Patent Publication Number: US-10308023-B2

Title: Method of making inkjet print heads by filling residual slotted recesses and related devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 14/985,984 filed on Dec. 31, 2015, which is a divisional of U.S. application Ser. No. 13/906,466 filed on May 31, 2013, now issued as U.S. Pat. No. 9,409,394 on Aug. 9, 2016, which applications are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to inkjet printers, and more particularly, to methods of making inkjet print heads. 
     BACKGROUND 
     Modern ink jet printers may produce photographic-quality images. An inkjet printer includes a number of orifices or nozzles spatially positioned in a printer cartridge. Ink is heated when an electrical pulse energizes a resistive element forming a thermal resistor. The ink resting above the thermal resistor is ejected through the orifice towards a printing medium, such as an underlying sheet of paper as a result of the applied electrical pulse. 
     The thermal resistor is typically formed as a thin film resistive material on a semiconductor substrate as part of a semiconductor chip, for example. Several thin film layers may be formed on the semiconductor chip, including a dielectric layer carried by the substrate, a resistive layer forming the thermal resistor, and an electrode layer that defines electrodes coupled to the resistive layer to which the pulse is applied to heat the thermal resistor and vaporize the ink. 
     A first phase of making a print head, which may include the components described above, may follow standard semiconductor processing techniques to form circuitry for controlling the inkjet print head. The control circuitry may be formed on a front side of a silicon wafer, for example, a silicon wafer having a &lt;100&gt;crystalline orientation and 675-725 micron thickness. 
     Once the circuit formation processing steps are completed, two additional phases for making a print head are typically followed. These phases are generally classified as micro electro-mechanical systems (MEMS) processing steps. One of these MEMS phases may include forming three-dimensional structures that function as inkjet chambers, which may be formed on the same side of the wafer as the control circuitry. The thermal resistor or heater, which is described above, may be carried by a floor of each inkjet chamber. Each inkjet chamber acts as a small room into which ink flows. A roof of each inkjet chamber typically includes an opening, which may be referred to as an orifice, bore, or nozzle plate, for example. 
     The other MEMS processing phase may include forming through-wafer ink channels to allow ink to flow from a reservoir or supply at the backside of the wafer to each inkjet chamber. This MEMS phase may be relatively expensive. For example, one method of forming the through-wafer ink channels is deep reactive ion etching (DRIE) of silicon, which uses relatively expensive equipment and has a very low throughput. Another common method is laser cutting, which also uses relatively expensive equipment and has a very low throughput. 
     One technique for forming a through-wafer ink channel includes forming an ink feed slot in a substrate using a saw. More particularly, U.S. Pat. No. 7,966,728 to Buswell discloses using a circular cutting disk or saw positioned above a first surface of a substrate to cut a desired depth of the substrate. 
     SUMMARY 
     A method of making a plurality of inkjet print heads may include forming, by sawing with a rotary saw blade, a plurality of continuous slotted recesses in a first surface of a wafer. The plurality of continuous slotted recesses may be arranged in parallel, spaced apart relation, and each continuous slotted recess may extend continuously across the first surface. The method may further include forming a plurality of discontinuous slotted recesses in a second surface of the wafer to be aligned and coupled in communication with the continuous slotted recesses to define a plurality of alternating through-wafer channels and residual slotted recess portions. The method may further include selectively filling the residual slotted recess portions to define a plurality of through-wafer ink channels. Accordingly, the inkjet print heads may be made more efficiently and with a reduced cost. 
     Forming the plurality of continuous slotted recesses may include forming the plurality of continuous slotted recesses before forming the plurality of discontinuous slotted recesses. In other embodiments, forming the plurality of discontinuous slotted recesses may include forming the plurality of discontinuous slotted recesses before forming the plurality of continuous slotted recesses. 
     Forming the plurality of discontinuous slotted recesses may include etching the plurality of discontinuous slotted recesses, for example. The method may further include forming a plurality of inkjet heaters and control circuitry on the wafer. 
     The method may further include forming at least one layer on the wafer to define a plurality of inkjet chambers. The at least one layer may have a plurality of inkjet orifices formed therein. 
     Filling may include filling with a dielectric material. The dielectric material may include a polymer, for example. The wafer may further include a silicon wafer. 
     A device aspect is directed to an inkjet print head that may include a silicon substrate having a plurality of continuous slotted recesses in a first surface. The plurality of continuous slotted recesses may be arranged in parallel, spaced apart relation, and each continuous slotted recess may extend continuously across the first surface. The silicon substrate may also have a plurality of discontinuous slotted recesses in a second surface aligned, and coupled in communication with the continuous slotted recesses to define a plurality of alternating through-wafer channels and residual slotted recess portions. The inkjet print head may also include a dielectric material filling the residual slotted recess portions to define a plurality of through-wafer ink channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an inkjet print head cartridge that incorporates an inkjet print head made according to the invention. 
         FIG. 2  is a flowchart of a method of making inkjet print heads in accordance with the invention. 
         FIG. 3  is a more detailed flowchart of a method of making inkjet print heads in accordance with the invention. 
         FIG. 4  is a diagram illustrating sawing continuous slotted recesses in a first surface of a wafer in accordance with the invention. 
         FIG. 5  is a top view of a second surface of a wafer in accordance with the invention. 
         FIG. 6  is an enlarged top view of a portion of a second surface of a wafer having masked through wafer channels according to the invention. 
         FIG. 7  is an enlarged top view of a portion of the wafer of  FIG. 6  after filling the residual continuous slotted recesses with a dielectric material and removing the mask according the invention. 
         FIG. 8  is a top view of a mask according to the invention. 
         FIG. 9  is an enlarged cross-sectional view of a portion of a wafer with dielectric material filling the residual continuous slotted recess portions according to the invention. 
         FIG. 10  is an enlarged schematic cross-sectional view of a inkjet print head according to the invention. 
         FIG. 11  is flowchart of a method of making inkjet print heads according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown. The embodiments may, however, be in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout and prime notation is used to describe like elements in different embodiments. 
     Referring initially to  FIG. 1 , an inkjet print head cartridge  20  is now described. This inkjet print cartridge  20  includes a cartridge body  22  that includes ink, for example, for an inkjet print head. The ink is channeled from an ink supply through through-wafer ink channels into a plurality of inkjet chambers, each associated with a respective orifice  24  or print head nozzle positioned on the body  22  and configured to eject ink onto the paper or other print media. Electrical signals are provided to conductive traces  26  to energize thermal resistors of heater that heat the ink and eject a droplet of ink through an associated orifice  24 . 
     The orifices  24  are typically located at an inkjet print head  27  of the print head cartridge  20 . In an example, the print head cartridge  20  may include  300  or more orifices  24 , each orifice  24  having an associated inkjet chamber  30 , as will be appreciated by those skilled in the art. During manufacture, many print heads  27  may be formed to be included on a single silicon wafer and separated. Such methods of making inkjet print heads are described in further detail below. 
     Referring now to the flowchart  60  in  FIG. 2 , a method of making inkjet print heads  27  is described. Beginning at Block  62 , the method includes, at Block  64 , forming, by sawing with a rotary saw blade, continuous slotted recesses in a first surface of a wafer. The continuous slotted recesses are arranged in parallel, spaced apart relation, and each continuous slotted recess extends continuously across the first surface. 
     At Block  66 , the method includes forming discontinuous slotted recesses in a second surface of the wafer to be aligned and coupled in communication with the continuous slotted recesses to define alternating through-wafer channels and residual continuous slotted recess portions. The method further includes, at Block  68 , selectively filling the residual continuous slotted recess portions to define a plurality of through-wafer ink channels  41  ( FIG. 10 ). The method ends at Block  70 . 
     Referring now to the flowchart  80  in  FIG. 3  and  FIGS. 4-10 , a more detailed method of making inkjet print heads  27  is now described. Beginning at Block  82 , the method includes, at Block  84 , forming inkjet heaters  44  and control circuitry  45  on the wafer  30  ( FIG. 10 ). It will be appreciated by those skilled in the art that the wafer  30  includes many inkjet print heads  27 , however, for ease of description, a portion of a single inkjet print head is illustrated in  FIG. 10 . In other words, the inkjet heaters  44  and the control circuitry  45  are formed for each inkjet print head  27  on the wafer  30 . 
     The method also includes forming, at Block  86 , a dielectric layer  47  and a substrate layer  48  on the wafer  30  to define inkjet chambers  49  . In some embodiments, a single silicon substrate (i.e., layer) or second wafer may be formed on the wafer  30  to define the inkjet chambers  49 . The substrate layer  48  has inkjet orifices  51  formed therein. Again, while a portion of a single inkjet print head  27  is illustrated, it will be appreciated by those skilled in the art that the wafer  30  includes many inkjet print heads  27  as illustrated in  FIG. 5 . 
     At Block  88 , the method includes forming, by sawing with a rotary saw blade  31 , continuous slotted recesses  32  in a first surface  33  of a wafer  30  ( FIG. 4 ). More particularly, the continuous slotted recesses  32  may be sawed with a diamond saw, for example, similar to a diamond saw used for wafer dicing. For example, a 675 micron thick wafer may be cut such that the remaining wafer has a thickness in the range of 50-200 microns. In other words, each continuous slotted recess  32  may be formed to have a depth of between 50%-95% of a thickness of the wafer  30 , for example. 
     The wafer  30  may be a silicon wafer or in some embodiments, a silicon substrate, for example. The continuous slotted recesses  32  are arranged in parallel, spaced apart relation. Each continuous slotted recess  32  extends continuously across the first surface  33  ( FIG. 4 ). 
     At Block  90 , the method includes forming discontinuous slotted recesses  34  in a second surface  35  of the wafer  30  by etching. For example, the discontinuous slotted recesses  34  may be formed in the second surface  35  by a wet or dry or reactive ion etching, plasma etching, abrasive jet erosion, etc. Of course, the discontinuous slotted recesses  34  may be formed by other techniques. 
     The discontinuous slotted recesses  34  are formed to be aligned and coupled in communication with the continuous slotted recesses  32  to define alternating through-wafer channels  37  and residual slotted recess portions  38  ( FIG. 7 ). In other words, the continuous slotted recesses  32  are formed before the discontinuous slotted recesses  34 . 
     The method includes, at Block  92 , positioning a mask  36  over the through-wafer channels  37  ( FIG. 6 ). The mask  36  may be in the form of a frame for example, that has slots  39  that expose the residual slotted recess portions  38  ( FIG. 8 ). Of course, in some embodiments, a mask  36  may not be used. 
     The method further includes selectively filling the residual slotted recess portions  38  to define through-wafer ink channels  41  (Block  94  and  FIG. 10 ). The residual slotted recess portions  38  may be filled with a dielectric material  42 , for example, a polymer ( FIG. 9 ). The dielectric material  42  may be chosen based upon its properties, for example, cost, ease of application, flow/fill, cure temperature, coefficient of thermal expansion, outgassing, toxicity, etc. The residual continuous slotted recess portions  38  may be fully filled or may be only partially filled. 
     As will be appreciated by those skilled in the art, the sawing reduces the overall strength of the wafer  30 . Filling the residual slotted recess portions  38  with the dielectric material advantageously strengthens the wafer  40 . 
     The through-wafer ink channels  41  are to be coupled to an ink supply  43 , as will be appreciated by those skilled in the art ( FIG. 10 ). At Block  96 , the mask  36  is removed, and in some embodiments, excess dielectric material may also be removed. 
     The cured polymer advantageously becomes part of the inkjet print head  27 . Moreover, by filling the residual slotted recess portions  38 , the wafer  30  may have increased strength, and may allow for easier processing of subsequent method steps, for example. It should be noted that for ease of explanation,  FIGS. 4-9  do not illustrate the inkjet  45  and control circuitry  46 , as these may be formed prior to the sawing. 
     At Block  98 , the wafer  30  is separated into inkjet print heads  27 , for example, using silicon wafer dicing techniques as will be appreciated by those skilled in the art. The method ends at Block  100 . 
     Referring now to the flowchart  80 ′ in  FIG. 11 , in another embodiment the discontinuous slotted recesses  34 ′ are formed (Block  90 ′) before forming the continuous slotted recesses  32 ′ (Block  88 ′). The other method steps are similar to those described above with respect to the flowchart  80  in  FIG. 3  and require no further discussion herein. 
     Many modifications and other embodiments will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.