Infrared Sensitive Film Of Vanadium Oxide Uncooled Focal Plane Imaging Array

Uncooled infrared sensor technolgy has accelerated rapidly in the past years. Uncooled sensors are being considered to replace cooled sensors in some applications, but most importantly, the unique characteristics of the uncooled sensors spawn novel uses of the technology.Bolometers and pyroelectric detectors are the most common thermal detectores in uncooled IR sensors technolgy. In this paper, we present the fabrication and the characteristics of the sensing films and the two kind sensors.Highly orientated V2O5 thin films were prepared by sol-gel method on SiO2/Si substrate. The thin films of V2O5 were found converting toVO2 thin films under a temperature above 400 and a pressure below 2Pa in air. It was observed that the reduction process follows the sequence as V2O5 -V3O7-V4O9-V6O13-VO2, namely from VnO2n+,(n=2,3,4,6) to VO2. Annealing the V2O5thin film at 480 , under l-2Pa for 20 minutes, the VO2 polycrystalline thin film with the resistivity change larger than 3 orders through the transition temperature was obtained. The transition temperature was influenced by the heating condition in vacuum.Meanwhile a new method was developed to prepare VO2 thin film directly from V2O5 powder. Pressed V2O5 powder of 99.7% purity was used as sputtering target by argon ion beam. A hydrogen and argon ions mixing beam was implanted into the deposited vanadium oxide film. After annealing, VO2 film with TCR (temperature coefficient of resistance) as high as 4% was obtained. The bombardment of Ar+ could break V-O bond of V2O5 molecule in deposited film and implanted H+ resulting in the deoxidization of V2O5, so the VO2 thin film could be prepared by proper control of the dose of Ar+/H+ implantation. Single sensor, 8*1 and 16*1 linear arrays based on this kind film were fabricated.Nanosized lead titanate (PT) and lead titanate doped with calcium and lanthanum (PCLT) powder obtained by the sol-gel method was added into vinylidene fluoride-trifluoroemylene [P(VDF-TrFE)] to form nanocomposite to be used as the sensing film of the pyroelectric detector. The experiment results show that after mixing in 0.16 volume fraction of PCLT powder, the pyroelectric coefficient of PTTP(VDF-TrFE) composite film was about 37% higher than that of the pure P(VDF-TrFE) film prepared under the same condition, and the voltage figure-of-merit of PT/P(VDF-TrFE) composite film was about 22.4% higher. After adding 0.12 volume fraction ofPT powder, the pyroelectric coefficient of PT/P(VDF-TrFE) composite film was about 30% higher and the detective merit was about 21% higher than that of sensors using pure P(VDF-TrFE).The different kinds of pyroelectric sensors were prepared on the porous silicon dioxide, plastic film and bulk silicon substrates respectively. The nanocomposite PCLTTP(VDF-TrFE) film was deposited by spin-coating used as the sensing film, and Ni-Cr film was chosen as upper electrode and absorb layer. The experimental results showed that the substrate of pyroelectric sensor could significantly affect the detectivity. The porous silicon dioxide and PET plastic film substrate could effectively decrease the thermal conduction and the thermal fluctuation noise of the pyroelectric element, increase the voltage responsivity and the detectivity obviously. The results indicated the specific detectivity of PCLT/P(VDF-TrFE) pyroelectric sensors based on porous silicon dioxide and PET plastic film substrates reached 4.2E6 and 3.4E7 cmHz1/2 W-1 respectively, about 1-2 orders of magnitude higher than that of the sensors on bulk silicon substrate formed under the same condition.A 256 elements infrared array was integrated by 3D CMOS technology. Nanosized lead titanate powder doped with calcium and lanthanum (PCLT) obtained by sol-gel method was homogeneously mixed with vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] as the sensing film. PMOSFETs and two 16-bits shift registers were used as the impedance converting and address selection of the elements respectively. The thermal insulation layer was a polyimide film of five mi...