1. An electronic device comprising two capacitors connected in series and sharing a common electrode; one of said capacitors comprising a region of a semiconductor substrate, with said region being spaced from the common electrode by dielectric; the other of said capacitors comprising a second electrode over the first electrode, with said second electrode being spaced from the first electrode by ion conductive material; wherein at least one of the first and second electrodes has an electrochemically active surface directly against the ion conductive material.