Open AccessPassive wireless integrated humidity sensor based on dual‐layer spiral inductors
Author(s) -
Zhang Cong,
Guo Li,
Wang LiFeng,
Huang JianQiu,
Huang QingAn
Publication year - 2014
Publication title -
electronics letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.375
H-Index - 146
eISSN - 1350-911X
pISSN - 0013-5194
DOI - 10.1049/el.2014.1240
Subject(s) - inductor , materials science , capacitor , optoelectronics , humidity , sensitivity (control systems) , capacitive sensing , radio frequency , planar , electrical engineering , electronic engineering , physics , engineering , computer science , voltage , thermodynamics , computer graphics (images)
An integrated humidity sensor capable of passive wireless sensing through inductive coupling is presented. The sensor chip consists of two stacked counter‐rotating planar aluminium inductors (0.5 μm thick, 100 μm in width, 50 μm space and 6 mm outer diameter) separated by a maskless polyimide film. The two inductors are inductively and capacitively coupled together to form a resonant tank, whose resonant frequency changes with humidity. This topology eliminates the need of a connection bridge or via as used in the usual inductor–capacitor humidity sensors and offers higher sensitivity due to the inner humidity‐sensitive parallel‐plate capacitor in contrast with the single‐layer self‐resonant inductor. Three sensor devices with different inductor turns were fabricated and characterised. Measurements show a sensitivity of 45 kHz/%RH with a centre frequency of 50.5 MHz for sensor A (8 turns), 15.8 kHz/%RH, 22 MHz for sensor B (10 turns) and 65 kHz/%RH, 74 MHz for sensor C (4 turns).