Abstract:
A method for manufacturing a fluid injection head. The fluid injection head structure is formed on a substrate and has a manifold therein, bubble generators, a conductive trace, and at least two rows of chambers adjacent to the manifold in flow communication with the manifold. The conductive trace disposed on a top surface of the substrate and partially disposed between the two rows of the chambers above the manifold is used to drive the bubble generator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a division of U.S. application Ser. No. 10/065,588 filed Oct. 31, 2002. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a fluid injection head structure and a method of fabricating the same, and more particularly, to a fluid injection head structure with a power line disposed between two rows of bubble generators and a method of fabricating the same.  
           [0004]    2. Description of the Prior Art  
           [0005]    Currently, fluid injection devices are widely applied in ink jet printers. Improvements in fluid injection devices are resulting in ink jets that are of higher quality, are more reliable, and less expensive to manufacture. Fluid injection devices can also be applied to many other fields, such as fuel injection systems, cell sorting, drug delivery systems, print lithography, and micro jet propulsion systems.  
           [0006]    Among the products available on the market, only a few can eject individual droplets in uniform shapes. One of the most successful designs uses thermal driven bubbles to eject droplets. This design is widely used due to its ease of manufacture and low cost.  
           [0007]    U.S. Pat. No. 5,774,148, “Print head with field oxide as thermal barrier in chip”, details a method of center feeding in a fluid injection head. To fabricate this kind of jet structure, a sand blasting, laser drilling, or chemical etching process must be performed to create a hole in the center of the chip for the ink to feed through.  
           [0008]    However, this method requires a larger chip size because the removed area of the chip is wasted, which results in less cost-efficiently manufacturing.  
         SUMMARY OF INVENTION  
         [0009]    It is therefore a primary objective of the claimed invention to provide a fluid injection head structure with increased layout integration to shrink the chip size and lower the costs of manufacture.  
           [0010]    In a preferred embodiment of the claimed invention, the fluid injection head structure comprises a substrate, a manifold formed inside the substrate, at least two rows of chambers formed on two sides of the manifold and connected to the manifold, at least one bubble generator, and a conductive trace disposed on a top surface of the substrate. In addition, a portion of the conductive trace is disposed between the two rows of chambers. The conductive trace is used to drive the bubble generators.  
           [0011]    It is an advantage of the present invention that ink is fed successfully without fully etching through the chips, making more space available. The area above the manifold may be used for electric circuit layouts. This not only reinforces the strength of the structure of the layers above the manifold, but also shrinks the chip size. Moreover, as chip size shrinks, the number of injection heads in the same area increases and, therefore, printing speed is improved.  
           [0012]    These and other objectives of the claimed invention will not doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a cross-sectional diagram of a print head structure according to the present invention.  
         [0014]    [0014]FIG. 2 is a cross-sectional diagram of a fluid injection head structure according to the present invention.  
         [0015]    [0015]FIG. 3 is a top view of the fluid injection head structure according to the present invention.  
         [0016]    [0016]FIG. 4 is a local amplified diagram of the fluid injection head shown in FIG. 3.  
         [0017]    [0017]FIG. 5 is a schematic diagram of a matrix driving circuit in the fluid injection head according to the present invention.  
         [0018]    [0018]FIG. 6 to FIG. 8 are schematic diagrams of forming the fluid injection head according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Please refer to FIG. 1, which is a cross-sectional diagram of a print head structure according to the present invention. The print head structure of the present invention is a fluid injection head structure with virtual valves. As shown in FIG. 1, a bubble generator  14  comprises two bubble generating devoces, a first heater  14   a  and a second heater  14   b , disposed adjacent to an orifice  12 . Because of differences, such as different resistances, between the two heaters  14   a  and  14   b , when the two heaters  14   a  and  14   b  heat fluid, (not shown) inside the chamber  16 , two bubbles are generated in turn. A first bubble (not shown) is generated by the first heater  14   a , which is closer to a manifold  11  than the second heater  14   b . The first bubble isolates the manifold  11  from the orifice  12  and acts as a virtual valve to reduce a cross talk effect between this chamber  16  and neighboring chambers  16 . A second bubble (not shown) is generated by the second heater  14   b . The second bubble squeezes fluid, such as ink, inside the chamber  16  to eject out of the orifice  12 . Finally, the second bubble combines with the first bubble to reduce the generation of satellite droplets.  
         [0020]    The fluid injection head structure of the present invention feeds ink successfully without fully etching through the chips. Based on this structure, power line layouts can be designed above the manifold  11  so as to reinforce the strength of the structure layer above the manifold  11 .  
         [0021]    Please refer to FIG. 2, which shows a cross-sectional diagram of a fluid injection head structure according to the present invention. A low temperature oxide layer  18  is deposited onto the first heater  14   a  and the second heater  14   b  as a protective layer. After that, a via layer is formed in a predetermined area and then a metal layer  13  is deposited on the top surface of the heaters  14   a  and  14   b  through the via layer. Thus, the metal layer  13  is electrically connected to the heaters  14   a  and  14   b.    
         [0022]    In the same manner, a drain  68  and a source  66  of a MOSFET  15  are electrically connected to the heaters  14   a  and  14   b , and a ground  20  via the metal layer  13 . Thus, when a gate  64  of the MOSFET  15  is turned on, an external voltage signal is applied to the print head from a pad made of the metal layer  13 . At this time, a current flows from the pad via the metal layer  13  to the first heater  14   a  and the second heater  14   b . Then, the current passes through the drain  68  and the source  66  of the MOSFET  15  to the ground  20  so as to complete a heating action. As the ink inside the chamber  16  is heated, two bubbles are generated to squeeze ink droplets out of the orifice  12 . It dependents upon the data to be printed to control which orifice  12  ejects ink droplets during a printing process. The material of the metal layer  13  can be any one of aluminum, gold, copper, tungsten, or alloys of aluminum-silicon-copper, or alloys of aluminum-copper.  
         [0023]    Please refer to FIG. 3 and FIG. 4. FIG. 3 is a top view of the print head according to the present invention. In the preferred embodiment, the orifices  12  of the print head is divided into sixteen Pgroups, P1 to P16, and each Pgroup comprises twenty-two addresses, A1 to A22. As shown in FIG. 5, which shows a schematic diagram of a matrix driving circuit, a select signal is generated by a logic circuit or microprocessor  32  according to the data to be printed. Then, the select signal is transmitted to a power driver  34  and an address driver  35  to determine which A (A1 to A22) should be turned on and to which P (P1 to P16) the power should be provided. For example, when providing power to P1 and turning on A22, the heaters  14   a  and  14   b  on the MOSFET  115  of P1-A22 will complete an operation of heating and ejecting ink at the predetermined time.  
         [0024]    [0024]FIG. 4 is a local amplified diagram of the region B shown in FIG. 3. As shown in FIG. 4, two rows of orifices  12 ,  12   a  are positioned on the center of the chip. When dividing the orifices into two parts by the line A-A″, as shown in FIG. 3, there are eight groups on the right side, P1 to P8, and eight groups on the left side, P9 to P16. The area above the manifold  11  between the two rows of orifices  12 ,  12   a  is used for a power line layout. Eight metal power lines corresponding to P1 to P8 are positioned to the right of line A-A″ and are electrically connected to I/O pads on the right. Eight power lines corresponding to P9 to P16 (not shown) are positioned to the left of line A-A″ and are electrically connected to I/O pads on the left.  
         [0025]    The driving circuit between each corresponding P pad and G pad uses a U-type circuit layout. The driving circuit between the pad P1 and the pad G1 is illustrated in a doshed block in FIG. 4. Each driving circuit is connected without crossing any other driving circuit. Only one metal layer  13  is used to form the power line  19  between the heaters  14   a ,  14   b  and the grounding pad G. There are eleven metal lines  22  positioned above the group of MOSFET  15  and another eleven metal lines  22  positioned below the groups of MOSFET  15  in the FIG. 4. The metal lines  22  are electrically connected to the pads A so as to transmit the output data of the address driver  35  to the corresponding groups of MOSFET  15  to control ink ejection. There are also eleven poly-silicon lines  23  positioned to the left of the groups of MOSFET  15  and another eleven to the right of the MOSFET  15 . Then, contact layers  24  are formed to electrically connect the metal lines  22  and the poly-silicon lines  23  to complete the connection of the driving circuits. The poly-silicon lines  23  are used to connect the metal lines  22  above and below the groups of MOSFET  15  (i.e. the upper parts and lower parts of the metal lines  22  in the FIG. 4). For example, if a signal is input from the pad A1 to turn on the heaters of P16, it has to be transmitted via the poly-silicon lines  23  through the metal lines  22  to the heaters of P16.  
         [0026]    Please refer to FIG. 6 to FIG. 8, which show schematic diagrams of forming the fluid injection head according to the present invention. First, a local oxidation process is performed to form a field oxide layer  62  on a silicon substrate  60 . Then a blanket boron implantation process is performed to adjust the threshold voltage of the driving circuit. A poly-silicon gate  64  is formed in the field oxide layer  62 . At the same time, twenty-two poly-silicon lines  23  are formed along two edges of the chip. An arsenic implantation is performed to form a source  66  and a drain  68  on both sides of the gate  64 . Then a low stress layer  72  such as silicon nitride is deposited to form an upper layer of the chamber  16  as shown in FIG. 6.  
         [0027]    Please refer to FIG. 7. An etching solution (KOH) is used to etch a back side of substrate  60  to form a manifold  11  for fluid supply. Then the field oxide layer  62  is partially removed with an etching solution (HF) to form the chamber  16 . After that, a precisely-timed etching process using KOH is performed to increase the depth of the chamber  16 . The chamber  16  and the manifold  11  are connected and filled with fluid, however this etching process needs special attention because convex corners in the chamber  16  are also etched.  
         [0028]    Next, a process of forming heaters is performed. This process should be obvious to those of ordinary skill in the art. A good choice of materials to use for the first heater  14   a  and the second heater  14   b  is alloys of tantalum and aluminum, but other materials like platinum or HfB 2  can also work effectively. A low temperature oxide layer  74  is deposited over the entire substrate  60 . In addition to protecting the first heater  14   a  and the second heater  14   b  and isolating the MOSFET  15 , the low temperature oxide layer  74  serves as a protective layer that covers the gate  64 , the source  66 , the drain  68 , and the field oxide  62 .  
         [0029]    Next, a conductive layer  13  is formed on the first heater  14   a  and the second heater  14   b  to electrically connect the first heater  14   a , the second heater  14   b , and the MOSFET  15  of the driving circuit. The driving circuit transmits a signal to individual heaters and drives a plurality of pairs of heaters, so that fewer circuit devices and linking circuits are required. The preferred material for the conductive layer  13  is an alloy of aluminum-silicon-copper, aluminum, copper, gold, or tungsten. A low temperature oxide layer  76  is deposited as a protection layer on the conductive layer  13 .  
         [0030]    Please refer to FIG. 8. An orifice  12  is formed between the first heater  14   a  and the second heater  14   b . So far, the specification has detailed the formation of a fluid injector array with a driving circuit integrated in one piece. The driving circuit and heaters are integrated on the same substrate and an integrated injection head structure is formed without the need for an attached nozzle plate.  
         [0031]    The following is a detailed description of the operation of the present invention. Please refer to FIG. 4 and FIG. 5. When printing starts, the logic circuit or microprocessor  32  determines which orifices  12  should eject ink according to the data to be printed and generates a select signal. The select signal is transmitted to the power driver  34  and the address driver  32  to turn on the proper A groups (A1 to A22) and apply power to the proper P groups (P1 to P16). Thus, a current is generated and applied to the heaters  14   a  and  14   b  to heat fluid and generate bubbles so that ink droplets are ejected. For example, suppose that a droplet is to be ejected from the orifice  12   a  of A1-P1. First, a voltage signal is input from an I/O pad of A1 and transmitted to the gate  64  of MOSFET  15  to turn on the gate  64 . Next, another voltage signal is input from an I/O pad of P1 to generate a current. The current passes via the heaters  14   a  and  14   b  to the drain  68 , the source  66 , and the ground  20  so as to heat the fluid and generate bubbles. The bubbles act to eject an ink droplet from the orifice  12   a  of A1-P1.  
         [0032]    Although the above description details monochromatic printers, the present invention can be applied to color printers or multi-color printers. In addition, the present invention also can be applied to other fields, such as fuel injection systems, cell sorting, drug delivery systems, print lithography, micro inject propulsion systems, and others.  
         [0033]    According to the present invention, the space above manifolds and between two rows of chambers is available for layouts of conductive trace. There are several advantages of the present invention. Since the print head is manufactured without etching through the entire chip, the circuit layouts can be performed above the manifolds, leading to a reduction in wafer size and a consequent increase in the number of dies per wafer. The placement of the circuit layouts on the structure layer above the manifold reinforces the strength of the structure layer. Using this method of improving the density of circuit layout, the area required for circuit layout is reduced, and more orifices can be disposed in the same wafer area to improve the printing speed.  
         [0034]    Those skilled in the art will readily observe that numerous modifications and alterations of the invention may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of appended claims.