Thermal print head

Abstract

This thermal print head comprises a substrate and a glaze layer. The substrate has a main surface. The glaze layer is disposed on the main surface. The glaze layer includes a hollow filler.

Description

thermal printhead

[0001] The present disclosure relates to thermal printheads.

[0002] Japanese Patent Laid-Open Publication No. 2022-180152 (Patent Document 1) discloses a thermal printhead including a substrate, a resistor layer, and a conductive layer. The thermal printhead has a heat generating portion.

[0003] Japanese Patent Application Laid-Open No. 2022-180152

[0004] [Summary] However, there is room for improvement in the heat accumulation of thermal printheads.

[0005] A thermal printhead according to one aspect of the present disclosure includes a substrate and a glaze layer. The substrate has a major surface. The glaze layer is disposed on the major surface. The glaze layer includes hollow fillers.

[0006] FIG. 1 is a schematic cross-sectional view of a thermal printhead according to a first embodiment. FIG. 2 is a schematic plan view of the thermal printhead according to the first embodiment. FIG. 3 is a schematic partial enlarged plan view of the thermal printhead according to the first embodiment. FIG. 4 is a schematic partial enlarged cross-sectional view of the thermal printhead according to the first embodiment. FIG. 5 is a schematic cross-sectional view of a glaze layer containing hollow fillers. FIG. 6 is a schematic partial enlarged cross-sectional view showing a step in a method for manufacturing a thermal printhead according to the first embodiment. FIG. 7 is a schematic partial enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 6 in the method for manufacturing a thermal printhead according to the first embodiment. FIG. 8 is a schematic partial enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 7 in the method for manufacturing a thermal printhead according to the first embodiment. FIG. 9 is a schematic partial enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 8 in the method for manufacturing a thermal printhead according to the first embodiment. FIG. 10 is a schematic partial enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 9 in the method for manufacturing a thermal printhead according to the first embodiment. FIG. 11 is a schematic partial enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 10 in the method for manufacturing a thermal printhead according to the first embodiment. FIG. 12 is a schematic, partially enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 11 in the method of manufacturing the thermal printhead of Embodiment 1. FIG. 13 is a schematic, partially enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 12 in the method of manufacturing the thermal printhead of Embodiment 1. FIG. 14 is a schematic, partially enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 13 in the method of manufacturing the thermal printhead of Embodiment 1. FIG. 15 is a schematic, partially enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 14 in the method of manufacturing the thermal printhead of Embodiment 1. FIG. 16 is a schematic, partially enlarged cross-sectional view of a thermal printhead of Embodiment 2. FIG. 17 is a schematic, partially enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 8 in the method of manufacturing the thermal printhead of Embodiment 2. FIG. 18 is a schematic, partially enlarged cross-sectional view showing a step subsequent to the step shown in FIG. 17 in the method of manufacturing the thermal printhead of Embodiment 2.

[0007] [Detailed Description] The details of the embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. At least some of the configurations of the embodiments described below may be combined in any manner.

[0008] (Embodiment 1) Fig. 1 is a schematic cross-sectional view of a thermal printhead 1 according to embodiment 1. Fig. 2 is a schematic plan view of the thermal printhead 1 according to embodiment 1. Fig. 3 is a schematic partial enlarged plan view of the thermal printhead 1 according to embodiment 1. Fig. 4 is a schematic partial enlarged cross-sectional view of the thermal printhead 1 according to embodiment 1.

[0009] The thermal printhead 1 is an electronic device that prints on a print medium 47 such as thermal paper by selectively generating heat from a plurality of heat-generating elements 31 (see FIG. 3 ). The thermal printhead 1 mainly comprises a substrate 10, an insulating layer 15, a wiring layer 20, a resistor layer 30, a protective layer 33, a drive circuit 35, conductive wires 36 and 37, a connector 40, a sealing member 43, and a heat sink 49.

[0010] As shown in Figure 4, the substrate 10 has a main surface 11 and a back surface 12 opposite to the main surface 11. The main surface 11 and the back surface 12 extend in the x direction and the y direction perpendicular to the x direction, respectively. The x direction is the longitudinal direction of the substrate 10 and the main scanning direction of the thermal printhead 1. The y direction is the lateral direction of the substrate 10 and the sub-scanning direction of the thermal printhead 1. The z direction is the thickness direction of the substrate 10. The normal direction of the main surface 11 is the z direction perpendicular to the x and y directions. The main surface 11 faces the +z direction. The back surface 12 faces the -z direction. The material constituting the substrate 10 is silicon.

[0011] 3 and 4, the substrate 10 has protrusions 14 on the main surface 11. The protrusions 14 are formed by wet etching using, for example, a potassium hydroxide (KOH) aqueous solution, as described below. In particular, when the protrusions 14 are formed by wet etching, the material constituting the substrate 10 is preferably silicon. In a plan view of the main surface 11, the longitudinal direction of the protrusions 14 is the x-direction, and the lateral direction of the protrusions 14 is the y-direction. The height direction of the protrusions 14 is the z-direction.

[0012] The protrusion 14 has a top surface 14s1 and a pair of inclined surfaces 14s2. The top surface 14s1 is the surface farthest from the main surface 11 in the z direction. The top surface 14s1 may extend in the x direction and the y direction. The pair of inclined surfaces 14s2 are spaced apart from each other in the y direction. The pair of inclined surfaces 14s2 connect the main surface 11 and the top surface 14s1. The pair of inclined surfaces 14s2 are inclined with respect to the main surface 11 so as to approach each other from the main surface 11 to the top surface 14s1. The inclination angle θ of each of the pair of inclined surfaces 14s2 with respect to the main surface 11 is, for example, 54.7°.

[0013] The substrate 10 having the protrusions 14 includes single crystal silicon (Si). In the crystal structure of the substrate 10, the plane orientation of the main surface 11 and the back surface 12 is the (100) plane. The plane orientation of the pair of inclined surfaces 14s2 is the (111) plane.

[0014] 3 and 4 , the insulating layer 15 is disposed on at least a portion of the main surface 11 and the protrusions 14, and covers at least a portion of the main surface 11 and the protrusions 14. The insulating layer 15 may cover the entire main surface 11.

[0015] The material constituting the insulating layer 15 is silicon dioxide (SiO ２ The oxide film such as silicon dioxide is formed by, for example, thermal oxidation.

[0016] An oxide film (TEOS oxide film) formed using, for example, tetraethyl orthosilicate (TEOS) may be disposed on the oxide film formed by thermal oxidation. The TEOS oxide film is formed by stacking thin silicon dioxide films multiple times using a plasma CVD method. The silicon dioxide is formed using tetraethyl orthosilicate as a source gas. The thickness of the TEOS oxide film in the z direction is, for example, 2.5 μm.

[0017] The substrate 10 is electrically insulated from the resistor layer 30 and the wiring layer 20 by the insulating layer 15. The thickness of the insulating layer 15 in the z direction is, for example, 1 μm or more and 15 μm or less. A glaze layer 16 containing hollow fillers 16 c is formed on the insulating layer 15 on the top surface 14s1 of the convex portion 14. The glaze layer 16 will be described in detail later.

[0018] The resistor layer 30 is formed on the insulating layer 15 and the glaze layer 16. The resistor layer 30 is connected to the insulating layer 15 and the glaze layer 16. The resistor layer 30 is formed of a material having a higher electrical resistivity than the wiring layer 20 described below. The material forming the resistor layer 30 is, for example, tantalum nitride (TaN). The resistor layer 30 is formed by sputtering. From the viewpoint of strength, the material forming the resistor layer 30 may be polysilicon. The thickness of the resistor layer 30 in the z direction is, for example, not less than 0.02 μm and not more than 0.1 μm. The thickness of the resistor layer 30 in the z direction may be 50 nm.

[0019] 2 to 4 , the wiring layer 20 is connected to the resistor layer 30. The wiring layer 20 forms a conductive path for supplying electricity to the plurality of heat generating portions 31 of the resistor layer 30. The wiring layer 20 is electrically connected to the plurality of heat generating portions 31. The wiring layer 20 may be made of a conductive material containing at least one of titanium (Ti) and copper (Cu), for example. The wiring layer 20 may also be made of aluminum (Al).

[0020] The wiring layer 20 includes a common wiring 21, a plurality of individual wirings 25, and a plurality of lead-out wirings 29. The plurality of individual wirings 25 are spaced apart from the common wiring 21 and the plurality of lead-out wirings 29. In order to selectively cause the plurality of heat-generating portions 31 to generate heat, a current flows from the common wiring 21 to the plurality of individual wirings 25 via the plurality of heat-generating portions 31.

[0021] The common wiring 21 is electrically connected to the plurality of heat generating portions 31. Specifically, as shown in FIGS. 3 and 4, the common wiring 21 includes a base 22 and a plurality of extension portions 23. In a plan view of the main surface 11, the base 22 is disposed on one side in the y direction (+y side) of the resistor layer 30. The longitudinal direction of the base 22 is the x direction, and the lateral direction of the base 22 is the y direction. The base 22 is spaced apart from the resistor layer 30 in the y direction. The plurality of extension portions 23 extend in the -y direction from the base 22 toward the resistor layer 30. The plurality of extension portions 23 are arranged at equal intervals along the x direction.

[0022] Each of the plurality of individual wires 25 is electrically connected to a corresponding one of the plurality of heat generating portions 31. Specifically, as shown in Figures 3 and 4, the plurality of individual wires 25 are arranged along the x direction. Each of the plurality of individual wires 25 includes a terminal portion 28 and an extension portion 26.

[0023] In a plan view of the main surface 11, the terminal portion 28 is disposed on the other side in the y direction (-y side) of the resistor layer 30. The terminal portion 28 is disposed on the opposite side in the y direction from the base portion 22 of the common wiring 21 with respect to the resistor layer 30. As shown in FIGS. 1 and 3 , the conductive wire 36 is bonded to the terminal portion 28 and the drive circuit 35. The terminal portion 28 is electrically connected to the drive circuit 35 through the conductive wire 36.

[0024] The extension portion 26 is connected to the terminal portion 28. An end portion 27 of the extension portion 26 opposite the terminal portion 28 is in contact with the resistor layer 30. In a plan view of the main surface 11, the end portion 27 of the extension portion 26 overlaps the protrusion 14.

[0025] 2 , in a plan view of the main surface 11, the plurality of lead wires 29 are arranged on the other side in the y direction (−y side) with respect to the drive circuit 35. In a plan view of the main surface 11, the plurality of lead wires 29 are arranged on the opposite side of the drive circuit 35 from the resistor layer 30 and the plurality of individual wires 25. A conductive wire 37 is bonded to the drive circuit 35 and the plurality of lead wires 29. The plurality of lead wires 29 are electrically connected to the drive circuit 35 through the conductive wire 37. The plurality of lead wires 29 are connected to a connector 40.

[0026] As shown in FIG. 4 , the resistor layer 30 is connected onto the insulating layer 15. In the normal direction (z direction) of the main surface 11, the resistor layer 30 is disposed on the opposite side of the insulating layer 15 from the substrate 10. In a plan view of the main surface 11, the longitudinal direction of the resistor layer 30 is the x direction, and the lateral direction of the resistor layer 30 is the y direction. In a plan view of the main surface 11, the resistor layer 30 intersects with the multiple extension portions 23 of the common wiring 21 and the ends 27 of the extension portions 26 of the multiple individual wirings 25. The resistor layer 30 straddles the multiple extension portions 23 of the common wiring 21 and the ends 27 of the extension portions 26 of the multiple individual wirings 25.

[0027] The resistor layer 30 includes a plurality of heat generating portions 31. One of the heat generating portions 31 is an area of ​​the resistor layer 30 sandwiched between a portion covered by one of the extension portions 26 of the common wiring 21 and a portion covered by one of the ends 27 of the individual wirings 25 adjacent to that portion in the x direction. The heat generating portions 31 are connected to the insulating layer 15. The heat generating portions 31 are arranged along the x direction. In a plan view of the main surface 11, the heat generating portions 31 overlap the protrusions 14. In a plan view of the main surface 11, the heat generating portions 31 are arranged inside the protrusions 14 in the short-side direction (y direction) of the resistor layer 30.

[0028] As shown in FIG. 4 , the protective layer 33 covers the resistor layer 30, the wiring layer 20, and the plurality of heat generating portions 31. The protective layer 33 is connected to the resistor layer 30, the wiring layer 20, and the plurality of heat generating portions 31. Portions of the wiring layer 20 to which the conductive wires 36 and 37 are bonded (e.g., terminal portions 28) are exposed from the protective layer 33. The material constituting the protective layer 33 may be, for example, at least one of silicon dioxide, silicon nitride (SiN), and silicon carbide (SiC). The protective layer 33 may be formed by a CVD method. The thickness of the protective layer 33 in the z direction may be, for example, 3.2 μm.

[0029] The drive circuit 35 is mounted on the main surface 11. For example, the drive circuit 35 is fixed to the insulating layer 15 using a bonding material (not shown) such as an adhesive. The drive circuit 35 may be mounted on a wiring board (not shown) separated from the substrate 10. The wiring board is, for example, a printed circuit board (PCB). The drive circuit 35 is electrically connected to the wiring layer 20 (specifically, the plurality of individual wirings 25 and the plurality of lead wirings 29). The drive circuit 35 applies current individually to the plurality of heat generating portions 31 through the plurality of individual wirings 25. The heat generating portions 31 to which the current is applied selectively generate heat.

[0030] As shown in FIGS. 1 and 2 , the connector 40 is disposed on the opposite side of the resistor layer 30 from the drive circuit 35 in the y direction. The connector 40 is attached, for example, to an end of the substrate 10 in the y direction. The connector 40 is electrically connected to the drive circuit 35 through the wiring layer 20 (specifically, a plurality of lead-out wirings 29). For example, the connector 40 includes a plurality of pins (not shown). Some of the plurality of pins are electrically connected to the plurality of lead-out wirings 29. Another portion of the plurality of pins is electrically connected to wiring (not shown) that is electrically connected to the base 22 of the common wiring 21. The connector 40 is connected to a thermal printer. A constant voltage is applied from the thermal printer to the common wiring 21 through the connector 40.

[0031] 1 and 4 , the sealing member 43 covers and seals the drive circuit 35. The sealing member 43 also covers and seals the conductive wires 36, 37. The sealing member 43 also covers the portions of the individual wirings 25 that are exposed from the protective layer 33 (e.g., the terminal portions 28, etc.). The sealing member 43 has electrical insulation properties. The sealing member 43 is formed of an insulating resin material such as epoxy resin.

[0032] As shown in FIG. 1 , the heat sink 49 is disposed on the opposite side of the substrate 10 from the insulating layer 15 and the resistor layer 30 in the z direction. The heat sink 49 is attached to the rear surface 12 of the substrate 10 by fastening members such as screws or joining members (not shown). The heat sink 49 supports the substrate 10. The heat sink 49 is formed of a highly thermally conductive material such as aluminum (Al). A portion of the heat generated from the multiple heat generating portions 31 of the resistor layer 30 is conducted to the heat sink 49 through the substrate 10. The heat conducted to the heat sink 49 is dissipated to the outside of the thermal printhead 1. The heat sink 49 can prevent an excessive temperature rise in the substrate 10. If the drive circuit 35 is mounted on a wiring board separate from the substrate 10, the heat sink 49 supports the substrate 10 and the wiring board.

[0033] 1 and 4 , the thermal printhead 1 includes a protrusion 45 formed on the principal surface 11. The protrusion 45 includes a convex portion 14, an insulating layer 15, a glaze layer 16, a wiring layer 20, a plurality of heat generating portions 31, and a protective layer 33. In the protrusion 45, the convex portion 14, the insulating layer 15, the glaze layer 16, the resistor layer 30, the wiring layer 20, the plurality of heat generating portions 31, and the protective layer 33 are stacked on the principal surface 11 in this order in the normal direction (z direction) of the principal surface 11.

[0034] A feature of the thermal printhead 1 according to the first embodiment is that, as shown in FIG. 4 , a glaze layer 16 containing hollow fillers 16c is disposed on the main surface 11. The hollow fillers 16c are granular members that surround a region V with low thermal conductivity. The hollow fillers 16c are, for example, spherical in shape. Any material can be used to form the hollow fillers 16c, but glass is an example. The region V with low thermal conductivity may be filled with air, for example. It is particularly preferable that the interior of the region V be a vacuum.

[0035] The glaze layer 16 suppresses the dissipation of heat generated in the heat-generating portion 31, improving the heat storage capacity of the thermal printhead 1. In particular, the inclusion of the hollow fillers 16c described above in the glaze layer 16 further improves the heat storage capacity of the thermal printhead 1. The improved heat storage capacity makes it possible to reduce the amount of current that flows when printing on the print medium 47.

[0036] FIG. 5 is a schematic cross-sectional view of a glaze layer 16 containing hollow fillers 16c. As shown in FIG. 5, the glaze layer 16 contains hollow fillers 16c. As described above, the hollow fillers 16c include hollow regions V. Such hollow fillers 16c are scattered throughout the glaze layer 16. If the hollow fillers 16c are spherical, the diameter of the hollow fillers 16c may be 10 μm or less, preferably 1 μm or less. Smaller hollow fillers 16c allow more hollow fillers 16c to be contained in the glaze layer 16. This increases the void ratio (air or vacuum regions) of the glaze layer 16, improving the heat storage capacity of the thermal printhead 1.

[0037] From a different perspective, in order to improve the heat storage capacity of the thermal printhead 1, the volume content of the hollow fillers 16c in the glaze layer 16 may be 50% or more, or 80% or more, and 90% or more is more preferable.

[0038] As mentioned above, the material constituting the hollow filler 16c preferably has low thermal conductivity and is strong enough. Furthermore, the material constituting the hollow filler 16c preferably has a high melting point so as not to melt due to heat during the manufacturing process of the thermal printhead 1, which will be described later. It is particularly preferable that the material constituting the hollow filler 16c has a melting point of 800°C or higher. As such a material, the material constituting the hollow filler 16c is preferably glass, and quartz glass is particularly preferred.

[0039] As shown in Figure 4, in a cross-sectional view of the thermal printhead 1, the glaze layer 16 is disposed between the resistor layer 30 and the insulating layer 15. In order to improve the heat storage capacity of the thermal printhead 1, it is necessary to prevent heat generated in the resistor layer 30 from flowing to the substrate 10 and being dissipated. Therefore, it is sufficient that the glaze layer 16 is disposed between the resistor layer 30 and the substrate 10. For example, as will be described later in a second embodiment, the glaze layer 16 may be disposed directly on the substrate 10. In other words, the glaze layer 16 may be disposed between the insulating layer 15 and the main surface 11 (see Figure 15).

[0040] In a plan view of the main surface 11 seen from the z direction, the glaze layer 16 is disposed so as to cover the top surfaces 14s1 of the convex portions 14 of the main surface 11. As shown in Fig. 4 , the glaze layer 16 is disposed so as to be sandwiched between a pair of inclined surfaces 14s2 in the y direction.

[0041] The glaze layer 16 includes a first glaze layer 16 a and a second glaze layer 16 b. The hollow filler 16 c is included in the first glaze layer 16 a. The first glaze layer 16 a is connected to the insulating layer 15. The second glaze layer 16 b is disposed on the first glaze layer 16 a. The second glaze layer 16 b is connected to the resistor layer 30.

[0042] As described below, when forming the first glaze layer 16a containing hollow fillers 16c, a fluid glaze is applied. Therefore, in a cross-sectional view of the thermal printhead 1 as shown in FIG. 4, the intersection between the top surface 14s1 and the inclined surface 14s2 is preferably not curved, but rather, for example, a corner where two straight lines intersect. This allows the glaze to be applied to the top surface 14s1 of the convex portion 14 by utilizing the surface tension of the glaze. To form the convex portion 14 having the above-described corners, the material constituting the substrate 10 is preferably silicon. The glaze is then dried. In this manner, the first glaze layer 16a containing hollow fillers 16c can be formed.

[0043] The second glaze layer 16b is formed on the first glaze layer 16a. The second glaze layer 16b is formed by glaze printing. The glaze layer 16 is then formed by baking. The glaze layer 16 formed in this manner has a curved surface portion 17. The curved surface portion 17 is the surface of the glaze layer 16 that is furthest from the substrate 10 in the z direction. In the thermal printhead 1 according to the first embodiment, the curved surface portion 17 is the surface that is connected to the resistor layer 30. In a plan view seen from the z direction, the curved surface portion 17 overlaps the convex portion 14.

[0044] The thickness h of the glaze layer 16 in the z direction is, for example, 20 μm to 250 μm, and can be changed as appropriate by changing the width of the top surface 14s1 in the y direction. The greater the thickness h, the better the heat storage capacity of the thermal printhead 1.

[0045] (Method of Manufacturing Thermal Printhead) A method of manufacturing the thermal printhead 1 of this embodiment will now be described.

[0046] First, a step (S1a) of preparing a wafer 10a is performed. In this step (S1a), the wafer 10a is prepared as a silicon substrate, which is a semiconductor material, as shown in Fig. 6. The wafer 10a includes a silicon single crystal.

[0047] Next, a step (S2a) of forming a mask layer 2 is carried out. In this step (S2a), as shown in FIG. 7, a mask layer 2 is formed in an area of ​​the main surface 11a where the protrusions 14 are to be formed. The material constituting the mask layer 2 is, for example, silicon nitride (SiN) or silicon dioxide (SiO ２ The mask layer 2 is formed by using a CVD method or sputtering.

[0048] Next, an etching step (S3a) is performed. In this step (S3a), as shown in FIG. 8, the wafer 10a is wet-etched using the mask layer 2 as a mask. In a plan view seen from the z direction, the wafer 10a is etched in the −z direction in areas where the mask layer 2 is not disposed. For example, wet etching is performed using an aqueous potassium hydroxide (KOH) solution as an etching solution. In this manner, the substrate 10 is formed. Furthermore, the wafer 10a is not etched in areas where the mask layer 2 is formed. As a result, convex portions 14 are formed on the main surface 11 of the substrate 10.

[0049] When an alkaline aqueous solution such as a potassium hydroxide (KOH) solution is used as an etching solution, the wafer 10a is etched so that the inclination angle θ of the inclined surface 14s2 with respect to the main surface 11 is 54.7°. After the convex portions 14 shown in FIG. 8 are formed, the mask layer 2 is removed by wet etching using hydrofluoric acid (HF).

[0050] Next, a step (S4a) of forming insulating layer 15 is performed. In this step (S4a), as shown in FIG. 9 , insulating layer 15 is formed to cover at least a portion of main surface 11 and protrusions 14. Specifically, insulating layer 15 is formed by thermal oxidation. A TEOS oxide film may be formed by stacking thin films of silicon dioxide multiple times using a plasma CVD method on an oxide film formed by thermal oxidation.

[0051] Next, a step (S5a) of forming a glaze layer 16 is performed. In this step (S5a), as shown in FIG. 10 , a glaze layer 16 is formed on insulating layer 15. Specifically, a glaze containing hollow fillers 16c is applied to top surfaces 14s1 of protrusions 14. The glaze is then dried. In this manner, a first glaze layer 16a containing hollow fillers 16c is formed.

[0052] Then, a glaze is applied onto the first glaze layer 16a by glaze printing, thus forming the second glaze layer 16b, and then the glaze layer 16 is formed by firing.

[0053] Next, a step (S6a) of forming a resistor layer 30 is performed. In this step (S6a), as shown in FIG. 11 , the resistor layer 30 is formed on the insulating layer 15. Specifically, the resistor layer 30 is formed by sputtering. The resistor layer 30 is made of a material such as tantalum nitride (TaN). The resistor layer 30 may also be made of polysilicon. The resistor layer 30 includes a plurality of heat generating portions 31.

[0054] Next, a step (S7a) of forming the wiring layer 20 is performed. In this step (S7a), as shown in FIG. 12 , the wiring layer 20 is formed on the resistor layer 30. Specifically, the wiring layer 20 is formed by sputtering. For example, the wiring layer 20 may be formed by laminating a copper thin film multiple times using sputtering. The wiring layer 20 may also be formed by laminating a titanium thin film on the resistor layer 30 using sputtering, and then laminating a copper thin film multiple times. The wiring layer 20 does not have to be formed by laminating a titanium thin film and a copper thin film, and may be formed by laminating an aluminum thin film.

[0055] After forming the wiring layer 20, lithography patterning is performed to remove a portion of the wiring layer 20. Specifically, a mask layer is formed on the wiring layer 20 by photolithography. Using the mask layer as a mask, the wiring layer 20 is partially etched away. Wet etching can be used to etch the wiring layer 20. In the wet etching, sulfuric acid (H ２ SO ４ ) and hydrogen peroxide (H ２ O ２ ) mixed solution is used. As a result, as shown in FIG. 3, a common wiring 21 and a plurality of individual wirings 25 are formed on the resistor layer 30. As shown in FIG. 12, a portion of the resistor layer 30 is exposed from the wiring layer 20. Next, reactive ion etching is used to etch a portion of the resistor layer 30. As a result, the insulating layer 15 is exposed on the protrusions 14 as shown in FIG. 3. A plurality of heat generating portions 31 are exposed on the top surfaces 14s1 of the protrusions 14.

[0056] Next, a step (S8a) of forming a protective layer 33 is carried out. Specifically, as shown in FIG. 13 , the protective layer 33 is formed on the insulating layer 15, on the plurality of heat generating portions 31, and on a portion of the wiring layer 20 using plasma CVD. The protective layer 33 is formed by laminating thin films of silicon nitride. Portions of the wiring layer 20 to which the conductive wires 36 and 37 are bonded (e.g., terminal portions 28) are exposed from the protective layer 33.

[0057] Next, a step (S9a) of mounting the drive circuit 35 is performed. In this step (S9a), the drive circuit 35 is mounted on the main surface 11 as shown in FIG. 14 . For example, the drive circuit 35 is fixed to the insulating layer 15 using a bonding material (not shown) such as an adhesive. As shown in FIG. 14 , conductive wires 36 and 37 are bonded. For example, the conductive wire 36 is bonded to the drive circuit 35 and the terminal portions 28 of the plurality of individual wirings 25 using a wire bonder (not shown). The conductive wire 37 is bonded to the drive circuit 35 and the plurality of lead-out wirings 29 using a wire bonder (not shown).

[0058] Next, a sealing step (S10a) is performed. In this step (S10a), as shown in FIG. 15, the drive circuit 35 is sealed with a sealing member 43. For example, a sealing resin material is potted on the drive circuit 35. The sealing resin material is then cured. In this manner, the sealing member 43 is formed.

[0059] Next, the connector 40 is attached to the substrate 10. The connector 40 includes a plurality of pins (not shown). Some of the pins are electrically connected to the plurality of lead-out wirings 29. Another portion of the pins is electrically connected to wiring (not shown) that is electrically connected to the base 22 of the common wiring 21.

[0060] Next, the heat sink 49 is attached to the substrate 10. Specifically, the heat sink 49 is attached to the rear surface 12 of the substrate 10 by fastening members such as screws or joining members (not shown). In this way, the thermal printhead 1 of this embodiment shown in Figures 1 to 4 is obtained.

[0061] The operation of the thermal printhead 1 of this embodiment will now be described. As shown in Figure 1, the protrusion 45 faces a platen roller 46 included in the thermal printer. The platen roller 46 feeds the print medium 47 toward the thermal printhead 1. As the platen roller 46 rotates, the print medium 47 is fed in the +y direction. The print medium 47 is sandwiched between the protrusion 45 and the platen roller 46.

[0062] The drive circuit 35 applies current individually to the plurality of heat generating portions 31 through the plurality of individual wirings 25. The heat generating portions 31 to which current is applied selectively generate heat. The heat generated in the plurality of heat generating portions 31 is transferred to the print medium 47. In this manner, printing is performed on the print medium 47 using the thermal printhead 1. The glaze layer 16 includes hollow fillers 16c. The hollow fillers 16c include vacuum regions V with low thermal conductivity. Therefore, the glaze layer 16 prevents some of the heat generated in the plurality of heat generating portions 31 from being dissipated. The remainder of the heat generated in the plurality of heat generating portions 31 is dissipated to the outside of the thermal printhead 1 through the substrate 10 and the heat sink 49.

[0063] <Operation and Effects> The thermal printhead 1 according to the present disclosure includes a substrate 10 and a glaze layer 16. The substrate 10 has a main surface 11. The glaze layer 16 is disposed on the main surface 11. The glaze layer 16 includes hollow fillers 16c.

[0064] In this way, the hollow fillers 16c included in the glaze layer 16 improve the heat storage capacity of the thermal printhead 1. The improved heat storage capacity reduces the amount of current that flows when printing on the print medium 47.

[0065] In the thermal printhead 1, the volume content of hollow fillers 16c in the glaze layer 16 is 50% or more. This provides a thermal printhead 1 with sufficiently improved heat storage. The improved heat storage reduces the amount of current that flows when printing on the print medium 47.

[0066] In the thermal printhead 1, the hollow filler 16c contains glass, which ensures the strength and heat storage capacity of the glaze layer 16. It also prevents the hollow filler 16c from melting due to heat during the manufacturing of the thermal printhead 1.

[0067] In the thermal printhead 1, the substrate 10 is made of silicon. In this way, when the protrusions 14 are formed by wet etching with a potassium hydroxide (KOH) aqueous solution, the protrusions 14 are configured as straight lines in a cross-sectional view. As a result, a fluid glaze can be applied to the top surface 14s1 by utilizing surface tension.

[0068] In the thermal printhead 1, convex portions 14 are formed on the main surface 11. The glaze layer 16 covers the top surfaces 14s1 of the convex portions 14. This prevents the heat generated in the heat generating portion 31 from being dissipated to the substrate 10. As a result, the heat storage capacity of the thermal printhead 1 is improved.

[0069] In the thermal printhead 1, the glaze layer 16 has curved portions 17. The direction perpendicular to the main surface 11 is the z direction. In a plan view seen from the z direction, the curved portions 17 overlap the protrusions 14. In this way, by forming the heat generating portions 31 on the protrusions 14, the surfaces of the heat generating portions 31 can be made curved.

[0070] In the thermal printhead 1, the thickness h of the glaze layer 16 in the z direction is 20 μm or more and 250 μm or less, which improves the heat storage capacity of the thermal printhead 1. In particular, the greater the thickness h, the better the heat storage capacity of the thermal printhead 1.

[0071] The thermal printhead 1 further includes an insulating layer 15 and a resistor layer 30. The insulating layer 15 is disposed on the main surface 11. The resistor layer 30 is disposed on the insulating layer 15. The glaze layer 16 is located between the main surface 11 and the resistor layer 30. This configuration suppresses the heat generated in the resistor layer 30 from dissipating to the substrate 10. In particular, it suppresses the heat generated in the heat-generating portion 31 from dissipating. As a result, the heat storage capacity of the thermal printhead 1 is improved. The improved heat storage capacity allows the amount of current flowing when printing on the print medium 47 to be reduced.

[0072] In the thermal printhead 1, the glaze layer 16 is disposed between the resistor layer 30 and the insulating layer 15. This arrangement prevents heat generated in the resistor layer 30 from being dissipated to the substrate 10. In particular, it prevents heat generated in the heat generating portion 31 from being dissipated.

[0073] Second Embodiment FIG. 16 is a schematic, partially enlarged cross-sectional view of a thermal printhead 1 according to a second embodiment. FIG. 16 corresponds to FIG. 4. The thermal printhead 1 shown in FIG. 16 has a configuration similar to that of the thermal printhead 1 shown in FIGS. 1 to 4 and can achieve similar effects. However, it differs from the thermal printhead 1 shown in FIGS. 1 to 4 in that the glaze layer 16 is disposed directly on the substrate 10. In other words, the glaze layer 16 may be disposed between the insulating layer 15 and the main surface 11. This configuration also provides a thermal printhead 1 with sufficiently improved heat storage. The improved heat storage reduces the amount of current flowing when printing on the print medium 47.

[0074] (Method of Manufacturing Thermal Printhead) A method of manufacturing the thermal printhead 1 of the second embodiment will now be described.

[0075] 6 to 8 in the method for manufacturing the thermal printhead 1 according to the first embodiment are performed. That is, a step (S1b) of preparing a wafer 10a is performed first. In this step (S1b), as shown in FIG. 6, the wafer 10a is prepared as a silicon substrate, which is a semiconductor material. The wafer 10a includes single crystal silicon.

[0076] Next, a step (S2b) of forming a mask layer 2 is carried out. In this step (S2b), as shown in FIG. 7, a mask layer 2 is formed in an area of ​​the main surface 11a where the protrusions 14 are to be formed. The material constituting the mask layer 2 is, for example, silicon nitride (SiN) or silicon dioxide (SiO ２ The mask layer 2 is formed by using a CVD method or sputtering.

[0077] Next, an etching step (S3b) is performed. In this step (S3b), as shown in FIG. 8, the wafer 10a is wet-etched using the mask layer 2 as a mask. In a plan view seen from the z direction, the wafer 10a is etched in the −z direction in the areas where the mask layer 2 is not disposed. For example, wet etching is performed using an aqueous potassium hydroxide (KOH) solution as an etching solution. In this manner, the substrate 10 is formed. Furthermore, the wafer 10a is not etched in the areas where the mask layer 2 is formed. As a result, convex portions 14 are formed on the main surface 11 of the substrate 10.

[0078] When an alkaline aqueous solution such as a potassium hydroxide (KOH) solution is used as an etching solution, the wafer 10a is etched so that the inclination angle θ of the inclined surface 14s2 with respect to the main surface 11 is 54.7°. After the convex portions 14 shown in FIG. 8 are formed, the mask layer 2 is removed by wet etching using hydrofluoric acid (HF).

[0079] Next, a step (S4b) of forming a glaze layer 16 is performed. In this step (S4b), as shown in FIG. 17 , a glaze layer 16 is formed on the top surface 14s1 of the substrate 10. Specifically, a glaze containing hollow fillers 16c is applied to the top surface 14s1 of the convex portion 14. The glaze is then dried. In this manner, a first glaze layer 16a containing hollow fillers 16c is formed.

[0080] Then, a glaze is applied onto the first glaze layer 16a by glaze printing, thus forming the second glaze layer 16b, and then the glaze layer 16 is formed by firing.

[0081] Next, a step (S5b) of forming insulating layer 15 is carried out. In this step (S5a), as shown in FIG. 18 , insulating layer 15 is formed to cover at least a portion of main surface 11, at least a portion of protrusions 14, and glaze layer 16. Specifically, insulating layer 15 is formed by thermal oxidation. A TEOS oxide film may be formed by stacking thin films of silicon dioxide multiple times using a plasma CVD method on an oxide film formed by thermal oxidation.

[0082] After the step (S5b) of forming the insulating layer 15, the steps from the step (S6a) of forming the resistor layer 30 to the sealing step (S10a) shown in Figures 11 to 15 are carried out in this order. In this manner, the thermal printhead 1 according to the second embodiment is manufactured.

[0083] <Effects> In the thermal printhead 1, the glaze layer 16 is disposed between the insulating layer 15 and the main surface 11. This provides a thermal printhead 1 with improved heat storage. The improved heat storage reduces the amount of current that flows when printing on the print medium 47.

[0084] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A thermal printhead comprising: a substrate having a main surface; and a glaze layer disposed on the main surface, the glaze layer including hollow fillers. (Appendix 2) A thermal printhead according to Appendix 1, wherein the hollow fillers include glass. (Appendix 3) A thermal printhead according to Appendix 1 or Appendix 2, wherein the substrate is made of silicon. (Appendix 4) A thermal printhead according to Appendix 3, wherein convex portions are formed on the main surface, and the glaze layer covers the top surfaces of the convex portions. (Appendix 5) A thermal printhead according to Appendix 4, wherein the glaze layer has curved portions, and wherein, when the direction perpendicular to the main surface is defined as the z direction, the curved portions overlap the convex portions in a planar view seen from the z direction. (Appendix 6) A thermal printhead according to Appendix 5, wherein the thickness of the glaze layer in the z direction is 20 μm or more and 250 μm or less. (Supplementary Note 7) The thermal printhead according to any one of Supplementary Notes 1 to 6, further comprising an insulating layer and a resistor layer, the insulating layer being disposed on the main surface, the resistor layer being disposed on the insulating layer, and the glaze layer being located between the main surface and the resistor layer. (Supplementary Note 8) The thermal printhead according to Supplementary Note 7, wherein the glaze layer is disposed between the resistor layer and the insulating layer. (Supplementary Note 9) The thermal printhead according to Supplementary Note 7, wherein the glaze layer is disposed between the insulating layer and the main surface.

[0085] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The basic scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0086] 1 Thermal print head, 2 Mask layer, 10 Substrate, 10a Wafer, 11, 11a Main surface, 12, 12a Back surface, 14 Convex portion, 14s1 Top surface, 14s2 Inclined surface, 15 Insulating layer, 16 Metal layer, 16a First glaze layer, 16b Second glaze layer, 16c Hollow filler, 17 Curved surface portion, 20 Wiring layer, 21 Common wiring, 22 Base portion, 23, 26 Extension portion, 25 Individual wiring, 27 End portion, 28 Terminal portion, 29 Lead wiring, 30 Resistor layer, 31 Heat generating portion, 33 Protective layer, 35 Drive circuit, 36, 37 Conductive wire, 40 Connector, 43 Sealing member, 45 Protrusion, 46 Platen roller, 47 Printing medium, 49 Heat sink, h Thickness, V Area.

Claims

1. A substrate having a main surface, The main surface comprises a glaze layer disposed on the main surface, The aforementioned glaze layer includes a hollow filler in the thermal printhead.

2. The thermal print head according to claim 1, wherein the hollow filler includes glass.

3. The thermal print head according to claim 1, wherein the material constituting the substrate is silicon.

4. A convex portion is formed on the main surface. The thermal print head according to claim 3, wherein the glaze layer covers the top surface of the protrusion.

5. The aforementioned glaze layer has a curved portion, If the direction perpendicular to the main surface is defined as the z-direction, The thermal print head according to claim 4, wherein in a plan view taken from the z-direction, the curved portion overlaps the convex portion.

6. The thermal print head according to claim 5, wherein the thickness of the glaze layer in the z-direction is 20 μm or more and 250 μm or less.

7. Insulating layer and, It further comprises a resistive layer, The insulating layer is arranged on the main surface. The resistive layer is placed on the insulating layer, The thermal print head according to any one of claims 1 to 6, wherein the glaze layer is located between the main surface and the resistor layer.

8. The thermal print head according to claim 7, wherein the glaze layer is disposed between the resistive layer and the insulating layer.

9. The thermal print head according to claim 7, wherein the glaze layer is disposed between the insulating layer and the main surface.