Ultrasensitive WO 3 gas sensors for NO 2 detection in air and low oxygen environment

Abstract

We report here on the results of a study into the response of a tungsten oxide based low power MEMS gas sensor to ppb of nitrogen dioxide at low levels of ambient oxygen. It was found that the resistive gas sensors not only had a high sensitivity to NO 2 (3.4%/ppb vs. 0.2%/ppb obtained for commercial MOX) but can still operate reliably at lower oxygen levels (down to 0.5 %) albeit with slightly longer response and recovery times. The optimal operating temperature was determined to be ca. 350°C and so easily within the range of a MEMS based SOI CMOS substrate. The response was sensitive to significant changes in ambient humidity, but was found to have low cross-sensitivity to CO, hydrogen, methane, and acetone even at much higher ppm levels. We believe that these tungsten oxide gas sensors could be exploited in harsh applications, i.e. with a low oxygen (lean) environment often associated in the exhaust gases from combustion systems.

Co3O4 as p-Type Material for CO Sensing in Humid Air

“…They have many advantages: high sensitivity, small size, fast response, and low cost in mass production. n-Type metal oxides are widely used as sensitive materials [1], for example, SnO 2 [2,3], ZnO [4,5,6], In 2 O 3 [7,8], WO 3 [9], TiO 2 [10] and so on. One of the main disadvantages of these materials is their high sensitivity to humidity, which makes it difficult to use them in real outdoor conditions.…”

High Bandwidth Sensor Module for Mobile Robot Applications-Wind Tunnel Characterization

“…The module contains the following sensors: non-dispersive infrared (NDIR, low-cost, low power device developed for CO2 sensing), solidly mounted resonator (SMR, high bandwidth device for VOC sensing), two MOX sensors (MOX1, Pd/Pt doped SnO2 and MOX2, WO3 coated device), temperature and humidity sensor (GE ChipCap2) and particle sensor (Fairchild H21A3). The MOX sensors (operated at 300 °C) are based on an SOI micro hotplate (AMS Sensors) [6]. Response data are recorded (5 Hz sampling rate) by a Freescale KL25Z microcontroller.…”

H2S Sensing in Dry and Humid H2 Environment With p-Type CuO Thick-Film Gas Sensors

“…The gas sensing measurements were performed at the Microsensors and Bioelectronics Laboratory at the University of Warwick using a fully-automated custom rig as illustrated earlier in [11,24]. The CMOS microhotplate substrates were connected to a custom made printed circuit board.…”

“…It is also well known that surface reactions that control detection of target gases by semiconducting metal oxides operating at temperatures below 500 °C generally involve changes in the concentration of surface oxygen species such as O2 − , O − or O 2− , which are stable over a different temperature range [4][5][6]. Only a few reports have been published on the mechanism of the response of MOX sensors in the absence or at trace levels of oxygen concentrations and these sensors employ mainly n-type metal oxides, such as WO3 and SnO2 [7][8][9][10][11]. Among p-type MOX semiconductors, CuO has received some attention for hydrogen sulfide (H2S) detection in air [12][13][14][15][16].…”