Research On Pyroelectric PZT Thick Film Materials And Uncooled Infrared Devices

Pb(Zr0.3Ti0.7)O3(PZT) thick film was an excellent material for pyroelectric infrared detectors because of its simple preparation proccess, low price and excellent material properties stability. In this dissertation, PZT thick film was prepared by electrophoretic deposition(EPD) method. The effect of low temperature sintering, Si/Pb interdiffusion barrier layer and isostatic cold pressing on the pyroelectric and dielectric properties of PZT thick film were studied. A new thick film detector structure was designed and developed based on bulk silicon micro-electromechanical system(MEMS) technology. The chopping frequency response of the PZT thick film infrared detector was tested. Moreover, the single crystalline PZT nanorod was researched and a porous PZT thick film infrared detector with high detectivity was obtained.Firstly, the effects of suspension(including PH value, PVP content, aging time) and electrophoresis(including voltage, current, time) on the quality of PZT thick film were studied. Patterned PZT thick film was directly deposited using EPD method. The optimal PVP content and PH value were 4 gL-1 and 5 when the concentration of PZT powders in ethanol solution was 20 gL-1, respectively. According to resistance change, the linear model between PZT thick film growing rate and EPD time was given. In our experiments, the line width of the thick film was less than one micron and surface roughness was about 213 nm under the condition of the above mentioned suspension parameters and 30 V electrophoretic voltage. The results indicated that the PZT thick film can be used in the pyroelectric detector.Secondly, the enhancements of pyroelectric coefficient of PZT thick film by Pb5Ge11O3(PGO) sintering additive, TiOx diffusion barrier layer and cool isostatic pressing treatment were studied. The lowest sintering temperature of PGO added PZT thick film could be reduced from 750 °C to 710 °C for the green film density enhanced by isostatic cold pressing. The electronic energy dispersive spectrometer(EDS) proved that thermal oxidized 400 nm TiOx barrier layer could effectively block the Si/Pb diffusion under the 750 °C/1h sintering condition. In case of 3wt% PGO, 400 nm TiOx barrier layer and 280 MPa pressure, the Pc, permittivity(εr), dielectric loss(tanδ), figure of merit for voltage(FV) and figure of merit for detectivity(FD) of the 750 °C/1 h sintered PZT thick film were1.71×10-8 Ccm2K-1, 330, 0.015, 0.023 m2C-1, and 1.0×10-5 Pa-1/2, respectively. The excellent material properties of the PZT thick film on silicon substrate indicated high detective performances of MEMS infrared detectors.Thirdly, a new detector structure with micro-bridges was designed and developed. The structure parameters, including micro-bridges length, width, and Si supporting layer thickness were optimized by Ansys thermal simulation. The detector was fabricated by MEMS technology, such as wet etching, inductively coupled plasma dry etching, photolithography, lift-off and so on. The micro-bridge length, width, and supporting layer thickness were 1 mm, 500 μm and 0 μm, respectively. The specific detectivity(D*) and the time constant of the single PZT thick film infrared were 7.5×108 cmHz1/2W-1(163Hz) and 51 ms, respectively.After that, a new route was proposed to fabricate porous PZT thick film by doping PZT single-crystal nanorod in the film body. Using surfactant PVA and PAA, the [001]-oriented PZT nanorod was synthesized by hydrothermal reaction. The mechanism of the porous structure formation was given based on the EPD process. The porous PZT thick film with low permittivity was developed as a single detector with the structure mentioned above. The D* of this detector was 1.0×109 cmHz1/2W-1.Finally, The growth mechanism of the [001]-oriented PZT nanorod was studied. By comparing the morphology and density of the PZT nanorod grown on different substrate such as Ti foil, TiO2 Al2O3 and NSTO, it was found that the density and adhension of the nanorod was greatly influenced by the Ti atomic activity on the substrate surface. The results indicated that the Ti atom of the substrate induced into nucleation. The PZT nanorod array with high-density was synthesized on NSTO substrate. It was firstly reported that the Pc of the unpolarized PZT nanorod array was about 1.5×10-9 Ccm2K-1.