Thermal printhead, its manufacturing method, and thermal printer

Abstract

This thermal print head is provided with: a head substrate (11) having a principal surface (11a) and a convex part (12) formed on the principal surface (11a); a resisting body layer (21) formed on the principal surface (11a) and the convex part (12); a wiring layer (22) covering the resisting body layer (21) so that the resisting body layer (21) is exposed at a heat generation part (20) that is a part of the convex part (12); and a protection layer (25) formed on the principal surface (11a) of the head substrate (11) so as to cover the resisting body layer (21) and the wiring layer (22). The resisting body layer (21) is provided with a main resisting body layer containing tantalum and at least one of a first sub-resisting body layer containing tantalum nitride and a second sub-resisting body layer containing tantalum nitride that are laminated on a lower side and an upper side of a tantalum layer, respectively. The first sub-resisting body layer and the second sub-resisting body layer have a nitrogen content of a certain value or more so as to be deposited on a stable structure.

Description

[Technical field]

[0001] The present invention relates to a thermal printhead, a manufacturing method thereof, and a thermal printer, and more particularly to a thermal printhead using a material containing tantalum and nitrogen in the resistor layer. [Background technology]

[0002] Conventionally, a thermal printhead has been provided in which a glaze layer is provided on the surface of a ceramic substrate, a partial glaze layer is further provided on a portion of the surface of the glaze layer, a heat generating resistor layer is provided spanning from the glaze layer to the partial glaze layer, and a conductor is provided on the surface of the heat generating resistor layer across the heat generating region of the heat generating resistor layer (see Patent Document 1).Also provided is a thermal printhead in which a semiconductor substrate is anisotropically etched to form a top surface having an inclined side surface on the main surface, and an insulating layer, a resistor layer, a wiring layer, an insulating protective layer, etc. are sequentially formed on this semiconductor substrate (see Patent Document 2).

[0003] The resistor layer of such a thermal printhead may be made of tantalum nitride, which contains a relatively low concentration of nitrogen to ensure electrical conductivity. 2 N etc. have sometimes been used (see Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 60-42069 [Patent Document 2] JP 2017-114057 A [Patent Document 3] Japanese Patent Application Publication No. 63-257653 [Patent Document 4] Japanese Patent Application Publication No. 4-93262 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a resistor layer is formed from tantalum nitride containing a low concentration of nitrogen, oxygen diffuses from the adjacent insulating layer and protective layer into the resistor layer, which can result in deterioration of characteristics such as an increase in resistivity.

[0006] This disclosure has been proposed in light of the above-mentioned circumstances, and aims to provide a thermal printhead including a resistor layer composed of tantalum and nitrogen that reduces the diffusion of oxygen from adjacent layers and inhibits deterioration of characteristics, as well as a manufacturing method thereof and a thermal printer. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the thermal printhead according to the present application comprises a substrate having a main surface and convex portions formed on the main surface, a resistor layer formed on the main surface and on the convex portions, a wiring layer covering the resistor layer so that the resistor layer is exposed in some of the heating portions of the convex portions, and a protective layer formed on the main surface of the substrate so as to cover the resistor layer and the wiring layer, the resistor layer comprising a main resistor layer containing tantalum, and at least one of a first sub-resistor layer containing tantalum nitride laminated on the underside of the main resistor layer and a second sub-resistor layer containing tantalum nitride laminated on the overside of the main resistor layer, the tantalum nitride contained in the first sub-resistor layer and the second sub-resistor layer including a eutectic having a face-centered cubic lattice structure with a (111) orientation and a (200) orientation.

[0008] The thermal printer according to this application comprises the thermal printhead and a platen disposed opposite to the heat generating portion of the thermal printhead.

[0009] The method for manufacturing a thermal printhead according to this application includes the steps of: providing a substrate having a main surface and having convex portions formed on the main surface; forming a resistor layer on the main surface and the convex portions; forming a wiring layer covering the resistor layer so that the resistor layer is exposed at some of the heat generating portions of the convex portions; and forming a protective layer on the main surface of the substrate so as to cover the resistor layer and the wiring layer, wherein the resistor layer includes a main resistor layer containing tantalum, and at least one of a first sub-resistor layer containing tantalum nitride laminated under the main resistor layer and a second sub-resistor layer laminated over the main resistor layer, and the tantalum nitride contained in the first sub-resistor layer and the second sub-resistor layer includes a eutectic having a face-centered cubic lattice structure with a (111) orientation and a (200) orientation. Effect of the Invention

[0010] According to this disclosure, it is possible to reduce the diffusion of oxygen from the adjacent insulating layer and protective layer to a resistor layer made of tantalum and nitrogen, and to suppress deterioration of the characteristics of the resistor layer due to oxygen diffusion. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view of a head substrate of a thermal printhead according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the resistor layer according to the first embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing another aspect of the resistor layer according to the first embodiment. [Figure 4] FIG. 4 is a process flow diagram of the thermal printhead according to the first embodiment. [Diagram 5] FIG. 5 is a process flow diagram of the thermal printhead according to the first embodiment. [Figure 6] FIG. 6 is a graph showing the relationship between the nitrogen content and the resistivity of tantalum nitride and its in-plane variation. [Figure 7] FIG. 7 is a graph showing the relationship between the nitrogen content of the resistor layer and the SST withstand voltage. [Figure 8]FIG. 8 is a process flow diagram of the thermal printhead according to the first embodiment. [Figure 9] FIG. 9 is a process flow diagram of the thermal printhead according to the first embodiment. [Figure 10] FIG. 10 is a cross-sectional view of a head substrate included in a thermal printhead according to the second embodiment. [Figure 11] FIG. 11 is a cross-sectional view of a resistor layer according to the second embodiment. [Figure 12] FIG. 12 is a cross-sectional view showing another aspect of the resistor layer according to the second embodiment. [Figure 13] FIG. 13 is a process flow diagram of the thermal printhead according to the second embodiment. [Figure 14] FIG. 14 is a process flow diagram of the thermal printhead according to the second embodiment. [Figure 15] FIG. 15 is a process flow diagram of the thermal printhead according to the second embodiment. [Figure 16] FIG. 16 is a process flow diagram of the thermal printhead according to the second embodiment. [Figure 17] FIG. 17 is a process flow diagram of the thermal printhead according to the second embodiment. [Figure 18] FIG. 18 is a process flow diagram of the thermal printhead according to the second embodiment. [Figure 19] FIG. 19 is a cross-sectional view of a resistor layer of an experimental example. [Figure 20] FIG. 20 is a diagram showing the distribution of elements in the resistor layer of the experimental example. [Figure 21] FIG. 21 is a graph showing the relationship between energy and heating efficiency and the rate of change in resistivity in an experimental example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A thermal printhead, a manufacturing method thereof, and a thermal printer will be described in detail below with reference to the drawings. The embodiments disclosed are all for illustrative purposes only, and it goes without saying that the disclosed embodiments are not limited to the embodiments, and various aspects are included within the scope of what is obvious to those skilled in the art.

[0013] The drawings used in the following description are all drawn in a schematic manner. In order to facilitate understanding, some parts of these drawings may be omitted or exaggerated. When describing which side of the drawing is to be described, the drawing should be placed so that the reference numerals in the drawing are upright and the drawing should be viewed accordingly.

[0014] (First embodiment) The thermal printhead of the first embodiment includes a substrate having a main surface and a convex portion formed on the main surface, a resistor layer formed on the main surface and the convex portion, a wiring layer covering the resistor layer so that the resistor layer is exposed at a heating portion of the convex portion, and a protective layer formed on the main surface of the substrate so as to cover the resistor layer and the wiring layer, the resistor layer includes a main resistor layer containing tantalum, and at least one of a first sub-resistor layer containing tantalum nitride laminated on the lower side of the main resistor layer and a second sub-resistor layer containing tantalum nitride laminated on the upper side of the main resistor layer, the tantalum nitride contained in the first sub-resistor layer and the second sub-resistor layer includes a eutectic of a face-centered cubic lattice structure with a (111) orientation and a (200) orientation. The first sub-resistor layer and the second sub-resistor layer reduce the diffusion of oxygen from the adjacent substrate and protective layer to the main resistor layer of the resistor layer, and can suppress the deterioration of the characteristics of the resistor layer due to the diffusion of oxygen.

[0015] The resistor layer may include both a first sub-resistor layer and a second sub-resistor layer, which can reduce the diffusion of oxygen from the adjacent substrate and protective layer, respectively, to the tantalum layer of the resistor layer.

[0016] The protective layer may include at least one of silicon nitride and silicon oxide. The protective layer can cover the resistor layer and the wiring layer to electrically and mechanically isolate them.

[0017] The wiring layer may include copper, which has high electrical conductivity and allows current to flow with low loss.

[0018] The heat generating device may further include an auxiliary resistor layer laminated between the resistor layer and the wiring layer, the wiring layer covering the auxiliary resistor layer so that the auxiliary resistor layer is exposed in the heat generating portion, and the exposed auxiliary resistor layer covering the resistor layer so that the resistor layer is partially exposed. The auxiliary resistor can further increase the heat generation efficiency.

[0019] The auxiliary resistor layer may contain titanium, which when formed into a thin film can generate heat as a resistor.

[0020] The substrate may be a ceramic substrate, and the protrusions may be formed by a glass glaze layer. The ceramic substrate provides electrical insulation, and the glass glaze layer can store heat generated from the resistor layer and the auxiliary resistor layer.

[0021] The heat generating portion may be formed in an area including the top of the protrusion, so that the paper can easily reach the heat generating portion.

[0022] The main resistor layer contains nitrogen at 22% atm or less, and the tantalum and nitrogen contained in the main resistor layer may form a body-centered cubic lattice structure. The main resistor layer containing such an extremely low concentration of nitrogen has low resistivity and can generate heat when a large current is passed through it.

[0023] The thermal printer of the first embodiment includes a thermal printhead and a platen disposed opposite the heat generating portion of the thermal printhead. Since the thermal printhead is designed to prevent deterioration of the resistor characteristics, it is possible to provide a thermal printer with stable performance.

[0024] The method for manufacturing a thermal printhead according to the first embodiment includes the steps of: providing a substrate having a main surface and a convex portion formed on the main surface; forming a resistor layer on the main surface and the convex portion; forming a wiring layer covering the resistor layer so that the resistor layer is exposed at a heating portion of the convex portion; and forming a protective layer on the main surface of the substrate so as to cover the resistor layer and the wiring layer, the resistor layer including a main resistor layer containing tantalum, and at least one of a first sub-resistor layer containing tantalum nitride laminated on the lower side of the main resistor layer and a second sub-resistor layer containing tantalum nitride laminated on the upper side of the main resistor layer, the tantalum nitride contained in the first sub-resistor layer and the second sub-resistor layer containing eutectic crystals having a face-centered cubic lattice structure with a (111) orientation and a (200) orientation. The first sub-resistor layer and the second sub-resistor layer reduce the diffusion of oxygen from the adjacent substrate and protective layer to the tantalum layer of the resistor layer, and can suppress the deterioration of the characteristics of the resistor layer due to the diffusion of oxygen.

[0025] The step of forming the resistor layer may be performed by depositing the main resistor layer and at least one of the first and second sub-resistor layers in a chamber by controlling the flow rate of nitrogen gas. This is easy because it is sufficient to control the flow rate of nitrogen gas.

[0026] The method may further include a step of forming an auxiliary resistor layer so as to be laminated between the resistor layer and the wiring layer after the step of forming the resistor layer and before the step of forming the wiring layer, and in the heat generating portion, the step of forming the wiring layer may cover the auxiliary resistor layer so that the auxiliary resistor layer is exposed, and the step of forming the auxiliary resistor layer may cover the resistor layer so that the resistor layer is exposed at a part of the exposed auxiliary resistor layer. The auxiliary resistor can further increase the efficiency of heat generation.

[0027] The step of providing a substrate may further include the steps of providing a ceramic substrate and forming a convex portion on a main surface of the ceramic substrate by a glass glaze layer, the ceramic substrate providing electrical insulation, and the glass glaze layer storing heat generated from the resistor layer and the auxiliary resistor layer.

[0028] FIG. 1 is a cross-sectional view showing a schematic structure of a head substrate 11 of a thermal printhead 10 of the first embodiment. In the thermal printhead 10 of the first embodiment, a flat main surface 11a of the head substrate 11 made of a ceramic such as alumina has convex portions 12 formed of a glass glaze layer, and the convex portions 12 extend in one direction on the main surface 11a. The convex portions 12 may have a curved cross section. The head substrate 11 may use other types of ceramic such as aluminum nitride (AlN) instead of alumina. A resistor layer 21 made of tantalum and nitrogen is formed on the main surface 11a and the convex portions 12 so as to cross the convex portions 12.

[0029] The wiring layer 22 covers the resistor layer 21 so that the resistor layer 21 is exposed at the plurality of heat generating parts 20 formed at a part of the protrusion 12. The plurality of heat generating parts 20 each have a rectangular planar shape and are arranged in a direction from the front to the back of FIG. 1. The plurality of heat generating parts 20 may be formed in a predetermined region including the top of the protrusion 12. The wiring layer 22 is formed of a metal such as copper. The wiring layer 22 may be formed by laminating copper on titanium, or may be formed of an alloy of copper and titanium. The wiring layer 22 has independent wiring connected to each of the plurality of heat generating parts 20. The wiring layer 22 transmits a current supplied from an external electrode 27 and supplies a current to the resistor layer 21 exposed at the plurality of heat generating parts 20 from both sides via independent wiring.

[0030] The protective layer 25 is made of an insulator such as silicon oxide, and is formed on the main surface 11a of the head substrate 11 so as to cover the resistor layer 21 and the wiring layer 22. The protective layer 25 may be made of other types of insulators such as silicon nitride. The external electrode 27 is exposed on the protective layer 25, and passes through the protective layer 25 to connect to the wiring layer 22.

[0031] The head substrate 11 is usually fixed to a heat sink (not shown). The heat sink is a fixing member to which the head substrate 11 is attached. The heat sink is made of a metal plate (for example, an aluminum plate or a steel plate).

[0032] The thermal printhead 10 is fixed to a mounting member (not shown) included in the thermal printer 110 by means of screws or the like. The thermal printer 110 has a roller-shaped platen 101. The platen 101 extends in the direction in which the multiple heat generating parts 20 of the thermal printhead 10 extend side by side (the direction from the front to the back in FIG. 1), and is disposed facing the multiple heat generating parts 20. When the thermal printer 110 is used, a print medium 102 (such as thermal paper) is disposed between the platen 101 and the multiple heat generating parts 20. The print medium 102 pressed against the platen 101 moves while being in contact with the multiple heat generating parts 20. The print medium 102 moves from the right side to the left side in FIG. 1. A flat platen (including a platen having a curved surface with a large radius of curvature) may be used instead of the roller-shaped platen 101.

[0033] As shown in Fig. 2, in the thermal printhead 10 of the first embodiment, the resistor layer 21 is formed by sequentially stacking a first sub-resistor layer 21a containing tantalum nitride, a main resistor layer 21b containing tantalum, and a second sub-resistor layer 21c containing tantalum nitride. The tantalum contained in the main resistor layer 21b has a body-centered cubic lattice structure (BCC) and may contain an extremely low concentration of nitrogen. This extremely low concentration is, for example, 22 atm% or less. The tantalum nitride contained in the first sub-resistor layer 21a and the second sub-resistor layer 21c is composed of a eutectic of a face-centered cubic lattice structure (FCC) with a (111) orientation and a (200) orientation.

[0034] In the resistor layer 21, the main resistor layer 21b has low resistivity, serves as the main electrical conduction path, and is the dominant factor in the electrical characteristics of the resistor layer 21. The main resistor layer 21b contains nitrogen at an extremely low concentration and has excellent ductility. Therefore, the main resistor layer 21b does not easily break even when a large current is intermittently passed through the main resistor layer 21b to heat the heating section 20, causing repeated cycles of expansion and contraction.

[0035] In the resistor layer 21, the main resistor layer 21b is laminated on and electrically connected to the first sub-resistor layer 21a and the second sub-resistor layer 21c. Therefore, even if the main resistor layer 21b, which is the main electrical conduction path, is broken, electrical conduction is maintained via the first sub-resistor layer 21a and the second sub-resistor layer 21c. Therefore, the entire resistor layer 21 is not easily broken.

[0036] The resistor layer 21 is formed on the main surface 11a of the head substrate 11, and a part of it is covered with a protective layer 25. The head substrate 11 is made of ceramic, but the ceramic is not coated with alumina (Al 2 O 3 The protective layer 25 is made of an insulator, but is made of a material containing oxygen, such as silicon oxide (SiO 2 In some cases, oxygen atoms may enter the resistor layer 21 from such oxygen-containing materials.

[0037] In the resistor layer 21, a first sub-resistor layer 21a is interposed between the head substrate 11 and the main resistor layer 21b to protect the main resistor layer 21b from being affected by the head substrate 11. For example, even if oxygen atoms penetrate into the resistor layer 21 from the head substrate 11 made of a material containing oxygen such as alumina, the first sub-resistor layer 21a acts as a barrier to keep the penetration within the first sub-resistor layer 21a and prevent it from reaching the main resistor layer 21b.

[0038] In addition, the second sub-resistor layer 21c is interposed between the protective layer 25 and the main resistor layer 21b to protect the main resistor layer 21b from being affected by the protective layer 25. For example, when the protective layer 25 is made of a material containing oxygen such as silicon oxide, even if oxygen atoms penetrate into the resistor layer 21 from the protective layer 25, the second sub-resistor layer 21c acts as a barrier to keep the penetration within the second sub-resistor layer 21c and prevent it from reaching the main resistor layer 21b.

[0039] In this way, even if oxygen atoms penetrate into the resistor layer 21 from the adjacent head substrate 11 and protective layer 25, the oxygen atoms are kept in the first sub-resistor layer 21a or the second sub-resistor layer 21c and are prevented from penetrating into the main resistor layer 21b, which is a dominant factor in the electrical characteristics. Therefore, deterioration of characteristics that may occur due to oxygen atoms penetrating into the main resistor layer 21b is reduced, and the electrical characteristics of the thermal printhead 10 including the resistor layer 21 are maintained, thereby extending the life of the thermal printhead 10. Furthermore, even if the main resistor layer 21b is broken, electrical conduction is maintained via the first sub-resistor layer 21a and the second sub-resistor layer 21c, thereby extending the life of the thermal printhead 10.

[0040] Fig. 3 is a cross-sectional view showing another embodiment of the resistor layer 21. In Fig. 2, the resistor layer 21 is formed by laminating the first sub-resistor layer 21a, the main resistor layer 21b, and the second sub-resistor layer 21c, but is not limited to such a structure. The first sub-resistor layer 21a and the second sub-resistor layer 21c may be provided only on one side where oxygen atoms may invade the resistor layer 21 from the adjacent layer.

[0041] 3(a) is a cross-sectional view showing a resistor layer 21 formed by laminating a main resistor layer 21b on a first sub-resistor layer 21a. For example, when the ceramic of the head substrate 11 (see FIG. 1) is alumina (Al 2 O 3 ), and the protective layer 25 (see FIG. 1) is made of silicon nitride (SiN), which does not contain oxygen, oxygen atoms may penetrate from the head substrate 11 into the resistor layer 21, but oxygen atoms are not supplied from the protective layer 25. Therefore, as a barrier for preventing the penetration of oxygen atoms into the main resistor layer 21b, it is sufficient to provide the first sub-resistor layer 21a between the head substrate 11 and the main resistor layer 21b, and the main resistor layer 21b may be in direct contact with the protective layer 25 without the second sub-resistor layer 21c being interposed.

[0042] In this case, even if oxygen atoms penetrate into the resistor layer 21 from the head substrate 11, the oxygen atoms are contained within the first sub-resistor layer 21a and are prevented from reaching the main resistor layer 21b, which is the dominant factor in determining the electrical characteristics. Therefore, the electrical characteristics of the thermal printhead 10 including the resistor layer 21 are maintained, thereby extending the life of the thermal printhead 10.

[0043] 3(b) is a cross-sectional view showing the resistor layer 21 formed by laminating the second sub-resistor layer 21c on the main resistor layer 21b. For example, if the ceramic of the head substrate 11 (see FIG. 1) is made of aluminum nitride (AlN) that does not contain oxygen, and the protective layer 25 (see FIG. 1) is made of silicon oxide (SiO 2 ), oxygen atoms are not supplied from the head substrate 11, but oxygen atoms may penetrate from the protective layer 25 into the resistor layer 21. Therefore, as a barrier for preventing the penetration of oxygen atoms into the main resistor layer 21b, it is sufficient to provide the second sub-resistor layer 21c between the main resistor layer 21b and the protective layer 25, and the main resistor layer 21b may be in direct contact with the head substrate 11 without the first sub-resistor layer 21a being interposed.

[0044] In this case, even if oxygen atoms penetrate into the resistor layer 21 from the protective layer 25, the oxygen atoms are contained within the second sub-resistor layer 21c and are prevented from reaching the main resistor layer 21b, which is the dominant factor in determining the electrical characteristics. Therefore, the electrical characteristics of the thermal printhead 10 including the resistor layer 21 are maintained, and the life of the thermal printhead 10 is extended.

[0045] In this way, even when the resistor layer 21 is formed by laminating only one of the first sub-resistor layer 21a and the second sub-resistor layer 21c on the main resistor layer 21b, the main resistor layer 21b is electrically connected to one of the first sub-resistor layer 21a and the second sub-resistor layer 21c. Therefore, even if the main resistor layer 21b, which is the main electrical conduction path, is broken, electrical conduction is maintained via one of the first sub-resistor layer 21a and the second sub-resistor layer 21c. For this reason, the entire resistor layer 21 is not easily broken, and the life of the thermal printhead 10 including the resistor layer 21 is extended.

[0046] The thermal printhead 10 of the first embodiment may be incorporated into a thermal printer 110. Such a thermal printer 110 has a thermal printhead 10 and a platen 101 disposed opposite the heat generating portion 20 of the thermal printhead 10. Since the thermal printhead 10 of the first embodiment is designed to have a long life, the thermal printer 110 constructed by incorporating such a thermal printhead 10 can also have a long life.

[0047] 4 to 5 are process flow diagrams of the thermal printhead 10 of the first embodiment. In the process shown in FIG. 4, a head substrate 11 made of ceramic such as alumina having a flat main surface 11a is provided, and a convex portion 12 extending in one direction is formed on the main surface 11a of the head substrate 11 by a glass glaze layer by printing or the like. The glass glaze layer is formed, for example, by firing a glass paste screen-printed on the main surface 11a. For the head substrate 11, other types of ceramics may be used instead of alumina. FIG. 4 to FIG. 5 show one head substrate 11 corresponding to one thermal printhead 10. In reality, a ceramic substrate having a rectangular planar shape when viewed along the thickness direction of the head substrate 11 (when viewed from above) includes a plurality of head substrates 11 in, for example, a lattice pattern. In other words, the ceramic substrate is a ceramic wafer.

[0048] 5, the resistor layer 21 is formed so as to cross the main surface 11a and the protrusions 12 of the head substrate 11. As shown in Fig. 2, the resistor layer 21 is configured by laminating a first sub-resistor layer 21a, a main resistor layer 21b, and a second sub-resistor layer 21c in this order.

[0049] In this step, the head substrate 11 having the convex portions 12 formed on the main surface 11a in the step shown in Fig. 4 is stored in a chamber, a mixed gas of nitrogen gas as a raw material gas and argon gas as a carrier gas is flowed into the chamber, and tantalum is sputtered as a target to deposit tantalum nitride on the main surface 11a and the convex portions 12. The flow rate of the nitrogen gas in the mixed gas is adjusted to be large, thereby depositing the first sub-resistor layer 21a and the second sub-resistor layer 21c containing a high concentration of nitrogen. The supply of nitrogen gas is then stopped, and only argon gas is flowed to sputter tantalum and deposit the main resistor layer 21b.

[0050] The deposition of the first sub-resistor layer 21a, the main resistor layer 21b, and the second sub-resistor layer 21c is performed by adjusting the flow rate of nitrogen gas in order while the head substrate 11 is stored in the sputtering chamber. Therefore, in the step of depositing the main resistor layer 21b, the nitrogen gas flowed in the step of depositing the first sub-resistor layer 21a remains in the chamber, and the main resistor layer 21b may contain a very low concentration of nitrogen.

[0051] 6 is a graph showing the relationship between the nitrogen content and the resistivity and its in-plane variation of tantalum nitride formed by sputtering. In the graph, curve a represents the resistivity of tantalum nitride, and curve b represents the in-plane variation of the resistivity of tantalum nitride.

[0052] In the deposited tantalum nitride, the nitrogen content increases with the flow rate of nitrogen gas, and the nitrogen content on the horizontal axis can be interpreted as the flow rate of nitrogen gas. The resistivity shown by curve a increases as the nitrogen content or the nitrogen gas flow rate increases. On the other hand, the in-plane variation of resistivity shown by curve b decreases as the nitrogen gas flow rate or the nitrogen content increases.

[0053] In the figure, the first region R1 containing a low concentration of nitrogen corresponds to the main resistor layer 21a containing tantalum in the resistor layer 21. The first region R1 has a low resistivity and is used to pass a large current through the heating section 20 to generate heat, but the in-plane variation in resistivity is large. In this first region R1, tantalum nitride is deposited in an unstable structure such as a body-centered cubic lattice structure. In regions with an even lower nitrogen content than the first region R1, tantalum nitride is also deposited in a body-centered cubic lattice structure.

[0054] The second region R2 containing a high concentration of nitrogen exceeding a predetermined concentration corresponds to the first sub-resistor layer 21b and the second sub-resistor layer 21c containing tantalum nitride in the resistor layer 21. The in-plane variation in resistivity in the second region R2 is small, indicating that the tantalum nitride is formed into a stable structure, but the resistivity is high. For this reason, the second region R2 is not suitable for generating heat by passing a large current through it.

[0055] The second region R2 is a region where an excess of nitrogen gas is supplied to the chamber, and the increase in the concentration of nitrogen contained in the tantalum nitride saturates even if the flow rate of the nitrogen gas increases. The tantalum nitride in the second region R2 is in a stable state like a eutectic of a face-centered cubic lattice structure with (111) and (200) orientations, in which the concentration of nitrogen contained exceeds a predetermined value. This predetermined value of the nitrogen concentration (predetermined concentration) corresponds to the lower end of the nitrogen content in the second region R2 (the left end in FIG. 6).

[0056] FIG. 7 is a graph showing the relationship between the nitrogen content and pressure resistance of tantalum nitride formed by sputtering. This pressure resistance was measured by a step stress test (SST). The pressure resistance decreases as the nitrogen content increases. In the figure, if the usable third region R3 has a pressure resistance of 0.11 mJ or more, the corresponding usable nitrogen content is approximately 22 atm% or less. Therefore, from the viewpoint of pressure resistance, extremely low concentration tantalum nitride with a nitrogen content of approximately 22 atm% or less can be used.

[0057] According to the first embodiment, as shown in Fig. 2, the resistor layer 21 is configured by sequentially stacking the first sub-resistor layer 21a, the main resistor layer 21b, and the second sub-resistor layer 21c. The tantalum nitride constituting the first sub-resistor layer 21a and the second sub-resistor layer 21c contains nitrogen in a stable state with a concentration exceeding a predetermined value, and the range of the nitrogen content may be within region R2 in Fig. 6. In this region R2, the tantalum nitride is formed into a stable structure composed of a eutectic of a face-centered cubic lattice structure with (111) orientation and (200) orientation.

[0058] The main resistor layer 21b is made of tantalum that may contain a very low concentration of nitrogen, and the range of the nitrogen content may be the first region R1 in FIG. 6 or a range with an even lower nitrogen content. In the first region R1 and a range with an even lower nitrogen content, the resistivity varies widely, and tantalum nitride is formed into an unstable structure. Although the main resistor layer 21b is formed into an unstable structure, it is laminated between the first sub-resistor layer 21a and the second sub-resistor layer 21c, which have stable structures. Therefore, the first sub-resistor layer 21a, the main resistor layer 21b, and the second sub-resistor layer 21c that constitute the resistor layer 21 form a stable structure as a whole.

[0059] In the resistor layer 21, the main resistor layer 21b, which has the lower resistivity among the first sub-resistor layer 21a, the main resistor layer 21b, and the second sub-resistor layer 21c, serves as the main electrical conduction path and is the dominant factor in the electrical characteristics of the resistor layer 21. The main resistor layer 21b is made of tantalum which may contain a very low concentration of nitrogen, and therefore the nitrogen concentration corresponds to the usable third region R3 shown in Fig. 7. This ensures the voltage resistance of the thermal printhead 10 including the resistor layer 21.

[0060] As another embodiment of the resistor layer 21 shown in Fig. 3, the resistor layer 21 may be configured by laminating the main resistor layer 21b and only one of the first sub-resistor layer 21a and the second sub-resistor layer 21c. That is, the resistor layer 21 may be configured by laminating the main resistor layer 21b on the first sub-resistor layer 21a as shown in Fig. 3(a), or may be configured by laminating the second sub-resistor layer 21c on the main resistor layer 21b as shown in Fig. 3(b).

[0061] In such a case, the head substrate 11 having the convex portion 12 formed on the main surface 11a is stored in a chamber, a mixed gas of nitrogen gas as a raw material gas and argon gas as a carrier gas is flowed into the chamber, and tantalum is sputtered as a target to deposit tantalum nitride on the main surface 11a and the convex portion 12. The flow rate of the nitrogen gas in the mixed gas is adjusted to be large, thereby depositing the first sub-resistor layer 21a or the second sub-resistor layer 21c containing a high concentration of nitrogen. The supply of nitrogen gas is stopped, and only argon gas is flowed to sputter tantalum and deposit the main resistor layer 21b. These operations are performed by adjusting the flow rate of nitrogen gas while the head substrate 11 is stored in the chamber so that the main resistor layer 21b and either the first sub-resistor layer 21a or the second sub-resistor layer 21c are deposited in a predetermined order.

[0062] In the resistor layer 21, the tantalum nitride constituting one of the first sub-resistor layer 21a and the second sub-resistor layer 21c has a nitrogen concentration exceeding a predetermined value and is in a stable state, and the range of the nitrogen content may be within region R2 in Fig. 6. In this region R2, the tantalum nitride is formed into a stable structure composed of a eutectic of a face-centered cubic lattice structure with (111) orientation and (200) orientation.

[0063] The tantalum layer 21b is made of tantalum that may contain a very low concentration of nitrogen, and the range of the nitrogen content may be the first region R1 in FIG. 6 or a range with an even lower nitrogen content. In the first region R1 and a range with an even lower nitrogen content, the resistivity varies widely, and tantalum nitride is formed into an unstable structure. Although the main resistor layer 21b is formed into an unstable structure, the main resistor layer 21b is laminated with one of the first sub-resistor layer 21a and the second sub-resistor layer 21c, which have a stable structure. Therefore, the main resistor layer 21b and one of the first sub-resistor layer 21a and the second sub-resistor layer 21c that constitute the resistor layer 21 form a stable structure as a whole.

[0064] 8 to 9 are process flow diagrams of the thermal printhead 10 of the first embodiment. FIGS. 8 and 9 are subsequent to the process flow shown in FIGS. 4 and 5. In the step shown in FIG. 8, a wiring layer 22 is formed on the main surface 11a of the head substrate 11 so as to cover the resistor layer 21 formed to cross the protrusions 12. The wiring layer 22 is made of a metal such as copper. The wiring layer 22 may be formed by laminating copper on titanium, or may be made of an alloy of copper and titanium. The wiring layer 22 is interrupted at a part of the protrusion 12 so that the resistor layer 21 is exposed at the heat generating portion 20.

[0065] In the process shown in Fig. 8, the resistor layer 21 is etched to form a plurality of heat generating portions 20 (see Fig. 1). The plurality of heat generating portions 20 each have a rectangular planar shape, and are aligned along a direction extending from the front to the back of Fig. 8. In the process shown in Fig. 8, a pattern of the wiring layer 22 is formed by etching. The pattern of the wiring layer 22 has independent wiring connected to each of the plurality of heat generating portions 20.

[0066] In the step shown in Fig. 9, a protective layer 25 is formed on the main surface 11a and the protrusions 12 of the head substrate 11 so as to cover the resistor layer 21 and the wiring layer 22. The protective layer 25 is made of an insulator such as silicon nitride. The protective layer 25 may be made of other insulators such as silicon oxide. Following the step shown in Fig. 9, external electrodes 27 are formed as shown in Fig. 1, and individual thermal printheads 10 are obtained through a step such as dicing (not shown). A plurality of head substrates 11 are produced from a ceramic substrate having a rectangular planar shape through a step such as dicing.

[0067] In the manufacturing method of the thermal printhead 10 of the first embodiment, in the step of forming the resistor layer 21 shown in Fig. 5, the nitrogen content is controlled by appropriately controlling the flow rate of nitrogen gas supplied to a chamber in which tantalum is used as a sputtering target. Compared to the conventional step of forming a resistor by sputtering, this step can be easily implemented since it is only necessary to add an operation of appropriately controlling the flow rate of nitrogen.

[0068] (Second embodiment) The thermal printhead of the second embodiment includes a substrate having a main surface and formed on the main surface, a resistor layer formed on the main surface and on the convex portion, a wiring layer covering the resistor layer so that the resistor layer is exposed at a part of the heating portion of the convex portion, and a protective layer formed on the main surface of the substrate so as to cover the resistor layer and the wiring layer, the resistor layer includes a main resistor layer containing tantalum, and at least one of a first sub-resistor layer containing tantalum nitride laminated on the lower side of the main resistor layer and a second sub-resistor layer containing tantalum nitride laminated on the upper side of the main resistor layer, the tantalum nitride contained in the first sub-resistor layer and the second sub-resistor layer includes a eutectic of a face-centered cubic lattice structure with a (111) orientation and a (200) orientation. The first sub-resistor layer and the second sub-resistor layer reduce the diffusion of oxygen from the adjacent substrate and protective layer to the main resistor layer of the resistor layer, and can suppress the deterioration of the characteristics of the resistor layer due to the diffusion of oxygen.

[0069] The resistor layer may include both a first sub-resistor layer and a second sub-resistor layer. The first sub-resistor layer and the second sub-resistor layer can reduce the diffusion of oxygen from the adjacent substrate and protective layer to the main resistor layer of the resistor layer, respectively.

[0070] The protective layer may include at least one of silicon nitride and silicon oxide. The protective layer can cover the resistor layer and the wiring layer to electrically and mechanically isolate them.

[0071] The wiring layer may include copper, which has high electrical conductivity and allows current to flow with low loss.

[0072] The heat generating section may further include an auxiliary resistor layer laminated between the resistor layer and the wiring layer, and in the heat generating section, the wiring layer may cover the auxiliary resistor layer so that the auxiliary resistor layer is exposed, and the exposed auxiliary resistor layer may cover the resistor layer so that the resistor layer is partially exposed. The auxiliary resistor can further increase the heat generation efficiency.

[0073] The thermal printer of the second embodiment includes a thermal printhead and a platen disposed opposite the heat generating portion of the thermal printhead. Since the thermal printhead is designed to prevent deterioration of the resistor characteristics, it is possible to provide a thermal printer with stable performance.

[0074] A method for manufacturing a thermal printhead according to a second embodiment includes the steps of: providing a substrate having a main surface and convex portions formed on the main surface; forming a resistor layer on the main surface and the convex portions; forming a wiring layer covering the resistor layer so that the resistor layer is exposed at some of the heat generating portions of the convex portions; and forming a protective layer on the main surface of the substrate so as to cover the resistor layer and the wiring layer, wherein the resistor layer includes a main resistor layer containing tantalum, and at least one of a first sub-resistor layer containing tantalum nitride laminated on the lower and upper sides of the tantalum layer, respectively, and a second sub-resistor layer containing tantalum nitride laminated on the upper side of the main resistor layer, and the first sub-resistor layer and the second sub-resistor layer contain eutectic crystals having a face-centered cubic lattice structure with a (111) orientation and a (200) orientation.

[0075] The first and second sub-resistor layers reduce the diffusion of oxygen from the adjacent substrate and protective layer to the main resistor layer of the resistor layer, thereby suppressing deterioration of the characteristics of the resistor layer due to oxygen diffusion.

[0076] The step of forming the resistor layer may be performed by depositing the main resistor layer and at least one of the first and second sub-resistor layers in a chamber by controlling the flow rate of nitrogen gas. This is easy because it is sufficient to control the flow rate of nitrogen gas.

[0077] The method may further include a step of forming an auxiliary resistor layer so as to be laminated between the resistor layer and the wiring layer after the step of forming the resistor layer and before the step of forming the wiring layer, and in the heat generating portion, the step of forming the wiring layer may cover the auxiliary resistor layer so that the auxiliary resistor layer is exposed, and the step of forming the auxiliary resistor layer may cover the resistor layer so that the exposed auxiliary resistor layer partially exposes the resistor layer. The auxiliary resistor can further increase the efficiency of heat generation.

[0078] The step of providing a substrate further includes a step of providing a semiconductor substrate, a step of forming a convex portion on a main surface of the semiconductor substrate by anisotropic etching, and a step of forming an insulating layer so as to cover the main surface of the substrate on which the convex portion is formed and the convex portion, the step of forming a resistor layer may include forming a resistor layer on the insulating layer, and the step of forming a protective layer may include forming a protective layer so as to cover the insulating layer, the resistor layer, and the wiring layer. The convex portion having an inclined surface can be easily formed by anisotropic etching.

[0079] The step of forming the protrusion includes a step of forming first inclined surfaces sandwiching the top surface of the protrusion from both sides by a first anisotropic etching, and a step of forming a second inclined surface between the top surface and the first inclined surface by a second anisotropic etching, and the resistor layer may be formed on at least one of the top surface of the protrusion, the first inclined surface, and the second inclined surface. By further having the second inclined surface, the paper can slide more smoothly.

[0080] FIG. 10 is a cross-sectional view showing a schematic structure of a head substrate 31 of a thermal printhead 30 of the second embodiment. In the thermal printhead 30 of the second embodiment, a convex portion 31b is formed by anisotropic etching on a flat main surface 31a of the head substrate 31 made of a semiconductor such as silicon. The convex portion 31b extends in one direction on the main surface 31a and is sandwiched on both sides by a first inclined surface 31c in contact with the main surface 31a and a second inclined surface 31d formed between the first inclined surface 31c and a top surface 31e of the convex portion 31b. The head substrate 31 may use another type of semiconductor such as silicon carbide instead of silicon. Also, the silicon may be doped with an appropriate impurity.

[0081] An insulating layer 32 made of silicon oxide is formed so as to cover the main surface 31a and the protrusions 31b. The insulating layer 32 also serves to store heat in the heat generating portion 40, and is also called a heat storage layer. A resistor layer 41 made of tantalum and nitrogen is formed on the main surface 31a and the protrusion 31b so as to cross the protrusion 31b. For the insulating layer 32, other types of insulators such as silicon nitride may be used instead of silicon oxide.

[0082] The auxiliary resistor layer 42 covers the resistor layer 41 so that the resistor layer 41 is exposed at the heating portion 40 formed on one of the second inclined surfaces 31d. The auxiliary resistor layer 42 is made of a metal such as titanium having excellent adhesion. Here, the one of the second inclined surfaces 31d faces the external electrode 47 with the protrusion 31b in between. Note that the heating portion 40 is not limited to being formed on one of the second inclined surfaces 31d, but may be formed on at least one of the top surface 31e of the protrusion 31b, the other second inclined surface 31d, and the two first inclined surfaces 31c.

[0083] The wiring layer 43 covers the auxiliary resistor layer 42 so that the auxiliary resistor layer 42 is exposed at the heat generating parts 40. The heat generating parts 40 each have a rectangular planar shape and are arranged in a direction from the front to the back in FIG. 10. The wiring layer 43 is made of a metal such as copper that has excellent electrical conductivity. The wiring layer 43 has independent wiring connected to each of the heat generating parts 40. The wiring layer 43 transmits a current supplied from the external electrode 47, and supplies the current to the auxiliary resistor layer 42 exposed at the heat generating parts 40 from both sides via independent wiring. The current supplied from the wiring layer 43 to the auxiliary resistor layer 42 is supplied to the resistor layer 41 exposed from the auxiliary resistor layer 42 at the heat generating part 40 from both sides.

[0084] The protective layer 45 is made of an insulator such as silicon nitride, and is formed on the main surface 31a of the head substrate 31 so as to cover the resistor layer 41, the auxiliary resistor layer 42, and the wiring layer 43. The protective layer 45 may be made of other insulators such as silicon oxide. The external electrode 47 is exposed on the protective layer 45, and is connected to the wiring layer 43 through the protective layer 45.

[0085] The head substrate 31 is usually fixed to a heat sink (not shown). The heat sink is a fixing member to which the head substrate 31 is attached. The heat sink is made of a metal plate (for example, an aluminum plate or a steel plate).

[0086] The thermal print head 30 is fixed to a mounting member (not shown) included in the thermal printer 130 by screwing or the like. The thermal printer 130 has a roller-shaped platen 101. The platen 101 extends in the direction in which the multiple heat generating parts 40 of the thermal print head 30 extend side by side (the direction from the front to the back in FIG. 10), and is disposed facing the multiple heat generating parts 40. When the thermal printer 130 is used, a print medium 102 (such as thermal paper) is disposed between the platen 101 and the multiple heat generating parts 40. The print medium 102 pressed against the platen 101 moves while being in contact with the multiple heat generating parts 40. The print medium 102 moves from the right side to the left side in FIG. 10. A flat platen (including a platen having a curved surface with a large radius of curvature) may be used instead of the roller-shaped platen 101.

[0087] As shown in Fig. 11, in the thermal printhead 30 of the second embodiment, the resistor layer 41 is formed by sequentially stacking a first sub-resistor layer 41a containing tantalum nitride, a main resistor layer 41b containing tantalum, and a second sub-resistor layer 41c containing tantalum nitride. The tantalum contained in the main resistor layer 41b has a body-centered cubic lattice structure (BCC) and may contain a very low concentration of nitrogen. The tantalum nitride contained in the first sub-resistor layer 41a and the second sub-resistor layer 41c is composed of a eutectic with a face-centered cubic lattice structure (FCC) with a (111) orientation and a (200) orientation.

[0088] In the resistor layer 41, the main resistor layer 41b has low resistivity, serves as the main electrical conduction path, and is the dominant factor in the electrical characteristics of the resistor layer 41. The main resistor layer 41b contains nitrogen at an extremely low concentration and has excellent ductility. Therefore, the main resistor layer 41b does not easily break even when a large current is intermittently passed through the main resistor layer 41b to heat the heating section 40, causing repeated cycles of expansion and contraction.

[0089] In the resistor layer 41, the main resistor layer 41b is laminated on and electrically connected to the first sub-resistor layer 41a and the second sub-resistor layer 41c. Therefore, even if the main resistor layer 41b, which is the main electrical conduction path, is broken, electrical conduction is maintained via the first sub-resistor layer 41a and the second sub-resistor layer 41c. Therefore, the entire resistor layer 41 is not easily broken.

[0090] The resistor layer 41 is formed on the insulating layer 32 that covers the head substrate 31, and a part of it is covered with a protective layer 45. The head substrate 31 is made of a semiconductor, but the insulating layer 32 is made of silicon oxide (SiO 2 The protective layer 45 is made of an insulator such as silicon nitride (SiN), but silicon oxide (SiO 2 In some cases, oxygen atoms may enter the resistor layer 41 from such oxygen-containing materials.

[0091] In the resistor layer 41, the first sub-resistor layer 41a is interposed between the insulating layer 32 and the main resistor layer 41b, and protects the main resistor layer 41b from being affected by the insulating layer 32. For example, even if oxygen atoms penetrate into the resistor layer 41 from the insulating layer 32 made of a material containing oxygen such as silicon oxide, the first sub-resistor layer 41a acts as a barrier to keep the penetration within the first sub-resistor layer 41a and prevent it from reaching the main resistor layer 41b.

[0092] In addition, the second sub-resistor layer 41c is interposed between the protective layer 45 and the main resistor layer 41b to protect the main resistor layer 21b from being affected by the protective layer 45. For example, when the protective layer 45 is made of a material containing oxygen such as silicon oxide, even if oxygen atoms penetrate from the protective layer 45 into the resistor layer 41, the second sub-resistor layer 41c acts as a barrier to keep the penetration within the second sub-resistor layer 41c and prevent it from reaching the main resistor layer 41b.

[0093] In this way, even if oxygen atoms penetrate into the resistor layer 41 from the adjacent insulating layer 32 and protective layer 45, the oxygen atoms are kept in the first sub-resistor layer 41a or the second sub-resistor layer 41c and are prevented from penetrating into the main resistor layer 41b, which is the dominant factor in the electrical characteristics. Therefore, deterioration of characteristics that may occur due to oxygen atoms penetrating into the main resistor layer 41b is reduced, and the electrical characteristics of the thermal printhead 30 including the resistor layer 41 are maintained, thereby extending the life of the thermal printhead 30. Even if the main resistor layer 41b is broken, electrical conduction is maintained via the first sub-resistor layer 41a and the second sub-resistor layer 41c, thereby extending the life of the thermal printhead 30.

[0094] Fig. 12 is a cross-sectional view showing another embodiment of the resistor layer 41. In Fig. 11, the resistor layer 41 is formed by laminating the first sub-resistor layer 41a, the main resistor layer 41b, and the sub-resistor layer 41c, but is not limited to such a structure. The first sub-resistor layer 41a and the second sub-resistor layer 41c may be provided only on one side where oxygen atoms may invade the resistor layer 41 from the adjacent layer.

[0095] 12(a) is a cross-sectional view showing a resistor layer 41 formed by laminating a main resistor layer 41b on a first sub-resistor layer 41a. For example, when the insulating layer 32 (see FIG. 10) is made of silicon oxide (SiO 2 ), and the protective layer 45 (see FIG. 10) is made of silicon nitride (SiN), which does not contain oxygen, oxygen atoms may penetrate from the insulating layer 32 into the resistor layer 41, but oxygen atoms are not supplied from the protective layer 45. Therefore, as a barrier for preventing the penetration of oxygen atoms into the main resistor layer 21b, it is sufficient to provide the first sub-resistor layer 41a between the insulating layer 32 and the main resistor layer 41b, and the main resistor layer 41b may be in direct contact with the protective layer 45 without the second sub-resistor layer 41c being interposed therebetween.

[0096] In this case, even if oxygen atoms penetrate into the resistor layer 41 from the insulating layer 32, the oxygen atoms are contained within the first sub-resistor layer 41a and are prevented from reaching the main resistor layer 41b, which is the dominant factor in determining the electrical characteristics. Therefore, the electrical characteristics of the thermal printhead 30 including the resistor layer 41 are maintained, and the life of the thermal printhead 30 is extended.

[0097] 12(b) is a cross-sectional view showing a resistor layer 41 formed by laminating a second sub-resistor layer 41c on a main resistor layer 41b. For example, the insulating layer 32 (see FIG. 10) is made of silicon nitride (SiN) that does not contain oxygen, and the protective layer 45 (see FIG. 10) is made of silicon oxide (SiO 2 ), oxygen atoms are not supplied from the head substrate 31, but oxygen atoms may penetrate from the protective layer 45 into the resistor layer 41. Therefore, as a barrier to prevent oxygen atoms from penetrating into the main resistor layer 41b, a second sub-resistor layer 41c may be provided between the main resistor layer 41b and the protective layer 45, and the main resistor layer 41b may be in direct contact with the insulating layer 32 without the first sub-resistor layer 41a being interposed.

[0098] In this case, even if oxygen atoms penetrate into the resistor layer 41 from the protective layer 45, the oxygen atoms are contained within the second sub-resistor layer 41c and are prevented from reaching the main resistor layer 41b, which is the dominant factor in determining the electrical characteristics. Therefore, the electrical characteristics of the thermal printhead 30 including the resistor layer 41 are maintained, and the life of the thermal printhead 30 is extended.

[0099] In this way, even when the resistor layer 41 is formed by laminating only one of the first sub-resistor layer 41a and the second sub-resistor layer 41c on the main resistor layer 41b, the main resistor layer 41b is electrically connected to one of the first sub-resistor layer 41a and the second sub-resistor layer 41c. Therefore, even if the main resistor layer 41b, which is the main electrical conduction path, is broken, electrical conduction is maintained via one of the first sub-resistor layer 41a and the second sub-resistor layer 41c. For this reason, the entire resistor layer 21 is not easily broken, and the life of the thermal printhead including the resistor layer 21 is extended.

[0100] A thermal printer 130 may be configured by incorporating the thermal printhead 30 of the second embodiment. Such a thermal printer 130 has a thermal printhead 30 and a platen 101 disposed opposite the heat generating portion 40 of the thermal printhead 30. Since the thermal printhead 30 of the second embodiment is designed to have a long life, a thermal printer 130 configured by incorporating such a thermal printhead 30 can also be designed to have a long life.

[0101] Figures 13 to 15 are process flow diagrams of a thermal printhead 30 according to the second embodiment. Figures 13 to 15 show one head substrate 31 corresponding to one thermal printhead 30. In reality, a silicon substrate having a substantially circular planar shape includes multiple head substrates 31, for example in a lattice pattern. In other words, the silicon substrate is a silicon wafer.

[0102] In the process shown in Fig. 13, a head substrate 31 made of a semiconductor such as silicon is provided, and a convex portion 31b extending in one direction is formed on a main surface 31a of the head substrate 31 by anisotropic etching. The convex portion 31b is sandwiched on both sides by a first inclined surface 31c in contact with the main surface 31a and a second inclined surface 31d formed between the first inclined surface 31c and a top surface 31e of the convex portion 31b. The head substrate 31 may be made of another type of semiconductor such as silicon carbide instead of silicon. Also, the silicon may be doped with an appropriate impurity.

[0103] 14, the insulating layer 32 is formed of silicon oxide on the main surface 31a and the protrusions 31b of the head substrate 31. The insulating layer 32 may be made of other types of insulators such as silicon nitride instead of silicon oxide.

[0104] 15, a resistor layer 41 is formed on the insulating layer 32 so as to cross the main surface 31a and the protrusions 31b of the head substrate 31. As shown in Fig. 11, the resistor layer 41 is configured by laminating a first sub-resistor layer 41a, a main resistor layer 41b, and a second sub-resistor layer 41c in this order.

[0105] In this step, the head substrate 31 on which the insulating layer 32 is formed on the main surface 31a and the protrusions 31b in the step shown in Fig. 14 is stored in a chamber, a mixed gas of nitrogen gas as a raw material gas and argon gas as a carrier gas is flowed into the chamber, and tantalum is sputtered as a target to deposit tantalum nitride on the insulating layer 32. The flow rate of the nitrogen gas in the mixed gas is adjusted to be large, thereby depositing the first sub-resistor layer 41a and the second sub-resistor layer 41c containing high concentrations of nitrogen. The supply of nitrogen gas is stopped, and only argon gas is flowed to sputter tantalum and deposit the main resistor layer 41b. Sputtering is performed by adjusting the flow rate of nitrogen gas in order while the head substrate 31 is stored in the chamber so that the first sub-resistor layer 41a, the main resistor layer 41b, and the second sub-resistor layer 41c are deposited in order. Therefore, in the process of depositing the main resistor layer 41b, the nitrogen gas flowed in the process of depositing the first sub-resistor layer 41a may remain in the chamber, causing the main resistor layer 41b to contain an extremely low concentration of nitrogen.

[0106] 6 is a graph showing the relationship between the nitrogen content and the resistivity and its in-plane variation of tantalum nitride formed by sputtering. In the graph, curve a represents the resistivity of tantalum nitride, and curve b represents the in-plane variation of the resistivity of tantalum nitride.

[0107] In the deposited tantalum nitride, the nitrogen content increases with the flow rate of nitrogen gas, and the nitrogen content on the horizontal axis can be interpreted as the flow rate of nitrogen gas. The resistivity shown by curve a increases as the nitrogen content or the nitrogen gas flow rate increases. On the other hand, the in-plane variation of resistivity shown by curve b decreases as the nitrogen gas flow rate or the nitrogen content increases.

[0108] In the figure, the first region R1 containing a low concentration of nitrogen corresponds to the main resistor layer 21a containing tantalum in the resistor layer 21, has a low resistivity, and is used to pass a large current through the heating section 40 to generate heat, but has a large in-plane variation in resistivity. In this first region R1, tantalum nitride is deposited in an unstable structure such as a body-centered cubic lattice structure. On the other hand, the second region R2 containing a high concentration of nitrogen exceeding a predetermined concentration corresponds to the first sub-resistor layer 21b and the second sub-resistor layer 21c containing tantalum nitride in the resistor layer 21, has a small in-plane variation in resistivity, and tantalum nitride is deposited in a stable structure such as a eutectic of a face-centered cubic lattice structure with a (111) orientation and a (200) orientation, but has a high resistivity. For this reason, the second region R2 is not suitable for passing a large current through it to generate heat.

[0109] The aforementioned Figure 7 is a graph showing the relationship between the nitrogen content and the pressure resistance of tantalum nitride formed by sputtering. This pressure resistance was measured by a step stress test (SST). The pressure resistance decreases as the nitrogen content increases. In the figure, if the usable third region R3 has a pressure resistance of 0.11 mJ or more, the corresponding usable nitrogen content is approximately 22 atm% or less.

[0110] According to the second embodiment, as shown in Fig. 11, the resistor layer 41 is configured by sequentially stacking a first sub-resistor layer 41a, a main resistor layer 41b, and a second sub-resistor layer 41c. The tantalum nitride constituting the first sub-resistor layer 41a and the second sub-resistor layer 41c has a nitrogen concentration exceeding a predetermined value and is in a stable state, and the range of the nitrogen content may be within region R2 in Fig. 6. In this region R2, the tantalum nitride is formed into a stable structure including a eutectic of a face-centered cubic lattice structure with a (111) orientation and a (200) orientation.

[0111] The main resistor layer 41b is made of tantalum that may contain a very low concentration of nitrogen, and the range of the nitrogen content may be the first region R1 in FIG. 6 or a range with an even lower nitrogen content. In the first region R1 and a range with an even lower nitrogen content, the resistivity varies widely, and tantalum nitride is formed into an unstable structure. Although the main resistor layer 41b is formed into an unstable structure, it is laminated between the first sub-resistor layer 41a and the second sub-resistor layer 41c, which have stable structures. Therefore, the first sub-resistor layer 41a, the main resistor layer 41b, and the second sub-resistor layer 41c that constitute the resistor layer 41 form a stable structure as a whole.

[0112] In the resistor layer 41, the main resistor layer 41b, which has the lower resistivity among the first sub-resistor layer 41a, the main resistor layer 41b, and the second sub-resistor layer 41c, serves as the main electrical conduction path and is the dominant factor in the electrical characteristics of the resistor layer 41. The main resistor layer 41b is made of tantalum which may contain a very low concentration of nitrogen, and therefore the nitrogen concentration corresponds to the usable third region R3 shown in Fig. 7. This ensures the voltage resistance of the thermal printhead 30 including the resistor layer 41.

[0113] As another embodiment of the resistor layer 21 shown in Fig. 12, the resistor layer 41 may be configured by laminating the main resistor layer 41b and only one of the first sub-resistor layer 41a and the second sub-resistor layer 41c. That is, the resistor layer 41 may be configured by laminating the main resistor layer 41b on the first sub-resistor layer 41a as shown in Fig. 12(a), or may be configured by laminating the second sub-resistor layer 41c on the main resistor layer 41b as shown in Fig. 12(b).

[0114] In such a case, the head substrate 31 having the insulating layer 32 formed on the main surface 31a and the protrusions 31b is stored in a chamber, a mixed gas of nitrogen gas as a raw material gas and argon gas as a carrier gas is flowed into the chamber, and tantalum is sputtered as a target to deposit tantalum nitride on the insulating layer 32. The flow rate of the nitrogen gas in the mixed gas is adjusted to be large, thereby depositing the first sub-resistor layer 41a or the second sub-resistor layer 41c containing a high concentration of nitrogen. The supply of nitrogen gas is stopped, and only argon gas is flowed to sputter tantalum and deposit the main resistor layer 41b. These operations are performed by adjusting the flow rate of nitrogen gas while the head substrate 31 is stored in the chamber so that the main resistor layer 41b and either the first sub-resistor layer 41a or the second sub-resistor layer 41c are deposited in a predetermined order.

[0115] In the resistor layer 41, the tantalum nitride constituting one of the first sub-resistor layer 41a and the second sub-resistor layer 41c has a nitrogen concentration exceeding a predetermined value and is in a stable state, and the range of the nitrogen content may be within region R2 in Fig. 6. In this region R2, the tantalum nitride is formed into a stable structure including a eutectic of a face-centered cubic lattice structure with a (111) orientation and a (200) orientation.

[0116] The tantalum layer 41b is made of tantalum that may contain a very low concentration of nitrogen, and the range of the nitrogen content may be the first region R1 in FIG. 6 or a range with an even lower nitrogen content. In the first region R1 and a range with an even lower nitrogen content, the resistivity varies widely, and tantalum nitride is formed into an unstable structure. Although the main resistor layer 41b is formed into an unstable structure, the main resistor layer 41b is laminated with one of the first sub-resistor layer 41a and the second sub-resistor layer 41c, which have a stable structure. Therefore, the main resistor layer 21b and one of the first sub-resistor layer 41a and the second sub-resistor layer 41c that constitute the resistor layer 41 form a stable structure as a whole.

[0117] Figures 16 to 18 are process flow diagrams for the thermal printhead 30 of the second embodiment. Figures 16 to 18 are subsequent to the process flows shown in Figures 13 to 15. In the step shown in Figure 16, an auxiliary resistor layer 42 is formed to cover a resistor layer 41 formed on an insulating layer 32 so as to cross the main surface 31a and the protrusions 31b of the head substrate 31. The auxiliary resistor layer 42 is made of a metal such as titanium that has excellent adhesion.

[0118] 17, a wiring layer 43 is formed so as to cover the auxiliary resistor layer 42. The wiring layer 43 is terminated at one of the second inclined faces 31d of the protrusion 31b, so that the resistor layer 41 is exposed at the heat generating portion 40. The wiring layer 43 is formed of a metal such as copper that has excellent electrical conductivity. The wiring layer 43 is terminated at one of the second inclined faces 31d of the protrusion 31b, so that the exposed resistor layer 41 and auxiliary resistor layer 42 form the heat generating portion 40.

[0119] In the step shown in Fig. 18, a protective layer 45 is formed on the main surface 31a and the protrusions 31b of the head substrate 31 so as to cover the resistor layer 41, the auxiliary resistor layer 42, and the wiring layer 43. The protective layer 45 is made of an insulator such as silicon nitride. The protective layer 45 may be made of other insulators such as silicon oxide. Following the step shown in Fig. 18, an external electrode 47 is formed as shown in Fig. 10. Furthermore, individual thermal printheads 30 are obtained through a step such as dicing (not shown). A plurality of head substrates 31 are produced from a silicon substrate having a substantially circular planar shape through a step such as dicing.

[0120] In the method for manufacturing the thermal printhead 30 of the second embodiment, in the step of forming the resistor layer 41 shown in Fig. 15, the nitrogen content is controlled by appropriately controlling the flow rate of nitrogen gas supplied to a chamber in which tantalum is used as a target for sputtering. Compared to the conventional step of forming a resistor by sputtering, this step can be easily implemented since it is only necessary to add an operation for appropriately controlling the flow rate of nitrogen.

[0121] (Experimental Example) An experimental example will be described below in comparison with the first and second embodiments described above. In this experimental example, the resistor layer 41 in the thermal printhead 30 of the second embodiment shown in Fig. 10 is replaced with a uniform tantalum nitride layer as shown in Fig. 19. In this experimental example, components common to the thermal printer 130 of the second embodiment are referred to by the same reference numerals.

[0122] The tantalum nitride of the resistor layer 41 in the experimental example has a nitrogen content corresponding to the first region R1 with low resistivity shown in curve a in the graph showing the relationship between the nitrogen content and the resistivity and the in-plane variation of the resistivity shown in Fig. 6, in order to pass a large current through the heating portion 40. In this first region R1, the nitrogen content is a relatively low concentration below a predetermined value, and the resistivity is low, but the in-plane variation of the resistivity shown in curve b is large, indicating that the structure of the formed tantalum nitride film is unstable.

[0123] Fig. 20 shows the distribution of elements in resistor layer 21 of an experimental example. Fig. 20(a) shows the result before the voltage resistance test, and Fig. 20(b) shows the result after the voltage resistance test. These figures show the distribution of elements measured by X-ray spectroscopic analysis for a cross section including resistor layer 41 in heat generating part 40 of a thermal print head, as well as a part of lower insulating layer 32 and upper protective layer 45 laminated on resistor layer 41.

[0124] 20(a) before the withstand voltage test and FIG 20(b) after the withstand voltage test, it can be seen that the nitrogen concentration decreased and nitrogen was lost from resistor layer 41 made of tantalum nitride to protective layer 45 made of silicon nitride above after the withstand voltage test. It can also be seen that after the withstand voltage test, oxygen diffused from insulating layer 32 made of silicon oxide below to resistor layer 41 made of tantalum nitride, and tantalum diffused from resistor layer 41 to the layers below, forming a reaction layer from resistor layer 41 to the layers below.

[0125] FIG. 21 is a graph showing the changes in heating efficiency and resistivity due to a withstand voltage test. In the figure, data series a is resistivity, and data series b is heating efficiency. These data series a and b were obtained by repeating the test in the direction of the arrow. It can be seen that the resistivity increases and the heating efficiency decreases as the withstand voltage test steps are repeated. This change in characteristics indicates that the resistivity has increased due to the diffusion of oxygen atoms into the tantalum nitride of the resistor layer 41, forming a reaction layer. [Industrial Applicability]

[0126] This disclosure can be used in the manufacture of thermal printheads and thermal printers. [Explanation of symbols]

[0127] 10 Thermal print head 11 Head substrate 12 Convex portion 20 Heating portion 21 Resistor layer 21a Main resistor layer 21b First sub-resistor layer 21c Second sub-resistor layer 22 Wiring layer 25 Protective layer 27 External electrode 30 Thermal print head 31 Head substrate 31b Convex portion 31c First inclined surface 31d Second inclined surface 31e Top surface 32 Insulating layer 40 Heating portion 41 Resistor layer 42 Auxiliary resistor layer 43 Wiring layer 45 Protective layer 47 External electrodes 110, 130 Thermal printer

Claims

1. A substrate having a main surface on which a protrusion is formed; a resistor layer formed on the main surface and the protrusions; a wiring layer covering the resistor layer such that the resistor layer is exposed at a heat generating portion of the protrusion; a protective layer formed on a main surface of the substrate so as to cover the resistor layer and the wiring layer; The resistor layer is a main resistor layer containing tantalum; at least one of a first auxiliary resistor layer containing tantalum nitride laminated on the lower side of the main resistor layer and a second auxiliary resistor layer containing tantalum nitride laminated on the upper side of the main resistor layer, The tantalum nitride contained in the first and second sub-resistor layers includes a eutectic having a face-centered cubic lattice structure with a (111) orientation and a (200) orientation.

2. 2. The thermal printhead according to claim 1, wherein the resistor layer includes both the first sub-resistor layer and the second sub-resistor layer.

3. 3. The thermal printhead according to claim 1, wherein the protective layer includes at least one of silicon nitride and silicon oxide.

4. The thermal printhead according to claim 1 , wherein the wiring layer contains copper.

5. 5. A thermal printhead as described in any one of claims 1 to 4, further comprising an auxiliary resistor layer laminated between the resistor layer and the wiring layer, the wiring layer covering the auxiliary resistor layer so that the auxiliary resistor layer is exposed in the heating portion, and the exposed auxiliary resistor layer covering the resistor layer so that a portion of the resistor layer is exposed.

6. 6. The thermal printhead of claim 5, wherein the auxiliary resistor layer comprises titanium.

7. 6. The thermal printhead according to claim 1, wherein the substrate is a ceramic substrate, and the protrusions are formed by a glass glaze layer.

8. The thermal printhead according to claim 7 , wherein the heat generating portion is formed in an area including the top of the protrusion.

9. 9. The thermal printhead according to claim 1, wherein the main resistor layer further contains nitrogen at 22% atm or less, and the tantalum and nitrogen contained in the main resistor layer form a body-centered cubic lattice structure.

10. 10. A thermal printer comprising: the thermal printhead according to claim 1; and a platen disposed opposite a heat generating portion of the thermal printhead.

11. providing a substrate having a main surface and a protrusion formed on the main surface; forming a resistor layer on the main surface and the protrusions; forming a wiring layer covering the resistor layer such that the resistor layer is exposed at a heat generating portion of the protrusion; forming a protective layer on a main surface of the substrate so as to cover the resistor layer and the wiring layer; The resistor layer is a main resistor layer containing tantalum; at least one of a first auxiliary resistor layer containing tantalum nitride laminated under the main resistor layer and a second auxiliary resistor layer laminated over the main resistor layer, A method for manufacturing a thermal printhead, wherein the tantalum nitride contained in the first sub-resistor layer and the second sub-resistor layer includes a eutectic having a face-centered cubic lattice structure with a (111) orientation and a (200) orientation.

12. 12. The method according to claim 11, wherein the step of forming the resistor layer comprises depositing the main resistor layer and at least one of the first sub-resistor layer and the second sub-resistor layer by controlling a flow rate of nitrogen gas in a chamber.

13. The method further includes a step of forming an auxiliary resistor layer between the resistor layer and the wiring layer after the step of forming the resistor layer and before the step of forming the wiring layer, The method according to claim 11 or 12, wherein the step of forming the wiring layer covers the auxiliary resistor layer so that the auxiliary resistor layer is exposed in the heating portion, and the step of forming the auxiliary resistor layer covers the resistor layer so that the resistor layer is exposed in a portion of the exposed auxiliary resistor layer.

14. The step of providing a substrate includes providing a ceramic substrate; The method according to claim 11 , further comprising the step of forming a convex portion on the main surface of the ceramic substrate by a glass glaze layer.

15. The step of providing a substrate includes providing a semiconductor substrate; forming a protrusion on a main surface of the semiconductor substrate by anisotropic etching; forming an insulating layer so as to cover the main surface of the substrate on which the convex portion is formed and the convex portion; The step of forming the resistor layer includes forming the resistor layer on the insulating layer, The method according to claim 11 , wherein the step of forming the protective layer forms the protective layer so as to cover the insulating layer, the resistor layer, and the wiring layer.

16. The step of forming the protrusions includes: forming first inclined surfaces sandwiching the top surface of the protrusion from both sides by a first anisotropic etching; forming a second inclined surface between the top surface and the first inclined surface by a second anisotropic etch; The method according to claim 15 , wherein the resistor layer is formed on at least one of the top surface of the protrusion, the first inclined surface, and the second inclined surface.

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