Investigation On The Properties Of Mn-Co-Ni-O Films And Devices

Manganese cobalt nickel oxide?Mn-Co-Ni-O?is a transition metal oxide with cubic spinel structure and excellent negative resistance temperature characteristic.They can be used for temperature sensor,rectifier,uncooled thermal infrared detector,etc.Mn-Co-Ni-O?MCNO?thin films have better physical properties than their bulk materials and they can be used for the preparation of thin film thermal infrared detectors.In this dissertation,MCNO thin films are mainly prepared by magnetron sputtering method and the effects of annealing temperature on the microstructure,surface morphology as well as electrical properties of the films,the performance of the devices are investigated.At the same time,the electrical and optical properties of MCNO thin films with different compositions are studied and the effect of element content on the properties of these samples is analyzed too.In addition to that,the influence of substrate thermal conductivity of thermal infrared detector on the device performance is also studied.In this paper,MCNO thin films doped with other elements are prepared by chemical solution deposition method and the effect of doping elements on the properties of thin films is studied.These results can be concluded as follows:?1?Mn_1.95Co_0.77Ni_0.28O₄ thin films are prepared by magnetron sputtering method and they are annealed at 400 ?,500 ?,600 ?,700 ? and 800 ? respectively.The effects of annealing temperature on the structure,surface morphology and film composition of the films are studied.It is found that the sample annealed at 700 ? has lots of pores in grain boundaries.The surface roughness always increases with the growing of annealing temperature.The mixing entropy of Mn_1.95Co_0.77Ni_0.28O₄ thin films is also calculated and the 800 ? annealed sample has the maximum entropy value.The element proportion for MCNO film with maximum entropy value is calculated according to the mixed entropy theory: When the Co ion in octahedron is +2 valence,the Mn2Co0.67Ni0.33O₄ component has the maximum entropy;When the Co ion in octahedron is +3 valence,the Mn1.5Co1Ni0.5O₄ component has the maximum entropy.?2?The electrical properties of Mn_1.95Co_0.77Ni_0.28O₄ thin films underwent different annealing temperatures are studied and the resistivity of 800 ? annealed sample is the minimal.At low temperature?K ? 215?,the small polaron hops in VRH and NNH conductivity model,but is more inclined to VRH model.The 800 ? annealed sample shows a larger NNH tendency.The calculation result shows that the carrier concentration has little change with the increase of annealing temperature.The optical properties of Mn_1.95Co_0.77Ni_0.28O₄ thin films are fitted by the near-infrared spectroscopic ellipsometry.By comparing the fitted conductivity with the experimental conductivity,we find that Drude model can simulate small polaron hopping conductance well.The experiment result shows that the free carriers of Mn_1.95Co_0.77Ni_0.28O₄ thin film have a high concentration,but the effective mass is big which is about 150m0.?3?The effect of annealing on the detector properties of Mn_1.95Co_0.77Ni_0.28O₄ thin films is investigated.It is found that the normalized noise spectral density of the sample annealed at 500 ??SV·VR/V2?is the minimal and the 700 ? sample has the biggest one.The detectivity of sample annealed at 500 ? for 1 hour is about 6.52×107?cm?Hz0.5/W@30Hz?which is the best one.?4?The structural and electrical properties of MCNO thin films with different cation distribution prepared by magnetron sputtering are studied.It is found that Mn1.2Co1.5Ni0.3O₄ has the lowest resistivity?235 ?·cm?and the highest |a295| value?4.7%·K-1?.The infrared transmission spectra and reflection spectra of MCNO films with different compositions in the range of 1.33²7 ?m are measured.It is found that Ni Co2O₄ thin film is not transparent in the whole test waveband,and the other MCNO thin films have higher transmittance in the 2.5⁶ ?m waveband.The effects of Mn,Co and Ni ions for MCNO films on the transmittance are analyzed.The n,k values of MCNO films with different compositions are obtained by fitting the ellipsometric spectra.?5?The variation of thermal conductivity for Mn_1.95Co_0.77Ni_0.28O₄ film detectors with different substrate thickness is studied.It is found that when the bias voltage increases,the thermal conductivity decreases with the increasing thickness.But the thermal conductivity change for films with substrate thickness between 200 ?m and 250 ?m is small.The variation of thermal conductivity for Mn_1.95Co_0.77Ni_0.28O₄ film detectors with different substrate area is studied.It is found that both of the time constant ? and the response rate RV of MCNO detector will increase with growing substrate area.The study of the microbridge structure shows that its responsivity is about 80% higher than that of the non microbridge and the detectivity will increases by about 44%.The study of MCNO film device with polishing copper in substrate shows that its thermal conductivity can increases by about 47%,while its response voltage will reduces by about 50%.The test results show that the response time for device with polishing copper is 22 ms,and the response time for device without polishing copper is 15 ms,and their thermal conductivity ratio is Ge1: Ge2=15:22.?6?The Mn1.5Co1Ni0.5O₄ thin films doped with Sb,Rh,Cu,Sc elements?Mn1.5Co1Ni0.35Sb0.15O₄,Mn1.5Co1Ni0.35Rh0.15O₄,Mn1.5Co1Ni0.35Cu0.15O₄,Mn1.5Co1Ni0.35Sc0.15O₄?by CSD method are studied.The effect of doping elements on the electrical properties of thin films is studied.It is found that only the Mn1.5Co1Ni0.35Cu0.15O₄ thin film has lower resistivity and higher negative temperature resistance coefficient.The optical properties of Mn1.5Co1Ni0.5O₄,Mn1.5Co1Ni0.35Cu0.15O₄ and Mn1.5Co1Ni0.2Cu0.15 Sc0.15O₄ thin films are studied.Based on the analysis of the film composition,the anti-aging test results are explained.It is found that the resistance of Mn1.5Co1Ni0.35Cu0.15O₄ thin film changes about 93.9% after 600 days,and the Mn1.5Co1Ni0.2Cu0.15Sc0.15O₄ thin film changes about 59.7%.So the Sc element can effectively improves the anti-aging properties of Mn1.5Co1Ni0.35Cu0.15O₄ thin film.The band structures of Mn1.5Co1Ni0.5O₄,CBP,PCBM,TCTA thin films are analyzed.It is found that the Mn1.5Co1Ni0.5O₄ thin film on ITO film prepared by CSD method has a band gap of 1.52 e V.The Mn1.5Co1Ni0.5O₄ film can forms PN junction with every one of three organics and their composite films show certain rectifying characteristics.