From a controls point of view, micro electromechanical systems (MEMS) can be driven in an open-loop and closed-loop fashion. Commonly, these devices are driven open-loop by applying simple input signals. If these input signals become more complex by being derived from the system dynamics, we call such control techniques pre-shaped open-loop driving. The ultimate step for improving precision and speed of response is the introduction of feedback, e.g. closed-loop control. Unlike macro mechanical systems, where the implementation of the feedback is relatively simple, in the MEMS case the feedback design is quite problematic, due to the limited availability of sensor data, the presence of sensor dynamics and noise, and the typically fast actuator dynamics. Furthermore, a performance comparison between open-loop and closed-loop control strategies has not been properly explored for MEMS devices. The purpose of this paper is to present experimental results obtained using both open-and closed-loop strategies and to address the comparative issues of driving and control for MEMS devices. An optical MEMS switching device is used for this study. Based on these experimental results, as well as computer simulations, we point out advantages and disadvantages of the different control strategies, address the problems that distinguish MEMS driving systems from their macro counterparts, and discuss criteria to choose a suitable control driving strategy.

The paper reviews the state-of-the-art of miniaturized tunable lasers constructed by microelectromechanical systems (MEMS) technology, covering various topics of laser configurations, theoretical studies and some design issues, with primary focus on the uniqueness of MEMS tunable lasers in comparison to conventional opto-mechanical counterparts. Further studies have also been presented to investigate the tuning range and stability in order to provide a deep understanding of the specialities of MEMS lasers in the sense of physics. The introduction of MEMS has endowed two special features to tunable lasers. One is that MEMS facilitates external cavities at very short (<100 µm) and even extremely short length (<10 µm), leading to unusual tuning behaviors and different design concerns. The other is that the photolithography of the MEMS process makes it possible to fabricate gratings/mirrors in arbitrary profiles, which may inspire the innovation of new laser configurations that can only be realized by MEMS technology. With further work on integration and packaging, MEMS lasers would be able to deliver their merits of small size, fast tuning speed, wide tuning range and IC integration compatibility, and to broaden their applications to many fields.

This paper studies the effect of surface roughness on up-state and down-state capacitances of microelectromechanical systems (MEMS) capacitive switches. When the root-mean-square (RMS) roughness is 10 nm, the up-state capacitance is approximately 9% higher than the theoretical value. When the metal bridge is driven down, the normalized contact area between the metal bridge and the surface of the dielectric layer is less than 1% if the RMS roughness is larger than 2 nm. Therefore, the down-state capacitance is actually determined by the non-contact part of the metal bridge. The normalized isolation is only 62% for RMS roughness of 10 nm when the hold-down voltage is 30 V. The analysis also shows that the down-state capacitance and the isolation increase with the hold-down voltage. The normalized isolation increases from 58% to 65% when the hold-down voltage increases from 10 V to 60 V for RMS roughness of 10 nm.

Two novel lateral metal-contact radio-frequency microelectromechanical system (RF MEMS) switches are reported. These switches are implemented with quasi-finite ground coplanar waveguide (FGCPW) configuration and actuated by applying electrostatic force on a high-aspect-ratio cantilever beam. It is demonstrated that the insertion loss of the switch is less than 0.2 dB up to 15 GHz and the isolation is higher than 20 dB up to 25 GHz. An RF model of the switches is used to analyse the effects of the switch design parameters and RF performance. The optimization of the switch mechanical design is discussed where the threshold voltage can be lower than 25 V. The lateral switches are fabricated by deep reactive ion etching (DRIE) process on a silicon-on-insulator (SOI) wafer with shadow mask technology.

A tunable bandstop filter applying the capacitive change of micromachined switches is designed, simulated and fabricated. The filter is realized by incorporating electromagnetic bandgap structures with the micromachined switches. These micromachined switches are used as high contrast capacitive elements between the coplanar waveguide ground plane and the signal line to tune the frequency. A new approach for finding the propagation characteristic of the periodic micromachined switches is determined by the dispersion behavior. Different types of parametric analysis are also investigated for the micromachined switches. The surface micromachining fabrication process is employed on the high resistivity silicon substrate to fabricate the filter. The measurement results for the tunable bandstop filter reveal a tuning range from 19 GHz to 17.3 GHz. The lower passband insertion loss is 0.7-2.2 dB and the 20 dB rejection bandwidth is 5.5 GHz.