Research On Thermal Conductivity Of Bismuth Telluride Sputter Deposited Film Based On 3? Method

With the rapid development of IC in the direction of high integration,high speed and multi-function,the power density of the chip is becoming larger and larger,which easily causes the overall temperature rise of the chip to exceed the limit and the local hot spot temperature to exceed the high heat dissipation problem.In order to ensure the working performance and life of the chip,it is often necessary to add micro thermoelectric refrigeration??TEC?and other forced heat dissipation means on the chip surface on the basis of providing conventional heat dissipation measures,so as to stabilize the temperature appreciation of local hot spots.Thin film bismuth telluride?Bi₂Te₃?thermoelectric material is an alternative material with good performance for the fabrication of?TEC devices.In order to further improve its thermoelectric value and enhance the working performance of?TEC,the effect of simply increasing the power factor is not ideal.It is necessary to reduce the thermal conductivity.Therefore,the accurate measurement of the thermal conductivity of the film is an important basis for the evaluation and optimization of the thermal performance.In this paper,the 3?method,which has low sample preparation requirements,fast response speed and accurate and effective results,is selected as the theoretical basis for measuring the thermal conductivity of Bi₂Te₃ thin film by comparing the currently developed characterization methods of micro/nano thin film thermal properties,and a set of measurement system for measuring the thermal conductivity of block and thin film materials at the same time is built.A complete layout of micro heater,a series of sample structures and overall test flow of multi-layer film step-by-step measurement were designed,and the Al heater with the designed structure was fabricated by Lift-off lithography.The thermal conductivity of Bi₂Te₃ film substrate,pre oxide film and Si O₂film were 132 W/?m·K?,1.49 W/?m·K?and 0.98 W/?m·K?,respectively.The above results are close to the literature values,which verify the measurement accuracy of the self-built system,and provide effective basic data for the subsequent measurement of the thermal conductivity of Bi₂Te₃ film.In order to analyze the influence of deposition thickness on the thermal conductivity of the films,the samples with thickness of 310nm,560nm,840nm and1080nm were sputtered on the substrate surface at the same temperature.The thermal conductivity data of the samples were measured by a self-built system.Combined with the phase composition,microstructure and electrical transmission properties measured by XRD,SEM and Hall effect with the change trend of film thickness,the reason why the thermal conductivity of Bi₂Te₃ film is much smaller than that of bulk material and decreases first and then increases with the increase of thickness was analyzed.Finally,it is determined that the thermoelectric optimal value of Bi₂Te₃ film with a thickness of310nm is the largest,but it is generally not high due to the low substrate temperature when the film is deposited.Therefore,it is necessary to further investigate the thermal conductivity and comprehensive thermoelectric properties of the film after the substrate temperature is increased.For Bi₂Te₃ films with the same thickness deposited at the substrate temperature of room temperature,100°C,150°C and 200°C,the thermal conductivity,phase composition,microstructure and electrical transmission properties of the samples were also measured and analyzed.The results show that the thermal conductivity of Bi₂Te₃films increases with the substrate temperature,and when the substrate temperature is150°C,the thermal conductivity of the films increases the best value is the largest.Therefore,in order to obtain Bi₂Te₃ films with better properties,thermoelectric films should be deposited at the substrate temperature as much as possible.