Research And Applications Of 3-dimensional Micro-electrode Array

As MEMS technology develops rapidly, three dimensional micro structures and devices which usually integrate mechanical, electrical, optical and biological functions are getting more attention from researchers. In this dissertation, three dimensional micro-electrode array and polymer substrate were applied into the research of MEMS probe card for IC testing and bio-stimulating micro-electrode:MEMS probe card has few limitations of probe direction, density and precision. Furthermore, it can improve test stability and efficiency by minimizing the influences of the operators. So MEMS probe card is the developing trend of probe card technology. In order to overcome the problems and shortcomings of current MEMS probe cards, we proposed a novel MEMS probe card based on PDMS-PI elastic substrate and optimized its design and fabrication to reduce the process steps and fabrication costs, and possessed ideal mechanical and electrical properties at the same time.Currently, retinal prosthesis research focuses on the lamellar pigment epithelium transplantation to alternate optical receptor and input the electrical stimulation signal. But stimulating the optical nerve can restore the patients'vision to some degree. The nerve stimulation method requires the height of micro-electrode higher than 50μm so that it can reach the optic nerve fiber layer. Therefore, we proposed a three dimensional nerve stimulating micro-electrode array base on polyimide substrate, with the characteristic of simple fabrication process, low cost, and high safety.The main contents and results are listed as follows:The elastic substrate probe card was designed to be fabricated on PDMS and polyimide. COMSOL finite elements analysis software was utilized to simulate the mechanical behavior of the designed structure and obtain the relationship between the probe tip displacement and the thickness of PDMS and PI. The PDMS-PI elastic substrate probe card was successfully fabricated by MEMS micro-fabrication technology. Then, Nano Indenter XP was introduced to measure the mechanical properties of the probe. When the thickness of PDMS and PI was 180μm and 50μm respectively, spring constant of the probe was 583 Nm-1. DC probes and Agilent E4991A RF Impedance/Material Analyzer were used to measure the electrical properties of the fabricated probe. The contact resistance from the probe tip to the end of strip line was 0.4 ?, and in the frequency range of 1-250 MHz, the characterized impedance between two probes was lager than 5 k?, which meets the requirement of a probe card.SU-8 fabrication process and AZ50XL thick photoresist fabrication process were experimented respectively and the latter method was finally applied to fabricate the bio-stimulating electrode array with a height of 80μm so that it can reach the optic nerve fiber layer. The electrochemical properties of electrodes was analyzed by three-electrode method, and the impedance varied from 1.5～0.3 k? at the frequency from 10-1～105 Hz. With the advantages of small size, light weight, good reliability and flexibility, the device is suitable for implantable bio-stimulation.