Microfabrication of thermoelectric generators on flexible foil substrates as a power source for autonomous microsystems

A flexible thermoelectric generator with overall dimensions of 16 x 20 x 0.05 mm has been fabricated using a unique low-cost procedure as part of our ongoing research efforts on developing economical and reliable energy sources for autonomous microsystems. The generator consists of a multiplicity of micro Sb-Bi thermocouple strips embedded in a 50 mum thick flexible epoxy film and is capable of generating a voltage of 0.25 V at a temperature difference of 30 K. Its fabrication involves only a few steps, such as foil lithography, electroplating, embedding and wet chemical etching. The exposure of aqueous photoresist on flexible foil substrates is carried out using a specially constructed mask aligner try Karl Suss GmbH. The thermocouple strips, with a cross section of 40 x 10 mum and a length of 20 mm, are electroplated galvanostatically from their associated acidic electrolytes into the patterned AZ 111XFS template on a 50 mum thick copper foil. After a top-over embedment of the electroplated structures with an epoxy film, the original copper substrate is removed completely by wet chemical etching, leaving the generator module to be embedded in the epoxy film. This process is proven to be cost-effective, easily manageable and highly reliable. It is now being applied to our current fabrication of more efficient thermoelectric generators based on n- and p-type Bi2Te3 compound materials.