Structural reliability and thermal insulation performance of flexible thermoelectric generator for wearable sensors

Present work highlights the progress in the field of polymeric package reliability engineering for a flexible thermoelectric generator realized by thin film semiconductor technology on Kapton®. Together with mechanical enhancement, the thermal insulation performance of the realized 3D custom package was tested. The effect of different plasma treatments on the mechanical performance and interface of a Polydimethylsiloxane (PDMS)/Kapton® assembly were investigated; in order to increase the package mechanical stability of the realized wearable power source, Kapton® surface wettability was investigated by static contact angle measurements using deionized water and PDMS as liquid test. In fact, well known weak adhesion between PDMS and Kapton® leads to delamination of the package with unrecoverable damage of the generator. Plasma effect on adhesion performances was evaluated by scratch test method. By a numerical thermal analysis, the device packaging was optimized by coupling the module realized onto Kapton foil (by thin film PVD technology) to a PDMS layer opportunely molded to thermally insulate TEG cold junctions and enhance the thermal gradient useful for thermocouples operation. Fabrication process with optical lithography steps allows high resolution definition of thermoelectric semiconductors alloys. The main advances in wearable generator packaging technology is represented by increased structural robustness of PDMS/Kapton® assembly in terms of delamination and fatigue resistance.