Patent Publication Number: US-6341848-B1

Title: Fluid-jet printer having printhead with integrated heat-sink

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to thermal inkjet printing. More particularly, this invention relates to an inkjet printhead apparatus having a dual-function heat sink, and to a method for manufacturing such an inkjet printhead. The dual-function heat sink of the present printhead is used during operation of the inkjet printhead to cool a resistor, or other energy-dissipation device. Such a resistor or other energy-dissipation device is used to eject fluid from the fully integrated fluid-jet printhead. During manufacturing of this inkjet printhead, the dual-function heat sink is used as a barrier preventing a chemical element or compound which is present in a substrate of the printhead from migrating by diffusion or other transport mechanism to another structure of the printhead. 
     2. Related Technology 
     Inkjet printers or plotters typically have a printhead mounted on a carriage. This carriage traverses back and forth across the width of a print medium (i.e., usually paper or a plastic plotting film, for example) as the medium is fed through the printer or plotter. Orifices on the printhead are fed ink (or other printing fluid) by one or more channels communicating from a reservoir. Energy applied individually to addressable resistors (or other energy-dissipating elements, for example, to piezoelectric actuators), transfers energy to ink which is within or associated with selected orifices, causing a portion of the ink to momentarily convert to vapor phase and to form a vapor bubble. Thus, this type of printer is also sometimes referred to as a “bubble jet printer.” As a result of the formation and expansion of the bubble, some of the ink is ejected out of the respective orifice toward the print medium (i.e., forming an “ink jet”). As the ink is ejected, the bubble collapses almost simultaneously, allowing more ink from the reservoir to fill the channel. This quick ejection of an ink jet from an orifice, and almost simultaneous collapse of the bubble which caused this ejection, allows for the ink jet printing cycle to have a high repetition rate. 
     Customer demands and competitive pressures continue to create a desire for faster ink jet printing combined with higher resolution. Thus, there is a strong desire in the inkjet printing art to increase the repetition rate at which ink can be ejected from a printhead. Increasing the repetition rate requires that more energy be applied to the resistors in the printhead, thereby causing the printhead to dissipate more heat, and possibly to become hotter. However, if the printhead becomes too hot, the ink will not be ejected from the printhead properly. That is, if the printhead becomes too hot, the ink may not be ejected in the proper amount, or perhaps not at all. This failure to properly eject ink from the printhead is sometimes referred to as a “misfire,” and causes poor print quality. 
     In addition, misfiring may cause the printhead to quit functioning at a particular print orifice because it is possible for the electrical resistor to open-circuit. This open circuiting of a printing resistor is similar to blowing a fuse, and can result from excessive temperature buildup at the printing resistors. This type of failure creates a permanent loss of printing ability at that orifice location of the printhead. Such a loss of printhead function is a terrible inconvenience to the user as the ink jet printing cartridge must be replaced, even though it may be nearly full of ink. Therefore, it is very important to more efficiently remove heat generated by the resistors or other energy dissipating elements of an ink jet printhead. 
     Another factor which works against cooling the resistors or other energy dissipating elements of an inkjet printhead is the pursuit of higher print densities. Higher print densities result in higher resolution in the characters of a printed document, or in an image, and make possible the reproduction of near-photographic quality inkjet images. However, as the resolution of an inkjet printhead increases, the amount of ink ejected during each firing of an orifice needs to be reduced. That is, the volume of ink in each “ink jet” ejected onto the print medium is decreased, making a greater number of firing cycles necessary to print a particular character or image. Further, the adjacent orifices are moved closer together. This increase in closeness of the adjacent orifices and their respective resistors or other energy dissipation elements, means that during operation of the printhead more energy is dissipated in a smaller volume of material. Thus, the amount of space and mass which is available to move the residual heat away from the energy dissipation elements or resistors is reduced. 
     In view of the above, it is seen that faster printing, higher print density and improved resistor cooling are all desirable improvements for an ink jet printhead. 
     Conventional ink jet print heads are seen in U.S. Pat. Nos. 3,930,260; 4,578,687; 4,677,447; 4,943,816; 5,560,837, and 5,706,039. However, none of these conventional ink jet printheads is believed to offer the combination, arrangement, and cooperation of components that is achieved in the present printhead. Particularly, none of these conventional printheads have a heat sink structure that also serves as a diffusion barrier during manufacturing of the printhead. 
     Additional conventional technology related to making semiconductor structures, or to making or using thin-film structures is know according to U.S. Pat. Nos. 2,801,375; 3,431,468; 3,518,494; 3,640,782; 3,909,319; 4,542,401; 5,068,697; 5,175,6133; 5,294;826; 5,371,404; 5,473,112; 5,589,711; 5,670,420; and 5,751,316. However, with the exception of the &#39;316 patent, none of this conventional technology is believed to related to an inkjet printhead. The &#39;316 patent is believed also to relate to a printhead based on silicon (or other semiconductor) processing technology, 
     SUMMARY OF INVENTION 
     In view of the deficiencies of the related technology, an object for this invention is to reduce or overcome one or more of these deficiencies. 
     Accordingly, the present invention provides an integrated ink jet printhead for ejecting printing fluid, this printhead comprising a substrate having a plan-view shape; a thin-film structure carried on the substrate, the thin-film structure including a metallic heat sink layer adjacent to the substrates, the metallic heat sink layer having a plan-view shape substantially the same as and congruent with the plan-view shape of the substrate; whereby the heat sink layer covers substantially the entire plan-view shape of the substrate. 
     According to another aspect, this invention provides a method of making an integrated thermal fluid jet print head, this method comprising steps of: forming a substrate having a plan-view shape; forming a thin-film structure on the substrate; including in the thin-film structure adjacent to the substrate a metallic heat sink layer; and forming the metallic heat sink layer to have a plan-view shape substantially the same as and congruent with the plan-view shape of the substrate, whereby the heat sink layer covers substantially the entire plan-view shape of the substrate. 
     Still another aspect of the present invention provides a printhead for ejecting printing fluid, the printhead comprising an amorphous substrate, a thin-film structure carried on the substrate; and a thin-film radio-frequency shield layer interposed between the substrate and the thin-film structure, whereby, the radio-frequency shield layer substantially prevents sodium, another chemical element, or chemical compound from transporting from the substrate to the thin-film structure during exposure of the substrate and thin film structure to radio frequency energy. 
     Other objects, features, and advantages of the present invention will be apparent to those skilled in the pertinent arts from a consideration of the following detailed description of a single preferred exemplary embodiment of the invention, when taken in conjunction with the appended drawing figures, which will first be described briefly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 is a diagrammatic side elevation view of an exemplary inkjet printer which uses an exemplary inkjet print cartridge with a printhead embodying the present invention; 
     FIG. 2 shows an exemplary inkjet print cartridge which may be used in the printer of FIG. 1, and which includes an inventive printhead embodying the present invention; 
     FIG. 3 provides a plan-view of a printhead portion of the inkjet print cartridge seen in FIG. 2; 
     FIG. 4 is a plan-view similar to FIG. 3, of the inkjet print cartridge, and has portions removed for clarity of illustration; 
     FIG. 5 provides a somewhat diagrammatic fragmentary cross sectional view taken at the line  5 — 5 , and is shown greatly enlarged in comparison to the illustration of FIG. 4; 
     FIG. 6 is a diagrammatic cross sectional view of a portion of a printhead embodying the present invention, and during a stage of the manufacturing process, and is similar to the portion seen in FIG.  5 ; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT OF THE INVENTION 
     FIG. 1 shows an exemplary inkjet printer  10 . This printer  10  includes a base  12  carrying a housing  14 . Within the housing  14  is a feed mechanism  16  for controllably moving a print medium (i.e., paper) through the printer  10 . The feed mechanism  16  controllably moves a sheet of paper  18  from a paper magazine  20  along a print path  22  within the printer  10 . The printer  10  includes a traverse mechanism  24  carrying an inkjet print cartridge  26 . The traverse mechanism moves the inkjet printing cartridge  26  perpendicularly to the direction of movement of the paper  18  (i.e., the cartridge  26  is moved perpendicularly to the plane of FIG.  2 ). The printer uses the inkjet printing cartridge  26  to controllably place small droplets of printing fluid (i.e., ink, for example) from the inkjet printing cartridge  26  on the paper  18 . By moving the inkjet printing cartridge  26  repeatedly back and forth across the paper  18  as this paper is advanced by the feed mechanism  16 , characters or images may be controllably formed by ejection of the small droplets of ink from the cartridge  26 . These small droplets of ink are ejected in the form of ink jets impinging on the paper  18  in controlled locations to form characters and images, as will be well known to those ordinarily skilled in the pertinent arts. 
     FIG. 2 illustrates the exemplary inkjet printing cartridge  26 . This inkjet printing cartridge  26  includes a cartridge body  28 , which defines a fluid delivery assembly (generally referenced with the numeral  30 ) supplying printing fluid (such as ink) to a printhead  32 . The printhead  32  is carried by the printing cartridge body  28 . The fluid delivery assembly  30  may include a sponge  34  carried within a chamber  36  of the body  28 , and a standpipe (not shown), conveying the printing fluid from the chamber  36  to the printhead  32 . The printhead  32  includes a printing circuit  38  which electrically couples the printhead  32  via circuit traces  38   a  and electrical contacts  40  with the printer  10 . That is, the electrical contacts  40  individually make electrical contact with matching contacts (not seen in the drawing Figures) on the traverse mechanism  24 , and provide for electrical interface of the printhead  32  with electrical driving circuitry (also not illustrated in the drawing Figures) of the printer  10 . Individual fine-dimension orifices  42  of the printhead  32  eject printing fluid when appropriate control signals are applied to contacts  40 . The fine-dimension orifices  42  are formed in a metallic plate member  44  adhesively attached to underlying structure (generally referenced with the numeral  46 , and seen in FIG. 4) of the printhead  32 . As is seen in FIG. 4, the underlying structure  46  of the printhead  32  defines a through hole  48  communicating printing fluid from the chamber  36  to a cavity  50  (best seen in FIG. 5) formed between the structure  46  and a portion of the plate member  44 . 
     The structure of the printhead  32  is shown in FIGS. 3-6 viewed in conjunction with one another. The thermal ink jet printhead  32  of FIGS. 3-6 includes a substrate  52  (best seen in FIGS.  5  and  6 ), which is most preferably formed as a plate of glass (i.e., an amorphous, generally non-conductive material). In this exemplary preferred embodiment, the substrate  52  is generally rectangular in plan view, although the invention is not so limited. Most preferably, this glass substrate is an inexpensive type of soda/lime glass (i.e., like ordinary window glass), which makes the printhead  32  very economical to manufacture, The printhead  32  is especially economical and inexpensive to manufacture when considered in comparison to printheads using the conventional technologies requiring a substrate of silicon or other crystalline semiconductor materials. 
     On the glass substrate  52  is formed a thin-film structure  54  of plural layers. As will be further explained, during manufacturing of the printhead  32  this thin-film structure  54  is formed substantially of plural thin-film layers applied one after the other and atop of one another, and each of which entirely covers and is congruent with the plan-view shape of the substrate. Again, this plan-view shape of the substrate  52  is seen in FIGS. 3 and 4. Once selected ones of these thin-film layers are formed on the substrate  52 , subsequent patterning and etching operations are used to define the contacts  40  and print circuit  38 , for example, as is further explained below. 
     The thin-film structure  54  includes a metallic multi-function heat sink, radio frequency shield, and diffusion barrier thin-film layer  56  (best seen in FIGS. 5 and 6) which is applied upon the substrate  52 . The layer  56  covers the entire plan-view shape of the substrate  52 , and is preferably formed of chrome about 1 to 2 microns thick. Alternatively, the layer  56  may be formed of other metals and alloys. For example, the thin-film heat sink, RF shield, and diffusion barrier layer  56  may be formed of aluminum, chrome, copper, gold, iron, molybdenum, nickel, palladium, platinum, tantalum, titanium, tungsten, a refractory metal, or of alloys of these or other metals. 
     Upon the metallic thin-film layer  56  is formed an insulator thin-film layer  58 . The insulator layer  58  is preferably formed of silicon oxide, and is about 1 to 2 microns thick. Again, this insulator layer  58  covers and is congruent with the entire plan-view shape of the substrate  52 . 
     Next, on the substrate  52  and on the insulator layer  56 , is formed a resistor thin-film layer  60 . The thin-film resistor layer is preferably formed of tantalum, aluminum alloy, and is preferably about 600 Angstroms thick. This resistor thin-film layer  60  is formed to cover and be congruent with the entire plan-view shape of the substrate  52 , but does not remain this extensive. That is, the resistor layer  60  is later patterned and etched back until it covers only an area congruent with the traces  38   a  of the print circuit  38 , with each of the contacts  40 , and with each one of plural print resistor areas  62  (best seen in FIG. 5, and generally indicated with the arrowed numeral  62  on FIG.  4 ). 
     Over the unpatterned and unetched resistor layer  60  is next formed a metallic conductor thin-film layer  64 . This metallic conductor thin-film layer  64  is formed preferably of an aluminum based alloy, and is about 0.5 micron thick. Again, this metallic conductor layer  64  is initially formed to cover and be congruent with the entire plan-view shape of the substrate  52 . However, this conductor layer  64  is also later patterned and etched back to cover only the area defining the traces  38   a  of print circuit  38 , and defining the contacts  40 . More particularly, the conductor layer  64  is first etched away at the location of the print resistors  62  so that a portion of the thin-film resistor layer  60  spanning between traces  38   a  of the print circuit  38  provides the only conduction path between these traces. Later, the etching operation is carried further, removing both the conductive layer  64  and the underlying resistive layer  60  over the entire plan-view shape of the substrate  52 , except at the locations of the traces  38  and contact pads  40 . This etching operation leaves the traces  38   a  and contact pads  40  standing in relief on the insulative layer  58 , as can be appreciated from a study of FIG.  5 . 
     Accordingly, an in view of the above, it will be understood that during operation of the printhead  32  when a current is applied between two of the contacts  40  leading via traces  38   a  to opposite sides of one of the print resistors  62 , the current to and from the respective print resistor  62  is carried in the traces of the print circuit  38  by a combination of the conductor thin-film layer  64  and the underlying resistor thin-film layer  60 . Because the conductive layer  64  has a much lower resistance than the resistive layer  60 , most of this current will flow in the layer  64 . However, at the print resistor  62  itself only the underlying resistor layer  64  is available to carry the current (the overlying conductive layer  64  having been locally etched away). The print resistors  62  are fine-dimension areas of the resistive layer  60 . Thus, these print resistors  62  can be caused to quickly dissipate energy, and to liberate heat. However, also viewing FIG.  3  and recalling that the metallic heat sink layer  56  covers substantially the entire plan-view shape of the substrate  52 , it will be understood that this heat sink layer both underlies the resistors  62  to absorb heat from these resistors, and has a large area (i.e., essentially the entire plan-view area of the printhead  32 ) from which to dissipate excess heat. Thus, the printhead  32  during operation maintains a desirably low temperature, and can operate at firing repetition rates not possible with conventional printheads using a glass substrate. 
     As FIG. 6 illustrates in fragmentary cross sectional view, a first manufacturing intermediate article  66  results from the above described manufacturing steps prior to the patterning and etching steps described above, and prior to the formation of the through hole  48 . This first manufacturing intermediate article includes the substrate  52 , and the thin-film layers  56 ,  58 ,  60 , and  64 , each of which substantially covers and is congruent with the entire plan-view shape of the substrate  52 . This first manufacturing intermediate article  66  is subjected to the patterning and etching processes described above to produce a second manufacturing intermediate article  68 , substantially as is seen in FIGS. 4 and 5. On this second manufacturing intermediate article  68  is formed a pair of passivating thin-film layers  70 , as is best seen in FIG. 5, and which are indicated on FIG. 6 with dashed lines. This passivating thin-film layer  70  includes a first sub-layer  70   a  of silicon nitride, followed by a second sub-layer  70   b  of silicon carbide. As FIG. 5 illustrates fragmentarily, the completion of the printhead  32  requires only the adhesive attachment of the metallic plate member  44 , with the print orifices  42  in alignment with the print resistors  62 . 
     In view of the above, those ordinarily skilled in the pertinent arts will understand that the thin-film structure  54  may be formed on the substrate  52  using a variety of techniques. These techniques including, but are not limited to, sputtering, and plasma enhanced chemical vapor deposition (PECVD) (i.e., physical vapor deposition. See, Thin-film Processes II, J. L. Vossen &amp; W. Kern, editors, Academic Press, New York, 1991, ch. 2-4). During one or more of these deposition processes, the workpiece that will become the first and second manufacturing intermediate articles, and which will become a completed printhead  32 , may be subjected to radio frequency energy. Particularly during the formation of the passivating layers  70   a  and  70   b , the second manufacturing intermediate article  68  is exposed to elevated temperatures and to radio frequency energy to assist in the deposition of these layers. During this exposure of the article  68  to radio frequency energy at elevated temperature, the metallic heat sink layer  56  serves as a radio-frequency shield, possibly preventing the localized heating of areas of the substrate that have comparatively higher conductivity, and preventing sodium or another chemical element or compound that is present in the soda/lime glass substrate  52  from being transported into the other thin-layer structures of the printhead. Particularly, were this sodium, other chemical element, or compound, not prevented from being partially transported into the passivation layer  70 , the sodium or other chemical element or compound could cause a lesion in the passivation layer at which this layer would not long withstand the cavitation occurring in the printing fluid each time a bubble collapses after an ink jet ejection. However, because the heat sink layer  56  covers the entire plan-view shape of the printhead  32 , there is no place where sodium, another chemical element, or compound, from the glass substrate  52  can be transported (perhaps by diffusion, for example) into the thin-film structures above this metallic heat sink layer  56 . Thus, contamination of the thin-film structure  54  with sodium, with another chemical element, or with a chemical compound from the glass substrate  52  is prevented in the present invention. 
     Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. Because the foregoing description of the present invention discloses only particularly a preferred exemplary embodiment of the invention, it is to be understood that other variations are recognized as being within the scope of the present invention. Accordingly, the present invention is not limited to the particular embodiment which has been described in detail herein. Rather, reference should be made to the appended claims to define the spirit and scope of the present invention.