Norio Fujitsuka

Topology optimization method using multistep mapping from 2D photomask to 3D MEMS

We have developed a topology optimization method for designing a two-dimensional (2D) photomask. It employs micromachining-process-like multistep mapping to analytically improve the characteristics of a three-dimensional (3D) MEMS fabricated by the photomask. We used this method to design reinforcing ribs for an electrostatic micromirror to reduce deformation caused by internal residual stress. Employing a dot-array pattern as the initial topology, the optimization calculation converged after 300 iterations. It predicts a 79.1% reduction in the maximum displacement. To verify this result, micromirror structures were fabricated and their deformations were measured. The deformation was reduced by 87.1% in this experiment. The calculation results agree well with the experimental results, demonstrating the effectiveness of the proposed method.

Silicon Angular Rate Sensor for Automotive Control with Open Beam Structure

An angular rate sensor of SOI (silicon on insulator) has been developed for automotive control. The sensor detects yaw rate of automobiles. The concept of the sensor design is the open beam structure (OBS). In the OBS, excitation and detection electrodes are open toward exterior bonding pads in a plane. The OBS has high independency between excitation and detection modes. The FEM analysis was carried out and the results showed the OBS was highly independent compared to other structures. This good feature contributed to the stability of vibration mode for the sensor. The OBS also made it possible to wire from the electrodes besides the mass to the exterior bonding electrodes with mono-layer silicon of the SOI. By means of the easy wirings the process and the packaging became simple. The sensor was fabricated by surface micro machining process to miniaturize the size. The measured characteristics show the OBS is suitable for angular rate sensor to be small, highly precise, and low cost