Patent Abstract:
An inkjet printhead die for an inkjet print head, wherein the inkjet printhead die comprises a composite substrate that includes a planar semiconductor member, a planar substrate member and an interface at which the planar semiconductor member is fused to the planar substrate member

Full Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the field of inkjet printing, and more particularly to ink passages in a printing device. 
       BACKGROUND OF THE INVENTION 
       [0002]    Inkjet printing has become a pervasive printing technology. Drop-on-demand (DOD) inkjet printing systems are relatively inexpensive and are capable of meeting high quality printing needs of the home or office. DOD printing systems include one or more arrays of drop ejectors provided on a DOD inkjet printing device, in which each drop ejector is actuated at times and locations where it is required to deposit a dot of ink on the recording medium to print the image. In addition to the drop forming mechanism (e.g. a heater or a piezoelectric structure) and the nozzle making up each drop ejector, there are also one or more ink feed holes through which ink from an ink source is provided to one or more drop ejectors. Thermal inkjet printing devices having several hundred or more drop ejectors per printing device, also typically include driver and logic electronics to facilitate electrical interconnection to the heaters. 
         [0003]    Continuous inkjet (CIJ) printing systems provide high throughput printing that is well matched to commercial printing requirements. In CIJ a continuous pressurized stream of ink is emitted from one or more nozzles and broken up into droplets, which are either directed toward the recording medium to make ink dots as needed to print the image, or are directed toward a gutter for recirculation. Controllable drop breakoff can be provided, for example as described in U.S. Pat. No. 6,505,921, by pulsing heaters at intervals that control the drop size. Drops of different sizes are then directed (e.g. by an air stream, or by asymmetric pulsing of heaters on different sides of the nozzle) either toward the recording medium or toward the gutter. Like DOD printing devices, CIJ printing devices also typically include one or more ink feed holes, as well as driver and logic electronics for controlling the heaters. 
         [0004]    In order to provide high resolution printing at low cost and high throughput, it is desirable to pack DOD nozzle arrays and ink feed holes at close spacing. Additionally, for CIJ printing devices it can be desirable to enable cross-flow for cleaning between ink feed holes (including cleaning of channels leading to nozzles) for improved long-term printing reliability. In such compact DOD and CIJ printing devices, fabrication challenges arise that can be difficult to achieve using conventional device geometries and fabrication methods 
         [0005]    Therefore, it would be advantageous to devise novel printing device geometries and fabrication methods that enable achieving one or more of the following requirements: 
         [0006]    1) providing fluidic connection to a plurality of closely spaced ink feed holes that are located near a nozzle array, either on the same side or on opposite sides of the nozzle array; and 
         [0007]    2) providing reliably sealed fluidic connection of ink supplies to ink feed holes for two different color inks where the ink feed holes for the different inks are significantly less than 1 mm apart on the nozzle face of the printing device. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention accordingly relates to an inkjet printhead die for an inkjet print head, wherein the inkjet printhead die comprises a composite substrate that includes a planar semiconductor member, a planar substrate member and an interface at which the planar semiconductor member is fused to the planar substrate member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic representation of an inkjet printer system; 
           [0010]      FIG. 2  shows a perspective cut-away view of a portion an inkjet printhead die according to a first embodiment of the present invention; 
           [0011]      FIG. 3  is a cross-sectional view along line A-A of  FIG. 2 ; 
           [0012]      FIG. 4  is a schematic top view of the printhead die of  FIG. 2 ; 
           [0013]      FIG. 5  is a top perspective view of a planar substrate member portion of the printhead die of  FIG. 2 ; 
           [0014]      FIG. 6  is a top perspective view of a planar semiconductor member bonded to the planar substrate member of  FIG. 5 ; 
           [0015]      FIG. 7  shows an array of resistive heaters formed on the planar semiconductor member of  FIG. 6 ; 
           [0016]      FIG. 8  shows a dielectric layer with feed openings on the planar semiconductor member of  FIG. 7 ; 
           [0017]      FIG. 9  shows a patterned chamber layer formed on the planar semiconductor member of  FIG. 8 ; 
           [0018]      FIG. 10  shows ink feed holes etched through the planar semiconductor member of  FIG. 9 ; 
           [0019]      FIG. 11  is a cross-sectional view along line B-B of  FIG. 10 ; 
           [0020]      FIG. 12  shows a nozzle plate and nozzles formed on the planar semiconductor member of  FIG. 10 ; 
           [0021]      FIG. 13  is a cross-sectional view along line C-C of  FIG. 12 ; 
           [0022]      FIG. 14  is a flow chart of a fabrication sequence of steps; 
           [0023]      FIG. 15  shows a perspective view of the inkjet printhead die of  FIG. 2 ; 
           [0024]      FIG. 16  shows a composite wafer substrate pair and a plurality of die sites; 
           [0025]      FIG. 17  shows a top perspective cut-away view of a portion of an inkjet printhead die according to a second embodiment of the present invention; 
           [0026]      FIG. 18  shows a bottom perspective cut-away view of a portion of the inkjet printhead die of  FIG. 17 ; 
           [0027]      FIG. 19  is a schematic top view of the printhead die of  FIG. 17 ; 
           [0028]      FIG. 20  is a top perspective view of a planar substrate member portion of the printhead die of  FIG. 17 ; 
           [0029]      FIG. 21  is a top perspective view of a planar semiconductor member bonded to the planar substrate member of  FIG. 20 ; 
           [0030]      FIG. 22  shows an array of resistive heaters formed on the planar semiconductor member of  FIG. 21 ; 
           [0031]      FIG. 23  shows a dielectric layer with feed openings on the planar semiconductor member of  FIG. 22 ; 
           [0032]      FIG. 24  shows a patterned chamber layer formed on the planar semiconductor member of  FIG. 23 ; 
           [0033]      FIG. 25  shows ink feed holes etched through the planar semiconductor member of  FIG. 24 ; 
           [0034]      FIG. 26  is a cross-sectional view along line D-D of  FIG. 25 ; 
           [0035]      FIG. 27  shows a nozzle plate and nozzles formed on the planar semiconductor member of  FIG. 26 ; 
           [0036]      FIG. 28  is a cross-sectional view along line E-E of  FIG. 27 ; 
           [0037]      FIG. 29  schematic representation of a partial section of a continuous inkjet printhead die according to a third embodiment of the present invention; 
           [0038]      FIG. 30  is a top perspective view of a planar substrate member portion of the printhead die of  FIG. 29 ; 
           [0039]      FIG. 31  is a top perspective view of a planar semiconductor member bonded to the planar substrate member of  FIG. 30 ; 
           [0040]      FIG. 32  shows an array of resistive heaters formed on the planar semiconductor member of  FIG. 31 ; 
           [0041]      FIG. 33  shows a dielectric layer with feed openings on the planar semiconductor member of  FIG. 32 ; 
           [0042]      FIG. 34  shows a patterned wall layer formed on the planar semiconductor member of  FIG. 33 ; 
           [0043]      FIG. 35  shows feed holes etched through the planar semiconductor member of  FIG. 34 ; 
           [0044]      FIG. 36  shows a nozzle plate and nozzles formed on the planar semiconductor member of  FIG. 35 ; 
           [0045]      FIG. 37  is a bottom perspective view of the continuous inkjet printhead die of  FIG. 29 ; and 
           [0046]      FIG. 38  is a perspective view of the inkjet printhead die of  FIG. 17  or  FIG. 29  affixed to a mounting substrate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    Referring to  FIG. 1 , a schematic representation of a drop on demand inkjet printer system  10  is shown. Inkjet printer system  10  includes a source  12  of data (for example, image data) which provides signals that are interpreted by a controller  14  as being commands to eject ink drops. Controller  14  outputs signals to a source  16  of electrical energy pulses which are sent to an inkjet printhead die  18 . Controller  14  is preferably, for example, a microprocessor that includes associated software and/or firmware. Typically, inkjet printhead die  18  includes a plurality of drop ejectors  20  arranged in at least one array  48 , for example, a substantially linear row disposed along array direction  22 . Each drop ejector includes a nozzle  32  formed in a nozzle plate  31 . Each drop ejector also includes a chamber, walls and a drop forming mechanism that are not shown in  FIG. 1 . Ink enters inkjet printhead die  18  from an ink source (not shown) at ink connection hole  40 . During operation ink drops  21  are deposited on a recording medium  19  to form an image corresponding to image data from image data source  12 . Inkjet printhead die  18  can be mounted on a mounting substrate (not shown) provided with ink passageways and electrical interconnections in order to provide an inkjet printhead 
         [0048]      FIG. 2  shows a perspective cut-away view (not to scale) of a portion of an inkjet printhead die  18  according to a first embodiment of the present invention. Inkjet printhead die  18  includes a planar semiconductor member  28  and a planar substrate member  44  that are joined together at interface  24  to form a composite substrate. At a first surface  29  (opposite interface  24 ) of planar semiconductor member  28  are a plurality of layers including an insulating dielectric layer  50 , a chamber layer  54 , and a nozzle plate  31 . Additional layers (not explicitly shown but near dielectric layer  50 ), can also be included to fabricate drop ejecting structures as well as logic and power electronics, and electrical interconnects. Nozzle plate  31  includes an array of nozzles  32  disposed along array direction  22 . Adjacent nozzles are spaced by a center to center spacing S. An end of inkjet printhead die  18  has been cut away in the view of  FIG. 2 , in order to show an ink passageway  55 . In addition, the cut-away view shows channel  38  in planar substrate  44 . An ink connection hole  40  extends from the bottom  39  of channel  38  to second surface  41  (opposite interface  24 ) of planar substrate  44 . The area of ink connection hole  40  is typically less than 20% of the area of the bottom  39  of channel  38 . 
         [0049]      FIG. 3  is a cross-sectional view of printhead die  18  along line A-A of  FIG. 2 . In addition to the features described above relative to  FIG. 2 ,  FIG. 3  shows ink feed holes  36   a  and  36   b,  which are on opposite sides of resistive heater  34 . In this embodiment, resistive heater  34  is the drop forming mechanism and inkjet printhead die  18  is a thermal inkjet printhead die. Ink is provided to resistive heater  34  from ink connection hole  40  to channel  38  through planar substrate  44 , then to ink feed holes  36   a  and  36   b  in planar semiconductor member  28 , then to feed openings  52   a  and  52   b  in dielectric layer  50 , and then to ink passageway  55  to resistive heater  34 . In other words, these passages are fluidically connected. in particular, channel  38  is fluidically connected to ink feed holes  36   a  and  36   b  at interface  24  between planar substrate  44  and planar semiconductor member  28 . Although in the cross-sectional view of  FIG. 3 , the resistive heater  34  and its underlying structure appear to be freely suspended, in other cross-sections parallel to A-A, it would be seen that portions of planar semiconductor member  28  surrounding ink feed holes  36   a  and  36   b  are connected to the underlying structure of resistive heater  34 . 
         [0050]    Referring to  FIG. 4 , a schematic representation of a top view (through nozzle plate  31 ) of a portion of a drop on demand inkjet printhead die  18  is shown in accordance with the first embodiment previously shown in  FIGS. 2 and 3 . Inkjet printhead die  18  includes an array of drop ejectors  20 , one of which is designated by the heavy dashed line in  FIG. 4  together with the ink feed holes  36   a  and  36   b  that provide ink. Drop ejector  20  includes walls  26 , extending upwardly toward nozzle plate  31  thereby defining a chamber  30 . Walls  26  separate adjacent drop ejectors  20  in the array. Each chamber  30  includes a nozzle  32  in nozzle plate  31  through which ink is ejected. A drop forming mechanism, for example, resistive heater  34  is also located in each chamber  30 . In  FIGS. 3 and 4 , the resistive heater  34  is positioned above the top surface of planar semiconductor member  28  in the bottom of chamber  30  and opposite nozzle orifice  32 , although other configurations are permitted. In other words, in this embodiment the bottom surface of chamber  30  is above the first surface  29  of planar semiconductor member  28 , and the top surface of the chamber  30  is the nozzle plate  31 . 
         [0051]    Referring to HG.  4 , the ink feed holes comprise two linear arrays of ink feed holes  36   a  and  36   b  that supply ink to the chambers  30 . Ink feed holes  36   a  and  36   b  are positioned on opposite sides of the drop ejector  20  containing chamber  30  and nozzle orifice  32 . Referring to  FIGS. 3 and 4 , the ink feed holes are arranged so that feed holes  36   a  and  36   b  are located on opposite sides of array  48  of drop ejectors  20 . Because each drop ejector  20  is fed by more than one ink feed hole  36   a  and  36   b,  this configuration is also called a dual feed drop ejector, and the dual feed drop ejector configuration has high frequency jetting performance. Other geometries of dual feed drop ejectors are disclosed in published patent application US 2008/0180485. Drop ejectors  20  (and corresponding nozzles  32 ) are formed in a linear array at a high nozzle per inch count. For example if the drop ejector array  48  has 1200 or 600 nozzles per inch, the drop ejectors  20  and their corresponding nozzles will be spaced with a center to center spacing S of about 21 to 42 μm, respectively. In the example of the dual feed drop ejector configuration, the length L of feed holes  36  in a plane of the first surface  29  of planar semiconductor member  28  can vary from 10 μm to 100 μm, depending on the design. The width W of the feedholes  36  can also vary similarly from 10 μm to 100 μm. 
         [0052]    Referring to  FIGS. 2 and 4 , an aspect of the present invention is that channel  38  in planar substrate member  44  is able to connect ink feed holes  36  having small dimensions. For dimensions of L and W ranging from 10 μm to 100 μm and drop ejector spacing S ranging from 21 μm to 42 μm, channel  38  fluidically connects ink feed openings  36   a,    36   b  having a dimension L or W in the plane of the first surface  29  of planar semiconductor member  28  of less than 5S, and more preferably less than 3S, or even less than S. In the example shown in  FIG. 4 , channel  38  connects the linear array of ink feed holes  36   a,    36   b  on one side of drop ejector array  48  so that they can all be supplied with ink. In addition, channel  38  also connects the linear array of ink feed holes  36   b  on the other side of drop ejector array  48  so that they can all be supplied with ink. Ink connection hole  40  (within channel  38 ) is shown as a dashed circle in  FIG. 4 . In the ink channel  38  there can be other structures such as support structure  42 . 
         [0053]      FIGS. 5-13  illustrate a fabrication method of an embodiment of the present invention for forming an inkjet printhead die  18  containing multiple small ink feed holes  36  aligned to drop ejectors  20 , for high frequency operation. A flow chart of the step sequence for fabricating inkjet printhead die  18  is shown in  FIG. 14 . 
         [0054]    As shown in  FIG. 5  and described in box  100  of  FIG. 14  a planar substrate member  44 , is patterned and channel  38  is etched into a surface, which will subsequently be located at interface  24  with reference to  FIG. 2 . The planar substrate member  44  is a silicon wafer in the thickness range 300 μm-1 mm with a preferred thickness range of 650-725 μm. The silicon wafer typically has several hundred die sites, a portion of one of which is shown in  FIGS. 5-13 . The channel  38  is formed by lithographic patterning and deep reactive ion etching of the silicon, as is well known in the art. The depth of the channel  38  is less than the thickness of the planar substrate member  44  and is in the range 300-900 μm with a preferred depth of 400-450 μm. As a result, channel  38  has a bottom  39  and does not extend all the way through to second surface  41 . The channel  38  can also contain support structures  42  formed with this etch process. 
         [0055]    As shown in  FIG. 6  and described in box  102  of  FIG. 14  a planar semiconductor member  28  (e.g. a silicon wafer) is bonded to the planar substrate member  44  at interface  24  to form a composite substrate wafer pair  46  with a plurality of die sites for inkjet printhead die  18  (with reference to  FIG. 16 ). The bonding of the two wafers can be done by high temperature fusion bonding of the two surfaces at interface  24 . Prior to bonding, a thermal oxide can be formed on the planar substrate member  44  and/or planar semiconductor member  28 . The bonded planar semiconductor member  28  can be of any initial thickness and then thinned after the bonding step.  FIG. 6  shows the planar semiconductor member  28  after the thinning process, where the thickness of the planar semiconductor member  28  is in the range 50-400 μm with a preferred thickness of 50-100 μm. First surface  29  of planar semiconductor member  28  is the top surface after the thinning process, and is thus less than 200 μm from the interface  24  in a preferred embodiment. In a preferred embodiment the thickness of the planar substrate member  44  and the planar semiconductor member  28  is adjusted so that the total thickness of the two wafers in the composite substrate is substantially equal to the thickness of a standard 200 mm diameter silicon wafer, for example, 750 μm. This is advantageous for subsequent wafer processing steps. 
         [0056]    As shown in  FIG. 7  and described in box  104  of  FIG. 14 , an array of drop forming mechanisms, in this case, an array of resistive heaters  34  is formed on top of an insulating dielectric layer  50  which is formed on top of the planar semiconductor member  28  of the composite substrate. Fabricated in the inkjet printhead die  18 , but not shown, are electrical connections to the resistive heaters  34 , as well as power LDMOS and CMOS logic circuitry to control drop ejection. The insulating dielectric layer  50  can also be deposited during these processes. The fabrication of the heater structure is described for example in copending U.S. patent application Ser. No. 12/143,880 filed Jun. 23, 2008. A difference between the present invention and previous inkjet printheads is that in the present invention an ink passageway (such as channel  38 ) is formed in a first wafer that is then bonded to a second wafer upon which the drop ejectors and associated electronics are subsequently formed. 
         [0057]    As shown in  FIG. 8  and described in box  106  of  FIG. 14 , the insulating dielectric layer  50  is patterned and etched through to the planar semiconductor member  28  forming feed openings  52   a  and  52   a.    
         [0058]    As shown in  FIG. 9  and described in box  108  of  FIG. 14 , a chamber layer  54  is coated and patterned to form chamber walls  26  between adjacent drop ejectors  20 , as well as an outer passivation layer  56  that extends over the rest of the inkjet printhead die  18  to protect the circuitry from the ink. The chamber layer  54  can be formed by spin coating, exposure, and development using a photoimageable epoxy such as a novolak resin based epoxy, for example TMMR resist available from Tokyo Ohka Kogyo. The thickness of the chamber layer  54  is typically in the range 8-25 μm. 
         [0059]    As shown in  FIGS. 10 and 11  and described in box  110  of  FIG. 14 , ink feed holes  36   a,    36   b  are etched through the planar semiconductor member  28  connecting the drop ejectors  20  with the channel  38  in the planar substrate member  44  at interface  24 . The ink feed holes  36  are formed using the feed openings  52   a,    52   b  as the mask and using anisotropic reactive ion etching of the silicon, as is well known in the art. The cross-sectional view of  FIG. 11 , taken through line B-B of  FIG. 10 , shows the ink feed holes  36   a  and  36   b  etched through the planar semiconductor member  28 . 
         [0060]    As shown in  FIGS. 12 and 13  and described in box  112  of  FIG. 14 , a photoimageable nozzle plate layer  31  in the form of a dry film resist is laminated, and patterned to form nozzles  32 . The photoimageable nozzle plate layer  31  can be formed using a dry film photoimageable epoxy such as a novolak resin based epoxy, for example TMMF dry film resist available from Tokyo Ohka Kogyo. The thickness of the photoimageable nozzle plate layer  31  layer is typically in the range 5-20 μm and in a preferred embodiment is 10 μm. The use of a dry film laminate for the nozzle plate enables the formation of the nozzle plate  31  on the inkjet printhead containing high topography features such as the ink feed holes  36   a,    36   b.  Up to this point, ink connection hole(s)  40  (shown in  FIGS. 2-4 ) has not yet been formed to connect channel  38  with second surface  41  of planar substrate member  44 . As a result, the ink feed openings  36  are not yet connected to the backside (i.e. second surface  41 ) of the composite substrate, so that there are no difficulties in applying vacuum at second surface  41  to hold down the composite substrate during lamination. The cross-sectional view of  FIG. 13 , taken through line C-C of  FIG. 12 , shows the nozzle  32  formed in the nozzle plate material  31  over the resistive heaters  34 . 
         [0061]    As shown in  FIGS. 2 and 3  and described in box  114  of  FIG. 14 , ink connection holes  40  are opened up from the second surface  41  of the planar substrate member  44  for access to the channel  38  in the planar substrate member  44 . Laser drilling or etching of the silicon can form the ink connection holes  40 . The diameter of the ink connection hole  40  is nominally the width of the channel  38  but can be larger or smaller. The cross-sectional view of  FIG. 3 , taken through line A-A of  FIG. 2 , shows the ink connection hole  40  connecting to the channel  38  of the planar substrate member  44 . The ink connection hole  40  is shown in  FIG. 2  as circular but can alternatively be rectangular or elliptical. The ink connection hole  40  can also be formed with a plurality of input holes (not shown). For example a particle filter can be formed in the ink connection hole  40  by creating a grid of small openings during the laser drilling or etching process to form ink connection hole  40 . 
         [0062]    As described in box  116  of  FIG. 14  and shown in  FIGS. 15 and 16 , the composite substrate wafer pair  46  is next diced into a plurality (typically several hundred) individual inkjet printhead die  18 . Because the dicing operation cuts the side edges of inkjet printhead die  18  substantially perpendicular to the plane of composite substrate wafer pair  46 , the width and length dimensions X and Y respectively of inkjet printhead die  18  are substantially the same for first surface  29  of planar semiconductor member  28  and for second surface  41  of planar substrate member  44 . As a result, the area A 1 =X i ×Y 1  of first surface  29  of inkjet printhead die  18  is substantially the same as the area A 2 =X 2 ×Y 2  of the second surface  41 . Because nozzle plate  32  and the other layers on first surface  29  are so thin, A 1  can equivalently be regarded as the product of width and length dimensions X 1  and Y 1  at the visible outer surface of the inkjet printhead die  18  at nozzle plate  31 , as shown in  FIG. 15 . If the dicing cut is tapered, A 2  can be slightly different from A 1 . Similarly if slots are etched into the edges of second surface  41 , for example when etching ink connection hole  40 , A 2  can be different from A 1 . However, generally A 1  and A 2  will be the same within 20%. In other words, 0.8&lt;A 2 /A 1 &lt;1.2. 
         [0063]      FIGS. 17 and 18  respectively show top and bottom perspective cut-away views (not to scale) of a portion of an inkjet printhead die  18  according to a second embodiment of the present invention. Inkjet printhead die  18  includes a planar semiconductor member  28  and a planar substrate member  44  that are joined together at interface  24  to form a composite substrate. At first surface  29  (opposite interface  24 ) of planar semiconductor member  28  are a plurality of layers including a nozzle plate  31 . In many inkjet printhead die it is advantageous to position drop ejectors ejecting different inks to be positioned close to each other. This is advantageous in making a smaller size multicolor inkjet printhead die or increasing the swath length of the inkjet printhead die without an increase in die area. Examples of this are described in copending U.S. patent application Ser. No. 12/413,729 filed Mar. 30, 2009. However, using conventional fabrication methods, it is difficult to supply ink of one type at a location that is very close to where ink of a different type is supplied, and still provide a reliable seal between passageways and ink connection holes for the two inks. 
         [0064]      FIG. 18  shows two ink channels  38   a  and  38   h  having a center-to-center spacing of d, and associated ink connection holes  40   a  and  40   b  respectively. Channels  38   a  and  38   b  have bottoms  39   a  and  39   b  respectively, and ink connection holes  40   a  and  40   b  extend from those respective channel bottoms to second surface  41  of planar substrate  44 . Different inks can be supplied to channels  38   a  and  38   b  by connecting different inks at ink connection holes  40   a  and  40   b.  By offsetting the position of the ink connection hole  40   b  relative to ink connection hole  40   a  along the length of the corresponding ink channels  38   a  and  38   b,  the ink connection holes can have a center-to-center spacing D, where D&gt;d. In particular, for making a smaller size multicolor inkjet printhead die  18 , it can be advantageous for d to he less than 0.5 mm (for example, between 0.05 mm and 0.5 mm), and for making a reliable ink connection at ink connection holes  40   a  and  40   b,  it can be advantageous for D to be greater than 1 mm (for example between 1 mm and 10 mm). 
         [0065]    Referring to HG.  19 , a schematic representation of a top view of a portion of a drop on demand inkjet printhead die  18  is shown in accordance with the second embodiment of the present invention previously shown in  FIGS. 17 and 18 . Inkjet printhead die  18  includes an array or plurality of drop ejectors  20 , two of which ( 20   a  and  20   b ) are designated by the heavy dashed line rectangles in  FIG. 19  together with their corresponding ink feed holes  36   a  and  36   b.  Drop ejectors  20  include walls  26 , extending upwardly toward nozzle plate  31 , thereby defining a chamber  30 . Walls  26  also separate and isolate adjacent drop ejectors  20   a  and  20   b ) in the array designed to eject different inks. In the example of  FIG. 19 , the drop ejectors for ejecting different inks are arranged in a single straight line, and walls  26  are formed as a serpentine wall structure. In other examples (not shown), drop ejectors  20   a  for ejecting one ink can be arranged in a line that is parallel to a line of drop ejectors  20   b  for ejecting a different ink. Each chamber  30  includes a nozzle orifice  32  in nozzle plate  31  through which liquid is ejected. A drop forming mechanism, for example, a resistive heater  34  is also located in each chamber  30 . In  FIG. 19 , the resistive heater  34  is positioned above the top surface of planar semiconductor member  28  in the bottom of chamber  30  and opposite nozzle orifice  32 , although other configurations are permitted. In other words, in this embodiment the bottom surface of chamber  30  is above the first surface  29  of planar semiconductor member  28 , and the top surface of the chamber  30  is the nozzle plate  31 . 
         [0066]    Referring to  FIG. 19 , the ink feed holes include two linear arrays of ink feed holes  36   a  and  36   b  that supply ink to the chambers  30 . Ink feed holes  36   a  are positioned on a first side of the nozzle array adjacent drop ejectors  20   a  and ink feed holes  36   b  are positioned on an opposite side of the nozzle array adjacent drop ejectors  20   b,  each drop ejector containing a chamber  30  and nozzle orifice  32 . Ink feed holes  36   a  can be fluidically connected to one another by channel  38   a,  but ink feed holes  36   a  are not fluidically connected to ink feed holes  36   b  in this embodiment. Drop ejectors  20  are formed at a high nozzle per inch count. In a preferred embodiment of the present invention the drop ejectors  20  are spaced with a period of 20-80 μm. The length of feed holes  36  can vary from 10 μm to 100 μm, depending on the design. The width of the feedholes  36  also can vary similarly from 10 μm to 100 μm. 
         [0067]      FIGS. 20-28  illustrates a fabrication method of the second embodiment of the present invention forming an inkjet printhead die  18  containing closely spaced separate ink channels for providing two different inks to be ejected from closely spaced sets of nozzles. Although the geometries and functions of the inkjet printhead die  18  of the second embodiment differ from that of the first embodiment, the flow chart of  FIG. 14  can be used to summarize a sequence of fabrication steps. 
         [0068]    As shown in  FIG. 20  and described in box  100  of  FIG. 14  a planar substrate member  44  is patterned and two channels  38   a  and  38   b  are etched into a surface, which will subsequently be located at interface  24  (with reference to  FIG. 17 . The planar substrate member  44  is a silicon wafer in the thickness range 300-μm-1 mm with a preferred thickness range of 650-725 μm. Channels  38   a  and  38   b  are formed by lithographic patterning and deep reactive ion etching of the silicon, as is well known in the art. The depth of channels  38   a  and  38   h  is less than the thickness of the planar substrate member  44  and is in the range 300-900 μm with a preferred depth of 400-450 μm. As a result, channels  38   a  and  38   b  have bottoms  39   a  and  39   b  respectively and do not extend all the way through to second surface  41 . 
         [0069]    As shown in  FIG. 21  and described in box  102  of  FIG. 14  a planar semiconductor member  28  (e.g. a silicon wafer) is bonded to the planar substrate member  44  at interface  24  to form a composite substrate wafer pair. The bonding of the two wafers can be done by high temperature fusion bonding of the two surfaces at interface  24 . Prior to bonding a thermal oxide can be formed on the planar substrate member  44  and for planar semiconductor member  28 . The bonded planar semiconductor member  28  can be of any initial thickness and then thinned after the bonding step.  FIG. 21  shows the planar semiconductor member after the thinning process, where the thickness of the planar semiconductor member is in the range 50-400 μm with a preferred thickness of 50-100 m. First surface  29  of planar semiconductor member  28  is the top surface after the thinning process, and is thus less than 200 μm from the interface  24  in a preferred embodiment. In a preferred embodiment the thickness of the planar substrate member  44  and planar semiconductor member  28  is adjusted so that the total thickness of the two wafers is substantially equal to the thickness of a standard 200 mm diameter silicon wafer, for example, 750 μm. This is advantageous for subsequent wafer processing steps. 
         [0070]    As shown in  FIG. 22  and described in box  104  of  FIG. 14 , an array of drop forming mechanisms, in this case, an array of resistive heaters  34  are formed on top of an insulating dielectric layer  50  which is formed on top of the planar semiconductor member  28  at first surface  29 . Fabricated in the inkjet printhead die  18 , but not shown, are electrical connections to the resistive heaters  34 , as well as power LDMOS and CMOS logic circuitry to control drop ejection. The insulating dielectric layer  50  can also be deposited during these processes. The fabrication of the heater structure is described for example in copending application U.S. Ser. No. 12/143,880. 
         [0071]    As shown in  FIG. 23  and described in box  106  of  FIG. 14 , the insulating dielectric layer  50  is patterned and etched through to the planar semiconductor member  28  forming feed openings  52   a  and  52   b.    
         [0072]    As shown in  FIG. 24  and described in box  108  of  FIG. 14 , a chamber layer  54  is coated and patterned to form chamber walls  26  between adjacent drop ejectors  20 , as well as an outer passivation layer  56  that extends over the rest of the inkjet printhead die  18  to protect the circuitry from the ink. The chamber walls  26  are patterned such that drop ejectors  20   a  and  20   b  are fluidically separated from each other, so that the different inks to be ejected by drop ejectors  20   a  and  20   b  are not mixed together. The chamber layer  54  can be formed by spin coating, exposure, and development using a photoimageable epoxy such as a novolak resin based epoxy for example TMMR resist available from Tokyo Ohka Kogyo. The thickness of the chamber layer  54  is in the range 8-25 μm. 
         [0073]    As shown in  FIGS. 25 and 26  and described in box  110  of  FIG. 14 , ink feed holes  36   a  and  36   b  are etched through the planar semiconductor member  28  connecting drop ejectors  20   a , 20   b  with the respective channels  38   a , 38   b  in planar substrate member  44 . In other words, channel  38   a  is fluidically connected to ink feed hole  36   a,  and channel  38   b  is fluidically connected to ink feed hole  36   b  at interface  24 . The ink feed holes  36  are formed using the feed openings  52  as the mask and using anisotropic reactive ion etching of the silicon, as is well known in the art. The cross-sectional view of  FIG. 26 , taken through line D-D of  FIG. 25  shows the ink feed hole  36   a  etched through the planar semiconductor member  28 . Line D-D does not pass through ink feed hole  36   b.    
         [0074]    As shown in  FIGS. 27 and 28  and described in box  112  of  FIG. 14 , a photoimageable nozzle plate layer  31  in the form of a dry film resist is laminated, and patterned to form nozzles  32 . The photoimageable nozzle plate layer  31  can be formed using a dry film photoimageable epoxy such as a novolak resin based epoxy for example TMMF dry film resist available from Tokyo Ohka Kogyo. The thickness of the photoimageable nozzle plate layer  31  layer is typically in the range 5-25 μm and in a preferred embodiment is 10 μm. The use of a dry film laminate for the nozzle plate enables the formation of the nozzle plate  31  on the inkjet printhead die containing high topography features such as the ink feed holes  36   a , 36   b.  Up to this point, ink connection holes  40   a  and  40   b  (shown in  FIGS. 18-19 ) have not yet been formed to connect channels  38   a  and  38   b  with second surface  41  of planar substrate member  44 . As a result, the ink feed openings  36   a  and  36   b  are not yet connected to the backside (i.e. second surface  41 ) of the composite substrate, so that there are no difficulties in applying vacuum at second surface  41  to hold down the composite substrate during lamination. The cross-sectional view of  FIG. 26 , taken through line E-E of  FIG. 27 , shows the nozzle  32  formed in the nozzle plate material  31  over the resistive heaters  34 . 
         [0075]    As shown in  FIGS. 17 and 18  and described in box  114  of  FIG. 14 , ink connection holes  40   a , 40   b  are opened up from the back of the planar substrate member  44  for access to respective channels  38   a , 38   b  in the planar substrate member  44 . Laser drilling or etching of the silicon can form the ink connection holes  40   a , 40   b.  The diameter of the ink connection hole is nominally the width of the channels  38   a , 38   b  but can be larger or smaller.  FIG. 18  shows the bottom of the planar substrate member  44  with two ink connection holes  40   a , 40   b  connecting to channels  38   a , 38   b  of the planar substrate member  44 . The ink connection holes  40   a , 40   b  are shown in  FIG. 18  as circular but can also be rectangular or elliptical.  FIG. 18  shows only a portion of the inkjet printhead die  18 . Along the entire printhead die there can be multiple ink connection holes. In addition, for inkjet printhead die including drop ejectors for more than two different inks, there can be channels, ink connection holes and ink feed holes corresponding to each different ink. 
         [0076]    As described in box  116  of  FIG. 14  and shown in  FIGS. 15 and 16 , the composite substrate wafer pair  46  is next diced into a plurality (typically several hundred) individual inkjet printhead die  18 . As discussed above relative to  FIG. 15 , because the dicing operation cuts the side edges of inkjet printhead die  18  substantially perpendicular to the plane of composite substrate wafer pair  46 , the width and length dimensions X and Y respectively of inkjet printhead die  18  are substantially the same for first surface  29  of planar semiconductor member  28  and for second surface  41  of planar substrate member  44 . 
         [0077]    Referring to  FIG. 29 , a schematic representation of a partial section of a continuous inkjet printhead die  118  is shown in accordance with a third embodiment of the present invention. Continuous inkjet printhead die  118  includes an array or plurality of pressurized liquid ejectors  120 . Walls  126  separate the pressurized liquid ejectors  120 . The walls  126  also define entrance paths  127   a , 127   b  on each side of a nozzle orifice  132  through which a pressurized stream of liquid is ejected. To break the stream into drops, resistive heaters  134   a , 134   b  are also located within the entrance paths  127   a , 127   b.  In an alternative configuration a single resistive heater is positioned directly below the nozzle orifice  132 . 
         [0078]    Referring to  FIG. 29 , the feed holes comprise two linear arrays of feed holes  136   a  and  136   b  formed in a planar semiconductor member  128 . Pressurized liquid flows from feed holes  136   a , 136   b  located on opposite sides of liquid ejectors  120 , through the entrance paths  127   a , 127   b,  to form a single stream flowing out of nozzle orifice  132 . Fluidically connected to the feed holes  136   a , 136   b  are channels  138   a , 138   b  respectively, formed in a planar substrate member  144 . In the back of this planar substrate member are liquid connection holes  140   a , 140   b  that connect to liquid sources (not shown) supplying the liquid to the liquid ejectors  120 . If liquid connection hole  140   a  is positively pressurized relative to liquid connection hole  140   b,  a cross-flow will be set up in the direction of the heavy arrows in  FIG. 29  to clean debris from the entrance paths  127   a , 127   b.    
         [0079]      FIGS. 30-37  illustrate a fabrication method of the third embodiment of the present invention for forming a continuous inkjet printhead die  118  utilizing multiple ink channels for cross-flow cleaning capabilities. Although the geometries and functions of the continuous inkjet printhead die  118  of the third embodiment differ from that of the first and second embodiments, the flow chart of  FIG. 14  can be used to summarize a sequence of fabrication steps. 
         [0080]    As shown in  FIG. 30  and described in box  100  of  FIG. 14  a planar substrate member  144 , is patterned and channels  138   a , 138   b  are etched into the planar substrate member  144 . The planar substrate member  144  is a silicon wafer in the thickness range 300-μm-1 mm with a preferred thickness range  of 650 -725 μm. The channels  138   a , 138   b  are formed by lithographic patterning and deep reactive ion etching of the silicon, as is well known in the art. The depth of the channels  138   a , 138   b  is less than the thickness of the planar substrate member  44  and is in the range 300-900 μm with a preferred depth of 400-450 μm. As a result, channels  138   a  and  138   b  have bottoms  139   a  and  139   b  respectively and do not extend all the way through to second surface  141 . 
         [0081]    As shown in  FIG. 31  and described in box  102  of  FIG. 14  a planar semiconductor member  128  (e.g. a silicon wafer) is bonded to the planar substrate member  144  at interface  124  to form a composite substrate wafer pair. The bonding of the two wafer can be done by high temperature fusion bonding of the two surfaces at interface  124 . Prior to bonding, a thermal oxide can be formed on planar substrate member  144  and/or planar semiconductor member  128 . The bonded planar semiconductor member  128  can be of any initial thickness and then thinned after the bonding step.  FIG. 31  shows the planar semiconductor member  128  after the thinning process, where the thickness of the planar semiconductor member  128  is in the range 50-400 μm with a preferred thickness of 50-100 μm. First surface  129  of planar semiconductor member  128  is the top surface after the thinning process, and is thus less than 200 μm from the interface  124  in a preferred embodiment. In a preferred embodiment the thickness of the planar substrate member  144  and the planar semiconductor member  128  is adjusted so that the total thickness of the two wafers is equal to the thickness of a standard 200 mm diameter silicon wafer, for example, 750 μm. This is advantageous for subsequent wafer processing steps. 
         [0082]    As shown in  FIG. 32  and described in box  104  of  FIG. 14 , a drop break-off mechanism, in this case, an array of resistive heaters  134   a , 134   b  are formed on top of an insulating dielectric layer  150  which is formed on top of the planar semiconductor member  128 . Fabricated in the continuous inkjet printhead  118 , but not shown, are electrical connections to the resistive heaters  134   a , 134   b , as well as power LDMOS and CMOS logic circuitry to control drop break-off. The insulating dielectric layer  150  can also be deposited during these processes. 
         [0083]    As shown in  FIG. 33  and described in box  106  of  FIG. 14 , the insulating dielectric layer  150  is patterned and etched through to the planar semiconductor member  128  forming feed openings  152   a  and  152   b.    
         [0084]    As shown in  FIG. 34  and described in box  108  of  FIG. 14 , a wall layer  154  is coated and patterned to form walls  126  between pressurized liquid ejectors  120 , as well as an outer passivation layer  156  that extends over the rest of the continuous inkjet printhead  118  to protect the circuitry from the ink. The wall layer  154  can be formed by spin coating, exposure, and development using a photoimageable epoxy such as a novolak resin based epoxy for example TMMR resist available from Tokyo Ohka Kogyo. The thickness of the wall layer  154  is typically in the range 4-25 μm. 
         [0085]    As shown in  FIG. 35  and described in box  110  of  FIG. 14 , feed holes  136   a , 136   b  are etched through the planar semiconductor member  128  connecting the pressurized liquid ejectors  120  with channels  138   a , 138   b  in the planar substrate member  144 . The feed holes  136   a , 136   b  are formed using the feed openings  152   a , 152   b  shown in  FIG. 33 , as the defining mask and using anisotropic reactive ion etching of the silicon, as is well known in the art. 
         [0086]    As shown in  FIG. 36  and described in box  112  of  FIG. 14 , a photoimageable nozzle plate layer  131  in the form of a dry film resist is laminated, and patterned to form nozzles  132 . The photoimageable nozzle plate layer  131  can be formed using a dry film photoimageable epoxy such as a novolak resin based epoxy for example TMMF dry film resist available from Tokyo Ohka Kogyo. The thickness of the photoimageable nozzle plate layer  131  is typically in the range 5-25 μm and in a preferred embodiment is 10 μm. The use of a dry film laminate for the nozzle plate enables the formation of the nozzle plate layer  131  on the liquid ejection printhead containing high topography features such as the feed holes  136   a , 136   b.  Up to this point, ink connection holes  140   a  and  140   b  (shown in  FIGS. 29 ) have not yet been formed to connect channels  138   a  and  138   b  with second surface  141  of planar substrate member  144 . As a result, the ink feed openings  136   a  and  136   b  are not yet connected to the backside (i.e. second surface  141 ) of the composite substrate, so that there are no difficulties in applying vacuum at second surface  141  to hold down the composite substrate during lamination. 
         [0087]    As shown in the bottom perspective view of  FIG. 37  and described in box  114  of  FIG. 14 , liquid connection holes  140   a , 140   b  are opened up through the back of the planar substrate member  144  connecting to channels  138   a , 138   b  respectively. Laser drilling or etching of the silicon can form the liquid connection holes  140   a,    140   b.  The diameter of the liquid ejection holes  140   a , 140   b  is nominally the width of the channels  138   a , 138   b  but can be larger or smaller. The liquid connection holes  140   a , 140   b  are shown in  FIG. 37  as circular but they can also be rectangular or elliptical. 
         [0088]    As described in box  116  of  FIG. 14  and shown in  FIGS. 15 and 16 , the composite substrate wafer pair  46  is next diced into a plurality (typically several hundred) individual inkjet printhead die  118 . As discussed above relative to  FIG. 15 , because the dicing operation cuts the side edges of inkjet printhead die  118  substantially perpendicular to the plane of composite substrate wafer pair  46 , the width and length dimensions of inkjet printhead die  118  are substantially the same for first surface  129  of planar semiconductor member  128  and for second surface  141  of planar substrate member  144 . 
         [0089]    A DOD or CIJ inkjet printhead can include inkjet printhead die  18  or  118  and a mounting substrate  60  to which the inkjet printhead die is affixed, as shown in  FIG. 38 . Second surface  41  of planar substrate member  44  is bonded to mounting substrate  60  with an adhesive that can provide mechanical strength, chemical compatibility with ink, a reliable fluidic seal, and optionally good thermal conductivity. Mounting substrate  60  typically includes electrical leads (not shown) as well as one or more ink ports, a first ink port  62  and a second ink port  64  being shown in  FIG. 38 . First ink port  62  is fluidically connected to ink connection hole  40   a,  and second ink port  64  is fluidically connected to ink connection hole  40   b  (for embodiments such as that shown in  FIG. 38  where there is a second ink connection hole  40   b ). A first ink source  66  is fluidically connected to the first ink port  62 . For an inkjet printhead die  18  that can eject two different kinds of ink, a second ink source  68  can be connected to second ink port  64 . For a CIJ printhead die designed to permit cross-flushing of channels for cleaning, the second ink port  64  on mounting substrate  60  can be fluidically connected to an ink source  68  which in this embodiment acts as an ink sink. By positively pressurizing ink at the first port relative to the second port, a flow of ink can be established. Also shown in  FIG. 38  are electrical interconnections  61  (such as wire bonds) between inkjet printhead die  18  and mounting substrate  60 . 
         [0090]    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 spirit and scope of the invention.

Technology Classification (CPC): 1