An investigation of wire electrical discharge machining (WEDM) of p-doped elemental semiconductors for wafer slicing and high-aspect-ratio microfabrication.

摘要

Virtually all space based defense, civil and commercial satellites are equipped with multijunction solar cells. However, even with photo-to-electric conversion efficiency reaching 35-39%, the high cost of these solar cells has never made it a viable alternative to silicon solar cells for terrestrial applications. In recent years the use of concentrator technology to multijunction solar cells has pushed its efficiency even further (>40%) and this increasing rate of efficiency will help it to balance out the cost advantage of silicon solar cells (efficiency 24%), as far less number of modules will be capable of generating similar wattage. This research adds another pathway in reducing the overall cost of these cells by seeking to develop an efficient process for better utilization of expensive germanium material which is used as a substrate in these cells. Germanium wafers have a similar lattice constant to that of gallium arsenide (GaAs), making it a perfect substrate for GaAs-based multijunction solar cells.;This research seeks to create a potential use of wire electrical discharge machining (WEDM) process in the slicing of germanium boules into wafers, making it a cost reducing and material saving alternative to existing multiwire saw (MWS) technology for conductive semiconductors. The advantage of WEDM is the fact that the wire used in the process (50-100 mum diameter) is significantly thinner than the steel wire used (160-180 mum) in the MWS process. This allows considerably more wafers to be cut from a single boule, thereby increasing the production yield and decreasing manufacturing cost.;This research also investigates the use of microwire electrical discharge machining (mu-WEDM) in manufacturing high aspect ratio microstructures. These can later be used in fabrication of devices such as neural electrode array, which are used in intracortical recording systems that record neural signals from the brain. As a top down approach that creates geometry through material removal, mu-WEDM is capable of producing these high aspect ratio structures monolithically. The ability of WEDM to machine complicated structures is used in fabrication of compliant 3D-structures. These if used in applications such as neural electrode arrays can do less damage to the tissues due to their low lateral stiffness.