| AVS 54th International Symposium | |
| MEMS and NEMS | Tuesday Sessions |
| Session MN-TuM |
| Session: | Integration and Packaging in MEMS/NEMS |
| Presenter: | M.I. Beyaz, University of Maryland |
| Authors: | M.I. Beyaz, University of Maryland N. Ghalichechian, University of Maryland A. Modafe, University of Maryland R. Ghodssi, University of Maryland |
| Correspondent: | Click to Email |
Micromachines require closed loop systems to facilitate synchronization and yield maximum performance. However, little effort has been spent on implementing feedback control in these devices. We present for the first time the design, fabrication and testing of an integrated feedback control system for a synchronous electrostatic micromotor. This system aims to synchronize the mechanical motion and the electrical excitation to improve stability and performance. The micromotor is composed of a stator and a movable slider supported on microball bearings. Interdigitated photodiodes are located on the stator to detect the position of the slider moving relative to the stator electrodes. Through holes, created by deep reactive ion etching, are aligned with the poles on the slider. This allows light, provided from the top, to reach the photodiodes on the stator. The design is such that the optical sensing of slider position is achieved by simultaneous alignment of pole-electrode and hole-photodiode pairs, causing an increase in photodiode current. The change in current is sensed and the appropriate voltages are applied to stator electrodes by a feedback circuit. The designed photodiodes have been implemented on n-type 20 Ω-cm silicon wafers. The fabrication consists of etching the native oxide on the wafer, aluminum sputtering and wet etching. Prior to the integration of the photodiodes with the micromotor, a test setup was built to verify the feasibility of the feedback system. In this setup the stator, on which only the photodiodes are fabricated, is fixed to an oscillating platform driven sinusoidally at 5 Hz at an amplitude of 1.6 mm. The slider is kept stationary and a light source is provided from the top. Resulting photodiode current depends on how much light it receives through the holes. The motion of the stator is monitored by the photodiode response that is in the form of a triangular wave. Each peak on the waveform corresponds to a complete alignment between the photodiode and a hole on the slider. Using this peak detection, the instantaneous platform speed is calculated showing good agreement with the applied sinusoidal motion with an R2 value of 0.925. This work verifies the feasibility of the feedback system for the given micromotor to achieve higher speeds and to stand varying load conditions. Detailed fabrication steps and experimental results of the micromotor with the control system will be presented.