(Invited) Ultra-Thin MEMS Thermoelectric Chip and Its Applications

Abstract

Ultra-thin MEMS Thermoelectric Chip and Its ApplicationsZhiyu HuInstitute NanoMicroEnergy, Department of Micro/Nano-ElectronicsShanghai Jiao Tong University, Shanghai, China, 200240Email: zhiyuhu@sjtu.edu.cn : For a long time, mankind has been seeking inexhaustible energy in nature. There is an urgent need to obtain new types of sustainable, environmentally friendly and green energy to reduce our dependence on petrochemical energy. The thermoelectric generator (TEG) can directly convert heat into electrical energy through the Seebeck effect, thereby obtaining electrical energy, which makes it a promising environmentally friendly energy conversion method. TEG has many special advantages, such as no moving parts, no pollution, no noise, no mechanical vibration, etc. At present, all TEGs on the market is made with traditional method which yields high cost, low efficiency, not suitable for massive and economic production.Thermoelectric generator (TEG) can directly convert heat into electrical energy. Due to its special advantages, such as no pollution, no noise, no mechanical vibration, etc., TEG has been widely used in vehicles, wearable devices, solar energy systems, and industrial waste heat recovery systems. In order to promote the application of thermoelectric devices, it is necessary to improve the performance of thermoelectric materials through nanostructures. Generally, thermal resources are concentrated on increasing the temperature at the hot end of the TEG. In this article, the heat in the environment is pumped into the external space through radiant cooling (RC), thereby generating the cold end of the TEG and a continuous self-powered system was obtained.Taking advantages of micro/nano-fabrication and the scale effects of heat theory, we are able to design and build a thermoelectric chip in a large array and maintain a stable temperature difference between sub-micrometer-thick of a thermoelectric unit on a silicon wafer. The submicron-thick TEG containing more than 46,000 thermoelectric modules in series was fabricated on SiO2/Si. The combined Seebeck coefficients of Sb2Te3 and Bi2Te3 were adopted the average value which were evaluated to be 250 μV/K. The details of the fabrication method were proposed first and demonstrated in our previous work.Nanostructured multilayer thermoelectric films have been developed to improve thermoelectric efficiency. The effects of interface microstructure on the cross-plane thermal conductivities of the multilayer thin films have been extensively examined and the thermal transfer mechanism has been explored. Experimental results indicate that ultrathin thermoelectric device works stable and reliable, and is suitable for fabrication of thinner and higher integrality devices in mass production.We have demonstrated a novel energy utilization that MEMS-based thermoelectric chip can produce electricity by radiative cooling (RC) in day and night. Thermal emitter composed evaporated Ag layer and 12 alternating SiO2 and Si3N4 layer periods deposited on a silicon by plasma enhanced chemical vapor deposition (PECVD). The absorptivity of the thermal emitter is 80.8%. Here, the emission is caused by phonon-polaron excitation in the Si3N4 layer. SiO2 was chosen to fully reduce the adverse radiation loss because it has an absorption peak close to 9 μm in the atmospheric window due to its phonon-polaron resonance. The silver-plated layer can enhance the electromagnetic wave reflection without resonance.In addition, the MOST material that collected solar energy in Gothenburg，Sweden has been delivered to Shanghai, China by express mail, and successfully generated electricity on the MEMS TE chip a few months later.MEMS-based thermoelectric chips can use ultra-low thermal energy to directly generate electricity with a very small temperature difference. In future, when such advanced energy technology is wildly available and at very low costs, we then will obtain truly sustainable, completely environmentally friendly clean energy, and greatly reducing our dependence on petrochemical energy. MEMS-based thermoelectric chip can also be used as an ultra-sensitive temperature sensor, several testing examples will be introduced and with further discussions.