Abstract:
A microinjector head with a driving circuit and the manufacturing method of the microinjector head are shown. The microinjector head uses a bubble as a virtual valve to eject fluid. The microinjector head has a manifold, chambers, a pair of first and second bubble generators, orifices, and a driving circuit. The driving circuit is used to control the pair of first and second bubble generating devices and eject fluid inside the corresponding chamber from the corresponding orifice. In addition, because the driving circuit and the bubble generators are integrated on a single substrate, the number of manufacturing processes is reduced and the circuit devices and connecting circuits of the microinjector array are fewer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a microinjector head and its manufacturing method, and more particularly, to a microinjector head with a driving circuitry and the manufacturing method of the microinjector head.  
           [0003]    2. Description of the Prior Art  
           [0004]    At present, droplet injectors are widely applied in inkjet printers. Droplet injectors also have many other applications in different fields such as fuel injection systems, cell sorting, drug delivery systems, direct print lithography and micro jet propulsion systems. The common aim of the above applications is to provide a droplet injector that is reliable, of low-cost, and provides high-quality droplets with a high frequency and a high spatial resolution.  
           [0005]    However not all apparatuses can successfully inject uniform droplets. In currently known and used droplet injection systems, one system using thermally driven bubbles to inject droplets is proved to be a successful system because of its comparatively simple architecture and lower cost.  
           [0006]    U.S. Pat. No. 6,102,530-“Apparatus and method for using bubbles as virtual valve in microinjector to eject fluid” mentions a droplet injection apparatus with virtual valves as shown in FIG. 1. Heaters  20 ,  22  are located around orifices  18 . A first bubble is generated between a manifold  16  and a fluid chamber  14 . Therefore the first bubble acts like a virtual valve and is capable of reducing a cross talk effect with the adjacent chambers. A second bubble is then generated and approaches the first bubble to push the fluid, causing a droplet to be ejected from the orifice  18 . Finally, the second bubble fuses with the first bubble and successfully reduces the production of satellite droplets.  
           [0007]    U.S. Pat. No. 5,122,812-“Thermal inkjet print head having driver circuitry thereon and method for making the same” mentions a structure of an inkjet print head with driving circuitry as shown in FIG. 2. Heating devices and driving circuitry are integrated on a same substrate. However there are still many steps in the process.  
           [0008]    And according to the structure, a barrier layer  130  of 20˜30 μm in thickness must be formed and an orifice plate is adhered on the barrier layer  130 . This adhesion procedure limits the spatial resolution due to unavoidable assembly tolerance. In addition, the adhesion procedure is not compatible with general IC processes. When microinjector arrays are integrated with driving circuitry to reduce layout and are tightly packed, such incompatibility problems become more obvious and lead to more complicated manufacturing processes and thus higher costs.  
         SUMMARY OF INVENTION  
         [0009]    It is therefore a primary objective of the claimed invention to provide a microinjector head with driving circuitry to control a plurality of first and second bubble-generating devices to eject fluid in a plurality of chambers from orifices. A secondary objective of the claimed invention is to provide a manufacturing method for making a microinjector head with driving circuitry in fewer steps and with fewer number of circuit devices and linking circuits.  
           [0010]    According to the claimed invention, the microinjector head with driving circuitry to eject fluid uses a bubble as a virtual valve. The microinjector head comprises a plurality of chambers, a manifold connected to the chambers for providing fluid to the chambers, a plurality of orifices open to corresponding chambers, a plurality of pairs of bubble generators, each pair of bubble generators comprising a first and a second bubble-generating devices near a corresponding orifice and above the corresponding chamber, the first bubble-generating device generating a first bubble that is used as a virtual valve, the second bubble-generating device generating a second bubble to cause liquid in the chamber to eject from the orifice when the chamber is filled with fluid, and a driving circuit comprising a plurality of functional devices disposed on a same substrate. The driving circuit can send a driving signal to a specific pair of bubble generators so as to eject droplets out of the corresponding orifices. The first bubble generator and the second bubble generator may be two resistive heaters with different resistances and may be connected to each other in series.  
           [0011]    It is an advantage of the claimed invention that the microinjector head and the manufacturing method provide a micro droplet injector head manufactured with lower cost and fewer procedures.  
           [0012]    These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a structural diagram of a prior art droplet injection apparatus with virtual valves.  
         [0014]    [0014]FIG. 2 is a structural dissection diagram of a prior art microinjector head with driving circuitry; and  
         [0015]    [0015]FIG. 3 to FIG. 8 are structural and schematic diagrams of procedures to manufacture the microinjector head with driving circuitry and structural diagrams of the microinjector head.  
         [0016]    [0016]FIG. 9 is a structural and schematic diagram of the microinjector head with driving circuitry of the present invention.  
         [0017]    [0017]FIG. 10 to FIG. 12 are structural and schematic diagrams of a second embodiment of procedures to manufacture the microinjector head with driving circuitry and structural diagrams of the microinjector head. 
     
    
     DETAILED DESCRIPTION  
       [0018]    The present invention offers an improvement over the prior art. Therefore, references to items shown in FIG. 1 and FIG. 2 will be made in the following description. As shown in FIGS.  3  to FIG. 5, making a microinjector array  10  with driving circuitry on a substrate  38  comprises forming a thin oxide layer  101  on the substrate  38 , forming a silicon nitride (SiN x ) layer  102  on the thin oxide layer (as shown in FIG. 3), exposing and developing a silicon nitride layer  102 , etching the silicon nitride layer  102  (as shown in FIG. 4), and using local oxidation to oxidize unprotected regions of the thin oxide layer  101  to form a field oxide layer. Until now, a dielectric layer  51  (as shown in FIG. 5) is formed and has a first part  52  and a second part  50 . The first part  52  is a part of the thin oxide layer  101  covered by silicon nitride layer  102 . The second part  50  is the field oxide layer formed by local oxidation. This field oxide layer can be etched in the following procedures to form the chambers  14 . Then the silicon nitride layer  102  is removed. Blanket boron ion implantation of the first part  52  and the second part  50  (as shown in FIG. 5) adjusts the threshold voltage of the driving circuit. A polysilicon gate  105  is formed on the first part  52  and a phosphorus ion implantation of the polysilicon gate  105  is performed to reduce resistance of the polysilicon gate  105 . Implanting arsenic ions in the substrate  38  forms a source  106  and a drain  107  close to the gate  105 . Therefore plural functional devices, which comprise the source  106 , the drain  107 , and the gate  105 , are formed on the substrate  38  (as shown in FIG. 6).  
         [0019]    Please refer to FIG. 7. A low stress layer  42 , like SiN x , is deposited on the second part  50  as an upper layer of chambers  14 .  
         [0020]    Please refer to FIG. 8. An etching solution KOH is used to etch a back side of the substrate  38  to form a manifold  16  for fluid supply, and then the second part  50  is removed by the etching solution HF. The etching time is precisely controlled to perform another etching using KOH to increase the depths of the chambers  14 . So the chambers  14  and the manifold  16  are connected and are capable of being filled with fluid. However this etching process needs special concern because the convex corners will also be etched.  
         [0021]    Heaters, including first heaters  20  and second heaters  22  are arranged in a pattern for helping to generate bubbles and eject droplets. The first heaters  20  and the second heaters  22  may be made of an alloy of tantalum and aluminum in a preferred embodiment. However, other materials or alloys, such as platinum or HfB 2  may also be the material of the first heaters  20  and the second heaters  22 . To protect the first heaters  20  and the second heaters  22  and isolate the plural functional devices, a low temperature oxide layer  45  is deposited as a protection layer on the whole substrate  38  which includes the gate  105 , the source  106 , the drain  107 , and the second part  50 .  
         [0022]    A conductive layer  44  is formed on the first heaters  20  and the second heaters  22  to connect the first heaters  20 , the second heaters  22 , and the functional devices of the driving circuit. The driving circuit including a plurality of functional devices can transmit driving signals to independently drive each of a specific pair of heaters (the first heaters  20  and the second heaters  22 ) and drive a plurality of pairs of heaters (the first heaters  20  and the second heaters  22 ), so fewer circuit elements and circuit lines are required. For example, in the preferred embodiment, the first heaters  20  and the second heaters  22  are connected in series. The driving circuit may use a matrix to control and activate a specific pair of heaters to generate bubbles and eject droplets. For example, the driving circuit sends a column signal to select a column of pairs of heaters, and sends a row signal to further select a specific pair of heaters out of the column of pairs of heaters. The conductive layer  44  may be made of an alloy of aluminum-silicon-copper in a preferred embodiment. The conductive layer  44  may also be made of aluminum, copper, gold, tungsten, or other materials. Afterwards, a low temperature oxide layer  46  is deposited as a protection layer on the conductive layer  44 .  
         [0023]    Please refer to FIG. 9. An orifice  18  formed between the first heater  20  and the second heater  22 . If a line width of 3 μm is allowed in photolithography, the diameter of the orifice  18  can be as small as 2 μm. The pitch between the orifice  18  and an adjacent orifice  18  can be as small as 15 μm. Until now, a microinjector array with driving circuitry in one piece is formed. The driving circuitry and heaters are integrated on the same substrate  38  and an integral microinjector head structure is formed without the need of adhesion of an orifice plate.  
         [0024]    The following is a description of another embodiment of the present invention. Compared with the first embodiment, the difference lies in the process of directly etching the second part  50  of FIG. 6 to form the chamber  14  as shown in FIGS. 7, 8, and  9 . This embodiment first etches a part of the second part  50  and forms a sacrificial layer  40  on the etched position, then performs upcoming processes. Please refer to FIG. 10. FIG. 10 continues the process of FIG. 6. A partial etching of the second part  50  of FIG. 6 is performed, and an oxide layer  40  is deposited on a part of the substrate  38  uncovered by the driving circuit so as to become a sacrificial layer  40  of the chamber  14 . A low stress layer  42 ″ is then deposited as the top of chamber  14 .  
         [0025]    Please refer to FIG. 11 and FIG. 12, which are similar in their processes to those of FIG. 8 and FIG. 9. As shown in FIG. 11, the substrate  38  and the sacrificial layer  40  are etched from the back side to form the manifold  16  and the chambers  14 . The first heater  20 , the second heater  22  and the protective low temperature oxide layer  45  are deposited. A conductive layer  44  is formed to conduct the first heater  20 , the second heater  22 , and the driving circuit and to deposit a low temperature oxide layer  46  on the conductive layer  44  as a protective layer. Finally, as shown in FIG. 12, photolithography is utilized to form an orifice  18  between the first heater  20  and the second heater  22 . Then a microinjector array with driving circuitry to drive the first heater  20  and the second heater  22  is formed.  
         [0026]    The order of the above processes can be changed according to real situations while still manufacturing a micro droplet injector head with appropriate driving circuitry.  
         [0027]    It is an advantage of the present invention that the microinjector head with a plurality of microinjectors and corresponding driving circuitry according to the present invention has driving circuitry and microinjectors integrated on a same substrate. The number of processes is fewer. In addition, the structure of the microinjector head with driving circuitry has fewer circuit elements and connecting circuits.  
         [0028]    Those skilled in the art will readily observe that numerous modifications and alterations of the present 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.