Abstract:
Fabricating a printhead includes providing a silicon wafer including first and second surfaces and a nozzle membrane layer on the first surface of the silicon wafer. The silicon wafer is sized to a thickness ranging from 10 to 250 microns. A plurality of chambers is defined on the second surface of the silicon wafer by depositing and patterning a mask on the second surface of the silicon wafer. The plurality of chambers is formed in the silicon wafer by etching portions of the silicon wafer that are exposed by the mask. A second wafer, permanently bonded to the second surface of the silicon wafer, includes a material property that is compatible with a material property of the silicon wafer. A preformed fluid channel of the second wafer is in fluid communication with the plurality of chambers of the silicon wafer after permanent bonding of the wafers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned, U.S. patent application Ser. No. ______ (Docket K001006), entitled “NOZZLE PLATE INCLUDING PERMANENTLY BONDED FLUID CHANNEL”, filed concurrently herewith. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to the field of digitally controlled printing systems and the manufacturing techniques associated with fabricating these systems, and in particular to printhead devices included in these printing systems and the manufacturing techniques associated with fabricating the printhead component of these systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfer and fixing. Ink jet printing mechanisms can be categorized by technology as either drop on demand ink jet (DOD) or continuous ink jet (CIJ). 
         [0004]    The first technology, “drop-on-demand” (DOD) ink jet printing, provides ink drops that impact upon a recording surface using a pressurization actuator, for example, a thermal, piezoelectric, or electrostatic actuator. One commonly practiced drop-on-demand technology uses thermal actuation to eject ink drops from a nozzle. A heater, located at or near the nozzle, heats the ink sufficiently to boil, forming a vapor bubble that creates enough internal pressure to eject an ink drop. This form of inkjet is commonly termed “thermal ink jet (TIJ).” 
         [0005]    The second technology commonly referred to as “continuous” ink jet (CIJ) printing, uses a pressurized ink source to produce a continuous liquid jet stream of ink by forcing ink, under pressure, through a nozzle. The stream of ink is perturbed using a drop forming mechanism such that the liquid jet breaks up into drops of ink in a predictable manner. One continuous printing technology uses thermal stimulation of the liquid jet with a heater to form drops that eventually become print drops and non-print drops. Printing occurs by selectively deflecting one of the print drops and the non-print drops and catching the non-print drops. Various approaches for selectively deflecting drops have been developed including electrostatic deflection, air deflection, and thermal deflection. 
         [0006]    Recently developed ink jet printing systems utilize drop forming devices associated with individual nozzles or groups of nozzles to control the formation of drops. For example, recently developed continuous ink jet printing systems utilize drop forming devices associated with individual nozzles or groups of nozzles to control breakup of the liquid streams flowing through nozzles into drops in response to the print data. U.S. Pat. No. 6,474,794, issued to Anagnostopoulos et al. on Nov. 5, 2002, and entitled INCORPORATION OF SILICON BRIDGES IN THE INK CHANNELS OF CMOS/MEMS INTEGRATED INK JET PRINT HEAD AND METHOD OF FORMING, describes a method for fabricating nozzle plates that can be used in these recently developed continuous inkjet systems. It involves forming integrated circuits for controlling the operation of the printhead on a silicon substrate, forming a thin membrane of insulating layers with nozzles and drop forming devices formed in the membrane, and forming a series of ink channels through the silicon substrate, the each of the ink channels being aligned with a nozzle. The silicon substrate includes ribs that separate the individual ink channels and provide strength to the nozzle plate. 
         [0007]    While this nozzle plate construction is effective and extremely well suited for its intended application, there are difficulties associated with etching the individual ink channels through the silicon. High aspect ratio ink channels can be etched through the silicon substrate using a Deep Reactive Ion Etching (DRIE) process. However, the etch efficiency and straightness/quality of the sidewalls decreases with increasing feature aspect ratio, which can limit the device design and performance. As such, there is an ongoing need to improve nozzle plate performance and nozzle plate construction. 
       SUMMARY OF THE INVENTION 
       [0008]    According to an aspect of the present invention, a method of fabricating a printhead includes providing a silicon wafer including first and second surfaces and a nozzle membrane layer on the first surface of the silicon wafer. The silicon wafer is sized to a thickness. A plurality of chambers is defined on the second surface of the silicon wafer by depositing and patterning a mask on the second surface of the silicon wafer. The plurality of chambers is formed in the silicon wafer by etching portions of the silicon wafer that are exposed by the mask. A second wafer is permanently bonded to the second surface of the silicon wafer. The second wafer includes a material property that is compatible with a material property of the silicon wafer. A preformed fluid channel of the second wafer is in fluid communication with the plurality of chambers of the silicon wafer after permanent bonding of the wafers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
           [0010]      FIG. 1  shows a device wafer including a nozzle membrane on a silicon substrate; 
           [0011]      FIG. 2  shows a handling wafer attached to a first surface of the device wafer with a temporary adhesive; 
           [0012]      FIG. 3  shows the device wafer, and the handling wafer, after thinning of the device wafer; 
           [0013]      FIG. 4  shows the second surface of the device wafer patterned for etching; 
           [0014]      FIG. 5  shows the device wafer, and handling wafer, after etching the fluid channels in the silicon substrate; 
           [0015]      FIG. 6  shows a prepared second wafer aligned with the device wafer prior to bonding of the second wafer and the device wafer; 
           [0016]      FIG. 7  shows the second wafer bonded to the device wafer; 
           [0017]      FIG. 8  shows the device wafer and the attached second wafer after removal of the handling wafer and the temporary adhesive; 
           [0018]      FIG. 9  shows a second wafer including a plurality of fluid channels in fluid communication with the plurality of fluid channels located in the device wafer; 
           [0019]      FIG. 10  shows a second wafer including an elongated trench in fluid communication with the plurality of fluid channels located in the device wafer; 
           [0020]      FIGS. 11 and 12  show partial schematic cross sectional views of a printhead made in accordance with the present invention; 
           [0021]      FIG. 13  shows a simplified schematic block diagram of an example embodiment of a printing system made in accordance with the present invention; 
           [0022]      FIG. 14  is a schematic view of an example embodiment of a continuous printhead made in accordance with the present invention; and 
           [0023]      FIG. 15  is a schematic view of an example embodiment of a continuous printhead made in accordance with the present invention. 
       
    
    
     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. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements. 
         [0025]    The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention. 
         [0026]    As described herein, the example embodiments of the present invention provide a printhead or printhead components typically used in inkjet printing systems. However, many other applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid,” “ink,” “print,” and “printing” refer to any material that can be ejected by the printhead, the printing system, or the printing system components described below. 
         [0027]    A process for making a nozzle plate structure, one or more of which is included in a printhead discussed in more detail below, is described with reference to  FIGS. 1-8 . Like the process outlined in U.S. Pat. No. 6,474,794, issued to Anagnostopoulos et al. on Nov. 5, 2002, the disclosure of which is incorporated herein in its entirety, the process set forth herein can begin with forming CMOS circuitry and the nozzle membrane structure  114  on a silicon substrate or wafer  112 , as shown in  FIG. 1 . The nozzle membrane structure can include drop forming devices  116 . The drop forming device can comprise resistive heating elements, piezoelectric devices, or electrode structures of electrohydrodynamic or dielectrophoresis stimulation devices, which are associated with one or more of the plurality of nozzles  118 . As the process steps for doing this have been described in U.S. Pat. No. 6,474,794, which is incorporated herein by reference in its entirety, the process steps will not be separately described here. The silicon wafer with the one or more layers that form the nozzle membrane structure on the first surface is commonly called a device wafer  110 . 
         [0028]    A temporary handling, or carrier, wafer  122  is attached to the first surface  120  of the device wafer  110 , as shown in  FIG. 2 . This surface of the wafer is referred to as the first surface of the wafer. Typically the handling wafer  122  is a silicon wafer so that its thermal expansion matches that of the device wafer, although glass (for example, quartz) or ceramic materials can also be used. The handling wafer  122  is attached to the device wafer  110  using a temporary adhesive material  124 , for example, WaferBOND HT 10.10 from Brewer Science. It can be applied by solution deposition methods known in the art such as, but not limited to, spin coating and spray coating to either the handling wafer or the device wafer. A baking step is used to remove the solvents from the adhesive. Other adhesives are known in the art that can be applied by dry transfer or stamping and lamination. The handling wafer and the device wafer are then pressed together in a vacuum chamber at elevated temperature to bond them together. The WaferBOND FIT material can be used with processing steps up to 300° C. The device wafer can be separated from the handling wafer by heating to about 200° C., which softens the thermoplastic material sufficiently to allow the two wafers to be slid apart. Another suitable temporary adhesive  124  is LC-3200, a UV curable adhesive from 3M. This adhesive can be applied by spin coating to the device wafer  110 . After a release layer, for example, a 3M Light-to-Heat Conversion coating (not shown) is applied to the handling wafer  122 , the handling wafer can be attached to the adhesive coated surface of the device wafer  110 . The adhesive is then quickly cured, for example, using UV light. To separate the handling wafer from the device wafer, a laser is shown through the handling wafer to strike the release layer, which lowers the adhesion to the handling layer, allowing the handling layer to be removed. The adhesive layer is then removed from the device layer using, for example, 3M Wafer De-Taping Tape 3305, a process that leaves minimal residuals and creates little stress on the device wafer. Typically the handling wafer is from 500-1000 micron thick. 
         [0029]    With the device wafer  110  firmly bonded to the handling wafer  122 , the back side of the device wafer can now be thinned. The back side of the device wafer is the side opposite the first surface that includes the membrane layer(s). The back surface of the device wafer is also called the second surface  126  of the device wafer. Processes for thinning the wafer are well known, and typically involve a grinding operation to quickly remove material, followed by polishing steps that can include one or more of the following: plasma etching, chemical etching, and chemical-mechanical planarization. The silicon substrate of the device wafer can be thinned to a final thickness ranging from 10 to 250 micron and more preferably to a final thickness ranging from 50 to 150 micron thick. The outcome is shown in  FIG. 3 . 
         [0030]    Photoresist  128  is then applied to the second surface  126  of the device wafer, and it is masked to define the pattern  129  for the etching of the fluid channels in the silicon, as shown in  FIG. 4 . During the photomask process, the mask is aligned so that pattern  129  for the fluid channels to be etched in the silicon are aligned with the nozzles  118  formed in the membrane layer(s) on the first surface of the silicon substrate. This is typically done using IR front to back alignment tools that are standard in the industry (for example, the EVG 620 Automated Bond Alignment system) or by using a transparent carrier wafer such as glass. 
         [0031]    Deep reactive ion etching (commonly referred to as DRIE) can then be used to etch the fluid channels  130  in the thinned silicon substrate  112 . The reduced thickness of the silicon substrate, when compared to the original thickness of the silicon substrate, lowers the aspect ratio of the fluid channels to be etched. As a result of the lower aspect ratio of the fluid channels to be etched, the fluid channels  130  can be etched more quickly and with better sidewall quality, due to the improved efficiency of the etch, when compared to conventional systems and techniques. Following the DRIE etching process, the photoresist is removed from the second surface  126  of the device wafer  110 . The result is shown in  FIG. 5 . 
         [0032]    A second wafer  132  is processed to form a permanent stiffening layer to the device wafer  110 . The second wafer  132  can be a silicon wafer or be a wafer of another material that has appropriate materials properties such as thermal expansion to be compatible with the silicon device wafer for use in an inkjet printhead. The processing of the second wafer includes preforming one or more fluid channels  134  in the second wafer  132  such that the one or more fluid channels  134  of the second wafer  132  is in fluid communication with the plurality of fluid channels  130  of the silicon device wafer  110  after bonding. Photolithographic and etching processes are typically used to form the one or more fluid channels in the second wafer. These process steps, which are well known, are not separately shown. The one or more fluid channels in the second wafer are located in the second wafer so as to provide fluid communication with the fluid channels etched in the silicon substrate when the second wafer is bonded to the device wafer. 
         [0033]    Referring to  FIG. 9 , in some embodiments the fluid channels  134  of the second wafer are etched in a one to one correspondence with the fluid channels  130  of the device wafer  110 . Referring to  FIG. 10 , in other embodiments the fluid channel  134  in the second wafer  132  is an elongated trench  138  etched through the second wafer. As shown in  FIGS. 6-8 , the elongated trench  138  or the plurality of fluid channels  134  extends into and out of the page. The length of the elongated trench  138  is sufficient to span the array of fluid channels etched in the device layer. The thickness of the second wafer typically ranges from 300-725 micron. In still other embodiments, one face of the second wafer includes an array of fluid channels in a one to one correspondence to the array of fluid channels of the device wafer. The array of fluid channels is located on the face of the second wafer such that they will align with the array of fluid channels of the device wafer once the device wafer and the second wafer are bonded together. The second face of the second wafer includes an elongated trench with the elongated trench being aligned with the array of fluid channels on the first face of the second wafer and etched to a depth sufficient to enable fluid communication between the elongated trench of the second face and the fluid channels of the array of fluid channels on the first face of the second wafer. The elongated trench includes a length sufficient to span the length of the array of fluid channels on the first side of the second wafer. The fluid channels on the first side of the second wafer and the fluid channel in the form of an elongated trench on the second face each are etched to sufficient depths to enable fluid communication between the elongated trench of the second face and the fluid channels of the array of fluid channels of the first face of the second wafer. In some of these embodiments, the second wafer can be an SOI wafer where the insulator layer serves as an etch stop to control the depth of the etching from each face of the wafer. 
         [0034]    The preferred configuration of the fluid channel(s) in the second wafer depends on the application contemplated. The use of an array of fluid channels in a one to one correspondence with the fluid channels of the device wafer can provide enhanced functionality to the resultant printhead, for example, improved flow conditioning to the fluid supplied to the nozzles depending on the specific application contemplated, when compared to the use of an elongated trench form of fluid channel. Flow conditioning is discussed in more detail in U.S. Pat. No. 7,607,766, issued to Steiner on Oct. 27, 2009. The use of an array of fluid channels in a one to one correspondence to the array of fluid channels in the device wafer, however adds manufacturing complexity, in forming the fluid channels and aligning them with the channels of the device wafer, when compared to the use of an elongated trench form of fluid channel. For some applications the enhanced functionality warrants the added fabrication complexity, while in other applications the added fabrication complexity isn&#39;t justified. 
         [0035]    A permanent adhesive layer  136  is applied to the bonding face of the second wafer  132  and the second wafer  132  is aligned with the device wafer  110  as shown in  FIG. 6 . The second wafer  132  is bonded to the device wafer  110  with the device wafer still being bonded to the handling wafer  122  as shown in  FIG. 7 . Suitable permanent bonding adhesives include SU8, benzocyclobutene (BCB), polyimide and parylene, each of which allows the wafers to be bonded together at temperatures that are safe for the CMOS circuitry. Methods known in the art for applying the adhesive to one or both of the wafer surfaces to be bonded include, but are not limited to, spin coating, spray coating, vapor deposition, dry transfer or stamping, and lamination. The SU8 and BCB materials are photosensitive, allowing photolithographic processes to be used to control the quantity of the adhesive used and the placement of the adhesive materials relative to the fluid channels. When bonding the second wafer to the device wafer, the second wafer should be aligned with the device wafer to ensure the fluid channels in the second wafer are appropriately aligned to the fluid channels in the device wafer. Wafer bonding equipment, with means for aligning the wafers, are available through vendors such as Suss MicroTec and EVG Group. 
         [0036]    With the second surface  126  of the device wafer  110  securely bonded to the second wafer  132 , the handling wafer  122  can be removed or debonded from the first surface  120  of the device wafer  110 , as shown in  FIG. 8 . The method used for debonding the handling wafer from the device wafer depends on the temporary bonding process used, as was discussed above. The nozzle plate made up of the device wafer and the second wafer is then cleaned to remove any residues left from the temporary bond. The handling wafer is then available for reuse as a handling wafer for another device wafer. 
         [0037]    In some applications, the process used for forming the thinned device wafer, temporarily bonding the device wafer to a handling wafer, grinding and polishing of the wafer to the desired thickness and then the etching the fluid channels, can be applied to the second wafer as well to form a thinned second wafer. Once the thinned second wafer is permanently bonded to the device wafer, the handling wafer of the second wafer is removed from the second wafer as is the handling wafer of the device wafer being removed from the device wafer. 
         [0038]    In the present invention, the temporary bond and the permanent bond can be contrasted with each other. The temporary bond is provided by a suitable adhesive, referred to herein as a temporary adhesive. Typically, the temporary adhesive includes curing conditions that do not damage the structures on the device wafer, sufficient adhesive strength at the process conditions used for wafer thinning, sufficient adhesive strength during the etch process used to form the ink channels, sufficient adhesive strength during the permanent bonding process, and a mechanism to significantly reduce the adhesive strength in order to release the device wafer from the handle wafer without damaging the structures on the device wafer, or leaving any significant residue or contamination on the device wafer. The permanent bond is typically provided by a suitable adhesive, referred to herein as a permanent adhesive. Typically, the permanent adhesive provides acceptable, stable adhesive strength between the device wafer and second wafer during the de-bonding of the handling substrate, acceptable adhesive strength during the subsequent steps used for integration of the printhead into the printing system, and acceptable adhesive strength during the operation of the printhead in the printing system, and compatibility with the liquids used in the printhead. 
         [0039]    In the fabrication process described above, alternatives are permitted. For example, nozzles  118  can be formed after the second substrate  132  is attached to the substrate  112  and the handling wafer  122  has been removed from substrate  112 . Another example includes applying a protective coating on the nozzle membrane  114  prior to coating the nozzle membrane  114  with an adhesive and then affixing the handle substrate  122 . 
         [0040]    Referring to  FIGS. 11 and 12  and back to  FIG. 8 , the device wafer  110  is divided into a plurality of nozzle plate structures  49 , also commonly referred to as nozzle plates, one or more of which are included in a printhead  30 . Typically, division of the device wafer  110  is accomplished using a conventional wafer dicing process. 
         [0041]    The printhead  30  includes nozzle membrane  114  and a plurality of fluid channels  130 , also commonly referred to as liquid chambers. Portions of the nozzle membrane  114  define a plurality, for example, an array  98 , of nozzles  118 . In the description presented below, reference sign  50  and reference sign  118  are used interchangeable to denote the nozzle  50 ,  118  of the printhead  30  of the present invention. The liquid chambers  130  are located in a first substrate  112 . In some example embodiments, the plurality of liquid chambers  130  of printhead  30  is located in a silicon substrate. Other substrate materials, however, are permitted. 
         [0042]    The nozzle membrane  114  includes a drop stimulation or drop forming device  28 , described in more detail below. In some example embodiments of the invention, the drop forming device  28  includes a resistive heating element associated with one or more nozzles  50 ,  118  of the array  98  of nozzles  50 ,  118 . In other example embodiments of the invention, the drop forming device  28  includes a piezoelectric device associated with one or more nozzles  50 ,  118  of the array  98  of nozzles  50 ,  118 . 
         [0043]    The nozzle array  98  includes a length  100  and each nozzle  50 ,  118  of the nozzle array  98  includes an axis  102 . Each of the plurality of liquid chambers  130  is in fluid communication with a respective one of the nozzles  50 ,  118  of the nozzle array  98 . Each of the plurality of liquid chambers  130  includes a height dimension  104  and a width dimension  106 . The height dimension  104  extends in a direction parallel to the axis  102  of the respective nozzle  50 ,  118 . The width dimension  106  extends in a direction along the length  100  of the nozzle array  98 . In the present invention, the height dimension  104  and the width dimension  106  have an aspect ratio of less than or equal to 9:1. This aspect ratio is smaller when compared to aspect ratios of conventional nozzle plates. 
         [0044]    The aspect ratio of the present invention controls the thickness of the wafer (and the substrate of the nozzle plate structure  49 ) resulting from the thinning of the wafer that includes the liquid chambers  130 . The fluid channel aspect ratio is defined as the ratio of the wafer thickness to the shortest dimension of the fluid channel in the plane of the device wafer surface. In most cases, the shortest dimension is along the axis of the array of nozzles, but it is also possible in some designs for the shortest dimension of the fluid channel in the plate of the device wafer surface is perpendicular to the axis of the array of nozzles. In the present invention, the feature aspect ratio is less than 9:1, and more preferably less than 5:1. 
         [0045]    As shown in  FIG. 12 , the liquid chambers  130  include an elliptical cross section when viewed in the direction parallel to the axis  102  of the nozzle  50 ,  118 . The ellipse includes a short dimension and a long dimension. The width dimension  106  of the liquid chamber  130  is the short dimension of the ellipse. The long dimension of the ellipse is also referred to as the length dimension  108  of the liquid chamber  130 . The elliptical cross sectional shape of liquid chamber  130  is oriented such that a line drawn through the center of the ellipse along the length dimension  108  of the ellipse is approximately perpendicular to the length  100  of the nozzle array  98 . Additionally, the elliptical cross sectional shape of liquid chamber  130  is oriented such that a line drawn through the center of the ellipse along the width dimension  106  of the ellipse is approximately parallel to the length  100  of the nozzle array  98 . This liquid chamber configuration allows for a high nozzle density along the row of nozzles while facilitating the nozzle plate structure  49  manufacturing process. The elliptical shape is one of a number of elongated, yet symmetrical, shapes for the liquid chamber  130 . Other cross sectional shapes are permitted. For example, in other example embodiments of the invention, the cross sectional shape of the liquid can include a circle, a square, or a rectangle. 
         [0046]    Referring additionally back to  FIG. 9 , as described above the plurality of liquid chambers  130  is located in a first substrate  112 . In one example embodiment of the present invention, printhead  30  also includes a second substrate  132  that includes a segmented fluid channel  134 . The second substrate  132  is permanently bonded to the first substrate  112 . For a given segment, for example,  134 A of the segmented fluid channel  134 , the segment  134 A is in fluid communication with one, for example,  130 A, or a subset of the plurality of liquid chambers  130 . CMOS circuitry  140  included in at least one of the nozzle membrane  114  and the first substrate  112 . The permanent bond between the first substrate  112  and the second substrate  132  is provided by an adhesive that includes a curing temperature that is compatible with the CMOS circuitry  140 . 
         [0047]    Referring additionally back to  FIG. 10 , as described above the plurality of liquid chambers  130  is located in a first substrate  112 . In another example embodiment of the present invention, printhead  30  also includes a second substrate  132  that includes a fluid channel  134 . The second substrate  132  is permanently bonded to the first substrate  112 . The fluid channel  134 , commonly referred to as an elongated trench  138 , is in fluid communication with the plurality of liquid chambers  130 . CMOS circuitry  140  included in at least one of the nozzle membrane  114  and the first substrate  112 . The permanent bond between the first substrate  112  and the second substrate  132  is provided by an adhesive that includes a curing temperature that is compatible with the CMOS circuitry  140 . 
         [0048]    Referring to  FIGS. 13-15 , example embodiments of a printing system and a continuous printhead are shown that include the invention described above. It is contemplated, however, that the present invention also finds application in other types of printheads or jetting modules including, for example, drop on demand printheads or other types of continuous printheads. 
         [0049]    Referring to  FIG. 13 , a continuous printing system  20  includes an image source  22  such as a scanner or computer which provides raster image data, outline image data in the form of a page description language, or other forms of digital image data. This image data is converted to half-toned bitmap image data by an image processing unit  24  which also stores the image data in memory. A plurality of drop forming mechanism control circuits  26  read data from the image memory and apply time-varying electrical pulses to a drop forming mechanism(s)  28  that are associated with one or more nozzles of a printhead  30 . These pulses are applied at an appropriate time, and to the appropriate nozzle, so that drops formed from a continuous ink jet stream will form spots on a recording medium  32  in the appropriate position designated by the data in the image memory. 
         [0050]    Recording medium  32  is moved relative to printhead  30  by a recording medium transport system  34 , which is electronically controlled by a recording medium transport control system  36 , and which in turn is controlled by a micro-controller  38 . The recording medium transport system shown in  FIG. 13  is a schematic only, and many different mechanical configurations are possible. For example, a transfer roller could be used as recording medium transport system  34  to facilitate transfer of the ink drops to recording medium  32 . Such transfer roller technology is well known in the art. In the case of page width printheads, it is most convenient to move recording medium  32  past a stationary printhead. However, in the case of scanning print systems, it is usually most convenient to move the printhead along one axis (the sub-scanning direction) and the recording medium along an orthogonal axis (the main scanning direction) in a relative raster motion. 
         [0051]    Ink is contained in an ink reservoir  40  under pressure. In the non-printing state, continuous ink jet drop streams are unable to reach recording medium  32  due to an ink catcher  42  that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit  44 . The ink recycling unit reconditions the ink and feeds it back to reservoir  40 . Such ink recycling units are well known in the art. The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir  40  under the control of ink pressure regulator  46 . Alternatively, the ink reservoir can be left unpressurized, or even under a reduced pressure (vacuum), and a pump is employed to deliver ink from the ink reservoir under pressure to the printhead  30 . When this is done, the ink pressure regulator  46  can include an ink pump control system. As shown in  FIG. 13 , catcher  42  is a type of catcher commonly referred to as a “knife edge” catcher. 
         [0052]    The ink is distributed to printhead  30  through an ink channel  47 . The ink preferably flows through slots or holes etched through a silicon substrate of printhead  30  to its front surface, where a plurality of nozzles and drop forming mechanisms, for example, heaters, are situated. When printhead  30  is fabricated from silicon, drop forming mechanism control circuits  26  can be integrated with the printhead. Printhead  30  also includes a deflection mechanism (not shown in  FIG. 13 ) which is described in more detail below with reference to  FIGS. 14 and 15 . 
         [0053]    Referring to  FIG. 14 , a schematic view of continuous liquid printhead  30  is shown. A jetting module  48  of printhead  30  includes an array or a plurality of nozzles  50  formed in a nozzle plate  49 . In  FIG. 14 , nozzle plate  49  is affixed to jetting module  48 . However, as shown in  FIG. 15 , nozzle plate  49  can be an integral portion of the jetting module  48 . 
         [0054]    Liquid, for example, ink, is emitted under pressure through each nozzle  50  of the array to form filaments of liquid  52 . In  FIG. 14 , the array or plurality of nozzles extends into and out of the figure. 
         [0055]    Jetting module  48  is operable to form liquid drops having a first size or volume and liquid drops having a second size or volume through each nozzle. To accomplish this, jetting module  48  includes a drop stimulation or drop forming device  28 , for example, a heater or a piezoelectric actuator, that, when selectively activated, perturbs each filament of liquid  52 , for example, ink, to induce portions of each filament to breakoff from the filament and coalesce to form drops  54 ,  56 . 
         [0056]    In  FIG. 14 , drop forming device  28  is a heater  51 , for example, an asymmetric heater or a ring heater (either segmented or not segmented), located in a nozzle plate  49  on one or both sides of nozzle  50 . This type of drop formation is known with certain aspects having been described in, for example, one or more of U.S. Pat. No. 6,457,807 B1, issued to Hawkins et al., on Oct. 1, 2002; U.S. Pat. No. 6,491,362 B1, issued to Jeanmaire, on Dec. 10, 2002; U.S. Pat. No. 6,505,921 B2, issued to Chwalek et al., on Jan. 14, 2003; U.S. Pat. No. 6,554,410 B2, issued to Jeanmaire et al., on Apr. 29, 2003; U.S. Pat. No. 6,575,566 B1, issued to Jeanmaire et al., on Jun. 10, 2003; U.S. Pat. No. 6,588,888 B2, issued to Jeanmaire et al., on Jul. 8, 2003; U.S. Pat. No. 6,793,328 B2, issued to Jeanmaire, on Sep. 21, 2004; U.S. Pat. No. 6,827,429 B2, issued to Jeanmaire et al., on Dec. 7, 2004; and U.S. Pat. No. 6,851,796 B2, issued to Jeanmaire et al., on Feb. 8, 2005. 
         [0057]    Typically, one drop forming device  28  is associated with each nozzle  50  of the nozzle array. However, a drop forming device  28  can be associated with groups of nozzles  50  or all of nozzles  50  of the nozzle array. 
         [0058]    When printhead  30  is in operation, drops  54 ,  56  are typically created in a plurality of sizes or volumes, for example, in the form of large drops  56 , a first size or volume, and small drops  54 , a second size or volume. The ratio of the mass of the large drops  56  to the mass of the small drops  54  is typically approximately an integer between 2 and 10. A drop stream  58  including drops  54 ,  56  follows a drop path or trajectory  57 . 
         [0059]    Printhead  30  also includes a gas flow deflection mechanism  60  that directs a flow of gas  62 , for example, air, past a portion of the drop trajectory  57 . This portion of the drop trajectory is called the deflection zone  64 . As the flow of gas  62  interacts with drops  54 ,  56  in deflection zone  64  it alters the drop trajectories. As the drop trajectories pass out of the deflection zone  64  they are traveling at an angle, called a deflection angle, relative to the undeflected drop trajectory  57 . 
         [0060]    Small drops  54  are more affected by the flow of gas than are large drops  56  so that the small drop trajectory  66  diverges from the large drop trajectory  68 . That is, the deflection angle for small drops  54  is larger than for large drops  56 . The flow of gas  62  provides sufficient drop deflection and therefore sufficient divergence of the small and large drop trajectories so that catcher  42  (shown in  FIGS. 13 and 15 ) can be positioned to intercept one of the small drop trajectory  66  and the large drop trajectory  68  so that drops following the trajectory are collected by catcher  42  while drops following the other trajectory bypass the catcher and impinge a recording medium  32  (shown in  FIGS. 13 and 15 ). 
         [0061]    When catcher  42  is positioned to intercept large drop trajectory  68 , small drops  54  are deflected sufficiently to avoid contact with catcher  42  and strike the print media. As the small drops are printed, this is called small drop print mode. When catcher  42  is positioned to intercept small drop trajectory  66 , large drops  56  are the drops that print. This is referred to as large drop print mode. 
         [0062]    Referring to  FIG. 15 , jetting module  48  includes an array or a plurality of nozzles  50 . Liquid, for example, ink, supplied through channel  47 , is emitted under pressure through each nozzle  50  of the array to form filaments of liquid  52 . In  FIG. 15 , the array or plurality of nozzles  50  extends into and out of the figure. 
         [0063]    Drop stimulation or drop forming device  28  (shown in  FIGS. 13 and 14 ) associated with jetting module  48  is selectively actuated to perturb the filament of liquid  52  to induce portions of the filament to break off from the filament to form drops. In this way, drops are selectively created in the form of large drops and small drops that travel toward a recording medium  32 . 
         [0064]    Positive pressure gas flow structure  61  of gas flow deflection mechanism  60  is located on a first side of drop trajectory  57 . Positive pressure gas flow structure  61  includes first gas flow duct  72  that includes a lower wall  74  and an upper wall  76 . Gas flow duct  72  directs gas flow  62  supplied from a positive pressure source  92  at downward angle θ of approximately a 45° relative to liquid filament  52  toward drop deflection zone  64  (also shown in  FIG. 14 ). An optional seal(s)  84  provides an air seal between jetting module  48  and upper wall  76  of gas flow duct  72 . 
         [0065]    Upper wall  76  of gas flow duct  72  does not need to extend to drop deflection zone  64  (as shown in  FIG. 14 ). In  FIG. 15 , upper wall  76  ends at a wall  96  of jetting module  48 . Wall  96  of jetting module  48  serves as a portion of upper wall  76  ending at drop deflection zone  64 . 
         [0066]    Negative pressure gas flow structure  63  of gas flow deflection mechanism  60  is located on a second side of drop trajectory  57 . Negative pressure gas flow structure includes a second gas flow duct  78  located between catcher  42  and an upper wall  82  that exhausts gas flow from deflection zone  64 . Second duct  78  is connected to a negative pressure source  94  that is used to help remove gas flowing through second duct  78 . An optional seal(s)  84  provides an air seal between jetting module  48  and upper wall  82 . 
         [0067]    As shown in  FIG. 15 , gas flow deflection mechanism  60  includes positive pressure source  92  and negative pressure source  94 . However, depending on the specific application contemplated, gas flow deflection mechanism  60  can include only one of positive pressure source  92  and negative pressure source  94 . 
         [0068]    Gas supplied by first gas flow duct  72  is directed into the drop deflection zone  64 , where it causes large drops  56  to follow large drop trajectory  68  and small drops  54  to follow small drop trajectory  66 . As shown in  FIG. 15 , small drop trajectory  66  is intercepted by a front face  90  of catcher  42 . Small drops  54  contact face  90  and flow down face  90  and into a liquid return duct  86  located or formed between catcher  42  and a plate  88 . Collected liquid is either recycled and returned to ink reservoir  40  (shown in  FIG. 13 ) for reuse or discarded. Large drops  56  bypass catcher  42  and travel on to recording medium  32 . Alternatively, catcher  42  can be positioned to intercept large drop trajectory  68 . Large drops  56  contact catcher  42  and flow into a liquid return duct located or formed in catcher  42 . Collected liquid is either recycled for reuse or discarded. Small drops  54  bypass catcher  42  and travel on to recording medium  32 . 
         [0069]    Alternatively, deflection can be accomplished by applying heat asymmetrically to filament of liquid  52  using an asymmetric heater  51 . When used in this capacity, asymmetric heater  51  typically operates as the drop forming mechanism in addition to the deflection mechanism. This type of drop formation and deflection is known having been described in, for example, U.S. Pat. No. 6,079,821, issued to Chwalek et al., on Jun. 27, 2000. 
         [0070]    Deflection can also be accomplished using an electrostatic deflection mechanism. Typically, the electrostatic deflection mechanism either incorporates drop charging and drop deflection in a single electrode, like the one described in U.S. Pat. No. 4,636,808, or includes separate drop charging and drop deflection electrodes. 
         [0071]    As shown in  FIG. 15 , catcher  42  is a type of catcher commonly referred to as a “Coanda” catcher. However, the “knife edge” catcher shown in  FIG. 13  and the “Coanda” catcher shown in  FIG. 15  are interchangeable and either can be used usually the selection depending on the application contemplated. Alternatively, catcher  42  can be of any suitable design including, but not limited to, a porous face catcher, a delimited edge catcher, or combinations of any of those described above. 
         [0072]    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]    
       
           20  continuous printer system 
           22  image source 
           24  image processing unit 
           26  mechanism control circuits 
           28  drop stimulation device; drop forming device 
           30  printhead 
           32  recording medium 
           34  recording medium transport system 
           36  recording medium transport control system 
           38  micro-controller 
           40  reservoir 
           42  catcher 
           44  recycling unit 
           46  pressure regulator 
           48  channel 
           50  jetting module 
           48  nozzle plate; nozzle plate structure 
           50  plurality of nozzles 
           51  heater 
           52  liquid 
           54  drops 
           56  drops 
           57  trajectory 
           58  drop stream 
           60  gas flow deflection mechanism 
           61  positive pressure gas flow structure 
           62  gas flow 
           63  negative pressure gas flow structure 
           64  deflection zone 
           66  small drop trajectory 
           68  large drop trajectory 
           72  first gas flow duct 
           74  lower wall 
           76  upper wall 
           78  second gas flow duct 
           82  upper wall 
           86  liquid return duct 
           88  plate 
           90  front face 
           92  positive pressure source 
           94  negative pressure source 
           96  wall 
           98  nozzle array 
           100  nozzle array length 
           102  nozzle axis 
           104  liquid chamber height 
           106  liquid chamber width 
           108  liquid chamber length 
           110  device wafer 
           112  silicon substrate 
           114  nozzle membrane layer; nozzle membrane 
           116  drop forming device 
           118  nozzle 
           120  first surface 
           122  handle wafer 
           124  temporary adhesive 
           126  second surface 
           128  photoresist 
           129  pattern 
           130  fluid channel; liquid chamber 
           132  second wafer; second substrate 
           134  fluid channel 
           136  permanent adhesive 
           138  elongated trench 
           140  CMOS circuitry