Reasearches On Uncooled Infrared Focal Plane Array With SiGe/Si Multi-quantum Wells Materials

The infrared ray,especially at 8-14?m,is radiated by targets at normal temperature,which helps people extend the visual spectrum.The uncooled infrared focal plane arrays have been well developed since 1990s with the development of the MEMS.Both the bolometer with vanadium oxide and that with amorphous silicon,developed by ULIS since 2000,achieved greatest success in both commercial and military markets during last three decades.The new generation of alternative solution with novel semi-conductivity materials was proposed in 2006.The material has received attracted great attention due to the advantages of high temperature resistance coefficient(TCR),low intrinsic noise and well compatibility with semi-conductivity processes.Under the background,aiming for the design and manufacture of the good performance(TCR,Thermal steady-state response and NETD)materials applied in bolometer,the work which has been taken in the dissertation lists below.(1)The design for SiGe/Si multi-quantum wells film.The semiconductor thermal electrical performance is dominated by the energy gap between valence and fermi bands.The paper established the relationship between the materials structures and the TCR with the energy bands analysis.Calculations and simulation combined with Finite Element Analysis were taken for the SiGe layer critical thickness epitaxial grown on silicon substrate.Based on the TCR,processes possibilities and other requirements about pixel,the material structures was designed.The TCR values would achieve-3.34%/K to-3.85%/K as calculations.(2)The pixel structures design for the uncooled infrared focal plane.There are differences in terms of infrared absorption,thermal distributions and supporting state between the SiGe/Si MQWs film and traditional detector.The researches have been carried out attentions on the differences.The optimized analysis was conducted with the silicon nitride layer as supporting layer.The "maximum offset" was observed in both theoretically and experimental analysis.The pixel thermal distribution was calculated with the "crosstalk model".The FEM was employed to calculate the thermal steady-state and transient responses in different vacuum levels.The dissertation also illustrated the mechanical characterizations for three common supporting styles with modal and stiffness analysis(L-type,U-type and I-type).The results of thermal and process stress were consistent between the calculations and experiments.(3)The epitaxial growth and characterization of the film.The growth of SiGe/Si cycles and high boron doped silicon layer with UHV-CVD(Ultra-High Vacuum Chemical Vaper Deposition)were carried out by the researchers.Buffer layer applied in the design achieved good lattice quality without obvious misfits and slips.The Ge and boron concentration of the film was characterized by XRD.Rocking curves is a more reasonable way in the film concentration characterization.The Ge concentration was between 27.08%and 29.93%.The thickness of the cycle was between 40.8nm to 41.1nm.The dissertation illustrated a simple structure in TCR tests.The structure consists of Al electrodes(also as masking layer in etching process)and highly-doped boron as electric channels.The material TCR was between-2.84%/K to-2.97%/K as the tests,showing the energy gaps is between 0.18eV and 0.19eV,which agrees the simulation value 0.22eV in Chapter 2.(4)The characterization of the bolometer.Both chips and devices level tests were conducted for the verification in signal transmission.The absorptivity and electrical performance of the pixel were tested with in-situ tests.The thermal conductivity and thermal time constant were tested by thermal response experiment in vacuum.Relative spectral response tests were carried out to characterize the noise-spectrum of SiGe/Si MQWs materials in the pixel.The NETD tests were taken to characterize the device noise quality in standard black body infrared radiation.The NETD value is 69.34mK for 4×4 test arrays in the paper.