Recording element substrate, and inkjet head and its production method

An inkjet head includes a recording element substrate for discharging ink, a supply port penetrating the recording element substrate and serving as an ink flow path, a protrusion formed at a position surrounding the supply port, projecting from one surface of the recording element substrate, and having a first metal layer at a distal end, and a supporting member having a second metal layer welded with the first metal layer and supporting the recording element substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording element substrate, an inkjet head, and a production method of the inkjet head. More particularly, the present invention relates to the ink jet head for holding and fixing a recording element substrate to a supporting member, and a production method of the ink jet head.

2. Description of the Related Art

An inkjet recording apparatus discharges ink in a minute droplet state from a plurality of discharge ports arrayed on an inkjet head, and records an image.

Generally, as a recording element substrate provided in a inkjet head, a silicon single crystal substrate having a clipping orientation of <100> (hereinafter refereed to as a silicon substrate) is used, and the silicon substrate is provided with a discharge pressure generating element for discharging ink. Further, to supply ink to the discharge pressure generating element, a supply port is provided, which penetrates the silicon substrate, and an ink flow path is formed from the supply port to the discharge pressure generating element. The ink, by pressure applied from the discharge pressure generating element, flies from the discharge port provided in the ink flow path, impacts on a recording surface such as a printing paper, and a desired image is obtained.

A through hole corresponding to the supply port of the recording element substrate is provided in the supporting member for holding and fixing the recording element substrate, and forms an ink flow path. A protrusion is provided on a second surface of the recording element substrate which is opposite to a first surface provided with the discharge pressure generating element. A leading edge of the protrusion and the supporting member are bonded by using an adhesive.

FIG. 7is a perspective view illustrating a partially broken recording element substrate1, which discharges multi-color inks, e.g., cyan, magenta, and yellow.FIG. 8is a cross-sectional view illustrating one example state in which the recording element substrate1is fixed on a supporting member13.

InFIG. 7, supply ports10are formed on a silicon substrate2corresponding to each color, along discharge port arrays18with discharge ports12arranged in parallel. As illustrated inFIG. 8, through holes16are also formed in the supporting member13corresponding to the supply ports10. In a conventional structure of the recording element substrate, an adhesive for bonding the silicon substrate2and the supporting member13is used to seal a contact part of the supply port10and the through hole16.

In recent years, customers have demanded an inkjet recording apparatus which shows high image quality, high brilliance, and high throughput with a low price. One method for lowering the cost of the inkjet recording apparatus is to lower a production cost of the inkjet head.

One method for lowering the cost is to increase the number of a silicon substrate taken from one silicon wafer. More specifically, an interval between the supply ports is narrowed to reduce the size of the silicon substrate, so that the number of the silicon substrate taken from one silicon wafer is increased.

However, as illustrated inFIG. 8, when the interval between the supply ports is narrowed, a bonding surface between the silicon substrate2and the supporting member13becomes small, so that it becomes difficult to coat an adhesive on the bonding surface. Further, since the bonding surface does not have a sufficient area, it becomes difficult to maintain sealing reliability of the adhesive. When the sealing reliability lowers, ink leakage from the bonding surface occurs, an amount of ink discharging from the discharge ports becomes irregular, so that a recording quality may degrade. In an inkjet head discharging multi-color inks, different color inks may be mixed, so that an image quality and definition may degrade.

To solve these problems, Japanese Patent Application Laid-Open No. 11-192705 discusses a sealing method other than use of an adhesive to increase adhesive strength between the recording element substrate and the supporting member. According to the method discussed in Japanese Patent Application Laid-Open No. 11-192705, a solder bump is used to weld the recording element substrate with the supporting member and form a fluid partition wall which partitions ink flow paths of different colors. However, since the solder bump is generally formed with a pattern of several-hundred microns, the size of the solder bump causes a trouble when the boding surface of the recording element substrate and the supporting member is to be narrowed.

As a method for sealing other than the method using an adhesive or a solder, a bump can be formed in a fine pattern and the recording element substrate is welded with the supporting member. As a general technique for forming the bump, there is a metal plating method as represented by a formation of a gold bump. However, to bond the supporting member and the bump formed on the recording element substrate by the metal plating method, it is necessary to secure a flatness of the bonding surface or to form a bump which has an enough height so that the flatness is negligible.

Particularly, when the supply port and the protrusion are formed on the silicon substrate, laser processing is used. However, in such a case, chipping and burrs are generated so that flatness is lowered. Generally, planarization processing such as chemical mechanical polishing (CMP) is indispensable for increasing flatness of a bonding surface. Further, the plating needs to be performed for a long time to form a high bump. Both of the planarization processing and the forming of the high bump increase production cost in acquiring a desired configuration.

SUMMARY OF THE INVENTION

The present invention is directed to an inkjet head capable of making a bonding surface between a recording element substrate and a supporting member finer than a conventional technique without reducing sealing reliability, and a production method thereof.

According to an aspect of the present invention, an inkjet head includes a recording element substrate, a supply port, protrusion, and a supporting member. The recording element substrate is configured to discharge ink and the supply port penetrates the recording element substrate and serves as an ink flow path. The protrusion is provided at a position surrounding the supply port, projects from one surface of the recording element substrate, and includes a first metal layer. The supporting member includes a second metal layer welded with the first metal layer and supports the recording element substrate.

According to the present invention, a bonding surface of a recording element substrate and a supporting member can be more miniaturized than a conventional technique without reducing sealing reliability. Further, the inkjet head can be produced with a lower cost.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1illustrates a representative cross section of a recording element substrate1according to a first exemplary embodiment of the present invention. As illustrated inFIG. 1, the recording element substrate1includes a silicon substrate2, and a flow path forming member3for forming an ink flow path. A thermally-oxidized film6for improving corrosion-resistance is formed on a surface of the silicon substrate2which is provided with the flow path forming member3. A discharge pressure generating element4for applying discharge pressure to ink is provided on the thermally-oxidized film6. Further, a drive circuit5for driving the discharge pressure generating element4is similarly provided on the thermally-oxidized film6. The drive circuit5and the discharge pressure generating element4are electrically connected by an electric wiring.

Furthermore, a passivation film7is formed on the thermally-oxidized film6to insulate the discharge pressure generating element4and the drive circuit5from ink. The discharge pressure generating element4and the drive circuit5are embedded in the passivation film7. A space formed by the flow path forming member3and the passivation film7becomes an ink flow path11. A discharge port12is provided at a position opposing the discharge pressure generating element4of the flow path forming member3. Ink, under pressure applied by the discharge pressure generating element4, discharges from the discharge port12.

In the silicon substrate2, a supply port10for supplying ink to the ink flow path11is provided which penetrates the silicon substrate2. A protrusion8is formed on a second surface of the silicon substrate2which is positioned opposing a first surface provided with the discharge pressure generating element4. The protrusion8is made of the same material as the silicon substrate2, and continuously formed so as to surround the supply port10. A metal layer9for welding and fixing the silicon substrate2is provided at a distal end of the protrusion8. The protrusion8and the metal layer9can be formed by general photolithographic etching, and thus can be formed with a 5 to 50 μm pitch.

The protrusion8and the metal layer9can be accurately formed and arranged by performing photolithography/etching, and can be formed near the supply port10.

A material for the first metal layer9can be selected from inactive metals which are not eluted in ink, or from alloys including metals which are not eluted in ink. For example, gold or platinum can be used. A thickness of the first metal layer9should be a thickness capable of performing metal-welding, and can be selected from 500 to 30000 Å. A method for forming the metal layer9can be selected from methods which do not affect the flatness, e.g., vacuum deposition, sputtering, chemical vapor deposition (CVD), and a screen printing method. After forming the metal layer9, patterning can be performed if necessary.

According to a production method of an inkjet head described below, the protrusion8having the metal layer9has a sufficient flatness when the protrusion8is metal-bonded with another material, and do not require a bump having a high thickness like a general bump-bonding. Accordingly its production cost is low. A height of the protrusion8can be determined considering a production cost and, for example, selected from 5 to 500 μm.

The supply port10and the protrusion8are rectangle inFIG. 1, but the present invention is not limited to these shapes. For example, the supply port10and the protrusion8can have a tapered shape or a curved shape with respect to a plane of the silicon substrate2.

FIG. 2illustrates a configuration in which the protrusion8of the recording element substrate1contacts the supporting member13, and is held and fixed. A material for the supporting member13can be selected from materials having high flatness and good processability, for example, a silicon single crystal substrate and a sintered body of an inorganic compound such as alumina can be selected. The silicon single crystal substrate can have an oxidized film on a surface to improve corrosion-resistance.

The supporting member13is coated with a second metal layer14. The second metal layer14is metal-welded with the first metal layer9formed on the recording element substrate1, so that the supporting member13and the recording element substrate1are bonded.

A material for the second metal layer14can be selected from inactive metals which are not eluted in ink or alloys including metals which are not eluted in ink, similar to the first metal layer9. For example, gold or platinum can be used. A thickness of the metal layer14can be selected from 1000 to 50000 Å. Further, a method for forming the metal layer14can be selected from methods which do not affect flatness, e.g., vacuum deposition, sputtering, CVD, and a screen printing method can be selected. After forming the metal layer14, patterning can be performed if necessary.

By performing metal-welding the first metal layer9and the second metal layer14, a fluid partition wall15can be formed. The fluid partition wall15prevents ink, which passes through the supply port10and the through hole16, from flowing out from a metal-bonded portion. As for a method for metal-bonding, for example, an ultrasonic welding can be used.

A sealing material for increasing adhesive property and sealing property can be filled in a part or a whole of a space other than an opening part in which ink flows-in. The space is formed between the recording element substrate1and the supporting member13by metal-welding. The sealing material can increase adhesive strength between the recording element substrate1and the supporting member13. Further, even when ink flows-out from the bonding part of the metal layer9and the metal layer14, the sealing material can prevent the ink from flowing into the supply port10and the through hole16in which another ink passes though. Therefore, sealing reliability of the fluid partition15can be improved by filling the sealing material.

As for a method for filling a sealing material, an under filling method is properly used. Since the fluid partition wall15is formed by metal-welding, controlling a dropping amount of the sealing material becomes easy. More particularly, even when the sealing material drops a lot, the fluid partition wall15prevents the sealing material from flowing into the through hole16and the supply port10in which ink passes through.

Now, a production method of the recording element substrate1according to the first exemplary embodiment of the present invention will be described with reference toFIGS. 4A to 4H.FIGS. 4A to 4Hillustrate a cross section of the recording element substrate1in each step.

First, the silicon substrate2provided with the discharge pressure generating element4, the drive circuit5, the thermally-oxidized film6, the passivation film7, and the flow path forming member3are prepared. At this stage, the supply port10and the protrusion8which are illustrated inFIG. 1are not formed in the silicon substrate2.

In step1, as illustrated inFIG. 4A, the first metal layer9is formed on the second surface of the silicon substrate2. The first metal layer9can be formed by a vacuum film formation technology, such as vacuum deposition, sputtering, or CVD.

In step2, as illustrated inFIG. 4B, patterning is performed on the first metal layer9. As for the patterning method, masking using a photoresist, forming an opening at a position of the metal layer9to be removed, by exposing/developing, etching the opening by an etching method corresponding to the metal layer9, and removing the photoresist are carried out. The etching method depends on the metal layer9. For example, when the metal layer9is made of gold, wet etching is performed using a solution of iodine and a potassium iodide. Further, a desired pattern can be obtained with high accuracy by photolithography/etching of the metal layer9.

In step3, as illustrated inFIG. 4C, a resist14is coated to form the supply port10on the second surface of the silicon substrate2provided with the metal layer9. At this time, the metal layer9patterned in step2is embedded in the resist14. The resist14is selected depending on etching/masking property for forming the supply port10and embeddable property of the metal layer9. For the purpose of easy handling, a liquid photo-resist capable of spin-coating or a dry film resist previously formed in a sheet shape can be properly used.

In step4, as illustrated inFIG. 4D, an opening15is formed at a desired position where the supply port10of the resist14is formed in step3, and the silicon substrate2is exposed. When a material having photosensitivity like the aforementioned photo-resist or the dry film resist is used as the resist14, the opening part15can be formed by exposing/developing and positioned with high accuracy.

In step5, as illustrated inFIG. 4E, the supply port10is formed from an exposure part of the silicon substrate2, that is, the opening part15of the resist14. A forming method can be selected depending on a shape of the supply port10to be formed. For example, reactive ion etching (RIE), chemical dry etching (CDE), crystal anisotropy etching, and other wet etchings can be used. As for the forming method of the supply port10inFIG. 4E, a dry etching method, so-called a Bosch process, in which the silicon substrate2is removed by repeating a deposition step and an etching step is used and the supply port10is vertically formed with respect to the silicon substrate2.

In step6, as illustrated inFIG. 4F, the resist14is removed. As for a method for removing the resist14, a separating liquid corresponding to the selected resist14is used. Further, the resist14can be removed by dry etching using a gas mainly including O2.

In step7, as illustrated inFIG. 4G, entire surface etching is performed from the second surface of the silicon substrate2coated with the metal layer9. In this etching, since the metal layer9acts as an etching mask, the portion of the silicon substrate2just under the metal layer9is not etched. Therefore, a portion of the silicon substrate2just under the metal layer9retains an original thickness, and the protrusion8illustrated inFIG. 4Gis formed. The distal end of the protrusion8has very good flatness because the flatness of the silicon substrate2remains. The etching method depends on a desired shape. For example, RIE, CDE, crystal anisotropy etching, or other wet etchings can be used.

Since the entire surface etching is performed in step7, an all silicon substrate2does not need to be removed when the supply port10is formed in step5as illustrated inFIG. 4E. More specifically, half-etching is performed in step5, the remaining silicon substrate2is removed by entire surface etching in step7, and the supply port10penetrating the silicon substrate2is formed. By taking these steps, over-etching of the supply port10can be suppressed.

Then, the thermally-oxidized film6and the passivation film7which are positioned at the supply port10, are removed by RIE, so that the supply port10and the ink flow path11are connected.

Finally, in step8, as illustrated inFIG. 4H, metal-bonding of the first metal layer9remaining at the distal end of the protrusion8of the silicon substrate2and the second metal layer14provided on the supporting member13is carried out, and the silicon substrate2is held and fixed to the supporting member13. As aforementioned, since the protrusion8having the first metal layer9has sufficient flatness for metal-bonding, the silicon substrate2and the supporting member13can easily bond each other in a large area even though there is not a structure for absorbing height difference such as the bump.

According to the inkjet head produced by the aforementioned steps of the exemplary embodiment of the present invention, the protrusion8can be formed while keeping the flatness with fine patterning. Sufficient sealing reliability is obtained by metal-welding even when a boding surface is miniaturized, and ink infiltration is reduced. Since the protrusion8can be formed with high positional accuracy, the protrusion8can be formed near the supply port10, so that the recording element substrate1can be miniaturized.

FIG. 3illustrates an inkjet head having a through electrode according to a second exemplary embodiment of the present invention. The recording element substrate1illustrated inFIG. 3includes a through electrode16electrically connecting to the drive circuit5of the discharge pressure generating element4provided in the silicon substrate2. The through electrode16penetrates the silicon substrate2, and is exposed in a surface having the protrusion8.

According to the configuration and production method of the second exemplary embodiment of the present invention, a connection of the trough electrode16to a wiring layer17provided on the supporting member13can be collectively performed together with the meta-bonding of the first metal layer9and the second metal layer14. The wiring layer17formed in the supporting member13can be a metal generally used for wiring and, for example, aluminum or gold is preferable. At this time, if the same material as the second metal layer14is used for the wiring layer17, the wiring layer17and the second metal layer14can be simultaneously formed.

The production method of the recording element substrate1provided with the through electrode16according to the second exemplary embodiment of the present invention will be described below with reference toFIGS. 5A to 5H. Detailed descriptions for a processing method will be omitted because the method is similar to the first exemplary embodiment.

The silicon substrate2is prepared which is provided with the discharge pressure generating element4, the drive circuit5, the thermally-oxidized film6, the passivation film7, and the flow path forming member3, and includes the through electrode16. The through electrode16electrically connects to the drive circuit5provided in the silicon substrate2. At this stage, the supply port10and the protrusion8which are illustrated inFIG. 3are not formed in the silicon substrate2.

In step1, as illustrated inFIG. 5A, the first metal layer9is formed on the second surface of the silicon substrate2opposing the first surface provided with the discharge pressure generating element4. In step2, as illustrated inFIG. 5B, patterning of the first metal layer9is performed. When the through electrode16is made of the same kind of metal as the metal layer9and the through electrode16is also removed by etching the metal layer9, a portion where the through electrode16exists needs to be masked.

In step3, as illustrated inFIG. 5C, the resist14for forming the supply port10is provided on the surface of the silicon substrate2coated with the metal layer9. At this time, the metal layer9patterned in step2and the through electrode16are embedded under the resist14. In step4, as illustrated inFIG. 5D, the opening15of the resist14formed in step3is made at a desired position where the supply port10is formed. In step5, as illustrated inFIG. 5E, the supply port10is formed from the opening15of the resist14. In step6, as illustrated inFIG. 5F, the resist14is removed.

In step7, as illustrated inFIG. 5G, entire surface etching is performed from the second surface of the silicon substrate2coated with the metal layer9. At this time, since the metal layer9acts as an etching mask, the protrusion8illustrated inFIG. 5Gis formed. Further, since the through electrode16is not etched but the silicon substrate2is etched back, the through electrode16has a shape projecting from the silicon substrate2.

The etching method depends on a desired shape and an etching selection ratio of the metal layer9and the through electrode16. For example, RIE, CDE, crystal anisotropy etching, and other wet etchings can be used. When the through electrode16is made of gold, for example, the aforementioned Bosch process can be used.

When the entire surface is etched using the metal layer9as an etching mask, the metal layer9and the through electrode16can maintain their original thickness, the protrusion8having the first metal layer9is formed, and the through electrode16projects from the silicon substrate2. Therefore, the flatness of the protrusion8having the first metal layer9, and the through electrode16becomes very good.

Since the entire surface etching is performed in step7, all of the silicon substrate2do not need to be removed when the supply port10is formed in step5. More specifically, half-etching can be performed in step5, the remaining silicon substrate2is removed by the entire surface etching in step7, and the supply port10is formed. By taking these steps, over-etching of the supply port10can be reduced.

Then, the thermally-oxidized film6and the passivation film7positioned at the supply port10are removed by RIE, and the supply port10is connected to the ink flow path11.

In step8, as illustrated inFIG. 5H, the protrusion8having the first metal layer9and the through electrode16are formed by etching back the silicon substrate2. Further, the metal layer14and the wiring layer17, which are formed on the supporting member13, are bonded. As aforementioned, since the protrusion8having the first metal layer9and the through electrode16have sufficient flatness for metal-bonding, the silicon substrate2and the supporting member13can be easily bonded in a large area even if there is not a structure for absorbing step-height such as a bump.

According to the inkjet head produced by the steps of the exemplary embodiment of the present invention, the protrusion8can be formed while maintaining the flatness with a fine pattern. Further, sufficient sealing reliability can be obtained by metal-welding even when a bonding surface is minute, and ink infiltration can be reduced. Since the protrusion8can be formed with high positional accuracy, the protrusion8can be formed near the supply port10, and the recording element substrate1can be miniaturized. Simultaneously, an electrical connection of the through electrode16and the wiring layer17can be achieved.

A production method of the inkjet head according to the first exemplary embodiment of the present invention will be described in detail below by a first example using reference toFIGS. 6A to 6H.

A single crystal silicon wafer having a basic thickness of 300 μm and an ingot pulling-out orientation of <100> was prepared as the silicon substrate2.

As illustrated inFIG. 6A, the thermally-oxidized film6is formed on one surface of the silicon substrate2, and, and the discharge pressure generating element4and the drive circuit5which drives the discharge pressure generating element4, are arranged on the thermally-oxidized film6. After forming the passivation film7for insulating ink from the discharge pressure generating element4and the drive circuit5, the flow path forming member3having the discharge port12is provided on the passivation film7.

As illustrated inFIG. 6B, the metal layer9is formed on the second surface of the silicon substrate2opposing the first surface provided with the discharge pressure generating element4. Gold is used as a material for the metal layer9, and the metal layer9is formed by vacuum deposition to obtain a film in thickness of 2000 Å.

A positive type photoresist14is spin-coated on the metal layer9, pattering is performed to have a desired pattern by exposing/developing, and the gold layer is wet-etched. For a gold etching liquid, a mixed solution of iodine and potassium iodide (AURUM-302, produced by KANTO CHEMICAL CO. INC.) was used. The processed silicon substrate2was dipped for 5 minutes in the gold etching liquid at 30° C., taken out from the gold etching liquid, well washed with water, dried, the photo resist14was exfoliated, and a configuration illustrated inFIG. 6Cwas obtained.

The positive type photo resist14was coated again on the surface of the silicon substrate2covered with the metal layer9, and the patterned metal layer9was coated with the photo resist. The patterning was performed on the photo resist14and the photo resist in a portion for forming the supply port10was opened. The etching of the silicon substrate2was started from the opening, etching was performed by 270 μm in a thickness direction of the silicon substrate2. Then, the etching was stopped, and a configuration illustrated inFIG. 6Dwas made. The silicon substrate2was dry-etched using an inductively coupled plasma (ICP) etching device (not illustrated). SF6 gas and C4F8 gas were used as etching gasses, and the Bosch process was implemented which alternatively performs an etching step and a deposition step.

Then, the positive resist was exfoliated as illustrated inFIG. 6E.

To remove the remaining silicon substrate2at the supply port10, an entire surface of the silicon substrate2coated with the metal layer9, was dry-etched by the Bosch process. As a result, as illustrated inFIG. 6F, etching did not proceed at the portion where the metal layer9which acts as a mask existed. As a result, the protrusion8was formed on the surface of the silicon substrate2coated with the metal layer9. By this process, the protrusion8having the metal layer9which shows very good flatness was formed. The etching of the supply port10was stopped at the thermally-oxidized film6of the silicon substrate2.

Then, as illustrated inFIG. 6G, the thermally-oxidized film6and the passivation film7were removed, which were positioned at the supply port10, by RIE, and the supply port10and the ink flow path11were connected. Then, the wafer was diced to be a small piece.

On the other hand, the supporting member13made of alumina was prepared, a gold paste was printed on a desired portion to have a thickness of 1 μm by screen printing, and sintered, so that the metal layer14is formed. Then, the metal layer14of the supporting member13and the metal layer9of the silicon substrate2which was diced to be a small piece were metal-welded by ultrasonic welding.

Finally, the sealing material19was filled in a portion other than a fluid flow path in which a fluid (ink) flows, by an under filling method. Then, the sealing material19was baked, and the inkjet head having the fluid partition wall illustrated inFIG. 6Hwas completed.

The present invention can be applied to an inkjet head mounted in an inkjet recording apparatus which records an image by discharging inks having predetermined color phases as minute droplets, on a desired position of a recording paper.

This application claims priority from Japanese Patent Application No. 2009-174178 filed Jul. 27, 2009, which is hereby incorporated by reference herein in its entirety.