Encapsulation of organic field effect transistors for flexible biomedical microimplants

Biomedical microimplants are used as neural prostheses to restore body functions after paraplegia by means of functional electrical stimulation (FES). This paper describes an approach of the integration of organic transistors into flexible biomedical microimplant for FES use. Encapsulation is used to ensure the electrical functionality of implants (insulation) and to protect them from the harsh environments in the human body. So far, biomedical microdevices have been fabricated using silicon or polyimide substrate, respectively. Highly flexible polyimide based microdevices that have been interfaced with nerves as neural prostheses showed excellent properties as implant material [1], [2], [3]. Therefore, we have developed transistors on polyimide, which is used as flexible substrate. Gold was sputtered as gate, drain and source. Silicon oxide formed the gate insulator and pentacene (C14H22) was evaporated at ultra high vacuum (UHV) and 75 °C substrate temperature as active layer in an organic field effect transistor (OFET). Parylene is used as encapsulation material. First transistors have been fabricated and characterized. So far, they are still in low scale integration. The first investigation on the electrical properties of the OFETs before and after encapsulation with Parylene at room temperature led to promising results.