ChemFET sensor array including overlying array of wells
Methods and apparatus relating to FET arrays for monitoring chemical and/or biological reactions such as nucleic acid sequencing-by-synthesis reactions. Some methods provided herein relate to improving signal (and also signal to noise ratio) from released hydrogen ions during nucleic acid sequencing reactions.
1. A method of fabricating a chemically-sensitive field effect transistor (chemFET) sensor device, comprising:
forming an array of chemFET sensors in a substrate; each chemFET sensor having a floating gate structure defining an array of floating gate structures, each floating gate structure including:
a top metal layer of a plurality of metal layers of the floating gate structure including a sensitive area formed upon the top metal layer; and
a first metal layer including a metal conductor providing an electrical connection tying each body connection of all chemFETs in the array to a body bias voltage and a signal line;
forming an array of wells in a dielectric layer that overlays the array of chemFET sensors; each well having a surface defined by sidewalls and a bottom, wherein forming the array of wells includes:
depositing a layer of dielectric material over the array of chemFET sensors; and
etching a defined pattern of an array of wells in the dielectric layer.
2. The method of claim 1 , wherein depositing the layer of dielectric material comprises depositing a layer of tetramethyl ortho silicate (TEOS).
3. The method of claim 1 , further comprising coating the surface of wells of the array of wells with a buffering inhibitor.
4. The method of claim 3 , wherein the buffering inhibitor has no buffer capacity.
5. The method of claim 4 , wherein the buffering inhibitor is cationic.
6. The method of claim 5 , wherein the buffering inhibitor is a quaternary ammonium compound.
7. The method of claim 6 , wherein the quaternary ammonium compounds a tetramethyl ammonium compound.
8. The method of claim 1 , wherein each well in the array of wells is capacitively coupled to between 1 to 4 sensors.
9. The method of claim 1 , wherein the sensitive area is selective for sensing hydrogen ion.
10. The method of claim 1 , wherein the sensitive area is selective for sensing pyrophosphate.