Research On The Vanadium Oxide Film And Uncooled Infrared Detector Array

The development of infrared detector arrays capable of imaging scenes at room temperature has been an outstanding technical achievement and enables a new revolution in infrared technology since 1990s. Compared with cryogenic photon infrared detector arrays, since cooling to cryogenic temperatures is not required, major reductions in package complexity and cost can be achieved for uncooled focal plane arrays (FPAs). The elimination of the cryogenic coolers also reduces power consumption and improves device reliability, thus, room temperature FPAs have significant cost, weight, power and reliability advantages over cryogenic IRFPAs.Major types of high performance uncooled thermal infrared FPAs include bolometer and pyroelectric detectors, in which the microbolometer has the lowest unit cost, as it uses a monolithic fabrication process that is compatible with standard silicon process. Chopperless operation can be obtained using the microbolometer, thereby eliminating all mechanical parts from the imaging system. This not only decreases the ultimate unit cost, but also improves both the reliability and the operating range. Greater dynamic range and a more linear response make the microbolometer technology more highly suited for wide range of civilian applications besides greatly increased military uses.In this dissertation, the thermal-sensitive materials, operating principles, thermal isolated structure and device integration in microbolometer FPAs have been described in detail. It mainly includes:In the aspect of vanadium oxide films fabrication, firstly, mixed vanadium oxide VOx and metastable phase VO2(B) thin films for uncooled bolometric detectors have been fabricated on Si3N4/Si substrates by methods of low temperature reactive ion beam sputtering and magnetic sputtering in a controlled oxygen atmosphere. The typical growth temperature is kept below 250℃?, which is compatible with the post-CMOS technology. The as-deposited film exhibits sheet resistance and temperature coefficient resistant of 20~50 k? and -2.2%~-2.5%K-1 at room temperature, respectively.Secondly, nanostructural vanadium dioxide thin films are fabricated on Si3N4-film-coated Si and silica substrates using reactive ion beam sputtering and post annealing. A reversible metal to semiconductor phase transition for as-fabricated VO2 films with grain size of 8~10 nm takes place at take place around 34℃, which lowers about 34℃in comparison with a phase transition temperature of 68℃in conventional VO2 films.In the aspect of bolometer FPAs developing, firstly, the heat balance equation for a microbolometer is simplified by introducing effective thermal conductance concept. From the the electrical and thermal model of microbolometer and V-I curve of TCR material, the useful practical equations and numerical estimates for the responsivity under different bias and large radiation signals are derived. Furthermore, the author also considered the noise properties of microbolometer. Using the expressions for signal and noise of bolometer, useful expressions of performance parameters such as noise equivalent temperature difference (NETD), noise equivalent power (NEP), and detectivity is derived, laying the groundwork for future device design.Secondly, one-level 128 linear array and two-level 32×32 array of microbridges have been designed and fabricated on Si substrate by means of surface micromachining, utilizing porous silicon and photo-sensitive polyimide sacrificial layer.Thirdly, Readout Integrated Circuits (ROIC) for microbolometer FPAs have been designed and fabricated on 4-inch silicon wafers. The CMOS fabrication processes produce about 2μm surface roughness on the silicon wafers, which is too rough for the integration with microbolometer array. To acquire a satisfying surface roughness, bisbenzocyclobutene (BCB) spin coating and electroless nickel-plating method have been developed. With those planarization processes, the surface roughness of ROIC dies smoothes from 2μm to less than 0.13μm, which is sufficient for subsequent bolometer FPAs fabrication.Fourthly, the 32×32 microbolometer array is fabricated onto the planarized ROIC using a micromachining process, which is completely compatible with CMOS technology. Measurements and calculations for the fabricated FPAs show that the responsivity of 1.4×104 V/W and a NEP of 8.4×10-10 W are obtained at a pulse bias of 1V and vacuum packaging environments.