Use of titanium nitride as an electrode in non-faradaic electrochemical cell
A nanopore cell includes a conductive layer. The nanopore cell further includes a titanium nitride (TiN) working electrode disposed above the conductive layer. The nanopore cell further includes insulating walls disposed above the TiN working electrode, wherein the insulating walls and the TiN working electrode form a well into which an electrolyte may be contained. In some embodiments, the TiN working electrode comprises a spongy and porous TiN working electrode that is deposited by a deposition technique with conditions tuned to deposit sparsely-spaced TiN columnar structures or columns of TiN crystals above the conductive layer.
1. A method of constructing a nanopore cell, comprising:
depositing a first dielectric layer over a conductive layer;
removing a portion of the first dielectric layer to form an opening over the conductive layer;
depositing a layer of titanium nitride (TiN) in the opening over the conductive layer to form a TiN electrode;
depositing a second dielectric layer over both the TiN electrode and the first dielectric layer; and
removing a portion of the second dielectric layer to expose a portion of the TiN electrode and to form a well.
2. The method of claim 1 , wherein the layer of TiN is deposited by a deposition technique with conditions tuned to deposit TiN columnar structures or columns of TiN crystals above the conductive layer.
3. The method of claim 1 , wherein the TiN electrode has a specific surface area that is ten to a thousand times that of a specific surface area of a flat TiN electrode with substantially identical dimensions.
4. The method of claim 1 , wherein the TiN electrode has an electrochemical capacitance that is ten to a thousand times that of an electrochemical capacitance of a flat TiN electrode with substantially identical dimensions.
5. The method of claim 1 , wherein the TiN electrode has an electrochemical capacitance between 10 picofarads and 1 nanofarads.
6. The method of claim 2 , wherein the deposition technique comprises direct current (DC) reactive sputtering from a titanium target.
7. The method of claim 1 , wherein a portion of the second dielectric layer covers a portion of the TiN electrode after the well is formed, and wherein the well has an opening above an uncovered portion of the TiN electrode, and wherein a base surface area of the TiN electrode is greater than a base surface area of the opening above the uncovered portion of the TiN electrode.
8. The method of claim 7 , wherein the base surface area of the TiN electrode and the base surface area of the opening above the uncovered portion of the TiN electrode are selected based on a ratio of a capacitance associated with the TiN electrode and a capacitance associated with a membrane that spans across the opening.
9. The method of claim 2 , wherein a portion of the second dielectric layer covers a portion of the TiN electrode after the well is formed, and wherein the well has an opening above an uncovered portion of the TiN electrode, and wherein the electrolyte can diffuse through spaces between the TiN columnar structures or columns of TiN crystals and diffuse vertically down the uncovered portion of the TiN electrode and then horizontally to the covered portion of the TiN electrode.
10. The method of claim 2 , and wherein the conditions are tuned to deposit TiN columnar structures or columns of TiN crystals above the conductive layer comprise using a pressure of at least 25 mTorr for sputtering.