JPH0491960A - Thermal head - Google Patents

Abstract

PURPOSE:To prevent a dielectric breakdown of a heating element by making up a protective film of an insulating film as a lower layer and a conductive protective film as a upper layer and forming the conductive protective film out of a conductive ceramic material to which a metal or a metallic compound is added. CONSTITUTION:Protective films 10a and 12 formed on a heating element 5 ranging to electrodes 6 and 8a consist of an insulating film 10a as a lower layer and a conductive protective film 12 as an upper layer. As a material of the conductive protective film 12, a conductive ceramic material in which a metal or a metallic compound is added to a ceramic material is used. As a ceramic material, such materials as SiAlON, boron nitride, and nitriding silicon are used, and TiC, Ti2B, TiSi, Ta, Taxi2, WSi, and MoSi are used as the metal or metallic compound. Accordingly, the electrification quantity in the protective films 10a and 12 can be reduced and a dielectric breakdown of the heating element 5 can be prevented.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a thermal head used in facsimile machines, printers, and the like. (Prior art) Thermal films are classified into thin film thermal films manufactured by the 1-thin film process, and thick film thermal films manufactured by the rry++9 process. The smell of the zu't type. Also, lol! , a heating element and an electrode are formed on the edge substrate,
At least a portion of the electrode from the heating element -11, -wa8,
A protective film is formed. Figure 2 shows the thin film ZERMARKETSU 1~・Example μ・Table A':
::h L';;monoean,),・? , an eye board, for example, 91 with a surface of Noras 1f7,
・-ZN ・Covered chisel ceramic substrate C 3、Substrate 2. 1 Go A1 Antibody No. 1 is patterned on the soil 9"5
Reku, -formation, k age 1, ・zo no 1. The electrodes 6 and 8 are separated and formed ζ, and the resistor 5 is exposed between the facing electrodes 6 and 8 as a heating element. 0 is a selection electrode that selects the heating element 5 individually. , ε3 is the common lj pole that supplies power for heat generation 4-1j, common @pole 8 is connected to all the heating elements E) L,'" is commonly connected., -10i: J
Insulating protective film R/Yes, heating element 5 or IE. At least part of the common electrode 8 and the selection electrode 6 are covered with an area (1 knee formed). (Problem to be solved by the invention) The heating weight is covered with an insulating protective film η. During printing, the insulating protective film is charged with static electricity due to friction with the recording paper, resulting in a high potential of 50 to 100 KV.・There is. When charged to such a high potential,
A discharge occurs in the resistor structure of the heating element. A dielectric breakdown phenomenon occurs and the resistance value decreases. In the case of a thin film thermal spatula 1-, a common electrode 1. supplies power for energizing the heating element. , -, a large current flows through them, so in order to increase the current capacity, it is necessary to increase the area of the common electrode or increase the film thickness. The distance from the edge of the thermal head to the heating element 5 (a in Fig. 2) can be increased by increasing the common electrode width (C in Fig. 2).
), which becomes an obstacle to downsizing devices such as printers equipped with a thermal head of τ.17. ! The ``l objective'' is to provide a protective film that can prevent dielectric breakdown of the heating element by reducing the electrical charge on the protective film due to the friction of the recording paper. It is something. The present invention also includes: Narrow the common electrode 1111

The object of the present invention is to provide a thermal head that is convenient for downsizing equipment equipped with a thermal head. (Means for Solving the Problems) In the present invention, at least part 1 of the @pole from the heating element
”: The protective film formed over the c-needle consists of one layer of insulating film and one layer of conductive protective film. In a preferred embodiment of the present invention, a part of the common electrode (of the electrode) is exposed from the insulating film, and the conductive protective film and the common electrode are connected at the exposed part. 1 Conductive protective film is S i A
ri, C, 1, "i2B, T in ceramic materials such as Q ON system, boron chi 1-dide system, silicon nitride system, etc.
It is a conductive ceramic material to which metals or metal-based compounds such as Si, Ta, TaSi, WSi, and MoSi are added. (Function) The surface layer of the protective film is a 4-electrode protective film, τ', when printing, r, = 1 Even if it is held against the recording paper and rubbed against the pupil, no charge will occur on the protective film. do not have. When the conductive protective film is connected to the extraction electrode, the conductive protective film is used as part of the common electrode in step 2. Because the current capacity of the common electrode can be reinforced. The common electrode width of the groups Vj, -, , t: can be reduced. (Example) Fig. 1 shows the application of the present invention to a bookkeeping type Garmal head.
Example survey table 1. Reference numeral 2 denotes a substrate 1, for example, a ceramic substrate whose surface is covered with a glassy glaze layer. A resistor layer 4 is patterned and formed on one substrate 21-, and electrodes 6,
8a is formed in a pattern, and the resistor 5 exposed between the picture electrodes 6 and 8a becomes a heating element. Reference numeral 6 designates a selection electrical connection for individually selecting the heating elements, and 8a represents a common electrode that supplies power for heating to the heating element 5. The common electrode 8a is commonly connected to the heating element F). Reference numeral 10a denotes an insulating protective film that extends from the heating element F) to a part of the selection electrode 6 and a part of the common electrode 8a.
) is formed. The insulating protective film 10.1 may be the same as a conventional protective membrane. The insulating protective film 10a of the thin-film thermal head has a three-layer structure in which a wear-resistant film is formed through an oxidation-resistant film, and an L-layer that also serves as an oxidation-resistant film and a wear-resistant film. There is. In the two-layer structure, S i O, is used as the anti-noise film. Si, N4, etc. are used, and the wear-resistant film is Ta, O.
l,5j3N4,5iAQON,Δp2o,. (2), a-8iON, BP, SiC, etc. are used. - As a protective film for the layer, S i A Q ON and S j
, 3 N 4, etc. are used. Insulating protective film 10a
Since the conductive protective film]-2 is formed on the conductive protective film, the film thickness can be made thinner than that of the conventional protective film. The thickness of the insulating protective film 1()a may be determined depending on the application. A conductive protective film 12 is formed on the insulating protective film 10aJ-, and the conductive protective film 2 is connected to the common electrode E3a exposed from the insulating protective film 10d. Conductive protective film] 2) T is added to SiAρON as a metal compound.
A material containing 5 to 10% by weight of iC is used, and its thickness is about 5 μm. The specific resistance of this conductive protective film 12 is approximately 1
It has a hardness of about 1600 pincus. By connecting the common electrode 8a and the conductive protective film 12 and using the conductive protective film 12 as a part of the common electrode as in this embodiment, the common electrode 11@d can be reduced to about 0.5 mm. This is about 115 mm compared to the conventional common electrode width C shown in FIG. As a result, the distance from the edge of the thermal head to the center of the heating element 5 can be reduced, and the equipment on which this thermal head is mounted can be downsized. The material of the conductive protective film 12 is not limited to those shown in the embodiments, and may include ceramic materials such as 5iAQON, boron nitride, and silicon nitride, TiC, Ti2B, and TiS.
i, Ta, TaSi2. It can be a conductive ceramic material added with a metal or a metal-based compound, such as WSi or MoSi. These conductive ceramic materials can be formed by a sputter link method using a ceramic material added with a metal or a metal-based compound as a target. In FIG. 1, the common electrode 88 and the conductive protective film 12 are connected, but if the purpose is simply to prevent charging of the protective film, the connection between the common electrode 8a and the conductive protective film 12 is not necessary. do not have. Although FIG. 1 shows an embodiment applied to a thin film type thermal head, the present invention can also be applied to a thick film type thermal head. In that case, overcoat glass or the like is used as the protective film, serving as both an oxidation-resistant film and an abrasion-resistant film. (Effects of the Invention) In the present invention, since the upper layer of the protective film is a conductive protective film, there is no charge during printing, and the heating element can be protected from dielectric breakdown, thereby eliminating problems caused by static electricity. can. By connecting the conductive protective film to the common electrode, the current capacity of the common electrode can be reinforced, and the width of the common electrode can be narrowed to reduce the size of the thermal head.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment, and FIG. 2 is a sectional view showing a conventional thermal head. 2...Substrate, 4...Resistor, 5...
・Heating element, 6...Selection electrode, 8a...
Common electrode, 10a... Insulating protective film, 12...
...Conductive protective film. Figure 1

Claims (2)

[Claims] (1) In a thermal head in which a heating element and an electrode are formed on an insulating substrate, and a protective film is formed over at least a portion of the electrode from the heating element, the protective film has a lower insulating film and an upper conductive layer. 1. A thermal head comprising a protective film, the conductive protective film being a conductive ceramic material in which a metal or a metal-based compound is added to a ceramic material. (2) The thermal head according to claim 1, wherein a part of the common electrode among the electrodes is exposed from the insulating film, and the conductive protective film is connected to the common electrode at the exposed part.