Project Details
Projekt
Temperature resistant electrochromic micro-iris with neutral color for quick image adaptation in micro-cameras for medical applications
Subject Area
Microsystems
Term
from 2016 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 317515858
The project aims at the technical realization and scientific investigation of a multilevel non-mechanical electrochromic (EC) iris. We intend to integrate the tunable EC-iris inside a human endoscope with chip on the tip technology, which limits its diameter to 5 mm. The endoscope with integrated iris would enable surgeons for the first time to adapt the important optical features like the depth of focus or the image contrast on-the-fly. However, as part of a medical system, the EC-iris has to fulfill all demanding requirements of an endoscope. This includes the small space requirements, the temperature stability up to 140°C during sterilization, and a response time below 0.5 s. Furthermore, the desired application demands a high optical image quality. Thus, each segment of the iris should have an optical contrast of at least 90%, low optical scattering, and a neutral spectral absorption response. The strong reduction of the response time can only be achieved by chemical binding the EC-molecules to a solid and transparent electrode. In fact, the desired high contrast of the iris demands to increase the overall absorption by establishing conductive porous layers made of nanoparticles. Their surface is coated with the EC molecules enabling a much more effective charge transfer to the underlying electrode. The nanoparticle material choice needs to be adapted to the electrochemical reaction on the individual electrode. The synthesis of proper EC-molecules including the chemical anchor group is imperative not only for the appropriate electronic coupling to the nanoparticle. Choosing complementary EC molecules for the two electrodes gives the freedom to achieve an almost neutral spectral response in the opaque state. In addition to these chemically oriented tasks, several technological challenges have to be solved. The deposition of highly porous nano-electrodes of homogeneous thickness will be attained by doctor-blading of an emulsion followed by calcination and sintering. Prior to this process, the ITO layers as well as gold/chromium contact electrodes are assembled by well-established microstructuring techniques. The assembly of the EC cell is one of the main challenges which requires the parallel alignment and mounting of sub- and superstrate. However, in the same process we need to establish an air and moisture tight sealing of the electrolyte by an UV-epoxy to avoid degradation of the EC-molecules. Therefore, the entire assembly must be performed under nitrogen atmosphere. The reduction of both, reflection and scattering losses will be advanced by matching the refractive index of the electrolyte and the nanoparticles. The choice of materials is subject to restrictions because they need to withstand the temperature cycles during the sterilization process. Finally, each single iris needs to be separated by core drilling, electrically contacted in a very tight space, and ultimately integrated into an endoscope to provide finally a demonstrator.
DFG Programme
Research Grants (Transfer Project)
Application Partner
KARL STORZ GmbH & Co. KG
