A passive wireless integrated humidity sensor

This paper presents a single-chip integrated humidity sensor (IHS) capable of wireless operation through inductive coupling with a remote transmitter. The 1.5/spl times/0.5/spl times/8mm/sup 3/ sensor chip consists of a planar electroplated copper coil (20 /spl mu/m thick, 30 /spl mu/m pitch, and 23 turns) and a silicon substrate separated by a 4100-5600 /spl Aring/ polyimide film. The resonant frequency of the IHS changes with humidity and the measured sensitivity ranges from 4-16 kHz/%RH. Measurements show a hysteresis of 4.5%RH over a range of 30-70%RH for a 5600 /spl Aring/-thick polyimide film IHS.