Research On Properties Of In₂O₃/ITO Transparent Thin Film Thermocouples Prepared By Magnetron Sputtering

Thin film thermocouples have attracted many researchers'attention due to their passivity,short response time,high accuracy and almost no impact on the test environment.Significant progress has been made in aerospace,microelectronic devices and biomedical fields of thin film thermocouples.The transparent semiconductor In₂O₃and ITO films with wide band-gap have the characteristics of wide use temperature range,oxidation resistance and high Seebeck coefficient.The thin film thermocouples composed of these two materials has broad application prospects in the field of temperature measurement.In₂O₃/ITO thin film thermocouples were prepared by radio frequency magnetron sputtering on quartz glass and transparent polyimide at room temperature.The structure,surface morphology and photoelectric properties of the films were characterized by XRD,SEM,AFM,ultraviolet spectrophotometer,four-probe and Hall Effect.The thermoelectric response of In₂O₃/ITO thin film thermocouples was calibrated by a laboratory-built measuring system.The main research contents and conclusions are as follows:Firstly,the thermoelectric properties of In₂O₃/ITO thin film thermocouples at different annealing temperatures were compared with those of the un-annealed samples.The results show that the surface of all ITO electrode films is smooth,compact,high transmittance and crystallization.The un-annealed samples have higher Seebeck coefficient,with an average value of 84.42?V/o?,which is an order of magnitude higher than the standard S-type thin film thermocouples.The thermal response of the un-annealed In₂O₃/ITO thin film thermocouples was great,and the thermoelectric voltage is as high as 13.6 mV.Secondly,the effects of gas pressure and oxygen content in oxygen argon mixture on the properties of ITO electrode films and In₂O₃/ITO thin film thermocouples were studied.The increase of sputtering pressure and oxygen content can lead to the increase of resistivity and transmittance of ITO thin films.The quality of ITO films became worse when the sputtering pressure was too high.In addition,the excessive oxygen in mixed gas can cause lattice distortion of ITO films.The thermoelectric voltage of In₂O₃/ITO thin film thermocouples increases with the increase of sputtering pressure and oxygen content.Finally,in view of the rapid development of flexible electronic devices and wearable devices,flexible In₂O₃/ITO thin film thermocouples were fabricated on transparent polyimide substrates.In the tensile test,the variation trend of resistance of In₂O₃ and ITO thin films is consistent with the applied tensile strain.The resistance of In₂O₃ thin films increases slightly when the tensile strain is less than 0.7%.With the further increase of strain,the resistance of In₂O₃ thin films increases sharply.When the tensile strain is 0.3%,there is a sudden change in resistance of ITO thin films,which increases about three times as compared with the initial value.The resistance of ITO films changed slightly when strain continues to increase.After applying 0.8%tensile strain and release,In₂O₃/ITO thin film thermocouples still have good thermoelectric stability.The resistance of the In₂O₃ and ITO changed relatively small when the electrode film is in the external bending state.When the bending radius is 23.28 mm,the thermoelectric output of the In₂O₃/ITO thin film thermocouples is relatively different during the heating and cooling process.When the SiO₂ transition layer is prepared between the electrode film and the flexible substrate,the thermoelectric response stability of the thin film thermocouples is improved.However,when the temperature is below 80?,the thermoelectric output of In₂O₃/ITO thin film thermocouples still has a lag effect.