Researches On Fabrication And Thermoelectric Properties Of ITO/In₂O₃ Thin-film Thermocouples

Accurate measurement of the surface temperature and its distribution of hot component of aircraft engines are essential for design and performance verification of the aero-engine.Thin film thermocouples?TFTCs?,which is directly deposited on the surface of the turbine blade by thin film deposition technology,has the advantages of small volume and mass,negligible influence on the flow field,small heat capacity and fast response.ITO and In₂O₃ are conductive oxide semiconductor materials with wide band gap.ITO/In₂O₃ TFTCs has the characteristics of higher temperature endurance and antioxidation.Furthermore,it has large Seebeck coefficient.And these make it most promising candidate in the field of ultra-high temperature measurement.In this thesis,the preparation and the thermoelectric properties of ITO/In₂O₃ TFTCs were investigated.The effect of nitrogen doping on the performance of ITO/In₂O₃ TFTCs was investigated emphatically.First,nitrogen-doped ITO thin films were prepared on alumina substrate by RF magnetron sputtering.The nitrogen/argon mixture was used as gas media during the deposition.Nitrogen could fill the oxygen vacancy and reduce the carrier concentration of the film,resulting in the increase of resistivity of ITO film.Some of the nitrogen tends to segregate the grain boundary and inhibit the crystallization of ITO film.During air annealing,the oxygen in the air diffuses into the ITO film and fills the oxygen vacancy,as a result,the resistivity of film increases.During the annealing in nitrogen,the nitrogen in gas media diffuses into the ITO film,meanwhile,the nitrogen in the ITO film could desorpt from the film.Finally,the carrier concentration in the film reaches a steady state and the resistivity of ITO film is stabilized as a compromise.Second,nitrogen doped ITO/In₂O₃ TFTCs were fabricated on alumina substrate by RF magnetron sputtering and characterized by static calibration at 300¹000?.The results show that the oxygen diffusion from the environment is inhibited and the carrier concentration is stabilized by the formation of oxynitrides in ITO and In₂O₃ films.As a result,the Seebeck coefficient of the films was stabilized and the thermoelectric stability of the ITO/In₂O₃ TFTCs was improved.The electromotive force?EMF?of the ITO/In₂O₃ TFTCs increases with increasing nitrogen partial pressure during the sputtering of ITO electrode,while decreases with increasing nitrogen partial pressure during sputtering of the In₂O₃ electrode.Excellent thermoelectric stability and repeatability of the TFTCs is realized when the ITO electrode and the In₂O₃ electrode were sputtered under nitrogen partial pressure of 10% and 20%,respectively.ITO/In₂O₃ TFTCs were post annealed through two different 2-step annealing processes?named as N2-Air and Vacuum-Air,respectively?in this thesis.The results showed that the EMF of ITO/In₂O₃ TFTCs increased after annealing.The high temperature thermoelectric stability and repeatability of N₂-Air annealed TFTCs has been greatly improved,and EMF increases linearly with increase of the temperature difference due to the formation of oxynitrides in the electrode films.The average Seebeck coefficient is 64.7?V /?.Finally,ITO/In₂O₃ TFTCs was fabricated on the surface of Nickel-based superalloy.NiCrAlY alloy layer,thermal grown Al₂O₃ layer,Al-O-N/Al₂O₃ composite insulation layer were deposited serially before the deposition of ITO/In₂O₃ thin film thermocouples layer.The electrode size of the thermocouples is 63mm×1mm×0.6?m and the hot junction is 1mm×1mm×1.2?m.The samples were annealed with N2-Air annealing and then calibrated at 300¹000 ?.The results showed that the thermoelectric output of ITO/In₂O₃ TFTCs is stable and the EMF increased slightly after the first two calibrations.The average Seebeck coefficient is 110?V/? which is one magnitude larger than that of metallic thermocouples and the test deviation is within 1%.