Fluid injection head structure and method for manufacturing the same

The present invention provides a fluid injection head structure and a method of fabricating the same. The fluid injection head structure is disposed on a substrate and has a bubble generator, a functional device for control the bubble generator, a first conductive trace composed of poly-silicon, a chamber, a manifold in flow communication with the chamber, and a second conductive trace. The second conductive trace electrically couples the functional device with the bubble generator and the first conductive trace. Moreover, the chamber further has at least one orifice through the substrate and a gate and the first conductive trace are formed in the same photo-etching process (PEP).

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a fluid injection head structure, and more particularly, to a fluid injection head structure with conductive traces made of one single metal layer and one single poly-silicon layer.

2. Description of the Related Art

Fluid injection devices are widely applied in ink jet printers. As a reliability of ink jets have improved, the cost of manufacturing ink jets has reduced significantly. Ink jets offering high-quality droplets with a high frequency and a high spatial resolution are commonplace. Fluid injection devices can be applied to many other fields in advance, such as fuel injection systems, cell sorting, drug delivery systems, print lithography, and micro jet propulsion systems.

Among all available products, some use a method of center feeding for ink supply, such as the model of C6578 cartridge of the Hewlett-Packard Company, and some use a method of edge feeding, such as the model of HP51645 cartridge of the Hewlett-Packard Company. In the former method, a sand blasting, laser drilling, or chemical etching process is performed to create a manifold through the center of the chips for feeding ink. However, this method requires a large chip size, and the area above the manifold is wasted, leading to needlessly high manufacturing costs. Although the process of penetrating through chips is not needed in the latter method, two metal layers and a poly-silicon layer are still needed. Therefore, many photo masks are used, and both the time and cost of fabrication are increased.

U.S. Pat. No. 5,774,148, “Print head with field oxide as thermal barrier in chip”, mentions a method for transmitting signals. A second metal layer is electrically connected to a first metal layer through a via and signals are transmitted between a heater44and a MOSFET device. Additionally, a poly-silicon layer is used as a gate of MOSFET device and a contact layer is used to electrically connect to the first metal layer for transmitting signals.

SUMMARY OF INVENTION

It is therefore a primary objective of the present invention to provide a fluid injection head structure and a method of manufacturing the same with conductive traces made of one metal layer and one poly-silicon layer to simplify the manufacturing process and lower manufacturing costs.

In a preferred embodiment, the fluid injection head structure comprises a substrate, a bubble generator, a functional device to control the bubble generator, a first conductive trace made of a poly-silicon layer, a chamber, a manifold connected to the chamber such that fluid can flow through the manifold to the chamber, and a second conductive trace to electrically connect to the functional device and the bubble generator, and the functional device and the first conductive trace. In addition, the chamber further comprises an orifice in a top surface of the substrate. Moreover, a gate of the functional device and the first conductive trace are formed in the same photo-etching process (PEP).

It is an advantage of the present invention that only one metal layer and one poly-silicon layer are used as conductive layers of the fluid injection head structure. The present invention overcomes the problem of time delay and heat generation. The fabrication method of the present invention also helps to reduce manufacturing expenses and fabrication time.

These and other objectives of the present 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.

DETAILED DESCRIPTION

Please refer toFIG. 1, which is a cross-sectional diagram of a print head structure according to the present invention. A fluid injection head structure with a virtual valve is used in the present invention. As shown inFIG. 1, a bubble generator14comprises two bubble generating devices, a first heater14aand a second heater14b, disposed adjacent to an orifice12. Because of differences, such as different resistances, between the two heaters14a,14b, when the two heaters14a,14bheat fluid (not shown) inside the chamber16, two bubbles are generated in turn. A first bubble (not shown) is generated by the first heater14a, closer to a manifold11than the second heater14b, wherein the first bubble isolates the manifold11from an orifice12and acts as a virtual valve to reduce a cross talk effect between this chamber16and neighboring chambers16. Then, a second bubble (not shown) is generated by the second heater14b. The second bubble squeezes fluid, such as ink, inside the chamber16to eject out of the orifice12. Finally, the second bubble combines with the first bubble so as to reduce the generation of satellite droplets.

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 manifold11. Not counting the resistance layers, only one single poly-silicon layer and one single metal layer (SPSM) process is performed in the present invention.

Please refer toFIG. 2, which shows a cross-sectional diagram of a fluid injection head structure according to the present invention. A low temperature oxide layer18is, deposited on top of the bubble generator14. After that, a via layer is formed in a predetermined area and a metal layer13is deposited on the top surface of the heaters14aand14bthrough the via layer. Thus, the metal layer13is electrically connected to the heaters14aand14b.

In the same manner, a drain68and a source66of a MOSFET15are electrically connected to the heaters14aand14b, and a ground20via the metal layer13. When a gate64of the MOSFET15is turned on, an external voltage signal is applied to the print head from a pad of the metal layer13. A current flows from the pad via the metal layer13to the first heater14aand the second heater14b. Then, the current passes through the drain68and the source66to the ground20so as to complete a heating process. As the ink inside the chamber16is heated, two bubbles are generated to squeeze ink droplets out of the orifice12. It dependents upon the data to be printed to control which orifice12ejects ink droplets during a printing process. The material of the metal layer13is any one of aluminum, gold, copper, tungsten, alloys of aluminum-silicon-copper, or alloys of aluminum-copper.

Please refer to FIG.3and FIG.4.FIG. 3is a top view of the print head according to the present invention. In the preferred embodiment, the orifice12of the print head is divided into sixteen Pgroups, P1to P16, and each Pgroup comprises twenty-two addresses A1to A22. As shown inFIG. 5A, which shows a schematic diagram of a matrix driving circuit, a select signal is generated by a logic circuit or a microprocessor32according to the data to be printed. Then, the select signal is transmitted to a power driver34and an address driver35to determine which A (A1to A22) should be turned on and to which P (P1to P16) the power should be provided. For example, providing power to P1and turning on A22, the heaters14aand14bon the MOSFET15of P1A22will complete an operation of heating and ejecting ink at the predetermined time.

FIG. 4is a local amplified diagram of the region B shown in FIG.3. Two rows of orifices12are positioned on the center of the chip. Dividing the orifices into two parts by a line A-A″ shown inFIG. 3, there are eight groups comprising P1to P8on the right and eight groups comprising P9to P16on the left. The place above the manifold11between the two rows of orifices12is used for a power line layout. Eight metal power lines corresponding to P1to P8are positioned to the right of the line A-A″ and electrically connected to I/O pads on the right. In the same manner, eight power lines corresponding to P9to P16(not shown) are positioned on the left of the line A-A″ and electrically connected to I/O pads on the left.

The driving circuit between each corresponding P pad and G pad uses a U-type circuit layout. The driving circuit between the pad P1and the pad G1is illustrated in a dashed block in FIG.4. Each driving circuit is connected without crossing any other driving circuit. Only one metal layer13is used to form the power line19between the heaters14a,14band the grounding pad G. There are eleven metal lines22positioned above the groups of MOSFET15and another eleven metal lines22positioned below the groups of MOSFET15in the page 4. The metal lines22are electrically connected to the pads A so as to transmit the output data of the address driver35to the corresponding MOSFET15to control ink ejection. There are also eleven poly-silicon lines23positioned to the left of the groups of MOSFET15and another eleven to the right of the groups of MOSFET15. Then, contact layers24are formed to electrically connect the metal lines22and the poly-silicon lines23to complete the connection of the driving circuits. The poly-silicon lines23are used to connect the metal lines22above and below the groups of MOSFET15(i.e. the upper parts and lower parts of the metal lines22in the FIG.4). For example, if a signal is input from the pad A1to turn on the heaters of P16, it has to be transmitted via the poly-silicon lines23through the metal lines22to the heaters of P16.

Please refer toFIG. 5BtoFIG. 5D, which show schematic diagrams of circuits for transmitting signals with the silicon line23according to the present invention. Although a poly-silicon line23with a length of 2901 μm is used as an address conductive trace A1to A22, the electrical characteristics of the circuits are not deteriorated. First, very little current exists in the gate64of the MOSFET15so the heat effect of the poly-silicon lines23can be ignored. Second, resistance in the conductive trace is increased due to the poly-silicon line23may occur the problem of time delay when the heaters in A1of all P groups (including P1to P16) inject. Take two A1addresses with the largest distance between them, A1-P1and A1-P16, as example. During printing operation, the frequency of ink-jet printing is set at about 10 KHz. Each address has a switching time of about 3.5 μs. Timing of a power supply for a P group must be within a pulse width of 3.5 μs so that the timing for power supply of a P group is about 2 μs. This means that there is only a time buffer of about 500 ns between each neighboring address. These limitations must be met or errors may occur. For example, in the group P1, the printhead A1stops and the printhead A2starts to inject, but the printhead A1in the group P16may still be injecting.

According to the sheet resistances of the metal line22(0.1 Ω/μm) and the poly-silicon line23(10 Ω/μm), the equivalent resistances of A1P1and A1P16while the gate64of all MOSFET device15is turned on can be obtained. The equivalent circuit of A1P1circuit is shown as FIG.5B and that of A1P16circuit is shown as FIG.5C. In contrast to A1P1, a signal must pass through additional poly-silicon line23and a metal line22when transmitted to A1P16. The resistance R1of the additional poly-silicon line23is about 2901 Ω, and the resistance R2of the additional metal line22is about 147 Ω. A HSPICE simulate is performed for these two circuits and a result is shown in FIG.5D. Comparing time of the clock 50% of A1P1and A1P16, which are 710 and 716 ns respectively, therefore, the time delay is only about 8 ns. Comparing to the time delay endurance of 500 ns, the time delay of the present invention has no influence on ink injecting.

Please refer toFIG. 6toFIG. 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 layer62on a silicon substrate60. A blanket boron implantation process is performed to adjust the threshold voltage of the driving circuit. A poly-silicon gate64is formed in the field oxide layer62. At the same time, twenty-two poly-silicon lines23are formed on both edges of the chip. An arsenic implantation is performed to form a source66and a drain68on both sides of the gate64. Then a low stress layer72such as silicon nitride is deposited to form an upper layer of the chamber16as shown in FIG.6.

Please refer to FIG.7. An etching solution (KOH) is used to etch a back side of substrate60to form a manifold11for fluid supply. Then the field oxide layer62is partially removed with an etching solution (HF) to form the chamber16. After that, a precisely-timed etching process using KOH is performed to increase the depth of the chamber16. The chamber16and the manifold11are connected and filled with fluid, however this etching process needs special attention because convex corners in the chamber16are also etched.

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 heater14aand the second heater14bis alloys of tantalum and aluminum, but other materials like platinum or HfB2can also work effectively. A low temperature oxide layer74is deposited over the entire substrate60. In addition to protecting the first heater14aand the second heater14band isolating the MOSFET15, the low temperature oxide layer74serves as a protective layer that covers the gate64, the source66, the drain68, and the field oxide62.

Next, a conductive layer13is formed on the first heater14aand the second heater14bto electrically connect the first heater14a, the second heater14b, and the MOSFET15of 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 layer13is an alloy of aluminum-silicon-copper, aluminum, copper, gold, or tungsten. A low temperature oxide layer76is deposited as a protection layer on the conductive layer13.

Please refer to FIG.8. An orifice12is formed between the first heater14aand the second heater14b. 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.

The present invention uses a single poly-silicon and a single metal (SPSM) process to complete the circuit connection. The poly-silicon lines23and the gate64can be formed in a photo-etching process (PEP) to simplify the manufacturing process. The present invention not only avoids using a second metal layer, but also completes the function of the MOSFET15without affecting performance.

The following is a detailed description of the operation of the present invention. Please refer to FIG.4and FIG.5A. When printing starts, the logic circuit or microprocessor32determines which orifices12should eject ink according to the data to be printed and generates a select signal. The select signal is transmitted to the power driver34and the address driver32to turn on the proper A groups (A1to A22) and apply power to the proper P groups (P1to P16). Thus, a current is generated and applied to the heaters14aand14bto heat fluid and generate bubbles so that ink droplets are ejected. For example, suppose that a droplet is to be ejected from the orifice12aof A1P1. First, a voltage signal is input from an I/O pad of A1and transmitted to the gate64of MOSFET15to turn on the gate64. Next, another voltage signal is input from an I/O pad of P1to generate a current. The current passes via the heaters14aand14bto the drain68, the source66, and the ground20so as to heat the fluid and generate bubbles. The bubbles act to eject an ink droplet from the orifice12aof A1P1.

Although the above description details a monochromatic printer, 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.

According to the present invention, only a single poly-silicon process and a single metal process are used to complete circuit layouts of the whole chip. There are several advantages of the present invention. The fluid injection head of the present invention uses two fewer photo masks than other similar products and therefore the cost of the photolithography processes are reduced. Moreover, fabricating time is reduced and throughput is improved. Since ink is supplied without the requirement of etching through the entire chip, the circuit layouts can be performed above the manifolds, leading to a reduction in wafer size and an increase the number of dies per wafer. Using this method of improving layout integration, the area required for circuit layout is reduced, and more orifices can be disposed in the same wafer area to improve the printing speed.