EFFECT OF SENSOR CONFIGURATION FOR LOW TEMPERATURE GAS DETECTION WITH SEMICONDUCTING OXIDES

This work presents the results obtained towards NO2 by using TBE and IDE sensor configurations with the same sensing semiconductor layers. It is known that dopants such as Al3+ or Cr3+ can improves the sensing properties of semiconductor TiO2. Nevertheless, temperatures exceeding 400°C are required for reasonable sensor signal. The use of TBE configuration reduces the operation temperature of these sensors far below 400°C requiring no heater. The schematic of such a TBE electrode system is presented in Fig. 1. The sensors with TBE configuration were fabricated in three steps: firstly, 200 nm thick and 300 μm wide bottom Pt electrodes BE were patterned (via sputtering) on a Al2O3 substrates. The possible sensing mechanism is the matter of discussion in terms of depletion region (LD) and the potential barrier between grains (eVs at grain boundaries)

A p-type double layer BaTi(1-x)RhxO3/Al-doped TiO2- sensing electrode for NO2-detection above 600°C

NO2 emission is mostly related to combustion processes, where gas temperatures exceed far beyond 500 °C. The detection of NO2 in combustion and exhaust gases at elevated temperatures requires sensors with high NO2 selectivity. The thermodynamic equilibrium for NO2/NO ≥ 500 °C lies on the NO side. High temperature stability of TiO2 makes it a promising material for elevated temperature towards CO, H2, and NO2. The doping of TiO2 with Al3+ (Al:TiO2) increases the sensitivity and selectivity of sensors to NO2 and results in a relatively low cross-sensitivity towards CO. The results indicate that NO2 exposure results in a resistance decrease of the sensors with the single Al:TiO2 layers at 600 °C, with a resistance increase at 800 °C. This alteration in the sensor response in the temperature range of 600 °C and 800 °C may be due to the mentioned thermodynamic equilibrium changes between NO and NO2. This work investigates the NO2-sensing behavior of duplex layers consisting of Al:TiO2 and BaTi(1-x)RhxO3 catalysts in the temperature range of 600 °C and 900 °C. Al:TiO2 layers were deposited by reactive magnetron sputtering on interdigitated sensor platforms, while a catalytic layer, which was synthesized by wet chemistry in the form of BaTi(1-x)RhxO3 powders, were screen-printed as thick layers on the Al:TiO2-layers. The use of Rh-incorporated BaTiO3 perovskite (BaTi(1-x)RhxO3) as a catalytic filter stabilizes the sensor response of Al-doped TiO2 layers yielding more reliable sensor signal throughout the temperature range