Buildup and Characterization of an Active Flexible Microelectrode Array [article]

Andreas Heid, Wharam, David (Prof. Dr.), Universitaet Tuebingen
The integration of CMOS-dies into flexible electrically active implants offers numerous new opportunities for smart implants. Due to a closed control loop such implants can measure and analyze body signals, before reacting to them with a specific response. This work was conducted as part of a project aiming for the development of a new kind of microelectrode array based on an array of small dies. Therefor a complete fabrication process starting with the separation and assembly of the dies,
more » ... y of the dies, continuing with their embedding into a foil, and ending with the fabrication of conducting tracks connecting the dies was developed. For the transfer and embedding of the dies a selective transfer printing process based on a silicone stamp was developed. The transfer of a subgroup of dies allows the increase of the spacing of neighboring dies to any integer multiple. The process works reliable with a yield between 90% and 100%. The maximum strength the stamps can pull off dies from a tape was determined. For a stamp with a profile of (300 µm)² square bumps it is – depending on the softness of the PDMS – 65 kPa or 83 kPa for a peeling speed of 10 mm/min. To equalize the height of the dies they were embedded in silicone. The die array was placed upside down in a thin shellac film before it was cast in silicone. Spacers together with a covering glass guaranteed for a homogeneous layer thickness. After curing of the silicone the shellac was used as a release layer. The resulting surface topography has an amplitude < 10 µm. This surface then allows the structuring of conducting tracks and VIAs (vertical interconnect access) using processes based on photolithography. To fabricate conducting tracks Ti/Au/Ti was sputter deposited on the surface and then dry etched against a resist mask. Etching of the VIAs required the structuring of an aluminum hardmask, as the surface moved in the vacuum leading to the formation of cracks in a resist mask. The different process steps have been successfully combined to build a demonstrator system b [...]
doi:10.15496/publikation-43962 fatcat:c3vhirrt2ndbtf5kpvvru4h75i