Studies on Curvature Deformation Control of Bilayer Cantilever Fabricated by Surface Micromachining of SOI Wafer
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0969-W05-01
Studies on Curvature Deformation Control of Bilayer Cantilever Fabricated by Surface Micromachining of SOI Wafer Yu-Ming Huang1, Masayuki Sohgawa1, Minoru Noda1, Kaoru Yamashita1, Masanori Okuyama1, and Haruo Noma2 1 Dept. of Systems Innnovation, Grad. School of Eng. Sci., Osaka Univ., 1-3 Machikaneyamacho, Toyonaka, Osaka, 560-8531, Japan 2 Knowledge Science Lab., ATR, 2-2-2- Hikari-dai, Seika, Souraku, Kyoto, 619-0288, Japan
ABSTRACT Cr/Si bilayer cantilevers for an integrated multi-axis tactile sensor were fabricated by Si surface micromachining process. Among the cantilevers with various shapes, the rectangular and semicircular cantilevers were deflected upward with good controllability. The maximum deflections were compared with those calculated by the finite element method. Calculated deflections of Cr/Si cantilevers agree considerably with the experimental results. So, it is considered that the analysis by finite element method is useful to optimize layer thickness and size to obtain Cr/Si bilayer cantilevers with accurate deflection.
INTRODUCTION A cantilever is one of the basic and important components of various devices for many microelectromechanical systems (MEMS) [1,2], such as AFM probes [3], micro actuators [4], accelerometers [5], humidity sensors [6] and surface acoustic wave (SAW) devices [7]. Recently, we have fabricated a stable and controllable cantilever with high precision as an intelligent tactile sensor [8-10]. It is proposed that an integrated multi-axis tactile sensor can be fabricated by using nano-scale thin film technology. Both pressure and shear forces can be detected by measuring tiny piezoresistance in the cantilevers that are deflected upward, so that it could be employed for many applications, such as man-machine interface or robotics. It is considered that key issues for the integrated cantilever fabrication are, 1) Si LSI process compatibility from viewpoints of cantilever material and its fabrication process to integrate with signal processing circuit on one chip, 2) controllability of deflection of the cantilever, and 3) precise design based on results of finite element method (FEM) analysis. We have found that SiGe epitaxial layer can be used to cause upward deflection of cantilevers. However, it is considered that more compatible materials for Si LSI process should be used instead of SiGe. In this work, cantilevers made with Cr/Si bilayer structures for an integrated tactile sensor were studied. Cr is very attractive because it is chemically stable and its linear coefficient of expansion is large, tensile strength is high and very effective to create upward deflection, so it is applied frequently to various MEMS devices.
CANTILEVER STRUCTURE FOR TACTILE SENSOR Schematic of cantilevers used for the tactile sensors are shown in figure 1. Two pairs of faced cantilevers are placed and cross at a right angle. A soft polymeric material covers all the cantilevers. When vertical pressure is added to the elastic surface homogeneously, all 4 cantilevers are deflected
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