Joni Huotari

Exploring the gas sensing performance of catalytic metal/ metal oxide 4H-SiC field effect transistors

Gas sensitive metal/metal-oxide field effect transistors based on silicon carbide were used to study the sensor response to benzene (C6H6) at the low parts per billion (ppb) concentration range. A combination of iridium and tungsten trioxide was used to develop the sensing layer. High sensitivity to 10 ppb C6H6 was demonstrated during several repeated measurements at a constant temperature from 180 to 300 °C. The sensor performance were studied also as a function of the electrical operating point of the device, i.e., linear, onset of saturation, and saturation mode. Measurements performed in saturation mode gave a sensor response up to 52 % higher than those performed in linear mode.

Improved chemical sensors track and control emissions

Sensitive, low-cost silicon carbide-based gas sensors can detect toxic emissions and hazardous nanoparticulate matter in previously untenable environments.

Chemical sensor systems for environmental and emission control

Focusing on environment and health aspects, the importance of monitoring and controlling dangerous gases and particulate matter increases. For this purpose we present a new version of silicon carbide based gas sensors with improved properties and suitable for high temperature and harsh environments such as power plants or car exhausts. Development of sulfur dioxide sensors for a power plant application is described as well as sensors for detection of ammonia in connection with the SCR process where urea is converted to ammonia, which reduces nitric oxide components in the exhausts. We also describe progress on nanoparticle detection, especially related to detection of the content of adsorbed particles through heating and detection of emitted molecules by a sensor array. Some results are also presented from impedance spectroscopy for detection of the concentration of nanoparticles but with the potential to reveal more details about the particles such as shape and kind of particles.

3.3.2 Gas Sensing Properties of Pulsed Laser Deposited Vanadium Oxide Thin Films

Vanadium oxide thin films were fabricated by pulsed laser deposition (PLD). The crystal structure and symmetry of the deposited films was studied with X-ray diffraction (XRD) and Raman spectroscopy, respectively. The surface morphology was studied with atomic force microscope (AFM). The thin films consisted mostly of V2O5 phase of vanadium oxides, but also of another phase, which is generally found in form of nanotubes. The measured optical transmission spectra of the films also supported the existence of different phases. The electrical resistivity of the films as a function of temperature behaved like in a typical semiconductor. The gas sensing properties of the films were characterized for different NO concentrations. The results showed a response to NO, which varied from oxidative to reducing according to the film composition.

Dielectric and Tunability Properties of Nanostructured Nd-modified Pb(ZrxTi1-x)O3 Thin Films up to Microwave Frequencies

Dielectric properties of nanocrystalline Nd-modified Pb(ZrxTi1-x)O3 thin films were studied in frequency range f = 100 Hz –20 GHz. Thin films were prepared by pulsed laser deposition on MgO(100) substrates. Inter-digital electrodes and coplanar waveguide transmission line technique were used for dielectric characterization. In the dielectric function ɛr(f, T), two interesting anomalies were found at low frequencies. Diffusive phase transition had relaxor-type behaviour, and an extra dielectric relaxation maxima were found below Curie temperature TC. At higher frequencies above 5 GHz, relative permittivity ɛr(f) response was flat up to 20 GHz, and high maximum tunability nr,max = 19% was achieved.

7.4.2 Chemical Sensor Systems for Emission control from Combustions

Environmental and health concern has increased the importance to monitor and control emissions from combustion processes like toxic gases and particulate matter. The SiC-FET technology offers versatile and powerful sensors for gas detection also in combination with combustion of particles. Emission control has been demonstrated e.g. for small and medium sized power plants and diesel exhausts. The potential danger of nanoparticles makes such detectors interesting not only for detection of concentration and size of particles but also detection of the content of particles. The SiC-FET technology lends itself for smart sensing and smart data evaluation, which largely improves the information from such a sensor system. Here we report progress on the sensor technology itself, the application of a sensor system as an alarm for ammonia emission and preliminary results of particle detection.