Flow sensing in hostile environments is of increasing interest for applications in the automotive, aerospace, and chemical and resource industries. There are thermal and non-thermal approaches for high-temperature flow measurement. Compared to their non-thermal counterparts, thermal flow sensors have recently attracted a great deal of interest due to the ease of fabrication, lack of moving parts and higher sensitivity. In recent years, various thermal flow sensors have been developed to operate at temperatures above 500 °C. Microelectronic technologies such as silicon-on-insulator (SOI), and complementary metal-oxide semiconductor (CMOS) have been used to make thermal flow sensors. Thermal sensors with various heating and sensing materials such as metals, semiconductors, polymers and ceramics can be selected according to the targeted working temperature. The performance of these thermal flow sensors is evaluated based on parameters such as thermal response time, flow sensitivity. The data from thermal flow sensors reviewed in this paper indicate that the sensing principle is suitable for the operation under harsh environments. Finally, the paper discusses the packaging of the sensor, which is the most important aspect of any high-temperature sensing application. Other than the conventional wire-bonding, various novel packaging techniques have been developed for high-temperature application.

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Thermoresistive properties of a Cubic Silicon carbide (3C-SiC) on glass sensor are studied. The negative temperature coefficient leads to an increasing signal with increasing flow velocity.  The relationship between the geometry of the SiC heater and the sensor performance is studied. A larger heater leads to a higher sensitivity.  Influence of flow direction on the sensor performance was studied. Downstream sensor is more sensitive.  The developed SiC thermal flow sensor combines the advantages of simplicity, low power consumption, high sensitivity and full dynamic range of air flow.

The experimentally observed inverse temperature dependence of the reverse gate leakage current in AlGaN/GaN HEMT is explained using a virtual gate trap-assisted tunneling model. The virtual gate is formed due to the capture of electrons by surface states in the vicinity of actual gate. The increase and decrease in the length of the virtual gate with temperature due to trap kinetics are used to explain this unusual effect. The simulation results have been validated experimentally.

Pb(Zr0.53Ti0.47)O3 (PZT) thin films have been successfully deposited on glass, silicon and ITO coated glass substrates by a 3.3 kJ Mather type dense plasma focus device. The x-ray diffraction spectra of the films deposited on glass substrates kept at a distance of 4.2 cm from the top of the anode with 10, 15 and 25 shots show peaks at 2θ = 31.3° corresponding to the perovskite phase of PZT. Transmission electron microscopy shows the presence of 0.5 nm grains of PZT. The leakage current density is found to be 10−6 A cm−2 at a reverse voltage of 1 V, from current density–voltage (J–V) characteristics. The capacitance–voltage (C–V) characteristics show a counter-clockwise hysteresis loop with a memory window of 1.2 V. The ferroelectric characteristic has been confirmed using the polarization–field hysteresis loop. The resistance of the film is about 1 GΩ. The spontaneous polarization, remanent polarization and coercive field values are found to be 20.1 µC cm−2, 8.6 µC cm−2 and 79.9 kV cm−1, respectively.