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. 
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 11a, a piezoelectric layer 12a, a lower electrode layer 11b and an upper-wall protection 12b 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. 
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.