What are the limits on capacitance measurement?
With the current state of capacitance measurement technology, it is possible to measure capacitance changes between 2 unearthed electrodes of 0.2 fF in the presence of stray capacitance to earth of 200pF at a rate of 2000 measurements per second. This sets a practical lower design limit on the smllest capacitance between any pair of electrodes of around 10fF. Sensors with inter-electrode capacitances lower than 10fF will usually produce very noisy and unstable images.
