Patent Application
20250065623
The present disclosure relates to liquid ejection heads.
One example of functional devices such as MEMS (Micro Electro Mechanical System) including pressure sensors and acceleration sensors, and microfluidic devices is a liquid ejection head of ejecting liquid. The liquid ejection head is also referred to as an inkjet recording head or a liquid jetting head, and is used for a printing apparatus of doing printing by ejection of liquid. In production of these devices, devices formed of joined substrate bodies which are substrates joined via organic films (adhesive) are produced. For stability in ejection of the liquid ejection head, and for improvement in appearance of print, mechanisms for circulating ink in the head have been often provided in recent years.
Japanese Patent Application Publication No. 2014-124887 proposes the method of forming a protective film for substrates joined via an organic film (adhesive) as a method of reducing damage to a joined substrate caused by ink.
As described, it is demanded to further improve the stability in ejection, and the appearance of print of the liquid ejection head which uses a joined substrate. Therefore, particularly, preferred protection for ink channels is demanded.
The present invention was made with the foregoing problem in view, and an object thereof is to provide a technique for protecting ink channels formed inside the liquid ejection head which uses a joined substrate.
The present invention provides a liquid ejection head comprising:
According to the present invention, the technique for protecting ink channels formed inside the liquid ejection head which uses a joined substrate can be provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter preferred embodiments of the technique in the present disclosure will be described with reference to the drawings. The dimensions, the materials, the shapes, the relative arrangements, etc. of the components described below should be changed appropriately according to the structure of an apparatus to which the invention is applied, and according to various conditions. The embodiments are thus not construed as limiting the scope of this invention to the following description. Any well-known or known art in this technical field may be applied to configurations and steps not particularly shown or described. Redundant descriptions may be omitted.
These embodiments describe joining of three substrates as an example. The present invention is however not limited to this, and is also applicable to joining of a plurality of substrates.
Here, the problem about conventional liquid ejection heads that was found by the inventor will be described. The inventor found that upon circulating ink in ink channels in a liquid ejection head which uses a joined substrate, bubbles adhere to areas of poor wettability when materials of different levels of wettability, such as a protective film and an adhesive, are present in a mixed manner on the inside of the ink channels. In addition, in the liquid ejection head, the inner wall surfaces of the ink channels tend to be eroded by ink, and the structure of the channels may decay if having been exposed to ink for a long time. Particularly, when the substrate is silicon, such damage by ink tends to occur.
Japanese Patent Application Publication No. 2014-124887 as described above proposes the method of forming a protective film for substrates joined via an organic film (adhesive) as a method of reducing damage to the substrates caused by ink. According to the inventor's studies, however, it was found that when a protective film is formed throughout the inner wall surfaces of the ink channels, and an organic film (adhesive) as Japanese Patent Application Publication No. 2014-124887, bubbles adhere, and the ink flow is impeded on any corner part of joining parts of the substrates. Remaining of bubbles like this leads to bad ink ejection, which may deteriorate the appearance of print.
Then, as a result of the inventor's studies, it was found out that gathering of bubbles, and impeding of the ink flow can be suppressed by providing corner parts in the ink channels with R's, and by equating the wettability on the inside of the ink channels. This can improve the efficiency in circulation of ink to improve the appearance of print. The following embodiments specifically describe such a structure of the invention of the present application.
Hereinafter substrates for a liquid ejection head according to embodiment 1 of the present invention will be described with reference to the drawings. This embodiment shows an example of using piezoelectric elements as energy generating elements. The present invention is however not limited to this, but is applicable to joining of substrates having elements which can boil ink by electric heating, such as heating elements. An example of a liquid ejection head to which the present invention is applicable is a member of a printing apparatus such as an inkjet printer. The printing apparatus is also provided with a liquid storing part of storing liquid to be fed to the liquid ejection head, a conveying mechanism for recording media for doing printing, etc.
The first substrate 1 is formed of, for example, a silicon substrate, and first openings 7a forming the ink channels 7 are formed therein. The second substrate 2 is formed of, for example, a silicon substrate, and has a vibrating film 11 on which the piezoelectric elements 5 are formed. The vibrating film 11 forms the ceilings of pressure chambers 10 to separate a plurality of the pressure chambers 10. Further, second openings 7b communicating with the first openings 7a to form the ink channels 7 which are for introducing liquid into the pressure chambers 10 are formed in the second substrate 2. The third substrate 3 is formed of, for example, a silicon substrate, and the ejection ports 8 via which liquid is ejected are formed therein. The ejection ports 8 penetrate the third substrate 3. When the pressure chambers 10 are viewed from the third substrate side, the side of a face which faces the pressure chambers 10, and the side of a face on the opposite side of the pressure chambers 10 communicate by means of the ejection ports 8. Therefore, the volume change in any of the pressure chambers 10 causes the liquid stored in the pressure chamber 10 to be ejected via the ejection port 8.
On the first substrate 1, an ink tank (not shown) is disposed. Therefore, the liquid in the ink tank is fed to the pressure chambers 10 through the first openings 7a.
On the vibrating film 11, the piezoelectric elements 5 are disposed to constitute piezoelectric actuators. The piezoelectric elements 5 are provided with lower electrodes (not shown) formed on a vibrating film formation layer, the piezoelectric elements 5 formed on the lower electrodes, and upper electrodes (not shown) formed on the piezoelectric elements. On the vibrating film 11, the electrodes 6 for external connection are also disposed.
The piezoelectric elements 5 are formed at positions facing the pressure chambers 10 across the vibrating film 11. That is, the piezoelectric elements 5 are formed so as to be in contact with a surface of the vibrating film 11 which is on the opposite side of the pressure chambers 10. It is characteristic of the vibrating film 11 to be deformable in a direction opposite to the pressure chambers 10. As shown, a protective film 18 may be provided on the second substrate 2. The protective film 18 is made from, for example, SiN, and has the function of protecting wiring layers, the piezoelectric elements, etc. In the following description, the protective film 18 provided on the second substrate 2 is considered to be part of the second substrate 2. That is, when the adhesive 4 is applied, the second substrate 2 and the protective film 18 form one body, and thus, based on this state, the boundary of the first substrate 1 and the second substrate 2 is determined.
Applying a driving voltage to the piezoelectric elements 5 from a driving IC (not shown) through wiring deforms the piezoelectric elements 5 by the inverse piezoelectric effect. This deforms the vibrating film 11 together with the piezoelectric elements 5, which brings about volume changes in the pressure chambers 10 to pressurize the liquid such as ink. The pressurized liquid is ejected via the ejection ports 8 in the form of microdroplets.
Next, joining of the first substrate 1 and the second substrate 2 according to the present invention will be described in detail. In the present invention, an example for the first substrate 1 and the second substrate 2 is shown, but the present invention is not limited to this. The present invention may be applied to the second substrate 2 and the third substrate 3, and when the number of the substrates is larger, may be applied to these substrates.
The expression of an arc is used because, in many cases, the surfaces become curved lines on cross sections thereof due to a characteristic of the adhesive 4 such that the adhesive 4 has flowability to some extent, whereas the surface is not necessary to be formed by a curved line only on the cross section as long as the surface is inside the line D1-D2 as descried above, and for example, may be a straight line and a curved line in combination. The part of the curved line may be a circular arc, an elliptical arc, or any other curved line. Any shape of the surface of the adhesive 4 brings about the effect to some extent as long as the shape does not rise more than the line D1-D2, but is depressed on the cross section.
In contrast,
For forming the openings which are formed through the substrates, a processing method such as dry etching and wet etching, or a processing method using a laser is used. The top views of
Further,
In any cases, it is important to form the adhesive inside the straight line formed by D1 and D2 as shown in
As described above, when the adhesive 4 stays inside the space held between the substrates, the effect of the present invention is not obtained. On the contrary, however, extreme spread of the adhesive 4 out of the space held between the joined substrates may clog the ink channels 7 formed on the joining faces, and/or may spread across the second openings where the piezoelectric elements are stored to influence ejection. Thus, the adhesive 4 is preferably of a type not having excessive flowability, and the applying amount thereof is necessary to be proper.
Here, a direction where the substrates are layered is defined as a layering direction (Z-direction in the drawings), a direction which crosses the layering direction, and where the substrates extend is defined as an extending direction (X-direction in the drawings), and a direction which crosses the layering direction and the extending direction, and where the end faces of the substrates are continuous in the opening parts (for example, a direction where the first substrate 1 forms the boundary with the first openings 7a) is defined as an end face direction (Y-direction in the drawings). The inventor found out that in the present invention, the distance (D2) of the concave part 4k of the adhesive 4 in the layering direction, and the distance (D1) thereof in the extending direction, where the substrates extend, is each preferably at least 3 μm and not more than 20 μm, and more preferably at least 5 μm and not more than 15 μm. In the case of
In the joined substrate 80, the areas where electrode pads or piezoelectric elements are formed, and the areas where the ink channels 7 are formed may be adjacent to each other via the substrates. For example, in
Thus, a method of appropriately spreading the adhesive 4 across desired positions is considered.
As shown in
As shown in
Next, a series of the steps of making the joined substrate 80 will be described. These steps start from the stage of producing the ink channels 7, the pressure chambers 10, the grooves 15, the electrode storing parts 16, etc. on the first substrate 1 to the third substrate by known methods such as etching and lithography in combination, and disposing the piezoelectric elements 5, the electrodes 6, wiring not shown, etc.
Silicon is preferable as the material of the first substrate 1, the second substrate 2 and the third substrate 3. Other than silicon, silicon carbide, silicon nitride, any of various glasses (silica glass, borosilicate glass, alkali-free glass, and soda-lime glass), any of various ceramics (alumina, gallium arsenide, gallium nitride, and aluminum nitride), or a resin may be used. For example, the first substrate 1 and the second substrate 2 are each set to have a thickness of 625 μm. The first openings 7a of the first substrate 1, and the second openings 7b of the second substrate 2 are formed at positions so as to communicate with each other after the joining to form the channels 7.
Lower electrodes (not shown), the piezoelectric elements 5 on the lower electrodes, and upper electrodes (not shown) on the piezoelectric elements are formed on the vibrating film formation layer of the first substrate 1. In the electrode storing parts 16, the electrodes 6 are formed. For example, the vibrating film formation layer is formed by plasma CVD. Next, hydrogen barrier films (not shown), the lower electrodes (not shown), piezoelectric body films, and the upper electrodes (not shown) are formed in order. For example, the lower electrodes and the upper electrodes are formed by sputtering, and the piezoelectric body films are formed by the sol-gel process, but may be formed by sputtering.
A PZT (lead zirconate titanate) film formed by, for example, the sol-gel process or sputtering can be applied for each of the piezoelectric elements 5. Such a piezoelectric element 5 is formed of a sintered compact of a metal oxide crystal. An actuator substrate can be formed by forming the interlayers, and wiring (not shown) so that an actuator unit can be driven.
In the second substrate 2, the pressure chambers 10 and the grooves 15 are formed by sputtering. The protective film 18 may be provided between the substrates. As shown in
The adhesive 4 is formed in a direct write manner by dispensing, or by patterning by photo lithography or the like. Because the wettability of the joining interface for the adhesive is also important, the substrates before joined may be surface-treated with oxygen plasma or the like. Examples of other methods of applying the adhesive 4 include a transfer method, screen printing, and dispensing application which use glass or PET as a base material. The thickness of the organic film is not particularly limited, but is preferably 0.1 μm to 10 μm, and more preferably 1 μm to 5 μm.
As the adhesive 4, any material with high adhesiveness to the substrates is preferably used. Any material with inclusion of less bubbles etc., and powerful application properties are preferable, and any material having such a low viscosity that the thickness of the adhesive is easily reduced are also preferable. The adhesive preferably contains any resin selected from the group consisting of epoxy resins, acrylic resins, silicone resins, benzocyclobutene resins, polyamide resins, polyimide resins, and urethane resins. Examples of the system of curing of the adhesive 4 include a heat curing system, and an ultraviolet delayed curing system. When any of the substrates is ultraviolet transparent, an ultraviolet curing system may be also used.
Here, one example of the transfer method will be shown. First, a base material for transferring the adhesive is prepared, and is spin-coated with a benzocyclobutene solution as the adhesive 4, so that the adhesive 4 is 3 μm. A PET film is used as the base material for the transfer. After the coating, baking is performed for five minutes at 100° C. for volatilizing a solvent. The adhesive 4 formed on the base material for the transfer is brought into contact with the joining face of the first substrate 1 while heating, and thereby, the adhesive 4 is transferred to the first substrate 1.
The first substrate 1 where the adhesive 4 is formed, and the second substrate 2 are heated to a predetermined temperature inside a joining device, and thereafter, pressurized for a predetermined period of time at a predetermined pressure to whereby join together. These joining parameters are properly set according to the material of the adhesive. Joining in a vacuum is preferable because inclusion of bubbles in the joining parts is suppressed. During the joining, the adhesive 4 is softened by heating, and further, pressurized, and thus, the adhesive 4 flows into the openings from the joining faces as shown in
A large amount of the degassed from the adhesive 4 in the step of forming a protective film which follows the joining step may lead to cracking or peeling of the protective film 9. Therefore, when the adhesive 4 is of a thermosetting type, the adhesive 4 may be heated inside the joining device until being cured. The curing may be accelerated by, after the joining, taking out, and separately heating the joined substrate body in an oven or the like. When the adhesive 4 is of an ultraviolet delayed type, preferably, the joining is performed after the adhesive 4 is irradiated with a prescribed quantity of ultraviolet rays in advance prior to the joining. After the joining, preferably, the joined substrate body is further heated to sufficiently accelerate the curing. When the adhesive 4 is of an ultraviolet curing type, the adhesive 4 is irradiated with a prescribed quantity of ultraviolet rays across the ultraviolet transparent substrate to be cured after the substrates are joined. After the joining, preferably, the joined substrate body is further heated to sufficiently accelerate the curing.
Here, an example of joining by heat curing when the foregoing benzocyclobutene solution is used as the adhesive 4 will be described. At this time, the first substrate 1 and the second substrate 2 are joined by heating in a vacuum while positioned using a joining alignment device. The degree of vacuum is set to be at most 100 Pa, and the temperature is set to be 150° C. The joined substrate 80 after the joining is completed is taken out of the device after cooling, and is subjected to heat treatment in an oven of a nitrogen atmosphere at 250° C. for one hour to cure the adhesive 4. At this time, the spreading width D of the adhesive 4 is 10 μm. The second substrate 2 is thinned with a grinding device until the thickness thereof reaches 100 μm. Similarly, the third substrate 3 made from silicon, and having a thickness of 625 μm is joined, and thereafter, thinned with a grinding device until the thickness thereof reaches 100 μm. The ejection ports 8 are formed through a second face of the third substrate 3 (opposite face of a face which faces the second substrate 2) to form the joined substrate 80. The joined substrate 80 as shown in
Next, as shown in
The protective film 9 contains an inorganic element, and preferably contains a simple substance, an oxide, a nitride, or a carbide of at least one element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf and Si. Among them, an oxide of at least one element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf and Si is preferably contained, and at least one compound selected from the group consisting of TaO, TiO, SiOC, SiC, SiCN, TaN, TiN and HfO is more preferably contained.
Direct formation of the protective film 9 on the organic film (adhesive 4) may cause the protective film 9 to peel by any force acting on the interface between the protective film 9 and the organic film (adhesive 4) when the adhesive force between the protective film 9 and the organic film (adhesive 4) is weak, when the rigidity of the protective film 9 is insufficient even when the adhesive force is maintained, or when both the adhesive force and the rigidity are insufficient. When the protective film 9 peels, it is considered that ink entering from the portion where the protective film 9 peeled damages the organic film (adhesive), which brings about bad joining of the substrates. It is also considered that the protective film 9 peeled to constitute foreign substances floating in the channels, which may influence ejection performance.
In view of the foregoing, desirably, the protective film 9 have a thickness to some extent or more. In contrast, too much a film thickness may cause, for example, peeling by the film stress of the protective film. Thus, the thickness is at least 50 nm and not more than 250 nm, and more preferably at least 80 nm and not more than 180 nm. The method of forming the protective film 9 may be any other method such as sputtering and CVD.
Here, an example of subjecting the joined substrate 80 produced by the foregoing heat curing method to ALD film formation will be described. At this time, a thermal ALD-TaO film is formed with an ALD film forming apparatus. At this time, the film formation cycle is as follows. A gas formed by vaporizing a substrate having Ta in a molecule thereof, and nitrogen are together conveyed into a furnace to be sprayed for 2.5 seconds, and thereafter, purging with nitrogen, and discharge are sufficiently performed. Next, a gas formed by vaporizing an oxidizing agent, and nitrogen are together conveyed into the furnace to be sprayed for 5 seconds, and thereafter, purging with nitrogen, and discharge are sufficiently performed. The above cycle, as one cycle, is repeated approximately 2000 times to layer a tantalum oxide film by 130 nm at a film formation temperature controlled to 230° C.±10° C., so that the joined substrate 80 coated with the protective film 9 is obtained. According to this, the joined substrate 80 as shown in
Next, as shown in
It was found out that using the joined substrate produced as the foregoing for the liquid ejection head can suppress gathering of bubbles, and impeding of the ink flow by providing corner parts in ink channels with R's, and by equating the wettability on the inside of the ink channels. This can improve the efficiency in circulation of ink to improve the appearance of print.
As the foregoing, using the present invention can lead to obtainment of a liquid ejection head such that bubble gathering, and impeding of the ink flow in the ink channels are suppressed by providing an adhesive which covers corner parts between joined substrates in an arcuate concave form, and providing a protective film which is continuous along the surfaces of the substrates, the channels, and the adhesive in the substrates formed by joining with the adhesive.
The method of producing the joined substrate 80 according to any of the embodiments can be used as the method of producing the liquid ejection head.
A printing element 121 in
The ink ejection substrate 124 is provided with a plurality of ink ejection ports 126 for ejecting ink. For them, the ejection ports 8 shown in embodiment 1 can be used. Ink channels 125 for introducing ink to a plurality of the ink ejection ports 126 are formed in the ink channel substrate 122. For them, the ink channels 7 shown in embodiment 1 can be used. The ink ejection energy generating substrate 123 is provided with energy generating elements (not shown) which generate energy to eject ink from the ink ejection ports 126. For supplying electricity to the energy generating elements, terminals 24 which serve as electric connection parts for electrical connection to the outside are also provided. Such a printing element 121 of the three-layered structure which has a space part 23 is obtained by the method of producing the joined substrate according to any of the embodiments.
The printing element unit 131 of
A liquid ejection head 141 of
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2023-134329, filed on Aug. 22, 2023, which is hereby incorporated by reference wherein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-134329 | Aug 2023 | JP | national |
