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We are developing a phase-modulating micro mirror-array spatial light modulator to be used for real holography within the EU-funded project REALHOLO, featuring millions of pixels that can be individually positioned in a piston mode at a large frame rate. We found earlier that an electrostatic comb-drive array offers the best performance for the actuators: sufficient yoke forces for fast switching even at low voltages compatible with the CMOS addressing backplane. In our first design, the well-known electrostatic cross-talk issue had already been much smaller than would have been possible for parallel-plate actuators, but it was still larger than the precision requirements for high-image-quality holography. In this paper, we report on our analysis of the crucial regions for the electrostatic cross-talk and ways to reduce it while observing manufacturing constraints as well as avoiding excessively high field strengths that might lead to electrical breakdown. Finally, we present a solution that, in FEM simulations, reduces the remaining cross-talk to well below the required specification limit. This solution can be manufactured without any additional processing steps and suffers only a very small reduction of the yoke forces. [ABSTRACT FROM AUTHOR]

We are developing a phase-modulating micro mirror-array spatial light modulator to be used for real holography within the EU-funded project REALHOLO, featuring millions of pixels that can be individually positioned in a piston mode at a large frame rate. We found earlier that an electrostatic comb-drive array offers the best performance for the actuators: sufficient yoke forces for fast switching even at low voltages compatible with the CMOS addressing backplane. In our first design, the well-known electrostatic cross-talk issue had already been much smaller than would have been possible for parallel-plate actuators, but it was still larger than the precision requirements for high-image-quality holography. In this paper, we report on our analysis of the crucial regions for the electrostatic cross-talk and ways to reduce it while observing manufacturing constraints as well as avoiding excessively high field strengths that might lead to electrical breakdown. Finally, we present a solution that, in FEM simulations, reduces the remaining cross-talk to well below the required specification limit. This solution can be manufactured without any additional processing steps and suffers only a very small reduction of the yoke forces.

In electrostatic comb drive-based sensors and actuators, often there is a possibility of nonparallel motion or bending in individual comb which considerably affects the device performance including pull-in characteristic. In this paper, we have presented a theoretical and experimental investigation to reduce such undesired beam bending in gap closing-type comb drive actuator. It has been envisaged that three key parameters, responsible for beam bending, are spring stiffness, beam stiffness, and number of actuation beams. Subsequently, a design guideline has been proposed to reduce the undesired bending by appropriate selection of these parameters. A specific comb drive actuator having multiple actuation regions with varying number of beams is designed, simulated, and analyzed using a semianalytical approach and FEM tool. Further, the structure is fabricated by establishing a silicon-on-insulator (SOI)-based single mask fabrication process and tested with an in-house experimental setup. The theoretical predictions are validated with the experimental results to demonstrate how the undesired beam bending can be reduced significantly by suitable selection of number of actuation combs for a given ratio of spring and beam stiffness. The proposed guidelines enable the micro-electromechanical system (MEMS) designers to cautiously choose the key parameters while designing in order to avoid the undesired comb bending and operate the device safely. [ABSTRACT FROM AUTHOR]

We develop an optical ring resonator with tunable coupling coefficients for use in wavelength division multiplexing routers. The coupling coefficients of the resonator are precisely tuned by the utilization of an electrostatic comb drive microelectromechanical system (MEMS) actuator. The MEMS actuator has the ability to accurately adjust gap spacing between cavity and waveguide. Moreover, integration of MEMS actuator with optical ring resonators overcomes the optical lithography challenges for patterning the small gap between cavity and waveguide. Different finite-element (FE) method simulations have been carried out in order to study the mechanical and optical operating characteristics of the ring resonator. The movable microring resonator can be displaced 1.33 μm with less than 3 V actuation voltage in 850 μs to control the transferred optical power and bandwidth of the resonator. Optical simulations show extinction ratios as high as 17 dB for the device with 90-nm gap spacing and 21.5 dB for the device with 60-nm gap spacing, respectively. In addition, the bandwidth of the filter is adjustable from 0.3 to 0.65 nm. [ABSTRACT FROM AUTHOR]

We have developed a MEMS (micro electro mechanical systems)-based method for fatigue testing of micrometer- millimeter-sized specimens of any material (hence 'universal'). The miniature, re-usable, stand-alone fatigue test frame is fabricated as a single MEMS chip. Specimens of any material can be manually mounted in the chip and fatigue-tested. We describe the design and construction of the MEMS device and specimens, the test protocol and data analysis procedure, and show stress versus number of cycles to failure (S-N) results for 25 μm thick Al 1145 H19 foil. The S-N results are in accord with expectations, and examination of the fracture surface by scanning electron microscopy shows distinct regions corresponding to slow and fast crack growth. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present the concept of a microelectromechanical systems ring laser gyroscope (MEMS-RLG) and its optical components. MEMS-RLG has a semiconductor optical amplifier (SOA) enclosed with mirrors that form an optical loop for an external laser oscillator in free space. To confirm the feasibility of MEMS-RLGs, we constructed an experimental device with commercially available SOA and mirrors for external oscillation. We also show the fabrication and characteristics of optical components such as movable mirrors and a lens-positioning device, which are required for a miniaturized MEMS-RLG. [Copyright &y& Elsevier]

We present a novel method for 3D microfabrication with LIGA process that utilizes a deep X-ray mask in which a microactuator is integrated. The integrated microactuator oscillates the X-ray absorber, which is formed on the shuttle mass of the microactuator, during the X-ray exposures to modify the absorbed dose profile in X-ray resist, typically PMMA. The 3D PMMA microstructures according to the modulated dose contour are revealed after GG development. An X-ray mask with integrated comb drive actuator is fabricated using deep reactive ion etching, absorber electroplating, and bulk micromachining with silicon-on-insulator wafer. Silicon shuttle mass (1 mm×1 mm, 20 μm thick) as a mask blank is supported by four 1 mm long suspension beams and is driven by the comb electrodes. A 10 μm thick, 50 μm line and spaced gold absorber pattern is electroplated on the shuttle mass before the release step. The fundamental frequency and amplitude are around 3.6 kHz and 20 μm, respectively, for a dc bias of 100 V and an ac bias of 20 VP–P (peak–peak). Fabricated PMMA microstructure shows 15.4 μm deep, S-shaped cross-section in the case of 1.6 kJ cm−3 surface dose and GG development at 35 °C for 40 min. [Copyright &y& Elsevier]

[Display omitted] • Electromechanical model of both the comb drive and its suspension is introduced. • The current drive topology is presented, including extensive leakage compensation. • Different feedback sensor topologies are presented. • Extensive displacement error analysis is performed. • A 50 nm resolution over a 200 μ m displacement is achieved. We present the design of a novel driver for a comb drive actuator. This actuator is required to have both a large displacement of 200 μ m and a high resolution of 50 nm. Traditionally, electromechanical MEMS actuation is done under voltage control. In this paper, we want to examine a charge controlled driver, as it might provide some advantages. A comb drive under charge control exhibits a longitudinal displacement proportional to Q 2 / 3 , rather than V 2 in case of voltage control. This more linear behavior might help to increase the achievable displacement resolution. It can also be shown that the stability range of an actuator under voltage control, for any type of actuator, will never be larger than the range of that same actuator under charge control. However, for a well-designed and well-fabricated comb drive actuator, where this instability is expressed in lateral pull-in, this effect is minimal. In this paper, we first create an electromechanical model of a comb drive, to be used in simulation of our driver. The created model is based on a previously designed comb drive with a displacement of 200 μ m at 91.6 V, or 138.1 pC. We then focus on the driver itself, minimizing the effects of leakage currents, as these are detrimental for a good charge controlled actuation. As the actuator will be driven dynamically, we cannot rely on the estimated charge on the comb drive to determine the immediate displacement. A sensor is needed that measures the position of the comb drive. Four different topologies of sensors are described, each of which uses the comb drive itself to estimate its position. A full electromechanical simulation is performed and a comparison is made between the different sensor topologies, evaluating their ability to determine the exact displacement. One of the proposed sensor topologies achieved the 50 nm resolution. [ABSTRACT FROM AUTHOR]