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Increasing complexity of today’s electrical circuits led to a growing demand for thin film “interface” substrates. Such substrates provide an important link between integrated electronics and peripheral accessories like amplifiers or signal processing units. Possible applications lie in the field of laser sub mounts with electrical connections for re-routing or even more sophisticated in the field of medical applications or implants. Whereas conventional thin film multilayer are mostly realized on stiff ceramic substrates (aluminum oxide, aluminum nitride), the extraordinary challenge with medical applications often comes from the required flexibility of the circuit. Biocompatibility and practical handling of the assembly play an important role in these applications.
This publication will show general aspects of the fabrication of thin film multilayer, stiff as well as flexible, and show the main differences which may appear, and be requested, in such systems.
A special focus shall be laid on an application for a retinal implant. In this application a vision chip, developed by the University of Ulm, is combined with a flexible thin film multilayer forming a human medical implant for regaining, at least partly, the eyesight for blind people. The special issues of the implantable chip are the low supply voltage and DC free external supply of the circuit.
The vision unit itself consists of a 40 x 40 pixels array with light sensors and electrode drivers, which are addressed sequentially to improve power consumption and spatial resolution of perception. This guarantees for a long-time operation and minimization of chemical reactions on the periphery.