Substrate for liquid discharge head, liquid discharge head, liquid discharge device, and manufacturing method for substrate for liquid discharge head

Abstract

To provide a technique that can suppress occurrence of breakage of a coating layer.SOLUTION: A liquid discharge head comprises: a first substrate; a second substrate in which wiring and a coating layer coating the wiring are formed on a joint surface between the first substrate and the second substrate; and a spacer that can secure a thickness of an adhesive, between the first substrate and the second substrate, when joining the first substrate to the second substrate. The spacer is positioned at a position where the spacer does not overlap with the wiring and the coating layer on the wiring, on a plane that is orthogonal to a laminating direction of the substrate, on the joint surface of at least either of the substrates, which has a height in which a second thickness of the adhesive between the joint surface to which the coating layer on the wiring opposes and the coating layer is larger than a first thickness of the adhesive between the joint surface to which the spacer opposes and the spacer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a substrate for a liquid ejection head, a liquid ejection head, a liquid ejection device, and a method for manufacturing a substrate for a liquid ejection head. [Background technology]

[0002] Known functional devices, such as microfluidic devices, include devices formed of substrate assemblies in which substrates are bonded together with an adhesive, such as liquid ejection heads that eject ink to perform recording.

[0003] Patent Document 1 discloses a liquid ejection device having a liquid ejection head with a substrate assembly. In Patent Document 1, the substrate assembly has a pressure generation chamber communicating with a nozzle opening, a piezoelectric layer, and a piezoelectric element having an electrode provided on the piezoelectric layer. In this liquid ejection head, the piezoelectric element is driven to apply pressure to liquid stored in the pressure generation chamber via the piezoelectric layer, thereby ejecting the liquid from the nozzle opening. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-091272 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the substrate assembly of Patent Document 1, when one substrate is bonded via an adhesive to the bonding surface of the other substrate, which has wiring connected to the piezoelectric element and a coating layer that protects the wiring, the other substrate may come into contact with the coating layer due to the load during bonding, which could damage the coating layer.Even if the other substrate does not come into contact with the coating layer, stress may be applied to the coating layer in areas where the adhesive on the coating layer is thin due to warping of the substrates during the bonding process or expansion and contraction of components due to temperature changes during the manufacturing process of the liquid ejection head, which could damage the coating layer.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a technique capable of suppressing the occurrence of damage to the coating layer. [Means for solving the problem]

[0007] In order to achieve the above object, one embodiment of the present invention is a substrate for a liquid ejection head, comprising a liquid chamber for storing liquid, an energy generating element for imparting energy to the liquid stored in the liquid chamber, and an ejection port for ejecting the liquid stored in the liquid chamber, the substrate comprising: a first substrate; a second substrate bonded to the first substrate via an adhesive, the second substrate having wiring connected to the energy generating element and a coating layer for covering and protecting the wiring formed on the bonding surface with the first substrate; and a spacer for ensuring the thickness of the adhesive between the first substrate and the second substrate when the first substrate and the second substrate are bonded, the spacer being provided on the bonding surface of at least one of the first substrate and the second substrate, and being positioned so that it does not overlap with the wiring and the coating layer on the wiring in a plane perpendicular to the stacking direction of the substrates when bonding, and having a height such that a second thickness of the adhesive between the bonding surface opposite the coating layer on the wiring and the coating layer is greater than a first thickness of the adhesive between the bonding surface opposite the spacer and the spacer. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the occurrence of damage to the coating layer. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of a substrate for a liquid ejection head. [Figure 2] FIG. 1 is a configuration diagram of a main part of a liquid ejection head according to a known technique. [Figure 3] FIG. 10 is a diagram showing the conditions and results of a simulation performed by the inventor of the present application. [Figure 4] 10A and 10B are diagrams showing the results of an experiment conducted by the inventor of the present application. [Figure 5] 4A and 4B are diagrams illustrating the arrangement of spacers on a substrate. [Figure 6] FIG. 10 is a diagram showing the thickness of the adhesive near the spacer when bonded. [Figure 7] 10A and 10B are diagrams showing the positional relationship between a recessed portion that may cause a crack in the substrate and a spacer. [Figure 8] 10A and 10B are diagrams showing the positional relationship between a recess that suppresses the occurrence of cracks in a substrate and a spacer. [Figure 9] 10A and 10B are diagrams showing the positional relationship between a recess that suppresses the occurrence of cracks in a substrate and a spacer. [Figure 10] 5A to 5C are diagrams illustrating a manufacturing process of a substrate for a liquid ejection head. [Figure 11] 5A to 5C are diagrams illustrating a manufacturing process of a substrate for a liquid ejection head. [Figure 12] 5A to 5C are diagrams illustrating a manufacturing process of a substrate for a liquid ejection head. [Figure 13] 5A to 5C are diagrams illustrating a manufacturing process of a substrate for a liquid ejection head. [Figure 14] FIG. 2 is a perspective view of the liquid ejection device and the liquid ejection head. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, with reference to the accompanying drawings, an example of an embodiment of a liquid ejection head substrate, a liquid ejection head, and a liquid ejection device will be described. Note that the following embodiment does not limit the present invention, and not all of the combinations of features described in the present embodiment are necessarily essential to the solution of the present invention. Furthermore, the positions, shapes, etc. of the components described in the embodiment are merely examples, and are not intended to limit the present invention to only those.

[0011] (Configuration of liquid ejection head substrate) First, the configuration of the substrate for a liquid ejection head will be described. Note that in this embodiment, an example in which three substrates are bonded together as the substrate for a liquid ejection head will be described, but the present invention is not limited to this and can be applied to cases in which two or four or more substrates are bonded together. Also, in this embodiment, an example in which wafers are bonded together will be described, but the present invention is not limited to this and can be applied to cases in which cut pieces (chips) are bonded to a wafer or cut pieces are bonded together.

[0012] Fig. 1(a) is a cross-sectional view of a liquid ejection head substrate, and Fig. 1(b) is an enlarged view of the area within frame Ib in Fig. 1(a). The liquid ejection head substrate 10 has a configuration for ejecting liquid. Specifically, the liquid ejection head substrate 10 has pressure chambers (hereinafter also referred to as "liquid chambers") 20 that store liquid, and flow channels 30 that supply liquid to the pressure chambers 20. The liquid ejection head substrate 10 also has piezoelectric elements 26 as energy generating elements that impart energy to the liquid stored in the pressure chambers 20, and ejection ports 32 from which the liquid stored in the pressure chambers 20 and to which energy has been imparted by the piezoelectric elements 26 is ejected.

[0013] The liquid ejection head substrate 10 includes a first substrate 12, a second substrate 14, and a third substrate 16, and the above-mentioned configuration for ejecting the liquid is formed in a bonded substrate formed by stacking and bonding the three substrates. One surface 12a of the first substrate 12 is bonded to one surface 14a of the second substrate 14 via an adhesive 18. Furthermore, one surface 16a of the third substrate 16 is bonded to the other surface 14b of the second substrate 14 via an adhesive 18. Hereinafter, the "liquid ejection head substrate" will be referred to as the "bonded substrate" where appropriate.

[0014] The first substrate 12 and the second substrate 14 are, for example, silicon substrates. The second substrate 14 is formed with openings 22 that form pressure chambers 20 when the substrates are bonded together, and a vibration membrane 24 that serves as the ceiling wall of the pressure chambers 20 and partitions the pressure chambers 20. The vibration membrane 24 is also provided with a piezoelectric element 26 at a position facing the opening 22 with the vibration membrane 24 interposed therebetween. The liquid ejection head substrate 10 is provided with, for example, a plurality of pressure chambers 20, and in this embodiment, a plurality of pressure chambers 20 are provided in a direction perpendicular to the plane of the paper in FIG. 1. Therefore, the second substrate 14 is provided with a plurality of openings 22 in that direction, and the vibration membrane 24 is provided with a piezoelectric element 26 at a position facing each opening 22 with the vibration membrane 24 interposed therebetween.

[0015] The first substrate 12 is formed with a piezoelectric element housing portion 28 that houses the piezoelectric element 26 on the vibration membrane 24, and a flow path 30 for supplying liquid to the pressure chamber 20 and recovering liquid from the pressure chamber 20. The bonded substrate 10 is provided with a housing portion (not shown) that houses liquid on the other surface 12b side of the first substrate 12. The liquid housed in the housing portion is supplied to the pressure chamber 20 via the flow path 30.

[0016] The third substrate 16 is, for example, a silicon substrate, and is provided with a plurality of discharge ports 32. The discharge ports 32 are provided at positions corresponding to the respective openings 22 (pressure chambers 20), and in this embodiment, a plurality of discharge ports 32 are arranged side by side in a direction perpendicular to the plane of the paper in Fig. 1. As a result, when energy is applied to the liquid stored in each pressure chamber 20 by driving the piezoelectric element 26, the liquid is discharged from the discharge ports 32 to the outside of the bonded substrate 10.

[0017] An insulating film 34, such as a TEOS film, is formed on one surface 14a of the second substrate 14, and wiring 36 connected to the piezoelectric elements 26 is formed on the insulating film 34. A covering layer 38 that protects the wiring 36 is provided on the insulating film 34 and the wiring 36. This covering layer 38 is formed in a predetermined region that includes the wiring 36, and in this specification, the portion of the covering layer 38 that covers the wiring 36 will be referred to as the covered portion that covers the wiring 36 or the covering layer 38 on the wiring 36, as appropriate. Furthermore, a spacer 40 is provided on the covering layer 38 to ensure the thickness of the adhesive 18 between the covering layer 38 on the wiring 36 and one surface 12a of the first substrate 12.

[0018] In this specification, unless otherwise specified, the term "thickness" refers to the length in the stacking direction of the substrates in the bonded substrate 10 (the vertical direction in FIG. 1). In the following description, the "stacking direction of the substrates in the bonded substrate 10" will be simply referred to as the "stacking direction." In this embodiment, one surface 12a of the first substrate 12 serves as the bonding surface with the second substrate 14, and one surface 14a of the second substrate 14 on which the above-described functional film is formed serves as the bonding surface with the first substrate 12. In other words, the bonding surface of the second substrate 14 with the first substrate 12 includes the above-described functional film together with one surface 14a. In addition, the other surface 14b of the second substrate 14 faces one bonding surface bonded to the first substrate 12 and serves as the other bonding surface bonded to the third substrate 16.

[0019] In the bonded substrate 10, a piezoelectric actuator section 42 including a piezoelectric element 26 is configured adjacent to the pressure chamber 20. A lower electrode (not shown) connected to the piezoelectric element 26 between the piezoelectric element 26 and the vibrating membrane 24, and an upper electrode (not shown) connected to the piezoelectric element 26 on the piezoelectric element 26 are formed on the vibrating membrane 24, which forms the ceiling wall of the pressure chamber 20. The vibrating membrane 24 is formed by, for example, plasma CVD. A hydrogen barrier film (not shown), the lower electrode, the piezoelectric element 26, and the upper electrode are formed on the vibrating membrane 24 in this order.

[0020] The lower electrode and upper electrode are formed by, for example, a sputtering method, and the piezoelectric element 26 is formed by a sol-gel method. The piezoelectric element 26 may also be formed by a sputtering method. For example, a PZT (lead zirconate titanate) film formed by a sol-gel method or a sputtering method can be used as the piezoelectric element 26. The piezoelectric element 26 is made of a sintered body of metal oxide crystal. On one surface 14a of the second substrate 14, an interlayer film and wiring 36 are formed so that the piezoelectric element 26 can be driven, and the piezoelectric actuator unit 42 is configured to be drivable.

[0021] The piezoelectric element 26 is disposed opposite the pressure chamber 20 via the vibration membrane 24. The vibration membrane 24 has deformable properties. The wiring 36 is connected to an electrical connection pad 44, which serves as a connection terminal with the outside, and is also connected to the piezoelectric element 26 via an upper electrode and a lower electrode. When a drive voltage is applied to the piezoelectric element 26 from an external drive IC (not shown) via the pad 44, wiring 36, upper electrode, and lower electrode, the piezoelectric element 26 deforms due to the reverse voltage effect. This deformation of the piezoelectric element 26 deforms the vibration membrane 24, which results in a change in the volume of the pressure chamber 20 and pressurizes the liquid stored in the pressure chamber 20. This pressurization causes the liquid to turn into droplets and be ejected from the ejection port 32 communicating with the pressure chamber 20 to the outside of the bonding substrate 10.

[0022] (Possible concerns when spacers are not provided) As described above, the bonded substrate 10 is provided with the spacers 40 to ensure the thickness of the adhesive 18 between the covering layer 38 on the wiring 36 and one surface 12a of the first substrate 12. Here, with reference to FIG. 2, concerns that may arise when the spacers 40 are not provided will be described.

[0023] 2A and 2B are diagrams illustrating concerns that may arise when spacers 40 are not provided. Fig. 2A is an enlarged view of the vicinity of wiring 36 in the adhesive portion between first substrate 12 and second substrate 14. Fig. 2B is an enlarged view of the vicinity of pad 44 connected to external terminal 200 and sealed with sealant 202.

[0024] If the spacer 40 is not provided between the first substrate 12 and the second substrate 14, when the first substrate 12 and the second substrate 14 are bonded via the adhesive 18, the load applied during bonding may cause contact between the one surface 12a and the covering layer 38 on the wiring 36 (see FIG. 2(a)). In this case, the load applied during bonding is directly applied to the covering layer 38 formed on the wiring 36, and there is a risk of damaging the covering layer 38. Furthermore, even in locations where the covering layer 38 on the wiring 36 and the one surface 12a are close to each other but not in contact, there is a risk of the covering layer 38 being damaged near the edge of the substrate due to warping of the substrate during the manufacturing process or stress caused by expansion and contraction of the sealant that seals the connection portion with the external terminal (see FIG. 2(b)).

[0025] Such damage to the coating layer 38 is likely to occur, for example, when the wiring 36 is made of a relatively soft metal, such as aluminum, and the coating layer 38 is formed of a hard film, such as a silicon compound (Si compound) film. That is, the wiring 36 made of a soft metal can be deformed by the stress described above, while the coating layer 38 made of a hard film will be damaged in the process of deformation due to the stress described above. Furthermore, when the relationship between the thickness T1 of the wiring 36 made of a soft metal and the thickness T2 of the coating layer 38 made of a hard film is T1 > T2, the coating layer 38 cannot deform in response to the deformation of the wiring 36, and is therefore prone to damage.

[0026] (Verification by the inventor of the present application) Here, the results of a simulation of compressive stress acting on the coating layer 38 and an experiment using a temperature cycle test conducted by the inventors of the present application will be described. FIG. 3 is a diagram illustrating the simulation conducted by the inventors of the present application. FIG. 3(a) is a diagram showing the configuration of the substrate used in the simulation. FIG. 3(b) is a graph showing the results of the simulation. FIG. 4 is a diagram showing the results of an experiment conducted by the inventors of the present application to verify the rate of crack occurrence in the coating layer 38 due to a temperature cycle test.

[0027] The substrate used for this simulation was a replica of bonded substrate 10, with Si used for first substrate 12 and second substrate 14, benzocyclobutene used for adhesive 18, AlCu wiring 36, and SiN coating layer 38 (see FIG. 3(a)). Resin was used as sealant 202. The temperature of the substrate replicating bonded substrate 10 was changed from 130°C to -40°C to simulate the compressive stress applied to coating layer 38 in region A (see FIG. 3(a)), which is the bonding portion between first substrate 12 and second substrate 14 and adjacent to sealant 202. In this simulation, the compressive stress was determined for a plurality of samples with different thicknesses of adhesive 18 bonding first substrate 12 and second substrate 14 together.

[0028] The results are shown in Figure 3(b), where the horizontal axis represents the thickness of adhesive 18 and the vertical axis represents the compressive stress. As shown in Figure 3(b), the compressive stress increases as the thickness of adhesive 18 joining first substrate 12 and second substrate 14 becomes thinner, and this tendency becomes more pronounced when the thickness is less than 0.2 µm.

[0029] In addition, a temperature cycle test was actually conducted using a substrate simulating the above-described bonded substrate 10 to examine whether or not cracks occurred in the coating layer 38 between the coating layer 38 on the wiring 36 and one surface 12a of the first substrate 12 depending on the thickness of the adhesive 18. In this temperature cycle test, the high temperature was 130°C and the low temperature was -40°C. The results of this temperature cycle test are shown in Figure 4. When the thickness of the adhesive 18 was less than 100 nm, cracks occurred in the coating layer 38 in all three samples, resulting in a 100% cracking rate. When the thickness of the adhesive 18 was 100 nm or more but less than 200 nm, cracks occurred in the coating layer 38 in two of four samples, resulting in a 50% cracking rate. When the thickness of the adhesive 18 was 200 nm or more but less than 300 nm, no cracks occurred in the coating layer 38 in any of the three samples, resulting in a 0% cracking rate. Furthermore, when the thickness of the adhesive 18 was 300 nm or more, no cracks occurred in the coating layer 38 of any of the four samples, and the rate of crack occurrence was 0%.

[0030] In this experiment, cracks were observed at thicknesses of less than 200 nm (0.2 μm), where the increase in compressive stress was significant in the simulation, but no cracks were observed at thicknesses of 200 nm or more, where the increase in compressive stress was relatively gradual in the simulation. Thus, the results of this experiment correspond to the results of the simulation.

[0031] (spacer) From the results of the above-described simulations and experiments, the inventors of the present application have found that damage to the covering layer 38 can be suppressed depending on the thickness of the adhesive 18 between the covering layer 38 on the wiring 36 and the first substrate 12. Therefore, in this embodiment, a spacer 40 is provided between the first substrate 12 and the second substrate, and the spacer 40 is used to provide the adhesive 18 between the covering layer 38 on the wiring 36 and the first substrate 12 with a thickness that can suppress damage to the covering layer 38 when they are bonded. In this embodiment, the thickness that can suppress damage to the covering layer 38 on the wiring 36 is based on the load during bonding and stresses due to warping of the substrates and expansion and contraction of the sealant during the manufacturing process.

[0032] <Spacer Overview> A plurality of spacers 40 are formed on at least one of the first surface 12a of the first substrate 12 and the second surface 14a of the second substrate 14. That is, all of the spacers 40 may be provided on the first surface 12a, on the first surface 14a, or on both the first surface 12a and the first surface 14a. Note that the number of spacers 40 is not limited to a plurality, and only one spacer may be provided depending on the size of the substrate, the pattern of the wiring 36, and the like.

[0033] The spacers 40 are positioned so as not to overlap the wiring 36 and the covered portions of the covering layer 38 that cover the wiring 36 in a plane perpendicular to the stacking direction (i.e., a plane parallel to the first substrate 12 and the second substrate 14) when the first substrate 12 and the second substrate 14 are bonded together. In other words, the spacers 40 are positioned so as not to overlap the wiring 36 and the covered portions when the bonded substrate 10 is viewed in the stacking direction (i.e., from the upper or lower side in FIG. 1 ). If the spacers 40 were positioned so as to overlap the wiring 36 and the covered portions, the load applied when bonding the first substrate 12 and the second substrate 14 would be concentrated on the wiring 36 and the covered portions via the spacers 40, which could damage the covered portions of the covering layer 38. Furthermore, the length of the spacers 40 in the stacking direction (hereinafter also referred to as "height") is greater than the sum of the thicknesses of the wiring 36 and the covered portions.

[0034] By appropriately adjusting the position of the spacer 40 and its length in the stacking direction, it is possible to control the thickness of the adhesive 18 between the coating layer 38 on the wiring 36 and the bonding surface of the substrate facing the coating layer 38. This makes it possible to suppress damage to the coating layer 38, even if the coating layer 38 is made of a hard film such as a Si compound film and is formed on the wiring 36 made of a relatively soft metal including aluminum. Furthermore, it is possible to suppress damage to the coating layer 38 even if the relationship between the thickness T1 of the wiring 36 and the thickness T2 of the coating layer 38 on the wiring 36 is T1 > T2.

[0035] There is a known technique for controlling the thickness of the adhesive layer bonding the first substrate 12 and the second substrate 14 together by using an adhesive containing fillers of a predetermined particle size as spacers, without providing spacers 40 on the first substrate 12 or the second substrate 14. However, with this technique, when bonding the first substrate 12 and the second substrate 14 together, there is a risk that the filler will overlap the coated portion of the coating layer 38 that covers the wiring 36, and that the filler will damage the coating layer 38 (coated portion).

[0036] When the present invention is applied to a multilayer wiring board, spacers are disposed only at positions corresponding to the wiring and the covering layer on the wiring that are convex from the substrate surface to be provided. However, if the non-convex multilayer wiring has sufficient strength, the spacers may be positioned on the multilayer wiring.

[0037] <Spacer placement> Next, the arrangement of the spacers 40 on the first substrate 12 and the second substrate 14 will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining the arrangement of the spacers 40 on the substrates, with (a) being a diagram showing the spacers 40 formed on the second substrate 14, (b) being a diagram showing the spacers 40 formed on the first substrate 12, and (c) being a diagram showing the spacers 40 formed on the first substrate 12 and the second substrate 14.

[0038] As described above, the spacers 40 may be provided on either the first substrate 12 or the second substrate 14 (see FIGS. 5(a) and 5(b)), as long as they do not come into contact with the wiring 36 or the coated portion of the coating layer 38 that covers the wiring 36. Alternatively, the spacers 40 may be provided on both the first substrate 12 and the second substrate 14 (see FIG. 5(c)).

[0039] The spacers 40 can be formed simultaneously with at least one functional film provided on the substrate. In other words, the spacers 40 can be formed using the same material and in the same process as at least one functional film provided on the substrate. Therefore, when a functional film is formed on one surface 14a of the second substrate 14 (see FIG. 5(a)), the spacers 40 can be formed using the same material as the functional film during the process of forming the functional film. Furthermore, when a functional film is formed on one surface 12a of the first substrate 12, the spacers 40 can be formed using the same material as the functional film during the process of forming the functional film. Note that the spacers 40 may be formed using a material different from that of the functional film. Furthermore, even when the spacers 40 are formed using the same material as the functional film, they may be formed in a process different from the process of forming the functional film made of the same material.

[0040] Furthermore, if the adhesion of the spacers 40 on the one surface 14a of the second substrate 14 is low, there is a risk that the spacers 40 will be chipped off during the process of forming the spacers 40. In such a case, if the adhesion of the spacers 40 on the one surface 12a of the first substrate 12 is relatively high, the spacers 40 may be formed on the one surface 12a of the first substrate 12 (see FIG. 5(b)). Therefore, in this case, the spacers 40 will be formed directly on the one surface 14a where no functional film is formed. In other words, the spacers 40 may be formed directly on the bonding surfaces of the substrates.

[0041] <Spacer height> Next, the height of the spacer 40 will be described. Fig. 6 is a diagram showing the thickness of the adhesive 18 near the spacer 40 during bonding. Note that the description here will be given taking as an example a case where the spacer 40 is formed on one surface 14a of the second substrate 14.

[0042] When the first substrate 12 and the second substrate 14 are joined together, the spacer 40 comes into contact with the one surface 12a, so that the thickness H3 (see FIG. 6) of the adhesive 18 between the first substrate 12 and the second substrate 14 can be adjusted to the height of the spacer 40. More specifically, the thickness H3 is the thickness of the adhesive 18 between the one surface 12a of the first substrate 12 and the functional film (the covering layer 38 that is not located on the wiring 36 in FIG. 6) provided on the one surface 14a of the second substrate 14. Furthermore, by adjusting the height of the spacer 40, the thickness H2 (see FIG. 6) of the adhesive 18 between the covering layer 38 on the wiring 36 and the one surface 12a can be adjusted.

[0043] When bonding the first substrate 12 and the second substrate 14, it is not necessary for all of the spacers 40 to be in contact with the one surface 12a. That is, due to variations in the height of the spacers 40 or variations in the thickness of the first substrate 12 and the second substrate 14, some spacers 40 may have adhesive 18 remaining between them and the one surface 12a (see FIG. 6). In order to suppress variations in thickness H3, it is preferable that the thickness H1 (see FIG. 6) of the adhesive 18 between the spacers 40 and the one surface 12a be 0 μm or more and 0.3 μm or less. In this embodiment, the thickness H2 (see FIG. 6) is adjusted by the spacers 40, so at least one of the multiple spacers 40 is in contact with the one surface 12a, i.e., the thickness H1 is 0 μm.

[0044] Furthermore, based on the findings of the inventors of the present application, in order to prevent damage to the covering layer 38 on the wiring 36, it is necessary to set the thickness H2 of the adhesive 18 between the covering layer 38 on the wiring 36 and the opposing substrate to be greater than the thickness H1 of the adhesive 18 between the spacer 40 and the opposing substrate. Note that this thickness H2 corresponds to the adhesive thickness in the table of FIG. 4.

[0045] Therefore, based on the results of the simulations and experiments described above, in order to prevent damage to the coating layer 38 on the wiring 36, H2 > H1 must be satisfied, and thickness H2 must be increased to alleviate stress generated during the manufacturing process. Based on the results of the simulations and experiments described above, thickness H2 is set to H2 ≈ 0.2 μm, the thickness at which damage occurs. Based on the stress at this thickness, it is preferable to set thickness H2 ≥ 0.6 μm, at which stress is reduced by 25% (see FIG. 3(b)). Although not shown in FIG. 3(b), it is more preferable to set thickness H2 ≥ 1.0 μm, at which stress is reduced by approximately 50% in the simulations performed by the inventors.

[0046] If the thickness H3 is too large, the flow path 30 and the piezoelectric element accommodating portion 28 may not be cohesively fractured during transfer of the adhesive 18, resulting in the adhesive 18 remaining in or overflowing from these openings. This may affect the functionality of the flow path 30 and the piezoelectric element accommodating portion 28. For this reason, the thickness H3, which can be adjusted by the spacer 40, is preferably 3.5 μm or less. Therefore, the upper limit of the height of the spacer 40 is set to, for example, 3.5 μm or a predetermined value smaller than 3.5 μm. The lower limit of the height of the spacer 40 is set to a value that satisfies the above-mentioned condition H2 (i.e., H2≧0.6 μm is preferable, and H2≧1.0 is more preferable), depending on the total value H4 of the thickness of the wiring 36 and the thickness of the coating layer 38 on the wiring 36. As described above, in this embodiment, the spacer 40 is configured to adjust the thickness of the adhesive 18 between the coating layer 38 on the wiring and the opposing substrate to a thickness that makes it difficult for the coating layer 38 to be damaged by the load during bonding, warping of the substrate due to temperature changes during the process, or stress due to expansion and contraction of the sealant.

[0047] <Board shape and spacers> When substrates are bonded together using an adhesive, recesses such as escape grooves for the adhesive may be formed on the bonding surfaces of the substrates to accommodate excess adhesive. However, if such recesses are formed on the bonding surface of the substrate facing the spacer 40 (one surface 12a in FIG. 6), cracks may occur in the substrate with the recesses formed therein.

[0048] Here, the occurrence of cracks due to spacers 40 in a substrate having recesses formed therein will be described with reference to Fig. 7. Fig. 7 is a diagram showing the positional relationship between a recess 700 for accommodating excess adhesive 18 and the spacer 40. Fig. 7(a) is a cross-sectional view of the first substrate 12 having the recess 700 formed therein and the second substrate 14 having the spacer 40 provided thereon, in the vicinity of the spacer 40. Fig. 7(b) is a diagram showing an area S1 on one surface 12a that can come into contact with the upper surface 40a of the spacer 40, and the position of the recess 700 in that vicinity.

[0049] When a first substrate 12 having a recess 700 formed on one surface 12a is bonded to a second substrate 14 having a spacer 40 provided on one surface 14a, a load generated between the first substrate 12 and the spacer 40 during bonding is applied to a portion of region S1 other than the recess 700. In other words, when no recess 700 is formed, the load is applied to the entire surface of region S1. On the other hand, when a recess 700 is formed, the load is applied to a region Sf in region S1 where no recess 700 is formed (see the hatched portion in FIG. 7(b)), that is, an area smaller than region S1. This may result in cracks occurring in the first substrate 12 having the recess 700 formed therein.

[0050] That is, when the ratio of the total area of ​​the recesses 700 in region S1 to the area of ​​region S1 increases, region Sf in region S1 shrinks, which increases the load on region Sf and causes cracks in first substrate 12. For example, when the total area of ​​the recesses 700 in region S1 is 50% of the area of ​​region S1, region Sf in region S1 where no recesses 700 are formed is subjected to twice the load compared to when no recesses 700 are formed in region S1.

[0051] Therefore, in this embodiment, the area variation of region S1 on one surface 12a that can come into contact with spacer 40 is taken into consideration, and recesses 700 are formed so that the total area of ​​recesses 700 within region S1 is 0% or more and less than 20% of the area of ​​region S1. Note that whether or not cracks occur in first substrate 12 depends on the load generated during bonding, the material of the substrates, the height variation of spacer 40, the material of spacer 40, etc. Therefore, the value of "20%" mentioned above is determined, for example, experimentally, depending on the material of the substrates to be bonded, the shape and material of spacer 40, etc.

[0052] A technique for suppressing cracks due to the spacers 40 in a substrate on which recesses 700 are formed will be described below with reference to FIGS. 8 and 9. FIG. 8 is a diagram showing an example of forming recesses 700 to suppress cracks. FIG. 8(a) shows an example of forming recesses 700 near the spacers 40, and FIG. 8(b) shows the region S1 in FIG. 8(a) and the position of the recesses 700 in that region. FIG. 8(c) shows another example of forming recesses 700 near the spacers 40, and FIG. 8(d) shows the region S1 in FIG. 8(c) and the position of the recesses 700 in that region. FIG. 9(a) is a diagram showing an example of forming recesses 700 when recesses 700 are formed in a second substrate 14 on which spacers 40 are provided. FIG. 9(b) is an enlarged view of the vicinity of the spacers of the second substrate 14 in FIG. 9(a). FIG. 9(c) shows the position of the recesses 700 in the region S2 overlapping with the spacers 40 and in that region on the other surface 14b on which the recesses 700 are formed.

[0053] In order to prevent cracks from occurring in the first substrate 12 having the recesses 700 formed therein, for example, the recesses 700 are not formed in the region S1 (i.e., the area of ​​the recesses 700 in the region S1 is set to 0% of the area of ​​the region S1) (see FIG. 8(a)). If there is concern about the influence of misalignment between the first substrate 12 and the second substrate 14 during bonding, spacers 40 may be formed in the region S1 (see FIG. 8(c)). This allows the spacers 40 to be positioned in the region S1 with high precision, thereby preventing the influence of the misalignment. While the explanation using FIG. 8 has been given of a case in which the area of ​​the recesses 700 in the region S1 with respect to the area of ​​the region S1 is 0%, the area of ​​the recesses 700 in the region S1 with respect to the area of ​​the region S1 may be any value as long as it is 0% or more and less than 20%.

[0054] Furthermore, during the manufacturing process of the bonded substrate 10 or a liquid ejection head including the bonded substrate 10, stress is generated around the spacer 40 due to differences in thermal expansion and elastic modulus between the spacer 40 and the adhesive 18. Therefore, if a recess 700 for accommodating excess adhesive 18 for bonding to the third substrate 16 is formed on the other surface 14b of the second substrate 14 on one surface 14a of which the spacer 40 is provided, the second substrate 14 may be damaged by the above-mentioned stress. For this reason, when the recess 700 is formed on the other surface 14b of the second substrate 14 on which the spacer 40 is provided, it is preferable that the recess 700 be positioned so as not to overlap with the spacer 40 in a plane perpendicular to the stacking direction (see FIG. 9(a)).

[0055] That is, the recesses 700 provided on the other surface 14b are formed at positions that do not overlap with the spacers 40 provided on one surface 14a in a plane parallel to the second substrate 14. Alternatively, the recesses 700 are selectively not formed so that the spacers 40 and the recesses 700 do not overlap in a plane parallel to the second substrate 14 (see FIGS. 9(b) and 9(c)). Note that, in the explanation using FIG. 9, a case has been described in which the area of ​​the recesses 700 in region S1 relative to the area of ​​region S2 is 0%, but the area of ​​the recesses 700 in region S2 relative to the area of ​​region S2 may be 0% or more and less than 20%.

[0056] <Spacer material> The material of the spacer 40 is not particularly limited, but is preferably a material that is resistant to deformation due to the load applied during bonding, and an inorganic material is suitable. The spacer 40 may be made of a single material or multiple materials. Furthermore, all or part of the spacer 40 is preferably formed on the second substrate 14. When forming the spacer 40 on the second substrate 14, it is preferable that the spacer 40 be formed during the formation of at least one type of functional film formed on one surface 14a of the second substrate 14, such as the upper electrode, the piezoelectric element 26, the lower electrode, the wiring 36, and the pad 44.

[0057] For example, when forming the spacers 40 simultaneously with the pads 44, the pads 44 are often formed by Au plating, and the spacers 40 are formed from relatively soft Au. In this case, the impact on the substrate when a load is applied to the spacers 40 during bonding is reduced. When forming the spacers 40 by Au plating, it is preferable to form a seed layer on the insulating film on one surface 14a of the second substrate 14. In this case, the insulating layer on the one surface 14a may be the same film as the coating layer 38. As will be described in detail later, for example, if the coating layer 38 is made of SiN, TiW and Au are deposited as a seed layer on the SiN by sputtering. Then, resist patterning is performed to define the positions where the pads 44 and spacers 40 will be formed, and Au plating is selectively grown in those positions. Subsequently, excess TiW and Au are removed, thereby simultaneously forming the pads 44 and spacers 40.

[0058] In this way, when the steps of growing the Au plating on the spacer 40 and the pad 44 are performed simultaneously, the spacer 40 and the pad 44 are formed to the same thickness, but the spacer 40 and the pad 44 may also be formed to different thicknesses. For example, when electrically connecting, a thick pad 44 can facilitate the electrical connection step and prevent short circuits with the substrate. When forming the pad 44 and the spacer 40 to different thicknesses, after forming TiW and Au films as seed layers, resist patterning and Au plating growth steps are performed on the pad 44 and the spacer 40, respectively. This allows the pad 44 and the spacer 40 to be formed to the desired thicknesses.

[0059] (Method of manufacturing the bonded substrate 10) Next, an example of a manufacturing method for the bonded substrate 10 according to this embodiment will be described with reference to FIGS. 10 to 13. FIGS. 10 to 13 are diagrams illustrating the manufacturing process for the bonded substrate 10. FIGS. 10(a) and 10(b) are diagrams illustrating the processing process for the first substrate 12, and FIGS. 10(c) and 10(d) are diagrams illustrating the forming process of the functional film for the second substrate 14. FIGS. 11(a) to 11(e) are diagrams illustrating the forming process of the functional film for the second substrate 14. FIG. 12(a) is a diagram illustrating the bonding process for the second substrate 14, and FIGS. 12(b) and 12(c) are diagrams illustrating the processing process for the second substrate 14. FIGS. 13(a) and 13(b) are diagrams illustrating the bonding process for the third substrate 16, and FIG. 13(c) is a diagram illustrating the processing process for the third substrate 16. FIG. 13(d) is a diagram illustrating the resulting bonded substrate 10. In the following description, a manufacturing method in which the spacers 40 and the pads 44 are formed simultaneously will be described. Furthermore, the methods for processing the substrate and forming the functional film described below are not limited to the methods described below, and various known techniques can be used.

[0060] <Processing of First Substrate 12> First, the first substrate 12 is prepared, and then the flow path 30, the piezoelectric element receiving portion 28, the pad receiving portion 1002 for receiving the pad 44, and the recess 700 are formed on the first substrate 12. For example, if the first substrate 12 is a silicon substrate, a semiconductor manufacturing process can be used to form these components. Specifically, the first substrate 12 can be processed by forming a desired etching mask on the surface of the first substrate 12 and then performing Si dry etching. The etching mask can be formed, for example, using a novolac-based photoresist and patterning it through exposure and development. The Si dry etching can be performed using an etching technique known as the Bosch process, which uses SF gas for the etching step and CF gas for the coating step. Furthermore, if necessary, thinning of the substrate can also be performed.

[0061] Specifically, using the above processing method, a flow path 30 is formed penetrating from one surface 12a to the other surface 12b of the first substrate 12. Also, on one surface 12a, a piezoelectric element accommodating portion 28, a pad accommodating portion 1002, and a recess 700 are formed (see FIG. 10(a)). These components may be formed simultaneously in the same process, or may be formed individually in different processes. The recess 700 for accommodating excess adhesive 18 is formed continuously around the flow path 30 and the piezoelectric element accommodating portion 28 on one surface 12a, but is not formed in a location corresponding to a spacer 40 provided on the second substrate 14 when the second substrate 14 is bonded to the first substrate 12.

[0062] Thereafter, the adhesive 18 is applied by transfer onto one surface 12a of the first substrate 12 (see FIG. 10(b)). At this time, the adhesive 18 is not transferred onto the flow path 30, the piezoelectric element accommodating portion 28, the pad accommodating portion 1002, or the recess 700. In this embodiment, the adhesive 18 is a thermosetting resin, benzocyclobutene resin, whose viscosity changes with temperature, making it easy to control the height of the spacer 40 during bonding. The thickness of the adhesive 18 is preferably thick to eliminate voids during bonding, and is set to be equal to or greater than the height of the spacer 40. If the adhesive 18 is too thick, it is likely to spill onto the flow path 30 and the piezoelectric element accommodating portion 28 on the one surface 12a. For this reason, in this embodiment, the thickness of the adhesive 18 is set to 2.3 μm for a spacer 40 with a height of 2.0 μm.

[0063] The adhesive 18 is made of a material having properties such as high adhesion to the substrate, high applicability with little air bubbles, and low viscosity that allows for easy thinning. The adhesive 18 is not limited to having all of these properties, but may have one or two of these properties. The properties of the adhesive 18 are not limited to those described above, and the adhesive 18 may have various known properties depending on the characteristics required for the bonded substrate 10. Therefore, the adhesive 18 is not limited to benzocyclobutene resin, and may be, for example, epoxy resin, acrylic resin, silicone resin, polyamide resin, polyimide resin, or urethane resin.

[0064] In this embodiment, the adhesive 18 is applied to one surface 12a by spin-coating the adhesive 18 onto a dry film and then transferring it to one surface 12a. However, the method for applying the adhesive 18 to the joining surface of the substrate is not limited to this. The application method may be, for example, screen printing, or if the adhesive 18 is a photosensitive adhesive, photolithography patterning technology may be used.

[0065] <Process for forming functional film on second substrate 14> Next, the second substrate 14 is prepared, and the vibrating membrane 24, lower electrode, piezoelectric element 26, upper electrode, wiring 36, and covering layer 38 are formed on one surface 14a of the second substrate 14 (see FIG. 10(c)). The vibrating membrane 24 and insulating film 34 are formed on the one surface 14a, and the lower electrode, piezoelectric element 26, upper electrode, and wiring 36 are formed. The method for forming these components is not limited to the above-described method, and various known techniques can be used. For example, the wiring 36 is formed by sputtering AlCu to a thickness of 0.7 μm. Then, a covering layer 38 of SiN is formed to a thickness of 0.2 μm so as to cover the wiring 36. Thereafter, a portion of the covering layer 38 is removed as necessary. In this embodiment, the covering layer 38 is patterned and removed to form an opening 1004 that will later communicate with the pressure chamber 20 and an opening 1006 that will connect the pad 44 and the wiring 36.

[0066] Then, a seed layer 1008 is formed on one surface 14a of the second substrate 14 on which the coating layer 38 has been formed (see FIG. 10(d)). Specifically, a TiW film is formed to a thickness of 0.2 μm by sputtering on the one surface 14a on which the various functional films up to the coating layer 38 have been formed, and then a Au film is formed to a thickness of 0.05 μm by sputtering to form the seed layer 1008.

[0067] Next, the spacers 40 and the pads 44 are formed. Specifically, first, a resist 1102 is applied to one surface 14a of the second substrate 14 on which the seed layer 1008 has been formed, and then patterning is performed after exposure and development so that the resist 1102 remains in areas other than the positions where the pads 44 and the spacers 40 are to be formed (see FIG. 11(a)). The positions where the pads 44 are to be formed include openings 1006. Then, a plating layer 1104 is formed on one surface 14a of the second substrate 14 (see FIG. 11(b)). In this embodiment, Au plating is used to form the plating layer 1104, and a known plating solution is used for forming the Au plating. The plating layer 1104 may be formed by either electrolytic plating or electroless plating, but electrolytic plating is preferably used when the plating layer 1104 is thick. In electrolytic plating, the second substrate 14 is immersed in an Au plating solution and a current is passed through its surface, causing a plating layer to grow in the areas where the resist 1102 has been removed by patterning. Thereafter, the resist 1102 is peeled off (see FIG. 11(c)).

[0068] When the spacer 40 and the pad 44 are to have different thicknesses, the steps of patterning with the resist 1102 and growing the Au plating, and the subsequent step of peeling off the resist, are performed for each of the spacer 40 and the pad 44. The order of formation is not particularly limited, but considering the applicability and coverage of the resist 1102, it is preferable to form the thinner Au plating first.

[0069] After the resist 1102 is stripped, the seed layer 1008 is then removed (see FIG. 11(d)). Specifically, after the resist 1102 is stripped, the seed layer 1008 that is exposed to the outside is etched. A solution such as aqua regia, which can selectively etch Au, is used to etch the Au that constitutes the seed layer 1008. Furthermore, a hydrogen peroxide solution diluted to a concentration of 30% is used to etch the TiW that constitutes the seed layer 1008.

[0070] By removing the seed layer 1008 exposed to the outside by etching, the plating layer 1104 remains in the positions where the spacers 40 and pads 44 are to be formed. The plating layer 1104 that remains in this manner becomes the spacers 40 and pads 44. Therefore, in this embodiment, the spacers 40 and pads 44 are composed of the seed layer 1008 and the plating layer 1104. In this embodiment, the height of the spacers 40 thus formed (the combined thickness of the seed layer 1008 and the plating layer 1104) is 2.0 μm.

[0071] After the spacers 40 and pads 44 are formed, the insulating film 34 exposed in the opening 1004 is then removed (see FIG. 11(e)). Specifically, the insulating film 34 located in the opening 1004 provided at the location where the flow channel 30 and the pressure chamber 20 communicate with each other is removed by etching. As a result, one surface 14a of the second substrate 14 is exposed in the opening 1004.

[0072] <Step of Bonding First Substrate 12 and Second Substrate 14> Next, the first substrate 12 and the second substrate 14 are bonded together (see FIG. 12(a)). Specifically, the first substrate 12 (see FIG. 10(b)) processed in the above-described process of forming the first substrate 12 is bonded to the second substrate 14 (see FIG. 11(e)) processed in the above-described process of forming the second substrate 14. More specifically, with one surface 14a of the second substrate 14 facing one surface 12a of the first substrate 12, the first substrate 12 and the second substrate 14 are aligned (positioned), and a load is applied to the first substrate 12 and the second substrate 14 to bond them together. At this time, the temperatures of the first substrate 12 and the second substrate 14 are raised to soften the adhesive 18. In the aligned state, the spacer 40 formed on one surface 14a of the second substrate 14 and the recess 700 formed on the opposing surface 12a of the first substrate 12 do not overlap in a plane perpendicular to the stacking direction. The adhesive 18 is then cured to bond the first substrate 12 and the second substrate 14. The adhesive 18 can be cured by a heat curing method, a delayed ultraviolet curing method, or the like. If either of the substrates to be bonded is ultraviolet transparent, the ultraviolet curing method can be used.

[0073] During this bonding, the spacer 40 prevents the one surface 12a of the first substrate 12 from coming into contact with the coating layer 38 on the wiring 36. The spacer 40 also ensures that the thickness of the adhesive 18 between the one surface 12a and the coating layer 38 on the wiring 36 (see H2 in FIG. 6) is constant. This prevents damage to the coating layer 38 on the wiring 36. Specifically, since the thickness of the wiring 36 is 0.7 μm, the thickness of the coating layer 38 is 0.2 μm, and the thickness of the spacer 40 is 2.0 μm, the thickness of the adhesive 18 between the one surface 12a and the coating layer 38 on the wiring 36 (H2 in FIG. 6) can be ensured to be at least 1.1 μm. Furthermore, since the adhesive is 2.3 μm thick and the spacer 40 is 2.0 μm thick, the thickness of the adhesive between the one surface 12a and the spacer 40 (H1 in FIG. 6) is 0 μm or more and less than 0.3 μm. That is, the conditions H2>H1 and H2≧1.0 μm, which are obtained from the results of the simulations and experiments conducted by the inventors of the present application and which are required to prevent damage to the coating layer 38 on the wiring 36, are satisfied. Thus, in this embodiment, the spacer 40 ensures that the thickness of the adhesive 18 between the one surface 12 a and the coating layer 38 on the wiring 36 (H2 in FIG. 6 ) is thick enough to prevent damage to the coating layer 38.

[0074] <Processing of Second Substrate 14> Thereafter, openings 22 and recesses 700 for forming the pressure chambers 20 are formed in the second substrate 14. Specifically, first, the surface of the second substrate 14 that is not bonded to the first substrate 12 is processed, and the second substrate 14 is thinned to form one surface 14a and the other surface 14b facing the one surface 14a of the second substrate 14 (see FIG. 12(b)). Note that various known techniques can be used to thin the second substrate 14, and therefore a description thereof will be omitted. Next, openings 22 are formed in the thinned second substrate 14 (see FIG. 12(c)). Note that, as described above, the spacers 40 are arranged so as not to overlap the openings 22 for forming the pressure chambers 20 in a plane perpendicular to the stacking direction. Furthermore, recesses 700 for accommodating excess adhesive 18 are formed in the thinned second substrate 14 (see FIG. 12(c)). These recesses 700 are also formed so as not to overlap the spacers 40 in a plane perpendicular to the stacking direction. The opening 22 is formed by patterning a resist on the other surface 14b and then etching the silicon.

[0075] If necessary, a film serving as an etching stop layer may be formed on the lower surface (on the pressure chamber 20 side) of the vibration membrane 24. In this embodiment, the openings 22 and recesses 700 are formed after the second substrate 14 bonded to the first substrate 12 is thinned, but this is not limited to this. For example, the second substrate 14 may be prepared with the openings 22 and recesses 700 formed in advance, and the second substrate 14 may be bonded to the first substrate 12. Alternatively, a second substrate 14 that has been thinned in advance may be used, and the openings 22 and recesses 700 may be formed after bonding to the first substrate 12.

[0076] <Third substrate bonding process> Next, the third substrate 16 is bonded to the other surface 14b of the second substrate 14. Specifically, first, the adhesive 18 is transferred and applied to the other surface 14b of the second substrate 14 (see FIG. 13(a)). At this time, care is taken to avoid transferring the adhesive 18 to the opening 22 and the recess 700. As for the method of applying the adhesive 18 used at this time, various adhesives and application methods can be used, as described above when transferring the adhesive 18 to one surface 12a of the first substrate 12.

[0077] Thereafter, a third substrate 16 is prepared, and with one surface 16a of the third substrate 16 facing the other surface 14b of the second substrate 14, the second substrate 14 and the third substrate 16 are aligned, and a load is applied to the second substrate 14 and the third substrate 16 to bond them together. At this time, the temperatures of the second substrate 14 and the third substrate 16 are raised to soften the adhesive 18. The adhesive 18 is then cured to bond the third substrate to the second substrate 14. The curing method of the adhesive 18 is changed as appropriate depending on the type of adhesive used.

[0078] <Third substrate processing process> Next, the discharge ports 32 are formed in the third substrate 16. Specifically, first, the surface of the third substrate 16 that is not bonded to the second substrate 14 is processed, and the third substrate 16 is thinned to form one surface 16a of the third substrate 16 and the other surface 16b that faces the other surface 16b. Note that various known techniques can be used to thin the third substrate 16, and therefore a description thereof will be omitted. Next, the discharge ports 32 are formed in the thinned third substrate 16 (see FIG. 13(c)). The discharge ports 32 are formed by patterning a resist on the other surface 16b and then performing silicon etching.

[0079] In this embodiment, the third substrate 16 is bonded to the second substrate 14, and then the third substrate 16 is thinned and the ejection ports 32 are formed therein. However, the present invention is not limited to this. For example, a third substrate 16 on which the ejection ports 32 are formed in advance may be prepared, and the third substrate 16 may be bonded to the second substrate 14. Alternatively, a third substrate 16 that has been thinned in advance may be used, and the ejection ports 32 may be formed therein after bonding to the second substrate 14. Thereafter, in the process of singulating into chips that can be mounted on a liquid ejection head, the removed portions 1302 (see FIG. 13(c)) located above the pad housing portions 1002 in the first substrate 12 are removed, thereby obtaining the bonded substrate 10 (see FIG. 13(d)).

[0080] (Application example of the bonded substrate 10) Next, a liquid ejection head including the bonding substrate 10 according to this embodiment and a liquid ejection device including the liquid ejection head will be described. As an example of the liquid ejection device, a recording device that ejects ink as a liquid to perform recording on a conveyed recording medium will be described. Fig. 14(a) is a schematic diagram of the recording device. Fig. 14(b) is a perspective diagram of the recording head as a liquid ejection head including the bonding substrate 10 in the recording device of Fig. 14(a).

[0081] The recording device 1400 in FIG. 14 is a so-called full-line type recording device, and is equipped with a long recording head 1402 that extends across the entire width of the recording medium M (see FIG. 14(a)). The recording device 1400 also has a transport unit 1404 that transports the recording medium M in a direction intersecting (orthogonal to) the width direction. In the recording device 1400, an image is recorded on the recording medium M by ejecting ink from the recording head 1402 while the recording medium M is transported by the transport unit 1404. In this embodiment, the recording head 1402 is configured to be able to eject four inks: cyan ink, magenta ink, yellow ink, and black ink. This allows the recording device 1400 to record color images.

[0082] The print head 1402 has a plurality of bonding substrates 10 as printing element substrates arranged in the extending direction of the print head 1402 on the surface facing the conveyed printing medium M (see FIG. 14(b)). The print head 1402 also has a liquid supply unit 1406 formed with a circulation flow path that supplies ink supplied from an ink tank (not shown) to each bonding substrate 10 and recovers ink that was not ejected from the ejection ports 32 during printing from the bonding substrate 10. The print head 1402 also has a negative pressure control unit 1410 that controls the pressure (negative pressure) in the circulation flow path, and a liquid connection part 1412 that serves as an ink supply port and an ink discharge port for the liquid supply unit 1406 (see FIG. 14(a)).

[0083] The recording head 1402 is also electrically connected to an electrical control unit that supplies power and ejection control signals to the recording head 1402. Specifically, each bonded substrate 10 is connected to the same electrical wiring board 1416 via a flexible wiring board 1414. The electrical wiring board 1416 is provided with a power supply terminal 1418 for receiving power and a signal input terminal 1420 for receiving ejection control signals. The recording elements (piezoelectric elements 26) provided on the bonded substrate 10 are driven using power supplied from the power supply terminal 1418 based on the ejection control signals input from the signal input terminal 1420. By driving the recording elements in this way, ink supplied from the liquid supply unit 1406 and stored in the pressure chambers 20 in each bonded substrate 10 is ejected from the ejection ports 32.

[0084] (Action and effect) As described above, the bonded substrate 10, which is a substrate for a liquid ejection head, includes a spacer 40 between one surface 14a of the second substrate 14, on which the wiring 36 is formed, and one surface 12a of the first substrate 12, which is bonded to the first surface 14a via the adhesive 18. The spacer 40 is positioned so as not to contact the wiring 36 or the covering layer 38 on the wiring 36. Furthermore, the spacer 40 is configured so that, when the substrates are bonded, the thickness H2 of the adhesive 18 between the covering layer 38 on the wiring 36 and the bonding surface of the opposing substrate is set to a value that prevents damage to the covering layer 38 due to the load during bonding, warping of the substrate due to temperature changes, and stress due to expansion and contraction of the sealant. Specifically, the height of the spacer 40 is set so that the thickness H2 is greater than the thickness H1 of the adhesive 18 between the spacer 40 and the bonding surface of the opposing substrate, and so that H2≧0.6 μm, preferably H2≧1.0 μm.

[0085] As a result, in the bonded substrate 10, damage to the covering layer 38 on the wiring 36 due to the load generated during bonding when the first substrate 12 and the second substrate 14 are bonded is suppressed. Furthermore, damage to the covering layer 38 on the wiring 36 due to warping of the substrate due to temperature changes and stress due to expansion and contraction of the sealant is suppressed during the manufacturing process of the bonded substrate 10 and the manufacturing process of a liquid ejection head using the bonded substrate 10.

[0086] (Other embodiments) The above-described embodiment may be modified as shown in the following (1) to (4).

[0087] (1) In the above embodiment, the spacer 40 is provided so as not to overlap the wiring 36 and the covering layer 38 on the wiring 36 in a plane perpendicular to the stacking direction of the substrate, and so as to satisfy H2>H1 and H2≧0.6, but this is not limitative. For example, If the warping of the substrate due to temperature changes and the stress due to expansion and contraction of the sealant are small, the spacer 40 only needs to be higher than the combined height of the wiring 36 and the covering layer 38 on the wiring 36, that is, H2>H1.

[0088] (2) In the above embodiment, the energy generating element is provided with a piezoelectric element 26, but this is not limited thereto. Various known energy generating elements, such as electrothermal conversion elements, may be used as the energy generating element. Furthermore, in the above embodiment, the recess 700 is hole-shaped, but this is not limited thereto, and it may be groove-shaped extending in a predetermined direction on the surface of the substrate. Furthermore, in the above embodiment, the liquid ejection head is a full-line type print head, but this is not limited thereto, and it may be a so-called serial scan type print head.

[0089] (3) Although not specifically mentioned in the above embodiment, the spacer 40 has a substantially cubic shape as shown in Figures 7(a) and 7(b), but is not limited to this and may have a columnar shape such as a cylindrical shape, an elliptical cylindrical shape, a polygonal prism shape, etc. Furthermore, the spacer 40 is not limited to a columnar shape and may have a substantially conical shape that gradually widens toward the opposing substrate.

[0090] (4) The above embodiment and the various configurations shown in (1) to (3) above may be combined as appropriate.

[0091] The disclosure of the above embodiment includes the following configurations and methods. (Configuration 1) A substrate for a liquid ejection head, comprising: a liquid chamber for storing a liquid; an energy generating element for applying energy to the liquid stored in the liquid chamber; and an ejection port for ejecting the liquid stored in the liquid chamber, a first substrate; a second substrate bonded to the first substrate via an adhesive, the second substrate having wiring connected to the energy generating elements and a covering layer covering and protecting the wiring formed on a bonding surface with the first substrate; a spacer that ensures a thickness of the adhesive between the first substrate and the second substrate when the first substrate and the second substrate are bonded together; The spacer is provided on a bonding surface of at least one of the first substrate and the second substrate, the wiring and the covering layer on the wiring are provided at a position where they do not overlap with each other in a plane perpendicular to the stacking direction of the substrates at the time of the bonding, A substrate for a liquid ejection head, characterized in that it has a height such that the second thickness of the adhesive between the covering layer and the bonding surface facing the wiring is greater than the first thickness of the adhesive between the spacer and the bonding surface facing the spacer. (Configuration 2) The spacer has a height as the second thickness that ensures a thickness that can suppress damage to the coating layer on the wiring due to the load during the bonding, warping of the substrate due to temperature changes, and stress due to expansion and contraction of the sealant that seals the connection portion with the external terminal. This is the substrate for a liquid ejection head described in configuration 1. (Configuration 3) 3. The liquid ejection head substrate according to configuration 1 or 2, wherein the second thickness is 0.6 μm or more. (Configuration 4) 4. The liquid ejection head substrate according to configuration 3, wherein the second thickness is 1.0 μm or more. (Configuration 5) 5. The liquid ejection head substrate according to any one of configurations 1 to 4, wherein the first thickness is 0 μm or more and less than 0.3 μm. (Configuration 6) 6. The liquid ejection head substrate according to any one of configurations 1 to 5, wherein the third thickness of the adhesive between the first substrate and the second substrate during the bonding is 3.5 μm or less. (Configuration 7) 7. The liquid ejection head substrate according to any one of configurations 1 to 6, wherein a first recess capable of accommodating an excess of the adhesive is formed on the bonding surface of the first substrate. (Configuration 8) the spacer is provided on the bonding surface of the second substrate, The substrate for a liquid ejection head according to configuration 7, wherein the first recess is formed within an area where the spacer may come into contact during bonding, such that the area of ​​the first recess formed within the area is greater than or equal to 0% and less than 20% of the area of ​​the area. (Configuration 9) the spacer is provided on the bonding surface of the first substrate, The substrate for a liquid ejection head according to configuration 7, wherein the first recess is formed within the region on the bonding surface where the spacer is provided, so that the area of ​​the first recess formed within the region is greater than or equal to 0% and less than 20% of the area of ​​the region. (Configuration 10) The liquid chamber is formed in the second substrate, 10. The liquid ejection head substrate according to any one of configurations 1 to 9, wherein the spacer is provided at a position where it does not overlap with the liquid chamber in a plane perpendicular to the stacking direction. (Configuration 11) a third substrate is bonded to one bonding surface of the second substrate opposite to one bonding surface bonded to the first substrate via the adhesive, the third substrate having the ejection port communicating with the liquid chamber; a second recess capable of accommodating excess adhesive is formed on the other joining surface; The second recess is formed in a region on a surface parallel to the second substrate that overlaps with the spacer during bonding, so that the area of ​​the second recess formed in the region is greater than or equal to 0% and less than 20% of the area of ​​the region. (Configuration 12) 12. The liquid ejection head substrate according to any one of configurations 1 to 11, wherein the spacer is made of an inorganic material. (Configuration 13) The spacer is provided on the bonding surface of the second substrate, 13. The liquid ejection head substrate according to any one of configurations 1 to 12, which is made of the same material as at least one functional film formed on the second substrate. (Configuration 14) 14. The liquid ejection head substrate according to configuration 13, wherein the spacers are made of the same material as the pads for electrical connection. (Configuration 15) 15. The liquid ejection head substrate according to configuration 14, wherein the spacers are formed to the same thickness as the pads. (Configuration 16) 15. The liquid ejection head substrate according to configuration 14, wherein the spacers are formed to a thickness different from that of the pads. (Configuration 17) 17. A liquid ejection head substrate according to configuration 16, wherein the pad is thicker than the spacer. (Configuration 18) the wiring is formed of a metal containing at least aluminum, 18. The liquid ejection head substrate according to any one of configurations 1 to 17, wherein the covering layer is formed of a silicon compound film. (Configuration 19) 19. The liquid ejection head substrate according to any one of configurations 1 to 18, wherein the thickness of the wiring is greater than the thickness of the covering layer. (Configuration 20) 20. The liquid ejection head substrate according to any one of configurations 1 to 19, wherein the spacer is formed from a metal seed layer and a metal plating layer. (Configuration 21) A liquid ejection head substrate according to any one of configurations 1 to 20, A liquid ejection head, characterized in that energy is applied to the liquid stored in the liquid chamber by the energy generating element, thereby ejecting the liquid from the ejection orifice. (Configuration 22) a liquid ejection head including the substrate for a liquid ejection head according to any one of configurations 1 to 20, wherein the liquid ejection head applies energy to the liquid stored in the liquid chamber by the energy generating element, thereby ejecting the liquid from the ejection port; a means for supplying power and a discharge control signal for causing the liquid discharge head to discharge liquid. (Configuration 23) A method for manufacturing a substrate for a liquid ejection head, the substrate comprising: a liquid chamber for storing a liquid; an energy generating element for applying energy to the liquid stored in the liquid chamber; and an ejection port for ejecting the liquid stored in the liquid chamber, the method comprising: a forming step of forming a functional film on a bonding surface of a second substrate to be bonded to the first substrate, the functional film including wiring connected to the energy generating elements, a covering layer that covers and protects the wiring, and a spacer that ensures a thickness of an adhesive between the first substrate and the second substrate when bonding the first substrate and the second substrate; The spacer is the wiring and the covering layer on the wiring are provided at a position where they do not overlap with each other in a plane perpendicular to the stacking direction of the substrates at the time of the bonding, a height such that, during the bonding, a second thickness of the adhesive between a bonding surface of the covering layer on the wiring facing the covering layer and the covering layer is greater than a first thickness of the adhesive between the bonding surface of the spacer facing the covering layer and the spacer; A method for manufacturing a substrate for a liquid ejection head, wherein in the forming step, the spacer is formed from the same material as at least one functional film. (Configuration 24) 24. The method of manufacturing a liquid ejection head substrate according to Configuration 23, wherein in the forming step, the spacers are formed simultaneously with the pads for electrical connection. (Configuration 25) 24. The method for manufacturing a substrate for a liquid ejection head according to Configuration 23, wherein in the forming step, the spacers and the pads for electrical connection are made of the same material, and the spacers are formed in a step different from that for forming the pads. [Explanation of symbols]

[0092] 10. Liquid ejection head substrate 12 First board 14 Second board 18 Adhesive 40 spacer

Claims

1. A substrate for a liquid ejection head, comprising: a liquid chamber for storing a liquid; an energy generating element for applying energy to the liquid stored in the liquid chamber; and an ejection port for ejecting the liquid stored in the liquid chamber, a first substrate; a second substrate bonded to the first substrate via an adhesive, the second substrate having wiring connected to the energy generating elements and a covering layer covering and protecting the wiring formed on a bonding surface with the first substrate; a spacer that ensures a thickness of the adhesive between the first substrate and the second substrate when the first substrate and the second substrate are bonded together; The spacer is provided on a bonding surface of at least one of the first substrate and the second substrate, the wiring and the covering layer on the wiring are provided at a position where they do not overlap with each other in a plane perpendicular to the stacking direction of the substrates at the time of the bonding, A substrate for a liquid ejection head, characterized in that it has a height such that the second thickness of the adhesive between the covering layer and the bonding surface facing the wiring is greater than the first thickness of the adhesive between the spacer and the bonding surface facing the spacer.

2. The substrate for a liquid ejection head according to claim 1, wherein the spacer has a height as the second thickness that ensures a thickness that can suppress damage to the coating layer on the wiring due to the load during the joining, warping of the substrate due to temperature changes, and stress due to expansion and contraction of the sealant that seals the connection portion with the external terminal.

3. 3. The liquid ejection head substrate according to claim 2, wherein the second thickness is 0.6 [mu]m or more.

4. 4. The liquid ejection head substrate according to claim 3, wherein the second thickness is 1.0 [mu]m or more.

5. 2. The liquid ejection head substrate according to claim 1, wherein the first thickness is equal to or greater than 0 [mu]m and less than 0.3 [mu]m.

6. 2. The substrate for a liquid ejection head according to claim 1, wherein the third thickness of the adhesive between the first substrate and the second substrate when they are bonded together is 3.5 [mu]m or less.

7. 2. The liquid ejection head substrate according to claim 1, wherein a first recess capable of accommodating an excess of the adhesive is formed on the bonding surface of the first substrate.

8. the spacer is provided on the bonding surface of the second substrate, The substrate for a liquid ejection head according to claim 7, wherein the first recess is formed within an area where the spacer may come into contact during the bonding so that the area of ​​the first recess formed within the area is greater than or equal to 0% and less than 20% of the area of ​​the area.

9. the spacer is provided on a bonding surface of the first substrate, The substrate for a liquid ejection head according to claim 7, wherein the first recess is formed within the region on the bonding surface where the spacer is provided, so that the area of ​​the first recess formed within the region is greater than or equal to 0% and less than 20% of the area of ​​the region.

10. the liquid chamber is formed in the second substrate, 2. The liquid ejection head substrate according to claim 1, wherein the spacer is provided at a position where it does not overlap with the liquid chamber in a plane perpendicular to the stacking direction.

11. a third substrate is bonded to one bonding surface of the second substrate opposite to one bonding surface bonded to the first substrate via the adhesive, the third substrate having the ejection port communicating with the liquid chamber; a second recess capable of accommodating excess adhesive is formed on the other joining surface; The substrate for a liquid ejection head described in claim 10, wherein the second recess is formed in a region on a surface parallel to the second substrate that overlaps with the spacer during bonding, so that the area of ​​the second recess formed in the region is greater than or equal to 0% and less than 20% of the area of ​​the region.

12. 2. The liquid ejection head substrate according to claim 1, wherein the spacer is made of an inorganic material.

13. The spacer is provided on the bonding surface of the second substrate, 2. The liquid ejection head substrate according to claim 1, wherein the substrate is made of the same material as at least one functional film formed on the second substrate.

14. 14. The liquid ejection head substrate according to claim 13, wherein the spacers are made of the same material as the pads for electrical connection.

15. 15. The liquid ejection head substrate according to claim 14, wherein the spacers are formed to have the same thickness as the pads.

16. The liquid ejection head substrate according to claim 14 , wherein the spacers are formed to have a thickness different from that of the pads.

17. 17. The liquid ejection head substrate according to claim 16, wherein the pad is thicker than the spacer.

18. the wiring is formed of a metal containing at least aluminum, 2. The liquid ejection head substrate according to claim 1, wherein the coating layer is formed of a silicon compound film.

19. 2. The liquid ejection head substrate according to claim 1, wherein the thickness of the wiring is greater than the thickness of the covering layer.

20. 2. The liquid ejection head substrate according to claim 1, wherein the spacer is formed from a metal seed layer and a metal plated layer.

21. A liquid ejection head substrate according to any one of claims 1 to 20, A liquid ejection head, characterized in that energy is applied to the liquid stored in the liquid chamber by the energy generating element, thereby ejecting the liquid from the ejection orifice.

22. a liquid ejection head comprising the liquid ejection head substrate according to any one of claims 1 to 20, wherein the liquid is ejected from the ejection port by applying energy to the liquid stored in the liquid chamber by the energy generating element; a means for supplying power and a discharge control signal for causing the liquid discharge head to discharge liquid.

23. A method for manufacturing a substrate for a liquid ejection head, the substrate comprising: a liquid chamber for storing a liquid; an energy generating element for applying energy to the liquid stored in the liquid chamber; and an ejection port for ejecting the liquid stored in the liquid chamber, the method comprising: a forming step of forming a functional film on a bonding surface of a second substrate to be bonded to the first substrate, the functional film including wiring connected to the energy generating elements, a covering layer that covers and protects the wiring, and a spacer that ensures a thickness of an adhesive between the substrates when bonding the first substrate and the second substrate; The spacer is the wiring and the covering layer on the wiring are provided at a position where they do not overlap with each other in a plane perpendicular to the stacking direction of the substrates at the time of the bonding, a height such that, during the bonding, a second thickness of the adhesive between a bonding surface of the covering layer on the wiring facing the covering layer and the covering layer is greater than a first thickness of the adhesive between the bonding surface of the spacer facing the covering layer and the spacer; The method for manufacturing a substrate for a liquid ejection head, wherein in the forming step, the spacer is formed from the same material as at least one functional film.

24. 24. The method for manufacturing a liquid ejection head substrate according to claim 23, wherein in the forming step, the spacers are formed simultaneously with pads for electrical connection.

25. 24. The method for manufacturing a substrate for a liquid ejection head according to claim 23, wherein in the forming step, the spacers and the pads for electrical connection are made of the same material, and the spacers are formed in a step different from that for forming the pads.

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