Chemical sensor with consistent sensor surface areas

Abstract

In one embodiment, a chemical sensor is described. The chemical sensor includes a chemically-sensitive field effect transistor including a floating gate conductor having an upper surface. A material defines an opening extending to the upper surface of the floating gate conductor, the material comprising a first dielectric underlying a second dielectric. A conductive element contacts the upper surface of the floating gate conductor and extending a distance along a sidewall of the opening.

What is claimed is: 
     
         1 . A chemical sensor comprising:
 a chemically-sensitive field effect transistor including a floating gate conductor having an upper surface;   a material defining an opening extending to the upper surface of the floating gate conductor, the material comprising a first dielectric underlying a second dielectric; and   a conductive element contacting the upper surface of the floating gate conductor and extending a distance along a sidewall of the opening.   
     
     
         2 . The chemical sensor of  claim 1 , wherein the opening includes a lower portion within the first dielectric, and an upper portion within the second dielectric. 
     
     
         3 . The chemical sensor of  claim 2 , wherein a width of the lower portion of the opening is substantially the same as a width of the upper portion. 
     
     
         4 . The chemical sensor of  claim 2 , wherein the conductive element is conformal with a shape of the opening. 
     
     
         5 . The chemical sensor of  claim 1 , wherein the conductive element extends to an upper surface of the second dielectric. 
     
     
         6 . The chemical sensor of  claim 1 , wherein the conductive element includes an inner surface defining a lower portion of a reaction region for the chemical sensor, and the second dielectric includes an inner surface defining an upper portion of the opening. 
     
     
         7 . The chemical sensor of  claim 1 , wherein the conductive element comprises an electrically conductive material, and an inner surface of the conductive element includes an oxide of the electrically conductive material. 
     
     
         8 . The chemical sensor of  claim 1 , wherein a sensing surface of the chemical sensor includes an inner surface of the conductive element. 
     
     
         9 . The chemical sensor of  claim 1 , wherein the chemically-sensitive field effect transistor generates a sensor signal in response to a chemical reaction occurring proximate to the conductive element. 
     
     
         10 . The chemical sensor of  claim 1 , wherein the floating gate conductor comprises a plurality of conductors electrically coupled to one another and separated by dielectric layers, and the floating gate conductor is an uppermost conductor in the plurality of conductors. 
     
     
         11 . A method for manufacturing a chemical sensor, the method comprising:
 forming a chemically-sensitive field effect transistor including a floating gate conductor having an upper surface;   forming a material defining an opening extending to the upper surface of the floating gate conductor, the material comprising a first dielectric underlying a second dielectric; and   forming a conductive element contacting the upper surface of the floating gate conductor and extending a distance along a sidewall of the opening.   
     
     
         12 . The method of  claim 11 , wherein forming the material and forming the conductive element include:
 forming the first dielectric on the floating gate conductor, the first dielectric defining a cavity extending to the upper surface of the floating gate conductor;   forming the second dielectric thereon;   etching the second dielectric to expose the conductive element, thereby defining an opening; and   forming the conductive element within the opening.   
     
     
         13 . The method of  claim 12 , wherein forming the conductive element within the opening comprises:
 depositing a conductive material within the opening and on an upper surface of the first dielectric; and   removing at least a portion of the conductive material from the upper surface of the second dielectric.   
     
     
         14 . The method of  claim 13 , wherein removing at least the portion of the conductive material comprises:
 depositing a layer of photoresist within the opening and; and   removing at least a portion of the conductive material together with the photoresist from the upper surface of the second dielectric.   
     
     
         15 . The method of  claim 14 , further comprising removing remaining photoresist. 
     
     
         16 . The method of  claim 11 , wherein the conductive material comprises titanium. 
     
     
         17 . The method of  claim 11 , wherein the opening is a nanowell. 
     
     
         18 . The method of  claim 11 , wherein the forming a conductive element includes depositing a conductive material conformally within the opening. 
     
     
         19 . The method of  claim 11 , wherein the conductive element includes an inner surface defining a lower portion of a reaction region for the chemical sensor, and the second dielectric includes an inner surface defining an upper portion of the opening