Thermoelectric micro devices: Interplay of highly effective thin film materials and technological compatibility

In the past years several attempts have been made to increase the thermoelectric figure of merit (FOM) of thin film materials by the use of low dimensional structures. In superlattices (SLs) a reduced lattice thermal conductivity λ_L was determined parallel as well as perpendicular to the SL-single layer interfaces. This reduced XL values resulted in more or less significant FOM enhancements depending on the investigated material systems as well as the transport directions. The use of these novel high quality materials normally implies the use of single crystalline substrates with a good lattice and linear thermal expansion coefficient match. The physical requirements are associated with technological limitations concerning insulating layers, diffusion barriers as well as metal electrodes needed to fabricated a micro device exploiting heat and current flows perpendicular to the SL interfaces. On the other hand in parallel devices the substrates used result in a thermal shortcut reducing the device performance significantly. Concepts to overcome these technological limitations will be evaluated and some key experimental steps will be shown. The impact of high FOM-technologies by nanostructures on different device applications will be discussed.