MEMS device, droplet discharge head, and inkjet printer

Abstract

To allow a state of joining of substrates to be checked with high precision easily in an MEMS device used in a droplet discharge head etc. of an inkjet printer.SOLUTION: In an MEMS device 1 formed by joining the other substrate (5) to one substrate (3), the other substrate (5) includes an open window (51) and an index (2) for joining on the one substrate (3) can be viewed through the open window (51).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to MEMS devices, droplet ejection heads, and inkjet printers.

Background Art

[0002] MEMS (Micro Electro Mechanical Systems) devices are widely used in sensors, actuators, etc. As a familiar example of an actuator, there is, for example, the droplet ejection head of an inkjet printer in Patent Documents 1 and 2.

[0003] An MEMS device integrates mechanical element components, electronic circuits, the above-mentioned sensors or actuators, etc. on a substrate by microfabrication technology. Therefore, for the substrate, a reinforcing sub-frame substrate, or in the case of the above-mentioned droplet ejection head, a pressure chamber substrate forming an ink chamber and a nozzle substrate are bonded together.

[0004] The substrate (wafer) of an MEMS device is inspected at a predetermined stage of microfabrication and at a predetermined stage where the above-mentioned mechanical element components, electronic circuits, sensors or actuators are mounted, and is managed so that defective products do not proceed to subsequent processes. Although it is such a managed substrate (wafer), it is necessary to confirm (inspect) whether the substrates (wafers) are properly bonded after bonding them together. Examples of improper bonding are misalignment of alignment.

[0005] Conventionally, the confirmation (inspection) of whether the bonding is proper is performed using a dedicated microscope equipped with an infrared camera or an inspection device. Such confirmation (inspection) utilizes the property that silicon allows a specific infrared ray, for example, an infrared ray with a wavelength of 1100 nm, to pass well, that is, becomes nearly transparent at that wavelength. Thus, it is possible to confirm (inspect) whether the alignment is proper (there is no deviation) from the infrared transmission image of the bonded substrate (wafer).

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Patent Document 2

[0007] [Summary] In the case of a droplet ejection head as a MEMS device, roughly, a nozzle substrate is placed on the back surface of an actuator substrate, and the surface is reinforced by a sub-frame substrate. The actuator substrate includes a diaphragm, a piezoelectric element mounted on the surface of the diaphragm, and a pressure chamber substrate that surrounds the outer peripheral side of the back surface of the diaphragm and forms an ink pressure chamber together with the nozzle substrate. The surface of the diaphragm is formed with wiring of the piezoelectric element, a passivation film, etc., and a lid-shaped sub-frame substrate that surrounds the piezoelectric element is adhered with the above adhesive.

[0008] In the case of a droplet ejection head, for example, since several hundreds of elements are formed on the same substrate, the sub-frame substrate is appropriately processed by etching or the like into a lid shape that surrounds the above piezoelectric element before being bonded to the actuator substrate. Therefore, the surface of the sub-frame substrate is relatively close to a mirror surface. On the other hand, after the actuator substrate is bonded and reinforced with the sub-frame substrate, the outer peripheral portion that becomes the pressure chamber substrate is left, and the actuator substrate is etched until the diaphragm is exposed. Therefore, before being bonded to the sub-frame substrate, it is not particularly processed, and its surface is a rough surface (matte finish).

[0009] Therefore, even if both the sub-frame substrate and the pressure chamber substrate are silicon substrates through which the infrared rays can pass, from the rough (matte) silicon substrate side, the infrared rays are diffusely reflected on the surface and do not pass through, so only the matte finish on the surface can be seen and the inside cannot be confirmed (inspected). Specifically, it will result in an image like sandstorm. Note that there are various types of diaphragms, such as single-crystalline silicon, polycrystalline silicon, and oxide films. Of course, single-crystalline silicon has the best infrared transmissivity, but the difference in their types hardly affects the appearance under infrared rays and is at a level that does not cause problems compared to the case where the surface is matte.

[0010] An object of the present disclosure is to provide a MEMS device in which another substrate is bonded to one substrate, a droplet ejection head using the same, and an inkjet printer, which can easily and highly accurately confirm the state of the bonding.

[0011] In order to solve the above-described problems, the MEMS device of the present disclosure is a MEMS device in which another substrate is bonded to one substrate, and the other substrate is provided with an opening window, and the opening window makes it possible to visually recognize an index for bonding on one substrate.

Brief Description of Drawings

[0012]

Figure 1

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[0013] [Detailed Description] Next, this embodiment will be described with reference to the drawings. In the description of the drawings below, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Therefore, specific structures, dimensions, etc. should be appropriately determined with reference to the following description.

[0014] Also, the embodiments shown below are examples of devices and methods for embodying the technical idea, and do not specify the materials, shapes, structures, arrangements, etc. of each component. Various changes can be made to this embodiment within the scope of the claims.

[0015] (Embodiment 1) FIG. 1 is a cross-sectional view showing the structure of a MEMS device 1 according to the first embodiment. This MEMS device 1 is an actuator device including a piezoelectric element 2. Although shown separately in FIG. 1, hundreds of such actuator devices are arranged in a matrix as shown in FIGS. 8 and 9 described later to form a droplet ejection head of an inkjet printer.

[0016] Therefore, since this MEMS device 1 is a droplet ejection head, generally, a nozzle substrate 4 is placed on the back surface of an actuator substrate 3 which is a substrate, and a sub-frame substrate 5 which is another substrate is bonded and reinforced on the surface. The actuator substrate 3 includes a diaphragm 31, a piezoelectric element 2 mounted on the surface of the diaphragm 31, and a pressure chamber substrate 32 that surrounds the outer peripheral side of the back surface of the diaphragm 31 and forms an ink pressure chamber (accommodation space) 42 together with the nozzle substrate 4. On the surface of the diaphragm 31, wiring of the piezoelectric element 2, a passivation film 33, etc. are formed, and a lid (cap)-shaped sub-frame substrate 5 that surrounds the piezoelectric element 2 is bonded with an adhesive 6.

[0017] The piezoelectric element 2 is configured by sandwiching a piezoelectric body 21 between front and back electrodes 22 and 23, and performs an expansion and contraction operation by repeatedly applying and removing power. By vibrating the diaphragm 31 in the vertical direction (the thickness direction of the diaphragm 31) in FIG. 1 by the expansion and contraction operation, this MEMS device 1 sucks ink from an ink flow path (not shown) into the pressure chamber 42 and ejects it from the droplet ejection hole 41.

[0018] And in the MEMS device 1 of this embodiment, the sub-frame substrate 5 includes an opening window 51. This opening window 51 makes it possible to visually recognize an alignment pattern for bonding provided on the actuator substrate 3 which is a substrate. Specifically, in this embodiment, the piezoelectric element 2 itself is used as the alignment pattern.

[0019] FIG. 2 is a cross-sectional view showing a stage during the fabrication of this MEMS device 1. FIG. 2 shows a state where the sub-frame substrate 5 is bonded to the actuator substrate 3. The sub-frame substrate 5 is bonded to the actuator substrate 3 on which the piezoelectric element 2 is mounted, and is formed in a lid (cap) shape that forms a storage space 52 for the piezoelectric element 2. In the etching process for forming such a storage space 52, at the same time, an opening window 51 is formed in the sub-frame substrate 5. Then, when the sub-frame substrate 5 is bonded to the actuator substrate 3, the inside of the storage space 52 can be visually recognized with visible light through the opening window 51.

[0020] Then, using a visible light microscope or the like, it is possible to determine whether the piezoelectric element 2 is at the correct position within a predetermined range from the position within the storage space 52 of the piezoelectric element 2 (which is indicated by the distances W1 and W2 from the inner wall in FIG. 2), which is the index (alignment pattern). Before this bonding process, the mounting position of the piezoelectric element 2 and the formation position of the storage space 52, etc. are each pre-inspected on the actuator substrate 3 and the sub-frame substrate 5, and only the products within the standard (good products) are sent to the bonding process. Therefore, by looking through the opening window 51, if the piezoelectric element 2 is at the correct position within the storage space 52, it can be determined that the actuator substrate 3 and the sub-frame substrate 5 are correctly aligned and bonded.

[0021] In a visible light inspection device, compared with an infrared inspection device, the accuracy of the autofocus of the microscope can be increased and the speed can also be increased. Also, in an infrared inspection device, in addition to an infrared camera, a special filter (such as one that selects the wavelength of 1100 nm mentioned above) etc. is required, and the inspection device itself becomes expensive, but general-purpose items can be used for a visible light inspection device.

[0022] When in the state of FIG. 2, the actuator substrate 3 is reinforced by the bonded sub-frame substrate 5, and in order to form the pressure chamber 42 of the ink as shown in FIG. 1, etching can be performed until the diaphragm 31 is exposed. Thereafter, the nozzle substrate 4 in which the droplet ejection holes 41 have been drilled separately by etching or the like is adhered to the actuator substrate 3, and the MEMS device 1 as shown in FIG. 1 is completed.

[0023] The indicator (alignment pattern) may be a predetermined mark or the like attached to the top surface 24 of the piezoelectric element 2, rather than the piezoelectric element 2 itself. The size of the indicator (alignment pattern) is about 0.1 to 1 mm, and does not significantly affect the strength of the sub-frame substrate 5. However, in order to form the pressure chamber 42 of the ink, etching is performed, and in the state where the diaphragm 31 is exposed as shown in FIG. 1, since it is also affected by the deflection of the diaphragm 31 and the like, it is desirable to perform inspection immediately after the sub-frame substrate 5 and the actuator substrate 3 are bonded together.

[0024] FIG. 3 is an example of a plan view showing the structure of the above-described MEMS device 1. In the example of FIG. 3, the opening window 51, the storage space 52, and the piezoelectric element 2 are all circular in plan view. Even when viewed in the cross section shown in FIGS. 1 and 2, like the sub-frame substrate 5a of the MEMS device 1a shown in FIG. 4A, the opening window 51a and the storage space 52a may both be square, and accordingly, the piezoelectric element 2a may also be square.

[0025] Also, even when viewed in the same cross section as FIGS. 1 and 2, like the sub-frame substrate 5a of the MEMS device 1a shown in FIG. 4A, where the opening window 51a and the storage space 52a are square, the piezoelectric element 2 may be circular as shown in FIG. 3, like the MEMS device 1b shown in FIG. 4B.

[0026] Furthermore, in the examples of FIGS. 3, 4A, and 4B, as described above, the indicators to be confirmed from the opening windows 51 and 51a were the piezoelectric elements 2 and 2a themselves, whereas in the MEMS device 1c shown in FIG. 5A and the MEMS device 1d shown in FIG. 5B, separate indicators are used. In FIGS. 5A and 5B, the same reference numerals are given to the portions corresponding to FIGS. 2 and 3.

[0027] In the MEMS device 1c shown in FIG. 5A, a pattern 33c formed on the surface of the diaphragm 31 facing the opening window 51a is used as an index. For example, a metal material may be used for the pattern 33c. FIG. 6 is a cross-sectional view of the MEMS device 1c shown in FIG. 5A. In FIG. 6, although a pressure chamber 42 and the like are not formed, the piezoelectric element 2 may be provided on the pressure chamber 42 side.

[0028] On the other hand, in the MEMS device 1d shown in FIG. 5B, a contact pattern 31d obtained by cutting the diaphragm 31 crosswise is used as an index. FIG. 7 is a cross-sectional view of the MEMS device 1d shown in FIG. 5(b). In FIG. 7, although a pressure chamber 42 and the like are not formed, the piezoelectric element 2 may be provided on the pressure chamber 42 side.

[0029] As described above, the index (alignment pattern) to be confirmed from the opening windows 51 and 51a only needs to be able to show the misalignment during the bonding of the actuator substrate 3 and the sub-frame substrate 5. In FIG. 2, an example is shown in which the adhesive 6a oozed (overflowed) from the bonding portion thereof is also used as an index (alignment pattern). Here, in the inspection with the infrared camera described above, the image becomes monochrome and may appear dark due to the unevenness of the pattern, and it is difficult to accurately confirm such an overflow of the adhesive 6a.

[0030] (Embodiment 2) FIGS. 8 and 9 are diagrams showing the structure of the MEMS device according to the second embodiment. FIGS. 1 to 7 are diagrams of the MEMS device 1 individually cut out (extracted) as described above. On the other hand, FIGS. 8 and 9 are diagrams of the configuration of the droplet ejection head of an inkjet printer. FIG. 8 is a front view of the actuator substrate 30, and FIG. 9 is a rear view of the sub-frame substrate 50. Therefore, after the piezoelectric element 2 and the like are mounted on the actuator substrate 30 in FIG. 8, the sub-frame substrate 50 in FIG. 9 is to be bonded with the surface turned over.

[0031] In the example of FIG. 8, for the sake of simplifying the drawing, on the actuator substrate 30, the mounting portions 30a to which the piezoelectric elements 2 are die-bonded are formed in 4 rows × 10 columns. Correspondingly, in the example of FIG. 9, an example is shown in which on the sub-frame substrate 50, the storage spaces 52 are formed in 4 rows × 10 columns. The portions of those mounting portions 30a and storage spaces 52 serve as the movable portions, wiring portions, etc. of the MEMS device (piezoelectric element 2), and pad portions 30b, etc. are formed at the peripheral portions.

[0032] And in the present embodiment, the opening window 51b is not provided in an individual MEMS device, but is provided in the empty space excluding the movable portion, wiring portion, and pad portion 30b. Therefore, the adhesion status of individual devices, particularly the seepage (oozing out) of the adhesive 6a as shown in FIG. 2, etc. cannot be confirmed. However, actually, this large actuator substrate 30 and sub-frame substrate 50 are made on a wafer of several tens of cm, and several tens of them are further fabricated collectively, and processes such as bonding are also handled while the wafers are intact. Therefore, regarding the misalignment of alignment in particular, it is sufficient to check only a part.

[0033] The technical idea understandable from the present disclosure is described in the following appendices. Note that, not with the intention of limitation, for the assistance of understanding, the reference numerals of the corresponding components in the embodiments are attached to the components described in the appendices. The reference numerals are shown as examples for the assistance of understanding, and the components described in each appendix should not be limited to the components indicated by the reference numerals.

[0034] <Appendix 1> The MEMS devices 1, 1a, 1b, 1c, 1d described in Appendix 1 are MEMS devices 1, 1a, 1b, 1c, 1d formed by bonding another substrate (5) to one substrate (3). In the other substrate (5), an opening window 51 is provided, and through the opening window 51, an index (2) for bonding in one substrate (3) can be visually recognized.

[0035] According to the above configuration, in the MEMS device 1 formed by bonding another substrate (5) to one substrate (3), by providing the opening windows 51 and 51a in the other substrate (5), the state of bonding with the one substrate (3) can be visually recognized. The state of the bonding can be confirmed by visually recognizing the predetermined indicators (alignment patterns) (2, 2a, 33c, 31d) on the one substrate (3). The predetermined indicators include components mounted on the one substrate (3) such as mechanical element parts, sensors, and actuators (2, 2a), patterns of electronic circuits, or marks (33c) formed so as not to functionally interfere with the one substrate (3).

[0036] Then, by visually recognizing these indicators (2, 2a, 33c, 31d) through the opening window 51, misalignment of alignment and the like can be confirmed. Therefore, the state of bonding of the substrates (3, 5) can be confirmed with high precision using low-cost and simple equipment with visible light. Also, even when a large number of devices (1, 1a, 1b, 1c, 1d) are batch-produced on the substrate (3) and later separated individually, the indicators (2, 2a, 33c, 31d) remain, so the state of bonding can be confirmed at an arbitrary time point for each individual device (1, 1a, 1b, 1c, 1d), and the yield can be improved.

[0037] <Appendix 2> The MEMS devices 1, 1a, 1b described in Appendix 2 are the MEMS devices 1, 1a, 1b described in Appendix 1, in which one substrate (3) is the actuator substrate 3 and the other substrate (5) is the sub-frame substrate 5.

[0038] According to the above configuration, among MEMS devices, since the actuator device handles relatively large energy, it is easily damaged due to defects in the bonding of the substrates 3 and 5. Therefore, the present MEMS devices 1, 1a, 1b are suitable for actuator devices.

[0039] <Appendix 3> The MEMS devices 1, 1a, 1b described in Supplementary Note 3 are the MEMS devices 1, 1a, 1b described in Supplementary Note 2, wherein the actuator substrate 3 mounts the piezoelectric element 2, and the sub-frame substrate 5 is joined to the actuator substrate 3 so as to form an internal space 52 for accommodating the piezoelectric element 2 on the mounting surface of the piezoelectric element 2 of the actuator substrate 3, and the indicators (2, 2a) are predetermined marks attached to the piezoelectric element 2 itself or the top surface of the piezoelectric element (the surface opposite to the surface mounted on the actuator substrate, the surface exposed to the internal space 52).

[0040] According to the above configuration, when visually recognizing the indicators (2, 2a) provided on one substrate (3) from the opening window 51 formed in the other substrate (5), when the actuator substrate 3 as one substrate (3) mounts the piezoelectric elements 2, 2a, the piezoelectric elements 2, 2a themselves or the predetermined marks attached to the top surface 24 of the piezoelectric elements 2, 2a are used as the indicators (2, 2a). That is, by looking through the opening window 51, it is confirmed whether there is misalignment in alignment or the like based on whether those piezoelectric elements 2, 2a or marks are positioned within the specified ranges (W1, W2).

[0041] Therefore, as the indicators (2, 2a) for confirming the bonding state of the substrates (3, 5), it can be realized with a simple configuration without providing separate components.

[0042] <Supplementary Note 4> The MEMS devices 1, 1a, 1b described in Supplementary Note 4 are the MEMS devices 1, 1a, 1b described in Supplementary Note 2, wherein the actuator substrate 3 and the sub-frame substrate 5 are joined with an adhesive 6, and the indicator is the seepage (6a) of the adhesive from the bonding portion.

[0043] According to the above configuration, when visually recognizing the indicator provided on one substrate (3) from the opening window 51 formed in the other substrate (5), when the substrates (3, 5) are joined with the adhesive 6, the seeped (overflowed) adhesive 6a from the bonding portion is used as the indicator.

[0044] Therefore, as an index (6a) for checking the state of bonding of substrates 3 and 5, it is possible to check for bonding defects without providing separate components.

[0045] <Appendix 5> The droplet ejection head (1) described in Appendix 5 includes the MEMS device 1 described in any one of Appendices 1 to 4, a pressure chamber substrate 32 that forms an ink storage space (42) on a surface of the actuator substrate 3 opposite to the mounting surface of the piezoelectric element 2, and a nozzle substrate 4 that closes the pressure chamber substrate 32 and is provided with droplet ejection holes 41.

[0046] According to the above configuration, in a droplet ejection head (1) mounted on an inkjet printer, a large number of actuators (2) are formed. Conventionally, however, it has not been possible to check the bonding portions of all the actuators by, for example, checking the marks of the bonding portions formed typically on the outer periphery of the substrates (3, 5).

[0047] Therefore, by applying the present disclosure that can check the bonding portions of individual actuators (1), the yield of the droplet ejection head (1) can be improved, and the reliability can be improved and the performance can be stabilized.

[0048] <Appendix 6> The inkjet printer described in Appendix 6 includes the droplet ejection head (1) described in Appendix 5.

[0049] According to the above configuration, it is possible to realize an inkjet printer that can improve reliability and stabilize performance.

Explanation of Reference Numerals

[0050] 1, 1a, 1b, 1c, 1d MEMS devices 2, 2a Piezoelectric elements 21 Piezoelectric body 22, 23 Electrodes 24 Top surface 3 Actuator substrate 30 Actuator substrate 30a Mounting portion 30b Pad portion 31 Diaphragm 31d Contact pattern 32 Pressure chamber substrate 33 Passivation film 33c Pattern 4 Nozzle substrate 41 Droplet ejection hole 42 Pressure chamber (accommodation space) 5, 5a Sub-frame substrate 50 Sub-frame substrate 51, 51a Opening window 52, 52a Storage space 6, 6a Adhesive

Claims

1. In a MEMS device formed by bonding another substrate to one substrate, the other substrate is provided with an opening window, and the opening window enables visual recognition of an index for the bonding on the one substrate. A MEMS device.

2. The MEMS device according to claim 1, wherein the one substrate is an actuator substrate and the other substrate is a sub-frame substrate.

3. The actuator substrate mounts a piezoelectric element, the sub-frame substrate is bonded to the actuator substrate so as to form an internal space for accommodating the piezoelectric element on the mounting surface of the piezoelectric element of the actuator substrate, and the index is the piezoelectric element itself or a predetermined mark attached to the top surface of the piezoelectric element. The MEMS device according to claim 2.

4. The actuator substrate and the sub-frame substrate are bonded with an adhesive, and the index is the exudation of the adhesive from the bonding portion. The MEMS device according to claim 2.

5. The MEMS device according to claim 3, a pressure chamber substrate that forms an ink accommodation space on a surface of the actuator substrate opposite to the mounting surface of the piezoelectric element, and a nozzle substrate that closes the pressure chamber substrate and is provided with droplet discharge holes. A droplet discharge head.

6. An inkjet printer including the droplet discharge head according to claim 5.

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