Novel polysilicon based implants for single neuronal recording and stimulation

It has been successfully demonstrated from prior experiments that thin film microelectrodes of polysilicon can be used for monitoring the electrical activity of single neurons. Machinability, biocompatibility and compatibility with complementary metal-oxide semiconductor (CMOS) processing make polysilicon particularly attractive to interface both digital circuits and present day microelectromechanical systems (MEMS) technology with biological entities. In this study, the structure-property relationships in ion-implanted (phosphorus) low pressure chemical vapor deposited (LPCVD) polysilicon thin films were first investigated. The polysilicon thin films were annealed at different times and temperatures and simultaneous characterizations were performed using various techniques. Optimization of these films was carried out for both recording and stimulation of single neurons. In the second part, using the optimized processing conditions, high and low doped polysilicon microelectrode arrays (MEAs) were fabricated using photolithography techniques and rodent cortical neurons were cultured. Spontaneous activation potentials were recorded and compared between different MEAs. Low doped polysilicon MEAs were fabricated with different sizes and shapes and the charge storage behavior in phosphate buffer saline (PBS) solution was analyzed using conventional cyclic voltammetry techniques. The results were compared with finite-element modeling. In the third part, novel current-voltage characteristics of doped polysilicon thin films under small amplitude excitation were evaluated. The inherent current-voltage characteristics could potentially improve noise suppression and hence signal-to-noise (SNR) ratio particularly in applications where the signal to be sensed is in the order of microvolts. Through a systematic study involving both experiments and simulation, the conduction properties of doped polysilicon thin films and its importance to recording neuronal action potentials were investigated. This comprehensive study of polysilicon thin films for neuronal recording/stimulation will assist in developing efficient interfaces that could integrate with CMOS/MEMS devices for future neural prosthesis.