Abstract:
A fluid-jet printhead has a substrate having at least one layer defining a fluid chamber for ejecting fluid. The printhead also includes a resistive layer disposed between the fluid chamber and the substrate wherein the fluid chamber has a smooth planer surface between the fluid chamber and the substrate. The printhead has a conductive layer disposed between the resistive layer and the substrate wherein the conductive layer and the resistive layer are in direct parallel contact. The conductive layer forms at least one void creating a planar resistor in the resistive layer. The planar resistor is aligned with the fluid chamber.

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
     The present application is a division of application Ser. No. 09/747,725, now U.S. Pat. No. 6,457,814 B1 which was filed on 20 th  Dec. 2000. 
    
    
     THE FIELD OF THE INVENTION 
     This invention relates to the manufacturer of printheads used in fluid-jet printers, and more specifically to a fluid-jet printhead used in a fluid-jet print cartridge having improved dimensional control and improved step coverage. 
     BACKGROUND OF THE INVENTION 
     One type of fluid-jet printing system uses a piezoelectric transducer to produce a pressure pulse that expels a droplet of fluid from a nozzle. A second type of fluid-jet printing system uses thermal energy to produce a vapor bubble in a fluid-filled chamber that expels a droplet of fluid. The second type is referred to as thermal fluid-jet or bubble jet printing systems. 
     Conventional thermal fluid-jet printers include a print cartridge in which small droplets of fluid are formed and ejected towards a printing medium. Such print cartridges include fluid-jet printheads with orifice structures having very small nozzles through which the fluid droplets are ejected. Adjacent to the nozzles inside the fluid-jet printhead are fluid chambers, where fluid is stored prior to ejection. Fluid is delivered to fluid chambers through fluid channels that are in fluid communication with a fluid supply. The fluid supply may be, for example, contained in a reservoir part of the print cartridge. 
     Ejection of a fluid droplet, such as ink, through a nozzle may be accomplished by quickly heating a volume of fluid within the adjacent fluid chamber. The rapid expansion of fluid vapor forces a drop of fluid through the nozzle in the orifice structure. This process is commonly known as “firing.” The fluid in the chamber may be heated with a transducer, such as a resistor, that is disposed and aligned adjacent to the nozzle. 
     In conventional thermal fluid-jet printhead devices, such as ink-jet cartridges, thin film resistors are used as heating elements. In such thin film devices, the resistive heating material is typically deposited on a thermally and electrically insulating substrate. A conductive layer is then deposited over the resistive material. The individual heater element (i.e., resistor) is dimensionally defined by conductive trace patterns that are lithographically formed through numerous steps including conventionally masking, ultraviolet exposure, and etching techniques on the conductive and resistive layers. More specifically, the critical width dimension of an individual resistor is controlled by a dry etch process. For example, an ion assisted plasma etch process is used to etch portions of the conductive and resistive layers not protected by a photoresist mask. The width of the remaining conductive thin film stack (of conductive and resistive layers) defines the final width of the resistor. The resistive width is defined as the width of the exposed resistive perpendicular to the direction of current flow. Conversely, the critical length dimension of an individual resistor is controlled by a subsequent wet etch process. A wet etch process is used to produce a resistor having sloped walls on the conductive layer defining the resistor length. The sloped walls of the conductive layer permit step coverage of later fabricated layers. 
     As discussed above, conventional thermal fluid-jet printhead devices require both dry etch and wet etch processes. The dry etch process determines the width dimension of an individual resistor, while the wet etch process defines both the length dimension and the necessary sloped walls commencing from the individual resistor. As is well known in the art, each process requires numerous steps, thereby increasing both the time to manufacture a printhead device and the cost of manufacturing a printhead device. 
     One or more passivation and cavitation layers are fabricated in a stepped fashion over the conductive and resistive layers and then selectively removed to create a via for electrical connection of a second conductive layer to the conductive traces. The second conductive layer is pattered to define a discrete conductive path from each trace to an exposed bonding pad remote from the resistor. The bonding pad facilitates connection with electrical contacts on the print cartridge. Activation signals are provided from the printer to the resistor via the electrical contacts. 
     The printhead substructure is overlaid with at least one orifice layer. Preferably, the at least one orifice layer is etched to define the shape of the desired firing fluid chamber within the at least one orifice layer. The fluid chamber is situated above, and aligned with, the resistor. The at least one orifice layer is preferably formed with a polymer coating or optionally made of an fluid barrier layer and an orifice plate. Other methods of forming the orifice layer(s) are know to those skilled in the art. 
     In direct drive thermal fluid-jet printer designs, the thin film device is selectively driven by electronics preferably integrated within the integrated circuit part of the printhead substructure. The integrated circuit conducts electrical signals directly from the printer microprocessor to the resistor through conductive layers. The resistor increases in temperature and creates super-heated fluid bubbles for ejection of the fluid from the fluid chamber through the nozzle. However, conventional thermal fluid-jet printhead devices can suffer from inconsistent and unreliable fluid drop sizes and inconsistent turn on energy required to fire a fluid droplet, if the resistor dimensions are not tightly controlled. Further, the stepped regions within the fluid chamber can affect drop trajectory and device reliability. The device reliability is affected by the bubble collapsing after the drop ejection thereby wearing down the stepped regions. 
     It is desirous to fabricate a fluid-jet printhead capable of producing fluid droplets having consistent and reliable fluid drop sizes. In addition, it is desirous to fabricate a fluid-jet printhead having a consistent turn on energy (TOE) required to fire a fluid droplet, thereby providing greater control of the size of the fluid drops. 
     SUMMARY OF THE INVENTION 
     A fluid-jet printhead has a substrate having at least one layer defining a fluid chamber for ejecting fluid. The printhead also includes a resistive layer disposed between the fluid chamber and the substrate wherein the fluid chamber has a smooth planer surface between the fluid chamber and the substrate. The printhead has a conductive layer disposed between the resistive layer and the substrate wherein the conductive layer and the resistive layer are in direct parallel contact. The conductive layer forms at least one void creating a planar resistor in the resistive layer. The planar resistor is aligned with the fluid chamber. 
     The present invention provides numerous advantages over conventional thin film printheads. First, the present invention provides a structure capable of firing a fluid droplet in a direction substantially perpendicular (normal or orthogonal) to a plane defined by the resistive element and ejection surface of the printhead. Second, the dimensions and planarity of the resistive material layer are-more precisely controlled, which reduces the variation in the turn on energy required to fire a fluid droplet. Third, the size of a fluid droplet is better controlled due to less variation in resistor size. Fourth, the corrosion resistance, surface texture, and electro-migration resistance of the conductive layers are improved inherently by the design. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged, cross-sectional, partial view illustrating a conventional thin film printhead substructure. 
     FIG. 2 is a flow chart of an exemplary process used to implement the conventional thin film printhead structure. 
     FIG. 3A is an enlarged, cross-sectional, partial view illustrating the invention&#39;s thin film printhead substructure. 
     FIG. 3B is an overhead view of the resistor element. 
     FIG. 4 is a flowchart of an exemplary process used to implement the invention&#39;s thin-film printhead structure. 
     FIG. 5 is a perspective view of a printhead fabricated with the invention. 
     FIG. 6 is an exemplary print cartridge that integrates and uses the printhead of FIG.  5 . 
     FIG. 7 is an exemplary recoding device, a printer, which uses the print cartridge of FIG.  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
     The present invention is a fluid-jet printhead, a method of fabricating the fluid-jet printhead, and use of a fluid-jet printhead. The present invention provides numerous advantages over the conventional fluid-jet or inkjet printheads. First, the present invention provides a structure capable of firing a fluid droplet in a direction substantially perpendicular (normal or orthogonal) to a plane defined by the resistive element and ejection surface of the printhead. Second, the dimensions and planarity of the resistive layer are more precisely controlled, which reduces the variation in the turn on energy required to fire a fluid droplet. Third, the size of a fluid droplet is better controlled due to less variation in resistor size. Fourth, the design inherently provides for improved corrosion resistance, improved electro-migration resistance of the conductive layers and a smoother resistor surface. 
     FIG. 1 is an enlarged, cross-sectional, partial view illustrating a conventional thin film printhead  190 . The thicknesses of the individual thin film layers are not drawn to scale and are drawn for illustrative purposes only. As shown in FIG. 1, thin film printhead  190  has affixed to it a fluid barrier layer  70 , which is shaped along with orifice plate  80  to define fluid chamber  100  to create an orifice layer  82  (see FIG.  5 ). Optionally, the orifice layer  82  and fluid barrier layers  70  may be made of one or more layers of polymer material. A fluid droplet within a fluid chamber  100  is rapidly heated and fired through nozzle  90  when the printhead is used. 
     Thin film printhead substructure  190  includes substrate  10 , an insulating insulator layer  20 , a resistive layer  30 , a conductive layer  40  (including conductors  42 A and  42 B), a passivation layer  50 , a cavitation layer  60 , and a fluid barrier structure  70  defining fluid chamber  100  with orifice plate  80 . 
     As diagrammed in FIG. 2, a relatively thick insulator layer  20  (also referred to as an insulative dielectric) is applied to substrate  10  in step  110  preferably by deposition. Silicon dioxides are examples of materials that are used to fabricate insulator layer  20 . Preferably, insulator layer  20  is formed from tetraethylorthosilicate (TEOS) oxide having a 14,000 Angstrom thickness. In one alternative embodiment, insulative layer  20  is fabricated from silicon dioxide. In another embodiment, it is formed of silicon nitride. 
     There are numerous ways to fabricate insulation layer  20 , such as through a plasma enhanced chemical vapor deposition (PECVD), or a thermal oxide process. Insulator layer  20  serves as both a thermal and electrical insulator for the resistive circuit that will be built on its surface. The thickness of the insulator layer can be adjusted to vary the heat transferring or isolating capabilities of the layer depending on a desired turn-on energy and firing frequency. 
     Next in step  112 , the resistive layer  30  is applied to uniformly cover the surface of insulation layer  20 . Preferably, the resistive layer is tantalum silicon nitride or tungsten silicon nitride of a 1200 Angstrom thickness although tantalum aluminum can also be used. Next in step  114 , conductive layer  40  is applied over the surface of resistive layer  30 . In conventional structures, conductive layer  40  is formed with preferably aluminum copper or alternatively with tantalum aluminum or aluminum gold. Additionally, a metal used to form conductive layer  40  may also be doped or combined with materials such as copper, gold, or silicon or combinations thereof A preferable thickness for the conductive layer  40  is 5000 Angstroms. Resistive layer  30  and conductive layer  40  can be fabricated though various techniques, such as through a physical vapor deposition (PVD). 
     In step  116 , the conductive layer  40  is patterned with a photoresist mask to define the resistor&#39;s width dimension. Then in step  118 , conductive layer  40  is etched to define conductors  42 A and  42 B. Fabrication of conductors  42 A and  42 B define the critical length and width dimensions of the active region of resistive layer  30 . More specifically, the critical width dimension of the active region of resistive layer  30  is controlled by a dry etch process. For example, an ion assisted plasma etch process is used to vertically etch portions of conductive layer  40  which are not protected by a photoresist mask, thereby defining a maximum resistor width as being equal to the width of conductors  42 A and  42 B. In step  120 , the conductor layer is patterned with photoresist to define the resistor&#39;s length dimension defined as the distance between conductors  42 A and  42 B. In step  122 , the critical length dimension of the active region of resistive layer  30  is controlled by a wet etch process. A wet etch process is used since it is desirable to produce conductors  42 A and  42 B having sloped walls, thereby defining the resistor length. Sloped walls of conductive layer  42 A enables step coverage of later fabricated layers such as a passivation layer that is applied in step  124 . 
     Conductors  42 A and  42 B serve as the conductive traces that deliver a signal to the active region of resistive layer  30  for firing a fluid droplet. Thus, the conductive trace or path for an electrical signal impulse that heats the active region of resistive layer  30  is from conductor  42 A through the active region of resistive layer  30  to conductor  42 B. 
     In step  124 , passivation layer  50  is then applied uniformly over the device. There are numerous passivation layer designs incorporating various compositions. In one conventional embodiment, two passivation layers, rather than a single passivation layer are applied. In the conventional printhead example of FIG. 1, the two passivation layers comprise a layer of silicon nitride followed by a layer of silicon carbide. More specifically, the silicon nitride layer is deposited on conductive layer  40  and resistive layer  30  and then a silicon carbide is preferably deposited. With this design, electromigration of the conductive layer can intrude into the passivation layer. 
     After passivation layer  50  is deposited, cavitation barrier  60  is applied. In the conventional example, the cavitation barrier comprises tantalum. A sputtering process, such as a physical vapor deposition (PVD) or other techniques known in the art deposits the tantalum. Fluid barrier layer  70  and orifice layer  80  are then applied to the structure, thereby defining fluid chamber  100 . In one embodiment, fluid barrier layer  70  is fabricated from a photosensitive polymer and orifice layer  80  is fabricated from plated metal or organic polymers. Fluid chamber  100  is shown as a substantially rectangular or square configuration in FIG.  1 . However, it is understood that fluid chamber  100  may include other geometric configurations without varying from the present invention. 
     Thin film printhead  190 , shown in FIG. 1, illustrates one example of a typical conventional printhead. However, printhead  190  requires both a wet and a dry etch process in order to define the functional length and width of the active region of resistive layer  30 , as well as to create the sloped walls of conductive layer  40  necessary for adequate step coverage of the later fabricated layers, such as the passivation  50  and cavitation  60  layers. 
     FIG. 3 is an enlarged, cross-sectional, partial view illustrating the layers for fluid-jet printhead  200  incorporating the present invention. The thicknesses of the individual thin film layers are not drawn to scale and are drawn for illustrative purposes only. FIG. 5 is an enlarged, plan view illustrating a fluid-jet printhead  200  incorporating the present invention. As shown in FIG. 4 in step  110 , insulative layer  20  is fabricated by being deposited through any known means, such as a plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), or a thermal oxide process onto substrate  10 . Preferably, insulator layer  20  is formed from tetraethylorthosilicate (TEOS) oxide of a thickness of 9000 Angstroms. In one alternative embodiment, insulative layer  20  is fabricated from silicon dioxide. In another embodiment, it is formed of silicon nitride. 
     In step  126 , a dielectric material  44  is deposited onto the insulator layer. This dielectric material  44  is then patterned in step  128  to create a resistor area, and then dry etched in step  130  to form thin-film layers which define the resistor&#39;s length dimension L. In one preferred embodiment, dielectric material  44  is formed from silicon nitride of approximately 5000 Angstroms of thickness. In an alternative embodiment dielectric material  44  is fabricated from silicon dioxide or silicon carbide. 
     In step  114 , conductive material layer  40  is then fabricated on top of insulative layer  20  and abuts the etched dielectric material  44  to form the resistor length L. In one embodiment, conductive material layer  40  is a layer formed through a physical vapor deposition (PVD) from aluminum and copper of approximately 5000 Angstrom of thickness. More specifically, in one embodiment, conductive material layer  40  includes up to approximately two percent copper in aluminum, preferably approximately 0.5 percent copper in aluminum. Utilizing a small percent of copper in aluminum limits electro-migration. In another preferred embodiment, conductive material layer  40  is formed from titanium, copper, or tungsten. 
     In step  132 , a photoimagable masking material such as photoresist is deposited on portions of conductive layer  40 , thereby exposing other portions of conductive layer  40 . 
     In step  134 , the top surface of conductive layer  40  is then planarized such that the top surface of dielectric material  44  is level with the top surface of conductive layer  40 . In one preferred embodiment, the top surface of conductive layer  40  is planarized through use of a resist-etch-back (REB) process. In another embodiment, the top surface of conductive layer  40  is planarized through use of a chemical/mechanical polish (CMP) process. 
     Next in step  112 , the resistive layer  30  is applied to uniformly cover the surface of the entire surface of substrate  10  and previously applied layers (wafer surface). Preferably, the resistive layer  30  is tungsten silicon nitride of a 1200 Angstrom thickness although tantalum aluminum, tantalum, or tantalum silicon nitride can also be used 
     In step  116 , a photoimagable masking material is deposited on the previously applied layers on the substrate surface. The photoimagable masking material is removed where the combined resistive layer  30  and conductive layer  60  are to be etched to define respectively the resistor width W and conductors  42 A and  42 B. 
     In step  136 , the exposed portions of resistive layer  30  and conductive layer  40  are removed through a dry etch process, several of which are known to those skilled in the art such as described in step  118  of FIG.  2 . This etching step defines and forms the resistor width. The photoresist mask is then removed, thereby exposing an exemplary substantially rectangular-shaped conductors  42 A and  42 B. The passivation  50 , cavitation  60 , barrier  70  and orifice  80  layers are then applied as described for the conventional printhead. 
     Conductors  42 A and  42 B provide an electrical connection/path between external circuitry and the formed resistive element. Therefore, conductors  42 A and  42 B transmit energy to the formed resistor to create heat capable of firing a fluid droplet positioned on a top surface of the formed resistive element in a direction perpendicular to the top surface of the resistive element. 
     As shown in FIG. 3B, conductors  42 A and  42 B define a resistor element  46  between conductors  42 A and  42 B. Resistive element  46  has a length L equal to the distance between conductors  42 A and  42 B. Resistive element  46  has a width W. However, it is understood that resistive element  46  may be fabricated having any one of a variety of configurations, shapes, or sizes, such as a thin trace or a wide trace of conductors  42 A and  42 B. The only requirement of the resistive element  46  is that it contacts conductors  42 A and  42 B to ensure a proper electrical connection. While the actual length L of resistive element  46  is equal to or greater than the distance between the outer most edges of conductors  42 A and  42 B, the active portion of resistive element  46  which conducts heat to a droplet of fluid positioned above resistive element  46  corresponds to the distance between the outermost edges of conductors  42 A and  42 B. 
     In FIG. 5, each orifice nozzle  90  is in fluid communication with respective fluid chambers  100  (shown enlarged in FIG. 2) defined in printhead  200 . Each fluid chamber  100  is constructed in orifice structure  82  adjacent to thin film structure  32  that preferably includes a transistor coupled to the resistive component. The resistive component is selectively driven (heated) with sufficient electrical current to instantly vaporize some of the fluid in fluid chamber  100 , thereby forcing a fluid droplet through nozzle  90 . 
     Exemplary fluid-jet print cartridge  220  is illustrated in FIG.  6 . The fluid-jet printhead device of the present invention is a portion of fluid-jet print cartridge  220 . Fluid-jet print cartridge  220  includes body  218 , flexible circuit  212  having circuit pads  214 , and printhead  200  having orifice nozzles  90 . Fluid-jet print cartridge  220  has fluid-jet printhead  200  in fluidic connection to fluid in body  218  using a fluid delivery system  216 , shown as a sponge to provide backpressure using capillary action in the sponge (preferably closed-cell foam) to prevent leakage of fluid though orifice nozzles  90  when not in use. While flexible circuit  212  is shown in FIG. 6, it is understood that other electrical circuits known in the art may be utilized in place of flexible circuit  212  without deviating from the present invention. It is only necessary that electrical contacts  214  be in electrical connection with the circuitry of fluid-jet print cartridge  220 . Printhead  200  having orifice nozzles  90  is attached to the body  218  and controlled for ejection of fluid droplets, typically by a printer but other recording devices such as plotters, and fax machines, too name a couple, can be used. Thermal fluid-jet print cartridge  220  includes orifice nozzles  90  through which fluid is expelled in a controlled pattern during printing. Conductive drivelines for each resistor component are carried upon flexible circuit  212  mounted to the exterior of print cartridge body  218 . Circuit contact pads  214  (shown enlarged in FIG. 6 for illustration) at the ends of the resistor drive lines engage similar pads carried on a matching circuit attached to a printer (not shown). A signal for firing the transistor is generated by a microprocessor and associated drivers on the printer that apply the signal to the drivelines. 
     FIG. 7 is an exemplary recording device, a printer  240 , which uses the exemplary fluid-jet print cartridge  220  of FIG.  6 . The fluid-jet print cartridge  220  is placed in a carriage mechanism  254  to transport the fluid-jet print cartridge  220  across a first direction of medium  256 . A medium feed mechanism  252  transports the medium  256  in a second direction across fluid-jet printhead  220 . Medium feed mechanism  252  and carriage mechanism  254  form a transport mechanism to move the fluid-jet print cartridge  220  across the first and second directions of medium  256 . An optional medium tray  250  is used to hold multiple sets of medium  256 . After the medium is recorded by fluid-jet print cartridge  220  using fluid-jet printhead  200  to eject fluid onto medium  256 , the medium  256  is optionally placed on media tray  258 . 
     In operation, a droplet of fluid is positioned within fluid chamber  100 . Electrical current is supplied to resistive element  46  via conductors  42 A and  42 B such that resistive element  46  rapidly generates energy in the form of heat. The heat from resistive element  46  is transferred to a droplet of fluid within fluid chamber  100  until the droplet of fluid is “fired” through nozzle  90 . This process is repeated several times in order to produce a desired result. During this process, a single dye may be used, producing a single color design, or multiple dyes may be used, producing a multicolor design. 
     The present invention provides numerous advantages over the conventional printhead. First, the resistor length of the present invention is defined by the placement of dielectric material  44  that is fabricated during a combined photo process and dry etching process. The accuracy of the present process is considerably more controllable than conventional wet etch processes. More particularly, the present process is in the range of 10-25 times more controllable than a conventional process. With the current generation of low drop weight, high-resolution printheads, resistor lengths have decreased from approximately 35 micrometers to less than approximately 10 micrometers. Thus, resistors size variations can significantly affect the performance of a printhead. Resistor size variations translate into drop weight and turn on energy variations across the resistor on a printhead. Thus, the improved length control of the resistive material layer yields a more consistent resistor size and resistance, which thereby improves the consistency in the drop weight of a fluid droplet and the turn on energy necessary to fire a fluid droplet. 
     Second, the resistor structure of the present invention includes a completely flat top surface and does not have the step contour associated with conventional fabrication designs. A flat structure (smooth planar surface) provides consistent bubble nucleation, better scavenging of the fluid chamber, and a flatter topology, thereby improving the adhesion and lamination of the barrier structure to the thin film. Third, due to the flat topology of the present structure, the barrier structure is allowed to cover the edge of the resistor. By introducing heat into the floor of the entire fluid chamber, fluid droplet ejection efficiency is improved. 
     Third, because there is no wet slope etch process used in the fabrication of the invention, slope roughness, and conductive layer residue on the resistive layer are no longer issues. 
     Fourth, due to the encapsulation and cladding of conductive layer  40  by resistive layer  30 , electro-migration of the conductive layer  40  is minimized into the passivation layer. 
     Further, by attaching the printhead  200  to the fluid cartridge  220 , the combination forms a convenient module that can be packaged for sale. 
     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the chemical, mechanical, electromechanical, electrical, and computer arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.