Method for producing a coating with improved adhesion

Abstract

A method of producing a coating for a medical device having high surface area and low porosity. The coating is formed by a PVD process in which a primary metallic component is deposited in the presence of a secondary reactive component in a high energy environment such that surface diffusion and intermixing can occur prior to the solidification of the condensate. The resulting coating consists of a zone 2 microstructure having a [1,1,1] crystal orientation, which provides a surface having well-defined pyramidal-shaped structures formed thereon.

1 . A method for producing a coating on a substrate comprising the steps of:
 a. providing a primary metallic component   b. providing a secondary reactive component;   c. raising the temperature of said substrate such that deposited atoms of said primary metallic component diffuse on the surface of said substrate and intermix with surface atoms prior to solidifying and such that deposited atoms of said secondary reactive component react with atoms of said primary metallic component prior to solidifying;   d. wherein the reaction of said primary metallic component and said secondary reactive component results in surface having pyramidal or tetragonal crystal structures defined thereon.   
   
   
       2 . The method of  claim 1  wherein said surface crystals have a predominantly [1,1,1] structure. 
   
   
       3 . The method of  claim 2  wherein said coating is formed by a physical vapor deposition process. 
   
   
       4 . The method of  claim 3  wherein the target in said physical vapor deposition process is composed of said primary metallic component and wherein said secondary reactive component is introduced with an inert gas to form a plasma consisting of ions of said inert gas and said secondary reactive component. 
   
   
       5 . The method of  claim 1  wherein said secondary reactive component is introduced with an inert gas to form a plasma during said physical vapor deposition process. 
   
   
       6 . The method of  claim 1  wherein said primary metallic component is selected from the group consisting of Ti, Ta, Nb, Hf, Zr, Au, Pt, Pd and W. 
   
   
       7 . The method of  claim 1  wherein said secondary reactive component is selected from a group consisting of nitrogen, oxygen and carbon. 
   
   
       8 . The method of  claim 1  wherein an inert gas is introduced without said secondary constituent to allow an intermix layer to form, said intermix layer being composed of intermixed atoms of said substrate and said primary metallic component, and further wherein said secondary reactive component is introduced after said intermix layer is thick enough such that the surface is composed primarily of atoms of said primary metallic component. 
   
   
       9 . The method of  claim 1  wherein said secondary reactive component is introduced with an inert gas in a flow ratio of approximately 1:1 to 1.25:1. 
   
   
       10 . The method of  claim 1  wherein two or more secondary reactive constituents are used, selected from a group consisting of nitrogen, oxygen and carbon. 
   
   
       11 . The method of  claim 1  wherein the temperature of said substrate is raised to between 20% and 50% of the melting point of said primary metallic component. 
   
   
       12 . The method of  claim 11  wherein the temperature of said substrate is raised to approximately 25% of the melting point of said primary metallic component. 
   
   
       13 . The method of  claim 1  wherein said coating is grown to a minimum thickness of approximately 2.5 microns. 
   
   
       14 . The method of  claim 4  wherein said target is arranged with respect to said substrate such that a percentage of atoms of said primary metallic component strike the surface at a normal angle or at an angle approaching a normal angle. 
   
   
       15 . The method of  claim 14  where multiple targets of said primary metallic component are used. 
   
   
       16 . The method of  claim 15  wherein said multiple targets tire arranged in a circular pattern with said substrate at the center. 
   
   
       17 . A method for producing a coating on a substrate using a physical vapor deposition comprising the steps of:
 a. providing one or more targets composed of a primary metallic component   b. raising the temperature of said substrate to between 20% and 50% of the melting point of said primary metallic component;   c. positioning said one or more targets with respect to said substrate such that a percentage of atoms of said primary component reach said substrate at a normal angle;   d. mixing a secondary reactive component with an inert gas to form a plasma;   e. wherein said primary metallic component, and said secondary reactive component react to form a surface having pyramidal or tetragonal crystals defined thereon.   
   
   
       18 . The method of  claim 17  wherein said primary metallic component is allowed to condense on said substrate in the absence of said secondary reactive component to form an intermix layer wherein the atoms of said primary metallic component an the atoms of said substrate are intermixed, and further wherein said secondary reactive component is introduced after the formation of said intermix layer. 
   
   
       19 . The method of  claim 18  wherein said secondary reactive component and said inert gas are introduced in an approximate 1.1 ratio. 
   
   
       20 . A coating for an implantable medical electrode comprising a zone 2 microstructure composed of a primary metallic component and a secondary reactive component, said surface having crystals with a [1,1,1] structure defined thereon. 
   
   
       21 . The coating of  claim 20  wherein said coating is a nitride of an element selected from the group consisting of Ti, Ta, Nb, Hf, Zr, Au, Ft, Pd and W. 
   
   
       22 . The coating of  claim 20  further comprising an intermix layer formed between the surface of said electrode and said coating, said intermix layer composed primarily of said primary metallic component intermixed at the surface of said electrode with atoms of the material of which said electrode is composed.