Abstract:
A fluid ejector having an inner surface, an outer surface, and an orifice that allows fluid in contact with the inner surface to be ejected. The fluid ejector has a non-wetting monolayer covering at least a portion of the outer surface of the fluid ejector and surrounding an orifice in the fluid ejector. Fabrication of the non-wetting monolayer can include removing a non-wetting monolayer from a second region of a fluid ejector while leaving the non-wetting monolayer on a first region surrounding an orifice in the fluid ejector, or protecting a second region of a fluid ejector from having a non-wetting monolayer formed thereon, wherein the second region does not include a first region surrounding the orifice in the fluid ejector.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/696,035, filed Jul. 1, 2005, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     This invention relates to coatings on fluid ejectors.  
         [0003]     A fluid ejector (e.g., an ink-jet printhead) typically has an interior surface, an orifice through which fluid is ejected, and an exterior surface. When fluid is ejected from the orifice, the fluid can accumulate on the exterior surface of the fluid ejector. When fluid accumulates on the exterior surface adjacent to the orifice, further fluid ejected from the orifice can be diverted from an intended path of travel or blocked entirely by interaction with the accumulated fluid (e.g., due to surface tension). Some materials from which fluid ejectors are fabricated (e.g., silicon) are hydrophilic, which typically exacerbates the problem of accumulation when fluids are ejected.  
         [0004]     Non-wetting coatings such as Teflon® and fluorocarbon polymers can be used to coat surfaces. However, Teflon® and fluorocarbon polymers typically are soft and are not durable coatings. These coatings also can be expensive and difficult to pattern.  
       SUMMARY  
       [0005]     In one aspect, the invention is directed to a fluid ejector having an inner surface, an outer surface, and an orifice that allows fluid in contact with the inner surface to be ejected. The fluid ejector has a non-wetting monolayer covering at least a portion of an outer surface of a fluid ejector and surrounding an orifice in the fluid ejector.  
         [0006]     Implementations of the invention may include one or more of the following features. The non-wetting monolayer may include molecules which include at least one atom of each of carbon and fluorine. The non-wetting monolayer may not cover any portion of an inner surface of the fluid ejector.  
         [0007]     In another aspect, the invention features a method for forming a non-wetting monolayer on a selected portion a fluid ejector. A non-wetting monolayer is removed from a second region of a fluid ejector while leaving the non-wetting monolayer on a first region surrounding an orifice in the fluid ejector.  
         [0008]     In another aspect, a non-wetting monolayer is formed on a first region and a second region of a fluid ejector, where the first region surrounds an orifice in the fluid ejector. The non-wetting monolayer is removed from the second region while leaving the non-wetting monolayer on the first region.  
         [0009]     Particular implementations may include one or more of the following features. The first region may be protected prior to removing the non-wetting monolayer from the second region. Protecting may include applying at least one of tape, photoresist, or wax to the first region prior to removing the non-wetting monolayer from the second region and removing the at least one of tape, photoresist, or wax after removing the non-wetting monolayer. Removing the non-wetting monolayer from the second region may include at least one of applying a plasma to the second region, laser ablating the second region, or applying ultraviolet light to the second region. The first region may include an outer surface of the fluid ejector and the second region may include an inner surface of the fluid ejector.  
         [0010]     In yet another aspect, the invention features a method for forming a non-wetting monolayer on a selected portion of a fluid ejector. A second region of a fluid ejector is protected and a non-wetting monolayer is formed on a first region of the fluid ejector, where the first region surrounds an orifice in the fluid ejector.  
         [0011]     In yet another aspect, a second region of a fluid ejector is protected from having a non-wetting monolayer formed thereon, wherein the second region does not include a first region surrounding an orifice in the fluid ejector.  
         [0012]     Particular implementations may include one or more of the following features. The second region may include an interior of the orifice. Protecting the second region may include bonding a silicon substrate to the fluid ejector. Protecting the second region may include applying at least one of tape, photoresist, or wax to the fluid ejector prior to forming the non-wetting monolayer and removing the at least one of tape, photoresist, or wax after forming the non-wetting monolayer.  
         [0013]     In still another aspect, the invention features a method for forming a non-wetting monolayer on a selected portion of a fluid ejector. An attachment region is formed on a fluid ejector substrate, where the attachment region includes a first material and the fluid ejector substrate includes a second material. A non-wetting monolayer is formed on the attachment region from a selective precursor, where the selective precursor attaches to the first material and substantially does not attach to the second material.  
         [0014]     Particular implementations may include one or more of the following features. The attachment region may surround an orifice in the fluid ejector substrate. The orifice may be formed in the fluid ejector substrate prior to forming the non-wetting monolayer. The selective precursor may include a thiol termination, the first material may include gold, and the second material may include silicon. Forming an attachment region may include sputtering the first material onto the fluid ejector substrate and patterning the first material.  
         [0015]     In still another aspect, the invention features a fluid ejector having an inner surface, an outer surface, and an orifice that allows fluid in contact with the inner surface to be ejected. An attachment region covers at least a portion of an outer surface of a fluid ejector and surrounds an orifice in the fluid ejector, and a non-wetting monolayer covers substantially the entire attachment region and covers substantially none of the outer surface of the fluid ejector apart from the attachment region.  
         [0016]     Particular implementations may include one or more of the following features. The attachment region may include a first material that is substantially not present in the outer surface of the fluid ejector. A precursor of the non-wetting monolayer may include a thiol termination, the attachment region may include gold atoms, and the outer surface of the fluid ejector may include silicon atoms. The attachment region need not cover any portion of an inner surface of the fluid ejector.  
         [0017]     The invention can be implemented to realize one or more of the following advantages.  
         [0018]     A non-wetting monolayer can reduce the accumulation of fluid on the outer surface of the fluid ejector. The monolayer can be durable and can be insoluble in most solvents, allowing multiple types of inks to be used with the fluid ejector. Coating material can be saved because of the thinness of the monolayer. Wet processes are not required after etching the fluid ejector, and therefore residue associated with a wet process can be avoided.  
         [0019]     If the non-wetting monolayer is removed post-deposition, the coating can be deposited without first protecting or masking regions of a substrate. If the underlying layer is masked before deposition of the coating, then processing steps to remove undesired regions of a non-wetting monolayer can be eliminated. A non-wetting monolayer can be deposited easily and accurately in desired regions on a substrate.  
         [0020]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description, drawings, and claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0021]      FIGS. 1A-1B  are cross-sectional views of implementations of an uncoated fluid ejector.  
         [0022]      FIG. 1C  is a cross-sectional view of an implementation of the fluid ejector from  FIG. 1B  with a non-wetting coating on an outer surface.  
         [0023]      FIG. 2  is a bottom view of the fluid ejector from  FIG. 1C .  
         [0024]      FIG. 3  is a cross-sectional view of a second implementation of a fluid ejector with a non-wetting coating on an outer surface.  
         [0025]      FIG. 4  is a cross-sectional view of a nozzle layer coated with a non-wetting coating.  
         [0026]      FIG. 5  is a cross-sectional view of a nozzle layer with protective tape on an outer surface.  
         [0027]      FIG. 6  is a cross-sectional view of a nozzle layer.  
         [0028]      FIGS. 7A-7D  illustrate process steps in one implementation of a method for forming a non-wetting coating on a nozzle layer.  
         [0029]      FIGS. 8A-8C  illustrate process steps in a second implementation of a method for forming a non-wetting coating on a nozzle layer.  
         [0030]      FIGS. 9A-9B  illustrate process steps in a third implementation of a method for forming a non-wetting coating on a nozzle layer. 
     
    
       [0031]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0032]      FIG. 1A  is a cross-sectional view of an uncoated fluid ejector  100  (e.g., an ink-jet printhead nozzle), which can be constructed as described in U.S. patent application Ser. No. 10/913,571, the contents of which are hereby incorporated by reference. The uncoated fluid ejector  100  includes a flow-path module  110  and a nozzle layer  120 , both of which can be made of silicon (e.g., single crystal silicon). In one implementation, the uncoated fluid ejector  100  is a single unit, and the flow-path module  110  and the nozzle layer  120  are not separate pieces. The uncoated fluid ejector  100  includes an inner surface  150  and an outer surface  160 . A membrane layer  182  is positioned above a pumping chamber  135 . An actuator  172  pressurizes fluid (e.g., an ink, for example, a water-based ink) in the pumping chamber  135  and the fluid flows through a descender  130  and is ejected through an orifice  140  in the nozzle layer  120 . The actuator  172  can include a piezoelectric layer  176 , a lower electrode  178  (e.g., a ground electrode), and an upper electrode  174  (e.g., a drive electrode). The membrane layer  182  and the actuator  172  are not shown in the following figures, but can be present.  
         [0033]     As shown in  FIG. 1B , the uncoated fluid ejector  100  optionally can include an inorganic layer  165  formed on the nozzle layer  120 , in which case the outer surface  160  of the uncoated ejector can be considered the outer surface of the inorganic layer  165 . The inorganic layer  165  is a layer of a material, such as SiO 2 , that promotes adhesion of a non-wetting coating. In one implementation, the inorganic seed layer  165  is a native oxide layer (such a native oxide typically has a thickness of 1 to 3 nm). In another implementation, the inorganic layer is a deposited seed layer. For example, an inorganic seed layer  165  of SiO 2  can be formed on the nozzle layer  120 , for example, by introducing SiCl 4  and water vapor into a chemical vapor deposition (CVD) reactor containing the uncoated fluid ejector  100 . A valve between the CVD chamber and a vacuum pump is closed after pumping down the chamber, and vapors of SiCl 4  and H 2 O are introduced into the chamber. The partial pressure of the SiCl 4  can be between 0.05 and 40 Torr (e.g., 0.1 to 5 Torr), and the partial pressure of the H 2 O can be between 0.05 and 20 Torr (e.g., 0.2 to 10 Torr). The deposition temperature is typically between room temperature and 100 degrees centigrade. Alternatively, the inorganic seed layer  165  can be sputtered onto the nozzle layer  120 . The surface to be coated by the inorganic seed layer  165  can be cleaned (e.g., by applying an oxygen plasma) before forming the inorganic seed layer  165 .  
         [0034]     The thickness of the seed layer can be, for example, 5 nm to 100 nm. For some fluids to be ejected, the performance can be affected by the thickness of the inorganic layer. For example, for some “difficult” fluids, a thicker layer, e.g., 30 nm or more, such as 40 nm or more, for example 50 nm or more, will provide improved performance. Such “difficult” fluids can include, for example, PEDOT and Light Emitting Polymer.  
         [0035]     One implementation of a fabrication process alternates between applying layers of the seed material and forming layers the non-wetting coating. In this case, the individual seed layers can be, for example, 5 to 20 nm thick. The exposed surfaces of the device can be cleaned (e.g., by applying an oxygen plasma) before forming the layer of seed material. Hypothetically, this fabrication process could result in a layer stack with alternating layers of seed material and non-wetting coating. However, without being limited to any particular theory, under some conditions the cleaning process might remove the immediately previously deposited non-wetting coating, such that the resulting device has a single continuous thick seed layer (rather than alternating layers of oxide and non-wetting coating).  
         [0036]     Another implementation of the fabrication process simply deposits the entire seed layer in a single continuous step to provide a unitary, monolithic seed layer.  
         [0037]     Referring to  FIGS. 1B and 1C , a non-wetting coating  170 , such as a self-assembled monolayer that includes a single molecular layer, is applied to the outer surface  160  of the uncoated fluid ejector  100  to form a coated fluid ejector  105 . The non-wetting coating  170  can be applied using vapor deposition, rather than being brushed, rolled, or spun on. The outer surface of the fluid ejector can be cleaned (e.g., by applying an oxygen plasma) before applying the non-wetting coating  170 . In one implementation, the inner surface  150 , the descender  130 , and the inner surface of orifice  140  are not coated in the final fluid ejector product. The non-wetting coating  170  can be deposited on the outer surface  160  of the uncoated fluid ejector  100 , for example, by introducing a precursor and water vapor into the CVD reactor at a low pressure. The partial pressure of the precursor can be between 0.05 and 1 Torr (e.g., 0.1 to 0.5 Torr), and the partial pressure of the H 2 O can be between 0.05 and 20 Torr (e.g., 0.1 to 2 Torr). The deposition temperature can be between room temperature and 100 degrees centigrade. The coating process and the formation of the inorganic seed layer  165  can be performed, by way of example, using a Molecular Vapor Deposition (MVD)™ machine from Applied MicroStructures, Inc.  
         [0038]     Suitable precursors for the non-wetting coating  170  include, by way of example, precursors containing molecules that include a non-wetting termination and a termination that can attach to a surface of the fluid ejector. For example, precursor molecules that include a carbon chain terminated at one end with a —CF 3  group and at a second end with an —SiCl 3  group can be used. Specific examples of suitable precursors that attach to silicon surfaces include tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS). Without being limited by any particular theory, it is believed that when a precursor (such as FOTS or FDTS) whose molecules include an —SiCl 3  termination are introduced into the CVD reactor with water vapor, silicon atoms from the —SiCl 3  groups bond with oxygen atoms from —OH groups on the inorganic seed layer  165  or on a native oxide of the nozzle layer  120 .  
         [0039]     In another implementation, the coated fluid ejector  105  does not include the inorganic seed layer  165 , and the non-wetting coating  170  is applied directly to the nozzle layer  120 . In this case, the outer surface  160  of the uncoated ejector can be considered the outer surface of the nozzle layer  120 .  
         [0040]      FIG. 2  shows a bottom view of the coated fluid ejector  105 . The orifice  140  is shown as a rectangular opening, though other opening geometries may be suitable, such as a circle or a polygon with five or more sides.  
         [0041]     As shown in  FIG. 3 , multiple layers of a non-wetting coating  370  can be applied to the outer surface  360  of a fluid ejector  300 . The multiple layers can be applied by repeatedly performing the deposition steps described in the context of  FIG. 1B . In one implementation, fluorocarbon chains of a non-wetting coating are cut to expose silicon atoms or —CH 2  groups before depositing a layer of the non-wetting coating  370 . Fluorocarbon chains can be cut (etched) by an oxygen plasma treatment. An inductively coupled plasma (ICP) source is used to generate active oxygen radicals, and the radicals etch the fluorocarbon chains of the non-wetting coating. The oxygen can be introduced into a CVD reactor, for example, at a pressure of 0.4 Torr and a with a flow rate of 260 sccm. RF power from the ICP source can be applied at 200 W for 30 seconds.  
         [0042]     Referring again to  FIGS. 1B and 1C , the non-wetting coating  170  can be deposited on the outer surface  160  of the uncoated fluid ejector before or after the flow-path module  110  and the nozzle layer  120  are joined and before or after the orifice  140  is formed in the nozzle layer  120 . When the orifice  140  is formed after depositing the non-wetting coating  170 , the non-wetting coating  170  typically should be masked while the orifice  140  is being formed to prevent damage to the non-wetting coating  170 . If the non-wetting coating  170  is applied after the orifice  140  is formed, non-wetting coating that is deposited on the inner surface  150  of the coated fluid ejector  105  can be removed while leaving the non-wetting coating deposited on the outer surface  160 . The orifice  140  can also be masked during the application of non-wetting coating  170  so that substantially no non-wetting coating is deposited on the inner surface  150 .  
         [0043]     It can be advantageous to apply the non-wetting coating  170  after forming one or more orifices (e.g., orifice  140 ) in the nozzle layer  120 .  FIG. 4  shows a nozzle layer  420  to which a non-wetting coating  470  (e.g., a non-wetting monolayer) has been applied before the nozzle layer  420  was joined to a flow-path module. The non-wetting coating  470  typically coats all exposed surfaces of the nozzle layer  420  when applied using a CVD process. The non-wetting coating  470  coats both an inner surface  450  and an outer surface  460  of the nozzle layer  420 . An inorganic layer (e.g., inorganic seed layer  165  in  FIG. 1B  or native oxide) can be present on nozzle layer  420 , but is not shown in  FIG. 4  for the sake of clarity.  
         [0044]     It can be advantageous for selected regions of the nozzle layer  420  not to be covered with a non-wetting coating. Therefore, non-wetting coating can be removed from the selected regions. For example, the non-wetting coating  470  can be removed from the inner surface  450  of the nozzle layer  420 . As shown in  FIG. 5 , a masking layer  580  (e.g., tape) can be applied over the non-wetting coating  470  on the outer surface  460  of nozzle layer  420 , and the masked nozzle layer can be placed on a solid surface, such as a silicon substrate  590 . An etchant (e.g., oxygen plasma) can be applied to the inner surface  450  of the nozzle layer  420  to remove the portion of the non-wetting coating  470  on the inner surface  450 . As shown in  FIG. 6 , the silicon substrate  590  and the masking layer  580  can be removed after applying the etchant, leaving the nozzle layer  420  with the non-wetting coating  470  only on the outer surface  460 .  
         [0045]     Alternatively, light (e.g., ultraviolet (UV), deep UV, or green light from a laser) can be used to remove non-wetting coating from selected regions. For example, referring again to  FIG. 4 , light can be used to irradiate the inner surface  450  of the nozzle layer  420  to remove the portion of the non-wetting coating  470  on the inner surface  450 . The light can be supplied, for example, by laser such as an excimer laser (e.g., an ArF or KrF excimer laser). The nozzle layer  420  can be tilted relative to the source of the light so that the walls of orifice  440  are irradiated.  
         [0046]     After removing the non-wetting coating  470  from the inner surface  450 , the nozzle layer  420  can be attached to a flow-path module (e.g., flow-path module  110  in  FIG. 1A ). The methods discussed here can also be used when the non-wetting coating  470  is applied after the nozzle layer  420  is attached to the flow-path module. For example, an etchant can be applied to the inner surface  450  through a descender (e.g., descender  130  in  FIG. 1A ) in the flow-path module. One method of applying an etchant through the descender is to connect an ozone generator to an inlet port of the assembled fluid ejector and supply ozone (e.g., at a 2% or greater concentration in oxygen gas or in a mixture of oxygen and nitrogen) to the descender and the inner surface  450  through the inlet port. The outer surface  460  can be protected with tape while the ozone is supplied to the descender and the inner surface  450 . In addition, the ozone can be heated (e.g., to above 80 degrees centigrade, for example, to 120 degrees centigrade) before being injected into descender. In an alternative implementation, oxygen plasma can be used instead of ozone.  
         [0047]     As an alternative to removing non-wetting coating from selected regions, the non-wetting coating can be prevented from forming in the selected regions. For example, the non-wetting coating  470  can be prevented from forming on the inner surface  450  of the nozzle layer  420  during a deposition step. Another alternative is to allow the non-wetting coating to form in the selected regions and deposit a layer of material (e.g., SiO 2 ) on top of the non-wetting coating to make the selected region hydrophilic.  
         [0048]     As shown in  FIG. 7A , a protective structure  785  can be formed for a region (e.g., orifice  740 ) on a nozzle layer  720 . The protective structure  785  can be formed on a silicon substrate  795 , for example, by forming a region of silicon oxide  787  over the protective structure  785  and etching the silicon substrate  795  using inductively-coupled plasma to form raised regions.  
         [0049]     As shown in  FIG. 7B , the nozzle layer  720  and the protective silicon substrate  795  can be placed in contact or bonded, thereby masking the region, in this case the orifice  740 , with the protective structure  785 . As shown in  FIG. 7C , vapor deposition can be used to apply a non-wetting coating  770  to the areas on the outer surface  760  of the nozzle layer  720  that are not masked by the protective structure  785 .  FIG. 7D  shows the nozzle layer  720  after the silicon substrate  795  has been removed, leaving non-wetting coating  770  on the outer surface  760  of nozzle layer  720  in the regions that were not covered by the protective structure  785 .  
         [0050]     Certain precursors for non-wetting coatings selectively attach to certain materials, while substantially not attaching to other materials. For example, a thiol-terminated precursor attaches to gold, but substantially does not attach to silicon. A precursor with a selective termination and a non-wetting termination can be used to control the regions in which a non-wetting coating forms on a substrate (e.g., silicon). For example, as shown in  FIG. 8A , an oxide layer  810  optionally is patterned on a silicon substrate  820 . In  FIG. 8B , a material (e.g., gold) to which a selective precursor attaches is sputtered onto the silicon substrate  820  or onto the oxide layer  810 , if present, and is patterned (e.g., using photoresist) into an attachment region  830 .  FIG. 8C  shows the silicon substrate  820  after an orifice  840  has been etched (e.g., using inductively-coupled plasma) and a non-wetting coating  870  has been formed using a selective precursor (e.g., a thiol-terminated precursor) that attaches to the attachment region  830 , but not to the oxide layer  810  or the silicon substrate  820 .  
         [0051]     Alternatively, as shown in  FIG. 9A , the material to which the selective precursor attaches is sputtered directly onto a silicon substrate  920  and is patterned into an attachment region  930 .  FIG. 9B  shows the silicon substrate  920  after an orifice  940  has been etched and a non-wetting coating  970  has been formed using the selective precursor.  
         [0052]     Various methods can be used to mask regions of a nozzle layer where a non-wetting coating is not desired before depositing the non-wetting coating. Masking can also be used to protect regions of a non-wetting coating when portions of the non-wetting coating are removed after deposition. For example, tape, wax, or photoresist can be used as a mask to prevent the non-wetting coating from being deposited in selected regions of the nozzle layer. The tape, wax, or photoresist can be removed after the non-wetting coating has been deposited on the nozzle layer. Likewise, tape, wax, or photoresist can be applied over selected regions of a non-wetting coating to prevent the removal of the non-wetting coating in those regions during processing steps that occur after the deposition of the non-wetting coating.  
         [0053]     A selected region of a non-wetting coating can be removed without removing the entire non-wetting coating by laser ablation using a hard mask or using a servo-controlled laser. A selected region of a non-wetting coating can also be removed by etching the non-wetting coating with plasma while protecting, using a mask (e.g., photoresist) for example, the regions of the non-wetting coating that are not to be removed. UV light can also be used to remove selected regions of a non-wetting coating, and regions not to be removed can be protected with a mask (e.g., a metal contact mask).  
         [0054]     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, method steps may be performed in a different order and still produce desirable results. Accordingly, other embodiments are within the scope of the following claims.