Control of Electrical and Optical Parameters of Humidity Sensors Active Elements Based on Tin Oxides Films with Variable Composition

Abstract

The aim of this work is development of technique for synthesis of tin oxides films with various stoichiometric composition, characterized by high electrical conductivity and light transmittance in the UV and visible range of the electromagnetic spectrum, for their further application as humidity and gas sensors, as well as electrodes for electro-and photocatalytic converters.Nonstoichiometric SnO/SnO2 /SnO2−δ films were synthesized by reactive magnetron sputtering of tin onto glass substrates in argon plasma with oxygen addition and with subsequent thermal oxidation of the formed layers in air. To change the structural, optical, and electrical properties of the films and to find out the optimal synthesis parameters, the oxygen content during the deposition process and the annealing temperature in air were varied in the range of 0–2 vol. % and of 200–450 °C, respectively. The characterization of the films was carried out using a 4-probe method for measuring the electrical resistance, X-ray diffraction, and optical spectroscopy of light transmission.As a result of a comprehensive analysis of the structural, optical and electrical properties of the films, it was found that the optimal synthesis parameters to obtain the most transparent and conductive coatings promising for use as humidity, gas sensors and in photovoltaic devices are the following: oxygen content in argon plasma during sputtering process is ≈ 0,8–1,2 vol. %, the annealing temperature in air is ≈ 350–375 °C. In this case a polycrystalline film with high electrical conductivity and high transmittance in the visible and UV regions of the electromagnetic spectrum with prevailing of tin dioxide phase with structural defects (oxygen vacancies) is formed.

Nonstoichiometric tin oxide films: study by X-ray diffraction, Raman scattering and electron paramagnetic resonance

“…Nonstoichiometric SnO/SnO 2 /SnO 2−δ films were fabricated by DC magnetron sputtering in the argon plasma of tin onto glass substrates with a subsequent thermal oxidation of the formed layers in air [20]. In order to change the phase and stoichiometric composition, the electrical conductivity and transmission coefficient of the films, reactive magnetron sputtering in the argon-oxygen plasma was applied.…”

“…Besides that, the structural, electrical and optical properties of the fabricated tin oxide films of a mixed stoichiometric composition were controlled by temperature of annealing in air atmosphere. It was found that the 2-stage heat treatment process with the isothermal annealing at 200°C (near the melting temperature of Sn) followed by high temperature annealing in the temperature interval 375-450°C provided a possibility to fabricate conductive and transparent tin oxide films [20].…”

“…We proposed earlier the method of fabrication of tin oxide films with a different phase and stoichiometric composition with a possibility to synthesize samples with various parameters (electrical conductivity, band gap width, transmission coef-ficient in the visible and UV range of electromagnetic spectra) [20].…”

Features of water vapor adsorption and desorption on the surface of non-stoichiometric tin dioxide films

“…Возможность управления стехиометрическим составом диоксида олова представляется очень важной для его использования в качестве активного материала датчиков влажности и газов. Ранее нами была предложена методика получения пленок оксидов олова, позволяющая варьировать их фазовый и стехиометрический состав (в том числе концентрацию кислородных вакансий в диоксиде олова) посредством изменения технологических параметров синтеза [17][18][19].…”

“…Напыление производилось в среде аргона с добавлением кислорода, содержание которого не превышало 1 об.%. Как нами было установлено ранее [17][18][19], данный метод позволяет получать нестехиометрические тонкие пленки с варьируемой в широком диапазоне величин электропроводностью (из-за различной концентрации кислородных вакансий), а также изменять их фазовый состав. В настоящей работе электропроводность пленок варьировалась посредством изменения температуры отжига на 2-й стадии в диапазоне 350-400 °C.…”