RW-Implantat

The inner implant consists of a receiver (photodiode) and an actuator. Both are connected by a flexible cable. The first prototypes of this cable were manufactured at the NMI using the in-house polyimide (PI) technology. A thin layer with an adjustable layer thickness (typically 5-7µm) is applied to a 4 inch glass substrate using the spin coating process with the precursor Pyraline 2611 (HD Microsystems) and imidized in a special imidization furnace at 350° under a nitrogen atmosphere. A new imidization furnace with integrated laminar flow was installed and the processes established in order to ensure that these PI cables are only slightly free of defects. A layer system of titanium and gold is then applied to this first PI layer using PVD and structured using optical lithography and dry etching. In the next step, a second layer of PI is applied. The contacts at the ends of the cable are etched free by a further lithography step. In order to connect the photodiode and actuator to the conductor paths of the cable, the thin gold conductor path (thickness about 400nm) must be reinforced by microplating in a gold bath to a layer thickness of about 3µm. This layer is suitable for making contacts by means of ultrasonic wire bonders.
Federal Minister Schavan presented the research project on 1.2.2011 as "Project of the Month".