The Structure And Property Of BST Thick Film Uncooled Infrared Focal Plane Array

Ferroelectric thick-film (FTF) uncooled infrared focal plane array (UIFPA) is a key part of new-generation thermal imaging system. Pyroelectric IFPA has advantages of low cost, no need of refrigeration, no requirement for infrared wavelength, etc, it has been used in military and civil field. BST FTF has predominant dielectric and pyroelectric effects and may be compatible with semi-conductor technology, so it has become excellent material of UIFPA. Dielectric calorimetry UIFPA use BST as UIFPA has particular advantages.This work has investigated the relation between the noise of the infrared detector, voltage response rate, current response rate and kinds of parameters of BST thick film and structure. The fabrication technology of uncooled infrared focal plane array was improved. The main contents are as follows:The one-dimension, two-dimension and three-dimension models, which were set up for pyroelectric detectors, were analyzed. A kind of micro-bridge structure was provided in this work with desk-type adiabatic frame support, and the analysis results by finite element method showed that the minor thermal conductivity and high responsivity can be obtained.The etching technology of micro-bridge thermal insulation structure and fabrication technology of porous silicon heat insulating layer are researched. The micro-bridge structure with etch-pit depth over 200μm and bridge surface about 200μm×200μm was prepared on a silicon substrate with depth of 240μm, and 16×16 micro-bridge structure array was successfully made. Porous silicon samples were prepared by electrochemical method. The aperture, porosity ratio and film thickness of porous silicon could be controlled by different concentrations of HF solution, current density and reaction time. Micro structure of porous silicon samples was observed and thermal conductivity was analyzed.The stoichiometric proportion and doping of film can be controlled exactly as the result of the preparation of film by sol-gel method. The particle with 60nm in diameter and the films with 200nm in thickness were prepared by microwave sintering technology. The dielectric temperature characteristicε_r was larger than 1000, and tanδwas less than 2%. The influence of La-Mn-Al co-doping on the micro-structure of BST thick film and dielectric properties was analyzed. The co-doping of La, Mn and Al could markedly inhibit the growth of BaSrTiO₃ grain, and polycrystalline particles were precipitated during crystallization of the thick film to enhance the uniformity and compactness of thick film. The influence of unequal-valence and doping amount on the leakage current, dielectric loss and dielectric property was discussed. The Mn-doped BST thick films with six different layers of composition gradients were fabricated in the Pt/Ti/SiO₂/Si silicon chip by improved sol-gel method. The thickness of the thick film was about 5μm. Then the micro structure and dielectric property of the gradient thick film is studied, with dielectric coefficient 920 and dielectric loss approximately 1.8×0^-2. Taking the BST thin film as the interlining between the thick films with different components, the BST dielectric-reinforced interlining thick films of around 20μm thickness were made in the composite LNO/Pt/Ti/SiO₂/Si bottom electrode. The XRD patterns showed that there was only perovskite phase in the interlining thick films through heating treatment at 650℃. The relative dielectric constantε_r and dielectric loss tanδof the interlining thick film by heating treatment at 750℃were approximately 1200 and 3% in the case of 25℃and 1 kHz, respectively. The dielectric-temperature change rate was over 1.2%/℃within a wide range near 25℃. The surface of BST interlining thick film was smooth and compact without any fracture.In this work, we put forward that vertical interconnection could be realized by making use of the technique of Through-Silicon-Via (TSV) to enhance the duty, shorten the interconnect metallic line and cut the signal delay time. A through-hole is formed by silicon wet etching method, and then is filled with high-temperature resisting Ag-Pd conductive paste through use of direct writing technology, so as to realize the interconnection between the bottom electrode of infrared focal plane array and flip chip bonding bump at the back side of silicon substrate.