Micromachined thermoelectric test device based on silicon/germanium superlattices: Simulation, preparation and characterization of thermoelectric behavior

J. Schumann1, H. Vinzelberg1, J. Thomas1, M. Hecker1,

C.A. Kleint2, J. Nurnus3, H. Boettner3, A. Lambrecht3, C. Künzel3 , F. Voelklein4

1Leibniz-Institute for Solid State and Materials Research Dresden, P.O.Box 27 01 16, D-01171 Dresden, Germany

2Infineon Technologies GmbH & Co. KG, M.-von-Ardenne-Ring 20, D-01090 Dresden, Germany

3Fraunhofer Institut Physikalische Meßtechnik (IPM), Heidenhofstr. 8, D-79110 Freiburg, Germany

4Fachhochschule Wiesbaden (FHW), FB Physikalische Technik, Am Brückweg 26, D-65428 Rüsselsheim, Germany

Thin film superlattice structures based on nanoscaled Si/Ge multilayers are expected to be promising systems for efficient thermoelectric micro-systems. However, the influences of Si substrates and buffer layers are unavoidable for the epitaxial growth of the strain symmetrized Si/Ge heterostructures. This complicates the evaluation of the parameters for the thermoelectric performance. We present the development of a thin film device consisting of Si/Ge superlattice and SixGe1-x legs allowing the study of the thermoelectric behavior at minimized influence of the Si substrates. By means of a combination of photolithograhic patterning, physical and chemical etching as well as chemico-mechanical polishing thermopile arrays with the size of 6´ 12 mm2 are manufactured in a nearly free-standing version. The layout parameters were determined by numerical simulations of the dependence of geometrical size relations on the temperature distribution within the device. In the layout the leg length and width are varied in the range (0.5...3.5)mm and (20...250)Ám, respectively. The Si/Ge films were prepared by magnetron sputter epitaxy under UHV conditions on Si (111) using shadowing masks for half-wafer deposition of n- and p-type material. As contact and interconnect material films of AlSi(4%) were used. This nearly freestanding thermopile arrays were placed on a silicon frame. First measurements of the functional parameters in the sensor regime are presented