Liquid discharge head

Abstract

To provide a technique for protecting an ink flow passage formed inside a liquid discharge head using a joint substrate.SOLUTION: A liquid discharge head includes a joint substrate in which a first substrate and a second substrate are jointed with each other with an adhesive to be laminated with each other. The joint substrate has a liquid flow passage through which the first substrate is communicated with the second substrate. At a corner part formed at a position corresponding to the liquid flow passage, at a position where the first substrate is jointed to the second substrate, which is formed by an end face that the first substrate has and a plane that the second substrate has, the adhesive is arranged so that a cross section thereof forms a convex arc-shape toward the corner part. A protective film continuously extending from the first substrate through the adhesive arranged at the corner part to the second substrate is formed at the joint position.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a liquid ejection head. [Background technology]

[0002] An example of a functional device such as a pressure sensor, an acceleration sensor, or other MEMS (Micro Electro Mechanical System) or a microfluidic device is a liquid ejection head that ejects liquid. A liquid ejection head is also called an inkjet recording head or a liquid jet head, and is applied to a recording device that ejects liquid to perform recording. In the manufacture of these devices, devices are produced that are composed of a substrate assembly in which substrates are bonded together via an organic film (adhesive). In recent years, in order to improve the ejection stability and print quality of the liquid ejection head, a mechanism for circulating ink within the head is sometimes provided.

[0003] Here, Patent Document 1 (JP 2014-124887 A) proposes a method of forming a protective film on substrates bonded via an organic film (adhesive) as a method for reducing damage to bonded substrates caused by ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-124887 A Summary of the Invention [Problem to be solved by the invention]

[0005] Thus, there is a demand for further improvements in ejection stability and print quality in liquid ejection heads using bonded substrates, and in particular for suitable protection of the ink flow paths.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a technique for protecting an ink flow path formed inside a liquid ejection head using a bonding substrate. [Means for solving the problem]

[0007] The present invention employs the following configuration. A liquid ejection head including a bonded substrate in which a first substrate and a second substrate are laminated and bonded together with an adhesive, the bonding substrate has a liquid flow path that communicates between the first substrate and the second substrate, a corner portion formed at a position corresponding to the liquid flow path at a joining position of the first substrate and the second substrate, the corner portion being formed by an end face of the first substrate and a flat surface of the second substrate, the adhesive being disposed so as to have a cross section having an arc-like shape that is convex toward the corner portion; At the joining position, a continuous protective film is provided so as to extend from the first substrate through the adhesive disposed at the corner portion to the second substrate. The liquid ejection head is characterized in that Effect of the Invention

[0008] According to the present invention, it is possible to provide a technique for protecting an ink flow path formed inside a liquid ejection head using a bonding substrate. [Brief description of the drawings]

[0009] [Figure 1] Schematic cross-sectional view of a bonding substrate used in a liquid ejection head [Diagram 2] Schematic cross-sectional view showing the manufacturing process of the bonded substrate [Diagram 3] Enlarged schematic diagram to explain the behavior of adhesive during bonding [Figure 4] Further enlarged schematic diagram to explain the behavior of the adhesive during bonding [Diagram 5] Cross-sectional view for examining the amount of adhesive protrusion [Figure 6]Cross-sectional view for comparison to examine the amount of adhesive protrusion [Figure 7] Cross-sectional view for comparison to examine the amount of adhesive protrusion [Figure 8] Top view showing variations in the opening shape of the bonded substrate [Figure 9] Cross-sectional view showing variations in board shape [Figure 10] Cross-sectional view showing variations in board shape [Figure 11] Cross-sectional view showing variations in board shape [Figure 12] Schematic cross-sectional view of adhesive control method [Figure 13] Schematic cross-sectional view of adhesive control method [Figure 14] Schematic cross-sectional view of adhesive control method [Figure 15] Schematic cross-sectional view of a bonded substrate according to embodiment 2. [Figure 16] FIG. 1 is a schematic diagram showing an example of a recording element. [Figure 17] FIG. 1 is a schematic diagram showing an example of a recording element unit; [Figure 18] Schematic diagram showing an example of a liquid ejection head configuration DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Below, a preferred embodiment of the technology disclosed herein will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described below should be appropriately changed depending on the configuration and various conditions of the device to which the invention is applied. Therefore, it is not intended to limit the scope of the invention to the following description. Well-known or publicly known technologies in the technical field can be applied to configurations and processes that are not particularly shown or described. Also, duplicated descriptions may be omitted.

[0011] Further, although the present embodiment has been described taking the bonding of three substrates as an example, the present invention is not limited to this and can also be applied to the bonding of a plurality of substrates.

[0012] Here, the inventors will explain the problems they found with conventional liquid ejection heads. They found that when ink is circulated in an ink flow path in a liquid ejection head using a bonded substrate, if materials with different wettabilities, such as a protective film and an adhesive, are mixed inside the ink flow path, air bubbles will adhere to areas with poor wettability. Furthermore, in liquid ejection heads, the inner wall surface of the ink flow path is easily eroded by ink, and if exposed to ink for a long period of time, the flow path structure may collapse. In particular, when the substrate is a silicon substrate, such damage by ink is likely to occur.

[0013] The above-mentioned Patent Document 1 (JP Patent Publication No. 2014-124887) proposes a method of forming a protective film on substrates bonded via an organic film (adhesive) as a method of reducing damage caused by ink to the substrate. However, according to the inventor's research, it was found that when a protective film is formed from the inner wall surface of the ink flow path to the organic film (adhesive) as in Patent Document 1 (JP Patent Publication No. 2014-124887), air bubbles adhere to the corners of the substrate bonding area and ink flow stagnation occurs. Such air bubble stagnation may lead to poor ink ejection and reduce print quality.

[0014] As a result of the inventor's investigation, it was found that by providing R at the corners of the ink flow path and making the wettability in the ink flow path uniform, it is possible to suppress air bubble accumulation and ink flow stagnation. This improves the ink circulation efficiency and improves the print quality. In the following embodiment, such a configuration of the present invention will be specifically described.

[0015] (Embodiment 1) Hereinafter, a liquid ejection head substrate according to a first embodiment of the present invention will be described with reference to the drawings. This embodiment shows an example in which a piezoelectric element is used as an energy generating element, but the present invention is not limited thereto and can also be applied to bonding of a substrate having an element capable of boiling ink by heating through electrical current, such as a heater element. The liquid ejection head to which the present invention is applied is a member of a recording device such as an inkjet printer. The recording device is also provided with a liquid storage unit that stores liquid to be supplied to the liquid ejection head, a transport mechanism for a recording medium on which recording is performed, and the like.

[0016] (Composition of the bonded substrate) 1 is a cross-sectional schematic diagram of a bonding substrate 80 for a liquid ejection head according to a first embodiment of the present invention. The bonding substrate 80 of this embodiment is formed by bonding a first substrate 1 having an ink flow path 7 (liquid flow path) formed therein, a second substrate 2 having a plurality of piezoelectric elements 5 and electrodes 6 formed therein, and a third substrate 3 having a plurality of ejection ports 8 formed therein, all of which are bonded together via an adhesive 4. In other words, the bonding substrate 80 has a plurality of bonding surfaces bonded together at least using an adhesive. If the adhesive 4 overflows from the bonding surfaces, it is absorbed by grooves 15.

[0017] The first substrate 1 is made of, for example, a silicon substrate, and has a first opening 7a that forms an ink flow path 7. The second substrate 2 is made of, for example, a silicon substrate, and has a vibration membrane 11, and a piezoelectric element 5 is formed on the vibration membrane 11. The vibration membrane 11 forms the ceiling wall of the pressure chamber 10, and divides the pressure chamber 10. Furthermore, the second substrate 2 is formed with a second opening 7b that communicates with the first opening 7a and forms an ink flow path 7 for introducing liquid into the pressure chamber 10. The third substrate 3 is made of, for example, a silicon substrate, and has an ejection port 8 that ejects liquid. The ejection port 8 penetrates the third substrate 3. The ejection port 8 communicates the surface facing the pressure chamber 10 with the surface opposite the pressure chamber 10 as viewed from the third substrate. Therefore, when a volume change occurs in the pressure chamber 10, the liquid stored in the pressure chamber 10 is ejected from the ejection port 8.

[0018] An ink tank (not shown) is disposed on the first substrate 1. Therefore, liquid in the ink tank is supplied to the pressure chamber 10 through the first opening 7a.

[0019] A piezoelectric element 5 is disposed on the vibration membrane 11 to form a piezoelectric actuator. The piezoelectric element 5 includes a lower electrode (not shown) formed on the vibration membrane forming layer, the piezoelectric element 5 formed on the lower electrode, and an upper electrode (not shown) formed on the piezoelectric element. An electrode 6 for external connection is also disposed on the vibration membrane 11.

[0020] The piezoelectric element 5 is formed at a position facing the pressure chamber 10 across the vibration membrane 11. That is, the piezoelectric element 5 is formed so as to contact the surface of the vibration membrane 11 on the opposite side to the pressure chamber 10. The vibration membrane 11 has a characteristic that it can deform in the direction facing the pressure chamber 10. As shown in the figure, a protective film 18 may be provided on the second substrate 2. The protective film 18 is made of, for example, SiN, and has a function of protecting the wiring layer, the piezoelectric element, and the like. In the following description, the protective film 18 provided on the second substrate 2 is considered to be a part of the second substrate 2. That is, since the second substrate 2 and the protective film 18 are integrated when the adhesive 4 is applied, the range of the first substrate 1 and the second substrate 2 is considered based on that state.

[0021] When a driving voltage is applied to the piezoelectric element 5 through wiring from a driving IC (not shown), the piezoelectric element 5 is deformed by the inverse piezoelectric effect. This causes the vibration film 11 to deform together with the piezoelectric element 5, which changes the volume of the pressure chamber 10 and pressurizes the liquid such as ink. The pressurized liquid is ejected from the ejection port 8 as minute droplets.

[0022] (Joints and adhesive behavior) Next, the bonding of the first substrate 1 and the second substrate 2 according to the present invention will be described in detail. The present invention will be described with reference to an example of the first substrate 1 and the second substrate 2, but is not limited thereto. The present invention may be applied to the second substrate 2 and the third substrate 3, or, when there are more substrates, between those substrates.

[0023] Figures 3(a) to 3(c) show how the second substrate 2 is bonded to the first substrate 1 via an adhesive 4 to form a Si protective film. Figures 4(a) to 4(c) are enlarged views of region B indicated by the dashed line in Figure 3(a). Figures 4(a) to 4(c) correspond to Figures 3(a) to 3(c), respectively. Figures 3(a) and 4(a) show how the adhesive 4 is applied to the underside of the first substrate 1 (the surface facing the second substrate 2), and then the first substrate and the second substrate are brought close to each other and bonded.

[0024] FIG. 3(b) and FIG. 4(b) show the state after bonding. At this time, the adhesive 4 flows out from the interface of the bonded substrates due to capillary action by bonding the substrates together, forming a protruding portion 4f. Then, the flowed-out adhesive 4 is caused to flow along the corner formed by the substrates, so that the cross-sectional shape of the surface of the adhesive 4 at the corner of the bonded interface becomes an arc shape having a recessed portion 4k. That is, in the cross section, at the corner C formed by the extension line of the end face 1t of the first substrate 1 and the plane 2p of the second substrate 2 (more precisely, the protective film 18 that is integrated with the second substrate 2 when the adhesive 4 is applied), the cross-sectional shape of the adhesive 4 forms an arc shape that is convex toward the corner C. For this reason, it is preferable to select an adhesive 4 that flows due to temperature, heat, or load. Here, the cross-sectional shape of the adhesive surface being arc-shaped means that, as shown in the cross-sectional view of Figure 4(b), at the joining position, the cross-section of the adhesive surface is on the inner side (closer to the corner) than the straight line (shown by a dashed line in the figure) formed by the distance D1 over which the adhesive 4 has spread onto the second substrate 2 (the distance from the point furthest from the corner of the adhesive 4 spread onto the second substrate 2) and the distance D2 over which the adhesive 4 has spread onto the first substrate 1 (the distance from the point furthest from the corner of the adhesive 4 spread onto the first substrate 1).

[0025] Note that, because the adhesive 4 has a certain degree of fluidity, the cross section of the surface is often curved, and therefore the term "arc" is used, but as long as the condition that the surface is inside the D1-D2 line is satisfied as described above, the cross section of the surface does not have to be composed of curves only, and may be, for example, a combination of straight lines and curves. The curved portion may be a circular arc, an elliptical arc, or another type of curve. Whatever the shape of the cross section of the surface of the adhesive 4, as long as it is a concave shape rather than a shape raised above the D1-D2 line, a certain degree of effect can be obtained.

[0026] 3(c) and 4(c) show the state after the protective film 9 is further formed. It can be seen that the presence of the recessed portion 4k in the base layer of the protective film 9 also results in the formation of a recessed portion (recessed rounded portion R) in the protective film 9 that comes into direct contact with the ink.

[0027] (Consideration of adhesive overflow) Figures 5 to 7 show examples with different amounts of adhesive overflowing. Figures 5(a), 6(a), and 7(a) show the state of adhesive overflowing, and Figures 5(b), 6(b), and 7(b) show the state after protective film 9 has been formed.

[0028] 5(a) and 5(b) show an example in which the distance D1 and the distance D2 are different due to the difference in wettability of the adhesive 4 between the first substrate 1 and the second substrate 2. In this case, the cross-sectional shape of the recess is closer to an elliptical arc rather than a circular arc, but the effect of the present invention can be obtained even in such a case.

[0029] 6(a) and 6(b) show cases where the amount of adhesive 4 protruding from the joint is small due to the surface characteristics of the first substrate 1 and the second substrate 2, the fluidity of the adhesive 4, etc. In this case, the effect of suppressing bubble accumulation when ink is circulated is smaller than in the cases of Fig. 4(c) and Fig. 5(a). However, a certain degree of effect can be obtained.

[0030] On the other hand, Figures 7(a) and 7(b) show a state in which the adhesive does not overflow and remains inside the space between the substrates. In this case, as shown in Figure 7(b), there is no R in the shape of the protective film 9. Therefore, the effect of suppressing bubble accumulation when ink is circulated in the ink flow path is significantly reduced.

[0031] (Modifications of opening and cross-sectional shape) The openings in the substrates are formed by processing methods such as dry etching, wet etching, or laser. The top views of Fig. 8(a) to Fig. 8(c) show examples of different shapes of the first openings 7a that constitute the ink flow path 7. The symbol B indicates the position corresponding to the region B in Fig. 3(a). The behavior of the bonded substrate interface between the substrates also differs depending on such differences in shape.

[0032] Furthermore, each cross-sectional view of Figures 9 to 11 shows how the behavior of the adhesive 4 changes depending on the cross-sectional shape of the first substrate 1. Figures 9(a) to 9(c) show a case where the width of the first substrate 1 becomes wider as it approaches the second substrate 2. In this case, the cross-section of the base of the first substrate 1 forms an acute angle. Figures 10(a) to 10(c) show a case where the width of the first substrate 1 becomes narrower as it approaches the second substrate 2. In this case, the base of the first substrate 1 forms an obtuse angle. Figures 11(a) to 11(c) show scallops when the first opening 7a is formed by the Bosch process of dry etching.

[0033] In either case, it is important to form the adhesive on the inside of the straight line formed by D1 and D2, as shown in Figures 9(b), 10(b), and 11(b). For this purpose, it is preferable to appropriately select the materials of the first substrate 1 and the second substrate 2, the type of adhesive 4, and the like. Even in these cases, it is possible to provide a suitable R to the protective film 9, just as in the case where the end face of the first substrate 1 is perpendicular to the plane of the second substrate 2.

[0034] (Adhesive overflow control) As described above, if the adhesive 4 remains inside the space between the substrates, the effect of the present invention cannot be obtained. However, if the adhesive 4 significantly protrudes from the space between the bonded substrates, it may block the ink flow path 7 formed on the bonded surface, or may protrude into the second opening housing the piezoelectric element and affect the ejection. Therefore, it is preferable that the type of adhesive 4 does not have excessive fluidity, and the amount of adhesive applied should be appropriate.

[0035] Here, the direction in which the substrates are stacked is the stacking direction (Z direction in the figure), the direction in which the substrates extend intersecting with the stacking direction is the extension direction (X direction in the figure), and the direction in which the substrates continue at the opening intersecting with the stacking direction and the extension direction (for example, the direction in which the first substrate 1 forms a boundary with the first opening 7a) is the end surface direction (Y direction in the figure). The inventors have found that in the present invention, the distance (D2) of the recessed portion 4k of the adhesive 4 in the stacking direction and the distance (D1) in the extension direction in which the substrates extend are preferably 3 μm or more to 20 μm or less, and more preferably 5 μm or more to 15 μm or less. In the case of FIG. 4(b), the recessed portion 4k is substantially arc-shaped, so the distances D1 and D2 can be collectively referred to as the "arc width D". The arc width D can be controlled by providing a groove for storing the adhesive on the substrate surface at the bonding interface or by optimizing the thickness of the adhesive appropriately. The same concept can be applied to the case where the recessed portion 4k is not arc-shaped. For example, as shown in FIG. 5(a), when the distance D2 in the stacking direction is different from the distance D1 in the substrate extension direction, either D1 or D2 Both are preferably 3 μm or more and 20 μm or less, and it is more preferable that both D1 and D2 are 5 μm or more and 15 μm or less.

[0036] In the bonding substrate 80, the region where the electrode pads and piezoelectric elements are formed and the region where the ink flow path 7 are formed may be adjacent to each other via the substrate. For example, in the region indicated by the dashed line A in FIG. 2(a), the ink flow path 7 is formed on the right side of the region A, and the electrode storage section 16 in which the electrode 6 is disposed is formed on the left side. In this case, if the adhesive 4 protrudes to the left of the dashed line A, it may cover the electrode, which is undesirable from the standpoint of performance and quality. The same is true for the piezoelectric element 5. On the other hand, it is desired that the adhesive 4 protrudes to the side of the region where the ink flow path 7 is formed to the extent that an appropriate recess is formed.

[0037] Therefore, a method for causing the adhesive 4 to appropriately overflow at the desired position is considered. FIG. 12(a) is an enlarged view of the area indicated by the dashed line A. As shown here, a groove 15 for accommodating the adhesive 4 is provided in the corresponding area of ​​the first substrate 1, closer to the side (left side) where overflow is not desired. This makes it possible to suppress overflow of the adhesive on the left side, as shown in FIG. 12(b). On the other hand, an appropriate amount of adhesive 4 overflows on the right side, forming a recessed portion 4k. For simplicity's sake, one groove 15 is shown in the figure, but multiple grooves may be provided.

[0038] 13(a) and 13(b), a groove 15 for accommodating adhesive 4 may be provided on the second substrate 2 side. Also, grooves 15 may be provided on both the first substrate 1 and the second substrate 2.

[0039] 14(a) and 14(b), overflow can also be controlled by controlling the area on the substrate where the adhesive 4 is applied. In the illustrated example, an adhesive non-application portion 4m is provided in the left side area of ​​the underside of the first substrate 1 where overflow of the adhesive 4 is to be prevented. Note that the amount of adhesive 4 applied in the left side area may not be zero, but may be less than that on the right side. Also, the amount applied may be gradually reduced from the right side to the left side.

[0040] <Joining process> Next, a series of steps for producing the bonded substrate 80 will be described. This process starts from the stage where the ink flow paths 7, pressure chambers 10, grooves 15, electrode housing portions 16, etc. are manufactured in the first substrate 1 to the third substrate by combining existing techniques such as etching and lithography, and the piezoelectric elements 5, electrodes 6, wiring (not shown), etc. are arranged.

[0041] (Substrate manufacturing process) Silicon is suitable as the material for the first substrate 1, the second substrate 2, and the third substrate 3. Other materials that can be used include silicon carbide, silicon nitride, various types of glass (quartz glass, borosilicate glass, alkali-free glass, soda glass), various types of ceramics (alumina, gallium arsenide, gallium nitride, aluminum nitride), and resin. The thickness of the first substrate 1 and the second substrate 2 is, for example, 625 μm. The first opening 7a of the first substrate 1 and the second opening 7b of the second substrate 2 are formed at positions where they can communicate with each other to form a flow path 7 after bonding.

[0042] On the first substrate 1, a lower electrode (not shown), a piezoelectric element 5 on the lower electrode, and an upper electrode (not shown) on the piezoelectric element are formed on a vibration membrane forming layer. An electrode 6 is also formed in the electrode housing portion 16. The vibration membrane forming layer is formed by, for example, plasma CVD. Next, a hydrogen barrier film (not shown), a lower electrode (not shown), a piezoelectric film, and an upper electrode (not shown) are formed in this order. The lower electrode and the upper electrode are formed by, for example, a sputtering method, and the piezoelectric film is formed by a sol-gel method, but may also be formed by a sputtering method.

[0043] The piezoelectric element 5 is made of PZT (titanium dioxide) formed by, for example, a sol-gel method or a sputtering method. A lead zirconate oxide film can be applied. Such a piezoelectric element 5 is made of a sintered body of metal oxide crystal. An actuator substrate can be formed by forming an interlayer film and wiring (not shown) so that the actuator part can be driven.

[0044] Pressure chambers 10 and grooves 15 are formed in the second substrate 2 by sputtering or the like. A protective film 18 may be provided between each substrate. As shown in Fig. 2(a), the second substrate 2 is configured such that piezoelectric elements and electrodes are formed on a substrate made of silicon.

[0045] (Adhesive application process) The adhesive 4 can be formed by a direct writing method using a dispenser or patterning such as photolithography. In addition, since the wettability of the bonding interface and the adhesive is also important, the substrate surface before bonding may be subjected to a surface treatment such as oxygen plasma. Other methods for applying the adhesive 4 include a transfer method using glass or PET as a substrate, screen printing, and dispense application. The thickness of the organic film is not particularly limited, but is preferably 0.1 μm to 10 μm, and more preferably 1 μm to 5 μm.

[0046] A material that has high adhesion to the substrate is preferably used as the adhesive 4. A material that has little air bubbles and is easy to apply is also preferred, and a low-viscosity material that makes it easy to make the adhesive thinner is also preferred. The adhesive preferably contains any resin selected from the group consisting of epoxy resin, acrylic resin, silicone resin, benzocyclobutene resin, polyamide resin, polyimide resin, and urethane resin. Examples of the curing method for the adhesive 4 include a heat curing method and an ultraviolet delayed curing method. If any of the substrates is ultraviolet transparent, an ultraviolet curing method can also be used.

[0047] Here, an example of the transfer method is shown. First, a substrate for adhesive transfer was prepared, and a benzocyclobutene solution was spin-coated to a thickness of 3 μm as the adhesive 4. A PET film was used as the substrate for transfer. After coating, a baking process was performed at 100°C for 5 minutes to volatilize the solvent. The adhesive 4 formed on the substrate for transfer was transferred to the first substrate 1 by contacting the bonding surface of the first substrate 1 while applying heat.

[0048] (Joining process) The first substrate 1 and the second substrate 2 on which the adhesive 4 has been formed are heated to a predetermined temperature in a bonding device, and then pressed for a predetermined time and pressure to be bonded. These bonding parameters are appropriately set according to the adhesive material. In addition, bonding in a vacuum is preferable to prevent air bubbles from being mixed into the bonded portion. As shown in Figure 3(b), during bonding, the adhesive 4 is softened by heating and is further pressurized, so that the adhesive 4 flows into the opening from the bonding surface.

[0049] In addition, if there is a large amount of gas emitted from the adhesive 4 during the protective film forming process following the bonding process, the protective film 9 may crack or peel off. Therefore, if the adhesive 4 is a thermosetting type, it may be heated in a bonding device until it hardens. Also, the substrate assembly may be removed after bonding and heated in an oven or the like to promote hardening. If the adhesive 4 is an ultraviolet-delay type, it is preferable to irradiate the adhesive 4 with a specified amount of ultraviolet light before bonding and then bond the substrates. Then, after bonding, it is preferable to further heat the substrate assembly to sufficiently promote hardening. If the adhesive 4 is an ultraviolet-curing type, after bonding the substrates together, it is preferable to irradiate the adhesive 4 with a specified amount of ultraviolet light through a substrate having ultraviolet light transparency to harden the adhesive 4. After bonding, it is preferable to further heat the substrate assembly to sufficiently promote hardening.

[0050] Here, an example will be described in which the above-mentioned benzocyclobutene solution is used as the adhesive 4 and then bonded by thermal curing. At this time, the first substrate 1 and the second substrate 2 are aligned using a bonding alignment device and heated in a vacuum to bond them. The degree of vacuum is 100 Pa or less. The temperature was 150°C. The bonded substrate 80 that had been bonded was cooled and then removed from the apparatus, and heat-treated in an oven in a nitrogen atmosphere at 250°C for 1 hour to harden the adhesive 4. At this time, the protruding width D of the adhesive 4 was 10 μm. The second substrate 2 was thinned to a thickness of 100 μm by a grinding device. Similarly, a third substrate 3 made of silicon and having a thickness of 625 μm was bonded, and then thinned to a thickness of 100 μm by a grinding device. An outlet 8 was formed on the second surface (the surface opposite to the surface facing the second substrate 2) of the third substrate 3 to form a bonded substrate 80. By performing bonding in this manner, a bonded substrate 80 as shown in FIG. 2(a) is formed.

[0051] (Protective film formation process) 2(b), a protective film 9 is formed uniformly from the first surface of the bonding substrate 80 along the inner wall of the ink flow path and the adhesive to the second surface. The protective film 9 is formed by repeating surface saturation adsorption of at least one agent selected from the group consisting of an oxidizing agent and a nitriding agent and a source gas by atomic layer deposition (ALD).

[0052] The protective film 9 preferably contains an inorganic element and at least one element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf, and Si in the form of a simple substance, oxide, nitride, or carbide. Among these, it preferably contains at least one oxide of an element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf, and Si, and more preferably contains at least one compound selected from the group consisting of TaO, TiO, SiOC, SiC, SiCN, TaN, TiN, and HfO.

[0053] When the protective film 9 is formed directly on the organic film (adhesive 4), if the adhesion between the protective film 9 and the organic film (adhesive 4) is weak, if the rigidity of the protective film 9 is insufficient even if the adhesion is ensured, or if both the adhesion and rigidity are insufficient, the protective film 9 may peel off due to the force acting on the interface between the protective film 9 and the organic film (adhesive 4). If the protective film 9 peels off, ink may penetrate from the peeled portion and damage the organic film (adhesive), resulting in poor bonding between the substrates. In addition, the protective film 9 may peel off and become debris that moves around in the flow path, affecting the ejection performance.

[0054] From these viewpoints, it is desirable for the protective film 9 to have a certain thickness, and since if the film thickness is too thick, peeling or the like may occur due to the film stress of the protective film, the thickness is 50 nm or more and 250 nm or less, and more preferably 80 nm or more and 180 nm or less. The protective film 9 may be formed by other methods such as sputtering or CVD.

[0055] Here, an example of ALD film formation on a bonded substrate 80 manufactured by the above-mentioned thermal curing method is described. At this time, a thermal ALD-TaO film was formed in an ALD film formation apparatus. At this time, the film formation cycle was such that a gas obtained by vaporizing a substance containing Ta in its molecules was transported together with nitrogen into the furnace and sprayed for 2.5 seconds, and then purging and exhausting with nitrogen were performed sufficiently. Next, a gas obtained by vaporizing an oxidizing agent was transported together with nitrogen into the furnace and sprayed for 5 seconds, and then purging and exhausting with nitrogen were performed sufficiently. This cycle was regarded as one cycle, and the same cycle was repeated about 2000 times to laminate a tantalum oxide film to a thickness of 130 nm at a film formation temperature controlled at 230°C ± 10°C, thereby obtaining a bonded substrate 80 coated with a protective film 9. As a result, a bonded substrate 80 as shown in FIG. 2(b) was formed.

[0056] (Liquid-repellent film formation process) Next, as shown in FIG. 2(c), a liquid-repellent film 12 was formed on the protective film 9 formed on the second surface (the surface on the ejection port 8 side) of the bonding substrate 80. The liquid-repellent film 12 is not particularly limited as long as it has water repellency against ink, and for example, a material containing a fluorine-based polymer can be used. When a fluorine-based polymer is used as the liquid-repellent film 12, a base film is appropriately provided. This can improve the adhesion between the protective film 9 and the liquid-repellent film 12. The base film is, for example, a silicon oxide film. Before forming the liquid-repellent film 12, a surface treatment such as ashing may be performed.

[0057] By applying the bonded substrate manufactured in this way to a liquid ejection head, it was found that by providing R to the corners of the ink flow path and making the wettability in the ink flow path uniform, it is possible to suppress air bubble accumulation and ink flow stagnation, thereby improving the ink circulation efficiency and print quality.

[0058] (Embodiment 2) Fig. 15 is an enlarged cross-sectional view of the area indicated by the dashed line C in Fig. 2(a). Here, the bonding of the second substrate 2 and the third substrate 3 will be described, but the basic structure is similar to that of the bonding of the first substrate 1 and the second substrate 2. Fig. 15(a) is a cross-sectional view of the area C before the substrates are bonded. The second substrate 2 has an overhanging portion 2h above the area where the adhesive 4 protrudes.

[0059] FIG. 15(b) shows a cross-sectional view of the substrates when they are bonded. By bonding the second substrate 2 having the overhanging portion 2h, a continuous recessed portion 2r is provided in the depth direction in the figure. By setting the film thickness when the adhesive 4 is applied and the adhesive storage portion under appropriate conditions, the amount of adhesive 4 that protrudes can be advanced from the bonding interface along the wall to the corner of the upper surface. As a result, in addition to the recessed portion 4k1 that continues to the bonding surface, a second recessed portion 4k2 can be formed at the corner of the overhanging portion 2h. The distance D2' in the stacking direction of the second recessed portion 4k2 and the distance D1' in the extension direction are set. This makes it possible to obtain a more preferable R shape for suppressing bubble accumulation in the ink circulation when the protective film 9 is formed as shown in FIG. 15(c).

[0060] As described above, by using the present invention, in substrates bonded together using an adhesive, the adhesive is provided in a concave arc shape to cover the corners between the bonded substrates, and a continuous protective film is provided along the substrate surface, flow path, and adhesive, thereby making it possible to obtain a liquid ejection head which suppresses the accumulation of air bubbles in the ink flow path and the stagnation of ink flow.

[0061] (Embodiment 3) (Examples) The manufacturing method of the bonding substrate 80 according to the embodiment is applicable as a manufacturing method of a liquid ejection head. Fig. 16 is a schematic diagram showing an example of a recording element applicable to a liquid ejection recording device or the like. Fig. 16(a) is a schematic diagram showing the ink supply port side as the upper surface, and Fig. 16(b) is a schematic diagram showing the ink ejection port side of a liquid such as ink as the upper surface. Fig. 17 is a schematic diagram showing an example of a recording element unit in which the recording element of Fig. 16 and an electric wiring board are electrically connected. Fig. 18 is a schematic diagram showing an example when the recording element unit of Fig. 17 is used as an inkjet type liquid ejection head.

[0062] 16 has a three-layer structure in which an ink flow path substrate 122, an ink discharge energy generating substrate 123, and an ink discharge substrate 124 are bonded together by an adhesive layer 21. The first substrate 1 of the embodiment corresponds to the ink flow path substrate 122. The portion corresponding to the second substrate 2 is the ink discharge energy generating substrate 123. The portion corresponding to the third substrate 3 is the ink discharge substrate 124.

[0063] The ink ejection substrate 124 is provided with a plurality of ink ejection ports 126 for ejecting ink. The ejection ports 8 shown in the first embodiment can be applied to this. The ink flow path substrate 122 is formed with an ink flow path 125 for guiding ink to the plurality of ink ejection ports 126. The ink flow path 7 shown in the first embodiment can be applied to this. The ink ejection energy generating substrate 123 is formed with an ink ejection energy generating circuit for generating energy for ejecting ink from the ink ejection ports 126. An energy generating element (not shown) is provided. Also, in order to supply power to the energy generating element, a terminal 24 is provided as an electrical connection portion for electrically connecting to the outside. A recording element 121 having such a three-layered space portion 23 is obtained by the bonded substrate manufacturing method of the embodiment.

[0064] A recording element unit 131 in Fig. 17 is obtained by connecting the recording element 121 and an electric wiring board 132 in Fig. 16. The terminals 24 of the recording element 121 and the lead portions 133 of the electric wiring board 132 are electrically connected one-to-one by an electric connection member 134 using wire bonding. The electric connection member 134 may be made of any one of gold, copper, aluminum, and silver, or an alloy containing two or more of these metals as a main component, for example. In addition, the electrical connection method is not limited to wire bonding, and may be bump bonding, a lead terminal, an NCP, or an ACF.

[0065] The liquid ejection head 141 in Fig. 18 is composed of a support member 142 that joins the recording element unit 131 in Fig. 17, a face cover 143 that protects the recording element unit 131, and a flow path member 144 that supplies ink. The recording element unit 131 has two units (131a, 131b) arranged, with the ink ejection orifices 126 on the upper side in the figure. Ink is supplied to the inkjet recording element unit 131 via the flow path member 144 and the support member 142, and ink can be ejected by applying an electrical signal to the electrical wiring board 132.

[0066] [Configuration 1] A liquid ejection head including a bonded substrate in which a first substrate and a second substrate are laminated and bonded together with an adhesive, the bonding substrate has a liquid flow path that communicates between the first substrate and the second substrate, a corner portion formed at a position corresponding to the liquid flow path at a joining position of the first substrate and the second substrate, the corner portion being formed by an end face of the first substrate and a flat surface of the second substrate, the adhesive being disposed so as to have a cross section having an arc-like shape that is convex toward the corner portion; At the joining position, a continuous protective film is provided so as to extend from the first substrate through the adhesive disposed at the corner portion to the second substrate. A liquid ejection head comprising: [Configuration 2] The adhesive placed at the corners is the adhesive applied to the joining surfaces when the first substrate and the second substrate are joined, and is the adhesive that protrudes during the joining. 2. The liquid ejection head according to configuration 1. [Configuration 3] When a direction in which the first substrate and the second substrate are stacked is defined as a stacking direction, and a direction intersecting the stacking direction and in which the planes of the first substrate and the second substrate extend is defined as an extension direction, in the cross section of the corner, the adhesive is located closer to the corner than a line connecting a position of the adhesive spread in the stacking direction that is farthest from the corner and a position of the adhesive spread in the extension direction that is farthest from the corner. 3. The liquid ejection head according to configuration 2. [Configuration 4] At least one of the first substrate and the second substrate is provided with a groove for accommodating the adhesive. 4. The liquid ejection head according to configuration 2 or 3. [Configuration 5] The groove is provided to control the amount of the adhesive that protrudes into the corner. 5. The liquid ejection head according to configuration 4. [Configuration 6] In the cross section of the corner portion, the width of the adhesive spreading in the stacking direction and the width of the adhesive spreading in the stretching direction are both 5 μm or more and 15 μm or less. 4. The liquid ejection head according to configuration 3. [Configuration 7] The thickness of the protective film is 80 nm or more and 180 nm or less. 4. The liquid ejection head according to claim 2, wherein the liquid ejection head is a liquid ejection head. [Explanation of symbols]

[0067] 1: first substrate, 2: second substrate, 3: third substrate, 4: adhesive, 7: ink flow path, 9: protective film

Claims

1. A liquid ejection head including a bonded substrate in which a first substrate and a second substrate are laminated and bonded together with an adhesive, the bonding substrate has a liquid flow path that communicates between the first substrate and the second substrate, a corner portion formed at a position corresponding to the liquid flow path at a joining position of the first substrate and the second substrate, the corner portion being formed by an end face of the first substrate and a flat surface of the second substrate, the adhesive being disposed so as to have a cross section having an arc-like shape that is convex toward the corner portion; At the joining position, a continuous protective film is provided so as to extend from the first substrate through the adhesive disposed at the corner portion to the second substrate. A liquid ejection head comprising:

2. The adhesive placed at the corners is the adhesive applied to the joining surfaces when the first substrate and the second substrate are joined, and the adhesive is the adhesive that protrudes during the joining.

2. The liquid ejection head according to claim 1.

3. When a direction in which the first substrate and the second substrate are stacked is defined as a stacking direction, and a direction intersecting the stacking direction and in which the planes of the first substrate and the second substrate extend is defined as an extension direction, in the cross section of the corner, the adhesive is located closer to the corner than a line connecting a position of the adhesive spread in the stacking direction that is farthest from the corner and a position of the adhesive spread in the extension direction that is farthest from the corner.

3. The liquid ejection head according to claim 2.

4. At least one of the first substrate and the second substrate is provided with a groove for accommodating the adhesive.

4. The liquid ejection head according to claim 2, wherein the liquid ejection head is a liquid ejection head.

5. The groove is provided to control the amount of the adhesive that protrudes into the corner.

5. The liquid ejection head according to claim 4.

6. In the cross section of the corner portion, the width of the adhesive spreading in the stacking direction and the width of the adhesive spreading in the stretching direction are both 5 μm or more and 15 μm or less.

4. The liquid ejection head according to claim 3.

7. The thickness of the protective film is 80 nm or more and 180 nm or less.

4. The liquid ejection head according to claim 2, wherein the liquid ejection head is a liquid ejection head.

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