Abstract:
The implantable electrode system of the preferred embodiments include a conductor, an interconnect coupled to the conductor, an insulator that insulates the interconnect, and an anchor that is connected to both the conductor and the insulating element, wherein the anchor is mechanically interlocked with at least one of the conductor and the insulator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/032,725, filed on 29 Feb. 2008, which is incorporated in its entirety by this reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to the implantable electrodes field, and more specifically to an improved implantable electrode with an anchoring element and the method of making this improved system. 
       BACKGROUND 
       [0003]    The adhesion of metals to polymers in conventional microfabrication techniques can be quite poor. Excellent adhesion, however, is critical for biomedical electrodes, which are implanted in tissue and are exposed to harsh environments. In such environments, poorly connected elements can lead to irreversible chemical reactions and possible device failure. The irreversible chemical reactions can include: 1) electrolysis of water, with consequent pH changes and gas formation, 2) electrode dissolution due to oxide formation of soluble metal complexes, and 3) corrosion or breakdown of passivity. In conventional electrodes, uneven charging across the electrode site is often seen. As an example, a much higher current density is typically seen in the perimeter of the electrode site than seen in the center, thus when the electrode is placed onto the tissue of the patient, the uneven charging may lead to unpredictable stimulation of the tissue of the patient. Uneven charging across the electrode site also leads to additional irreversible chemical reactions. In the case of higher current density along the perimeter than seen in the center, a relatively high potential difference between the perimeter of the electrode and the center of the electrode develops, leading to a higher chance of irreversible chemical reactions at the edge of the electrode site. This invention provides an improved and useful system and method for connecting layers within an electrode, increasing the reliability of an electrode, and decreasing the chance of irreversible chemical reactions within an electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
         [0004]      FIG. 1  is a cross-sectional view of the implantable electrode of the preferred embodiment including a first variation of the anchoring element. 
           [0005]      FIG. 2  is a cross-sectional view of the implantable electrode of the preferred embodiment including a second variation of the anchoring element. 
           [0006]      FIG. 3  is a cross-sectional view of the implantable electrode of the preferred embodiment including a third variation of the anchoring element. 
           [0007]      FIG. 4  is a top view and cross-sectional view of an implantable electrode. 
           [0008]      FIG. 5  is a graphical representation of the effect on current density across the electrode site of the preferred embodiment with the third variation of the anchoring element. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0009]    The following description of preferred embodiments of the invention is not intended to limit the invention to these embodiments, but rather to enable any person skilled in the art to make and use this invention. 
         [0010]    As shown in  FIG. 1 , the implantable electrode  10  of the preferred embodiments includes an electrode site  12 , an interconnect  14  coupled to the electrode site  12 , an insulating element  16  that functions to insulate the interconnect  14 , and an anchoring element  18  that functions to anchor the electrode site  12  to the implantable electrode  10 . The implantable electrode  10  of the preferred embodiment is preferably designed for an implantable electrode lead system to interface with brain tissue, the implantable electrode  10  of the preferred embodiments, however, may be alternatively used in any suitable environment (such as the spinal cord, peripheral nerve, muscle, or any other suitable anatomical location) and for any suitable reason. 
       1. The Implantable Electrode 
       [0011]    As shown in  FIGS. 1 and 4 , the electrode site  12  of the preferred embodiment functions to record, stimulate, perform any other suitable function, or any combination thereof. The implantable electrode preferably includes a plurality of electrode sites  12 , which may be independently tuned to record, stimulate, perform any other suitable function, or any combination thereof. Two or more electrode sites  12  may be grouped to form a larger composite site that enables tuning the neural interface region for recording and/or stimulation. The electrode site  12  is preferably a thin film metal, preferably made from gold, iridium, or platinum, but may alternatively be made from any suitable material. 
         [0012]    The implantable electrode  10  of the preferred embodiments may further include a bond pad, which is electrically coupled to the electrode site  12  and functions to provide a point of contact to an external connector and/or device to provide a site from which recorded signals are accessed and/or to which stimuli are applied. The implantable electrode preferably includes a plurality of bond pads. The ratio of electrode sites  12  to bond pads is preferably 1:1, but may be any other suitable ratio. The bond pads are preferably gold, but may alternatively be any suitable material. 
         [0013]    The implantable electrode  10  of the preferred embodiments may further include a plug  20  (also know as “leg”), which couples the electrode site  12  to the interconnect  14  and functions to transfer signals between the electrode site  12  and the interconnect  14 . The implantable electrode preferably includes a plurality of plugs  20 . The ratio of electrode sites  12  to plugs  20  is preferably 1:1, but may be any other suitable ratio. The plug  20  is preferably gold or platinum, but may alternatively be any suitable material. 
         [0014]    As shown in  FIGS. 1 and 4 , the interconnect  14  of the preferred embodiment is coupled to the electrode site and functions to electrically couple the electrode site  12  to a bond pad or directly to an external connector and/or device and to transfer signals between the electrode site  12  and the bond pads, connector, and/or device. The implantable electrode preferably includes a plurality of interconnects  14 . The ratio of electrode sites  12  to interconnects  14  is preferably 1:1, but may be any other suitable ratio. The interconnect  14  is preferably metal (such as platinum or gold) or polysilicon, but may alternatively be made out of any suitable material. 
         [0015]    As shown in  FIGS. 1 and 4 , the insulating element  16  of the preferred embodiment functions to insulate the interconnect  14 , preferably on the top and bottom side of the interconnect  14 . The insulating element  16  is preferably one of several variations, and in some variations the insulating element  16  preferably includes multiple layers: a first layer  16  and a second layer  16 ′. In a first variation, where the interconnect  14  is preferably a metal such as platinum or gold, the insulating element  16  is preferably a polymer such as polyimide, parylene, or polydimethylsiloxane (PDMS). In a second variation, where the interconnect  14  is preferably polysilicon, the insulating element preferably includes a first layer  16  of inorganic dielectrics such as silicon dioxide or silicon nitride and a second layer  16 ′ of a polymer. In a third variation, where the interconnect  14  is preferably polysilicon, the insulating element preferably includes a first layer  16  of inorganic dielectrics such as silicon dioxide or silicon nitride that are supported by a silicon substrate. The first layer  16  of inorganic dielectrics are preferably a tri-layer stack of silicon dioxide, silicon nitride, and silicon dioxide. Alternatives to the first layer  16  include silicon carbide and other polymers such as polyimide or parylene. The second layer  16 ′ may be the same as the first layer, or may alternatively be a vapor deposited polymer such as parylene, Polytetrafluoroethylene (PTFE), other fluoropolymers, silicone, or any other suitable material. The second layer  16 ′ preferably provides additional electrical insulation to leads. 
         [0016]    As shown in  FIGS. 1-3 , the anchoring element  18  of the preferred embodiment functions to anchor the electrode site  12  to the implantable electrode  10 . The anchoring element is preferably one of several variations. In a first variation, as shown in  FIG. 1 , the anchoring element  18  is a layer of metal. This metal layer is preferably located above the interconnect  14  such that it will not short or interfere with the interconnect  14 . The metal layer is preferably located on the top surface of the second layer  16 ′ of the insulation element  16 . The metal electrode site  12  will adhere to the metal anchoring element  18 . The strong metal-to-metal adhesion of the electrode site  12  to the anchoring element  18  preferably complements the adhesion of the electrode site  12  to the implantable electrode  10  (i.e. the top polymer surface). The anchoring element  18  in this variation is preferably buried in and/or under an additional layer  16 ″ (preferably a polymer) of the insulation element  16  with a portion of the anchoring element  18  exposed to contact the electrode site  12 . The exposed portion of the anchoring element  18  of this variation is preferably patterned to have a ring geometry that coincides with a perimeter portion of the electrode site  12 . Alternatively, the exposed portion of the anchoring element  18  may form a semi-ring, may have multiple points, or may have any other suitable geometry. The geometry of the exposed portion of the anchoring element  18  may be defined by the anchoring element  18  and/or the additional layer  16 ″ of the insulation element  16  and the pattern in which the anchoring element  18  is exposed. 
         [0017]    In a second variation, as shown in  FIG. 2 , the anchoring element  18  is also a layer of metal, but this layer of metal is preferably located at the level of the interconnects  14  and is preferably insulated by the insulation element layers  16  and  16 ′. The metal electrode site  12  will adhere to the metal anchoring element  18 . The strong metal-to-metal adhesion of the electrode site  12  to the anchoring element  18  preferably complements the adhesion of the electrode site  12  to the implantable electrode  10  (i.e. the top polymer surface). The anchoring element  18  of this variation preferably does not require the additional layer  16 ″ of the insulation element  16 , but rather, is preferably buried in the second layer  16 ′ with a portion of the anchoring element  18  exposed to contact the electrode site  12 . The anchoring element  18  of this variation is preferably patterned to have multiple points or “spots” that coincide with the perimeter portion of the electrode site  12 , and are preferably positioned such that the multiple points will not cross over or connect adjacent interconnects  14 . Alternatively, the exposed portion of the anchoring element  18  may form a semi-ring or may have any other suitable geometry. The anchoring element  18  of this variation may further include a plug  22 , which couples the electrode site  12  to the anchoring element  18 . The plug  22  is preferably gold or platinum, but may alternatively be any suitable material. 
         [0018]    In a third variation, as shown in  FIG. 3 , the anchoring element  18  is a layer of an insulating material, such as a polymer, that functions to mechanically couple the electrode site  12  to the implantable electrode  10 . The mechanical coupling of the electrode site  12  to the anchoring element  18  preferably complements the adhesion of the electrode site  12  to the implantable electrode  10  (i.e. the top polymer surface). The anchoring element  18  is preferably an additional layer of the insulation element  16 . The anchoring element  18  is preferably located on the top surface of the second layer  16 ′ of the insulation element  16 . The electrode site  12  in this variation is preferably buried in and/or under the anchoring element  18  with a portion of the electrode site exposed. The exposed portion will record, stimulate, perform any other suitable function, or any combination thereof. The anchoring element  18  is preferably patterned to form a lip or a rim around the perimeter portion of the electrode site  12 . Alternatively, the anchoring element  18  may have any other suitable geometry. 
         [0019]    As shown in  FIG. 5 , the third variation of the anchoring element  18  also functions to normalize (or “make more uniform”) the initial current distribution along the electrode site  12 . In conventional implantable electrodes, as a stimulation pulse is sent to the electrode site  12 , the initial current density along the electrode site  12  is not uniform. The current density along the perimeter of the electrode site  12  is higher than that at the center of the electrode site  12 , leading to uneven changing across the electrode site  12  and creating a potential difference between the perimeter and the center of the electrode site  12 . The difference in potential may lead to unpredictable stimulation of the tissue of the patient, such as charge spikes along the electrode site  12 , and an increased chance of irreversible chemical reactions at the perimeter of the electrode site  12 , thereby potentially releasing toxic products into the tissue of the patient and decreasing the effectiveness of the electrode  10 . The third variation of the anchoring element  18  provides a raised lip along the perimeter of the electrode site  12 . This raised lip has been shown to decrease the difference in initial current densities along the electrode site  12 , as shown in  FIG. 5   a,  leading to a more normalized final voltage potential distribution along the electrode site  12 , as shown in  FIG. 5   b , increasing the reliability of the electrode and decreasing the chance of irreversible chemical reactions. 
         [0020]    The anchoring element  18  of the third variation may alternatively be shaped to accommodate to the type of charge distribution desired across the electrode site  12 . For example, a higher charge distribution may be desired in a first region than in a second region of the electrode site  12 . To achieve this, the raised lip may be thicker in the second region than in the first region. Alternatively, the raised lip of the anchoring element  18  may be of a uniform thickness around the perimeter of the electrode site  12  to achieve higher mitigation of the current density at the perimeter. However, any other arrangement of the anchoring element  18  suitable to regulate the charge distribution across the electrode site  12  may be used. 
         [0021]    The anchoring element  18  of the third variation may also be shaped to accommodate to the type of mechanical interlock desired across the electrode site  12 . For example, the raised lip of the anchoring element  18  may be shaped as an “X” across the electrode site  12 , but may alternatively also be shaped as parallel ridges across the electrode site  12 . However, any other arrangement of the anchoring element  18  suitable to provide an adequate mechanical interlock across the electrode site  12  may be used. 
       2. Method of Making the Implantable Electrode 
       [0022]    The implantable electrode  10  of the preferred embodiment is preferably micro-machined using standard microfabrication techniques, but may alternatively be fabricated in any other suitable fashion. As shown in  FIG. 4 , the method of building an implantable electrode of the preferred embodiments includes building a first layer of the insulating element  16  S 102 , building an interconnect  14  S 104 , building a second layer  16 ′ of the insulating element S 106 , removing a portion of the second layer  16 ′ to expose a portion of the interconnect  14  S 108 , building a layer of conductive material to fill the second layer  16 ′ S 110 , and building the electrode site  12  S 112 . 
         [0023]    The method of building an implantable electrode with an anchoring element  18  of the preferred embodiments preferably includes additional and/or alternative steps to build the anchoring element  18  in one of several variations. In a first variation, as shown in  FIG. 1 , after Step S 106  the method of the first variation includes building an anchoring element  18  S 114 , building a third layer  16 ″ of the insulating element  16  S 116 , removing a portion of the third layer  16 ″ to expose a portion of the anchoring element  18  and to expose a portion of the second layer  16 ′ above the interconnect  14  S 118 , removing a portion of the second layer  16 ′ to expose a portion of the interconnect  14  S 108 , building a layer of conductive material to fill the second layer  16 ′ and the portion of the third layer  16 ″ above the interconnect  14  S 110 ′, and building the electrode site  12  S 112 . 
         [0024]    In a second variation, as shown in  FIG. 2 , the method of the second variation includes an alternative Step S 104 ′: building an interconnect  14  and an anchoring element  18 , and an alternative Step S 108 ′: removing a portion of the second layer  16 ′ to expose a portion of the interconnect  14  and the anchoring element  18 . In a third variation, as shown in  FIG. 3 , the method of the third variation includes two additional steps after Step S 112 . Those steps include building an anchoring element  18  S 120 , and removing a portion of the anchoring element  18  to expose a portion of the electrode site  12  S 122 . The method is preferably designed for the manufacture of implantable electrodes, and more specifically for the manufacture of implantable electrodes with anchoring elements. The method and any variation thereof, however, may be alternatively used in any suitable environment and for any suitable reason. 
         [0025]    Step S 102 , which recites building a first layer of the insulating element  16 , functions to provide the base layer of the implantable electrode  10 . The adding of material is preferably performed through any suitable deposition process that grows, coats, or transfers a material in any other suitable method. These deposition processes may include spinning and curing, physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and more recently, atomic layer deposition (ALD), or any other suitable process. 
         [0026]    Step S 104  and S 104 ′, which recite building an interconnect  14  and building an interconnect  14  and an anchoring element  18  respectively, function to create the interconnects and/or the metal anchoring elements  18 . This step is preferably performed by building a layer of material and then patterning the layer of material to form the interconnects  14  and/or the anchoring elements  18 . The adding of material is preferably performed through any suitable deposition process that grows, coats, or transfers a material in any other suitable method. These deposition processes may include sputtering, evaporating, physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and more recently, atomic layer deposition (ALD), or any other suitable process. The removal or patterning of material is preferably performed through reactive ion etching (RIE), but may alternatively be performed through any other suitable removal process, such as other dry etching methods, wet etching, chemical-mechanical planarization, or any combination thereof. The interconnects  14  and/or the anchoring elements  18  may alternatively be created by any suitable combination of deposition, removal, and or patterning. 
         [0027]    Step S 106 , which recites building a second layer  16 ′ of the insulating element is preferably performed in a similar fashion to Step S 102  above. 
         [0028]    Step S 108 , S 108 ′, and S 118 , which recite removing a portion of the insulating element to expose a portion of the interconnect  14 , the anchoring element  18 , and/or a lower layer of the insulating element function to expose a contact through the insulating element to the layer below. The removal or patterning of material is preferably performed through reactive ion etching (RIE), but may alternatively be performed through any other suitable removal process, such as other dry etching methods, wet etching, chemical-mechanical planarization, or any combination thereof. The interconnects  14  and/or the anchoring elements  18  may alternatively be created by any suitable combination of deposition, removal, and or patterning. 
         [0029]    Step S 110  and S 110 ′, which recite building a layer of conductive material to fill a layer of the insulating element, function to build a “plug” (also known as “leg”) to fill the contact hole with conductive material and to form the plugs  20  and/or  22 . The step is preferably performed through electroplating, but may alternatively be performed through any suitable deposition process that grows, coats, or transfers a material in any other suitable method. 
         [0030]    Step S 112 , which recites building the electrode site  12 , functions to create electrode site  12 . This step is preferably performed by building a layer of material and then patterning the layer of material to form the electrode site  12 . This step preferably uses a method to add material and then remove material as described in Step S 104 . 
         [0031]    Step S 114 , which recites building an anchoring element  18 , functions to create the metal layer anchoring element  18  of the first variation. This step is preferably performed by building a layer of material and then patterning the layer of material to form the anchoring element  18 . This step preferably uses a method to add material and then remove material as described in Step S 104 . 
         [0032]    Step S 116  and Step S 120 , which recite building an anchoring element  18  and building a third layer  16 ″ of the insulating element  16 , function to create the anchoring element  18  of the third variation (which is preferably an insulating material) and to build the third layer of the insulating element, respectively. This is preferably performed in a similar fashion as described in Step S 102 . 
         [0033]    Step S 122 , which recites removing a portion of the anchoring element  18  to expose a portion of the electrode site  12 , functions to expose a contact through the anchoring element  18  to the electrode site  12 . The removal or patterning of material is preferably performed through a deep reactive ion etching (DRIE), but may alternatively be performed through any other suitable removal process, such as other dry etching methods, wet etching, chemical-mechanical planarization, or any combination thereof. The interconnects  14  and/or the anchoring elements  18  may alternatively be created by any suitable combination of deposition, removal, and or patterning. 
         [0034]    Although omitted for conciseness, the preferred embodiments include every combination and permutation of the various implantable electrodes, the various interconnects, the various insulation elements, the various anchoring elements, and the various methods of making the various implantable electrodes. 
         [0035]    As a person skilled in the art will recognize from the previous detailed description and from the figures and claim, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claim.