Four-Wire Impedance Spectroscopy on Planar Zeolite/Chromium Oxide Based Hydrocarbon Gas Sensors

Abstract

Impedometric zeolite hydrocarbon sensors with a chromium oxide intermediate layer show a very promising behavior with respect to sensitivity and selectivity. The underlying physico-chemical mechanism is under investigation at the moment. In order to verify that the effect occurs at the electrode and that zeolite bulk properties remain almost unaffected by hydrocarbons, a special planar setup was designed, which is very close to real sensor devices. It allows for conducting four-wire impedance spectroscopy as well as two-wire impedance spectroscopy. Using this setup, it could be clearly demonstrated that the sensing effect can be ascribed to an electrode impedance. Furthermore, by combining two- and four-wire impedance measurements at only one single frequency, the interference of the volume impedance can be suppressed and an easy signal evaluation is possible, without taking impedance data at different frequencies.

Zeolite-based Impedimetric Gas Sensor Device in Low-cost Technology for Hydrocarbon Gas Detection

“…The influence of the Cr 2 O 3 film on the zeolite-based impedimetric sensor is clearly demonstrated in Fig. 1, a result of the previous study [28] showing the state-of-the-art. Two sensors are shown, one without and one with Cr 2 O 3 interfacial layer (Fig.…”

“…During the firing process of the zeolite paste, chromium diffused through the gold, got oxidized, and formed a thin Cr 2 O 3 film [8]. As suggested in [8] and as clearly demonstrated in a subsequent study [28], the Cr 2 O 3 interfacial layer between Au electrodes and zeolite functional material is essential for the gas-dependent sensor behavior. The influence of the Cr 2 O 3 film on the zeolite-based impedimetric sensor is clearly demonstrated in Fig.…”

“…In these initial studies, this very thin layer of Cr 2 O 3 developed during the standard preparation process of the gold electrodes, where chromium is used as a bonding agent. By XPS analyses it has been proven that a closed chromium oxide film occurred on top of the gold interdigitated electrodes during the firing step of the zeolite thick-film paste [28]. If the zeolite/Cr 2 O 3 interface is missing (Fig.…”

“…Data of the sensor as it is state-of art (modified from [28]). Nyquist plots of measurements in base gas and with 500 ppm C 3 H 8 added to the base gas of 2.5 % H 2 O and 10 % O 2 in N 2 .…”

Planar Microstrip Ring Resonator Structure for Gas Sensing and Humidity Sensing Purposes

“…In typical chemiresistors, gas sensitive functional films [1,2], especially of zeolite films, are applied on interdigital electrodes and their resistances or their complex impedances are determined [3][4][5][6][7][8]. Mostly, sensors are operated in the range of room temperature to 400 °C.…”