JPS6127264A - Formation of thermal head - Google Patents

Abstract

PURPOSE:To stabilize printing quality and to reduce the number of manufacturing processes to simplify said processes, by forming a protective layer (abrasion resistant layer) before applying heat treatment thereto at the temp. higher than that generated by a heat generating resistor. CONSTITUTION:In preparing a thermal head, an abrasion resistant layer 6 being a protective layer comprising tantalum pentoxide (Ta2O5) is formed in a thickness of about 5mum by a sputtering method and heat-treated in air or a nitrogen atmosphere. This heat treatment is performed at temp. equal to or higher than a peak temp. (Tmax) generated by the pulse driving or a heat generating resistor 3 to make it possible to impart a good characteristic for reducing the change ratio in the resistance value of the heat generating resistor 3. The relation of the resistance change ratio of thus formed thermal head and a pulse number is reduced in variation and printing quality is stabilized over a long period of time and, because a heat treatment process is performed after each layer was formed by a sputtering method, there is no interruption in the process and manufacturing cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention relates to a thermal head, and more particularly to a method for forming a thermal head.

[Conventional examples and problems]

Figure 4 is a cross-sectional view of the main parts of a conventional thermal head.
In the figure, l is an insulating substrate made of alumina or the like, 2 is semicircular arc-shaped glazed glass formed on the insulating substrate l, 3 is a heating resistor made of Ta2N, etc., and 4 is an electrode layer. The plate is formed of aluminum or the like only at a predetermined portion on the thermal resistor/body 3. 5 is silicon oxide (
The oxidation-resistant layer 5 is made of StO, ), etc., and covers the surface except for the terminals 8. 6 is tantalum pentoxide (Ta
, 0. ), etc. Although the wear-resistant layer 6 is not shown, it comes into contact with recording paper for printing.

A recess 6a is formed in the wear-resistant layer 6 at a position facing the heating resistor 3, and the recording paper is pressed against the recess 6a to perform thermal recording. Note that 7 is a Ni layer and 8 is a solder layer.

Next, the thermal recording operation of the thermal head configured as described above will be explained. First, connect the terminal 8 to the heating resistor 3.
, when a pulse voltage having a pulse width t1 as shown in FIG. 2(a) is applied via the electrode layer 4, the heating portion 3a of the heating resistor 3 has the characteristics as shown in FIG. 2(b). It is heated and cooled. The heat of this heat generating portion 3a is transferred to the oxidation-resistant layer 5.
The heat is transmitted through the recess 5alC of the wear-resistant layer 6 to the recording paper (not shown) pressed against the recess 6a, and one dot's worth of thermal recording is performed by one pulse.
An image can be printed on the recording paper by selectively applying a pulse voltage to each heat generating portion (dot) of the thermal head and moving the recording paper relative to the thermal head.

In addition, in order to print at a higher speed than this, it is necessary to increase the relative movement speed between the thermal head and the recording paper, and for this reason, the pulse voltage to the heating resistor 3 of the thermal head is "Pulse width as shown in figure (a)"
* (tl > t2) and narrow (and the applied voltage ■2 is vl
This pulse is set higher than
Compared to the temperature T1, the temperature characteristic is higher at the temperature T2 (Tx<Tz).

In general, the printing life of a thermal head is approximately 100 million pulse repetitions, and even after recording, the resistance value of the heating resistor 3 is
It is necessary to suppress the change to within ±109g from the initial value, and also the characteristics in the so-called step stress test, and the resistance value of the heating resistor 3 until the thermal head breaks, must change within ±10g. That is required.

In general ttc+s, heating resistors, in continuous pulse energization and step stress tests, the resistance value changes in a direction lower than the initial value, and the value is -1O
It tends to be about -2O4.

In order to prevent the resistance value of the heat generating resistor from changing as described above, after forming the heat generating resistor or forming the electrode layer, the heat generating resistor is removed during printing using a thermal head as disclosed in Japanese Patent Application Laid-Open No. 56-130375. A method has been used in which heat treatment is performed at a temperature higher than the heat generation temperature of the heat generating resistor to change the crystal structure of the heat generating resistor.

However, the above-mentioned processing steps are performed on heating resistors or
After the electrode layer is formed, it is necessary to form, for example, aluminum on the entire surface of the heating resistor (not shown) in order to prevent oxidation during heat treatment of the heating resistor.
requires a process to remove surface oxides such as aluminum and aluminum itself. Because of this heat treatment step, it is necessary to temporarily interrupt each forming step and the photo process, which has the drawback of increasing the number of steps and making the process complicated.

[Purpose of the invention]

The present invention provides a solution to the above-mentioned drawbacks,
It is an object of the present invention to provide a thermal head in which the rate of change in the resistance value of a heating resistor is small, the printing quality is stable even during long-term continuous operation, and the manufacturing process is simple with few steps.

[Embodiments of the invention]

FIG. 1 is a sectional view of a main part of a thermal head showing an embodiment of the present invention. In the figure, a first step is to form a semicircular arc-shaped glazed glass 2 at a predetermined position on an insulating substrate l made of alumina, etc., and then a T
A second step is to form a heat generating resistor 3 made of a2N or the like to a thickness of, for example, 500A by reactive sputtering of Ta, and an electrode layer 4 of, for example, aluminum is formed on the formed heat generating resistor 3. approximately 2 μm by sputtering method.
After this third step, the heating resistor 3 and the electrode layer 4 are formed by photo-etching.
a fourth step of forming a heat generating part 3a and a wiring conductor part 4a of a heat generating resistor 3, respectively, and a silicon oxide (sio
, ) etc. to a thickness of about 2 μm by sputtering, and tantalum pentoxide (Ta20
A sixth step is to form a wear-resistant layer 6, which is a so-called protective film layer, to a thickness of approximately 5 μm by sputtering, and the thermal head formed as described above is placed in the air or in a chip. and a seventh step of performing heat treatment in an elementary atmosphere.The conditions for this heat treatment are equal to or equal to the peak temperature (Tmax) of heat generated by pulse driving of the heat generating resistor 3, or
By performing the heating at a temperature higher than the peak temperature, the heating resistor 3 can have good characteristics such as a small rate of change in resistance value. For example, the pulse drive of this thermal head has an on-time of 1.1 ms,
When the cycle was 5.4 m s and the applied power was 1 w/dot, the surface peak temperature of the resistor was 450°C. Therefore, if heat treatment conditions higher than the surface peak temperature under these driving conditions are applied, changes in the resistance value of the heating resistor under the above driving conditions can be suppressed. The heat treatment conditions in this example are 500° C. and 36 m1n. After this heat treatment, there is an eighth step of removing the surface oxide formed on the surface of the terminal portion 4b of the electrode layer 4 by photoetching, and a ninth step of plating a nickel (Ni) layer 7 on the terminal portion 4b. A thermal head is formed by this step and a tenth step of coating and forming a solder layer 8 on the Ni layer by a reflow soldering method.

FIG. 5 shows the relationship between the resistance change rate and the applied power in a step stress test of the thermal head formed by the process as described above and the conventional thermal head. Characteristic A
is the characteristic curve of the thermal head according to this embodiment, characteristic B
is a characteristic curve of a conventional thermal head. Also, the 6th
The figure shows the relationship between the rate of change in resistance at 1 W/dot and the number of pulses in a continuous pulse energization test, where characteristic a is the characteristic curve of this embodiment and characteristic curve of the conventional thermal head.

〔Effect of the invention〕

As described above, in the thermal head of the present invention, after forming the protective layer (wear-resistant layer), heat treatment is performed at a temperature higher than the heating temperature of the heating resistor during printing, thereby reducing the change in resistance value of the resistor over time. (The printing quality is stable over a long period of time, and since a heat treatment process is performed after each layer is formed by continuous sputtering, there is no interruption in the process, making it possible to reduce manufacturing costs.) This effect is achieved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part of a thermal head showing an embodiment of the present invention, FIGS. 2(A) and 3(B), and FIG. 3(A). (b) is a diagram showing the relationship between the pulses during printing operation of the thermal head and the temperature of the head surface, Figure 4 is a sectional view of the main part showing a conventional thermal head, Figure 5 is a characteristic diagram of a step stress test, FIG. 6 is a characteristic diagram of the Norls life test. 1... Insulating substrate, 3... Heat generating resistor, 4... Electrode layer, 6... Wear resistant layer (protective layer) Fig. 1 6 the law of nature

Claims (1)

[Claims] an insulating substrate, a heating resistor formed on the insulating substrate, an electrode layer for energizing the heating resistor, and a protective layer for protecting predetermined portions of the heating resistor and the electrode layer. A method for forming a thermal head comprising: after forming the protective layer, heat treatment is performed at a temperature higher than the heat generation temperature of the heat generating resistor caused by energization of the heat generating resistor.