Abstract:
A micro electro-mechanical device embodied within an ink ejection nozzle having an actuating arm that is caused to move an ink displacing paddle when heat inducing electric current is passed through the actuating arm is disclosed. The paddle is located in an ink chamber and the actuating arm passes through an actuator aperture in the chamber. The actuating arm including the paddle is moved to eject a droplet. The chamber includes a plurality of vents for venting to atmosphere air bubbles which may form in the chamber when the device operates to eject droplets of ink.

Description:
FIELD OF THE INVENTION 
     This invention relates to a vent 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 vents within other types of MEM devices. 
     CO-PENDING APPLICATIONS 
     Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention simultaneously with the present application Ser. Nos.:
         09/575,197, 09/575,197, 09/575,197, 09/575,197, 09/575,197, 09/575,148, 09/575,130, 09/575,165, 09/575,153, 09/575,118, 09/575,131, 09/575,116, 09/575,144, 09/575,139, 09/575,186, 09/575,185, 09/575,191, 09/575,145, 09/575,192, 09/609,303, 09/610,095, 09/575,596, 09/575,181, 09/575,193, 09/575,156, 09/575,183, 09/575,160, 09/575,150, 09/575,169, 09/575,184, 09/575,128, 09/575,180, 09/575,149, 09/575,179, 09/575,187, 09/575,155, 09/575,133, 09/575,143, 09/575,196, 09/575,198, 09/575,178, 09/575,164, 09/575,146, 09/608,920, 09/575,174, 09/575,163, 09/575,168, 09/575,154, 09/575,129, 09/575,124, 09/575,188, 09/575,189, 09/575,162, 09/575,172, 09/575,170, 09/575,171, 09/575,161, 09/575,141, 09/575,125, 09/575,142, 09/575,140, 09/575,190, 09/575,138, 09/575,126, 09/575,127, 09/575,158, 09/575,117, 09/564,034, 09/575,147, 09/575,152, 09/575,176, 09/575,151, 09/575,177, 09/575,175, 09/575,115, 09/575,114, 09/575,113, 09/575,112, 09/575,111, 09/575,108, 09/575,109, 09/575,182, 09/575,173, 09/575,194, 09/575,136, 09/575,119, 09/575,135, 09/575,157, 09/575,166, 09/575,134, 09/575,121, 09/575,137, 09/575,167, 09/575,120, 09/575,122.       

     The disclosures of these co-pending applications are incorporated herein by reference. 
     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 A 4  sheet paper to provide photographic quality image printing at 1,600 dpi. In order to achieve the nozzle density, the nozzles are fabricated by integrating MEMS-CMOS technology and 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 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. 
     SUMMARY OF THE INVENTION 
     The present invention provides a micro electro-mechanical device comprising:
         a fluid chamber for containing a fluid,   an outlet aperture in the chamber for allowing exit of fluid from the chamber,
           an actuator for dispensing fluid from the chamber through the outlet aperture, and   
           at least one vent in the chamber for venting to the exterior of the chamber air bubbles which form within the chamber.       

     PREFERRED FEATURES OF THE INVENTION 
     Preferably the actuator includes a paddle located within the chamber, the chamber including a peripheral wall, and the at least one vent is arranged within the peripheral wall adjacent a peripheral portion of the paddle. 
     Preferably a plurality of vents are arranged in the peripheral wall, the plurality of vents being disposed about the peripheral wall adjacent to peripheral portions of the paddle. 
     Preferably the vent is defined by a first layer and a second layer spaced apart from the first layer, a sacrificial layer being deposited between the first and second layers and the sacrificial layer being etched away to form the vent between the first and second layers. 
     Preferably the first and second layers have a raised section defined by a pair of shoulders, the sacrificial material being deposited on the raised section of the first layer so as to define a vent passage which forms said vent when the sacrificial material is etched away, the second layer being deposited on the sacrificial material and the portion of the second layer deposited on the sacrificial material having a pair of side walls and a roof which, with the first layer, define the vent passage of the vent. 
     Preferably the shoulders include apertures for preventing wicking of fluid from the shoulders onto a substrate. 
    
    
     
       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 detailed view of a portion of the preferred embodiment shown in  FIGS. 1  to  3 ; and 
         FIG. 5  is a view from the direction of arrow A in FIG.  4 . 
     
    
    
     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  1  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/AU00/0038 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” (Reference: 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 upper and lower arm portions  31  and  32 . Lower portion  32  of the arm  28  is an 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 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 . The block  8  includes a generally T-shaped portion  50  (when viewed in plan) which has a peripheral wall  10 . The upper wall  23  of the chamber  24  has a generally T-shaped slot  60 , defined by edge portion  52  of the wall  23 , which receives the T-shaped portion  50  of the block  8 . 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 portion  50  of the wall  23  defines an actuator aperture  54  which is substantially entirely closed by T-shaped portion  50  of the block  8  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 wall  10  of the portion  50  is separated from the edge  52  by a distance of less than one micron so as to define a fine slot between the edge  57  and the wall  10 . 
     As the actuator arm  28  moves up and down to eject droplet D from the chamber  24 , the block  8  and wall  10  move up and down relative to edge  52  of slot  60  of the wall  23  whilst maintaining a closely spaced apart relationship with the edge  52  of the wall  23 . A meniscus M is formed between the wall  10  and the edge  52  as the wall  10  moves up and down relative to the edge  52  in view of the close proximity of the wall  10  to the edge  52 . The maintenance of the meniscus M, forms a seal between edge  52  and wall  10 , 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  52  may carry a lip  81  and the wall  10  may also carry a lip  83  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  81  may extend completely about the periphery of the wall  23  and similar lips may also be provided on the aperture  13 . 
     As shown in  FIG. 1 , a plurality of vents  5  are arranged in the peripheral wall  23   a  of the chamber  24 . In the preferred embodiment, five vents  5  are included. The vents  5  are arranged adjacent to the periphery of paddle  27  (which is generally circular in configuration matching the configuration of the chamber  24 ) when the paddle  27  is in the quiescent position shown in FIG.  2 . 
     As shown in more detail in  FIGS. 4 and 5 , the vent  5  is formed by a first deposited titanium nitride layer  14  which includes a ledge portion  16 , and a second titanium nitride layer  15  which has a ledge portion  17 . In the formation of the nozzle shown in the drawings, a sacrificial material is despotised on the layer  14  onto which the layer  15  is then deposited and the sacrificial material is etched away to leave a vent passage  11  between the layers  14  and  15 , which forms the vent  5 , and which has an outlet opening  11   a . The passage  11  communicates with the interior of the chamber  24 . 
     As best shown in  FIG. 5 , the vent opening la is formed in a raised portion of the layers  14  and  15 . The layers  14  and  15  are generally annular in configuration extending about the periphery of the chamber  24 . The layers  14  and  15  are in contact with one another except at the positions where the vent passages  11  are formed. As best shown in  FIG. 5 , the layers  14  and  15  extend upwardly at the vents  5  to form shoulders  80 . The portion of the layer  14  between the shoulders  80  is generally planar as shown in FIG.  5 . However, the layer  15  diverges upwardly from the layer  14  to define walls  82  and a roof section  84  which with the layer  14  define the vent passage  11  and vent opening  11   a . The sacrificial material is deposited generally to take the shape of the vent passage  11  so that the layer  15  is deposited on the layer  14  except for where the sacrificial material is located, and the layer  15  extends over the sacrificial material where the vent passage  11  is to be formed so as to form the side walls  82  and roof  84  shown in FIG.  5 . As noted above, the sacrificial material is then etched away leaving the vent passage  11  between the layers  14 , and  15 . 
     The shoulders  80  are provided with slots  25  and  26  which prevent the possibility of any fluid which may leak from the chamber  24  through the vents  5  wicking along the lower surface of the layer  14  and reaching the layer  22  which may cause damage to the layer  22 . In general, fluid is prevented from leaking out of the vents  5  by an ink meniscus which forms across the vent opening  11   a  between the layers  13  and  14  to thereby form a seal which reduces the likelihood of any ink leaking from the vents  5 . 
     During the operation of the nozzle, when the paddle  27  moves from the quiescent position shown in  FIGS. 1 and 2  to the position shown in  FIG. 3  to eject a drop D of fluid, there is a possibility that bubbles may form particularly adjacent the ledges  16  and  17 . Any bubbles which form will be able to pass through the vent passage  11  and out of the vent opening  11   a  of each vent  5  to expire to the external ambient atmosphere.