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 sourc es 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 diff erence of 30 K. Its fabrication involves only a few steps, such as foil lit hography, electroplating, embedding and wet chemical etching. The exposure of aqueous photoresist on flexible foil substrates is carried out using a s pecially constructed mask aligner try Karl Suss GmbH. The thermocouple stri ps, with a cross section of 40 x 10 mum and a length of 20 mm, are electrop lated galvanostatically from their associated acidic electrolytes into the patterned AZ 111XFS template on a 50 mum thick copper foil. After a top-ove r embedment of the electroplated structures with an epoxy film, the origina l copper substrate is removed completely by wet chemical etching, leaving t he generator module to be embedded in the epoxy film. This process is prove n to be cost-effective, easily manageable and highly reliable. It is now be ing applied to our current fabrication of more efficient thermoelectric gen erators based on n- and p-type Bi2Te3 compound materials.