Abstract:
A method of creating an active electrode that may include providing a flex circuit having an electrode made of a first material and providing a first mask over the flex circuit, the first mask having an offset region and an opening that exposes the electrode. The method may also include depositing a second material over the offset region and the opening, the second material being different from the first material and providing a second mask over the second material, the second mask having an opening over a portion of the second material that is over the offset region.

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119 
     The present Application for Patent claims priority to Provisional Application No. 60/777,135 filed Feb. 27, 2006, and assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to flex circuit technology. More specifically, the invention relates to using flex circuit technology to create an electrode. 
     BACKGROUND 
     Flex circuits have been used in the micro-electronics industry for many years. In recent years, flex circuits have been used to design microelectrodes for in vivo applications. One flex circuit design involves a laminate of a conductive foil (e.g., copper) on a flexible dielectric substrate (e.g., polyimide). The flex circuit is formed on the conductive foil using masking and photolithography techniques. Flex circuits are desirable due to their low manufacturing cost, ease in design integration, and flexibility in motion applications. 
     SUMMARY 
     The invention relates to a method of creating an active electrode that may include providing a flex circuit having an electrode made of a first material and providing a first mask over the flex circuit, the first mask having an offset region and an opening that exposes the electrode. The method may also include depositing a second material over the offset region and the opening, the second material being different from the first material and providing a second mask over the second material, the second mask having an opening over a portion of the second material that is over the offset region. 
     The invention relates to an electrode that may include a substrate having a conductive trace made of a first material, and a first mask positioned over the conductive trace, the first mask having a first opening over a portion of the conductive trace. The electrode may also include a material of interest made of a second material and positioned over a portion of the conductive trace and over a portion of the first mask and a second mask over the material of interest, the second mask having a second opening over a portion of the material of interest, the second opening being offset from the first opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, objects, and advantages of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein: 
         FIG. 1  is a cross-section view of an active electrode that is created using a flex circuit according to an embodiment of the invention. 
         FIG. 2  is a top view of a flex circuit according to an embodiment of the invention. 
         FIG. 3  is a top view of a mask that is used to cover the flex circuit of  FIG. 1  according to an embodiment of the invention. 
         FIG. 4  is a top view showing one or more materials of interest deposited into and above the openings in the mask according to an embodiment of the invention. 
         FIG. 5  is a top view of a mask that is used to cover the material of interest shown in  FIG. 4  according to an embodiment of the invention. 
         FIGS. 6A and 6B  are top views showing vertical and horizontal offsets according to various embodiments of the invention. 
         FIG. 7  is a flow chart showing a method of creating the electrode of  FIG. 1  according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is directed toward using a flex circuit to create an active electrode. The flex circuit has a copper trace that is masked and imaged onto a polyimide substrate. Flex circuits with copper traces have a low manufacturing cost. The end of the copper trace may be plated with a first material of interest (e.g., gold). A first mask is used to create an opening for an active electrode. A second material of interest (e.g., graphite and/or platinum) may be deposited or screen-printed into the opening and on an offset region. A second mask is used to cover the second material of interest that is over the opening. A membrane may be placed over the offset region to form the active electrode. The second material of interest over the offset region acts as a diffusion barrier to prevent, for example, electrolytes from coming into contact with the copper trace. The offset region prevents the copper trace from oxidizing at a positive potential, such as would be the case for a glucose electrode measuring peroxide vs. silver-silver chloride for example. 
       FIG. 1  is a cross-section view of an active electrode  10  that is created using a flex circuit  100  according to an embodiment of the invention. The flex circuit  100  may include a substrate  105 , one or more contacts  110 , one or more traces  115 , and one or more electrodes  120  ( 705 ). For illustrative purposes, the contacts  110 , the traces  115 , and the electrodes  120  are shown as different elements; however, the contacts  110 , the traces  115 , and the electrodes  120  may be collectively referred to as traces and may be formed using the same material (e.g., copper). The contacts  110 , traces  115  and electrodes  120  are masked and imaged onto the substrate  105 . A mask  200  is placed over the flex circuit  100  ( 710 ). The mask  200  may have an opening  220  that expose the electrodes  120  and that receive a material of interest  300 , which is used to form the active electrode  10  ( 715 ). The material of interest  300  is also deposited over the mask  200  in an offset region  305 . The offset region  305  is shown to be adjacent to the opening  220 . A mask  400  having an opening  405  is deposited over the material of interest  300  ( 720 ). The opening  405  is located above the offset region  305  and is used for placement of a membrane  500  ( 725 ). The opening  220  is positioned along a first axis or plane and the opening  405  is positioned along a second axis or plane. The first axis or plane is not coincident with the second axis or plane. Hence, the first axis or plane is vertically and/or horizontally offset from the second axis or plane.  FIGS. 1 and 6B  show a horizontal offset and  FIG. 6A  shows a vertical offset. The horizontal offset may be along the length of the substrate  105  and the vertical offset may be along the width of the substrate  105 . The mask  200  and/or the material of interest  300  may act as a diffusion barrier to prevent electrolytes coming in from the membrane  500  from contacting the electrodes  120 . The offset region  305  prevents the electrodes  120  from undesirable electrochemical activity. 
       FIG. 2  is a top view of a flex circuit  100  according to an embodiment of the invention. The contacts  110 , the traces  115 , and the electrodes  120  are made of a copper material and are formed on the substrate  105  using masking and photolithography techniques. The substrate  105  may be a flexible dielectric substrate such as a polyimide. The contacts  110  are used to connect to measurement devices such as a potentiostat. The traces  115  are used to carry voltage or current from the electrodes  120  to the contacts  110 . As an example,  FIG. 1  shows the flex circuit  100  having the substrate  105 , three contacts  110   a - c , three traces  115   a - c , and three electrodes  120   a - c.    
       FIG. 3  is a top view of a mask  200  that is used to cover the flex circuit  100  shown in  FIG. 2  according to an embodiment of the invention. The mask  200  may be made of a dielectric material such as a photoimagable epoxy or an ultraviolet curable epoxy material. The mask  200  has openings  210   a - c  and  220   a - c . In one embodiment, the mask  200  covers the entire top surface of the flex circuit  100  except for areas that are above the contacts  110  and/or the electrodes  120 . Hence, the openings  210   a - c  are positioned directly above the contacts  110   a - c  so that the contacts  110   a - c  are exposed through the openings  210   a - c  of the mask  200 . Similarly, the openings  220   a - c  are located directly above the electrodes  120   a - c  so that the electrodes  120   a - c  are exposed through the openings  220   a - c  of the mask  200 . Conventional lithography techniques may be used to deposit or place the mask  200  on the flex circuit  100 . 
       FIG. 4  is a top view showing one or more materials of interest  300   a - c  deposited into and above the openings  220   a - c  in the mask  200  according to an embodiment of the invention. The materials of interest  300   a - c  provide a working surface for the electrodes  120   a - c . The same material of interest  300  or different materials of interest  300  may be deposited over each of the openings  220   a - c . The materials of interest  300  may be an ink or material made of carbon, gold, graphite, platinum, silver-silver chloride, rodium, palladium, other metals, and other materials having specific electrochemical properties. As an example, a platinum ink or material may be deposited over the openings  220   a  and  220   c  and a silver-silver chloride ink or material may be deposited over the opening  220   b . The one or more materials of interest  300  may also be deposited over offset regions  305   a - c  that are adjacent to the openings  220   a - c  but are not directly over the openings  220   a - c . The size of the offset regions  305   a - c  may vary depending on the particular application and the arrangement and configuration of the electrodes  120   a - c . In one embodiment, the sizes of the offset regions  305   a - c  are about 0.010 inches, 0.003 inches and 0.050 inches, respectively. 
       FIG. 5  is a top view of the mask  400  that is used to cover the material of interest  300  shown in  FIG. 4  according to an embodiment of the invention. The mask  400  may be made of a dielectric material such as a photoimagable epoxy or an ultraviolet curable epoxy material. The mask  400  has an opening  405  located above the offset region  305 . In one embodiment, the mask  400  covers the entire top surface of the materials of interest  300  except for an area that is above the offset region  305 . Hence, the opening  405  may be positioned directly above the material of interest  300 , which is directly above the offset region  305 . Conventional lithography techniques may be used to deposit or place the mask  400  on the material of interest  300 . 
     Referring back to  FIG. 1 , a membrane  500  is deposited in the opening  405  and on the material of interest  300  (i.e., a working surface) to act as a sensing region. The membrane  500  may contain, for example, a glucose oxidase enzyme. The membrane  500  may allow molecules to pass at a certain rate so the material of interest  300  can accurately measure, for example, the glucose level in blood. That is, molecules in the blood can pass through the membrane  500  at a certain rate to the material of interest  300  for a specific measurement of the glucose in the blood. The membrane  500  and/or the material of interest  300  may be suitable for immersion into a fluid or solution containing species of interest (e.g., blood) and/or electrolyte. The contacts  110 , the traces  115 , and/or the electrodes  120  may not be suitable for immersion into a fluid or solution containing species of interest and therefore should be protected by a suitable encapsulant with appropriate dielectric properties. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other changes, combinations, omissions, modifications and substitutions, in addition to those set forth in the above paragraphs, are possible. Those skilled in the art will appreciate that various adaptations and modifications of the just described embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.