Rapid prototyping of mesoscopic devices

The trend towards miniaturization closes the gap between conventional macroscopic manufacturing techniques (milling, turning, casting,) and microfabrication techniques (lithography, etching, thin-film deposition. electroplating, LIGA). Yet there still exist some distinctive differences: Macrofabrication (part or feature size usually > 1mm) deals with a wide variety of materials which can be fabricated in fairly complex, three- dimensional shapes. Ail three dimensions are equal and there is no upper size-limit in one dimension. Microfabrication (part or feature size usually < 100 mum) allows arbitrary shapes in two dimensions (the "wafer plane"), but shapes in the third dimension usually have to be decomposed into prismatic layers. In most cases these layers cannot exceed a certain thickness (due to limited cure or irradiation depth of photoresist, limitations of the etching process or constraints in the deposition of thin Alms). Additionally. the number of available materials is fairly small, due to restrictions in the etching or deposition process. In this work we show how micro and macro-techniques can be used together in order to fabricate mesoscopic parts (part or feature size between 100 mum and 10mm) in a variety of materials, including ceramics. metals and polymers, The starting point for fabricating these parts are molds which are either machined conventionally or using photolithography and deep plasma-etching of silicon. These techniques are applied to tile fabrication of a miniature gas turbine engine. Two parts of this engine are described in more detail in this work: The ceramic rotor and a thrust bearing.