Circularly Arranged Radial Thermoelectric Energy Harvester with Dual Cavities Based On CMOS-MEMS Technology

Abstract

As the Internet of Things, i.e. IOT industry is being developed vastly and fast, various smart devices are emerging and will demand the new kinds of power-supply systems. To meet this demand, energy harvesting field is increasingly growing in many ways. As the energy harvesting field is growing larger and deeper, so will be thermoelectric device technology. In the future, micro thermoelectric device technology seems to be an effective way of converting waste heat into electricity. The design of more energy-efficient thermoelectric devices is expected to contribute to more efficient energy harvesting of the waste heat. In this paper, we briefly present the design of the micro thermoelectric device of low heat. The energy harvesting from the human body waste heat was intended by making the thermoelectric device smaller with body-friendly material, i.e. silicon (Si). Formerly, much progress in the micro thermoelectric device development was made based on the bismuth-telluride (Bi2Te3). However, in addition to the very poor quality of the deposited Bi2Te3, its toxicity has limited its very own supplies or applications. Thus, most of the micro thermoelectric devices have been developed, adopting body-friendly materials such as Si, Ge, etc. To our knowledge, this kind of research has rarely been reported domestically and our research work will make a meaningful contribution to the progress in the future thermoelectric device technology. Our research aims to improve the output voltage and power factor, which can be achieved by adjusting the thermal gradient by cavities, increasing the Seebeck coefficient by dopant concentration control, selecting more appropriate materials, and locating thermocouples in novel ways. In this work, we designed a new Si-based micro thermoelectric device, followed by the demonstration of the simulation results obtained by the COMSOL Multiphysics simulator. In addition, a large amount of the simulation data needs to be accumulated to support the further study of the micro thermoelectric devices in the future. In this research field, although we believe that the use of the COMSOL Multiphysics simulator will provide many researchers with plenty of applications, the simulator has been very scarcely used for the development of thermoelectric devices, leading to much lack of useful examples and data in this research field. At this point, we hope that our work will make bigger progress in the future thermoelectric device simulation, using the COMSOL simulator. Figure 1. Thermoelectric couples in radial arrangement

Figure 1 shows the proposed thermoelectric couples in radial arrangement. As it is shown, the bottom cavity is located below the thermocouples to secure the air convection.[1] Besides, to enlarge the temperature gradient, the three layers with different materials are coated on the polysilicon hot part.

Figure 2. Top cavity on the hot part

To make heat preserved as long as possible, the vacuum top-cavity is located on top of the polysilicon hot part. Figure 2 shows the top-cavity on the polysilicon hot part while deactivating those three-layered top-coatings.[2] So this design is enabled to keep the heat in the hot part area while providing fresh room temperature air in the cold part area, eventually maximizing the thermal gradient. Starting with this radial arrangement concept, we will be able to try various kinds of novel thermocouple arrangements. Based on the design and simulation results in this work, the fabrication of real thermoelectric devices will be made experimentally, but remains as the next challenge.