Electrostatic Actuation Method Research Articles

Electro-Thermally Actuated Non-Volatile Mechanical Memory With CMOS-Level Operation Voltage and Low Contact Resistance

A non-volatile mechanical memory device with CMOS-level operation voltage and low contact resistance is proposed utilizing electro-thermal actuation method for the first time. Unlike the most widely used electrostatic actuation method in microelectromechanical systems (MEMS) devices, electro-thermal actuation is known to produce large actuation force and displacement with low operation voltage, which are preferable attributes of a mechanical memory. In addition, stiction, one of the most notable failure mechanisms of MEMS devices referring to the inadvertent permanent adhesion between two surfaces, can be exploited to significantly improve the energy efficiency of mechanical memory by retaining the ON-state without power. We devised a non-volatile mechanical memory device capable of performing multiple cycles of write and erase operations with CMOS-level voltage by utilizing electro-thermal actuation and stiction. The fabricated electro-thermally actuated mechanical memory successfully performed 200 repeated cycles of write and erase operations at 0.9V and 1.0V, respectively. Thanks to the high contact force generated by electro-thermal actuation, the fabricated device achieved the contact resistance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$17 \boldsymbol {\Omega }$ </tex-math></inline-formula> . Lastly, we confirmed that the fabricated device successfully retained both ON and OFF states upon removal of power beyond 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> seconds. [2021-0178]

Design and Analysis of RF MEMS Cantilever Switches for Parameter Enhancement

This paper investigates some of the disadvantages of Radio Frequency Micro Electro Mechanical System (RF MEMS) switches, such as high actuation voltage and high switching time. RF MEMS switches are among the most widely used technologies since the past two decades owing to their abundant advantages such as low insertion loss, high isolation loss, low power consumption, and very high Q. In this paper, we focus on reducing the high actuation voltage and high switching time; a novel design of an RF MEMS metal contact switch was proposed and designed using the software Intellisuite 8.7v, and simulations were performed by finite element modeling. Analysis was carried out by the electrostatic actuation method. The actuation voltage depends on the spring constant, area of the actuation electrode, and air gap. From the simulation, we obtained a very low actuation voltage (1.2 V) and low switching time (approximately 7.98 µs).

A High Sensitivity Electric Field Microsensor Based on Torsional Resonance.

This paper proposes a high sensitivity electric field microsensor (EFM) based on torsional resonance. The proposed microsensor adopts torsional shutter, which is composed of shielding electrodes and torsional beams. The movable shielding electrodes and the fixed sensing electrodes are fabricated on the same plane and interdigitally arranged. Push–pull electrostatic actuation method is employed to excite the torsional shutter. Simulation results proved that the torsional shutter has higher efficiency of charge induction. The optimization of structure parameters was conducted to improve its efficiency of charge induction further. A micromachining fabrication process was developed to fabricate the EFM. Experiments were conducted to characterize the EFM. A good linearity of 0.15% was achieved within an electrostatic field range of 0–50 kV/m, and the uncertainty was below 0.38% in the three roundtrip measurements. A high sensitivity of 4.82 mV/(kV/m) was achieved with the trans-resistance of 100 MΩ, which is improved by at least one order of magnitude compared with previously reported EFMs. The efficiency of charge induction for this microsensor reached 48.19 pA/(kV/m).

A MEMS Fishbone-Shaped Electrostatic Double-Ended Tuning Fork Resonator With Selectable Higher Modes

In this paper, a microelectromechanical systems fishbone-shaped electrostatic double-ended tuning fork (DETF) resonator with selectable higher modes is presented. The resonator can realize ten vibration modes with resonant frequencies from 137.929 to 913.476 kHz and multi-mode selection function. Different from conventional electrostatic actuation methods, the proposed fishbone-shaped structure combined with tooth-shaped electrode generates bending moment on the beam and leads to vibration of the DETF. The vibration mode and the resonant frequency can be selected and measured according to the configuration of electrodes. Consequently, the proposed fishbone-shaped DETF resonator can provide multi-mode vibration and variable resonant frequency. The device is fabricated by the silicon-on-insulator process and tested via open-loop spectral response measurement. Finally, electrical parameters of the equivalent circuit model are extracted for further research. [2016-0315]

Stepwise Actuation of an Electrostatic Bimorph Cantilever Actuator Using a Patterned Bottom Electrode

The electrostatic actuation method has not been used widely in bimorph cantilevers despite its advantage of large displacement and low power consumption, mostly owing to the fact that it is limited to just two stable positions: 1) initial curled; and 2) final flat positions. In this paper, we first demonstrate a bimorph cantilever actuator having multiple steady-state positions in between those two boundary positions, accomplished by simply dividing the bottom electrode. We found that the number of steady-state positions and the steady-state tip heights can be controlled by the design of the bottom electrode. In our test experiment, the steady-state bimorph cantilever tip heights were 48 $\mu \text{m}$ at 0 V, 28 $\mu \text{m}$ at 21 V, 7 $\mu \text{m}$ at 25 V, and 0 $\mu \text{m}$ (flat) at 29 V, respectively. In order to relieve low reliability of the electrostatic bimorph cantilever, we devised non-contact actuation method and demonstrated that the lifetime of the electrostatic bimorph actuator greatly increased. This paper will pave the way to utilize bimorph cantilever actuators with greater versatility. [2016-0081]

A novel micro electric field sensor with X–Y dual axis sensitive differential structure

This paper presents a novel X–Y dual axis sensitive sensor for static electric field measurement. Compared with the existent electric field micro sensors, which can only detect one axial direction electric field, this sensor is capable of two-dimensional electric field sensing. In the design of the micro sensor, the combination of angular comb-drives and serpentine springs can bring the advantage of achieving large in-plane rotation, which enlarges the vibration amplitudes and results in more induced charges. Moreover, the push–pull electrostatic actuation method and the adopted differential sensing electrodes both can reduce the impact of common mode interference. Two pairs of sensing elements are located differentially to form a cross-like shape, with each pair to get X and Y component of the electric field respectively. Experimental results agree well with the electric field calibration theory and show high measurement accuracy. In the range from 0 to 25kV/m, the errors of electric field value are better than 8%.

Eloctrostatic Pull-in Characteristic of Silicon Diaphragm for MEMS Micropump Design

Abstract Electrostatic actuation method is commonly employed for MEMS micropump mechanism which consists of diaphragm microstructure and parallel electrode. This work discussed on design and simulation of square silicon diaphragms and it characteristics for micropump application which supply voltage range of 0V-20 V. The characterizations of these diaphragms were based on the measurement on parameters such as diaphragm displacement as function of voltage applied and stress distribution. The simulations were carried out using CoventorWare2007. Results show that simulation deviate theoretical value in a range of below 15%. The displacement of the diaphragm was proportional to the physical geometry of the diaphragm. Pull-in voltage defines the limitation value for micropump operation.

Direct actuation of cantilever in aqueous solutions by electrostatic force using high-frequency electric fields

We recently developed a method to directly actuate a cantilever in aqueous solutions by electrostatic force [K.-I. Umeda et al., Appl. Phys. Express 3, 065205 (2010)]. However, the cantilever was actuated by surface stress in a low frequency regime. We solved this problem by applying amplitude-modulated high-frequency electric fields, which actuates the cantilever solely by electrostatic force. The time variations of the self-oscillation frequency of a cantilever and the Au(111) surface images by frequency-modulation atomic force microscopy using acoustic, photothermal, and the improved electrostatic actuation methods were compared, which demonstrates the advantages of the last method such as stability and simplicity in instrumentation.

Design and Simulation of RF-MEMS Tunable Capacitors Using Multiple Voltage Sources

A novel tunable RF-MEMS variable capacitor(varactor) is presented. The Flip -Flop structure of the design makes it possible to either increase or decrease the capacitance. Dimensions, sizes and the materials used in the device are chosen so that it can be manufactured in Urmia MEMS Lab. Silicon surface micromachining thechnology is used for the structure, which is CMOS compatible. Electrostatic actuation method is selected because of it's low power consumption so it can be used in low-power wireless applications. The value of the capacitor is changed by varying the gap between the two plates. Tuning voltage is in the range of 0-2 volts. The capacitor has the initial value of 0.43pF, maximum value of 0.92pF and minimum value of 0.3pF. Actuation and varactor plates are separate from each other. The structure is simple and can be fabricated by employing only 3 masks.

Enhanced‐image‐quality raster‐scanning chipset using feedback‐control actuation

Abstract— A new raster‐scanning chipset which provides enhanced projection performance is presented. The design is novel in that it combines electrostatic and electromagnetic actuation methods, along with a unique feedback‐control scheme to produce SVGA and WVGA projected images. A micromirror, the actuators, and drive electronics are integrated into a small, power‐efficient system, a scanning chipset, to increase its reliability and manufacturability.

High performance microshutter device with space-division modulation

This paper presents a microshutter device with space-division modulation for high brightness and improved grayscale level. High brightness is achieved with a large aperture that originates from out-of-plane movement with a large deflection, and space-division modulation improves the grayscale level by overcoming the operating speed limitation of digital modulation. The proposed microshutter device has multiple microshutters consisting of a single pixel, and the grayscale level is modulated by the number of actuated microshutters. We adopted a novel electrostatic actuation method in which the number of actuated microshutters is proportional to the applied analog voltage level. The actuation method was verified theoretically by means of an equivalent electrical circuit model. Furthermore, to test the proposed actuation method, we fabricated quarter-circle curl-shaped microshutters and demonstrated the proposed microshutter device with a control signal of 20 V to 33 V. The switching time is 20 µs from the open state to the closed state, and the lifetime is estimated to be 500 billion cycles.

Minimum Energy Actuation and Bounce-Back Behavior of Microbeams Using $\delta$ Voltage Pulses

Minimizing impact force during actuation reduces damage to contacting surfaces. An electrostatic actuation method for creating a soft contact between dielectric and semiconductor surfaces is described and applied to cantilevers and clamped beams. The method utilizes a short high-voltage delta-pulse followed by a low dc hold voltage to pull in the cantilever or beams. Removal of the hold voltage releases the beam back to its rest position. The height and the shape of the delta-pulse control the energy transferred to the beams and are shown to be critical in predicting minimum actuation voltages. Actuation pulses with heights even a few tenths of a volt above minimum can lead to stuck devices, whereas minimum pulses do not. The actuation method has been experimentally tested, and a simplified mathematical model has been simulated to confirm the experiment results. In addition, it is observed that a high-voltage actuation pulse applied for a longer time than necessary to actuate, but in phase with the apparent elastic response of the beam, will cause the beam to bounce upward rather than stick during actuation.

Contribution of cross talk to the uncertainty of microphone calibrations by the electrostatic actuator method

Cross talk in electrostatic actuator calibrations is defined as the response of a test microphone to the actuator excitation voltage when the microphone membrane is frozen, i.e., when the actuator polarization voltage is zero—an unavoidable nuisance effect that contributes to the calibration uncertainty. Two models for the cross talk are considered. In the first, the actuator excitation voltage is coupled to the microphone output through the stray capacitance between the actuator electrode and the microphone backplate; in the second, it is coupled through the ground resistance, which provides a common element between the input and output loops. In the stray capacitance model, at frequencies below the membrane resonance, the cross talk is independent of frequency, but in the ground resistance model it varies inversely with frequency. The frequency dependence of the cross talk thus serves as a discriminator between the two models. Measurements on condenser microphones of various sizes yield results that favor the stray capacitance model. The ratio of cross-talk signal to actuator pressure signal (at 94 dB re: 20 mPa) is found experimentally to be −74 dB for a 1-in. condenser microphone and nearly the same for 1/2-in. and 1/4-in. microphones.

Polycrystalline diamond MEMS resonator technology for sensor applications

Due to material limitations of poly-Si resonators, polycrystalline diamond (poly-C) has been explored as a new MEMS resonator material. The poly-C resonators are designed, fabricated and tested using electrostatic (Michigan State University) and piezoelectric (Sandia National Laboratories) actuation methods, and the results are compared. For comparable resonator structures, although the resonance frequencies are similar, the measured Q values in the ranges of 1000–2000 and 10,000–15,000 are obtained for electrostatic and piezoelectric actuation methods, respectively. The difference in Q for the two methods is related to different pressures used during the measurement and not to the method of measurement. For the poly-C cantilever beam resonators, the highest value of their quality factor ( Q) is reported for the first time (15,263).

Out-of-plane electrostatic actuation of microcantilevers

An electrostatic actuation method to generate useful out-of-plane motion of a cantileverstructure is described. The critical design feature is to create an asymmetric electric fieldsuch that an electrostatic force is generated in a direction perpendicular to the wafersurface. The technical application of the actuation method is to large arrays ofmicrofabricated sensors such as cantilevers and in particular to resonator type sensors. Thedesign approach also overcomes several problems associated with exposure ofmicrofabricated cantilever structures to fluid environments, either during processing orduring application of such devices as bio-sensors, e.g. stiction, condensation, squeezedamping, exposure to a biological sample, cleaning and biological activation treatmentsof the cantilever surfaces. The viability of the technique is demonstrated usingmicrofabricated silicon cantilevers utilizing both optical and piezoresistive detection of thecantilever displacement.

Laterally driven electrostatic repulsive-force microactuators using asymmetric field distribution

We present a new electrostatic actuation method using a lateral repulsive-force induced by an asymmetric distribution of planar electrostatic field. The lateral repulsive-force has been characterized by a simple analytical equation, derived from a finite element simulation. Quality-factors are estimated from the computer simulation based on creep flow model. A set of repulsive-force polycrystalline silicon microactuators has been designed and fabricated by a four-mask surface-micromachining process. Static and dynamic response of the fabricated microactuators has been measured at the atmospheric pressure for the driving voltage range of 0-140 V. The static displacement of 1.27 /spl mu/m is obtained at the dc voltage of 140 V. The resonant frequency of the repulsive-force microactuator increases from 11.7 kHz to 12.7 kHz when the dc induction voltage increases from 60 V to 140 V. The measured quality-factors are increased from 12 to 13 in the voltage range of 60-140 V. Fundamental characteristics of the force, frequency and quality-factor of the electrostatic repulsive-force microactuator have been discussed and compared with those of the conventional electrostatic attractive-force microactuator.

The surface/bulk micromachining (SBM) process: a new method for fabricating released MEMS in single crystal silicon

This paper presents the surface/bulk micromachining (SBM) process to allow fabricating released microelectromechanical systems using bulk silicon. The process starts with a [111]-oriented silicon wafer. The structural patterns are defined using the reactive ion etching technique used in surface micromachining. Then the patterns, as well as sidewalls, are passivated with an oxide film, and bare silicon is exposed at desired areas. The exposed bare silicon is further reactive ion etched, which defines sacrificial gap dimensions. The final release is accomplished by undercutting the exposed bulk silicon sidewalls in aqueous alkaline etchants. Because {111} planes are used as etch stops, very clean structural surfaces can be obtained. Using the SBM process, 5-, 10-, and 100-/spl mu/m-thick arbitrarily-shaped single crystal silicon structures, including comb-drive resonators, at 5-, 30-, and 100-/spl mu/m sacrificial gaps, respectively, are fabricated. An electrostatic actuation method using p-n junction isolation is also developed in this paper, and it is applied to actuate comb-drive resonators. The leakage current and junction capacitance of the reversed-biased p-n junction diodes are also found to be sufficiently small for sensor applications. The developed SBM process is a plausible alternative to the existing micromachining methods in fabricating microsensors and microactuators, with the advantage of using single crystal silicon.

Measurement microphone calibrations and their uncertainty

Today, there is an increasing need for obtaining legal acceptance of and confidence in calibrations performed by laboratories in other countries. This is especially true and clearly observable in Europe where the number of accredited laboratories and calibrations per year are rapidly increasing. To obtain accreditation the laboratories must analyze and state their calibration uncertainty. This leads to focus on uncertainty of microphone sensitivity and sound level calibrations. The overall calibration uncertainty valid for ordinary measurement microphones and pistonphones have been determined by studying error sources and their influence on the calibration results. The uncertainties of the methods, which directly and indirectly influence the uncertainty valid for the user of a Bruel &amp; Kjær transducer calibration, are discussed. The methods include free-field and pressure reciprocity calibration of refrence standard microphones performed by the Danish Primary Laboratory of Acoustics (operated by Bruel &amp; Kjær in cooperation with the Danish Technical University, Lyngby) and the electrostatic actuator method which is widely applied by the Bruel &amp; Kjær Production Department and Calibration Service Centers. Contributions to the uncertainty which are due to the free-field and diffuse-field corrections and to the influence of microphone protection grids will be presented.

Field tests of a high‐temperature fiber optic lever microphone

The operating principle of a high‐temperature fiber optic lever microphone (FOLM), rated at 538 °C (1000 °F) continuous service, is based on intensity modulation of light reflected from a vibrating membrane. The frequency response of the microphone, calibrated in the laboratory at ambient temperature and 538 °C by the electrostatic actuator method, is typically 60–70 kHz. Applications to high‐temperature field testing include the thermal acoustic fatigue apparatus at Langley Research Center, an advanced short takeoff and vertical landing model at Lewis Research Center, the Mach 22 helium tunnel at Langley (ambient temperature only), interior mixer‐ejector surfaces at GE Aircraft Engines, Cincinnati, and a high temperature acoustic impedance tube at Langley. In most of these applications the FOLM made possible high‐temperature, high‐frequency acoustic data to be taken for the first time. Typical test results will be discussed.

Some recent developments in phase match of microphones

Phase match data for condenser microphones obtained with a new coupler are discussed. The protective grids of the microphones have some influence on the phase match at frequencies above 1 kHz. The phase match theory is based on the exchange microphone method [J. Acoust. Soc. Am. 90, 1253–1255 (1991)], which is also capable of discerning the phase match between the amplifiers of the two measuring channels. The performance of the coupler is verified with direct electrical measurement of the phase difference between the two channels and by comparison with the corresponding measurements provided by the coupler. A comparison is made between the data obtained with the coupler and those acquired with the electrostatic actuator method. Since the electrostatic actuator method does not expose the microphone back cavity pressure equalizing vent to the same excitation, the phase match readings provided by the electrostatic actuator method are confirmed to be not valid, particularly at low frequencies.