JP3667862B2 - Method for adjusting heating element resistance value of thin film thermal print head and thin film thermal print head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a method of adjusting the heating element resistance value of the thin film type thermal print head, and relates to a thin film type thermal print head, and more specifically, the heating element resistance value of the thin film type thermal printhead desired To adjust the technology.
[0002]
[Prior art]
2. Description of the Related Art A thermal print head for performing printing by a thermal method or a thermal transfer method is configured by arranging a large number of heating elements that can be individually driven to generate heat on an insulating substrate. The thermal print head can be classified into a thick film type and a thin film type according to the heating element forming method. In the thick film type thermal print head, the heating element is formed by a thick film printing method. On the other hand, in a thin film type thermal print head, the heating element is formed into a thin film by CVD or sputtering.
[0003]
Thick film thermal print heads have the advantage that they can be manufactured relatively easily and at a low cost. On the other hand, since each heating element is thick, the print dots are blurred and the print density is reduced. It has the disadvantage that it cannot be raised beyond a predetermined level. Thin-film thermal printheads are suitable for high-speed printing because they have a thin film of 500 to 1500 mm in each heating element, and have less blur in printed dots and excellent thermal responsiveness. Although it has the advantage that the printing density can be increased, there is a disadvantage that the manufacturing cost is high because the film forming process and the photolithographic process by CVD and sputtering are repeated.
[0004]
For example, when a thermal print head is configured to print on an A4 size recording paper at a printing density of 200 dpi, 1728 heating elements are arranged in a line. And, it is desirable that the resistance value of each of the heating elements is constant in order to improve the printing quality. However, when the heating elements are formed on the substrate, the resistance value of each heating element inevitably varies. Arise. This is because variations occur in the pattern size and thickness of the heating element.
[0005]
In the case of a thick film type thermal print head, resistance value adjustment called pulse trimming is performed in order to correct the variation in resistance value of each heating element as described above. That is, while a measurement probe is brought into contact with an appropriate part of the substrate and the resistance value of each heating element is monitored, a pulse current is passed through the heating element so that the measured resistance value of the heating element falls within a predetermined range.
[0006]
[Problems to be solved by the invention]
However, in the thin film type thermal print head, since the thickness of the heating element is as extremely thin as 500 to 1500 mm as described above, the resistance value adjustment by the pulse trimming as described above is impossible.
[0007]
By the way, in recent years, attempts to perform color printing by a thermal print head have been actively made. In this case, a thin film type thermal print head is often employed in order to obtain a print quality of a certain level or more. In color printing by a thermal print head, overprinting is performed using a sublimation ink ribbon having an area of Y (yellow), M (magenta), C (cyan), or B (black) in addition to this. . The sublimation type ink ribbon can change the amount of ink transferred to the recording paper according to the applied heat, and therefore the printing energy given to the heating element when printing each color is changed in multiple stages. By doing so, multi-tone color printing can be performed. When such multi-tone printing is performed, it is more strongly required to suppress variation in resistance value of each heating element of the thermal print head within a predetermined range. As is well known, when color printing is performed, even if the blending ratio of each color is slightly changed, the color tone changes greatly. However, if there is a large variation in the resistance value of the plurality of heating elements constituting the thermal print head, even if each heating element is driven under the same conditions, the generated printing energy differs for each heating element, and as a result, The quality of color printing is significantly reduced.
[0008]
When a thin film thermal print head is formed by a normal manufacturing process, it is said that it is difficult to suppress the variation in resistance value between the heating elements within ± 10% even if the film forming process is improved. ing. Such a variation in resistance value between the heating elements is too large to perform the color printing as described above with high quality.
[0009]
The present invention has been conceived under the circumstances described above, and the resistance value of a thin film resistor formed by CVD or sputtering can be easily and more accurately measured after the formation of the thin film resistor. The challenge is to provide new technology that can be adjusted well.
[0010]
DISCLOSURE OF THE INVENTION
According to a first aspect of the present invention, there is provided a method for adjusting a heating element resistance value of a thin film type thermal print head, the method comprising: a plurality of thin film resistors formed by CVD or sputtering on an insulating substrate. A method of adjusting the resistance value of each heating element by irradiating each of the heating elements in a thin film thermal print head in which the heating elements are arranged , the center of the surface of each heating element in the longitudinal direction This is characterized in that the excimer laser is irradiated to a plurality of band-like regions extending in the width direction at a predetermined interval in the length direction .
[0012]
In a preferred embodiment, the excimer laser irradiation is performed at an ultra-low energy density, and the resistance value of each heating element is set to a desired resistance by selecting the energy density and / or the number of pulse irradiations. To be a value . The energy density of the excimer laser is preferably 60 to 180 mJ / cm ² , more preferably 80 to 150 mJ / cm ² in the case of a thin film resistor formed with TaSiO ₂ to a thickness of 500 to 1300 mm.
[0013]
An excimer laser is a laser that can oscillate ultraviolet rays, and has characteristics such as a high photon energy, a short pulse width, and a high peak output as compared with other lasers such as a YAG laser and a CO ₂ laser. The inventor of the present application selects the energy value of the excimer laser having such characteristics and / or the number of times of pulse irradiation, for example, to determine the resistance value of each heating element of the thin film type thermal print head made of TaSiO ₂ as desired. Found that it can be lowered. It is considered that the photon energy causes SiO ₂ which is an insulating component of each of the heating elements to partially cause dissociation between molecules, thereby reducing the overall resistance value. However, the irradiation energy density of the excimer laser, as described above, 60~180mJ / cm ^2, more preferably it is known that should be selected very low range of 80~150mJ / cm ^2.
[0014]
As described above, in the region irradiated with the excimer laser, the resistance value is lowered according to the energy density of the laser or the number of pulse irradiations. In the present invention, the excimer laser is applied to a partial region of the surface of each heating element. Therefore, the resistance value of each heating element can be adjusted more precisely at a finer stage.
[0015]
Therefore, according to the method of adjusting the heating element resistance value of the thin film type thermal print head according to the first aspect of the present invention, the thin film type thermal print head has conventionally been impossible to adjust the resistance value after film formation. It is possible to make the resistance value of each heating element in the above match the desired resistance value. Thus, the thin film thermal print head in which the variation in resistance value of each heating element is aligned within a predetermined range can further improve the print quality and can be used for multi-tone color printing using a sublimation ink ribbon. Can be made sufficiently suitable.
[0016]
In particular, when the central portion in the width direction and / or length direction of the surface of the heating element is selected so that the resistance value of the limited region is reduced by excimer laser irradiation, heat storage is performed when the heating element is driven. As a result, the tendency of the central region to become higher than the peripheral region is relaxed, and the temperature distribution in each part of the surface of the heating element is leveled. Thereby, generation | occurrence | production of the printing blur etc. at the time of high-speed printing can be suppressed, and printing quality can be improved more.
[0017]
According to a second aspect of the present invention, a thin film thermal print head is provided, which is a thin film thermal print in which a plurality of heating elements made of thin film resistors formed by CVD or sputtering are formed on an insulating substrate. In the print head, each of the heating elements is irradiated with an excimer laser at a central portion in the longitudinal direction of the surface, with a plurality of strip-like regions extending in the width direction at a predetermined interval in the longitudinal direction. It is characterized in that the resistance value is adjusted by being lowered by.
[0018]
As can be seen from the above, this thin film type thermal print head has a variation in the resistance value existing during the film formation of each heating element within a predetermined range. It is also suitable for multi-tone color printing using a sublimation ink ribbon.
[0023]
Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the drawings.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings. The present invention relates to a new technique for easily adjusting the resistance value of a thin film-formed resistor, but the present invention technique is used when adjusting the resistance value of a heating element in a thin film thermal print head. It can be suitably applied.
[0025]
FIG. 1 shows a typical cross-sectional structure of the heat generating portion 2 of the thin film thermal print head 1 with emphasis in the thickness direction. FIG. 2 shows a planar arrangement of the heat generating parts. A partial glaze 4 is formed on an insulating substrate 3 made of alumina ceramic or the like for increasing the pressure concentration on the recording paper and for imparting heat storage to the heat generating portion. The partial glaze 4 is formed by printing and baking using a glass paste, and has a smooth arcuate cross section due to fluidization of the glass component during baking.
[0026]
A thin film resistor layer 5 is formed on the surface of the insulating substrate 3 or the partial glaze 4. The resistor layer 5 is formed in a thin film shape of 500 to 1500 mm by, for example, a CVD method using TaSiO ₂ or sputtering. Conductor layers 6 a and 6 b are formed on the upper layer of the resistor layer 5 so as to expose the resistor layer 5 over a predetermined range at the top of the partial glaze 4. The conductor layers 6a and 6b are formed to a thickness of 0.5 to 2.0 μm, for example, by sputtering using Al. A portion of the resistor layer 5 that is exposed without being covered with the conductor layers 6 a and 6 b near the top of the partial glaze 4 functions as the heating element 7.
[0027]
The resistor layer 5 and the conductor layers 6a and 6b are provided with slits 8 as shown in FIG. 2, so that each heating element 7 can be driven independently. The conductor layers 6a that extend to the left in FIGS. 1 and 2 with respect to the respective heating elements 7 and are separated from each other by the slits 8 function as individual electrodes, and are output pads of a drive IC (not shown). Are electrically connected to each other. The conductor layers 6b extending to the right in FIGS. 1 and 2 with respect to the respective heating elements 7 are connected to each other and function as a common electrode.
[0028]
In FIG. 1, reference numeral 9 denotes an oxidation resistant layer made of, for example, SiO ₂ , and reference numeral 10 denotes a protective layer made of, for example, Ta ₂ O ₅ or Si ₃ N ₄ , both of which are formed by CVD or sputtering. In addition, the thickness of the oxidation resistant layer 9 is set to 0.5 to 1.5 μm, for example, and the thickness of the protective layer 10 is set to 3 to 6 μm, for example.
[0029]
In the above configuration, when any one of the individual electrodes 6a is turned on, the heating element 7 composed of the resistor layer 5 exposed without being covered with the conductor layers 6a and 6b is individually driven to generate heat.
[0030]
The thin film thermal print head 1 having the above-described configuration of the heat generating portion 2 is manufactured through the following processes, for example.
[0031]
First, as shown in FIG. 3, after forming the partial glaze 4 on the insulating substrate 3, the resistor layer 5 and the conductor layer 6 are sequentially formed into a thin film by CVD or sputtering. The materials and suitable thicknesses of the resistor layer 5 and the conductor layer 6 are as described above.
[0032]
Next, as shown in FIG. 4, a circuit pattern is formed by forming slits 8 extending in the width direction of the partial glaze 4 in the resistor layer 5 and the conductor layer 6 by the first photolithography process. To do.
[0033]
Next, as shown in FIG. 5, only the conductor layer 6 is etched and the underlying resistor layer 5 is exposed by the second photolithography process. The resistor layer 5 thus exposed functions as the heating element 7 as described above.
[0034]
Next, the oxidation resistant layer 9 and the protective layer 10 are formed by CVD or sputtering. The materials and suitable thicknesses of the oxidation resistant layer 9 and the protective layer 10 are also as described above.
[0035]
For example, when a printing density of 200 dpi is achieved, the heating element 7 has a rectangular dot shape with a longitudinal dimension L of 182 μm and a width dimension W of 112 μm, as shown in FIG. Is 540 mm, for example, and is arranged in the longitudinal direction of the partial glaze 4 at a pitch of 125 μm. As the material for the heating element 7, TaSiO ₂ is suitable as described above, and its sheet resistance is 358Ω / □. In the present invention, such adjustment of the resistance value of the heating element 7 is performed as follows in the stage before the oxidation resistant layer 9 and the protective layer 10 are formed.
[0036]
That is, as shown by the oblique lines in FIGS. 6B, 6C and 6D, a part of the surface of each heating element 7 is selected and irradiated with an ultra-low energy density excimer laser, thereby generating each heating. The resistance value of the body 7 is reduced. FIG. 6 (b) shows the case where a central region of 1/4 of the longitudinal dimension in the heating element 7 of the form shown in FIG. 6 (a) is selected, and FIG. The case where the center area | region of 1/4 of a direction and 1/2 of a width direction is selected is shown. In this case, a region of 1/8 of the entire surface of the heating element 7 is selected. FIG. 6D shows a case where a plurality of strip-like regions extending in the width direction are selected in the central region in the longitudinal direction of the heating element 7.
[0037]
More specifically, a probe (not shown) is brought into contact between the common electrode 6b and the individual electrode 6a, and the resistance value of the heating element 7 corresponding to the individual electrode 6a is monitored, as described above. Excimer laser is irradiated onto a selected partial region through a predetermined mask. More preferably, while the energy density of the excimer laser is set to a constant selected energy density, the number of irradiation pulses is increased until the resistance value of the heating element becomes a desired resistance value. By performing such an operation for all the heating elements 7, the resistance value of the heating element 7 in the thin film thermal print head in which a plurality of the heating elements 7 are arranged is within a certain allowable variation range. Can fit.
[0038]
FIG. 7 shows an irradiation energy density of 86 mJ / cm ² and an irradiation pulse frequency of 50 Hz when a KrF excimer laser is irradiated to a thin film resistor having a thickness of 540 mm made of TaSiO ₂ having a sheet resistance of 358 Ω / □. It is a graph which shows the change of resistance value change rate when it sets to (2) and the number of irradiation pulses is changed variously. As can be seen from this graph, as the number of irradiation pulses increases, the resistance value change rate (resistance value decrease rate) of the heating element 7 increases. Therefore, by selecting the number of irradiation pulses, the resistance value of the thin film resistor can be lowered as desired. From the graph of FIG. 7, in the region where the number of irradiation pulses is relatively small, the change in resistance value is abrupt. However, when the number of irradiation pulses exceeds a certain level, the relationship between the number of irradiation pulses and the resistance value change rate is linear. Become. Therefore, more accurate resistance value adjustment can be performed by using a range having this linear relationship. Then, as shown in FIG. 6 (b), when a quarter region in the longitudinal direction of the heating element 7 is selected and the excimer laser is irradiated to that portion, the resistance value of the portion related to laser irradiation is 10 %, The resistance value of the heating element 7 as a whole is reduced only by 2.5%. Similarly, as shown in FIG. 6 (c), when a region of 1/8 of the entire surface of the heating element is selected and the excimer laser is irradiated to that portion, the resistance value of the portion related to laser irradiation is reduced by 10%. Then, the resistance value of the heating element 7 as a whole is reduced only by 1.25%. Therefore, according to the resistance value adjusting method of the thin film resistor of the present invention, finer resistance value adjustment can be performed.
[0039]
FIG. 8 shows that when a KrF excimer laser is irradiated to a thin film resistor formed of TaSiO ₂ having a sheet resistance of 358 Ω / □ and having a thickness of 540 mm, the irradiation pulse frequency is set to 10 Hz and the number of irradiation pulses is set to 10, respectively. It is a graph which shows the change of the resistance value change rate when setting and changing irradiation energy density variously. As can be seen from this graph, the resistance value of the thin film resistor gradually decreases as the irradiation energy density is increased from around 60 mJ / cm ² . Therefore, the resistance value of the heating element can be adjusted to the target resistance value by selecting the irradiation energy of the excimer laser according to the tendency indicated by this graph. Of course, according to the present invention, even in this case, as shown in FIGS. 6A, 6B and 6C, the excimer laser is irradiated to the selected partial region of the surface of the resistor. The body resistance value can be adjusted more finely.
[0040]
FIG. 9 shows how the resistance value change rate changes in the process of increasing the number of irradiation pulses to the same object when irradiating the excimer laser to a resistor formed of TaSiO ₂ with a thickness of 654 mm. It is a graph showing the result of having investigated about various energy densities. From this graph, it can be seen that if the energy density is optimally set with respect to the material and thickness of the resistor, a desired resistance value can be obtained by increasing the number of irradiation pulses.
[0041]
Further, in the thin film type thermal print head, as shown in FIG. 6C in particular, the resistance value is adjusted by selecting a central region in the longitudinal direction and the width direction of the heating element 7 and irradiating this region with an excimer laser. In doing so, there are the following advantages. That is, when the heating element 7 having a constant resistance value is driven in each part of the surface, as shown in FIG. This is because the heat dissipation is greater in the periphery of the heating element, and the effect of heat storage is greater in the central region. However, when the resistance value is adjusted by selecting the central region of the heating element 7 and reducing its resistance value below the surrounding region as described above, the heat value in the central region is smaller than the heat value in the peripheral region. Therefore, the temperature distribution is leveled. By doing so, the occurrence of blurring of printing dots is avoided particularly when high-speed printing is performed, and the printing quality is improved.
[0042]
FIG. 11 is a schematic configuration diagram of an example of an apparatus 20 for adjusting the heating element resistance value of the thin film thermal print head using the excimer laser as described above. On the XYZ stage 21 that can be precisely driven, an intermediate product of the thin-film thermal print head at the stage where the heating element 7 is formed as described above is installed as a workpiece W. Excimer laser light from the reduction projection lens 22 is irradiated onto the workpiece W. The laser light is oscillated by a laser oscillator 24 connected to the gas supply device 23. The oscillation pulse frequency, the number of irradiation pulses, etc. of the excimer laser oscillated by the laser oscillator 24 can be controlled by the control unit. The laser light oscillated by the laser oscillator 24 travels through the shaping optical system 25 and the variable attenuator 26, is changed in direction by the reflection mirror 27, and is introduced into the reduction projection lens 22. In this example, a mask 28 is interposed between the shaping optical system 25 and the reflection mirror 27. This mask 28 is a window hole corresponding to a selected region where the surface of the heating element 7 is to be irradiated with a laser, that is, a window hole having a shape corresponding to the shaded portion in FIGS. 6 (b) (c) (d). It is what has. Above the reflection mirror 27, an optical system 30 for monitoring the work W illuminated by the illumination light from the light source 29 is disposed. Although not shown, the resistance value of the heating element 7 to be adjusted on the thin film thermal print head as the work W is monitored by bringing a predetermined measurement probe into contact with the individual electrode and the common electrode. Is done. The mask 28 can also be disposed at an appropriate position between the workpiece W and the reduction projection lens 22.
[0043]
While driving the XYZ stage 21 and step-feeding the thin-film thermal print head 1 as the work W in the arrangement direction of the heating elements 7, each heating element 7 is irradiated with an excimer laser, and the resistance value of the heating elements is determined as desired. The operation to adjust to the value of is performed sequentially. As described above, there are two methods for adjusting the resistance value of the heating element: a method of increasing the number of laser irradiation pulses and a method of changing the laser irradiation energy density. In the configuration shown in FIG. 10, the work W is stepped to adjust the resistance value of each heating element 7. However, the work W is fixed and the reduction projection lens 22 is stepped to adjust the resistance value of each heating element. It is also possible to perform.
[0044]
Of course, the scope of the present invention is not limited to the embodiment described above. As a gas for the excimer laser, ArF or XeCl can be selected as well as KrF as described above. In addition, when adjusting the resistance value of the heating element of the thin-film thermal print head, the form of the heat-generating part of this thin-film thermal print head is not limited to the type having the partial glaze as shown in the figure, but over the entire glaze. In addition, there is a type in which heating elements are arranged, or an individual electrode pattern having a so-called folded pattern, and appropriate resistance value adjustment can be similarly performed on these.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing the structure of a heat generating portion of a thin film thermal print head as a target for resistance value adjustment according to the method of the present invention, emphasized in the thickness direction.
FIG. 2 is an enlarged plan view of a heat generating portion of the thin film thermal print head shown in FIG.
3 shows a manufacturing process of the thin film thermal print head shown in FIG. 1, and shows a stage in which a partial glaze, a resistor layer and a conductor layer are formed on an insulating substrate.
4 shows a manufacturing process of the thin film thermal print head shown in FIG. 1, and shows a stage in which slits are formed in the resistor layer and the conductor layer.
5 shows a manufacturing process of the thin film type thermal print head shown in FIG. 1, and shows a stage in which a part of the conductor layer is removed by etching and a resistor layer is partially exposed to form a heating element.
FIG. 6A is a schematic plan view showing details of a planar form of a heating element. (b), (c) and (d) are schematic diagrams showing examples of regions to be irradiated with laser on the surface of the heating element.
FIG. 7 is a graph for explaining the operation of the method of the present invention.
FIG. 8 is a graph for explaining the operation of the method of the present invention.
FIG. 9 is a graph for explaining the operation of the method of the present invention.
FIG. 10 is an explanatory diagram of the operation of the method of the present invention.
FIG. 11 is a schematic configuration diagram of an example of an apparatus for carrying out the method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Thin film type thermal print head 2 Heat generating part 3 Insulating substrate 4 Partial glaze 5 Resistor layer 6 Conductor layer 6a Individual electrode 6b Common electrode 7 Heating element 8 Slit 9 Oxidation resistant layer 10 Protective layer 20 Lexima laser irradiation device 28 Mask

Claims (3)

Adjusting the resistance value of each heating element by irradiating each of the heating elements in a thin-film thermal print head in which a plurality of heating elements consisting of thin film resistors formed by CVD or sputtering on an insulating substrate is arranged A way to
The excimer laser is irradiated to a plurality of band-like regions extending in the width direction at a predetermined interval in the length direction at the center portion in the length direction of the surface of each heating element. A method for adjusting the heating element resistance value of the thin-film thermal printhead.   The excimer laser irradiation is performed with an ultra-low energy density, and a desired resistance value of each heating element is obtained by selecting the energy density and / or the number of pulse irradiations. Item 2. A method of adjusting a heating element resistance value of the thin film thermal printhead according to Item 1. A thin-film thermal print head in which a plurality of heating elements made of thin-film resistors formed by CVD or sputtering on an insulating substrate is disposed, and each heating element is at the center in the longitudinal direction of the surface. A thin film type characterized in that a plurality of strip-like regions extending in the width direction at predetermined intervals in the length direction are adjusted in resistance value by reducing the resistance value by excimer laser irradiation. Thermal print head.

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