High fill-factor two-axis gimbaled tip-tilt-piston micromirror array actuated by self-Aligned vertical electrostatic combdrives

In this paper, we present a high fill-factor micromirror array actuated by self-aligned vertical electrostatic combdrives. To meet the requirements of applications in free-space communication and imaging, each micromirror has three degrees of freedom of motion: rotation around two axes in the mirror plane and linear translation perpendicular to the mirror plane. Our approach is to integrate the high fill-factor reflectors into the fabrication process of the actuators on the wafer-scale. Multilevel silicon-on-insulator (SOI) bonding is utilized to form the high optical quality reflectors and high aspect-ratio vertical combdrive actuators. The wiring for electrical access to the multielectrode per pixel array is fabricated on separate wafers by thin film processing, and flip-chip bonded to the reflector/actuator chip. This architecture overcomes the fill-factor limitation of top-side accessed electrical addressing of mirrors made on SOI. Our 360/spl mu/m pixel size mirror array achieves a 99% fill-factor with optically flat reflectors.     

A circular micromirror array fabricated by a maskless post-CMOS process

This work studies the fabrication of a circular micromirror array by the standard 0.35 m SPFM (Single Polysilicon Four Metals) CMOS (complementary metal oxide semiconductor) process and a maskless postprocess. The advantages of the post-process are its compatibility with conventional CMOS process and this method provides a way to designer to quickly construct micromachined structures using the standardized procedures. The mentioned circular micromirror array that contains 10 × 10 micromirror switches is integrated with a 1 × 8 de-multiplexer control circuit and a four-stage charge pump on a chip. The radius of each micromirror is about 25 ìm, and the gap from the bottom electrode to the top mirror plate is about 5 m. The micromirror array is actuated using an electrostatic force. Simulated results show that the micromirror has a tilting angle of around 9° at a driving voltage of 30 V. The root-mean-square roughness and the average roughness of the mirror surface are measured at 15.31 nm and 12.58 nm respectively. In addition, the first and the second mode of natural frequency of the micromirror switch are around 492 KHz and 508 KHz, respectively.The authors would like to thank Song-Nan Chen, Yao-Tian Huang of the Institute of Applied Mechanics, National Taiwan University, Professors Lung-Jieh Yang, and Chien-Liu Chang for their valuable advice and assistance in experiment. In addition, we would, finally, like to thank the NSC Northern Region MEMS Research Center, the National Chip Implementation Center and the National Center for High-performance Computing for kindly making their complete research facilities available.     

Development of a novel micromirror based on surface micromaching technology

A novel 3 × 3 micromirror array is designed and successfully fabricated with multi-layer silicon surface micromaching technology. It is composed of bottom electrode, support part and mirror plate, in which a T type beam structure is used to support the mirror plate. It can provide mirror with the vertical movement and the rotation about two horizontal axes, thus enabling phase modulation and amplitude modulation for the incident light. The test results show that the maximum deflection length along the vertical direction of the mirror plate is 2 μm, while the rotation angle about X- and Y-axis are ±2.3° and ±1.45°, respectively.     

Fabrication of metallic micromirror using electroplating technology

A nickel micromirror array was designed and successfully fabricated using a thick photoresist as a sacrificial layer and as a mold for nickel electroplating. It was composed of two address electrodes, two support posts and a nickel mirror plate. The mirror plate, which is supported by two nickel posts, is overhung about 10 μm from the silicon substrate. The nickel mirror plate is actuated by an electrostatic force generated by electrostatic potential difference applied between the mirror plate and the address electrode. Optimized fabrication processes have been developed to reduce residual stress in mirror plate and prevent contact between the mirror plate and the substrate, which ensure a reasonable flat and smooth micromirror for operation at low actuation voltage.

     

Design, Modeling, and Demonstration of a MEMS Repulsive-Force Out-of-Plane Electrostatic Micro Actuator

An analytical model is developed for a two-layer repulsive-force out-of-plane micro electrostatic actuator by using conformal mapping techniques. The model provides the means to establish the performance characteristics in terms of stroke and generated force of the actuator and is used to develop design and optimization rules for the actuator. Numerical simulations were conducted in order to verify the analytical model. A simple physical model is also presented that explains the mechanism for generating the repulsive force. A Multi-User-MEMS-Processes repulsive-force out-of-plane rotation micromirror is developed to experimentally verify the analytical model and to demonstrate the repulsive-force actuator's capability of driving large-size rotation plates by using surface micromachining technology. Experimental measurements show that the repulsive-force rotation micromirror with a size of 312 mum times 312 mum achieved a mechanical rotation of 0deg-2.1deg at a dc driving voltage of 0-200 V. The micromirror achieved an open-loop settling time of 2.9 ms for a mechanical rotation of 2.3deg and an open-loop bandwidth of 150 Hz (-3 dB).     

Design, Fabrication, and Characterization of a High Fill-Factor, Large Scan-Angle, Two-Axis Scanner Array Driven by a Leverage Mechanism

We report on the design, fabrication, and characterization of a high fill-factor, large scan-angle, two-axis scanner array. The two-axis microelectromechanical-systems (MEMS) mirror is driven by electrostatic vertical comb-drive actuators through four motion amplifying levers. The maximum mechanical rotation angles are$pm 6.7^circ$at 75 V for both axes, leading to total optical scan angle of 26.8$^circ$. The resonant frequency is 5.9 kHz before metallization. A linear fill factor of 98% is achieved for the one-dimensional (1-D) micromirror array. This 1D array of two-axis micromirrors was designed for$1times N ^2$wavelength-selective switches (WSSs). In addition to two-axis rotation, piston motion with a stroke of 11.7$mu m$is also attained.1731     

Pull-in-based μg-resolution accelerometer: Characterization and noise analysis

The pull-in time (t_pi) of electrostatically actuated parallel-plate microstructures enables the realization of a high-sensitivity accelerometer that uses time measurement as the transduction mechanism. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. Parallel-plate MEMS structures have been designed and fabricated using a SOI micromachining process (SOIMUMPS) for the implementation of the accelerometer. This paper presents the experimental characterization of the microdevices, validating the concept and the analytical models used. The accelerometer has a measured sensitivity of 0.25 μs/μg and a bandwidth that is directly related to the pull-in time, BW = 1/2t_pi ≈ 50 Hz. These specifications place this sensor between the state of the art accelerometers found both in the literature and commercially. More importantly, the resolution of the measurement method used is very high, making the mechanical-thermal noise the only factor limiting the resolution. The in-depth noise analysis to the system supports these conclusions. The total measured noise floor of 400 μg (100 μs) is mainly due to the contribution of the environmental noise, due to lack of isolation of the experimental setup from the building vibrations (estimated mechanical thermal noise of 2.8 μg/√Hz). The low requirements of the electronic readout circuit makes this an interesting approach for high-resolution accelerometers.     

Investigation of the torsion and bending effects on static stability of electrostatic torsional micromirrors

In this paper the electromechanical behavior of a torsional micromirror was investigated using of a static model with considering torsion and bending characteristics of micro-beams. A set of nonlinear equations based on the parallel plate capacitor model was derived to represent the relationships between the applied voltage, torsion angle, and vertical displacement of the torsional micromirror. Step by step linearization method (Newton’s method) was used to calculate the rotation angle and vertical displacement of the micromirror due to the applied voltage. This method is fast and gave acceptable and accurate results which were in good agreement with the experimental data.     

Arrays of large-area, tip/tilt micromirrors for use in a high-contrast projector

Arrays of two-degree of freedom analog micromirrors are designed for use within an high-contrast projector and fabricated using a multi-user MEMS fabrication process. We demonstrate a novel way of optimizing the tradeoffs between tilt angle and mirror size by subdividing the mirrors into smaller functional subsections that move synchronously. The mirror design employs multiple mirrors within a gimbal frame. The frame rotates around one axis, and each mirror within the frame rotates around a perpendicular axis, resulting in two-degree of freedom rotation. The design employs specific electrode shapes to allow one-layer connections. Using these fabricated mirrors, simultaneous actuation of mirrors within a composite structure is achieved. A prototype array of fabricated mirrors is described, with 6 × 5 mirrors each of 160 μm × 160 μm forming one composite mirror of an array, giving total active area of 960 μm × 800 μm. The mirrors can achieve a maximum tilt angle of 2.25°. The fill factor of this design is 68%.     

Modeling, Design, Fabrication, and Demonstration of a Digital Micromirror With Interdigitated Cantilevers

We present the modeling, design, fabrication, and measurement results of a novel digital micromirror based on a new actuator called interdigitated cantilevers. In contrast to conventional micromirrors that rotate through the twisting actuation of a hinge, this micromirror has a symmetric bidirectional rotation through a bending actuation of interdigitated cantilevers hidden under a mirror plate. For the static and dynamic characteristics of the proposed micromirror, analytical models were developed first on the basis of the Euler–Bernoulli beam equation, as well as both distributed- and lumped-parameter models. The results of the developed analytical models are in good agreement with those of a finite-element-method (FEM) simulation, having just a 10% deviation. On the basis of these analytical models, we successfully designed, fabricated, and evaluated a micromirror with a mirror size of $16 muhbox{m} times 16 muhbox{m}$. The fabricated micromirror has a mechanical rotation angle of $pm 10^{circ}$, a pull-in voltage of 54 V, a resonant frequency of 350 kHz, and a switching response time of 17 $muhbox{s}$. The measurement results compare favorably with those of analytical models and FEM simulations, with deviations of less than 15% and 10%, respectively. $hfill$[2009-0139]      

Dynamic response of a torsional micromirror to electrostatic force and mechanical shock

In this paper dynamic characteristics of a capacitive torsional micromirror under electrostatic forces and mechanical shocks have been investigated. A 2DOF model considering the torsion and bending stiffness of the micromirror structure has been presented. A set of nonlinear equations have been derived and solved by Runge–Kutta method. The Static pull-in voltage has been calculated by frequency analyzing method, and the dynamic pull-in voltage of the micromirror imposed to a step DC voltage has been derived for different damping ratios. It has been shown that by increasing the damping ratio the dynamic pull-in voltage converges to static one. The effects of linear and torsional shock forces on the mechanical behavior of the electrostatically deflected and undeflected micromirror have been studied. The results have shown that the combined effect of a shock load and an electrostatic actuation makes the instability threshold much lower than the threshold predicted, considering the effect of shock force or electrostatic actuation alone. It has been shown that the torsional shock force has negligible influence on dynamic response of the micromirror in comparison with the linear one. The results have been calculated for linear shocks with different durations, amplitudes, and input times.     

An Electrothermal Tip–Tilt–Piston Micromirror Based on Folded Dual S-Shaped Bimorphs

This paper presents the design, optimization, fabrication, and test results of an electrothermally actuated tip-tilt-piston micromirror with a large optical aperture of 1 mm. The fabrication of the device is a combination of thin-film surface micromachining and bulk silicon micromachining based on silicon-on-insulator wafers. The device has 3-DOF of actuations, including rotations around two axes in the mirror plane, and out-of-plane piston actuation. The micromirror shows an optical scan range of plusmn30^deg about both x- and y-axes and displaces 480 mum in the z-axis, all at dc voltages that are less than 8 V. Dynamic testing of the micromirror shows that the thermal response time of each actuator is about 10 ms. Resonant frequencies of the piston and rotation motion are 336 and 488 Hz, respectively. The unique structural design of the device ensures that there is no lateral shift for the piston motion and no rotation-axis shift for the rotation scanning. With the large tip-tilt-piston scan ranges and low driving voltage, this type of device is very suitable for biomedical imaging and laser beam steering applications.     

A MEMS micromirror fabricated using CMOS post-process

This work describes the fabrication of a micromachined micromirror by the conventional 0.35 μm CMOS process and a simple maskless post-CMOS process. The micromirror contains a rectangular mirror plate and four pairs of serpentine supported beams, is integrated with a 1 × 4 demultiplexer and a four-stage charge pump circuits on a chip. Maskless dry and wet etching processes are the only requirement to suspend the structure. The primary limitation in the fabrication of microstructures has been overcome by the development of a hybrid processing technique, which combines both an anisotropic dry etch and an isotropic wet etch step. A highly reliable wet etching step with high selectivity between aluminum and sacrificial oxide is also reported. Experimental results reveal that the micromirror has a tilting angle of around 5° at operation voltage of 22.5 V and a dynamic response less than 5 ms. The surface properties of the CMOS micromirror, detailed process flows, measurement set-up and the experimental results are also presented in this work.     

Fabrication of metallic micromirror using electroplating technology

A nickel micromirror array was designed and successfully fabricated using a thick photoresist as a sacrificial layer and as a mold for nickel electroplating. It was composed of two address electrodes, two support posts and a nickel mirror plate. The mirror plate, which is supported by two nickel posts, is overhung about 10???m from the silicon substrate. The nickel mirror plate is actuated by an electrostatic force generated by electrostatic potential difference applied between the mirror plate and the address electrode. Optimized fabrication processes have been developed to reduce residual stress in mirror plate and prevent contact between the mirror plate and the substrate, which ensure a reasonable flat and smooth micromirror for operation at low actuation voltage.     

一种新型梳齿驱动式微镜

提出一种采用梳齿驱动方式的新型微镜结构,通过外加电压使处于不同高度的可动梳齿与固定梳齿产生转动,带动镜面发生偏转。研究表明:在外加电压为101V时,微镜的转动范围达15.4°,超过平行板驱动微镜。同时,采用有限元方法进行了仿真模拟,结果显示:其固有频率、抗干扰性高于平行板驱动微镜。     

Fabrication and characterization of a piezoelectric micromirror using for optical data tracking of high-density storage

A micromirror actuated by three piezoelectric microcantilevers is presented for optical data tracking of high-density storage application. The microcantilevers are actuated by 2.5-μm-thick lead zirconate titanate (PZT) films which are deposited on the silicon-based substrate by a compatible sol–gel route. The X-ray diffraction result shows that the PZT film is perovskite structure and has a typical good ferroelectric loop. The quasi-static displacement of the mirror plate increases linearly with increasing the driving voltage and the tracking resolution on disk is as high as 8 nm/V. The micromirror also provides a high bandwidth of about 21 kHz, which is high enough to support the optical data tracking of future high-density storage.     

Preparation and characterization of unimorph actuators based on piezoelectric Pb(Zr0.52Ti0.48)O3 materials

This paper describes the preparation and characterization of unimorph actuators for deformable mirrors, based on Pb(Zr_0.52Ti_0.48)O₃ (PZT52) thin film. As comparison, two different designs, where the PZT layer in the unimorph actuators was driven by either interdigitated electrodes (IDT-mode) or parallel plate electrodes (d₃₁-mode), were investigated. The actuators utilize a unimorph membrane (diaphragm) structure consisting of an active PZT piezoelectric layer and a passive SiO₂/Si composite layer. To fabricate the diaphragm structures, n-type (1 0 0) silicon-on-insulator (SOI) wafers with 1 μm thermal SiO₂ were used as substrates (for d₃₁-mode actuators, the upper Si part of SOI need to be heavily doped and used as bottom electrodes simultaneously). Sol-gel derived PZT piezoelectric layers with PbTiO₃ (PT) bufferlayer in total of 0.86 μm were then fabricated on them, and 0.15 μm Al reflective layers were deposited and patterned into top electrode geometries, subsequently. The diaphragms were released using orientation-dependent wet etching (ODE) with 5-10 μm residual silicon layers. The complete unimorph actuators comprise 4 × 4 discrete units (4 mm² in size) with patterned PZT films for parallel plate configuration or 3 × 3 individual pixels (2 mm in IDT diameter) with continuous PZT films in graphic region for IDT configuration. The measurement results indicated that both of the two configurations can generate considerable deflections at low voltage. The measured maximum central deflections at 15 V were approximately 2.5 μm and 2.8 μm, respectively. The intrinsic strain conditions shaping the deflection profiles for the diaphragm actuators were also analyzed. In this paper, the behaviors of clamped parallel plate configuration without a diaphragm were also evaluated.     

Reduction of squeeze-film damping in a wafer-level encapsulated RF MEMS DC shunt switch

This paper presents the design, fabrication and characterization aspects of a wafer-level encapsulated RF MEMS shunt switch with a perforated base substrate and a corrugated diaphragm. A three-wafer stacking concept was proposed to achieve a RF MEMS shunt switch based on metal-metal contact. The introduction of damping holes in the base substrate wafer is proven to be an effective way to reduce squeeze-film damping and thus increase the switching speed of the switch. It is also demonstrated by analytical calculation that some factors play important roles on the damping characteristics, such as the physical location of damping holes in the base substrate, hole size, and number of holes per radius ring. By means of the implementation of damping holes, the pull-in and release time of the fabricated MEMS switch are significantly reduced by about 13 times, from 5.4 ms to 0.435 ms and 40.6 ms to 3.2 ms, respectively.     

Development of a dehydrogenase-based glucose anode using a molecular assembly composed of nile blue and functionalized SWCNTs and its applications to a glucose sensor and glucose/O2 biofuel cell

A simple and new way to immobilize glucose dehydrogenase (GDH) enzyme onto nile blue (NB) covalently assembled on the surface of functionalized single-walled carbon nanotubes (f-SWCNTs) modified glassy carbon (GC) electrode (GDH/NB/f-SWCNTs/GC electrode) was described. The GDH/NB/f-SWCNTs/GC electrode possesses promising characteristics as glucose sensor; a wide linear dynamic range of 100-1700 μM, low detection limit of 0.3 μM, fast response time (1-2 s), high sensitivity (14 μA cm⁻² mM⁻¹), anti-interference ability and anti-fouling. Moreover, the performance of the GDH/NB/f-SWCNTs/GC bioanode was successfully tested in a glucose/O₂ biofuel cell. The maximum power density delivered by the assembled glucose/O₂ biofuel cell could reach 32.0 μW cm⁻² at a cell voltage of 0.35 V with 40 mM glucose. The present procedure can be applied for preparing a potential platform to immobilize different enzymes for various bioelectrochemical applications.