Abstract:
A fluid ejection device, a method and an operation method thereof are disclosed. The fluid ejection device includes a substrate, a beam and an activation pad. The substrate has an orifice, and the beam includes a fixed portion and a cantilever portion and is disposed over the substrate, wherein the cantilever portion is disposed over the orifice. Furthermore, the activation pad is disposed between the cantilever portion of the beam and the substrate. Because the fluid ejection device of the present invention is fabricated by using micro-electromechanical technology, and therefore it possible to obtain a fluid ejection device capable of ejecting the fluid from the orifice at a high-speed and also the quantity fluid ejected can be very small.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a fluid ejection device, a fabrication method and an operating method thereof, adapted for an ink-jet printing head; and more particularly to a micro-electromechanical system (MEMS) fluid ejection device, a fabrication method and an operating method thereof. 
   2. Description of Related Art 
   To date, the ink-jet technology includes the bubble ink-jet technology and the piezoelectric ink-jet technology. 
     FIGS. 1A and 1B  are schematic drawings showing an ink-jet head and an operation of the prior art bubble ink-jet technology. Referring to  FIG. 1A , in the ink-jet head  100  adopted by the prior art bubble technology, the ink  104  is heated by a heater  102  for generating the bubble  106 . Thereafter, the ink  104  is ejected from a nozzle  108  under the pressure of the bubble  106 . 
   Referring to  FIG. 1B , when the heater  102  stops heating, the bubble  106  in the ink  104  will not be inflated and remain flat as the result of cooling down. The surface tension of the ink  104  will create tensile force to pull back the ink  104 . Accordingly, the operation of the thermal sensing ink-jet technology is performed. The printing speed of the bubble ink-jet technology is about micro-second level. The disadvantage is that the ink is easily ejected due to pressure and the ejection force of the ink cannot be controlled. The ink is adversely affected by law of inertia at the nozzle, resulting in non-uniformity or ink residuals. The other disadvantage is that, because the ink-jet head of the bubble ink-jet technology is usually under high temperature situation due to use of heater, and therefore the ink-jet head is easily damaged, especially in absence of ink therein. 
     FIGS. 2A-2C  are schematic drawings showing an ink-jet head and an operation of the prior art piezoelectric ink-jet technology. Referring to  FIG. 2A , the ink-jet head  200  of the prior art piezoelectric ink-jet technology uses a quartz crystal  202  to control the ejection of the ink  204 . The ink-jet head  200  comprises a nozzle  208 . When electricity is applied to the quartz crystal, the quartz crystal  202  generates a fixed oscillation frequency. When electricity applied to the quartz crystal is removed, the ink is pulled back. 
   Referring to  FIG. 2B , when electricity is applied to the quartz crystal  202 , the quartz crystal  202  expands and ejects the ink  204  from the nozzle  208 . Because the piezoelectric ink-jet technology does not need thermal transformation, the damage the to ink-jet head due to thermal issue can be avoided. 
   Referring to  FIG. 2C , when the supply of electricity to the quartz crystal is cut, the quartz crystal  202  shrinks to the original size for pulling the ink  204  back. The printing speed of the piezoelectric ink-jet technology is also about micro-second level. The problem is that it is not possible to further reduce the quantity of ejected ink. 
   SUMMARY OF INVENTION 
   Accordingly, the present invention is directed to a fluid ejection device, adapted for ejecting the fluid at a nano-second level speed and to precisely control the quantity of the fluid ejected thereby. The fluid ejection device is suitable for an ink-jet printer. 
   The present invention is also directed to a method of fabricating a fluid ejection device. The fabrication method is capable of further reducing the size of the fluid ejection device. 
   The present invention is also directed to a method of operating a fluid ejection device, which is capable of enhancing the fluid ejection speed and precisely controlling the quantity of the fluid rejected thereby. 
   According to an embodiment of the present invention, a fluid ejection device comprises a substrate, a beam and an activation pad. The substrate comprises an orifice. The beam is disposed over the substrate. The beam comprises a fixed portion and a cantilever portion, wherein the cantilever portion is disposed over the orifice. The activation pad is disposed between the cantilever portion of the beam and the substrate. 
   According to an embodiment of the present invention, a method of fabricating the fluid ejection device is provided. First, a substrate is provided. Next, an activation pad is formed on the substrate. Next, a patterned sacrificial layer is formed over the substrate covering the activation pad, the patterned sacrificial layer comprises an opening exposing a portion of the substrate there-within. A patterned mold layer comprising a trench is formed over the patterned sacrificial layer, wherein the trench positioned over the opening exposing the opening. Next, a first conductive layer is formed over the mold layer filling the opening and the trench. Next, a hole formed in a backside of the substrate. Thereafter, the patterned sacrificial layer and the patterned mold layer are removed. The first conductive layer constitutes a beam structure. 
   According to an embodiment of the present invention, a method of operating the fluid ejection device is provided. First, a fluid ejection device is provided. Next, the fluid ejection device is filled with a fluid. For ejecting the fluid out of the orifice, a voltage is applied to the activation pad, as a result, the cantilever portion of the beam is pulled down from an initial position toward the orifice and thereby ejecting the fluid out of the orifice. When the voltage applied to the activation pad is removed, the cantilever portion of the beam gradually moves away from the orifice. 
   According to an embodiment of the present invention, a micro-electromechanical structure is used for fluid ejection, and therefore the fluid ejection speed can be at a nano-second level and the fluid quantity ejected thereby can be precisely controlled. Moreover, according to an embodiment of the present invention, the micro-electromechanical technology is applied for fabricating the fluid ejection device, and therefore the size of the fluid ejection device can be effectively reduced and can be adapted for meeting the high resolution requirement of ink-jet printers. Additionally, a voltage is applied for controlling the fluid ejection instead of using a heater, and therefore damage attributed to the high temperature can be effectively avoided. 
   In order to make the aforementioned and other objects, features and advantages of the present invention understandable, a preferred embodiment accompanied with figures is described in detail below. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIGS. 1A and 1B  are schematic drawings showing an ink-jet head and a method of operating a prior art bubble ink-jet device. 
       FIGS. 2A-2C  are schematic drawings showing an ink-jet head and a method of operating the prior art piezoelectric ink-jet device. 
       FIG. 3A  is a cross-sectional view showing a fluid ejection device according to an embodiment of the present invention. 
       FIGS. 3B and 3C  are schematic drawings showing a method of operating of the fluid ejection device of  FIG. 3A  according to an embodiment of the present invention. 
       FIGS. 4A-4G  are cross-sectional views showing a method manufacturing a fluid ejection device according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 3A  is a cross-sectional view showing a fluid ejection device according to an embodiment of the present invention.  FIGS. 3B and 3C  are schematic drawings showing a method of operating the fluid ejection device of  FIG. 3A  according to an embodiment of the present invention. 
   Please referring to  FIG. 3A , the exemplary fluid ejection device  30  comprises: a substrate  300 , a beam  302  and an activation pad  304 . The substrate  300  comprises an orifice  306  formed thereon. The beam  302  comprises a fixed portion  312  and a cantilever portion  310 , wherein the cantilever portion  310  is disposed over and correspond to the orifice  306 . The activation pad  304  is disposed between the cantilever portion  310  of the beam  302  and the substrate  300 . 
   In an embodiment of the present invention, the fixed portion  312  is, for example, a pillar structure formed on the substrate  300  and is adapted for supporting the cantilever portion  310 . The activation pad  304  on the substrate  300  is separated from the beam  302  by a distance  305 . In another embodiment of the present invention, the fluid ejection device  30  further comprises a stopper  308 , which is disposed on the cantilever portion  310  of the beam  302 , and is aligned to the orifice  306  of the substrate  300 . According to an embodiment of the present invention, the dimension of the stopper  308  can be larger than that of the orifice  306 . 
   According to an embodiment of the present invention, the point of attachment on the cantilever portion  310  with the fixed portion  312  is such that a length ratio of a portion including the end with stopper  308  to the portion including the opposite end thereof on either side of the point of attachment is 4:1. For example, as shown in  FIG. 3A , the length ratio of the portion cantilever portion  310  having the stopper  308  on the right side of the fixed portion  312  to the portion of the cantilever portion  310  the left side of the fixed portion  312  about 4:1. However, the ratio of the beam  302  of the present invention is not limited thereto. In addition, the material of the activation pad  304  and the beam  302  can be metal. It is preferred that it is a non-corrosive conductive metal, such as gold. In addition, the shape of the orifice  306  can be, for example, a funnel shape as shown in  FIG. 3A , or the other suitable shape, such as cylindrical shape or bowl shape. 
   According to an embodiment of the present invention, the method of operating the fluid ejection device  30  for ejecting the fluid through the orifice of the ink-jet printing head will be described with reference to  FIG. 3B . First, the fluid  314  is filled into the fluid ejection device  30 . Then a voltage is applied to the activation pad  304  of the fluid ejection device  30 . A voltage difference occurs between the activation pad  304  and the beam  302 . As a result, the cantilever portion  310  of the beam  302  is pulled down from an initial position toward the orifice  306  for ejecting the fluid  314  out of the orifice  306 . 
   When the voltage is applied to the activation pad  304  of the fluid ejection device  30 , a corresponding voltage can be optionally applied to the beam  302  of the fluid ejection device  30  according to the practical design or requirement. In an embodiment, when the cantilever portion  310  of the beam  302  is pulled down, the stopper  308  on the cantilever portion  310  will stick to the orifice  306  for precisely controlling the fluid  314  ejected from the orifice  306 . 
   Referring to  FIG. 3C , when the voltage applied to the activation is removed, the cantilever portion  310  of the beam  302  moves away from the orifice  306  and return to, for example, to its original position  316 . Meanwhile, the fluid  314  is pulled back and the fluid  314  will be maintained in the fluid ejection device  30  because of its viscosity. 
   The method of fabricating a fluid ejection device according to an embodiment to the present invention is described with reference to  FIGS. 4A-4G . The fluid ejection device is fabricated by using the micro-electromechanical technology.  FIGS. 4A-4G  are cross-sectional views showing progression steps of the method of fabricating a fluid ejection device according to an embodiment of the present invention. 
   Referring to  FIG. 4A , a substrate  400  is provided. An oxide layer  402  is formed on the substrate  400 , and a conductive layer  404  is formed on the oxide layer  402 . The method of forming the conductive layer  404  can be, for example, a sputtering process, and the material of the conductive layer  404  can be metal, such as gold. 
   Referring to  FIG. 4B , the conductive layer  404  and the oxide layer  402  are etched to form an activation pad  406 . Next, a sacrificial layer  408  is formed over the substrate  400  covering the activation pad  406 , wherein the thickness of the sacrificial layer  408  will determine the gap between the activation pad  406  and the subsequent beam. In an embodiment of the present invention, the thickness of the sacrificial layer  406  can be, for example, from about 4000 Å to about 6000 Å, and preferably about 5000 Å. The material of the sacrificial layer  408  can be, for example, photoresist or any other material having an etching selectivity different from conductive material. 
   Referring to  FIG. 4C , the sacrificial layer  408  is etched to form an opening  410  and an indentation  411  therein. In an embodiment of the present invention, the indentation  411  defines the subsequently formed stopper. Before performing the next process, it is optional to sputter a seed layer  412 , such as Cr, Au or the combination thereof, on the surface of the patterned sacrificial layer  408 , the indentation  411  and the sidewalls of the opening  410 . The thickness of the seed layer  412  can be, for example, from about 800 Å to about 1200 Å, and preferably about 1000 Å. 
   Referring to  FIG. 4D , a patterned mold layer  414  is formed on the sacrificial layer  404 , wherein the mold layer  414  comprises a trench  416  exposing the opening  410 . In an embodiment of the present invention, the material of the mold layer can be, for example, same or similar to that of the sacrificial layer  408 . Next, another conductive layer  418  is formed in the opening  410  and the trench  416 . The method of forming the conductive layer  418  can be, for example, a sputtering method, and the material of the conductive layer  418  can be a metal, such as gold. 
   Referring to  FIG. 4E , a first patterned mask layer  420  is formed on the backside  400   a  of the substrate  400 . Next, an etching process is carried out to remove a portion of the substrate  400  exposed by the first patterned mask layer  420  using the first patterned mask layer  420  as an etching mask to form a notch  422 . For example, etching process can be a wet etching process using a solution containing, for example, KOH. 
   Referring to  FIG. 4F , the first patterned mask layer  420  is removed. Next, a second mask layer  424  is formed on the backside  400   a  of the substrate  400  covering the sidewalls and a portion of the bottom of the notch such that a portion of the bottom of notch  422  is exposed. Next, an etching process is carried out using the second mask layer  424  as an etching mask to remove a portion of the substrate  400  until a portion of the sacrificial layer is exposed to form a hole  426 . The etching process can be, for example, a dry etching process. 
   According to another embodiment, the second mask layer  424  can be formed on the first patterned mask layer  420  without removing the first patterned mask layer  420 . Thereafter, the etching process can be carried out to form the hole  426  through the substrate  400 . 
   According to another embodiment of the present invention, the hole  426  can be formed by directly forming a patterned mask layer (not shown) on the backside  400   a  of the substrate  400  for exposing a portion of the substrate  400 . Thereafter, an etching process is carried out to form the hole  426  through the backside  400   a  using the mask layer as an etching mask layer. 
   Referring to  FIG. 4G , the sacrificial layer  408  and the mold layer  414  are removed and the conductive layer  418  constitutes the beam structure. Noticeably, the materials of the mask layers  422  and  426  are similar to those of the sacrificial layer  408  and the mold layer  414 , and accordingly, the mask layers  422  and  426  can be removed simultaneously. The substrate  400  is encapsulated to form an encapsulation structure  428  covering the activation pad and the conductive layer  418 . The method of encapsulating the substrate  400  includes a frit glass seal method or a thermal compression method. 
   Accordingly, the micro-electromechanical technology is applied to fabricate the fluid ejection device. Therefore, the size of the fluid ejection device can substantially reduced such the fluid ejection can be at a nano-second level speed and the quantity of the fluid ejected can be precisely controlled. 
   According to an embodiment of the present invention, the micro-electromechanical technology is applied to fabricate the fluid ejection device so that the size of the fluid ejection device can be substantially reduced. 
   Moreover, a voltage applied to control the fluid ejection instead of using a heater, and therefore damage attributed to the high temperature due to heater can be effectively avoided. 
   Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be constructed broadly to include other variants and embodiments of the invention which may be made by those skilled in the field of this art without departing from the scope and range of equivalents of the invention.