Prepration Of Bismuth Telluride Thin Films And Micro-thermoelectric Devicespreperation Attempt

The reported maximum conversion efficiency of thermoelectric(TE) devices is less than 15%, limited by the thermal and electrical properties of thermoelectric materials.So, expanding the application of TE materials,such as micro-thermoelectric(MTE) devices which are used for chips refrigerating or powering wireless sensors, attracted a lot of attention. Bi2Te3 was the most promising TE material for MTE devices because of its outstanding performance at room temperature.Researchers around the world havedeveloped a lot of methods for high qualityBi2Te3 thin films preparation, such as MBE, MOCVD and magnetron sputtering since 1980 s.All of these methods need complex equipments and suffering from high cost, were not available for commercial application. In this dissertation, thin Te and Bi films were alternatelydeposited by evaporation then followed by annealing,By the optimization of the annealing temperature and ratio of Te/Bi, high performance Bi2Te3 films with Seebeck coefficient of-172?VK-1and power factor of 8×10-4Wm-1K2 was achieved with Te/Bi=1.2 annealed at 200°C-250°C.A thickness of more than 10?m isrequired for TE films because MTE devices need high ratio aspect to achieve higher output voltage. Electrochemical deposition(ECD) could produce thick films easier with low cost compared with physical evaporation methods, and it also could develop thermocouples in a cheaper way. In the fourth chapter of this dissertation, an ECD system composed of glass/Cr/Au substrates and a conventional three electrode cell wereapplied for Bi2Te3 films preparation. Pulse electrochemical depositionmethod could fabricate a smoother surface withcontrollablestoichiometrythan potentiostatic method. Withoptimized pulse electrochemical deposition parameters, Bi2Te3 filmswith Seebeck coefficient of-46?VK-1and power factor of 3.9×10-4Wm-1K2 were gained.In chapter five, cross-plane and in-plane MTE devices were prepared by evaporation and micro-fabrication technologies. Cr film was chosen as electrode, n-type Bi2Te3 and p-type Sb2Te3 were deposited in sequence,the adhesion between thermocouples and substrates(or electrodes) were studied. For cross-plane MTE devices, thermocouples were deposited on the surface of Cr electrodes, a thin layer of Te could improve the adhesion between thermocouples and Cr electrodes. Thermocouples of in-plane MTE devices were deposited on quartz glass and Si/SiO2 wafer substrates. Due to bad adhesion between thermocouples and SiO2, small defects on the surface of substrates caused serious peeling off of TE materials. New substrate materials should be developed for in-plane MTE devices preparation.