Parylene Technology for Neural Probes Applications

Abstract

Neural probes are important tools in detecting and studying neuron activities. Although people have been working on neural probe development for a long time, the current neural probes (including metal-wire probes and silicon neural probes) are still far from being satisfactory. An ideal neural probe array should have good biocompatibility, high-density electrodes with high signal-to-noise ratio, flexible cables for interconnections, integrated electronics, and even integrated actuators to track neuron movement. The work of this thesis focused on applying parylene technology to neural probes development to make a new generation of neural probes with better functions. With the properties of high electrical resistivity, mechanical flexibility, biocompatibility, low coefficient of friction, and an easy deposition/etching process, parylene is a good material for neural probe applications. In this thesis, we have designed, fabricated, and characterized a new parylene neural probe with a long, flexible parylene cable for a neural prosthesis system. Parylene layers are first used on the silicon probe shank with multiple electrodes as insulation and protective layers. And long parylene flexible cables are first monolithically integrated with silicon neural probes. A 96-electrode high-density, 3-D neural probe array for chronic implantation has been demonstrated. Different types of electrolysis actuators (including a silicon diaphragm actuator and a parylene balloon actuator) have been made and tested. The research on electrolysis-based actuators shows their great potential to be used for movable neural probes. Compared with the traditional silicon neural probes (e.g., the Michigan probes, the Utah electrode arrays), our microfabricated neural probes have much longer and stronger probe shanks (8 or 12 mm long, able to penetrate the human pia) and much longer flexible parylene cable (about 7 or 12 cm, long enough to go through a percutaneous connector and the human skull). At the same time, our new probe arrays are shown to have better biocompatibility (being totally covered with parylene material), lower stress, better penetration ability, and greater flexibility for making high-density 3-D arrays and for use in chronic neural signal recording implantation.