Design,modeling, and mechanical characterizations of micromachined InP-based actuator for tunable MOEMS applications

A novel InP-based microactuator, which is actuated by electrostatic means, has been proposed, designed, fabricated, and characterized for tuning applications in the 1.5 μm wavelength domains. Its structural design is based on the global optimization method. The tunable device is a big square membrane, which is supported by four identical cantilever beams. The three alternating layers Si₃N₄/SiO₂ as a distributed Bragg reflector (DBR) mirror, which were previously reported, have been formed on the top of the membrane. Based on the optical interferometric measurements, the proposed Fabry–Perot filter has demonstrated a maximum deflection of ∼321 nm with an applied voltage up to 12 V, an average sensitivity of ∼27 nm/V, a pull-in voltage of 12.7 V, and a release voltage of 10.7 V. It is also observed that its natural frequency is 88.4 kHz. This measured frequency implies that the tuning speed of our device is fast for optical operations within 0.01 ms. In addition, our device’s mirror remains so flat with a good planarity of 0.07°, which is strictly required for the filter’s optical performance. This optical performance can be achieved, when the micromachined structure has a tuning displacement up to ∼38 nm with a low tuning voltage up to 5 V. When compared with the finite element models (FEM), which were generated by the commercialized software, Coventor™, our experimental results agree well in terms of the natural frequency, pull-in voltage and deflections. Thus, our tunable filter, which is based on the optimized design, enables better performances including reduced actuation voltages, large pull-in voltage, improved device reliability, and fast switching times. Our device can also quickly snap back to the original position. In addition, the undesired spring-softening effect has been reduced.     

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.     

Effect of residual stress on RF MEMS switch

Studies have been carried out on a RF MEMS shunt switch to analyze the effect of residual stress on its electromechanical characteristics. This paper presents the simulated results as well as theoretically calculated results of a shunt switch due to the presence of residual stress gradient in respect of resonant frequency, pull down voltage and switching characteristics. The effect of introduction of holes in the beam is also studied. The calculated results, corresponding to the switch (without holes) at zero residual stress, of resonant frequency, pull-down voltage and switch on and off time are 28.14 kHz, 28.2 V, 16.35 μsec and 8.6 μsec respectively. Modal analysis of the both the structures (with and without holes) are carried out for different values of residual stress gradients. Modal analysis predicted that higher values of tensile stress gradient are not favorable for switching action. The pull-down voltages and switch on and off times are simulated at different stress gradients. With the increase in compressive stress gradient, the pull-down voltage is found to increase, whereas, switch on and off times is decreased. Corresponding to −20 MPa/μm residual stress gradient, the resonant frequency, pull-down voltage and switch on and off times are found to be 74.5 kHz, 63.5 V, 7.5 μsec and 3.36 μsec respectively. Introduction holes in the structure modified these values to 63.77 kHz, 53.1 V, 8.7 μsec, 3.92 μsec respectively.     

A micro electromagnetic low level vibration energy harvester based on MEMS technology

This paper presents a micro electromagnetic energy harvester which can convert low level vibration energy to electrical power. It mainly consists of an electroplated copper planar spring, a permanent magnet and a copper planar coil with high aspect ratio. Mechanical simulation shows that the natural frequency of the magnet-spring system is 94.5 Hz. The resonant vibration amplitude of the magnet is 259.1 μm when the input vibration amplitude is 14 μm and the magnet-spring system is at resonance. Electromagnetic simulation shows that the linewidth and the turns of the coil influence the induced voltage greatly. The optimized electromagnetic vibration energy harvester can generate 0.7 μW of maximal output power with peak–peak voltage of 42.6 mV in an input vibration frequency of 94.5 Hz and input acceleration of 4.94 m/s² (this vibration is a kind of low level ambient vibration). A prototype (not optimized) has been fabricated using MEMS micromachining technology. The testing results show that the prototype can generate induced voltage (peak–peak) of 18 mV and output power of 0.61 μW for 14.9 m/s² external acceleration at its resonant frequency of 55 Hz (this vibration is not in a low ambient vibration level).     

A lateral RF MEMS capacitive switch utilizing parylene as dielectric

A novel lateral RF MEMS capacitive switch was reported in this paper. This switch employed parylene as the dielectric material, taking advantages of its low temperature deposition and conformal coating. The low resistivity single crystalline silicon served as the material of the mechanical structures. The switch was fabricated by bulk micromachining processes with only two lithographic masks and a shadow mask. The dynamical response, parylene insulation performance, and RF performances of the fabricated switch were characterized, respectively. The switching time from the open state to the close state was 105 μs at a loaded voltage of 78 V, while 15.6 μs from the close state to the open state. The isolation was better than 15 dB from 20 to 40 GHz, and the maximal isolation was 23.5 dB at 25 GHz; while the insertion loss was below 1.4 dB at 25 GHz, when bonding wires connected the ground lines. These results verify that the parylene is a good candidate material to act as sidewall dielectric to realize the lateral capacitive switch.     

Integrated optical micro structures for signal processing in the position metrology

The miniaturisation of functional components and a high integration depth of sensor systems are the fundamental demands of the micro system technology. Within the, ‘Sonderforschungsbereich 516,’ the development of a position sensor for a micro linear motor is also directed towards these goals; and so a sensor with a size smaller than 10 mm and a measurement accuracy of better than 100 nm is desirable. Additionally, the electromagnetic sensitivity should be minimised. An optical interferometric measurement principle meets these requirements. Light from both of the first diffraction orders from a grating on the motor armature is coupled into a glass-chip waveguide coupler. The interference of the signals results in a beat frequency signal when the grating is shifted. It can be detected as an intensity modulation at the three outputs. The velocity as well as the movement direction of the armature can be derived from the signal phases. The investigations were focused on the coupler design and its numerical field simulations as well as manufacturing and qualification of the coupler itself. Its geometry essentially affects the total sensor length. Refractive index modification by a femtosecond pulse laser was chosen for the creation of the waveguide coupler. This process does not restrict the waveguide geometry to the surface of the glass-chip, and enables arbitrarily positioning of waveguides in the substrate volume. Thus, it also enables non-planar cross section formations of three waveguides e.g. in the form of an equilateral triangle.     

Modeling of grating/moiré based micro motion sensor

 The design of a micro optical motion sensor is proposed. Fourier series analysis is used to determine the optical transmission function (OTF) of gratings. The optical flux generated by a grating (pair) and received by photodetector is then calculated through an integration of the OTF over the receiving window. A general relationship between photo-detector output current and grating translation displacement is finally established. The analysis is carried out for linear binary grating sensors, with single and double grating sensors. The influence of grating (pair) structure and receiving window on sensor sensitivity and linearity of output response is investigated. A numerical work is completed to simulate the various cases of optical structure design. Several types of photoresist gratings are fabricated and are used to experimentally characterize the grating sensor. The tested result is found to be in general agreement with the analysis result.     

A MEMS-based resonant-scanning lamellar grating Fourier transform micro-spectrometer with laser reference system

A lamellar grating Fourier transform infra-red (FTIR) micro-spectrometer is presented in which the device is electromagnetically actuated in resonant mode so as to achieve larger displacements with a lower driving voltage. By actuating at resonance, we can also have a design with a higher spring stiffness design such that the micro-spectrometer will have little influence from external perturbation. A data acquisition electronic system is designed such that the interferogram of the IR source can still be acquired at a fixed optical path distance (OPD) intervals. This is achieved by using a reference laser source. Working at a resonant frequency of 330 Hz, a 100 μm (bi-directional) displacement is achieved by the device with an input voltage of 2.2 V. A tunable laser source is used to demonstrate the system performance. The peak of the recorded spectra is very close to the actual wavelength of the IR, with a maximum difference of less than 5 nm.     

Manufacture of diffraction grating on tiny parts by means of ultraprecision milling

The study deals with the manufacture of diffraction grating by applying the ultraprecision microgrooving technology. Microgrooving is performed by the use of a lathe-type ultraprecision milling machine having 1 nm positioning accuracy, together with a rotating diamond cutter. As an example of microgroove, a diffraction grating with 32 768 V-shaped grooves is fabricated in a pitch of 1 μm and a depth of 0.5 μm around the circumference of copper disk of 12 mm in diameter. The high-speed rotating cutter allows the microgrooves to be sharply machined without burrs and accumulative pitch errors, taking account of cutting order. The surface roughness of machined grooves is 1 nm (Ra), which experimentally shows good optical properties. Received: 21 December 1998 / Accepted: 18 January 1999     

A voltage source model on thermoelectric power sensor based on MEMS technology

In order to achieve monolithic integration of thermoelectric power sensor and its amplification system and improve the measurement accuracy of microwave power, a voltage source model is researched in this paper. And the thermoelectric power sensor is designed and fabricated using MEMS technology and GaAs MMIC process. It is measured in the X-band (8–12 GHz) with the input power in 100 mW range. When the input microwave power is at 10, 50 and 100 mW, respectively, the frequency dependent coefficient k₁ is −0.073, −0.39 and −0.82 mV/GHz, respectively. The sensitivity coefficient k₂ is 0.311, 0.303, 0.293, 0.284 and 0.279 mV/mW at 8, 9, 10, 11 and 12 GHz, respectively, and has an excellent linearity. Based on the voltage source model, the feedback coefficient of its amplification system is set to 0.0078 × P_in to compensate the loss power caused by frequency dependent characteristic. In addition to miniaturization and low cost, an advantage using this model is significantly improved measurement accuracy.     

Non-resonant electromagnetic wideband energy harvesting mechanism for low frequency vibrations

A novel non-resonant energy harvesting mechanism with wide operation frequency band is investigated for collecting energy from low frequency ambient vibration. A free-standing magnet is packaged inside a sealed hole which is created by stacking five pieces of printed circuit board substrates embedded with multi-layer copper coils. This device was tested under various acceleration conditions. Considering the air damping effect, two types of device structures with different covered plates are investigated. For type I, one covered acrylic plate with drilled air holes and another plate with no holes are used to package the moving magnet. For type II, the middle hole is sealed by two acrylic plates with drilled air holes. The output voltage of type II is better than the one of type I at the same acceleration. When the energy harvester of type II is shook at 1.9 g acceleration along longitudinal direction of the hole, the 9 mV output voltage with 40 Hz bandwidth, i.e., from 40 to 80 Hz, is generated. The maximum output power within the ranges of 40–80 Hz, i.e., operation bandwidth, is measured as 0.4 μW under matched loading resistance of 50 Ω. Experimental results show that type I device has wider frequency bandwidth, higher center frequency and smaller output voltage than type II device because type I device experiences severe damping influence.     

A large thrust trans-scale precision positioning stage based on the inertial stick–slip driving

In this paper, a large thrust trans-scale precision positioning stage based on the inertial stick–slip driving is proposed, which can output long range motion. The stage consists of a piezoelectric actuator, a cross roller guide, a pair of cantilever beams, the flexure hinge system and the gather system of grating ruler, and the volume is 30 mm (L) × 17 mm (W) × 17.5 mm (H). The structure and the driving principle are introduced in detail. To investigate the working performance, a prototype is fabricated and a series of experiments is carried out. Experimental results demonstrate that the displacement outputs under various driving voltages, various driving frequencies and various step response time show good linear relationships with the time. The maximum thrust and the maximum load capacity are 6.1 N and 2500 g. The displacement and the driving resolution can reach 20 mm and 5 nm. The velocity can reach 12 mm/s when the driving frequency is 2.5 kHz. The experimental results also confirm that the designed stage can achieve various speeds by changing the driving voltage and driving frequency.

     

Synthesis and application of an alkylated pyrazole‐based azo dye for electrofluidic display

Electrofluidic display (EFD) is one of the most promising reflective displays for its full color and video speed. Colored EFD oil, normally formulated by soluble organic dyes in non‐polar solvent, dominates the color, electro‐optical behavior, and reliability performances for EFD devices. In this paper, a novel yellow electrofluidic dye with excellent solubility in non‐polar EFD solvent was achieved based on the introduction of long alkyl chain into pyrazole azo dye. The resulting EFD device fabricated by the dye showed excellent application properties, such as fast switching speed (17.8 ms), high aperture ratio (68.5%), low threshold voltage (24v), good light stability (240 h under accelerated conditions), and low backflow phenomenon.     

Design and fabrication of a resonant scanning micromirror suspended by V shaped beams with vertical electrostatic comb drives

A scanning micromirror suspended by a pair of V-shaped beams with vertical electrostatic comb drives was designed, modeled, fabricated and characterized. The dynamic analyses were carried out by both theory calculation and FEM simulation to obtain frequency response, stiffness characteristics, oscillation modes and their resonance frequencies. The device was fabricated using the silicon-on-insulator process by only two photolithography masks. Some problems during the process such as the micromirror distortion and the side sticking of the comb fingers were effectively solved by thermal annealing and alcohol-replacement methods, respectively. Based on the fabricated device, the typical scanning patterns for 1-D and 2-D operation were obtained. The experimental results reveal that the micromirror can work in resonant mode with the resonant frequency of 2.38 kHz. The maximum deflection angles can reach ±4.8°, corresponding to a total optical scanning range of 19.2° at a driving voltage of 21 V.     

A numerical hydrodynamic and thermal characterization of an inter-strata liquid cooling solution for 3D ICs

A novel integrated thermal management solution is proposed to alleviate hot spots in a contemporary 3D IC architecture. The solution employs a series of integrated microchannels, interconnected through each stratum by through silicon fluidic vias (TSFVs), and permits the transfer of heat, via a coolant, from hot to cold zones. This microfluidic system is driven by an integrated AC electrokinetic pump embedded in the channel walls. Recent advancements in electrokinetic micropump technology have allowed greater increases in fluid velocity (mm/s) while operating within the voltage constraints of a 3D IC. This paper presents a 2D simulation of an electrokinetic micropump operating at V_pp = 1.5 V in a 40 μm channel and examines its velocity profile for six frequencies in the range 100 ≤ ω ≤ 100 MHz. An optimum frequency of 100 kHz was established within this range and this was further examined with a constant heat flux of 186 W/cm2 imposed on the wall for an inlet fluid temperature of 40°C. Temperature profiles are presented at the channel-silicon interface and compared with theory.     

Emission of dispersed‐type inorganic EL devices with frequency‐variable high‐voltage oscillation circuit

Dispersed‐type inorganic electroluminescent (EL) devices composed of a transparent electrode, a phosphor, a dielectric, and a back electrode were prepared under various conditions using a zinc sulfide (ZnS)‐based phosphor. Additionally, a voltage/frequency variable circuit was designed. A compact high‐voltage/frequency variable circuit including three modules for boosting, frequency conversion, and voltage conversion was designed. A 140 V_pp voltage and a frequency in the range of 270 Hz to 2.4 kHz can be controlled by this circuit. The emission has begun to be observed at a voltage about 60 V_pp and a frequency of 400 Hz, at a voltage about 40 V_pp and a frequency of 1.4 kHz, 2.4 kHz, respectively. The emission intensity increased with an increase in frequency; emission with a wavelength of 450 nm was strongly influenced by the frequency. The luminescence and the electrical properties were affected by the preparation conditions including device structures, dispersion of ZnS:Cu, and Cl particles because of the current path generated by defects in the EL cell.     

Novel U-shape gold nanoparticles-modified optical fiber for localized plasmon resonance chemical sensing

A novel fiber-optic localized plasma resonance (FO-LPR) sensor composed of a U-shape optical fiber was proposed and demonstrated in this study. The U-shape optical fiber was fabricated by a femtosecond laser micromachining system. The dimensions of the U-shape zone were 100 μm in depth measured from the surface of the polymer jacket layer, 80 μm in width in the jacket layer, 60 μm in width in the cladding layer. The total length is 5 mm. After laser annealing treatment, the average surface roughness was 205.8 nm as determined by Atom Force Microscope (AFM). The exposed surface of the U-shape fiber was modified with self-assembled gold nanoparticles to produce the FO-LPR sensor. The response of the sensor shows that the signal increases linearly with increasing refractive index. The sensor resolution of the sensor was determined to be 1.06 × 10⁻³ RIU.     

High standoff dual-mode-actuation MEMS switches

MEMS switches based on a dual-mode actuation scheme that simultaneously allows for large standoff heights and low clamping voltages have been designed and fabricated. These devices are based on the use of a transient external magnetic field to bring the actuating portion of the switch close to a dielectric-coated clamping electrode, followed by application of an electrostatic clamping voltage to keep the switch closed. Since the clamping voltage is applied when the switch is closed, this voltage can be relatively small. This approach is particularly attractive for RF applications such as arrays of switches in reconfigurable aperture antennas. The arrays of switches are simultaneously closed by the magnetic field generated by an external magnetic source, then selected switches are clamped by electrostatic force using low voltages to maintain the ON state. Their utility in such an array has been demonstrated and several different design variations have been explored to improve switch performance. Contact resistance as low as 0.37 Ω has been achieved, with actuating field strength of 40 Gauss. These switches possess a large open state air gap (25 μm), and are able to pass high currents in excess of 1 A under low frequency or DC operation. The large OFF state impedance allows for their usage in switching applications in RF devices. Their high frequency functionality has been tested to find that their open-state impedance was identical to that of a perfect open up to 9 GHz and their RF reconfigurability has been demonstrated in a monopole/dipole test bed.     

Droplet transportation using a pre-charging method for digital microfluidics

A new droplet-driving scheme for digital microfluidics termed the “pre-charging of a droplet” is demonstrated. In this method, a droplet is initially charged by applying “pre-charging” voltage between the droplet and an electrode buried under dielectric layers. The droplet is then driven to the next electrode by applying “driving” voltage between two adjacent buried electrodes. The concept of pre-charging was proved by the polarity of the charge stored in the droplet. When the droplet is pre-charged with positive voltage, it is driven with negative voltage and vice versa. Therefore, the magnitudes of the pre-charging and driving voltages are identical, but only with the opposite polarity. A 2.5-μL deionized water droplet is pre-charged and driven at a minimal voltage of 12 V. The charge stored in the droplet by this pre-charging method remained for more than 2 min, and the driving actuation could be repeated more than 150 times while the droplet remained its charged state. This method suggests a new means of driving a droplet for digital microfluidics at a relatively low voltage by utilizing both the electrostatic and dielectrophoretic force in the droplet transport process with a simpler structure compared to other single-plate structured devices.     

Modeling and analysis of a 2-DOF bidirectional electro-thermal microactuator

In this paper, a four hot-arm U-shape electro-thermal actuator that can achieve bidirectional motion in two axes is introduced. By selectively applying voltage to different pairs of its four arms, the device can provide actuation in four directions starting from its rest position. It is shown that independent in-plane and out-of-plane motions can be obtained by tailoring the geometrical parameters of the system. The lumped model of the microactuator was developed using electro-thermal and thermo-mechanical analyses and validated using finite element simulations. The device has been fabricated using PolyMUMPs and experimental results are in good agreement with the theoretical predictions. Total in-plane deflections of 4.8 μm (2.4 μm in either direction) and upward out-of-plane deflections of 8.2 μm were achieved at 8 V of input voltage. The large achievable deflections and the higher degree-of-freedom of the proposed device compared to its counterparts, foresee its use in diverse MEMS applications.