Fabrication And Performances Of High Temperature Thin-film Thermocouples

Temperature is one of the key parameters which affect the performance and lifetime of hot-end components of aircraft engine.The real-time monitoring and acquiring the surface temperatures of engine and combustion chamber is very important for engine safety monitoring and performance verification.Thin film thermocouple?TFTC?has the disadvantages of small measuring terminal,low thermal mass,fast response,having little effect on thermal field and doing no harm to components surface.It becomes one of the most accurate temperature-measurement technologies and the developing trend of surface temperature measurement for engine components.For thin film thermocouple on the turbine blades,the transition layer,insulating layer and sensitive layer are required at least to output the electrical signals correctly at high temperature.As part work of the project on developing TFTCs on turbine blade,this study focuses on high-temperature thin-film thermocouples fabricated on Al₂O₃ ceramic substrate using micromachining technology,especially Pt-Pd and Pt-PtRh13 thermocouples.According to thermocouple theory,the structure of the TFTCs is designed.The masks for photo lithography are designed based on micromachining technology and wire bonding process.And the suitable materials for the thin film thermocouples are selected for the device to work at high temperature for a long time.Two kinds of the fabrication processes,which are the dry MEMS technology and the wet MEMS technology are proposed by optimizing key individual process including the sputtering process,ion beam etching process,and wire bonding process.By comprehensively comparing the two flow processes,the optimal process is determined for preparing the high temperature TFTCs.The testing system is built to characterize the performances of thin-film high temperature thermocouple.The experimental results show that the lifetime of the Pt-Pd thin-film thermocouples is 20 min at 1300?.The difference between the Seebeck coefficient of platinum and palladium is not constant,which varies with temperature.And the lifetime of the Pt-PtRh13 thin-film thermocouples is 14 hours at 1300?,and the difference between the Seebeck coefficient of platinum and platinum rhodium is constant,independent on temperature.In addition,the effects of the hot junction size and the adhesion layer on the performance of the TFTCs are studied in the paper.And the experimental results show the size of hot junctions doesn't affect the performance of the device.The lifetime of the TFTCs with tantalum adhesion layer is the longest among the three adhesion layers?Cr,Ti,Ta?.The failure of the TFTCs at the high temperature is attributed to the film fractures and the circuit discontinues.