A PVT-compensated capacitive sensor with sub-1fF sensitivity

Capacitive sensors can be used by biologists, chemists, and medical professionals to detect the presence of specific molecules, or foreign bodies. Using an electrode array with specific surface preparation, and monitoring the capacitive change relative to a control array, one can determine if the molecules of interest are present in the medium. Due to the small size and potentially low concentration of the target objects, the capacitive sensor must have a very high degree of sensitivity. This paper describes the design of a capacitive sensor in a 180 nm CMOS process capable of detecting a change in capacitance as low as 500 aF.