Research On The Characteristics Of Micro/nano Structured Vanadium Dioxide And Their Applications

The appearance of high-sensitivity uncooled infrared focal plane arrays is considered as the most significant achievement in IR engineering during the last twenty years. The devices have recently gained broad attention for infrared imaging applications, due to their advantages such as low cost, light weight, low power, wide spectral response, and long term operation compared to cooled photon detectors.Microbolometer is a type of uncooled infrared thermal detectors. It uses a surface-micromachined process to integrate heat-sensitive detector arrays with CMOS read-out IC. Currently, microbolometer arrays based on VOx heat-sensitive material have been fabricated with 640×480 array formats and 25μm×25μm pixel sizes, and the NETD approaches 12mk. However, there is still amounts of room to improve the performance of these devices through improving the properties of the heat-sensitive material.In this dissertation, the fabrication and performance of microstructure and nanostructure heat-sensitive VO2 thin films for microbolometer are presented. The major work is to investigate the applications of the two kinds of VO2 thin films on infrared detectors, described as followings.(1) Conventional microstructure VO2 thin films have been fabricated by DC magnetic sputtering. The phase transition temperature for as-fabricated heat-sensitive VO2 films with the grain size of 1~2μm is around 68℃, and the TCR of this heat-sensitive material is about -2.2%/K in the semiconductor region.(2) Novel nanostructure VO2 thin films are prepared using reactive ion beam sputtering and post annealing. The phase transition temperature for the nano-VO2 films with the grain size of 8~10 nm is 35℃. The TCR of this heat-sensitive material is about -7%/K in the semiconductor region, which is more than 3 times higher than that of the conventional microstructure VO2 thin films.(3) Linear infrared sensors with 128 elements based on both the nanostructure VO2 thin films and the conventional microstructure VO2 thin films are fabricated with the same design, respectively. The comparative tests of the two kinds of sensors are conducted. The results of the tests show that the performance of the device based on the nanostructure VO2 thin film is improved greatly compared with the device based on the conventional microstructure VO2 film. The former is 2~3 times better than the latter.(4) The flexible microbolometers based on the microstructure VO2 thin film are fabricated on bisbenzocyclobutene (BCB) substrates. The test results show that the responsivity and the detectivity of the device at the black body temperature of 800K and with the chopper frequency of 3Hz are 7×103V/W and 7×107cmHz1/2/W, respectively.(5) The 32×32 microbolometer array are fabricated based on the microstructure VO2 thin films. The responsivity of 1.47×104 V/W and the NEP of 4.14×10-10 W are obtained at a pulse bias of 1V.(6) The improvement of the low transmittance in the visible region of the smart window based on the low-temperature phase transition nanostructure VO2 thermochromic thin films is studied. A decent result is obtained by coating a SiO2 anti-reflection layer on nanostructure VO2 smart window. The transmittances of the smart window of the VO2 thermochromic thin films at both the semiconductor phase and the metallic phase are improved to some degree.