Abstract:
A method for the electrodeposition of an electrode including a metallic electrode material ( 40 ) on a dielectric substrate ( 10 ), including the following steps: depositing an electrically conductive polymer layer ( 20 ); masking the electrically conductive polymer layer ( 20 ) using a mask; electrodepositing the metallic electrode material ( 40 ) on the electrically conductive polymer layer ( 20 ); removing the mask; and removing or deactivating the excess conductive polymer layer ( 20 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of co-pending U.S. Provisional Patent Application No. 61/413,493, filed on Nov. 15, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to a method for the electrodeposition of an electrode on a dielectric substrate. 
       BACKGROUND 
       [0003]    Various methods for depositing metallic electrodes on a substrate are known. According to a first method, to prevent diffusion between an electrode metal and the substrate, a barrier layer (e.g., Ni) and then the electrode metal (e.g., Au) are plated onto a base metal, such as, for example, Cu. The electrode is therefore comprised not merely of the electrode metal. Since a barrier layer is not perfect, an alloy may form and the electrode metal may therefore become contaminated. In addition, corrosion problems can occur in the barrier layer if it contains inhomogeneities. 
         [0004]    According to another method, the electrode metal (e.g., Au) is selectively deposited onto a metallic foil (e.g., a Cu foil), which is disposed on a carrier. After the electrode metal has been deposited, the foil is separated from the carrier and is laminated into a base material using the electrode-metal side. Next, the foil is removed in an etching step and only the electrode metal remains on the base material. When metals are used that alloy easily with one another, such as, for example, Cu and Au, these metals can inter-diffuse during deposition and the subsequent processes. The impurities that are created as a result can cause problems when the electrode metal is used for electrodes that are implanted in an animal or human body. 
         [0005]    Furthermore, it is known to sputter a carrier foil with the electrode metal, to apply and pattern a photoresist, and to plate the electrode metal thereon via electrodeposition. The photoresist is removed and a gentle etching step is used to etch away the layer that was applied by sputtering. To ensure good adhesion of the electrode metal on the substrate, another metal layer such as, for example, Cr is usually required to promote adhesion. In addition to the process steps being elaborate and numerous, such an adhesion-promoting layer can negatively influence the biocompatibility of the electrode metal. 
         [0006]    The problem addressed by the invention is that of creating a method for depositing an electrode on a dielectric substrate, in the case of which the diffusion of foreign material into the electrode is at least reduced. 
       SUMMARY 
       [0007]    The problem is solved according to the invention by the features of the independent claim(s). Favorable embodiments and advantages of the invention result from the further dependent claims and the description. 
         [0008]    A method for the electrodeposition of an electrode including a metallic electrode material on a non-conductive dielectric substrate is provided, comprising the following steps:
       Depositing an electrically conductive polymer layer on the substrate;   Masking the electrically conductive polymer layer using a mask;   Electrodepositing of the metallic electrode material on the electrically conductive polymer layer;   Removing the mask; and   Removing or deactivating the excess conductive polymer layer.       
 
         [0014]    The excess conductive polymer layer can be deactivated (i.e., minimize the conductivity), e.g., by reduction or oxidation of the conductive polymer. As an alternative, the conductive polymer can also be removed, e.g., by using selective chemical etching or plasma etching. 
         [0015]    Advantageously, contamination of the electrode with another metal can be prevented since the electrode material is applied additively to the substrate and is not deposited onto the substrate using a (metallic) intermediate carrier. Electrodes comprised of highly pure metals can be created on dielectric substrates, in particular on polymers. For example, it is possible to deposit pure gold on a dielectric, i.e., non-conductive, organic substrate (e.g., polyimide, LCP, etc.), without it becoming contaminated by other metals. Once deposition is complete, only the gold remains, as the electrode, on the surface of the substrate. It is therefore possible to create electrodes for components that are designed to be implanted in a human or animal body, and that have biocompatible properties and that are not expected to interfere with the function or the implantation site due to unwanted metallic components in the electrodes. 
         [0016]    There is no risk whatsoever of uncontrolled alloying of the metallic electrode material with another metal. The metallic electrode material is applied to the substrate only in an additive manner. Less chemistry and material are therefore required. 
         [0017]    According to an advantageous development, current can flow primarily across the electrically conductive polymer layer during electrodeposition. To perform electrodeposition, the substrate is coated only in conductive regions, thereby ensuring that the metallic electrode material is deposited only on exposed, i.e., resist-free, regions of the electrically conductive polymer layer. Electrodeposition basically makes it possible to deposit a metal having very high purity. A highly pure electrode can be deposited on a dielectric substrate. The electrically conductive polymer layer makes it possible to avoid using metallic leads on the substrate, thereby eliminating the need to apply foreign metals in the vicinity of the metallic electrode material to close the electrical circuit during electrodeposition. 
         [0018]    Furthermore, as an alternative, a method for the electrodeposition of an electrode including a metallic electrode material on a dielectric substrate is provided, comprising the following steps:
       Applying a metallic conductive layer onto the substrate;   Patterning the metallic conductive layer to create exposed regions on the substrate;   Depositing an electrically conductive polymer layer at least in the exposed regions;   Masking the electrically conductive polymer layer in the exposed regions and/or mask the remaining metal layer using a mask;   Electrodepositing of the metallic electrode material on the electrically conductive polymer layer;   Removing the mask; and   Removing or deactivating the excess conductive polymer layer.       
 
         [0026]    When depositing the electrically conductive polymer layer at least in the exposed regions, then, depending on the process used to deposit the conductive polymer, the deposition can take place selectively on the exposed polymer or on the entire surface, including the metallic electrode material. Favorable deposition processes are, e.g., selectively from an aqueous solution only on the polymer using Enthone Envision HDI (formerly DMS-E process) from Enthone, Inc., in West Haven, Conn., USA, selectively from an aqueous solution only on the polymer using Atotech Seleo CP Plus from Atotech Deutschland GmbH in Berlin, or a non-selective deposition from the gas phase using plasma coating. 
         [0027]    The excess conductive polymer layer can be deactivated (i.e., minimize the conductivity), e.g., by reduction or oxidation of the conductive polymer. As an alternative, the conductive polymer can also be removed, e.g., using selective chemical etching or plasma etching. 
         [0028]    Favorable materials for electrically conductive polymers are, e.g., polyaniline, polypyrrole, polythiophene, and the like. 
         [0029]    The polymer layer should be as thin as possible to ensure easy removal, but should be so thick that the electrical conductivity suffices for metal deposition. A reasonable thickness can be, e.g., below 10 μm at the most. Exact limits can vary depending on the actual system and are identified easily using tests. A thickness of the noble metal layer is defined by the necessary stability of the conductor and the current intensity or resistance that is acceptable for the application. The advantage of such a deposition compared to direct noble metal deposition from the gas phase is that greater thicknesses of noble metal can be deposited, which is useful. The maximum thickness of the conductor is limited in practical application only by the thickness of the resist. Favorable conductor thicknesses can be, e.g., in a range of 0.5 μm to 100 μm. 
         [0030]    Advantageously, according to the alternative variant, contamination of the electrode with another metal can be prevented since the electrode material is applied additively to the substrate and is not deposited onto the substrate using a (metallic) intermediate carrier. Electrodes comprised of highly pure metals can be created on dielectric substrates, in particular polymers. For example, it is possible to deposit pure gold on a dielectric, i.e., non-conductive, organic substrate (e.g., polyimide, LCP, etc.), without it becoming contaminated by other metals. Once deposition is complete, only the gold remains, as the electrode, on the surface of the substrate. It is therefore possible to create electrodes for components that are designed to be implanted in a human or animal body, and that have biocompatible properties and that are not expected to cause interference due to unwanted metallic components in the electrodes. 
         [0031]    There is no risk whatsoever of uncontrolled alloying of the metallic electrode material with another metal. The metallic electrode material is applied to the substrate only in an additive manner. Less chemistry and material are therefore required. 
         [0032]    According to an advantageous development of the alternative variant, during electrodeposition through a portion of the mask, the metallic conductive layer can be separated from the region in which the metallic electrode material is to be deposited, wherein the metallic conductive layer tightly encloses the region. A portion of the current can therefore flow across the relatively low ohmic metallic conductive layer during electrodeposition. 
         [0033]    According to an advantageous development of the alternative variant, current can flow primarily across the conductive layer during electrodeposition. Advantageously, this takes place into the vicinity of the electrode to be electrodeposited. The electrically conductive polymer layer can carry the current flow in the region between the conductive layer and the electrode to be deposited. The metallic conductive layer does not come in contact with the metallic electrode material. The metallic conductive layer has lower resistance than does the electrically conductive polymer layer, thereby resulting in better current distribution and therefore better distribution of the layer thickness of the electrode metal. 
         [0034]    During electrodeposition, the substrate is coated only in conductive regions, thereby ensuring that the metallic electrode material is deposited only on the electrically conductive polymer layer since the conductive layer is advantageously covered with photoresist during electrodeposition. The electrically conductive polymer layer that exists in the region in which the metallic electrode material is to be deposited makes it possible to avoid using metallic leads in this region, thereby preventing foreign metals from coming in contact with the metallic electrode material to close the electrical circuit during electrodeposition. 
         [0035]    According to an advantageous development of the alternative variant, the conductive layer can be coated with a diffusion barrier layer before the electrodeposition of the metallic electrode material. This further reduces the risk of contamination of the metallic electrode material with the material of the metallic conductive layer. 
         [0036]    According to an advantageous development of the alternative variants, nickel and/or palladium can be used as the diffusion barrier layer. These materials are characterized, e.g., by an effective inhibition of diffusion processes. 
         [0037]    Advantageously, a photoresist mask can be used to mask the electrically conductive polymer layer in both variants of the proposed method. A photoresist is easily applied, patterned, and removed. The surface of the deposited electrode does not come in contact with the photoresist during electrodeposition, and does so only briefly in the solvent when the photoresist is removed, or practically not at all when a physical etching method or oxidation method is used. 
         [0038]    Advantageously, for both variants of the proposed method, the electrically conductive polymer layer outside of the deposited metallic electrode material can be removed, or the electrical conductivity of the electrically conductive polymer layer outside of the deposited metallic electrode material can be reduced. 
         [0039]    A noble metal or an alloy of noble metals (e.g., platinum/iridium) can be used as the metallic electrode material for both variants of the proposed method. For example, gold or platinum are advantageously used as the metallic electrode material. A suitable organic substrate is a polymer that is well suited for use for components having electrodes that are implantable in the human and/or animal body, in particular PI (PI=polyimide) or LCP (LCP=liquid crystal polymer). The methods can be operated, in all, at low temperatures, e.g., room temperature, thereby protecting the organic substrate from the effect of excessive temperatures. 
         [0040]    Various other objects, aspects and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0041]    The invention is explained in the following in greater detail with reference to embodiments that are depicted in drawings. They show, in a diagrammatic representation: 
           [0042]      FIGS. 1A-1F  show various method steps in the galvanic coating of a dielectric substrate with a metallic electrode material; 
           [0043]      FIGS. 2A-2H  show various method steps in the galvanic coating of a dielectric substrate with a metallic electrode material, using a metallic conductive layer; and 
           [0044]      FIGS. 3A-3H  show various method steps in an alternative galvanic coating of a dielectric substrate with a metallic electrode material, using a metallic conductive layer that is in contact with a barrier layer at selective points. 
       
    
    
       [0045]    Elements that are functionally identical or similar-acting are labeled using the same reference numerals in the figures. The figures are schematic depictions of the invention. They do not depict specific parameters of the invention. Furthermore, the figures merely show typical embodiments of the invention and are not intended to limit the invention to the embodiments shown. 
       DETAILED DESCRIPTION 
       [0046]      FIGS. 1A-1E  show sectional views of various method steps to coat a dielectric, in particular organic, substrate  10  with a pure metallic electrode material  40 , in particular a noble metal, e.g., gold. Metallic electrode material  40  can be deposited, e.g., in the form of a trace on substrate  10 . Suitable layer thicknesses are, e.g., between 1 μm and 20 μm, although greater layer thicknesses, e.g., up to 100 μm can be used. A plurality of electrodes comprised of metallic electrode material  40  can also be deposited, of course, without departing from the spirit and scope of the present invention. 
         [0047]    Dielectric organic substrate  10 , which is comprised of a biocompatible polymer such as, for example, PI or LCP in particular, is provided ( FIG. 1A ) and an electrically conductive polymer layer  20  is deposited, e.g., onto the entire surface ( FIG. 1B ). 
         [0048]    Electrically conductive polymer layer  20  is provided with a mask by applying and patterning a photoresist, wherein regions  30  of electrically conductive polymer layer  20  are covered and one region  32  of electrically conductive polymer layer  20  is exposed ( FIG. 1C ). 
         [0049]    Metallic electrode material  40  is electrodeposited on exposed region  32  of electrically conductive polymer layer  20  which is used as the power supply ( FIG. 1D ). Next, the photoresist is removed ( FIG. 1E ), thereby leaving pure electrode material  40  on substrate  10 . In the final step ( FIG. 1F ), exposed electrically conductive polymer layer  20  around metallic electrode material  40  is removed, e.g., using chemical and/or plasma etching. As an alternative, the electrical conductivity of exposed electrically conductive polymer layer  20  can be reduced. This can take place, e.g., using chemical oxidation or reduction. 
         [0050]      FIGS. 2A-2H  are explained with reference to sectional views of various method steps to coat a dielectric substrate  10  with a metallic electrode material  40 , in particular a noble metal, e.g., gold, using a metallic conductive layer  12  which is comprised, e.g., of copper. Metallic electrode material  40  can be deposited, e.g., in the form of a trace on substrate  10 . A plurality of electrodes comprised of metallic electrode material  40  can also be deposited, of course, without departing from the spirit and scope of the present invention. 
         [0051]    A metallic conductive layer  12  is applied to a dielectric substrate  10 , which is comprised of a biocompatible polymer such as PI or LCP or the like, in particular being laminated thereon or deposited using a coating technique ( FIG. 2A ). Conductive layer  12  is patterned to create an exposed region  14  on substrate  10  ( FIG. 2B ). An electrically conductive polymer layer  20  is deposited in exposed region  14  of substrate  10  ( FIG. 2C ). Deposition onto the conductive layer  20  does not create interference if, after deposition of metallic electrode material  40 , conductive polymer layer  20  is removed everywhere, as shown in  FIGS. 2F and 2G , or if conductive polymer layer  20  does not interfere with the etching step in  FIGS. 2G and 2H . 
         [0052]    Conductive layer  12  and electrically conductive polymer layer  20  disposed in exposed region  14  are masked using a mask comprised of a photoresist, wherein covered regions  30  of conductive layer  12  and a region  34  of electrically conductive polymer layer  20  are covered and a region  32  of electrically conductive polymer layer  20  is exposed ( FIG. 2D ). Conductive layer  12  is moved close to exposed region  32 —to be coated—of electrically conductive polymer layer  20 , while remaining separated from exposed region  32  by regions  34  of the photoresist. 
         [0053]    Metallic electrode material  40  is electrodeposited onto exposed regions  32  of electrically conductive polymer layer  20  ( FIG. 2E ). During electrodeposition, current flows mainly across (covered) conductive layer  12  and across electrically conductive polymer layer  20  only in the direct vicinity of region  32  to be coated. Despite the relatively low—compared to conductive layer  12 —electrical conductivity of electrically conductive polymer layer  20 , homogeneous electrodeposition can take place on exposed electrically conductive polymer layer  20 . Due to the coverage by regions  34 , the metal of conductive layer  12  does not come in direct contact with deposited metallic electrode material  40 , thereby preventing or at least minimizing inter-diffusion between the two metals. 
         [0054]    After the photoresist is removed from around the deposited metallic electrode material  40  ( FIG. 2F ), the excess exposed electrically conductive polymer layer  20  is removed, e.g., using chemical etching or plasma etching or chemical oxidation, or at least the electrical conductivity thereof is greatly reduced ( FIG. 2G ). Conductive layer  12  can then be removed selectively, e.g., etched selectively. For this purpose, a photoresist having a negative mask of the pattern of the photoresist in  FIG. 2D  can be applied. 
         [0055]    A portion of conductive layer  12  can remain where only electrical currents are transported on the same plane of substrate  10  ( FIG. 2H ), thereby rendering a function as an electrode unnecessary. It is therefore possible to minimize the quantity of metallic electrode material  40  that is deposited. If electrical contacting is required between remaining conductive layer  12  and the electrode comprised of metallic electrode material  40 , conductive layer  12  can be coated locally in the contact region with a diffusion barrier layer, e.g., comprised of nickel or palladium. 
         [0056]    Metallic electrode material  40  can be electrically connected to metallic conductive layer  12  using the process chain described in  FIGS. 3A-3H . Diffusion into the electrode, which is composed of metallic electrode material  40 , is prevented or at least reduced by applying a diffusion barrier layer  16  in the connection region. If the connection region is separated from the electrode region by a considerable distance, e.g., a few millimeters, then any residual diffusion that occurs is negligible. If diffusion barrier  16  is a metal that can be etched at the same time as metallic conductive layer  12  (e.g., Cu and Ni), then diffusion barrier  16  can be applied to the entire surface. 
         [0057]    A metallic conductive layer  12  is applied to a dielectric substrate  10 , which is comprised of a biocompatible polymer such as PI or LCP or the like in particular, i.e., being laminated thereon or deposited using a deposition technique ( FIG. 3A ). Conductive layer  12  is patterned on substrate  10  to create an exposed region  14 , and a diffusion barrier layer  16 , which is comprised, e.g., of nickel or palladium, is deposited onto conductive layer  12  ( FIG. 3B ). This variant is favorable if the aim is to electrically connect metallic electrode material  40  to metallic conductive layer  12 . An electrically conductive polymer layer  20  is deposited in exposed region  14  of substrate  10  ( FIG. 3C ). Deposition onto metallic conductive layer  12  does not create interference if, after deposition of metallic electrode material  40 , conductive polymer layer  20  is removed everywhere, as shown in  FIGS. 3F and 3G , or if conductive polymer layer  20  does not interfere with the etching step in  FIGS. 3G and 3H . 
         [0058]    Conductive layer  12  and electrically conductive polymer layer  20  disposed in exposed region  14  are masked using a mask comprised of a photoresist, wherein covered regions  30  of conductive layer  12  and a region  34  of electrically conductive polymer layer  20  are covered, and a region  32  of electrically conductive polymer layer  20 , and a region  35  of the conductive layer are exposed ( FIG. 3D ). Since perfect registration is not possible, a small region above the conductive layer must also be exposed. 
         [0059]    Metallic electrode material  40  is electrodeposited onto exposed regions  34  of electrically conductive polymer layer  20  ( FIG. 3E ) and region  35  on the exposed conductive layer. During electrodeposition, current flows mainly across (covered) conductive layer  12  and across electrically conductive polymer layer  20  only in the direct vicinity of region  32  to be coated. Despite the relatively low—compared to conductive layer  12 —electrical conductivity of electrically conductive polymer layer  20 , homogeneous electrodeposition can take place on exposed electrically conductive polymer layer  20 . The electrodeposited electrode metal is in contact with the conductive metal only in selective region  35 . The diffusion of the conductive metal into the electrode metal is minimized there by a diffusion barrier of the electrode material. Since contact between the two metals is only very local, the contact region can be selected in a manner such that it is separated from the active electrode surface by a very large distance, thereby making it possible to further minimize the risk of diffusion. 
         [0060]    After the photoresist is removed from around the deposited metallic electrode material  40  ( FIG. 3F ), the excess exposed electrically conductive polymer layer  20  is removed, e.g., using chemical etching or plasma etching, or at the least the electrical conductivity thereof is greatly reduced ( FIG. 3G ). Conductive layer  12  and diffusion layer  16  can then be removed selectively, e.g., etched selectively. For this purpose, a photoresist having a negative mask of the pattern of the photoresist in  FIG. 3D  can be applied. 
         [0061]    A portion of conductive layer  12  can remain where only electrical currents are transported on the same plane of substrate  10  and a function as an electrode is therefore unnecessary ( FIG. 3H ). It is therefore possible to minimize the quantity of metallic electrode material  40  that is deposited. If electrical contacting is required between remaining conductive layer  12  and the electrode comprised of metallic electrode material  40 , diffusion barrier layer  16  protects conductive layer  12  locally in contact region  16   a.  This region is situated far enough away from the actual electrode region. If, e.g., nickel is used as diffusion barrier layer  16 , then nickel can be etched using copper and does not interfere with this final etching step. If the diffusion layer interferes with the subsequent processes, they can be removed by selectively etching the conductive layer. The diffusion layer remains intact in the interface region ( 16   a ). 
         [0062]    This embodiment is favorable when the aim is to use substrate  10 , which has been coated in this manner, as a biocompatible electrode and as a carrier for components or as a cable outside of the body. A cost advantage is obtained if noble metal is used only to form the critical regions. The non-critical regions can be made of metallic conductive layer  12  which is already disposed on substrate  10 . 
         [0063]    The invention results in a patterned galvanic structure of metal conductors (e.g., Au) on a dielectric base material (substrate  10 ) using a conductive polymer. The metallic electrode material is applied only in an additive manner, thereby minimizing the chemistry and materials required. 
         [0064]    It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range.