Patent Publication Number: US-7901064-B2

Title: Ink jet recording head with ink filter formed of a plurality of stacked films

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet recording head and manufacturing method thereof, and more particularly to an ink jet recording head provided with a filter preventing foreign matters from entering an ink flow path. 
     2. Description of the Related Art 
     The structure of a typical ink jet recording head will be described with reference to  FIG. 8A . In the ink jet recording head illustrated in  FIG. 8B , ink is discharged in an orthogonal direction relative to a discharge energy generating element  50  which generates energy for discharging ink. 
     Recently, in order to implement further downsizing and higher density of ink jet recording heads, there has been proposed a method of incorporating by use of a semiconductor manufacturing technique an electrical control circuit for driving the discharge energy generating elements into a substrate. The ink jet recording head illustrated in  FIG. 8A  is one manufactured by such technique. More specifically, in the substrate  51  illustrated in  FIG. 8A , there are also incorporated an electrical control circuit (not illustrated) for driving the discharge energy generating elements  50 , and other components. 
     Further, in order to supply ink to a plurality of ink discharge ports  52  through which ink is discharged, an ink flow path  53  is formed for each ink discharge port  52 ; and these ink flow paths  53  communicate with a common ink supply opening  54  formed in the substrate  51 . The ink supply opening  54  extends through the substrate  51 ; and ink is supplied from the rear face side of the substrate  51  through the ink supply opening  54  to each ink flow path  53 . When an Si substrate is used as the substrate  51 , the ink supply opening  54  can be formed using an Si anisotropic etching technique (refer to U.S. Pat. No. 6,139,761). 
     Here, factors of reliability required of an ink jet recording head include one that printing failure ascribable to non-discharging (ink is not discharged from the particular nozzle) caused by nozzle blockage hardly occurs. As the typical reasons for occurrence of such printing failure, there are thought to be cutoff, etc., of ink to be supplied to the interior of the nozzle caused by solidification and dust entering the nozzle. Further, details of the latter reason are roughly classified as follows: (1) dust and foreign matters enter the nozzle during the ink jet recording head manufacturing process; or (2) dust and foreign matters come from the outside into the nozzle after the ink jet recording head manufacturing (during its use). 
     Particularly, regarding concern about the above reason (2), it is highly likely that when the ink supply system has a configuration separable from the ink jet recording head, dust and foreign matters come in through a connecting portion therebetween. As one measure against such reason, for example, there has been used a method of arranging a filter in the vicinity of the ink supply opening of ink jet recording head. However, in the case where a filter is arranged in the ink supply opening, when the filter is manufactured and mounted separately from the ink jet recording head, this is not always satisfactory in terms of manufacturing cost, component cost, quality control, connection reliability between components, or the like, resulting in requests for further improvement. 
     As an invention for solving these problems, Japanese Patent Application Laid-Open No. 2000-94700 has disclosed a technique of using an anisotropic etching mask for forming an ink supply opening in a substrate (Si substrate) to thereby form a filter. More specifically, as illustrated in  FIG. 8A , a filter pattern is formed directly in a thermally-oxidized film layer  55  being the above anisotropic etching mask, and when the ink supply opening  54  is formed by anisotropic etching, a filter  56  is simultaneously formed using the thermally-oxidized film layer  55  which is an etching-resistant layer. 
     In the ink jet recording head disclosed in Japanese Patent Application Laid-Open No. 2000-94700, the filter  56  is arranged in the substrate rear face side opening portion of the ink supply opening  54 ; thus the filter  56  is exposed to the outside. 
     Consequently, during the post-process of forming the discharge energy generating element  50 , the filter is exposed to various liquids, or when conveyed within the semiconductor manufacturing apparatus, minor flaws occur therein. Also, when the ink jet recording head is mounted, it is highly likely that minor flaws occur in the filter  56 . As a result, for example, a pinhole  57  as illustrated in  FIG. 8B  occurs in the filter  56 , thus reducing production yield or deteriorating filter performance. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to make it possible to manufacture at low cost and high production yield an ink jet recording head provided with a filter capable of preventing dust or foreign matters from coming in. 
     According to an aspect of the present invention, an ink jet recording head comprises: a substrate; a plurality of ink discharge ports formed at a front face side of the substrate, and a plurality of ink flow paths communicating with the ink discharge ports; an ink supply opening extending through the substrate and communicating with the plurality of ink flow paths; and a filter formed in an opening portion of the ink supply opening arranged at the front face side of the substrate, the filter being constituted of two or more stacked films having formed therein a plurality of opening portions, wherein the stacked films are arranged with a spacing therebetween. 
     According to an embodiment of the present invention, a filter for preventing foreign matters from entering the ink flow path is formed to the substrate front face side opening portion of the ink supply opening. Therefore, the filter is not exposed to the outside of the substrate, and flaws rarely occur in the filter during the manufacturing process or the process of mounting it in a recording device. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view illustrating an exemplary ink jet recording head according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the ink jet recording head illustrated in  FIG. 1  taken along the line II-II. 
         FIG. 3  is an enlarged view of the filter illustrated in  FIG. 2 . 
         FIGS. 4A ,  4 B,  4 C and  4 D are schematic cross-sectional views illustrating part of a basic process of fabricating the ink jet recording head illustrated in  FIG. 1 . 
         FIGS. 5A ,  5 B,  5 C and  5 D are schematic cross-sectional views illustrating part of the basic process of fabricating the ink jet recording head illustrated in  FIG. 1 . 
         FIGS. 6A ,  6 B,  6 C and  6 D are schematic cross-sectional views illustrating part of the basic process of fabricating the ink jet recording head illustrated in  FIG. 1 . 
         FIG. 7  is a schematic cross-sectional view illustrating another exemplary ink jet recording head according to an embodiment of the present invention. 
         FIGS. 8A and 8B  are schematic cross-sectional views illustrating an exemplary ink jet recording head according to conventional art. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described with reference to the drawings.  FIG. 1  illustrates a schematic perspective view of an ink jet recording head according to the present embodiment; and  FIG. 2  illustrates a cross-sectional view of the ink jet recording head illustrated in  FIG. 1  taken along the line II-II. This ink jet recording head includes an Si substrate  1  and an orifice plate  3  formed on a front face  2  of the Si substrate  1 . 
     On the front face  2  of the Si substrate  1 , there are formed in parallel two lines of discharge energy generating elements each constituted of a plurality of discharge energy generating elements  4  arranged at a predetermined pitch. Though not illustrated in the drawings, in the Si substrate  1 , there are formed not only the discharge energy generating elements  4  but also various wires, drive elements for driving the discharge energy generating elements  4 , and the like. 
     In the Si substrate  1 , there is further formed an ink supply opening  5  extending through the front and rear faces of the Si substrate  1 . The ink supply opening  5  is formed by anisotropic etching using a strong alkaline solution such as TMAH or KOH, with a thermally-oxidized film layer used as a mask. 
     The orifice plate  3  is constituted of a coated photosensitive resin layer  30  and a water-repellent layer  31 . In the orifice plate  3 , there are formed ink discharge ports  6  which open immediately above each discharge energy generating element  4 , and an ink flow path  7  allowing the ink supply opening  5  and each ink discharge port  6  to communicate with each other. 
     Further, a filter  10  for preventing dust and foreign matters from entering the ink flow path  7  is formed to the substrate front face side opening portion of the ink supply opening  5 . This filter  10  is a multilayer filter including a first filter layer  12  and a second filter layer  13  stacked via a void portion  11 , and a first filter reinforcement layer  14  and a second filter reinforcement layer  15  stacked on the second filter layer  13 . 
       FIG. 3  illustrates an enlarged view of the filter  10 . In the first filter layer  12 , there are formed a plurality of fine opening portions  12   a ; and in the second filter layer  13 , there are formed a plurality of fine opening portions  13   a . Here, when the diameter of each fine opening portion  12   a  is x and the diameter of each fine opening portion  13   a  is y, a relationship x&gt;y holds. Also, the central position of the fine opening portion  12   a  agrees with that of the fine opening portions  13   a . There is concern that, when ink moves past the fine opening portions  12   a  and  13   a  of the two filter layers  12  and  13 , pressure loss (flow resistance) occurs, adversely affecting ink supply performance. However, when the central position of the fine opening portion  12   a  agrees (aligns) with that of the fine opening portions  13   a , the above pressure loss is suppressed to a minimum. The structure and manufacturing method of the filter  10  will be described later. 
     The ink jet recording head according to the present embodiment is mounted so that the orifice plate  3  faces the recording plane of a recording medium to be recorded on. Then, when pressure generated by the discharge energy generating element  4  is applied to ink (liquid) which is filled via the ink supply opening  5  into the ink flow path  7 , ink droplet is discharged from the ink discharge port  6  and attached to the recording medium to be recorded on, whereby printing is performed. According to the multilayer filter configuration of the present embodiment, even when foreign matters are picked up by the first filter  12 , since a sufficient opening diameter (x) and void portion  11  are provided therein, a necessary and sufficient quantity of ink can be supplied. 
     This ink jet recording head can be mounted in a facsimile machine having a printer, copier and communication system, an apparatus having a printer unit such as a word processor, or further an industrial recording apparatus combined with various types of processing apparatuses in a composite manner. When this ink jet recording head is used, recording can be made on various types of recording media to be recorded on, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood or ceramics. It is noted that, in the embodiments of the present invention, the term “recording” means not only a case where meaningful images such as characters and figures are formed on recording media to be recorded on, but also a case where images such as a pattern having no meaning are formed thereon. 
     First Embodiment 
     Examples of an ink jet recording head according to embodiments of the present invention will be described below.  FIGS. 4 to 6  are schematic cross-sectional views illustrating a basic process of fabricating an ink jet recording head according to an embodiment of the present invention. The Si substrate  1  illustrated in the drawings has crystal orientation &lt;100&gt;, but the crystal orientation of the Si substrate  1  is not limited to a particular crystal orientation. 
     First, as illustrated in  FIG. 4A , an Si nitride film  20  is formed on a front face  2  of the Si substrate  1 ; and the Si nitride film  20  thus formed is patterned corresponding to a pattern of the first filter layer  12 . Thereafter, as illustrated in  FIG. 4B , a thermally-oxidized film layer (Si oxidized film)  21  which is an insulating film is formed on the front face  2  of the Si substrate  1 . Subsequently, as illustrated in  FIG. 4C , the Si nitride film  20  is completely removed, whereby fine opening portions  12   a  ( FIG. 3 ) are formed to the Si oxidized film  21 . 
     Subsequently, as illustrated in  FIG. 4D , there is formed a sacrifice layer  22  attaching firmly to the front face  2  of the Si substrate  1  and to the Si oxidized film  21 . More specifically, the sacrifice layer  22  is formed through each process of photoresist coating, exposure, development, etching and photoresist removal. When these processes are performed, the fine opening portions  12   a  previously formed are once filled up with the sacrifice layer  22 . In the present embodiment, the sacrifice layer  22  was formed using Al, but this is not limited thereto as long as a material is used which dissolves in strong alkaline solution, such as TMAH or KOH, used as an anisotropic etching solution when the ink supply opening  5  ( FIG. 2 ) is later formed. 
     Subsequently, as illustrated in  FIG. 5A , there is formed a thermally-oxidized film (Si oxidized film)  23  attaching firmly to the sacrifice layer  22  and to the Si oxidized film  21  positioned in the outer side thereof. Further, on the Si oxidized film  23  thus formed, by use of processes of exposure and development, there is formed an etching mask (not illustrated) patterned after the second filter layer  13  illustrated in  FIG. 2 , and then each process of etching and photoresist removal is performed. 
     Subsequently, as illustrated in  FIG. 5B , discharge energy generating elements  4  are formed on the Si oxidized film  23 . Though not illustrated in  FIG. 5B , on the Si substrate  1 , there are also formed wires, drive elements for driving the discharge energy generating elements  4 , and the like. 
     Subsequently, there is formed an Si nitride film  24  attaching firmly to the sacrifice layer  22 , the Si oxidized film  23  and the discharge energy generating elements  4 . Further, spin coating with photoresist is performed on the Si nitride film  24  formed, and processes of exposure and development are performed, whereby an etching mask for forming the first filter reinforcement layer  14  illustrated in  FIG. 2  is formed. Thereafter, as illustrated in  FIG. 5C , processes of etching and photoresist removal are sequentially performed. 
     Subsequently, a Poly-Si layer  26  ( FIG. 5C ) formed on a rear face  25  of the Si substrate  1  is completely removed by dry etching, etc. Thereafter, as illustrated in  FIG. 5D , on the front face  2  side of the Si substrate  1 , there is formed a thermoplastic resin layer  27  which firmly attaches to the sacrifice layer  22 , the Si oxidized film  23  and the Si nitride film  24 . Also, on the rear face  25  side of the Si substrate  1 , there is formed a thermoplastic resin layer  28 . In the present embodiment, thermoplastic polyether amide was used as the thermoplastic resin layers  27  and  28 , but this is not limited thereto as long as a material is used which has resistance to ink and strong alkaline solution such as TMAH and KOH. After the thermoplastic resin layers  27  and  28  have been formed, spin coating with photoresist is performed, and processes of exposure and development are performed, whereby an etching mask for forming the second filter reinforcement layer  15  illustrated in  FIG. 2  is formed. Thereafter, processes of etching and photoresist removal are sequentially performed. 
     Subsequently, as illustrated in  FIG. 6A , there is performed spin coating with a soluble resin layer  29  which firmly attaches to the Si oxidized film  23 , the Si nitride film  24  and the thermoplastic resin layer  27 . 
     Subsequently, as illustrated in  FIG. 6B , spin coating with a coated photosensitive resin layer  30  is performed so that the layer  30  attaches firmly to the soluble resin layer  29 , and those parts of the Si nitride film  24  and thermoplastic resin layer  27  which are not covered with the soluble resin layer  29 , and then coating with a water-repellent layer  31  is performed on the coated photosensitive resin layer  30 . Thereafter, ink discharge ports  6  are patterned. 
     Subsequently, as illustrated in  FIG. 6C , the water-repellent layer  31 , the soluble resin layer  29  and the side face of the Si substrate  1  are coated with a protective layer  32  by spin coating or the like. The protective layer  32  is not limited as long as a material is used which has resistance to strong alkaline solution such as TMAH and KOH and is capable of preventing deterioration of the water-repellent layer  31 . After coating with the protective layer  32 , the thermally-oxidized film layer  33  is etched with the thermoplastic resin layer  28  used as the etching mask, whereby a silicon surface of the Si substrate  1  which becomes the anisotropic etching initiation surface is exposed. 
     Subsequently, as illustrated in  FIG. 6D , an ink supply opening  5  is formed in the Si substrate  1 . This ink supply opening  5  is formed by anisotropic etching using strong alkaline solution such as TMAH or KOH. When this anisotropic etching is performed, the Si substrate  1  and the sacrifice layer  22  ( FIG. 6C ) dissolve in the etching solution. As a result, when the anisotropic etching is completed, a first filter layer  12  composed of a part of the Si oxidized film  21  is formed together with the ink supply opening  5 . 
     Subsequently, after the protective layer  32  has been completely removed, Deep UV is irradiated on the entire surface from the water-repellent layer  31  side, and the soluble resin layer  29  is completely removed by a wet processing. As a result of completely removing the soluble resin layer  29 , a second filter layer  13  illustrated in  FIG. 2  is formed using a part of the Si oxidized film  23 . Also, a first filter reinforcement layer  14  is formed using a part of the Si nitride film  24 ; and a second filter reinforcement layer  15  is formed using a part of the thermoplastic resin layer  27 . In addition, an ink flow path  7  is also formed. From the drawings, it is evident that the second filter layer  13 , the first filter reinforcement layer  14 , the second filter reinforcement layer  15  and the ink flow path  7  are simultaneously formed when the soluble resin layer  29  is removed. 
     The Si substrate  1  formed by the above described processes is separated and cut with a dicing saw or the like, and is made into a chip, and electrical junction for allowing the discharge energy generating element  4  to be driven is made. Thereafter, a chip tank member for supplying ink is connected, whereby the main manufacturing process of the ink jet recording head is completed. 
     In the present embodiment, the first and second filter layers were formed using Si oxidized films. However, the material of the first and second filter layers is not limited to a particular one as long as a material is used which has resistance to ink and strong alkaline solution, such as TMAH and KOH, used as the anisotropic etching solution when the ink supply opening is formed. For example, instead of Si oxidized film, the first and second filter layers can also be formed using Si nitride film. 
     Also, in the present embodiment, the first filter reinforcement layer was formed using Si nitride film. However, the material of the first filter reinforcement layer is not limited as along as a material is used which has resistance to ink and strong alkaline solution such as TMAH and KOH. 
     In the present embodiment, the Si nitride film formed on the face of the Si substrate was patterned and then the thermally-oxidized film layer (Si oxidized film) was formed and thereafter the Si nitride film was removed, whereby the first filter layer was formed. However, the process of forming the first filter layer is not limited to the above one; for example, the first filter layer can also be formed by the following process. First, without forming the above Si nitride film, a thermally-oxidized film is formed on the face of the Si substrate, and then spin coating with photoresist is performed on the thermally-oxidized film. Subsequently, an etching mask for forming a pattern which becomes the first filter layer is formed and then a pattern which becomes the first filter layer is formed through processes of etching and photoresist removal. 
     Second Embodiment 
     In the first embodiment, there was described an example where the central position of the fine opening portion  12   a  of the first filter layer  12  is made to agree with that of the fine opening portion  13   a  of the second filter layer  13 . However, as illustrated in  FIG. 7 , it is also possible that the central position of the fine opening portion  12   a  is displaced from that of the fine opening portion  13   a . Also, in the example of  FIG. 7 , when the diameter of the fine opening portion  12   a  is x and the diameter of the fine opening portion  13   a  is y and the diameter of the ink discharge port  6  is z, then a relationship x&gt;y, z&gt;y holds. 
     With certainty, when the central position of the fine opening portion  12   a  is displaced from that of the fine opening portion  13   a , there is a tendency that pressure loss increases and thus ink supply performance deteriorates, compared to Embodiment 1. On the other hand, however, finer dust and foreign matters can be picked up, compared to Embodiment 1. Also, when small droplet is discharged, it is possible to ensure a certain degree of margin in supplying ink, whereas it is more likely that ink supply is cut off by blockage caused by dust and thus printing failure occurs. Accordingly, when prevention of printing failure has priority, it is effective that the central position of the fine opening portion  12   a  is displaced from that of the fine opening portion  13   a.    
     As a method of implementing the configuration as illustrated in  FIG. 7  with the central position of the fine opening portion  12   a  displaced from that of the fine opening portion  13   a  illustrated in  FIG. 3 , there is one in which the position of the fine opening portion  12   a  illustrated in  FIG. 3  remains unchanged and the position of the fine opening portion  13   a  is made to move laterally from the position illustrated in  FIG. 3 . It is also possible that the position of the fine opening portion  13   a  remains unchanged and the position of the fine opening portion  12   a  is made to move laterally from the position illustrated in  FIG. 3 . Further, it is also possible that both the positions of the fine opening portion  12   a  and fine opening portion  13   a  are made to move laterally from those illustrated in  FIG. 3 . 
     As a method of moving the position of the fine opening portion  12   a  illustrated in  FIG. 3  laterally from the position illustrated in  FIG. 3 , there is one in which the pattern forming position of the Si nitride film  20  illustrated in  FIGS. 4A and 4B  is changed and the position of holes formed to the Si oxidized film  5  is thereby changed. It is also possible that the etching position is changed when the Si oxidized film  5  is patterned. 
     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. 2006-025893, filed Feb. 2, 2006, which is hereby incorporated by reference herein in its entirety.