Electron-beam lithography for polymer bioMEMS with submicron features

摘要

Flexible, polymer-coated electrodes with features as narrow as 250 nm have been produced using electron-beam lithography. The polymer Parylene C is widely used in implantable devices such as neural probes as a biocompatible and insulating coating for electrodes. However, it is challenging to pattern this polymer with electron beams because of its sensitivity to heat and charge. Ellis Meng and Kee Scholten from the University of Southern California, United States, overcame these limitation with a chromium-capped methacrylate resist mask. Depositing this mask onto a Parylene C-encapsulated titanium thin film helped to reduce thermal stress effects and electric charge build-up, which improved feature resolution by an order of magnitude beyond that of existing approaches. A prototype neural probe with 32 data recording sites along a 2-mm span—an electrode density that greatly exceeds previous polymer implants—demonstrated the potential of the technique.