Testing of "Venetian-Blind" silicon microstructures with optical methods

In this paper, we illustrate the design and testing of new silicon microstructures, fabricated by means of a conventional planar process. These "Venetian-blind" structures consist of arrays of narrow, rectangular suspended masses (width =31 /spl mu/m, length =400 /spl mu/m, thickness =15 /spl mu/m), which can be tilted using electrostatic actuation. Characterization of their static and dynamic behavior was performed with optical methods. The diffraction patterns in monochromatic light were analyzed and vibration measurements were performed by means of semiconductor laser feedback interferometry: experimental data on the tilt angle as a function of the applied voltage and on the resonance frequencies are reported. A maximum tilt angle of approximately 1.9/spl deg/ was obtained with a driving voltage in the range of 70-95 V. All the tested devices showed resonance frequencies higher than 80 kHz, which is fast enough (i.e., switching time in the millisecond range) for future use in optical interconnections. Numerical analyses were performed to evaluate the coupled electromechanical behavior of the microstructures, confirming the observed experimental behavior.     

Novel H-beam electrothermal actuators with capability of generating bi-directional static displacement

A new H-beam electrothermal microactuator is proposed for providing bi-directional static displacement. The design concept and preliminary experimental results of H-beam actuators are presented in this paper. Due to its symmetric structural design, this H-beam actuator can avoid the influence from rotational torques during its bi-directional dynamic and static movement. The restoring force generated by cold beam of H-beam actuator potentially renders this new actuator capability of faster returning speed than conventional electrothermal actuator designs. H-beam actuator is able to generate 50 μm static stroke under 0.9 W electrical dc load. This H-beam electrothermal actuator is well functioned and exhibits good characteristics with high-level performance for industrial applications.     

Micro-mirror laser scanner combined with a varifocal mirror

A laser beam scanning system consisting of a scanning micro-mirror and a varifocal micro-mirror is fabricated for laser beam sensing with variable beam diameter. The scanning micro-mirror is operated under the resonant oscillation condition with an electrostatic comb-drive actuator. The varifocal micro-mirror is driven by a bending moment generated at the circumference of mirror with a parallel-palate electrostatic actuator. The scanning micro-mirror and the varifocal mirror are fabricated on a silicon on insulator wafer. The rotational angle of 9° at 766 Hz is obtained at the voltage of 300 V. The spot size of the laser beam is adjusted from 0.5 to 3.5 cm at the distance of 43 m by changing varifocal voltage. The proposed scanning system can be useful for several sensing techniques.     

A MEMS-based tracking milli-mirror for high-density optical disk drives

We present a new MEMS-based milli-mirror for precise tracking in high-density optical disk drives (ODDs). The device consists of a torsionally suspended mirror plate, one pair of torsion springs, which support the mirror plate and offer a restoring torque, and two pairs of electrodes attached to the mirror plate and glass substrate. The dimensions of mirror plate and torsion springs were determined so that a 5 V dc bias ±4.5 V ac drive voltage would provide the mirror with ±0.02° rotation to transmit laser beam spot on spinning disk. The MEMS-based milli-mirror was successfully fabricated using MEMS technology. Displacement–voltage linearization scheme was implemented by differential voltage driving. The static and dynamic performances of mirror prototype, such as capacitance versus driving voltage, rotation angle versus driving voltage, and resonant frequency were characterized and compared well with the simulation solutions. The mechanical resonant frequency of the mirror is expected to be high enough to satisfy the requirement of the servo bandwidth of precise tracking-control in high-density blue-laser optical disk drive.     

Tilt-angle stabilization of electrostatically actuated micromechanical mirrors beyond the pull-in point

Recently proposed optical subsystems utilizing microelectromechanical system (MEMS) components are being developed for use in optical crossconnects, add-drop multiplexers, and spectral equalizers. Common elements to these subsystems are electrostatically actuated micromechanical mirrors that steer optical beams to implement the subsystem functions. In the past, feedback control methods were used to obtain precise mirror orientations to minimize loss through optical switch fabrics or to stabilize attenuation through spectral equalizers. However, the mirror tilt angle range is limited because of inherent instability beyond a critical tilt angle (pull-in angle), and the usual feedback schemes do not counteract this effect. This work presents a feedback control method to enable operation of electrostatic micromirrors beyond the pull-in angle, yielding advantages including greater scalability of switch arrays and increased dynamic range of optical attenuators. Both static and dynamic tilting behaviors of electrostatic micromirrors under the feedback control are studied. In addition, a practical implementation of the feedback control system by using linear voltage control law is developed. A voltage slightly larger than the pull-in voltage is first applied when the mirror is at small angle positions, and the voltage is then linearly reduced as the mirror approaches the desired position. Experimental measurements, showing that tilt angles beyond the pull-in point can be achieved, are in good agreement with theoretical analysis.     

A new scanning MEMS mirror

This paper introduces the development of a new MEMS-based optical mirror, which performs optical scanning function with discrete reflection angles in an out-of-plane configuration. The device was fabricated through Deep Reactive Ion Etching (DRIE) process on silicon-on-insulator (SOI) wafer, followed by assembly with two metalised glass dies. The optical mirrors can be tilted by electrostatic forces between the opposite electrodes on the SOI and glass dies. The most outstanding performance that can be expected from the device is the discrete and therefore, reliable tilting angle of the mirror, which is guaranteed by its unique mechanical structure and the electrostatically driven mechanism. In this paper, the working principle of the new MEMS mirror was presented, followed by the introduction of device design, mechanical simulation, microfabrication process, assembly solution, and some testing results. The potential application of this new MEMS mirror is for light beam scanning or optical sensing (detection).     

Using dynamic voltage drive in a parallel-plate electrostatic actuator for full-gap travel range and positioning

The nonlinear dynamics of the parallel-plate electrostatically driven microstructure have been investigated with the objective of finding a dynamic voltage drive suitable for full-gap operation. Nonlinear dynamic modeling with phase-portrait presentation of both position and velocity of a realistic microstructure demonstrate that instability is avoided by a timely and sufficient reduction of the drive voltage. The simulation results are confirmed by experiments on devices fabricated in an epi-poly process. A 5.5-V peak harmonic drive voltage with frequency higher than 300 Hz allows repetitive microstructure motion up to 70% of gap without position feedback. The results of the analysis have been applied to the design of a new concept for positioning beyond the static pull-in limitation that does include position feedback. The measured instantaneous actuator displacement is compared with the desired displacement setting and, unlike traditional feedback, the voltage applied to the actuator is changed according to the comparison result between two values. The "low" level is below the static pull-in voltage and opposes the motion, thus bringing the structure back into a stable regime, while the "high" level is larger than the static pull-in voltage and will push the structure beyond the static pull-in displacement. Operation is limited only by the position jitter due to the time delay introduced by the readout circuits. Measurements confirm flexible operation up to a mechanical stopper positioned at 2 /spl mu/m of the 2.25 /spl mu/m wide gap with a 30 nm ripple.     

Angular vertical comb actuators assembled on-chip using in-plane electrothermal actuators and latching mechanisms

We have designed, fabricated and tested self-aligned angular vertical comb-drive (AVC) actuators by on-chip assembly using in-plane electrothermal actuators and latching mechanisms. The on-chip assembly process is carried out by engaging latching mechanism connected to the torsion bars through the off-centered thinned down silicon beams. When the latching mechanism is fully engaged, the assembled AVC actuator forms permanent initial tilt angle by the retraction force of electrothermal actuators. The AVC actuators and latching mechanisms are fabricated on a silicon-on-insulator (SOI) wafer using three photomasks and three times of deep etch steps. The maximum optical scan angle of 30.7° is achieved at 4.56 kHz under the sinusoidal driving voltage of 0–80 V applied to the AVC actuator. After the reliability test performed by operating the actuator for 1.6 × 10⁸ cycles at its resonance, the measured optical scan angle variation and resonant frequency change were within 1.1% and 8 Hz, respectively, and the robustness of the latched mechanism was ensured.     

Development of X-beam electrothermal actuators

A new electrothermal actuator with X-shaped single crystal silicon beam structure is proposed and characterized. This new actuator is made by using SOI-DRIE processes. X-beam actuator of 2000 m projection length and 0.5° tilted angle can generate 90 m static displacement. This new design shows a better static displacement and stability in long travel range than the other actuators. From these experimental data, we conclude the feasibility of our new X-beam actuators. Any movable structure connected with one side of this X-beam can be pushed toward the other side. Therefore, it can be a basic actuation element in association with various structures for different applications.     

A micromachined reaction force actuator (RFA) for a nanomanipulator preparation

A reaction force actuator (RFA) was fabricated to translate a microstage with nanostep movement, and its performance was experimentally evaluated using an optical fiber based built-in microinterferometer. The proposed RFA consists of a shuttle mass, movable electrode, fixed electrode, springs, and spring anchor, all of which reside on the movable substrate. The RFA placed on the platform is free to move when the driving force is larger than the static friction. The fixed electrodes are gold-wired to the external electrodes on the platform covered with a dielectric layer for electrical isolation. When external voltage is applied to the electrodes, the springs experience deflections, and the electrostatic force and restoring force react on the movable substrate through the spring anchor and the fixed electrode, respectively. If the driving voltage is large enough that the resultant force overcomes the friction from the platform, the RFA including the movable substrate can make a displacement with no physical collision between the movable and fixed electrodes. In order to suppress the drift motion due to external noise, electrostatic pressure was applied between the movable substrate and the platform on which a 100-/spl mu/m-thick dielectric thin film is positioned. The nanomotion of the fabricated actuator was evaluated with various voltages using an optical fiber interferometer. The minimum step movement 1.21/spl plusmn/0.24 nm was experimentally obtained at the driving voltage of 18 V, and the estimated total displacement was 450 nm at the highest affordable driving voltage of 85 V.     

Development of copper based miniature electrostatic actuator using WEDM with low actuation voltage

Fabricating electrostatic micro actuator, such as comb-drive actuator, is one of the demanding areas of the MEMS technology because of the promising applications in modern engineering, such as, micro-switches, attenuators, filters, micro-lenses, optical waveguide couplers, modulation, interferometer, dynamic focus mirror, and chopper. For the fabrication, most of the cases silicon monocrystalline wafers are used through complex process. To etch the silicon substrates, researchers often use deep reactive-ion etching or anisotropic wet etching procedure which are time consuming and unsuitable for batch fabrication process. Again, resent research shows that comb-drive actuators need comparatively high voltage for actuation. In solving these problems, the study presents a copper based electrostatic micro actuator with low actuation voltage. Using wire electrical discharge machine (WEDM), the actuator is fabricated where a light weight flexible spring model is introduced. Capacitor design model is applied to present a voltage controlling electronic circuit using Arduino micro controller unit. The experimental result shows that the actuator is able to produce 1.38 mN force for 15 V DC. The experiment also proves that coper based actuator design using WEDM technology is much easier for batch processing and could provide the advantages in rapid prototyping.     

Latching micromagnetic optical switch

In this paper, we report a new type of latching micromagnetic optical switch. The key component of this optical switch is a cantilever made of soft magnetic material with a reflective surface serving as a mirror. The cantilever has two stable positions, therefore two stable states for the device, with presence of an external magnetic field. Input optical signal to the device is switched selectively to one of the two output ports when the device transitions between the two states upon short electromagnetic actuations. The optical switch is bistable because the cantilever has a tendency to align with the external magnetic field, and the torque to align the cantilever can be bidirectional depending on the angle between the cantilever and the magnetic field. Switching between the two stable states is accomplished by momentarily changing the direction and/or the magnitude of the cantilever's magnetization by passing a short current pulse through a planar coil underneath the cantilever. In either of its stable state, the cantilever is held in position by the combined influence of the static external magnetic field and mechanical force, such as from a physical stopper or a mechanical torque produced by the torsion flexures supporting the cantilever. Stable vertical position for the cantilever is obtained by using a tilted external magnetic field. When the cantilever mirror is at this UP state, light is reflected to the desired output port. Large angle deflection and bistable latching operations have been demonstrated. The measured mechanical switching speed between the two states of the prototype is 3.2 ms. Optical insertion loss is -4 dB, and the energy consumption is 44 mJ for each switching event.     

Bidirectional actuation of ferrofluid using micropatterned planar coils assisted by bias magnetic fields

This paper reports a ferrofluid control method that enables both attraction and repelling of ferrofluid on micropatterned planar coils coupled with permanent magnets. A combinational use of a controlled magnetic field and a bias field is shown to provide lateral forces that attract/repel the ferrofluid to/from the coil depending on the direction of the current passed through the coil. Active mirror devices whose mirrors are switched by ferrofluids are developed as a proof-of-concept of the actuation method toward the application to imaging devices and optical switches. The planar devices lithographically fabricated to have arrays of mirror-coil cells are used to demonstrate activation/deactivation of individual cells enabled by the bidirectional radial motion of the ferrofluid layer with ∼100 μm thickness. The static and dynamic behaviors of the ferrofluid in the devices are characterized through an image processing approach. Multiple mirror cells are selectively and simultaneously operated to show enhanced ferrofluid control uniquely available with the two modes of the actuation as well as to demonstrate pattern generation with the arrays.     

Spatially resolved temperature mapping of electrothermal actuators by surface Raman scattering

In this paper, we report spatially resolved temperature profiles along the legs of working V-shaped electrothermal (ET) actuators using a surface Raman scattering technique. The Raman probe provides nonperturbing optical data with a spatial resolution of 1.2 /spl mu/m, which is required to observe the 3-/spl mu/m-wide actuator beams. A detailed uncertainty analysis reveals that our Raman thermometry of polycrystalline silicon is performed with fidelity of /spl plusmn/10 to 11 K when the peak location of the Stokes-shifted optical phonon signature is used as an indicator of temperature. This level of uncertainty is sufficient for temperature mapping of many working thermal MEMS devices which exhibit characteristic temperature differences of several hundred Kelvins. To our knowledge, these are the first quantitative and spatially resolved temperature data available for thermal actuator structures. This new temperature data set can be used for validation of actuator thermal design models and these new results are compared with finite-difference simulations of actuator thermal performance.     

Design of moving magnet type pickup actuator using inserted coil

Recently, the demand of the information storage devices with large storage capacity such as Blu-ray Disc and high-definition television is increased. In keeping with this trend, the optical storage devices are also required to have high data transfer rate and large storage capacity. To satisfy these requirements, the actuator for optical disc drive should have a high servo bandwidth to compensate the vibration of optical disc. The servo bandwidth is limited by some flexible modes of the actuator, thus it is essential to make these frequencies of flexible modes to high frequency region. The frequency of flexible mode depends on materials and shape. Stiff materials and simple shape is useful to increase the frequency of flexible mode. In this paper, we suggested a moving magnet type actuator having flexible modes which are happened at high frequency region. Generally, the moving magnet type actuator has an advantage to increase the frequency of flexible mode because the moving magnet type actuator has simple structure and the Young’s modulus of magnet is high. However, large moving mass and inefficiency of Electromagnetic (EM) circuit cut down driving sensitivities of actuator. To improve driving sensitivities, we designed the model with the closed EM circuit for tracking actuation. The design of experiments (DOE) procedure is applied to get proper design parameters and the variable metric method (VMM) which is a technique of optimization is used to improve driving sensitivity. The lens holder is also improved based on the optimization result of EM circuit. And to make up for the low efficiency of EM circuit, the thermal stability is checked on condition that the input current is very high. At last, the final design of moving magnet type actuator is suggested and it is verified that the driving performance and the structural stiffness of the final design is sufficient.     

Modeling of single and multilayer polyvinylidene fluoride film for micro pump actuation

Micro pumps are essential components of micro devices such as drug delivery systems. Large numbers of pumps have been proposed based on different actuating principles. Piezoelectric actuation offers advantages such as reliability and energy efficiency. Lead zirconate titanate (PZT) based piezoelectric actuation for micro pumps is predominantly explored despite its disadvantages such as brittle nature, low straining and difficulties in processing. Polymer piezoelectric materials like polyvinylidene fluoride (PVDF) could be promising replacements for PZT owing to their availability in form of films and good strain coefficients. Very limited literature on micro pump with PVDF as an actuator is available. In this paper, finite element analysis (FEA) model of a micro pump actuator using single and multilayer PVDF for actuation is developed in ANSYS^?. The model takes into account the influence of driving voltage and actuator geometry. The central deflection of the pump diaphragm which is instrumental in defining the pump performance is studied for driving voltages of 100?C200?V. The deflection of the pump diaphragm for single layer and multilayer actuation are determined from the model. It could be inferred from the initial part of the study that pump performance depends on driving voltage and actuator film thickness. In order to reduce driving voltage requirement multilayer stacked actuator is tried with four different configurations of the layers. It is concluded that stacking configuration of parallel energized straight polarity PVDF layers yielded best central deflection. An attempt is made to compare the performance of multilayer actuator with an equivalent single thick layer actuator. It is noticed that the multilayer actuator performance was better by about 101% when number of layers is doubled.     

A novel microelectrostatic torsional actuator

Presently, the torsional actuator has gained a lot of attention in the area of microactuators. Because the torsional actuator cannot carry a substantial mechanical load in the out-of-plane direction, it is frequently used in some optical or electrical applications such as light modulators and spatial scanner devices. However, the performance of the torsional actuator is limited to the fabrication process and operating conditions. For instance, it is difficult to fabricate a torsional actuator with both a large rotating angle and large size moving plate. A novel electrostatically driven torsional actuator is proposed in this paper. The torsional actuator is fabricated through the integration of surface and bulk micromachining processes. Thus, the goal of fabricating a torsional actuator with a cavity right beneath the edge of the moving plate is reached. In addition, the thin film residual stress is exploited to modify the shape of the torsional actuator. The advantage of the proposed design is to increase the traveling distance of the actuator as well as to increase the area of the moving plate. In short, the proposed design provides the possibility of increasing the size of a moving plate without reducing its rotating angle. Therefore, the applications for the torsional actuator, such as image scanner and positioner, are increased.     

集成式微操作器的研制

微操作器是微操作机器人的关键部件，本文基于压电扫描器的工作原理，研制出 压电陶瓷管驱动的三自由度微操作器，通过对四分压电陶瓷管的变形进行静力学分析，建立 了微操作器微位移量与驱动电压的关系模型．研制出微位移检测电路，实现了微操作器机构 、驱动、检测的集成化，设计了微位移闭环控制实验系统，对微操作器进行了静态、动态测 试，得到了微操作器的主要性能指标.实验表明，所研制的微操作器能够满足微纳米定位精 度的微操作需要．     

Impact of design parameters on working stability of the electrothermal V-shaped actuator

This paper mentions a detail calculation of the equivalent dynamic parameters in differential equations of motion of the electrothermal V-shaped actuator. A heat transfer model for a thin beam (including the dependence of material properties on the temperature) is applied in order to solve more exactly temperature distribution and displacement of V-shaped beam system. Comparing the values of displacement in both calculation and simulation confirmed a higher accuracy of proposed equations. Moreover, a related formula between the minimum conversion stiffness and driving voltage amplitude is analyzed and examined to avoid the buckling phenomenon may occur in V-shaped beam system while working at a high voltage.

     

基于压电双晶片的微型无人机增稳驱动系统研究

研究了一种,基于压电双晶片的微型无人机增稳驱动系统,并设计了一种基于升压电路原理的压电驱动电源,该驱动电源采用机载电池供电,通过 0～5V 控制信号控制其运动,对驱动电源的动态特性进行了测试.同时为实现对整个驱动系统的自适应控制,采用光纤 Bragg 光栅(FBG)传感器对压电双晶片的位移变化特性进行了测量.研究结果表...