Project Image:
Title of the project:
Spherical round window implant for the hearing impaired
Project leader:
Dr. Claus J. Burkhardt
Project funding:
  • Bundesministerium für Bildung und Forschung (BMBF)
Project management:
  • Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)
Funding reference number:

In this new type of hearing implant, the sound signal is converted into an optical signal and transmitted through the eardrum to a photodiode in the middle ear. At the NMI, the inner part of the implant consists of a flexible cable based on polyimide. The photodiodes and the actuator for stimulating the inner ear are integrated on this cable using the appropriate connection technology.


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".

Project partners:
  • 2E Mechatronic
  • Auric Hörgeräte
  • Frauenhofer IPA Stuttgart
  • HNO Klinik Tübingen
  • Institut für Systemdynamik (isys) Stuttgart