Ion sensing with deep trench isolation varactors

A method, comprising:

• sensing an ionized fluid via a sense electrode;
• charging a first varactor via the sense electrode based on the sensing an ionized fluid, wherein the first varactor comprises a conductor in a dielectric in a deep trench in a substrate, the conductor biased to create a depletion region in the substrate proximate the deep trench;
• measuring a capacitance on the first varactor;
• and
• outputting a fluid property signal corresponding to the measured capacitance on the first varactor.

A fluid property sensor made by a process comprising:

• doping a substrate to form a first well;
• etching a deep trench in the substrate;
• forming a dielectric in the deep trench;
• forming a conductor within the dielectric in the deep trench, wherein the substrate forms a bottom electrode of a deep trench isolation varactor and the conductor in the deep trench forms a top electrode of the deep trench isolation varactor;
• and
• electrically communicating with the top electrode of the deep trench isolation varactor a sense electrode operable to become electrically charged when interacting with an ionized fluid.