Abstract
As the growth of the biomedical and micro electromechanical technique, various micro transducers which apply in correlative technique of micro biomedical system have gradually been respected and developed. In the field of MEMS (Microelectromechanical Systems), wafer is the elementary material which used to manufacture IC (integrated Circuit) and usually composed of semiconducting material such as silicon or gallinium arsenide (GaAs). Generally, we use silicon wafer as the main. Silicon is a representative brittle material; besides, affected by its own characteristic, major wafer can merely be represented in 2D manner after the manufacturing process. However, lots of biological tissue evolves into non-planar, 3D, geometrical patterns. When a 2D structural micro transducer is implanted into an organic body, the effects of the measurement might be confined due to the shape of the wafer. This study proposes using silicon nitride (Si3N4) thin film which contains high tensile stress to deposit on silicon wafer. The stress of thin film allows chips to have simple geometric deformation; furthermore, utilizing wafer back grinding technique to make 3D geometric chip. A chip that is curved as spherical surface, for example, can be applied to become artificial retina. When the chip is implanted into human eyes, it can perfectly fit the retina which has several advantages. For instance, this can enhance the pixel of image and decrease the impedance of stimulated electrode. On the side, through this non-planar standard procedure, general planar chips can also be molded into other 3D chips that are made use of other aspects. In the beginning of the study, we use CAE analysis software, COMSOL V Multiphysics, to establish a plausible model to discuss the factors that contributing curvature of chip and provide numerical solutions. Experimentally, we use CVD (Chemical Vapor Deposition) to deposit silicon nitride thin film that contains high stress. With the coordination of micro electromechanical manufacturing process technique which defines the shape of chips and silicon nitride thin films, and then by way of wafer thinning technique removes the silicon substrate at the back side of chip allow the integral thickness of a 3mm diametric circle chip to turn into 13μm from 500μm. Finally, using optical measuring instruments to measure the surface profile of a completed chip and comparing with the simulating result to test and verify its consistency.