Bernd Haehnlein

Pressure sensors based on silicon have proven to be robust for a wide range of operating conditions. However, maintaining the electromechanical device parameters as well as their stability is of crucial importance. To obtain high sensitivities, piezoresistive measurement bridges are used based on different implantation processes. At higher implantation doses dislocation networks are formed in the silicon substrate which affect directly or indirectly the sensor performance in a way so that p-n-junctions can be shorted. To analyse this behavior, these networks are investigated in detail by lock-in thermography and transmission electron microscopy in terms of the total dose of the implanted elements. It is found that depth and density of the network correlate with the applied dose. A special defect is found in highly doped structures with nanowire shaped structure which appears to be preferably aligned along the and crystal axes. These 1D defects can be correlated to hot spots measured in lock-in thermography. An element dispersive analysis revealed that these nanowires consist of a Fe/Ni core/shell heterostructure which can open electrical paths through p-n-junctions.

Bernd Hähnlein has made his masters degree in Technical Physics at the Technical University of Ilmenau, Germany, investigating the mechanical properties of AlGaN/GaN/SiC heterostructures. During PhD he studied the epitaxial growth of graphene and electronic devices based upon. Currently, he is part of the analytics group of the CiS GmbH research institute in Erfurt where his focus is on failure analysis of silicon based sensor devices.