P4.1 - Self Propagating High Temperature Syntheses and Gas Sensing Properties of BiFeO3 Thin Films

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
P4 - Gas
N. Martirosyan - State Engineering University of Armenia, Yerevan (Armenia)
749 - 754


The acetone, ethanol, petrol and natural gas microminiaturized sensors based on BiFeO3 perovskite oxide are prepared to use the Self Propagating High Temperature syntheses (SHS) method. The SHS’s general laws and characteristics for fabrication of BiFeO3 are studied, that enables more cost effective production than existing commercial processes. One of the most important advantages of SHS are simplicity of the process, no need for external heating, and high reaction rates. As to structural refinement the XRD data are concerned, they are collected over a 2θ range of 20°-60° with a step size of 0.008° and an acquisition time per step of 10.6 s.

The synthesized compositions are grounded by agate boil mill until to obtain particle sizes of 5 to 8 μm. 10% solution of polyvinyl alcohol was added in the milled powders to form a paste, which is pressed under 1000 kg/cm2 pressure and sintered at 750 oC temperature for two hours to create Bi1.1FeO3 ceramic with Bi excess as a target to compensate for the Bi volatilization during pulsed laser deposition. The Au/TiO2 (500/50 nm thick) IDC electrodes are deposited by magnetron sputtering on fused silica substrates and subsequently patterned by Ar ion milling. The BFO films (700 nm thick) are grown by PLD using a KrF excimer laser (λ = 248 nm, τ = 30 ns) operating at 10 Hz with an energy density of 1.5 Jıcm-2. The oxygen pressure during deposition was maintained at 0.01 mbar. A series of samples prepared at different BFO film growth temperatures (varying in the range 550-650 °C) is fabricated. The Au/Ti (500/50 nm thick) pads are deposited by e-beam evaporation on top of BFO films and patterned by lift-off process for electrical characterisations. The pads are coactively connected (using BFO as dielectric) to the bottom contact pads of the IDC structure.

The gas sensitivity as a function of temperature (up to 450 °C) and the concentration (up to 10 vol.%) of analyzed gas in the air present in the test chamber is investigated, the sensors show high sensitivity at temperature of 250-400 °C. The response and recovery times, long-term stability and reproducibility of gas-sensitive elements, as well as the effect of humidity are studied as well.