forward end portion into a two-stepped configuration and thereby decrease the level difference of the protective film (e.g., Published Examined Japanese Patent Application No. S-55-30468), a manufacturing method wherein high frequency bias sputtering is added during formation of the protective film to thereby prevent generation of cracks (e.g., Published Unexamined Japanese Patent Application No. S-63-135261), etc. have been made publicly known.
However, while in the conventional thermal head a wiring electrode thereof was such that a specific configuration was imparted to only a forward end portion thereof that is connected to the heat generating resistor, the effect thereof upon enhancement of the printing durability and reliability was not sufficient. Namely, faults and level differences in the protective film that result from the level differences in the wiring electrode occur not only in t
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Nakamura Yuji
Saita Yoshiaki
Sato Yoshinori
Seiko Instruments Inc.
Tran Huan
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