Chemically sensitive sensor with lightly doped drains

Abstract

A chemically sensitive sensor with a lightly doped region that affects an overlap capacitance between a gate and an electrode of the chemical sensitive sensor. The lightly doped region extends beneath and adjacent to a gate region of the chemical sensitive sensor. Modifying the gain of the chemically sensitive sensor is achieved by manipulating the lightly doped region under the electrodes.

What is claimed is: 
     
         1 . A chemically sensitive sensor, comprising:
 a floating gate electrically coupled to a gate electrode on a substrate;   a drain terminal connection;   a source terminal connection;   a pair of doped regions in the substrate, each doped region including a lightly doped region and a highly doped region, wherein each of the lightly doped regions extends beneath the gate electrode on the substrate and each of the highly doped regions extend to couple respectively to the drain terminal and the source terminal.   
     
     
         2 . The chemically sensitive sensor of  claim 1 , further comprising:
 a microwell to accept a sample.   
     
     
         3 . The chemically sensitive sensor of  claim 1 , wherein the microwell has an oxide layer at the bottom of the well adjacent to the floating gate. 
     
     
         4 . The chemically sensitive sensor of  claim 1 , wherein a parasitic capacitance is present between the gate electrode and lightly doped regions beneath. 
     
     
         5 . The chemically sensitive sensor of  claim 1 , wherein gain of the chemically sensitive sensor is modified according to an amount of dopant used in the lightly doped region. 
     
     
         6 . The chemically sensitive sensor of  claim 1 , wherein the lightly doped region is doped at a dopant density level that is less than the dopant density level of the highly doped region.