Electromagnetically Actuated Micromirror Along Two-axis


A new micromirror structure has been proposed and fabricated. The proposed micromirror is electromagnetically actuated along two-axis at low voltage using an external magnetic field. The main purpose of this work is to obtain a micromirror in a mechanically robust structure with large deflection angles at low voltage. The mirror plates and torsion bars are made of bulk silicon using a SOI wafer and the actuation coils are made of electroplated copper. The maximum deflection angles have been measured as ±4.35° for x-axis actuation and ±15.7° for y-axis actuation. The actuation voltages are below 4.2V for x-axis actuation and 1.76V for y-axis actuation, respectively. The magnitude of external magnetic field is 0.16 Tesla. The maximum operating current is 200mA and power consumption is less than 650mW. Another type of micromirror is proposed and fabricated as shown in Fig. 3. The proposed micromirror is made of electroplated copper and this process makes it easy to gain large gap for rotation in case of surface micromachining. It actuates using electrostatic force between mirror plate and elevated electrode under mirror plate. These fabricated micromirrors can be applied to optical switch, optical scanner and display.

Figure 1. Schematic diagram and simulated actuation of proposed micromirror with external magnetic field.

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Figure 2. FEM simulation using ANSYS: (a) x-axis actuation using cantilever actuator, (b) y-axis actuation using coils on the mirror plate.
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Figure 3. SEM pictures of fabricated micromirror which is actuates electromagnetically. (a) Diced micromirror. (b) Cantilever actuator used for x-axis actuation.
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Figure 4. Comparison graph of angular deflection according to the applied current between simulation results and measured data: (a) x-axis actuation, (b) y-axis actuation

Related Publication
  1. Il-Joo Cho, Kwang-Seok, Yun, Hyung-Kew Lee, Jun-Bo Yoon and Euisik Yoon, "A Low Voltage Two- Axis Electromagnetically Actuated Micromirror with Bulk Silicon Mirror Plates and Torsion Bars", IEEE MEMS 2002 Conference, Las Vegas, USA, Jan., 2002.