Patent Publication Number: US-6338548-B1

Title: Seal in a micro electro-mechanical device

Description:
CO-PENDING APPLICATIONS 
     Various methods, systems and apparatus relating to the present invention are disclosed in the following copending applications filed by the applicant or assignee of the present invention simultaneously with the present application: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
             
            
               
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     The disclosures of these copending applications are incorporated herein by cross-reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a seal within a micro electro-mechanical (MEM) device. The invention has application in ejection nozzles of the type that are fabricated by integrating the technologies applicable to micro electro-mechanical systems (MEMS) and complimentary metal-oxide semiconductor (“CMOS”) integrated circuits, and the invention is hereinafter described in the context of that application. However, it will be understood that the invention does have broader application to seals within various types of MEM devices. 
     BACKGROUND OF THE INVENTION 
     A high speed page width ink jet printer has recently been developed by the present applicant. This typically employs in the order of 51, 200 ink jet nozzles to print on A4 size paper to provide photographic quality image printing at 1,600 dpi. In order to achieve this nozzle density, the nozzles are fabricated by integrating MEMS-CMOS technology and in this context reference may be made to International Patent Application No. PCT/AU00/00338 lodged by the present applicant and entitled “Thermal Actuator”. 
     These high speed page width ink jet printers produce an image on a sheet by causing an actuator arm to move relative to a substrate by forming the actuating arm in part from an electrically resistive material and by applying a current to the arm to effect movement of the arm. The arm is connected to a paddle so that upon movement of the arm the paddle is moved to eject a droplet of ink onto the sheet. In order to eject the droplet of ink the paddle extends into a nozzle chamber which has a nozzle aperture and movement of the paddle causes the droplet to be ejected from the nozzle aperture. It is therefore necessary for the actuator arm and the paddle to move relative to the nozzle chamber in order to effect ejection of the droplet. Also, in view of the need for the actuator arm and paddle to move relative to the nozzle chamber there is also a need to seal the nozzle chamber where the actuator arm enters the chamber so the ink does not spuriously leak from the chamber during operation of the printer. 
     SUMMARY OF THE INVENTION 
     The present invention provides a micro electromechanical device comprising; 
     a fluid chamber for containing a fluid, the fluid chamber having a first chamber wall, the chamber wall having a substantially straight peripheral edge portion; 
     an outlet aperture in the chamber wall for allowing exit of fluid from the chamber; 
     an actuator aperture defined partly by said edge portion of the chamber wall; 
     an actuator extending into said chamber through the actuator aperture and being moveable to dispense fluid from the chamber through the outlet aperture; 
     a second wall carried by the actuator and covering at least a part of said actuator aperture, the second wall being substantially planar and moveable relative to the edge portion of the chamber wall when the actuator moves to dispense fluid from the chamber; and 
     when the actuator moves in the chamber to dispense fluid from the chamber the second wall moves in closely spaced apart relationship with respect to the edge portion so that a meniscus is formed between the edge portion and second wall by fluid within the chamber thereby creating a seal between the edge portion and the second wall. 
     PREFERRED FEATURES OF THE INVENTION 
     Preferably the second wall substantially entirely covers the actuator aperture. 
     Preferably the second wall is provided on a block coupled to the actuator. 
     Preferably the block is substantially rectangular in configuration. 
     Preferably the second wall has a width in a direction perpendicular to the direction of movement of the actuator which is substantially the same as the length of the straight edge portion of the chamber wall. 
     Preferably the actuator includes an upper arm portion and an lower arm portion, the upper arm portion having an opening and a portion of the block including a flange projecting through said opening to facilitate coupling of the block to the actuator. 
     Preferably the second wall is spaced from the edge portion of the chamber wall by a distance of less than one micron when the actuator is in a rest position. 
     Preferably the actuator is coupled to a paddle arranged within the chamber for the ejection of fluid in the form of droplets from the chamber upon movement of the actuator. 
     Preferably the actuator is supported at one end in a support structure and electrical circuit elements for operation of the device are embodied in CMOS structures within or on the support structure. 
     Preferably the chamber wall and the block having the second wall are formed by deposition at the same time and wherein the block has an upper surface which is substantially level with the chamber wall when the actuator is in the rest position. 
     Preferably a lip is formed on the edge portion which extends outwardly of the chamber the second wall also has a lip which extends outwardly of the chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings in which; 
     FIG. 1 is a plan view of one embodiment of the invention in an ink jet nozzle for a printer; 
     FIG. 2 is a cross-sectional view of the nozzle of FIG. 1 along line  2 - 2  of FIG. 1; 
     FIG. 3 is a more detailed cross-sectional view similar to FIG. 2 of the preferred embodiment of the invention in an extreme actuated position showing a drop being ejected from the nozzle; 
     FIG. 4 is a perspective view of a portion of the preferred embodiment shown in FIGS. 1 to  3 ; 
     FIG. 5 is a cross-sectional view along the line  5 - 5  of FIG. 4 according to one embodiment of the invention; and 
     FIG. 6 is a view along the line  5 - 5  of FIG. 4 according to a further embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated with approximately 3000×magnification in FIG. 1, and other relevant drawing Figures, a single ink jet nozzle device is shown as a portion of a chip which is fabricated by integrating MEMS and CMOS technologies. The complete nozzle device includes a support structure having a silicon substrate  20 , a metal oxide semiconductor layer  21 , a passivation layer  22 , and a non-corrosive dielectric coating/chamber defining layer  29 . Reference may be made to the above identified International Patent Application No. PCT/AU00/00338 for disclosure of the fabrication of the nozzle device. Operation of the device is also more fully disclosed in co-pending application entitled “Movement Sensor In A Micro Electro-mechanical Device” (MJ12) by the same applicant. The contents of these two applications are incorporated into this specification by this reference. 
     The nozzle device incorporates an ink chamber  24  which is connected to a source (not shown) of ink. The layer  29  forms, amongst other components as will be described hereinafter, a chamber wall  23  which has a nozzle aperture  13  for the ejection of a droplet from ink  25  contained within the chamber  24 . As best shown in FIG. 1 the wall  23  is generally cylindrical in configuration with the aperture  13  being provided substantially in the middle of the cylindrical wall  23 . The wall  23  has a straight edge portion  10  which forms part of the periphery of the wall  23 . 
     As best seen in FIG. 3, the chamber  24  is also defined by a peripheral side wall  23   a , a lower side wall  23   b , a base wall (not shown), and by an edge portion  39  of substrate  20 . An actuating arm  28  is formed on layer  22  and support portion  23   c  is formed at one end of the actuating arm  28 . 
     The actuating arm  28  is deposited during fabrication of the device and is pivotable with respect to the substrate  20  and support  23   c . The actuating arm  28  comprises outer and lower arm portions  31  and  32 . Inner portion  32  of the arm  28  is in electrical contact with the CMOS layer  21  for the supply of electrical current to the portion  32  to cause movement of the arm  28 , by thermal bending, from the position shown in FIG. 2 to the extreme position shown in FIG. 3 so as to eject droplet D through aperture  13  for deposition on a sheet (not shown). The layer  22  therefore includes the power supply circuitry for supplying current to the portion  32  together with other circuitry for operating the nozzle shown in the drawings as described in the aforesaid co-pending applications. 
     A block  8  is mounted on the actuator arm  28  and includes a flange portion  50  which extends through an opening  52  in the portion  31  to facilitate securement of the block  8  to the actuator  28 . The actuator  28  carries a paddle  27  which is arranged within the chamber  24  and which is moveable with the actuator as shown in FIGS. 1 and 3 to eject the droplet D. 
     The peripheral wall  23   a , chamber wall  23 , block  8  and support portion  23   c  are all formed by deposition of material which forms the layer  29  and by etching sacrificial material to define the chamber  24 , nozzle aperture  13 , the discrete block  8  and the space between the block  8  and the support portion  23   c . The lower wall portion  23   b  is also formed during deposition with the substrate  20 . 
     The space between end edge  22   a  of layer  22  and edge  10  of the wall  23  defines an actuator aperture  54  which is substantially entirely closed by wall  9  when the actuator  28  is in a rest or quiescent state as shown in FIGS. 1 and 2. In the quiescent position shown in FIGS. 1 and 2, the edge portion  10  of the wall  23  is separated from the wall  9  by a distance of less than one micron so as to define a fine slot between the wall  9  and the edge  10 . 
     As the actuator arm  28  moves up and down to eject droplet D from the chamber  24 , the planar wall  9  moves up and down relative to edge  10  of the wall  23  whilst maintaining a closely spaced apart relationship with the edge  10  of the wall  23 . A meniscus M is formed between the wall  9  and the edge  10  as the wall  9  moves up and down relative to the edge  10  in view of the close proximity of the wall  9  to the edge  10 . The maintenance of the meniscus M, forms a seal between edge portion  10  and wall  9 , and therefore reduces opportunities for ink leakage and wicking from chamber  24 . A meniscus M 2  is also formed between support flange  56  formed on the layer  22  and portion  58  of the actuator  28  on which block  8  is formed. When in the quiescent position the portion  58  rests on the flange  54 . The formation of the meniscus M 2  also reduces opportunities for ink leakage and wicking during movement of the actuating arm  28  and the paddle  27 . A meniscus (not shown) is also formed between the sides (not shown) of actuator aperture  54  and the edges (not shown) of wall  23   a  which define the aperture  54 . 
     As shown in FIG. 3, the edge portion  10  may carry a lip  80  and the wall  9  may also carry a lip  82  to further reduce the likelihood of wicking of ink from the chamber  24  onto the block  8  or upper surface of the wall  23 . The lip  80  may extend completely about the periphery of the wall  23  and similar lips may also be provided on the aperture  13 . 
     With reference to FIGS. 5 and 6 the paddle  27  is coupled to the remainder of the actuator arm  28  by a strut portion  120  which extends outwardly from the block  8 . The strut portion  120  can include a reinforced structure to strengthen the strut portion  120  and therefore connection of the paddle  27  with the remainder of the actuating arm  28 . 
     FIG. 5 shows one embodiment of the reinforcing structure and in this embodiment the portion  120  is formed from titanium nitrate layers  122  and  123  which surround and enclose a sacrificial material  124 . In a second embodiment shown in FIG. 6 the layer  122  is a corrugated layer enclosing sacrificial material  126 ,  127  and  128 . The structures shown in FIGS. 5 and 6 increase the strength of the strut portion  120  connecting the block  8  with the paddle  27 .