Hydrogen sensing characteristics of TiO2 thin films grown by atomic layer depositon using TTIP precursor with H2O vs. O3 reactants
It has been shown that passive chemiresistive thin film hydrogen gas sensors fabricated using physical vapour deposited (PVD) sandwich of Pt/TiO2/Pt can provide sufficient sensitivity even when operating at room temperature [1,2]. It was also shown that thickness, microstructure and crystallinity of TiO2 have strong effect on the hydrogen sensing characteristics of these thin film sensors [3].
In this work, we have fabricated TiO2 thin films in Pt/TiO2/Pt hydrogen sensing structures using atomic layer deposition (ALD). Using ALD, conformal, pinhole-free and crystalline TiO2 films can be obtained even for thicknesses of 10 and 20 nm, at a moderate temperature of 300 °C [4], which were the conditions used also in this study. In one of our previous works we have shown that ALD TiO2 process using TTIP precursor and O3 reactant produces films with smaller grains as compared to the process with TiCl4 precursor and H2O reactant, which produced larger grains [5]. As the crystallinity and microstructure are key properties for the hydrogen sensing characteristics of TiO2, in this study we have compared 10 and 20 nm thick films made using TTIP with two different reactants, namely H2O and O3. The resulting hydrogen sensing characteristics of these films are discussed in regards to the microstructure of these films, characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). Finally, we discuss the suitability of the Pt/TiO2/TiN diode structure [4] with TiN bottom electrode for the hydrogen sensors in comparison to more commonly used Pt/TiO2/Pt structure.
TiO2, ALD, hydrogen, sensor, TTIP
This work was supported by the Operational Program Integrated Infrastructure for the project: New fabrication technology of sensors, detectors and memristors for intelligent microelectronics in the 21st century, ITMS project code 313011BVN5, co-financed by the European Regional Development Fund (ERDF) (0.5). This work was supported by the Slovak Research and Development Agency under the contract No. APVV-21-0053, an project VEGA 2/0099/22.
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