Patent Publication Number: US-6701593-B2

Title: Process for producing inkjet printhead

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan applications serial nos. 90100340, 90100341, 90100342, 90100343, filed Jan. 8, 2001, the full disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for producing a piezoelectric inkjet printhead. More specifically, the present invention relates to a process for producing a piezoelectric inkjet printhead having an ink chamber by using exposure/development of photosensitive polymer. 
     2. Description of the Related Art 
     Conventional inkjet printing technology mainly includes thermal bubble inkjet printing and piezoelectric inkjet printing. In thermal bubble inkjet printing, a heater is used to evaporate the ink quickly and generate pressurized bubbles to eject the ink through a nozzle. This type of printer has been successfully commercialized by HP and CANON. However, a thermal bubble inkjet printer operates at a high temperature so that the selectivity of the ink is limited to aqueous solvents and its application is therefore limited. 
     In piezoelectric inkjet printing, an actuator is deformed by applying a voltage to pressurize and eject the liquid ink. Piezoelectric inkjet printing has the following advantages over the thermal bubble inkjet printing. First, no chemical reaction occurs because of a high temperature, so the color of material printed is not adversely affected. Second, high thermal cycles are not required, resulting in superior duration of the inkjet printhead. The piezoelectric ceramics has high response speed, which help increase the printing speed. Third, it is easy to control ink drops in the piezoelectric inkjet printing process. However, the printing speed in the thermal bubble inkjet printing process is limited by thermal conductivity. 
     FIG. 1A is a side view of a conventional piezoelectric inkjet printhead. The conventional inkjet printhead is obtained by forming an upper electrode layer  11   a , a piezoelectric layer  12   a , a lower electrode layer  11   b  and an upper-wall protection  12   b  made of ceramic, chamber walls  13  made of a green sheet and a bottom film  14  made of a green sheet, then laminating these layers as desired, and sintering. An example of the conventional piezoelectric inkjet printhead is commercially available from the EPSON company. 
     FIG. 1B is a top view showing the conventional piezoelectric inkjet printhead. An ink chamber  17  is an ink storage region of the inkjet printhead for storing the ink from the ink inlet  15 . To effect printing by the printhead, an ink material is supplied to the ink chamber  17  to fill the same, and the pressure within the ink chamber  17  is raised by displacement of the piezoelectric layer, so that ink droplets are ejected through the ink outlet  16  which communicates with the ink chamber  17 . 
     In the above process, all the elements are created by a ceramic thick film process and an alignment and laminating process. The inkjet printhead obtained is so compact that it is not easy to align and assemble, causing poor yield and increased production cost and time. 
     In the prior art process, a sintering process must be performed after the alignment and laminating process. Non-uniform shrinkage of ceramics during sintering results in structural damage and thus low yield of the product. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide a process to form a piezoelectric inkjet printhead that uses alignment of patterned photosensitive polymer layers instead of laminating thick ceramic layers and sintering. The process of the present invention can solve the problems of piezoelectric inkjet printhead assembly and structural damage that may be caused during sintering. Therefore, with the process of the present invention, an increased yield, a more simplified process and lowered cost can be achieved. 
     In a first aspect of the present invention, a process for producing a piezoelectric inkjet printhead is provided. A substrate having a plurality of metallic lower electrodes thereon is provided. A piezoelectric layer is formed over the substrate and the metallic lower electrodes. Then, metallic upper electrodes are formed on the piezoelectric layer. A photosensitive polymer layer is formed on the piezoelectric layer having the upper electrodes and the lower electrodes to define chamber wall patterns and then to form chamber walls. Finally, a second photosensitive polymer layer is formed on the chamber walls to define a top film having a plurality of ink inlets and ink outlets. A piezoelectric inkjet printhead is thus obtained. 
     In a second aspect of the present invention, a process for producing a piezoelectric inkjet printhead is provided. A substrate having at least two through holes therein is provided. A first photosensitive polymer layer is formed on the substrate. The first photosensitive polymer layer is defined to form a bottom film having a plurality of ink inlets and a plurality of ink outlets. A second photosensitive polymer layer is formed on the bottom film to form chamber walls that define the ink chamber. Finally, a ceramic layer having upper and lower electrodes thereon is attached on the top of the chamber walls in a manner that a pair of an upper and lower electrode corresponds to an ink chamber. An inkjet printhead is thus obtained. Furthermore, the substrate can be removed after the inkjet printhead is completed. Alternatively, the position of the ink inlet can be changed to be on the ceramic layer. 
     In the third aspect of the present invention, a process for producing a piezoelectric inkjet printhead is provided. A substrate having a through hole therein is provided. The substrate can be made of silicon, a ceramic material or metal. Then, a first photosensitive polymer layer is formed on the substrate to define a bottom film having a plurality of ink outlets. One or more photosensitive polymer layers are formed in sequence on the bottom film to define a plurality of ink chambers and chamber walls. Finally, a ceramic piezoelectric layer having electrodes thereon is attached on the tops of the walls in a manner that a pair of an upper and lower electrode corresponds to an ink chamber. 
     In a fourth aspect of the present invention, an ink cartridge having a piezoelectric inkjet printhead is provided. The ink cartridge of the present invention consists of an ink storage module having a hollow storage region, a piezoelectric jet module having a plurality of ink chambers and a connection circuit for the piezoelectric layer, and an ink channel communicating with the ink storage module and the piezoelectric jet module. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principle of the invention. In the drawings, 
     FIG. 1A is a schematic, side view showing a process for producing a conventional piezoelectric inkjet printhead; 
     FIG. 1B is a schematic, top view showing a process for producing a conventional piezoelectric inkjet printhead; 
     FIGS. 2,  3 ,  4 ,  5 , and  6  are schematic views showing a process for producing a piezoelectric inkjet printhead according to a first preferred embodiment of the present invention; 
     FIG. 7 is a schematic top view showing the process for producing the piezoelectric inkjet printhead according to the first preferred embodiment of the present invention; 
     FIG. 8 is a schematic view showing a process for producing a piezoelectric inkjet printhead according to a second preferred embodiment of the present invention; 
     FIG. 9 is a schematic view showing the process for producing the piezoelectric inkjet printhead according to the second preferred embodiment of the present invention; 
     FIG. 10 is a schematic top view showing the process for producing the piezoelectric inkjet printhead according to the second preferred embodiment of the present invention; 
     FIG. 11 is a schematic view showing a process for producing a piezoelectric inkjet printhead according to a third preferred embodiment of the present invention; 
     FIG. 12 is a schematic view showing a process for producing a piezoelectric inkjet printhead according to a fourth preferred embodiment of the present invention; 
     FIG. 13 is a schematic view showing a process for producing a piezoelectric inkjet printhead according to a fifth preferred embodiment of the present invention; 
     FIG. 14 is schematic view showing a process for producing a piezoelectric inkjet printhead having side inlets according to a sixth preferred embodiment of the present invention; 
     FIG. 15 is a schematic view showing the process for producing the piezoelectric inkjet printhead having chamber walls and ink inlets according to the sixth preferred embodiment of the present invention; 
     FIG. 16 is a schematic side view of view showing the process for producing the piezoelectric inkjet printhead according to the sixth preferred embodiment of the present invention; 
     FIG. 17 is a schematic, perspective view showing the process for producing the piezoelectric inkjet printhead according to the sixth preferred embodiment of the present invention; and 
     FIG. 18 is a schematic view showing a process for producing a piezoelectric inkjet printhead according to a seventh preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     First Embodiment 
     FIGS. 2-6 show a process for producing a piezoelectric inkjet printhead according to one preferred embodiment of the present invention. As shown in FIG. 2, a substrate  20  made of a material such as silicon or ceramic is provided. A plurality of upper electrodes  21   a  is formed on the substrate  20  by screen printing, as shown in FIG. 3. A material used to form the upper electrode  21   a  includes copper (Cu), gold (Au), silver (Ag), platinum (Pt), palladium (Pd), alloys thereof, and the like. The lower electrode  21   a  can be formed in any shape and size as desired. 
     Alternatively, a physical vapor deposition process such as sputtering and evaporation, or a chemical deposition process such as electrical plating and electroless plating can be used to form a metal layer over the substrate  20 . After the metal layer is partially removed, the upper electrodes  21   a  are obtained. The material used to form the metal layer includes copper, gold, silver, platinum, palladium, alloys thereof, and the like. The upper electrode  21   a  can be formed in any shape and size as desired. 
     With reference to FIG. 4, a piezoelectric layer  22  is formed on the substrate  20  and the upper electrodes  21   a . A method of forming the piezoelectric layer  22  can include film spin coating, screen printing or doctor blading, which are well known in the art. The piezoelectric layer  22  can be formed of, for example, a ceramic piezoelectric material such as lead zirconate titanate (PZT), or a piezoelectric polymer such as poly(vinylidene fluoride) (PVDF). 
     A plurality of lower electrodes  21   b  are formed on the piezoelectric layer  22  by using the same method of forming the upper electrodes  21   a , as shown in FIG.  3 . The lower electrodes  21   b  can be formed of the same material as the upper electrodes  21   a , and in any shape or size, the same as or different from the upper electrodes  21   a.    
     With reference to FIG. 5, a first photosensitive polymer layer is formed on the piezoelectric layer  22  and the lower electrodes  21   b . The first photosensitive polymer layer has a thickness of about 10-1000 microns. Then, a plurality of chamber walls  23 , which define ink chambers  27 , are formed in the first photosensitive layer by an photolithography process. Each of the ink chambers  27  is formed in such a manner that one lower electrode  21   b  is located on a bottom of the chamber  27  and a portion of piezoelectric layer  22  and an upper electrode  21   a  is located under the bottom of the chamber  27 . Each of the ink chambers is surrounded by portion of the chamber walls  23 . 
     With reference to FIG. 6, a second photosensitive polymer layer is formed on tops of the ink chambers  27  and the chamber walls  23 . Then, the second photosensitive polymer layer is subject to photolithography or laser processing to form a top film  24  having a plurality of ink ports  28  which penetrate through the top film  24 . 
     FIG. 7 is a schematic top view of the piezoelectric inkjet printhead as shown in FIG.  6 . In FIG. 7, the ink port  28  includes an ink inlet  25  and an ink outlet  26 . The ink inlet  26  has a diameter of about 50 to about 1000 microns. The ink outlet  26  has a diameter of about 10 microns to about 100 microns. 
     Examples of photosensitive polymer layer include dry film photoresist, liquid type photoresist, a positive type photoresist, a negative type photoresist, a photosensitive polyimide and photosensitive epoxy. 
     The dry film photoresist can have a protective layer, a release layer, and a photosensitive polymer layer of about 10-200 microns in thickness. When a dry film photoresist is used to form the top film  24  or the chamber walls  23 , the release layer is removed and then the photosensitive polymer layer is attached on a top of the chamber walls  23  or the piezoelectric layer  22 . Thereafter, a UV exposure process is carried out and the protective layer is removed. Then,the photosensitive polymer layer is developed to form desired patterns. 
     When a liquid type photoresist, which is a flowable liquid photosensitive polymer, is used to form the top film  24  or the chamber walls  23 , the flowable type liquid is coated as a film on the top of the chamber walls  23  or the piezoelectric layer  22 . Thereafter, an UV exposure process is carried out. Then, the liquid type photoresist is developed to form desired patterns. 
     Second Embodiment 
     FIG. 8 is a schematic view of a piezoelectric inkjet printhead according to a second preferred embodiment of the present invention. A substrate  130  such as a silicon substrate or ceramic substrate is provided. A through hole  129  is formed in the substrate  130 . Etching, mechanically drilling or particle bombing, for example, can achieve formation of the through hole  129 . The through hole  129  can be in the form of a rectangular trench. The dimension of the through hole  129  can be determined as desired. 
     Then, a first sensitive polymer layer is formed on the substrate  130  and subsequently subjected to an photolithography process to form a bottom film  124  having a plurality of ink inlets  125  and ink outlets  126 . The ink inlet  125  has a diameter of about 10-1000 microns. The ink outlet  126  has a diameter of about 10-200 microns. 
     A second sensitive polymer layer is formed on the bottom film  124 . A UV photolithography process is performed to form a plurality of chamber walls  123  defining a plurality of ink chambers  127  in the second sensitive polymer film. Under each of the ink chambers  127  is located a portion of the bottom film  124  having an ink inlet  125  and an ink outlet  126 . Alternatively, the ink inlet  125  and the ink outlet  126  can be formed in the substrate  130  by etching, mechanically drilling or particle bombing, for example. As such, the above first photosensitive polymer layer can be omitted and the production process can be thus simplified. 
     Finally, a ceramic layer  122   b  is formed on tops of the chamber walls. A piezoelectric layer  122   a  is formed on ceramic layer  122   b . A plurality of upper electrodes  121   a  is provided on a top surface of the piezoelectric layer  122   a . A plurality of lower electrodes  121   b  corresponding to the upper electrodes  121   a  is provided on a bottom surface of the piezoelectric layer  122   b . Each of the ink chambers  127  has at least one pair of the upper electrode  121   a  and the lower electrode  121   b . Examples of the material used to form the upper electrode  121   a  and the lower electrode  121   b  include copper, gold, silver, platinum, palladium, alloys thereof, and the like. The piezoelectric layer  122   a  can be formed of, for example, lead zirconate titanate, or a piezoelectric polymer such as poly(vinylidene fluoride). The ceramic layer  122   b  has a thickness of about ten microns to several millimeters. 
     FIG. 9 is a schematic perspective view of a piezoelectric inkjet printhead according to the second preferred embodiment of the present invention. FIG. 10 is a schematic top view of FIG.  9 . FIG.  9  and FIG. 10 clearly show the configuration of the inkjet printhead produced according to the present invention and the relative position of respective elements of the inkjet printhead. 
     The photosensitive polymer layer, which can be used in the present invention, includes a dry film photoresist, a liquid type photoresist, a positive photoresist, a negative photoresist, a photosensitive polyimide and a photosensitive epoxy. 
     When a dry film photoresist is used, the dry film photoresist can be attached directly on the substrate by thermal pressing. When a liquid type photoresist that is a flowable liquid photosensitive polymer is used, the flowable liquid is coated as a film on the substrate or on the bottom film, and then subjected to a UV exposure and development process to form desired patterns. 
     Third Embodiment 
     FIG. 11 is a schematic side view of a piezoelectric inkjet printhead according to a third preferred embodiment of the present invention. The piezoelectric inkjet printhead obtained from the second preferred embodiment is put in an etchant to remove the substrate  130 . The piezoelectric inkjet printhead of this example is thus accomplished. In the third preferred embodiment of the present invention, the substrate  130  acts as a carrier for the piezoelectric inkjet printhead during the manufacturing process. 
     Fourth Embodiment 
     FIG. 12 is a schematic side view of a piezoelectric inkjet printhead according to a fourth preferred embodiment of the present invention. A substrate  140  such as a silicon substrate or ceramic substrate is provided. A through hole  139  is formed in the substrate  140 . Etching, mechanically drilling or particle bombing, for example, can achieve the formation of the through hole  139 . The through hole  139  can be in the shape of a rectangular trench. The dimension of the through hole  139  can be determined as desired. 
     Then, a first sensitive polymer layer is formed in the substrate  140  and then subject to an photolithography process to form a bottom film  134  having a plurality of ink outlets  136 . The ink outlet  136  has a diameter of about 10-200 microns. 
     A second sensitive polymer layer is formed on the bottom film  134 . A UV exposure and development process is performed to form a plurality of chamber walls  133  defining a plurality of ink chambers  137  in the second sensitive polymer film. A portion of the bottom film  134  having an ink outlet  136  is located under each of the ink chambers  137 . 
     A plurality of ink inlets  135  are formed through a ceramic layer  132   b  by etching, mechanically drilling or particle bombing, such that the ink inlet  135  is provided opposite to and misaligned with the ink outlet  136 . The ink inlet  135  has a diameter of about 20-1000 microns. Then, the ceramic layer  132   b  is attached on tops of the chamber walls  133  and the ink chambers  137 . A plurality of lower electrodes  131   b , piezoelectric layers  132   a  and upper electrodes  131   a  is formed in sequence as stacks on the ceramic layer  132   b , such that each of the stacks corresponds to one of the ink chambers  137  and the ink inlet  135  is exposed. Examples of the material used to form the upper electrode  131   a  and the lower electrode  131   b  include copper, gold, silver, platinum, palladium, alloys thereof, and the like. The piezoelectric layer  132   a  can be formed of, for example, lead zirconate titanate, or a piezoelectric polymer such as poly(vinylidene fluoride). The ceramic layer  132   b  has a thickness of about ten microns to several millimeters. 
     The photosensitive polymer layer that can be used in the present invention includes a dry film photoresist, a liquid type photoresist, a positive photoresist, and a negative photoresist, a photosensitive polyimide and photosensitive epoxy. 
     When a dry film photoresist is used, the dry film photoresist can be attached directly on the substrate by thermal press. When a liquid type photoresist, which is a flowable liquid photosensitive polymer, is used, the flowable photoresist liquid is coated as a film on the substrate or on the bottom film and then subjected to a UV exposure and development process to form desirable patterns. 
     Fifth Embodiment 
     FIG. 13 is a schematic side view of a piezoelectric inkjet printhead according to a fifth preferred embodiment of the present invention. The piezoelectric inkjet printhead obtained from the fourth preferred embodiment is put in an etchant to remove the substrate  140 . The piezoelectric inkjet printhead of this example is thus accomplished. In the fifth preferred embodiment of the present invention, the substrate  140  acts as a carrier for the piezoelectric inkjet printhead during the manufacturing process. 
     Sixth Embodiment 
     FIG. 14 is a schematic, exploded view of a piezoelectric inkjet printhead according to a sixth preferred embodiment of the present invention. A substrate  300  such as a silicon substrate or ceramic substrate is provided. A through hole  209  is formed in the substrate  300 . The formation of the through hole  209  can be achieved by etching or the like. The through hole  209  can be in the shape of a rectangular trench. The dimension of the through hole  209  can be determined as desired. 
     Then, a first sensitive polymer layer is formed in the substrate  300  and subsequently subjected to an photolithography process to form a bottom film  204  having a plurality of ink outlets  206 . The ink outlet  206  has a diameter of about 10-200 microns. 
     One or more second sensitive polymer layers are formed on the bottom film  204 . An UV exposure and development process is performed to form a plurality of chamber walls  243  defining a plurality of ink chambers  207  in the second sensitive polymer film. A portion of the bottom film  204  having an ink outlet  206  is located under each of the ink chambers  207 . 
     FIG. 15 is a schematic, exploded view of a structure of chamber walls shown in FIG.  14 . The chamber walls define the ink chambers  207 , at least one of which has at least one ink inlet  205 . The ink inlet  205  and the ink outlet  206  can be one or more in number. The ink inlet  205  is located in the second photosensitive polymer layer. The second photosensitive polymer layer consists of three photosensitive polymer layers. The formation of the chamber wall can include three stages. 
     In the first stage of forming the chamber wall, a third photosensitive polymer layer is formed on the bottom film  204  and subjected to an exposure and development process to define the chamber walls  213 . 
     In the second stage of forming the chamber wall, a fourth photosensitive polymer film is formed on the chamber walls  213  and subjected to an exposure and development process to define chamber walls  223  and ink inlets  205 . 
     In the third stage of forming the chamber wall, a fifth photosensitive polymer film is formed on the chamber walls  223  and subjected to an exposure and development process to define chamber walls  233 . The chamber walls  213 ,  223  and  233  form the chamber wall  243 , as shown in FIG.  15 . 
     Finally, with reference to FIG. 14, a ceramic piezoelectric layer  222  having electrode patterns thereon is attached on the top of the chamber walls  243 . The piezoelectric layer  222  includes upper electrodes  211 , piezoelectric layers  212  and lower electrodes  221  thereon, such that one upper electrode  211  and one lower electrode  221  are located above each of the ink chambers  207 , respectively. 
     FIG. 16 is a side view of the piezoelectric inkjet printhead according to the sixth preferred embodiment of the present invention. FIG. 17 is a schematic, perspective view of FIG.  16 . FIG.  16  and FIG. 17 clearly show the configuration of the inkjet printhead obtained according to the present invention and the relative position of respective elements of the inkjet printhead. 
     Alternatively, the piezoelectric layer can be used as a substrate of the present invention. In this case, the ink outlet  206  can be formed on the photosensitive polymer layer on the chamber wall. Thus, the substrate can be omitted and the production process can be simplified. 
     The photosensitive polymer layer that can be used in the present invention includes a dry film photoresist, a liquid type photoresist, a positive photoresist, and a negative photoresist, a photosensitive polyimide and a photosensitive epoxy. The photosensitive polymer layer before exposure has a thickness of about 10-500 microns. 
     When a dry film photoresist is used, the dry film photoresist can be attached directly on the substrate by thermal press. When a liquid type photoresist, which is a liquid photosensitive polymer, is used, the flowable liquid is coated as a film on the substrate or on the bottom film and then subjected to a UV exposure and development process to form desirable patterns. 
     Seventh Embodiment 
     FIG. 18 is a schematic exploded view of a piezoelectric inkjet printhead according to a seventh preferred embodiment of the present invention. The ink cartridge  400  has an ink storage module  406  with an opening  408 , an ink channel  404  and a piezoelectric jet module  402  in sequence. 
     The ink storage module  406  is used to store the ink in the ink cartridge. Therefore, the ink storage module  406  is a hollow cartridge defined by lids and cartridge walls. The opening  408  in the bottom of the ink storage module  406  enables the ink in the ink storage module  406  to flow into the piezoelectric jet module  402  through the ink channel  404 . 
     Furthermore, in order to prevent the ink in the ink cartridge from leaking when not printing, a leak proof device can be further provided in the ink storage module  406  to balance the pressure therein. The leak proof device can be made of, but is not limited to, microporous material or resilient elastomer so as to provide capillary attraction or an elastic force for leakage prevention. Examples of the microporous material include plastics and foamed rubbers. The resilient elastomer can include spring elements. Furthermore, in order to prevent the ink from contacting with the outside air and from generating micro bubbles therein, an ink bag can also be provided in the ink storage region of the storage module  406  to store the ink. In the case that the ink storage region of the ink storage module  406  is isolated from the air outside, an air bag can be further provided for balancing the pressure in the module  406 . Alternatively, both the ink bag and the air bag can be used together in the ink storage module  406 . 
     The ink channel  404  is located between the ink storage module  406  and the piezoelectric jet module  402 . The ink channel  404  has a passage through the ink channel  406 . One end of the passage communicates with the opening  408  in the bottom of the ink storage module  406  and the other end of the passage communicates with an opening at the top of the piezoelectric jet module  402 , such that the ink can flow from the module  406  to the module  402 . If the ink channel  404  is made of microporous material, a function of temporary ink storage can be further provided. 
     The piezoelectric jet module  402  is located beneath the ink channel  404 . The piezoelectric jet module  402  consists of piezoelectric connection circuits and an inkjet printhead with a plurality of ink chambers therein. At least one opening is provided on the top of the piezoelectric jet module  402  to enable the ink to flow from the ink channel  404  into the ink chamber of the inkjet printhead. The piezoelectric connection circuit of the piezoelectric jet module  402  includes upper and lower electrodes connected to ends of the piezoelectric layer and a control circuit connected to the electrodes and edges of the ink cartridge. When a printer sends a signal for printing out, the control circuit transmits the signal to a designated electrode to carry out the printing operation. 
     Other elements of the piezoelectric jet module  402  of this example are similar to those described in the above Embodiments 1-6. Therefore, their descriptions are omitted. 
     The piezoelectric jet module of the present invention includes a substrate, a bottom film, chamber walls, an ink chamber, an upper-wall protection layer, a lower electrode, piezoelectric layer and an upper electrode. The ink chamber is a hollow region that is defined by the bottom film, the chamber walls and the upper-wall protection layer, respectively. The bottom film having an ink inlet and an ink outlet forms the bottom of the ink chamber. The chamber walls form sidewalls of the ink chamber. The upper-wall protection layer is located at the top of the ink chamber. The material used to form the upper-wall protection layer includes ceramics. The upper-wall protection layer can be optionally removed. 
     In this example, one ink chamber and single ink outlet are described for ease of illustration. However, for some applications, a plurality of small chambers connected to each other can be used instead of a big chamber to receive a single ink outlet. 
     In light of the foregoing, after the piezoelectric layer is formed, the chamber walls and the bottom film can be obtained by exposure/development using the photosensitive polymer to integrally form an inkjet printhead. The cycle time can be significantly reduced and the cost and labor of production can thus be reduced, while the yield is increased. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the forgoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.