Thermo-mechanical modelling and design of SiGe-based thermo-electric modules for high temperature applications

Thermal electric modules (TEMs) utilise the Seebeck effect that occurs in thermally-insulating semiconductors to generate electricity from a sufficient thermal gradient. This has specific applications in the automotive industry where TEMs can be used as energy harvesters in vehicle engines, exhaust systems and large scale industrial applications, leading to lower greenhouse emissions and fuel consumption [1]. In this work, the proposed thermo-electric (TE) material for the TEM is nanostructured SiGe, designed to enhance TE performance. The TEM needs to ultimately be able to operate from ~40°C on the cold side of the device up to a maximum of at least 650°C on the hot side. Using the thermo-mechanical models developed, thermo-mechanical loads have been modelled. The modelling results have then been used to select the packaging materials to ensure that the thermo-mechanical stresses on the TEM are manageable. The thermo-mechanical simulations were used to determine the best combination materials used for packaging and found that using W/AlN/W substrates on both the hot side and cold side of the module produces a maximum stress of ~130 MPa when 650°C is applied to the hot side and 45°C is applied to the cold side, which is below the AlN flexural stress of 600 MPa [2]. This indicates that it may be possible to produce a high temperature TEM that does not crack at the first instance when a large thermal gradient is applied.