Study On The (Ba_0.65Sr_0.35)TiO₃ Pyroelectric Thin Films Materials And Infrared Detectors

Infrared sensors using pyroelectric materials shows some advantages as compared with the other types of infrared sensors such as photoconductors, thermopiles and resistance bolometers, because the pyroelectric can be operated even at room temperature, has little wavelength dependence of the response over wide infrared ranges and has fast response. (Ba,Sr)TiO3 (BST) thin film is currently one of the most interesting pyroelectric materials for uncooled infrared detectors and focal plane arrays application due to its high dielectric constants under the operational temperatures and fields coupled with very high pyroelectric coefficients. In the dissertation, BST thin films were deposited by inverted cylindrical magnetron sputtering, time dependent dielectric breakdown of BST films and fabrication of integrated BST thin film single element detectors were detail investigated. The main results are as follow:1.New inverted cylindrical magnetron (ICM) sputtering gun was developed to avoid re-sputtering and increase deposition speed. In the new ICM sputtering gun, hollow cylindrical BST ceramic target were double open-ended, and NdFeB magnets were even well-distributed arranged at the outside of BST ceramic target. Comparing to conventional inverted cylindrical sputtering gun, BST films deposition was increased by 4-5 times in radio frequency sputter system. For 500nm BST thin films, the deposition time was shortened to 8 hours. The improvement promoted the temperature compatibility of the Pt-Ti-W metallization readout IC to the BST thin films preparation process.2.Low-temperature self-buffer layer was developed to decrease leakage current and increase pyroelectric coefficient of BST films. For BST films grown on Pt/Ti bottom electrodes, large leakage current was attributed to coarse Pt/BST interface, and low pyroelectric coefficient was attributed to random orientation of BST films. (001) BST thin films were deposited on Pt/Ti/SiO2/Si substrates by using a low-temperature self-buffered layer. XRD and AFM investigations show that the microstructure of BST films strongly depends on surface morphology of annealed self-buffered layer. The mechanism of nucleus formation and growth initiation of BST films on self-buffered layers was proposed. It was found that the pyroelectric properties of BST films can be greatly enhanced. The pyroelectric coefficient and material merit figure of (001)-BST films are 7.57×10-7 C cm-2 K-1 and 2.18×10-4 Pa-1/2, respectively.3.Mechanism and controlling method of TDDB were investigated to make BST films work reliably under DC biased voltages. The TDDB of BST thin films were divided into two process, soft breakdown and hard breakdown, according to leakage current dependent with measuring time. At soft breakdown state, BST thin films had dielectric and pyroelectric properties, just leakage currents were sharply increased. At hard breakdown state, BST thin films were dielectric breakdown. The leakage currents of soft breakdown BST thin films can be recovered to initial low leakage current status by reverse bias voltages.The phenomena can be explained using oxygen vacancies. When electrons were injected into BST films, they were trapped by oxygen vacancies, and formed space charge. The process changed built-in electric field, and influenced leakage current through BST films. Leakage currents in BST thin films double capacitance element were almost independent with measuring time under dynamic bias voltages. The method eliminate BST thin films' TDDB, would make BST thin films infrared detectors work reliably under biased voltages.4. BST thin films single element infrared detectors were fabricated using semiconductor patterning method. Pt bottom electrodes and NiCr top electrodes were patterned by lift-off method. BST thin films were patterned by wet etching method. The optimized etching parameters were that HF:HCl:H2O=1:2:20, temperature 30℃,etching velocity 21.2nm/s, error amount 0.6um. BST thin film detectors were prepared with sensitive area ranging from 0.13 mm2 to 0.79mm2. The detectivity of 1.2×108cmHz1/2W-1 was obtained in the BST thin films infrared detectros thermally isolated by 500nm SiO2 thin films.