Research On The Green Thermoelectric Conversion Materials And Devices For Low Power Consumption Wireless Communication Sensors

Thermoelectric conversion is a kind of static energy conversion,which can directly convert the heat energy from environment into electrical energy.It has the unique advantages of small size,no noise,no pollution emission and low maintenance cost.At the same time,it is easy to combine with the sensor circuit,which is one of the best choices for its energy source.At present,the thermoelectric generation devices used in wireless sensors are mainly traditional commercial thermoelectric materials such as bismuth telluride and so on.Most of the components of them are highly toxic,contain heavy metals or are thermally-unstable,which are not suitable for the large-scale construction of green Internet of Things communication in the future and the sustainable development of the environment.As the most widely used semiconductor,silicon（Si）based materials have the unique advantages of environmental friendliness,abundant resources and stable properties,and have the potential to be used for energizing wireless sensor.However,Si based thermoelectric materials usually serve at high temperature zone,and they have larger intrinsic thermal conductivity,which results in low figure of merit（ZT）and low thermoelectric conversion efficiency.In view of the problems and challenges of the application of wireless sensor thermoelectric energy collection,this paper starts with the materials of power generation devices,optimizing the thermoelectric properties of Si based materials,including Si Ge Sn thin film and Si Ge bulk of oxide composite.On this basis,thin-film and bulk thermoelectric devices are fabricated,and successfully drive the Zig Bee-based wireless temperature sensor work.Finally,a monolithic thermoelectric device was proposed and its generating performance was evaluated.The main achievements of this thesis are as follows:（1）Enhance the power factor through modulation doping strategyIn this thesis,a process for the preparation of the in-situ precipitation of Sn nanoparticles in Si_1-x-yGe_ySn_x films was proposed.The results show that the Sn nanoparticles can produce modulation doping effect,and provide charge carriers without introducing additional ionizing impurities.To a certain extent,the independent regulation of electrical conductivity can be achieved,and the power factor is greatly increased.The obtained power factor is 12.21μW m^-1K^-2 at near room temperature.At the same time,the short-time annealing can inhibit the grain growth and obtain the microcrystalline structure in the low-dimensional film structure,which can greatly hinder the phonon transport and maintain the low thermal conductivity.In this work,the power factor of Si based thermoelectric films is enhanced while the thermal conductivity is not increased excessively,and the ZT value is enhanced at the near room temperature area.（2）Exploration in-situ decomposition of Ga₂O₃ on thermoelectric propertiesSi Ge bulk composites of Ga₂O₃ were synthesized by ball milling and spark plasma sintering.The effect of in-situ decomposition behavior of Ga₂O₃ on thermoelectric properties of n and p Si Ge bulk materials was investigated.The results shown that for n-type Si Ge:the Ga generated by in-situ decomposition reacted with the doped element P to enrich and form the second phase.At the same time,some Ga doping introduces hole carriers and finally reduces the electrical properties.The decreased thermal conductivity failed to compensate for the deterioration of the power factor,resulting in a decrease in thermoelectric performance.For P-type Si Ge:Ga doping not only introduced homogenous carriers（holes）,and promoted crystallization of Si Ge matrix,which enhanced the power factor of the composite sample,but also increased the thermal conductivity,resulting in inapparent increase of ZT value,which needed to be further optimized.（3）Construct a full-scale phonon scattering structure to reduce the lattice thermal conductivityBased on the study of Ga₂O₃ composite,Si O₂ aerogel co-composite strategy was used to further reduce the thermal conductivity.The results show that the combination of Si O₂aerogel powder not only significantly inhibited the grain growth of Si Ge matrix,but also introduced small amorphous Si O₂ second phases,which inhibited the increase of thermal conductivity and enhances the ZT value.By means of carrier optimization and sintering process optimization,the electron thermal conductivity was regulated and the microstructure was optimized,and the lattice thermal conductivity was reduced to construct the full-scale scattering center of phonon.Combined with the weakened of the overall chemical bond strength,the phonon transport was effectively inhibited,and the final thermal conductivity was reduced by 32.6%,which greatly increased the ZT value than before.（4）Thermoelectric device fabrication and thermoelectric self-power wireless sensor applicationBased on the study of Si based materials,the thermoelectric devices of thin film and bulk materials were fabricated respectively to verify the thermoelectric conversion ability of the materials.Si Ge Sn thin film thermoelectric devices were fabricated by using home-made mask combined with magnetron sputtering,ion implantation and rapid thermal annealing.The oxide composite Si Ge bulk thermoelectric device was fabricated by ball milling,spark plasma sintering and hot pressing,and its output performance was evaluated.The device was used to power the Zig Bee-based wireless temperature sensor instead of the button battery.After the connecting with BQ25570 booster conversion module,the sensor was successfully driven to work and the temperature information was received at the receiving end.（5）Design,manufacture and performance evaluation of integrated thermoelectric devicesAiming at the disadvantages of wireless sensor application scenarios and surface thermoelectric devices,a novel integrated thermoelectric device is made.This strategy simplified the electros,solder,bearing substrate and the gap between thermoelectric arm array,directly contacting the n and p thermoelectric materials and insulating layer materials,which was integrated and formed to reduce the size of the device and improve the robustness of application.The optimal insulating layer thickness was obtained by finite element simulation.The thermoelectric device was fabricated by simple multiple hot-pressing process,and the additional junction resistance generated by n and p material interface was quantitatively analyzed by combining simulation and actual measurement.The output performance of the integrated thermoelectric device was evaluated.The miniaturized structure design idea provided important guidance for the development of wireless sensor thermoelectric self-power sample.