Thin film thermal print head and manufacturing method thereof

Abstract

The present invention relates to the technical field of thermal print head manufacturing, and more specifically to a thin-film thermal print head and a method for manufacturing the same, which have reasonable processes and can significantly improve the corrosion resistance and high-temperature resistance of the print head and reduce its thermal stress, thereby effectively improving product quality and service life. The invention is characterized in that the wire electrode is composed of an aluminum nanolayer and an aluminum-based alloy nanolayer stacked alternately, and the uppermost layer and the lowermost layer are both aluminum nanolayers. The aluminum-based alloy nanolayer contains aluminum, copper, chromium and zirconium, wherein the mass percentage of copper in the aluminum-based nanolayer does not exceed 5%, and the mass percentage of chromium and zirconium in the aluminum-based nanolayer does not exceed 1%. Compared with the existing technology, the thin-film thermal print head has the properties of resistance to thermal migration, good bonding strength, corrosion resistance, low thermal stress, etc., which is conducive to improving the product quality and service life of the thermal print head.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal print head manufacturing, and more specifically to a thin-film thermal print head and a method for manufacturing the same, which has a reasonable process and can significantly improve the corrosion resistance and high-temperature resistance of the print head and reduce its thermal stress, thereby effectively improving product quality and service life. Background Art

[0002] As is well known, a thin-film thermal print head is provided with a substrate made of an insulating material, on which a heat storage layer, i.e., a base glaze, is made. Then, a heating resistor is formed on the surface of the substrate and the heat storage layer, and a wire electrode is formed on the upper or lower side of the heating element. The wire electrode is divided into individual electrodes and common electrodes. One end of the individual electrode is connected to the heating resistor along the sub-printing direction, and the other end is connected to the control IC. One end of the common electrode is connected to the heating resistor band along the sub-printing direction, and the other end is connected to the power supply. The electrical part of the thermal print head is composed of the wire electrode, heating resistor, control IC, etc. on the ceramic substrate, and the electrical part is adhered to the base as a whole.

[0003] Metals such as Au, Ag, and Cu offer excellent conductivity when it comes to conductive electrodes. However, Au is expensive and complex to manufacture, while Ag exhibits poor thermal stability. Cu exhibits poor adhesion and solderability to ICs. Therefore, thin-film printhead electrodes are currently typically made of pure aluminum, typically around 1 μm thick. Aluminum is an excellent conductor of electricity, with a resistivity less than 2.8 x 10-8 Ω·m. It is also a good thermal conductor, with a thermal conductivity exceeding 200 W / mK, facilitating heat dissipation. However, aluminum has a high coefficient of thermal expansion (CTE), approximately 23 ppm / °C, compared to the 4-9 ppm / °C CTE of other thermal printhead components. This can easily generate significant thermal stress during operation. Furthermore, aluminum has a temperature resistance of only around 600°C and is susceptible to corrosion and thermomigration. This occurs when Al atoms undergo directional migration under temperature gradients, causing them to aggregate at either the hot or cold end. This can cause defects such as voids and cracks, shortening the lifespan of thin-film printheads under high-load and high-temperature conditions.

[0004] Existing thermal printhead products, such as the technical proposal described in patent document JP2022078438, mention that the electrode wire is composed of Cu, Cu alloys, Al, Al alloys, Au, Ag, Ni, W, etc., with a thickness of 800nm. However, no further investigation is conducted on the bonding strength of the electrode wire material with the substrate and protective layer, heat dissipation, thermal migration resistance, or process difficulty.

[0005] To improve adhesion between the Al Com and the feed electrode, JP2003154967 proposes a two-layer structure using one of the following metals: Ti, Cr, Nb, Ta, W, or Zr for the adhesion layer and Au or an Au alloy for the corrosion-resistant layer. However, Au is expensive, increasing product costs.

[0006] Patent document US5077563A states that the electrical contact portion of each recording electrode of a print head has a thickness of at least one micron and is essentially composed of a conductive material that resists oxidation and degradation. The conductive material is selected from nitrides, each of which contains at least one element selected from chromium, titanium, tantalum, zirconium, and niobium. While the patent mentions elements such as chromium and zirconium, it emphasizes that they are nitrides.

[0007] Patent document 202211551818.3 mentions that the electrode layer includes a first electrode layer and a second electrode layer, with the first electrode layer located on the side of the second electrode layer closer to the insulating substrate. The first electrode layer is made of at least one of aluminum, tungsten, titanium, molybdenum, and silver, or an alloy thereof; the second electrode layer is made of aluminum. Using two layers, one of which is made of materials such as tungsten and titanium to form a corrosion-resistant electrode, is complex and costly compared to pure aluminum or aluminum-based electrodes. Summary of the Invention

[0008] In response to the shortcomings and deficiencies in the prior art, the present invention proposes a thin-film thermal print head and a manufacturing method with reasonable process, which can significantly improve the corrosion resistance and high-temperature resistance of the electrode wires in the print head and reduce their thermal stress, thereby effectively improving product quality and service life.

[0009] The present invention is achieved by the following measures:

[0010] A thin film thermal print head is provided with an insulating substrate, an underglaze layer is provided on the insulating substrate, a heating resistor and an electrode wire are provided on the underglaze layer, the electrode wire includes individual electrodes and common electrodes, and is characterized in that the wire electrode is composed of aluminum nanolayers and aluminum-based alloy nanolayers stacked alternately, and the topmost layer and the bottommost layer are both aluminum nanolayers, and the aluminum-based alloy nanolayers contain aluminum, copper, chromium and zirconium, wherein the mass percentage of copper in the aluminum-based nanolayer does not exceed 5%, and the mass percentage of chromium and zirconium in the aluminum-based nanolayer does not exceed 1%.

[0011] In the aluminum-based alloy nanolayer of the present invention, the proportion of Cr in the total mass of Cr and Zr is between 35% and 65%.

[0012] The thickness of each aluminum nanolayer and aluminum-based alloy nanolayer described in the present invention is between 5-20nm. This thickness can maintain the independent characteristics of each layer and enable interaction between adjacent layers. The total thickness of the electrode wire is between 0.1-2um to adapt to the current range passing through the electrode wire.

[0013] The present invention further provides a protective layer on the electrode wire, the protective layer comprising an insulating layer located on the upper surface of the electrode wire, and a wear-resistant layer is selectively formed on the insulating layer according to wear-resistant requirements.

[0014] The present invention also provides a method for manufacturing the thin film thermal print head as described above, wherein a heating resistor and an electrode wire are formed on an insulating substrate provided with an underglaze by a thin film patterning process, wherein the electrode wire is formed by the following steps:

[0015] Step 1: Prepare Al / Cu alloy target material using a vacuum induction melting furnace and a graphite crucible. The Al matrix uses 99.99% aluminum particles, and the Cu, Cr, and Zr components use high-purity particles, where the Cu purity is ≥99.99%, the Cr purity is ≥99.95%, and the Zr purity is ≥99.95%. The raw materials remain molten in the melting furnace for a long time. The liquid is in a high-temperature, high-vacuum environment. The temperature, vacuum, and heating power need to be controlled at all times. Inert gas (such as Ar) can also be filled and a deoxidizer can be added to prevent oxidation and boiling.

[0016] Step 2: Using a magnetron sputtering process on the surface of the substrate on which the heating resistor has been prepared, the alloy target material and the pure Al target material obtained in step 1 are placed in the same equipment chamber, and the alloy target material and the pure Al target material are sputtered alternately, so that the two materials are alternately stacked and sputtered onto the substrate, and the top and bottom layers are both pure Al nanolayers. The alloy nanolayers and the pure Al nanolayers are alternately stacked to form electrode wires, each layer having a thickness of 5-20nm, and the total thickness of the electrode wire is 0.1-2um;

[0017] Step 3: Annealing: The electrode is annealed below 400°C before patterning. After heat treatment, weak bonds, vacancies, and lattice defects are reduced to lower the resistivity of the alloy.

[0018] Step 4: Apply positive photoresist and perform photolithography to retain the photoresist at the corresponding position of the conductive pattern and perform etching. After etching, a wet etching process such as mixed acid is used to remove the alloy without photoresist protection to form an electrode pattern.

[0019] The present invention adopts an electrode conductor with multiple nanolayers stacked together, which can take advantage of the high melting point, low expansion coefficient and other characteristics of the alloy nanolayer to make the electrode conductor have better corrosion resistance and stress resistance. At the same time, since the bottom and top of the electrode conductor are both made of pure Al nanolayers, the adhesion of the electrode conductor to the base material and good welding characteristics with the IC can be guaranteed. The alternating stacking arrangement with a very thin thickness can make the two materials fully contact and fuse, and the two advantages are fully utilized. Therefore, under the premise of ensuring that the electrode conductor meets the current requirements during operation, it has the properties of resistance to thermal migration, good bonding strength, corrosion resistance, low thermal stress, etc., which is beneficial to improving the quality and service life of thermal print head products. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attachment Figure 1 It is a cross-sectional view of the thin film thermal print head of the present invention.

[0021] Attachment Figure 2 It is a structural schematic diagram of the heating resistor and electrode wire in the present invention.

[0022] Attachment Figure 3 This is an electron microscope image of the electrode conductor composed of multiple nanolayers in the present invention.

[0023] Attachment Figure 4 It is a manufacturing flow chart of the thin film thermal print head in the present invention.

[0024] Attachment Figure 5 1 is a curve showing the change of leakage current of Al and Al-Cu alloy electrodes over time in the embodiment of the present invention.

[0025] Attachment Figure 6 This is a comparison of the morphology of the alloy nanofilm in the embodiment of the present invention and the traditional aluminum-copper alloy film layer.

[0026] Attachment Figure 7 This is a comparison chart of the Cr sputtering effect in the alloy nanofilm layer.

[0027] Reference numerals: ceramic substrate 1 , heat storage layer 2 , heating resistor 3 , lead electrode 4 , individual electrode 4 a , common electrode 4 b , protective layer 5 . DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] Example 1:

[0030] This embodiment provides a thin-film thermal print head, comprising a ceramic substrate 1 with a heat storage layer 2, i.e., an underglaze. A heating resistor 3 is formed on the substrate using a thin-film patterning process. The thin-film process is generally implemented using processes such as PVD, CVD, ion plating, vapor deposition, electroplating, and chemical plating. The patterning process involves applying a photoresist, photolithography, and etching. Etching can be performed using either a dry or wet RIE process. The heating resistor is made of a Ta-based material, typically TaSiO2.

[0031] In this example, a similar thin film patterning process is used to form individual electrodes 4a and common electrodes 4b. One end of the individual electrode 4a is connected to the heating resistor 3 and the other end is connected to the IC. One end of the common electrode 4b is connected to the heating resistor 3 and the other end is connected to the positive pole of the power supply. The electrodes are composed of two nano-film layers stacked in an alternating manner. One nano-film layer is an alloy nano-film layer mainly composed of Al, and the other nano-film layer is a pure Al nano-film layer. The top and bottom layers of the formed electrode wires are both pure Al nano-film layers.

[0032] In this example, the alloy nanofilm layer of the electrode conductor is mainly composed of Al, and Cu is added. Cu is a good conductor and is widely used. Cu has good conductivity and a resistivity of 1.710E-8Ω·m; Cu has a higher temperature resistance than aluminum, about 1000℃; Cu has a relatively high thermal conductivity of about 400W / mK, and a low thermal expansion coefficient of about 16.6ppm / ℃. The Cu content is controlled below 5%. By utilizing the segregation of Cu at the grain boundary of Al atoms, the Cu-Al bond at the grain boundary is much stronger than the Cu-Cu and Al-Al bond, which means that Cu strengthens the grain boundary of Al atoms, thereby inhibiting the grain boundary diffusion of Al atoms. However, the electrode conductor formed by the alloy nanofilm layer at this time Under the thermal migration effect, there is still the problem of atomic diffusion, and the thermal expansion coefficient is large, which leads to large thermal stress during the printing process. Therefore, in this example, Cr and Zr are further added on the basis of Cu, and the addition amount of Cr and Zr accounts for less than 1% of the total mass of the electrode wire. This is because too high a content will affect the conductivity of the electrode. The percentage of Cr in the total mass of Cr and Zr is between 35-65%. The thermal expansion coefficient of chromium Cr is 6.2ppm / ℃, and the thermal expansion coefficient of zirconium Zr is 9.6ppm / ℃, which is much smaller than the thermal expansion coefficient of Cu and Al, which can significantly reduce thermal stress. In addition, adding Cr and Zr to the Al-Cu alloy can make the alloy show a positive interaction, turning the alloy elements into a network structure. Figure 6 , a multi-element Al / Cu alloy electrode with uniform texture can be obtained, thereby effectively inhibiting the migration of Al and Cu atoms. At the same time, the addition of Cr and Zr can also weaken the preferential sputtering caused by the difference in injection effect during magnetron sputtering, making the target material more uniformly sputtered, such as Figure 7The resulting film is more uniform, as doping with either Cr or Zr alone cannot achieve the same effect as doping with both metals. The top and bottom layers of the electrode conductors utilize pure Al nanofilms, ensuring consistent bonding between the electrodes and the upper and lower layers, as well as the solderability of the IC substrate, similar to pure aluminum.

[0033] In this example, the production of electrode wires first requires the preparation of Al / Cu alloy targets. A vacuum induction melting furnace and graphite crucible are used. The Al matrix uses 99.99% aluminum particles, and the Cu, Cr, and Zr components use high-purity particles (Cu ≥ 99.99%, Cr ≥ 99.95%, Zr ≥ 99.95%). The raw materials remain molten in the melting furnace for a long time. The liquid is in a high-temperature, high-vacuum environment. The temperature, vacuum degree, and heating power need to be controlled at all times. Inert gas (such as Ar) can also be filled and a deoxidizer can be added to prevent oxidation and boiling.

[0034] Then, a magnetron sputtering process is used on the surface of the substrate on which the heating resistor has been prepared. The alloy target and the pure Al target are placed in the same equipment cavity, and the alloy target and the pure Al target are sputtered alternately, so that the two materials are alternately stacked and sputtered onto the substrate, and the top and bottom layers are both pure Al. The alloy has better corrosion resistance, temperature resistance, and low stress performance, and pure Al has adhesion. The alternating stacking arrangement is very thin, which can make the two materials fully contact and fuse, and give full play to the two advantages. In particular, the top and bottom layers are both pure Al, which can better ensure the bonding between the upper and lower layers and the welding characteristics between the IC. The thickness of each layer is about 5 to 20 μm. This thickness can maintain the independent characteristics of each layer and also allow them to partially interact. The total thickness is 0.1 to 2 μm to meet the working current requirements. The electrode is annealed below 400°C before patterning. After heat treatment, weak bond bonding, vacancies, and lattice defects are reduced to make the resistivity of the alloy lower.

[0035] Finally, positive photoresist is applied and photolithography is performed to retain the resist at the corresponding position of the conductive pattern and perform etching. After etching, a wet etching process such as mixed acid is used to remove the alloy without photoresist protection to form an electrode pattern.

[0036] In order to determine the film quality, XRD detection, scratch adhesion detection, four-probe square resistance detection, laser stress testing and other means can be used to characterize and inspect the film quality.

[0037] After the film quality inspection is passed, an insulating layer is formed on the electrode. The insulating layer is made of SIALON film. SIALON has excellent insulation performance and can prevent external ions, water vapor, etc. from corroding the electrodes and heating resistors. According to the need for wear resistance, a wear-resistant layer is formed on the insulating layer. The wear-resistant layer is made of SIC film. SIC has high hardness and can play a good role in scratch resistance and wear resistance.

[0038] Compared with the prior art, the present invention provides an aluminum-based alloy electrode wire, so that the wire electrode exhibits a positive interaction while maintaining a low expansion coefficient, making the alloy texture uniform, thereby effectively inhibiting the migration of Al and Cu atoms and improving the poor bonding strength of the traditional Cu component with the substrate and protective film. It can also weaken the preferential sputtering caused by the difference in injection effect during magnetron sputtering, so that the target material is sputtered more evenly and the resulting film quality is more uniform. The obtained wire electrode has better adhesion, heat dissipation, conductivity and low thermal stress, which can significantly improve the service life and quality of the product. Note that the above is only a preferred embodiment of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it can also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A thin film thermal print head, comprising an insulating substrate, an underglaze layer on the insulating substrate, a heating resistor and electrode wires on the underglaze layer, wherein the electrode wires include individual electrodes and a common electrode, characterized in that: The electrode conductor is composed of alternating layers of aluminum nanolayers and aluminum-based alloy nanolayers, and the top and bottom layers are both aluminum nanolayers. The aluminum-based alloy nanolayers contain aluminum, copper, chromium and zirconium, wherein copper accounts for no more than 5% by mass of the aluminum-based nanolayer, and chromium and zirconium account for no more than 1% by mass of the aluminum-based nanolayer.

2. A thin film thermal print head according to claim 1, characterized in that: In the aluminum-based alloy nanolayer, Cr accounts for 35% to 65% of the total mass of Cr and Zr.

3. A thin film thermal print head according to claim 2, characterized in that: The thickness of each aluminum nanolayer and aluminum-based alloy nanolayer is between 5-20nm, which can maintain the independent characteristics of each layer and enable interaction between adjacent layers. The total thickness of the electrode wire is between 0.1-2um to adapt to the current range passing through the electrode wire.

4. A thin film thermal print head according to claim 3, characterized in that: A protective layer is also provided on the electrode conductor. The protective layer includes an insulating layer located on the upper surface of the electrode conductor. A wear-resistant layer is selectively formed on the insulating layer according to wear-resistant requirements.

5. A method for manufacturing a thin film thermal print head according to any one of claims 1 to 4, wherein a heating resistor and an electrode conductor are formed on an insulating substrate provided with an underglaze by a thin film patterning process, wherein: The electrode wire is formed by the following steps: Step 1: Prepare Al / Cu alloy target using a vacuum induction melting furnace and graphite crucible. The Al matrix uses 99.99% aluminum particles, and the Cu, Cr, and Zr components use high-purity particles, where the Cu purity is ≥99.99%, the Cr purity is ≥99.95%, and the Zr purity is ≥99.95%. The raw materials remain molten in the melting furnace for a long time. The liquid is in a high-temperature, high-vacuum environment, and the temperature, vacuum, and heating power need to be controlled at all times. Step 2: Using a magnetron sputtering process on the surface of the substrate on which the heating resistor has been prepared, the alloy target material and the pure Al target material obtained in step 1 are placed in the same equipment chamber, and the alloy target material and the pure Al target material are sputtered alternately, so that the two materials are alternately stacked and sputtered onto the substrate, and the top and bottom layers are both pure Al nanolayers. The alloy nanolayers and the pure Al nanolayers are alternately stacked to form electrode wires, each layer having a thickness of between 5 and 20 nm, and the total thickness of the electrode wires is between 0.1 and 2 μm; Step 3: Annealing: The electrode is annealed below 400°C before patterning. After heat treatment, weak bonds, vacancies, and lattice defects are reduced to lower the resistivity of the alloy. Step 4: Apply positive photoresist, perform photolithography, retain the photoresist at the corresponding position of the conductive pattern, and perform imaging. After imaging, use a mixed acid wet etching process to remove the alloy without photoresist protection to form an electrode pattern.

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