Abstract:
PROBLEM TO BE SOLVED: To enhance ink ejection efficiency by deforming a diaphragm, constituting a part of an ink carrying path communicating with a nozzle at the forward end, gradually toward the nozzle from the rear of the ink carrying path thereby producing an unidirectional ink flow.  
     SOLUTION: A diaphragm  55  constituting a part of an ink carrying path  51  communicating with a nozzle  54  and an electrode  72  facing the diaphragm are divided, between an ink supply chamber  52  and the nozzle  54 , into a plurality of individual electrodes  72   a - 72   c  which are connected with a head ejection drive section  105  through respective terminals  74 . The diaphragm  55  is displaced from the rear side by applying a voltage sequentially, at a constant time interval, to the individual electrodes  72   a - 72   c  starting from the rear electrode  72   c  close to the ink supply chamber  52 . Since the diaphragm  55  exhibits squeezing effect, unidirectional ink flow can be produced in the ink carrying path  51  and ink can be carried surely to the nozzle  54  at the forward end.

Description:
[0001]     This application is a divisional of U.S. patent application Ser. No. 10/360,942 filed Feb. 6, 2003, in the name of Anagnostopoulos et al., and assigned to the Eastman Kodak Company. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to micro-electromechanical (MEM) drop-on-demand liquid emission devices such as, for example, inkjet printers, and more particularly such devices which employ an electrostatic actuator for driving liquid from the device.  
       BACKGROUND OF THE INVENTION  
       [0003]     Mechanical grating devices with electrostatic actuators are known for spatial light modulators. U.S. Pat. No. 6,307,663, which issued to Kowarz on Oct. 23, 2001, discloses a mechanical grating device for modulating an incident beam of light by diffraction. The grating device includes an elongated element having a light reflective surface. The elongated element is positioned over a substrate and is supported by a pair of end supports. At least one intermediate support is positioned between the end supports. The device also includes a means for applying a force (for example, an electrostatic force) to the elongated element to cause the element to deform between first and second operating states. U.S. Patent Application Publication No. U.S. 2001/0024325 A1, which published in the names of Kowarz et al. on Sep. 27, 2001, discloses a method of manufacturing a mechanical conformal grating device.  
         [0004]     Drop-on-demand liquid emission devices with electrostatic actuators are also known for ink printing systems. U.S. Pat. No. 5,644,341 and No. 5,668,579, which issued to Fujii et al. on Jul. 1, 1997 and Sep. 16, 1997, respectively, disclose such devices having electrostatic actuators composed of a single diaphragm and opposed electrode. The diaphragm is distorted by application of a first voltage to the electrode. Relaxation of the diaphragm expels an ink droplet from the device. Other devices that operate on the principle of electrostatic attraction are disclosed in U.S. Pat. No. 5,739,831, No. 6,127,198, and No. 6,318,841; and in U.S. Publication No. 2001/0023523.  
         [0005]     U.S. Pat. No. 6,345,884, teaches a device having an electrostatically deformable membrane with an ink refill hole in the membrane. An electric field applied across the ink deflects the membrane and expels an ink drop.  
         [0006]     IEEE Conference Proceeding “MEMS 1998,” held Jan. 25-29, 2002 in Heidelberg, Germany, entitled “A Low Power, Small, Electrostatically-Driven Commercial Inkjet Head” by S. Darmisuki, et al., discloses a head made by anodically bonding three substrates, two of glass and one of silicon, to form an ink ejector. Drops from an ink cavity are expelled through an orifice in the top glass plate when a membrane formed in the silicon substrate is first pulled down to contact a conductor on the lower glass plate and subsequently released. There is no electric field in the ink. The device occupies a large area and is expensive to manufacture.  
         [0007]     U.S. Pat. No. 6,357,865 by J. Kubby et al. teaches a surface micro-machined drop ejector made with deposited polysilicon layers. Drops from an ink cavity are expelled through an orifice in an upper polysilicon layer when a lower polysilicon layer is first pulled down to contact a conductor and is subsequently released.  
         [0008]     In the devices described above, the diaphragm (or membrane, etc.) is actuated (deformed and relaxed) as a whole, or an entire unit, when a drop is desired. As such, there is little control over the size of the ejected drop created during actuation of the diaphragm.  
       SUMMARY OF THE INVENTION  
       [0009]     According to one feature of the present invention, an emission device for ejecting a liquid drop includes a structure defining a chamber volume adapted to receive a liquid having a nozzle orifice through which a drop of received liquid can be emitted and a membrane portion of the chamber volume defining structure. The membrane portion has a plurality of individually deformable portions. A controller is adapted to selectively actuate at least one of the plurality of individually deformable portions.  
         [0010]     According to another feature of the present invention, an emission device for ejecting a liquid drop includes a structure defining a chamber volume adapted to receive a liquid having a nozzle orifice through which a drop of received liquid can be emitted and an actuator. The actuator includes a first electrode associated with the chamber volume defining structure and a second electrode. The first electrode has a plurality of deformable portions. A controller is adapted to selectively move at least one of the plurality of deformable portions.  
         [0011]     According to another feature of the present invention, a method of operating a liquid emission device includes providing a structure defining a chamber volume adapted to receive a liquid and having a nozzle orifice through which a drop of received liquid can be emitted; providing a member associated with the chamber volume defining structure, the member having a plurality of deformable portions; and selectively actuating at least one of the plurality of deformable portions of the member such that the drop of received liquid is emitted through the nozzle orifice.  
         [0012]     According to another feature of the present invention, a method of manufacturing an emission device includes providing a substrate; forming a member on the substrate, the member having a plurality of individually deformable portions; and forming a chamber volume defining structure over the deformable member. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:  
         [0014]      FIG. 1  is a schematic illustration of a drop-on-demand liquid emission device according to the present invention;  
         [0015]      FIG. 2  is a cross-sectional side view of a portion of the drop-on-demand liquid emission device of  FIG. 1 ;  
         [0016]      FIGS. 3-5  are top plan views of alternative embodiments of a nozzle plate of the drop-on-demand liquid emission device of  FIGS. 1 and 2 ;  
         [0017]      FIGS. 6   a - 6   c  are cross-sectional views of the drop-on-demand liquid emission device of  FIG. 2  shown in a first actuation stage;  
         [0018]      FIGS. 7   a - 7   c  are cross-sectional views of the drop-on-demand liquid emission device of  FIG. 2  shown in a second actuation stage;  
         [0019]      FIG. 8  is a top view of a portion of the drop-on-demand liquid emission device of  FIG. 2 ;  
         [0020]      FIGS. 9-30  are cross-sectional views through line A-A′ of  FIG. 8  showing a sequence of fabrication of the liquid emission device of  FIG. 2 ;  
         [0021]      FIG. 31  shows a cross-section through line B-B′ of  FIG. 8 ;  
         [0022]      FIG. 32  shows a cross-section through line C-C′ of  FIG. 8 ; and  
         [0023]      FIG. 33  shows a cross-section through line D-D′ of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.  
         [0025]     As described in detail herein below, the present invention provides a liquid emission device and a process for fabricating drop-on-demand liquid emission devices. The most familiar of such devices are used as printheads in inkjet printing systems. Many other applications are emerging which make use of devices similar to inkjet printheads, but which emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision.  
         [0026]      FIG. 1  shows a schematic representation of a drop-on-demand liquid emission device  10 , such as an inkjet printer, which may be operated according to the present invention. The system includes a source  12  of data (say, image data) which provides signals that are interpreted by a controller  14  as being commands to emit drops. Controller  14  outputs signals to a source  16  of electrical energy pulses which are inputted to a drop-on-demand liquid emission device such as an inkjet printhead  18 .  
         [0027]     Drop-on-demand liquid emission device  10  includes a plurality of electrostatic drop ejection mechanisms  20 .  FIG. 2  is a cross-sectional view of one of the plurality of electrostatically actuated drop ejection mechanisms  20 . A nozzle orifice  22  is formed in a nozzle plate  24  for each mechanism  20 . A wall or walls  26  bound each drop ejection mechanism  20 . The wall(s)  26  may comprise a single material as shown in  FIG. 2 , or may comprise a stack of material layers, as is known in the art.  
         [0028]     A portion of a first electrode  28  is sealingly attached to outer wall(s)  26  to define a liquid chamber  30  adapted to receive the liquid, such as for example ink, to be ejected from nozzle orifice  22 . The liquid is drawn into chamber  30  through one or more refill ports  32 , shown in  FIG. 8 , from a supply, not shown, through a liquid conduit(s)  48 . The liquid typically forms a meniscus in the nozzle orifice  22 . A flow restrictor(s)  46 , shown in  FIG. 8 , is located at one or both ends of liquid chamber  30 , and acts to reduce liquid back flow during ejection. Liquid chamber  30  is typically positioned over at least one structural support  44 .  
         [0029]     Dielectric fluid, delivered along a fluid path  50 , fills a fluid region  34  positioned on a side of first electrode  28  opposite liquid chamber  30 . Fluid region  34  is at least partially created during the formation of pedestal(s)  68 , described below. The dielectric fluid is preferably air or other dielectric gas, although a dielectric liquid may be used.  
         [0030]     Typically, first electrode  28  (deformable membrane, member, etc.) is made of a somewhat flexible conductive material such as titanium aluminide, or, in the preferred embodiment, a combination of layers having a conductive layer positioned over a dielectric layer. For example, a preferred first electrode  28  comprises a thin film of titanium aluminide stacked over a thin film of silicon nitride, each film for example, being one micron thick. In this case, the nitride acts to insulate the titanium aluminide from the second electrode  36  during the first stage of actuation, described below with reference to at least  FIGS. 6   a - 6   c . Additionally, first electrode  28  is preferably at least partially flexible, and is electrically addressable through an electrical lead  42 , shown in  FIG. 8 .  
         [0031]     A second electrode  36  is positioned on the side of first electrode  28  opposed to liquid chamber  30 , and is electrically addressable separately from first electrode  28 . Typically, second electrode  36  is made of a somewhat flexible conductive material such as polysilicon, or, in the preferred embodiment, a combination of layers having a central conductive layer surrounded by an upper and lower insulating layer. For example, a preferred second electrode  36  comprises a thin film of polysilicon stacked between two thin films of silicon dioxide, each film for example, being one micron thick. In the latter case, the oxide acts to insulate the polysilicon from the first electrode  28  during the first stage of actuation. Second electrode  36  is divided into at least two, and preferably more than two, segments individually electrically addressable through electrical leads  42 , shown in  FIG. 8 .  
         [0032]     A fluid path  50  is defined by structural supports  44  which provide structural rigidity to the mechanism  20  and serve to anchor the second electrode  36 . This helps to prevent second electrode  36  from moving toward first electrode  28  during the first stage of actuation. Both the outer wall(s)  26  and structural supports  44  may either comprise a single layer or comprise a stack of material layers.  
         [0033]     At least one pedestal  68  separates first and second electrodes. Pedestal(s)  68  can be electrically insulating, which term is intended to include a pedestal of conductive material but having a non-conductive break therein. Patterning of second electrode  36  defines each individually addressable segment(s) of second electrode  36 . Pedestal(s)  68  are preferably located between the segments of second electrode  36 . However, pedestal(s)  68  can be located at various locations over a segment(s) of second electrode  36  depending on the desired application of the mechanism  20 . The location of each pedestal  68  also defines each individual portion of the first electrode  28  (deformable membrane, member, etc.) that corresponds to and interacts with each individually addressable segment(s) of second electrode  36 .  
         [0034]     A flow restrictor  46 , shown in  FIGS. 8 and 32 , restricts the return of fluid from liquid chamber  30  to the fluid reservoir. The fluid path  50  allows the dielectric fluid in fluid region  34  to flow into and out of a dielectric fluid reservoir (not shown). In the preferred embodiment, the dielectric fluid is air, and the ambient atmosphere performs the function of a dielectric fluid reservoir.  
         [0035]      FIGS. 3-5  are top plan views of nozzle plate  24 , showing several alternative embodiments of layout patterns for the several nozzle orifices  22  of a nozzle plate  24 . Note that in  FIGS. 3 and 4 , the interior surface of walls  26  are annular, while in  FIG. 5 , walls  26  form rectangular chambers. Other shapes are of course possible, and these drawings are merely intended to convey the understanding that alternatives are possible within the spirit and scope of the present invention.  
         [0036]     Referring to  FIGS. 6   a - 6   c , to eject a drop, a voltage difference is applied between the conductive portion of addressable first electrode  28  and at least one of the segments of the conductive portion of second electrode  36 . Typically, this is accomplished by energizing at least one segment of addressable second electrode  36  while maintaining addressable first electrode  28  at ground. In this manner, liquid in chamber  30  is not subjected to an electrical field. As shown in  FIGS. 6   a - 6   c , at least a portion of addressable first electrode  28  is attracted to the energized segment(s) of second electrode  36  until it is deformed to substantially the surface shape of the second electrode  36 , except in the region very near to the pedestal(s)  68 . Since addressable first electrode  28  forms a wall portion of liquid chamber  30  behind the nozzle orifice  22 , movement of first electrode  28  away from nozzle plate  24  expands the chamber, drawing liquid into the expanding chamber through refill ports  32 .  
         [0037]     In  FIG. 6   a , only the portion of first electrode  28  located opposite nozzle orifice  22  has been deformed toward the corresponding energized segment of second electrode  36 . In  FIG. 6   b , the portions of first electrode  28  peripherally located opposite nozzle orifice  22  have been deformed toward the corresponding energized segments of second electrode  36 . In  FIG. 6   c , all three portions of first electrode  28  have been deformed toward the corresponding energized segments of second electrode  36 .  FIGS. 6   a - 6   c  are provided to illustrate various ways of actuating first electrode  28 . In other embodiments, more or fewer segments of second electrode  36  can be provided and energized. Additionally, different combinations of segments of second electrode  36  can be energized. Doing this will vary how first electrode  28  portion(s) is actuated or deformed to its second position.  
         [0038]     Referring to  FIGS. 7   a - 7   c , subsequently (say, several microseconds later), the segment(s) of addressable second electrode  36  is de-energized, that is, the potential difference between electrodes  36  and  28  is made zero, causing the portion of addressable first electrode  28  to return to its first position. This action pressurizes the liquid in chamber  30  behind the nozzle orifice  22 , causing a drop to be ejected from the nozzle orifice. To optimize both refill and drop ejection, refill ports  32  should be properly sized to present sufficiently low flow resistance so that filling of chamber  30  is not significantly impeded when electrode  28  is energized, and yet present sufficiently high resistance to the back flow of liquid through the refill port  32  during drop ejection.  FIGS. 7   a - 7   c  also illustrate how the size of the ejected drop varies depending on the number of segments of second electrode  36  energized (and corresponding portions of first electrode  28  deformed) in  FIGS. 6   a - 6   c.    
         [0039]      FIG. 8  is a schematic top view of a portion of drop ejection mechanism  20  of  FIG. 2 . In  FIG. 8 , nozzle plate  24 , wall(s)  26 , and first electrode  28  have been removed exposing electrical lead lines  42 , pedestal(s)  68 , addressable second electrode  36 , and at least a portion of fluid region  34 . Nozzle orifice  22  remains to illustrate relative locations of these elements with respect to the nozzle orifice of the preferred embodiment.  
         [0040]     Still referring to  FIG. 8 , during operation, electrical signals are sent via electrical leads  42  to the first and second electrodes  28  and  36  of  FIG. 2 . Each segment(s) of second electrode  36  is provided with its own lead line  42  (represented by the three smaller lead lines  42  in  FIG. 8 ) while first electrode  28  is provided with a single lead line  42  (represented by the larger lead line  42  in  FIG. 8 ). Fabricating the device in this manner helps to keep the liquid in chamber  30  isolated from any electric field during operation. However, in situations where this is not a concern, the first electrode  28  can be segmented with each segment having its own lead line  42  while second electrode  36  has a common lead line  42 . In this situation, during operation, the appropriate segment(s) of first electrode is energized while second electrode  36  is maintained at ground.  
         [0041]     A line A-A′ in  FIG. 8  indicates the plane of the cross-sections depicted in  FIGS. 9-30  which illustrate a single liquid emission device. Typically, many of these devices would be batch fabricated simultaneously.  
         [0042]      FIG. 9  shows a substrate  52  of, say, a 675 μm thick, single crystal silicon wafer, for example. Substrate  52  supports the electrode structure; helps&gt;form liquid conduits  48  that bring liquid to chamber  30 ; and forms fluid path(s)  50  that bring the dielectric fluid to fluid region  34 .  
         [0043]      FIG. 10  shows the preferred embodiment after deposition of a first dielectric layer  54  (e.g. 0.35 μm thermally grown silicon dioxide) on substrate  52 .  FIG. 11  shows the preferred embodiment after deposition of a second dielectric layer  56  (e.g. 1.2 μm low-stress silicon nitride) over first dielectric layer  54 . Second dielectric layer  56  can be deposited, for example, using plasma enhanced chemical vapor deposition (PECVD).  
         [0044]      FIG. 12  shows the preferred embodiment after deposition of a third dielectric layer  58  (e.g. 0.21 μm PECVD silicon dioxide) over second dielectric layer  56 .  FIG. 13  shows the preferred embodiment after deposition of a first conductive layer  60  (e.g. 0.35 μm doped polysilicon) over third dielectric layer  58 . The first conductive layer  60  acts as the second electrode  36 .  
         [0045]      FIG. 14  shows the preferred embodiment after patterning and etching the first conductive layer  60 . Individual segments of the second electrode  36  are defined during this step, as are the electrical leads  42  that convey power to the individual segments of the second electrode  36 . Fluid conduits  48  are also defined during this step of the fabrication process.  FIG. 15  shows the preferred embodiment after deposition of the fourth dielectric layer  62  (e.g. 0.02 μm thermally grown silicon dioxide) over the first conductive layer  60 . The third dielectric layer  58  and the fourth dielectric layer  62  provide electrical isolation for the first conductive layer  60 .  
         [0046]      FIG. 16  shows the preferred embodiment after deposition of the fifth dielectric layer  64  (e.g. 0.02 μm PECVD silicon nitride) over the fourth dielectric layer  62 .  FIG. 17  shows the preferred embodiment after deposition of the sixth dielectric layer  66  (e.g. 0.16 μm silicon dioxide) over the fifth dielectric layer  64 . Sixth dielectric layer  66  forms pedestals  68  that are preferably located between individually addressable segments of the second electrode  36 ; define the portions of first electrode  28  that are correspondingly deformed toward the second electrode  36  segment(s); and acts as a stop layer for planarization of a future sacrificial layer.  
         [0047]      FIG. 18  shows the preferred embodiment after patterning and etching the sixth dielectric layer  66 . This step defines fluid path  50 ; creates pedestals  68 ; and prevents liquid conduits  48  from becoming obstructed.  
         [0048]      FIG. 19  shows the preferred embodiment after patterning and etching the first dielectric layer  54 , the second dielectric layer  56 , the third dielectric layer  58 , the fourth dielectric layer  62 , and the fifth dielectric layer  64 . This etch removes material from liquid conduits  48  and the fluid paths  50 .  
         [0049]      FIG. 20  shows the preferred embodiment after deposition of a first sacrificial layer  70  (e.g. 3 μm polysilicon). The removal of first sacrificial layer  70  forms fluid region  34 .  FIG. 21  shows the preferred embodiment after planarization of the first sacrificial layer  70 , down to the sixth dielectric layer  66 . This provides a flat surface for the subsequent deposition of the first electrode  28 .  
         [0050]      FIG. 22  shows the preferred embodiment after deposition of the seventh dielectric layer  72  (e.g. 0.1 μm silicon nitride) and the second conductive layer  74  (e.g. 0.07 μm titanium aluminide). Second conductive layer  74  is typically comprised of a material that is not attacked by the liquid contained in liquid chamber  30 . These two layers form first electrode  28  (deformable membrane, member, etc.).  FIG. 23  shows the preferred embodiment after patterning and etching of the seventh dielectric layer  72  and the second conductive layer  74 . Again, liquid conduits  48  remain obstruction free.  
         [0051]      FIG. 24  shows the preferred embodiment after deposition of a second sacrificial layer  76  (e.g. 5 μm polyimide).  FIG. 25  shows the preferred embodiment after patterning of the second sacrificial layer  76  (e.g. by UV exposure of a photosensitive polyimide). This defines the wall(s) and top of liquid chamber  30 . This patterning process can result in the sloped sidewalls shown in  FIG. 25 .  FIG. 26  shows the preferred embodiment after deposition of an eighth dielectric layer  78  (e.g. 8 um oxynitride). This layer serves as the nozzle plate  24  and the wall(s)  26 . As mentioned previously, this structure can be formed with multiple layers.  FIG. 27  shows the preferred embodiment after patterning and etching of the eighth dielectric layer  78 . The nozzle orifice  22  is formed during this step.  
         [0052]      FIG. 28  shows the preferred embodiment after thinning the substrate  52  (e.g. by lapping or mechanical grinding). Any thin layers that have been deposited on the side of the wafer opposed to nozzle plate  24  are removed during this step.  
         [0053]      FIG. 29  shows the preferred embodiment after patterning and etching the backside of the substrate  52  (e.g. using a Bosch process), and continuing to etch isotropically to remove the first sacrificial layer  70 . (e.g. using xenon difluoride gas). This extends the fluid conduits  48  and the fluid paths  50  through the substrate  52 .  
         [0054]      FIG. 30  shows the preferred embodiment after removal of the second sacrificial layer  76  (e.g. by isotropically etching polyimide with an oxygen plasma). The removal of the second sacrificial layer  76  creates the liquid chamber  30  that connects the nozzle orifice  22  with the fluid conduits  48  through refill ports  32 . This steps completes formation of the mechanism  20 . A continuous path to fluid region  34  through fluid path  50  is shown in  FIG. 30 . Although there does not appear to be a contiguous path from the fluid conduit  48  to the nozzle orifice  22  from the view shown in  FIG. 30 , a continuous path exists, shown in  FIG. 31 .  
         [0055]      FIG. 31  shows the preferred embodiment as viewed along line B-B′ of  FIG. 8 . In  FIG. 31 , there is a continuous path from the fluid conduits  48  to the nozzle orifice  22  through refill ports  32  and liquid chamber  30 .  FIG. 32  shows the preferred embodiment as viewed along line C-C′ of  FIG. 8  in which fluid region  34  and flow restrictor  46  can be seen.  FIG. 33  shows the preferred embodiment as viewed along line D-D′ of  FIG. 8  through nozzle orifice  22 .  
         [0056]     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.  
       Parts List  
       [0000]    
       
           10  Drop-on-demand liquid emission device  
           12  Source of data  
           14  Controller  
           16  Source of energy pulses  
           18  Inkjet printer  
           20  Electrostatic drop ejection mechanism  
           22  Nozzle orifice  
           24  Nozzle plate  
           26  Wall  
           28  First electrode  
           30  Liquid chamber  
           32  Refill ports  
           34  Fluid region  
           36  Second electrode  
           42  Electrical leads  
           44  Structural supports  
           46  Flow restrictor  
           48  Liquid conduit  
           50  Fluid path  
           52  Substrate  
           54  First dielectric layer  
           56  Second dielectric layer  
           58  Third dielectric layer  
           60  First conducting layer  
           62  Fourth dielectric layer  
           64  Fifth dielectric layer  
           66  Sixth dielectric layer  
           68  Pedestals  
           70  First sacrificial layer  
           72  Seventh dielectric layer  
           74  Second conductive layer  
           76  Second sacrificial layer  
           78  Eighth dielectric layer