Fabrication of poly-Ge-based thermopiles on plastic

Fabrication of Ge-based thermocouple on polyethylene-terephthalate (PET) plastic substrates is reported. The amorphous Ge film, deposited using electron beam evaporation, is post treated to form a polycrystalline film. The annealing process has been performed at temperatures ranging from 120°C to 175°C and study of physical characteristics of Ge films using XRD and SEM confirms its crystallinity. A value of 100 μV/°C is extracted for the Ge-Al junctions. The thermocouple fabrication and its response to flow are reported. A novel approach is described to perform the micromachining of PET substrates for the formation of craters and membranes. Di-methyl-formamide (DMF) is used as the solvent of the PET substrate, masked with a Ge/Cu multilayer. An average chemical etch rate of 12 μm/h is achieved in the presence of 6.5 mW/cm² of 360-nm UV at ambient temperature.