I. Hotovy

Sensing characteristics of NiO thin films as NO2 gas sensor

Abstract In this paper we present the results concerning the characterisation of nickel oxide thin films deposited by d.c. reactive magnetron sputtering. Different NiO thin films have been prepared by changing some deposition parameters, as the oxygen content in the reactive plasma and the sputtering mode (metal- or oxide-sputtering mode). The structure and surface morphology of the samples have been analysed by XRD and by atomic force microscopy and scanning electron microscope, respectively. The electrical responses of the NiO films towards NO 2 have been also considered. NiO thin films showed good responses to low NO 2 concentrations (1–10 ppm) with a maximum at 160 °C operating temperature.

Preparation of nickel oxide thin films for gas sensors applications

Abstract Nickel oxide (NiO) thin films were prepared by dc reactive magnetron sputtering from a nickel metal target in an Ar+O2 mixed atmosphere in two sputtering modes. The oxygen content in the gas mixture varied from 15% to 45%. The films prepared in the oxide-sputtering mode were amorphous while the films in metal-sputtering mode exhibited polycrystalline (fcc) NiO phase. In this case TEM observations showed a dense fine-grained structure with the grain size in the range 4–10 nm and AFM micrograph showed a rough surface with RMS=2.21 nm. We have found that good NiO stoichiometric films are obtainable with a polycrystalline (fcc) structure at 40% oxygen content in the metal-sputtering mode.

Study of Annealed NiO Thin Films Sputtered on Unheated Substrate

Nickel oxide (NiO) thin films were deposited on unheated Si substrates by reactive dc magnetron sputtering. Post-deposition annealing was carried out for NiO films in dry air. The effect of annealing temperature (from 500 to 900°C) on the structural, compositional and surface morphological properties of thin NiO films was investigated. The films were characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). Only the as-deposited films in the metal-sputtering mode were crystalline. Annealing in dry air led to the formation of crystalline phases in all samples. During the annealing process, changes in the crystal structure occurred. All examined NiO films were semiconductors and their conductance increased by four orders of magnitude between 25 and 350°C.

RBS study of amorphous silicon carbide films deposited by PECVD

We present properties of nitrogen-doped amorphous silicon carbide films that were grown by a plasma enhanced chemical vapour deposition (PECVD) technique and annealed by pulsed electron beam. Samples with different amounts of N were achieved by a small addition of ammonia NH3 into the gas mixture of silane SiH4 and methane CH4, which were directly introduced into the reaction chamber. The actual amount of nitrogen in the SiC films was determined by Rutherford backscattering spectrometry (RBS). A simulation of the RBS spectra was used to calculate the concentration of carbon, silicon and nitrogen.

The compound oxides based on TiO 2 and NiO thin films for low temperature gas detection

The multilayer compound thin films, consisted of metal oxides (TiO2 and NiO) prepared by dc magnetron sputtering technique, have been studied. The structural, compositional, electrical and gas sensing properties have been investigated by XRD, GDOES and Van der Pauw method considering changes in layout, annealing temperature and addition of Au noble metal catalyst. The Au modified compound oxides exhibit fast response and enhanced sensitivity to hydrogen at low operating temperatures.

Preparation and structural characterization of nickel oxide films for gas sensor devices

Nickel oxide (NiO) thin films were prepared on Si substrates by dc reactive magnetron sputtering from a nickel metal target in Ar+O/sub 2/ with O/sub 2/ content varied from 15 to 50%. The effects of the O/sub 2/ gas content on the deposition rate, structure, composition and electrical properties were investigated. We have found that the good NiO stoichiometric films are obtainable with a polycrystalline structure and a resistivity of near 300 /spl Omega/cm at 25% oxygen content. But either the resistivity or the composition and structure suffer variations with the discharge parameters. Depending on the oxygen content, the deposited films have both amorphous and polycrystalline structures and the Ni/O ratio ranges between 0.71 and 1.02.

Sputtered NiO thin films for organic vapours testing

NiO thin films were prepared by dc reactive magnetron sputtering with thicknesses of about 50 and 100 nm on alumina and KCl substrates. The deposited films were annealed in a furnace at 500°C in nitrogen atmosphere for 2 hours. From XRD and TEM investigations were found that annealed NiO thin films have a polycrystalline structure with the size of grains below 25 nm. The electrical responses of NiO sensor structures towards different ethanol, acetone and toluene concentrations have been measured. It was found that the thickness of NiO films is an important parameter in determining the sensitivity of prepared gas sensors.

Study of optical and electrical properties of sputtered indium oxide films

The indium oxide films were deposited by dc reactive magnetron sputtering from In target on unheated Si substrate with oxygen flow in the ranging from 40 to 80 sccm. The deposited films were annealed in a conventional tube at T=400°C for 1 hour in N<inf>2</inf> atmosphere. Measured absorption coefficients of all indium oxide films were in the range the values of 2.6÷12.5×10⁶ m⁻¹. It was found that calculated values of the direct band gap and indirect band gap depend on oxygen content in the sputtering gas mixture. Electrical resistivity increased from 6.8×10³ to 28.5×10³ Ωcm with increasing oxygen flow 40 – 80 sccm. Finally, the correlation between optical properties and surface roughness of examined samples was identified.

Preparation and properties of micro-hotplates for gas sensors based on GaAs

In this work, analysis of three different heating systems for two types of Pt micro-hotplate is reported: GaAs bulk structure (bulk GaAs), polyimide/GaAs bulk structure (PI-GaAs) and AlGaAs/GaAs suspended membrane structure (AlGaAs/GaAs). Complex electro-thermal characterization of prepared micro-hotplates was realized. Maximal reachable temperature of suspended membrane heating structure was 260degC with corresponding power 36 mW compared with the GaAs bulk structure with maximal temperature 220degC and corresponding power 1.5 W. At temperatures and powers above maximal limits, degradation and destruction of heating meanders occurred. Power consumption P200degC of sample on GaAs bulk substrate was 850 mW, and on PI/GaAs bulk substrate 380 mW, whereas power consumption of sample prepared on AlGaAs/GaAs suspended membrane was significantly lower about 26 mW.

Au-NiO nanocrystalline thin films for sensor application

Nanocrystalline NiO thin films were deposited by dc reactive magnetron sputtering in a mixture of oxygen and argon and subsequently coated by Au on a NiO film surface. Very thin Au overlayers with a thickness of about 1 and 7 nm have been prepared by magnetron sputtering. Then, the surface modified NiO films have been analysed by TEM, EDX and SEM. NiO thin films showed a polycrystalline structure with the size of nanocrystals ranging from a few nanometers to 10 nm. Electrical responses of NiO-based structure towards hydrogen have been measured.