The performance of a VO 2 thin-film microbolometer has been investigated. The device is operated within 35°C Ͻ T Ͻ 60°C, in the hysteretic metal-insulator transition region. An algebraic hysteresis model has been used to model the resistance-temperature characteristic of the sensor. It accurately describes the resistance versus temperature characteristics of the material. Employing this model, and in conjunction with established bolometer theory, the responsivity of a VO 2 film is calculated and compared with experimental data. Superior performance of the device is achievable under conditions of single pulse incident radiation where the operating point remains on the major hysteresis loop. This results in a pronounced responsivity peak within the center of the metal-insulator transition. Continuous periodic excitation, in contrast, leads to a steadily decreasing and much lower sensitivity at higher temperature, due to the formation of minor hysteresis loops and the loop accommodation process.
Published by the AIP PublishingArticles you may be interested in Studies on electric triggering of the metal-insulator transition in VO2 thin films between 77 K and 300 K Geometric confinement effects on the metal-insulator transition temperature and stress relaxation in VO2 thin films grown on silicon J. Appl. Phys. 109, 063512 (2011); 10.1063/1.3556756Thermal conductivity and dynamic heat capacity across the metal-insulator transition in thin film VO 2 Appl. Phys. Lett. 96, 151906 (2010); 10.1063/1.3394016
Near-zero IR transmission in the metal-insulator transition of V O 2 thin filmsThe thermal dynamics of thin vanadium dioxide films at the martensitic metal-insulator phase transition has been evaluated experimentally by thermal excitation spectroscopy. Over the transition region, the device becomes highly nonlinear, and its bolometric performance is affected. At low thermal cycling rates for a temperature around the percolation threshold, the device stochastically switches into an unusual pattern. The originally smooth and monotonic shape of the R(T) curve for minor loops suddenly becomes unstable and unpredictable. By direct observation of at least two strange attractors, the phenomenon clearly has been identified as chaotic. Bolometric performance of VO 2 based devices in the transition region may suffer strong degradation for low thermal cycling rates. In this region, sensor responsivity for periodic thermal excitation is significantly reduced. Resistance noise is 1/f -type and self-generated oscillations were observed at frequency Ͻ10 Ϫ2 Hz.
An experimental prototype of an anemometer with PWM excitation is described. The instrument employs a thermistor as a flow detection sensor heated by a PWM voltage. An electronic negative feedback circuit substitutes the thermal power absorbed by the fluid from the heated sensor, and maintains it at a constant temperature. The pulse width contains the information about the fluid velocity and using a timer counter, the velocity information can be available in the digital form, without the use of a conventional A/D c0nverter.Tes.t results are also presented.
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