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With the increasing application of thin-film sensors in high-temperature applications, there is an escalating demand for insulation layers that provide enhanced resistance to elevated temperatures. However, failure often occurs because of the mismatch in thermal expansion coefficients between the insulation layer and the substrate. This study proposes an underlayer comprising a double ceramic layer of CeYSZ and Al 2 O 3 , which preserves the high thermal expansion coefficient and corrosion resistance of CeYSZ while enhancing its electrical insulating properties. The high-temperature electrical insulation performance of underlayers with different ceramic layer structures was experimentally evaluated. The results indicate that the CeYSZ/Al 2 O 3 double ceramic layer exhibits an electrical resistance of 2.1*106 Ω at 800 °C and minimal drift after 5 h, demonstrating high stability. Finally, PdCr thin-film strain gauges were fabricated on CeYSZ/Al 2 O 3 double ceramic layer, revealing the stability of the electrical resistance at high temperatures. The porosity of the underlayer cross-sections was also compared, revealing that the double ceramic layer coating effectively fills pores and cracks inherent in single-layer coatings. This mitigation of conductive pathways reduces the occurrence of such defects, thereby enhancing the high-temperature insulation performance of the underlayer. © 2014 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved. [ABSTRACT FROM AUTHOR]

Thick/thin-film sensors are used for health monitoring of components such as aero-engines, which are mainly cast from electrically conductive nickel-based superalloys. It is necessary to prepare an insulating layer between the nickel-based superalloys and the thick/thin film sensor. For this purpose, a thermally matched multilayer ceramic composite insulating layers for thick/thin-film sensors have been designed. Three dielectric pastes with coefficients of thermal expansion similar to those of the metal substrate and Pt/Rh–Pt thick-film thermocouples were prepared on nickel-based superalloys by screen printing technique. Problems regarding the bonding strength of the insulating layers were solved, which improved the insulating properties. The microstructural characteristics of the insulating layers were characterized by scanning electron microscopy, and their insulation resistance at high temperatures was tested. The results show that the insulation resistance of insulating layers is increased by a factor of about 10 in this paper compared to the insulation resistance of insulating layers prepared by sputtering and other techniques in previous articles. When the temperature is 800 °C, the resistance value of the samples reaches 30.47 MΩ. It is noteworthy that the insulation resistance is still higher than 21 MΩ after annealing at 800 °C for 10 h. Moreover, the insulating coating survived thermal shock tests without cracking or delaminating. A S-type thermocouple is prepared on the insulating layers to verify its high-temperature electrical insulation performance. Test results show that the output voltage of the S-type thermocouple had a high linearity with an average Seebeck coefficient of 10.5 μV/°C during the temperature range of 200–1000 °C. Experiments show that the S-type thermocouple works stably at high temperatures and thermally matched multilayer composite insulation layers have good insulating properties. [ABSTRACT FROM AUTHOR]

There are numerous and significant uses for accurate and reliable humidity detection in day-to-day living. In this study, a QCM humidity sensor based on cellulose acetate/konjac glucomannan (CA/KGM) film was constructed. The elemental composition, morphology and nanostructure of the film were characterized using scanning electron microscopy (SEM), water contact angle tester, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The CA/KGM QCM humidity sensor exhibited excellent stability, selectivity and repeatability with low humidity hysteresis and short response/recovery time (12.3 s/0.1 s). The experimental results show that the introduction of CA in KGM can dramatically improve the mechanical properties and stability of the composite membrane. The humidity sensing mechanism of the sensor was systematically investigated, and water droplet counting test, fingertip moisture detection and human breath detection were performed. The sensor offers a wide range of potential applications. • Electrospinned CA/KGM network-like film was successfully prepared. • CA/KGM thin-film sensors have a maximum humidity hysteresis of 0.64% RH for ultra-low hysteresis. • CA/KGM thin-film sensors have potential for application in a variety of scenarios. [ABSTRACT FROM AUTHOR]

Metal oxide semiconductor heterojunctions and homojunctions are considered to have better performance than single phase material for room temperature hydrogen gas sensing. In this work, TiO 2 facet homojunction (TiO 2 -FH) thin films were prepared by a two-step hydrothermal method. The TiO 2 -FH thin films were decorated with Pt nanoparticles using a green photodeposition method and then evaluated for H 2 sensing. Non-noble metal Al was used as finger electrodes instead of noble metal Pt. Compared with the TiO 2 -FH sensor, the H 2 detection limits of the platinum loaded TiO 2 -FH@Pt sensors are remarkably decreased from 8000 ppm to 1 ppm at room temperature. The optimized sensor achieves an excellent sensing performance of S = 1.21 and fast response / recovery times of about 42 s / 30 s when exposed to 1 ppm H 2 concentration. The synergy between the Schottky barrier at the Pt/TiO 2 interface and the barrier between the (110) and (001) facets of TiO 2 is the key to the improvement of the sensing performance. Replacement of noble metal Pt with Al and C electrodes greatly help to clarify the mechanism of the junctions in the thin film sensors, especially the function of the Pt/TiO 2 junction and the (110)/(001) TiO 2 junction. The simple and green fabrication method and cheap Al interdigitated electrodes are advantageous for practical applications. • Noble metal electrodes of gas sensors were substituted by non-noble metal Al and C. • Trace Pt decorated TiO 2 homojunction was designed for hydrogen sensing. • The sensors maintain the wide detection range and high response. • The Schottky barrier at Pt/TiO 2 interface is the main factor for the sensing performance. • The function of the barrier between the (110) and (001) facets of TiO 2 is clarified. [ABSTRACT FROM AUTHOR]

[Display omitted] • The HfO 2 /Al 2 O 3 multilayer heterogeneous thin-film insulation layer was designed and fabricated. • The multilayer heterogeneous insulation layer could increase the high-temperature electrical resistance from 7.39 × 104 Ω to 1.09 × 106 Ω at 1100 °C. • The equiaxed crystal HfO 2 grains could prevent the cracks detrimental to the electrical insulation from penetrating the insulation structure. • The Hf-O-Al amorphous layer with defects as electron and hole traps at the interface could inhibit the longitudinal migration of carriers. • The simulation analysis of the ITO-In 2 O 3 heat flux sensors with different insulation layers demonstrated that the multilayer heterogeneous insulation layer could meet the high-temperature application requirement of sensors with large sensitive layer resistance. The real-time monitoring of the equipment operating in harsh environment is important for the cooling design and reliability analysis. However, the insulation layer of the thin-film sensors still faces challenges at high temperature, especially for sensors with large sensitive layer resistance. In this study, the HfO 2 / Al 2 O 3 multilayer heterogeneous thin-film insulation layer was designed and fabricated. The minimum resistance of the control structure was 7.39 × 104 Ω at 1100 °C during multiple thermal cycles. However, the minimum resistance of the modified insulation layer was 1.09 × 106 Ω, exhibiting significant electrical insulation improvement. The HfO 2 film could maintain the columnar grains of the TGO film by inhibiting the oxygen transport. Besides, the equiaxed crystal HfO 2 grains could prevent the cracks detrimental to the electrical insulation from penetrating the insulation structure. Meanwhile, the Hf-O-Al amorphous layer with defects as electron and hole traps at the interface could inhibit the longitudinal migration of carriers. As a result, the high-temperature insulation performance of the HfO 2 / Al 2 O 3 insulation layer was greatly improved. Furthermore, the simulation analysis of the ITO-In 2 O 3 heat flux sensors with different insulation layers demonstrated that the multilayer heterogeneous insulation layer could meet the high-temperature application requirement of sensors with the large sensitive layer resistance. [ABSTRACT FROM AUTHOR]