Thin Film Actuator Research Articles

Metallic thin film composites with shape memory alloys for microswitches and tactile graphical displays

A new mechanism to switch thin film actuators between two stable states has been developed. Bistable membrane switches can be realized by snap-dome shaped metallic foils which are coated on opposite surfaces with Ti(Ni,Cu) and (Ti,Hf)Ni respectively whereby the narrow hysteresis of Ti(Ni,Cu) is within the broad one of (Ti,Hf)Ni. If both SMAs are martensitic or both are austenitic, they apply similar forces on the intermediate foil and the shape of the membrane remains constant. However, if one of them is austenitic and the other one martensitic, the austenitic one determines the curvature of the membrane. Switching is possible by two different heat pulses. Therefore, energy is only required to change the state of the membrane. The new mechanism is described and first successful processing steps are presented. The mechanism allows the fabrication of microswitches and tactile displays.

Thermomechanical Behaviors of Shape Memory Alloy Thin Films and Their Application

The thermomechanical behaviors of SMA thin film actuator and their application are investigated. The numerical algorithm of the 2-D SMA thermomechanical constitutive equation is developed and implemented into the ABAQUS finite element program by using the user defined material (UMAT) subroutine. To verify the numerical algorithm of SMAs, the results are compared with experimental data. For the application of SMA thin film actuator, the methodology to maintain the precise configuration of inflatable membrane structure is demonstrated.

Piezoelectric thin-film unimorph actuator for optical fibre alignment applications

Feasibility of a piezoelectric unimorph thin-film actuator for optical fibre alignment was investigated. The main interest was focused on the fabrication, and electrical and mechanical characterization of a low-voltage driven component which was small-sized, efficient and suitable for integration into the low-temperature co-fired ceramic (LTCC) environment. Lead zirconate titanate (PZT) was chosen as ferroelectric thin-film material due to its excellent piezoelectric properties. A specific thin-film actuator structure was designed, modelled, and fabricated on silicon substrates. The structural, electrical and mechanical properties of the actuator structures were characterized, and the actuator structures were hybrid-integrated on LTCC substrates together with optical fibres to form a cantilever-type high-precision alignment device. Using a semiconductor laser diode as a light source, the alignment of an optical fibre was tested. Cantilever displacements up to 57??m were achieved enabling adjustability of optical power coupling.

Compensation of parasitic effects for a silicon tuning fork gyroscope

This paper refers to a silicon micromachined tuning fork gyroscope, which is driven via two piezoelectric thin film actuators. The device responds to an external angular rate by a torsional motion about its sensitive axis due to the Coriolis effect. The shear stress in the upper torsional stem, which is proportional to the angular rate, is detected via a piezoresistive readout structure. In addition to the wanted signal corresponding to the angular rate, there are unwanted contributions from the drive motion, e.g., from mechanical unbalances and from asymmetries of the piezoelectric excitation induced by fabrication tolerances. These effects, which disturb the sensor signal with varying contributions in amplitude and phase, have already been examined for capacitive surface micromachined sensors. In this paper, they are identified for a piezoelectrically driven, bulk-micromachined gyro and compared to results of FEM simulations. System-level simulations are performed and show possibilities to compensate the main parasitic effects. Results of eliminating the mechanical unbalance by femtosecond laser trimming are presented and compared with the simulations.

Geometric and Mechanical Considerations for the Design of the Magnetostrictive Thin Film Actuators#

The driving field of the magnetostrictive thin film actuator should be as small as possible in order to develop miniature devices. The aim of this paper is to reduce the driving field by varying the structural and the material parameters of the substrate of the cantilever in the actuator based on the finite element calculation. The influences of the geometric and the material parameters on the reference driving field have been studied. The results show that the reference driving field is sensitive to the length of the cantilever, the thickness of both the magnetostrictive film and the substrate, and also the Young's modulus of the substrate. The length of the cantilever should be long enough. In order to achieve a small driving field, the thickness of both the magnetostrictive film and the substrate should be carefully designed according to the ratio of the Young's modulus of the substrate to that of the film.

Shape memory thin film actuator for holding a fine blood vessel

In this paper, we describe a shape memory alloy (SMA) thin film actuator which can hold a fine blood vessel for a pulsation monitor. The device has a function of two-step actuation with integrated micro-heaters which can heat up the SMA locally. The TiNiCu ternary SMA thin film was deposited onto a sacrificial copper substrate by flash evaporation method. Phase transformation temperatures can be controlled to be higher than human body temperature for secure actuation by timed operation of a shutter during flash evaporation of a series of pellets. The actuator holds the vessel securely by the first actuation, and allows continuous monitoring after microsurgery. After using, it can release the blood vessel easily by the second actuation and is removed completely without any additional surgical invasions. The micro-heaters can heat up the SMA actuator over 65 °C locally within 10 s when it was heated by an electric current of 10 mA.

Development of transparent thin film speaker and its application for active sound transmission control through windows

Homes close to airports and highways in major metropolitan areas suffer from serious noise problems. Typically, windows constitute the primary path through which noise enters a home. As an effective method for attenuating low frequency noise, active noise cancellation approach has drawn increasing interest. A small voice coil actuator can be used to vibrate a glass panel and achieve significant reduction in noise transmission at its location. However, global noise cancellation over the entire panel can not be achieved with such a single point actuator. Using multiple voice coil actuators is also not practical, since several actuators on a windowpane would destroy the aesthetics of the window. This necessitates the development of thin film actuators that can provide distributed canceling sound over the entire surface of large sized glass panels. The need of transparence for the windows application poses a great challenge to the development of such thin film actuators. In this paper, transparent thin film speakers are developed, based on the use of carbon nanotubes for conductive films that are coated on polzerized PVDF films. Preliminary experimental results show that the transparent thin film speaker has the potential to be a promising solution for the ANC windows.

Effects of corner frequency on bandwidth and resonance amplitude in designing PZT thin-film actuators

In the last decade, lead zirconate titanate oxide (PZT) thin-film actuators have received increasing attention because of their high frequency bandwidth, large actuation strength, fast response, and small size. The PZT film thickness is usually less than several microns as opposed to hundreds of microns for bulk PZT patches that are commercially available. As a result, PZT thin-film actuators pose unique vibration issues that do not appear in actuators with bulk PZT. Two major issues affecting actuator performance are the frequency bandwidth and the resonance amplitude. As an electromechanical device, a PZT thin-film actuator's bandwidth and resonance amplitude depend not only on the lowest natural frequency ω n of the actuator's mechanical structure but also on the corner frequency ω c of the actuator's RC-circuit. For PZT thin-film actuators, the small film thickness implies large film capacitance C and small ω c. When the size of the actuator decreases, ω n increases dramatically. As a result, improper design of PZT thin-film actuators could lead to ω c ≪ ω n substantially reducing the actuator bandwidth and the resonance amplitude. This paper is to demonstrate this phenomenon through theoretical analyses and calibrated experiments. In the theoretical analyses, frequency response functions of a PZT thin-film actuator are obtained to predict 3 dB actuator bandwidth and resonance amplitude for cases when ω c ≪ ω n, ω c ≈ ω n and ω c ≫ ω n. In the experiments, frequency response functions of a fixed–fixed silicon beam with a 1 μm thick PZT film are measured through use of a laser Doppler vibrometer and a spectrum analyzer. The silicon beam has multiple electrodes with a wide range of resistance R and corner frequency ω c. The experimental results confirm that the actuator bandwidth and resonance amplitude are substantially reduced when ω c ≪ ω n.

Resonant micro-mirror excited by a thin-film piezoelectric actuator for fast optical beam scanning

A silicon resonant torsional micro-mirror excited by piezoelectric bimorph actuators is presented. The bimorph actuators consist of a single-crystal silicon flexible beam or membrane and a PZT thin film. The mechanical elements are etched in the 20 μm thick superficial layer of a SOI substrate, thereby ensuring the flatness of the 500 μm-diameter gold-coated mirror. This device achieves optical beam scanning with large angular deflection at high frequency. In air, we have measured scanning up to 19.8° at 1.8 kHz, 99.1° at 10.6 kHz and 40.8° at 25.4 kHz. The applied driving voltage is sinusoidal with an amplitude under 42 V PP and with a 6 V DC bias voltage. At large oscillation amplitude, a non-linear hard-spring effect has been observed. In vacuum, a 78° optical scanning has been obtained with less than 1 V PP.

High Responsiveness Induced by Palladium Deposition on Thin Film Actuator of LaNi<SUB>5</SUB> Hydrogen Storage Alloy

The unimorph actuator of the LaNi5 thin film deposited on polyimide substrates can be expected as a sensor and/or a controller of hydrogen gas flux in various hydrogen-related devices, since controlling the hydrogen concentration in the film by pressure change drives this actuator reversibility. In this study, the effect of the palladium deposition was investigated on the mechanical response of this thin film actuator. It was shown that the initiating time (incubation period) for the actuation to be measured after hydrogen gas exposure was reduced from 100 to 1 s by the palladium deposition. This significantly improvement of the mechanical response was attributed to the change in the rate determining steps: the dissociation of hydrogen gas molecules on the sample surface for the sample without palladium deposition, and hydrogen diffusion in the LaNi5 film for the palladium deposited sample. It was also suggested that the high permeability of hydrogen in palladium film at room temperature resulted in the high responsiveness.

Comparison of In-Plane Actuation from a Thin Film and a Bulk Actuators

ABSTRACTThis contribution reports the results of a comparative method on the properties of the in-plane actuation of lead zirconate titanate thin films. Our aim is to dynamically measure the force generated by a thin film on its substrate in order to evaluate their potential for plate wave generation. As there is a difficulty to obtain a quantitative measure, we used a comparaison with a thin bulk disk having same diameter. It is then shown that thin film above 2 μ m can provide the same amount of mechanical output than bulk disk under the same voltage.

259 PZT/SUS ユニモルフマイクロアクチュエータの開発と進行波型マイクロポンプへの応用

The traveling wave micropump with a thin flow layer is suitable for particle separation and quantification without valves, heat and strong electric field. We have proposed a traveling wave micropump driven by the traveling wave, and demonstrated high efficiency. In this paper, we fabricated a traveling wave micropump composed of flexible microchannel wall made of Polydimethylsiloxane (PDMS) with piezoelectric thin-film unimorph actuators. The piezoelectric thin films were deposited directly on cantilever-shaped stainless steel (SUS) substrates using rfagnetron sputtering technique. The active motion of the particles in the fluid was confirmed by the actuation of the microchannel wall by the piezoelectric actuators.

Analog Piezoelectric-Driven Tunable Gratings With Nanometer Resolution

This work presents the design, fabrication, and characterization of a piezoelectrically actuated MEMS diffractive optical grating, whose spatial periodicity can be tuned in analog fashion to within a fraction of a nanometer. The fine control of the diffracted beams permits applications in dense wavelength-division multiplexing (DWDM) optical telecommunications and high-resolution miniaturized spectrometers. The design concept consists of a diffractive grating defined on a deformable membrane, strained in the direction perpendicular to the gratings grooves via thin-film piezoelectric actuators. The tunable angular range for the first diffracted order is up to 400 /spl mu/rad with 0.2% strain (/spl sim/8 nm change in grating periodicity) at 10 V actuation, as predicted by device modeling. The actuators demonstrate a piezoelectric d/sub 31/ coefficient of -100 pC/N and dielectric constant /spl epsiv//sub r/ of 1200. Uniformity across the tunable grating and the out-of-plane deflections are also characterized and discussed.

Demonstration and characterization of PZT thin-film sensors and actuators for meso- and micro-structures

Recent development of next-generation medical devices, such as endoscopes and hearing aids, call for PZT (lead zirconate titanate oxide) thin-film sensors and actuators with thickness in the range of 1–30 μm to enhance actuation strength and sensor sensitivity. Currently, sol–gel derived PZT films often have thickness less than 0.2 μm per coating. Moreover, thermal stresses in the films limit the crack-free area to less than 1 mm 2. This paper has four specific goals. The first goal is to demonstrate an improved sol–gel process using rapid thermal annealing and a diluted sealant coating. The resulting thickness can reach 2 μm in three coatings with a crack-free area as large as 5 mm×5 mm . The second goal is to characterize piezoelectric properties of the fabricated PZT films experimentally. The resulting piezoelectric constant d 33 is 120 pC/N and the dielectric constant ranges from 200 to 400. The third goal is to demonstrate the use of the PZT thin film as a calibrated sensor. The specimen is a silicon cantilever ( 30 mm×7.5 mm×0.4 mm ) with a PZT thin film ( 4 mm×4 mm×1 μm ). Moreover, a tiny shaker excites the cantilever at the fixed end, and a charge amplifier detects the charge accumulated in the PZT film. In the meantime, a laser vibrometer measures the deflection of the cantilever at three points along the PZT film, from which the strain is calculated using Euler–Bernoulli beam theory. Comparison of the strain and the charge amplifier voltage determines the calibration constant of the PZT thin-film sensor. The last goal is to demonstrate the use of the PZT thin film as a powerful actuator through active vibration control. In experiments, a tiny bulk PZT patch is first glued to the silicon cantilever. A function generator drives the bulk PZT simulating a source of disturbance exciting the silicon cantilever. In the meantime, a laser Doppler vibrometer (LDV) measures velocity of the cantilever tip. With a phase shifter as the controller, the LDV measurement is fed back to the PZT thin-film actuator to actively control the cantilever vibration. To evaluate the effectiveness of the active vibration control, a spectrum analyzer measures the frequency response functions (FRF) from the bulk PZT voltage to the LDV response. Experimental results show that the simple active vibration control scheme can reduce resonance amplitude of the first bending mode by 66%.

Fabrication and characterization of diamond AFM probe integrated with PZT thin film sensor and actuator

In order to develop a diamond probe with a piezoelectric sensor and actuator for atomic force microscope (AFM), we fabricated lead zirconate titanate (PZT) thin film on a diamond thin film substrate and examined its piezoelectric properties. The PZT thin film was sputtered at room temperature and then annealed to obtain a perovskite structure. After rapid thermal annealing at temperature ramp rate of more than 10 °C/s and at temperatures of more than 500 °C in a nitrogen (N 2) ambient, the PZT thin film fabricated on flat Si substrates showed high piezoelectric constant, d 31, of about −90 pC/N, as well as in an oxygen (O 2) ambient. On diamond thin film substrates, the value of piezoelectric constant was as low as about −20 pC/N due to rough surface of the diamond film. After a poling treatment, however, its piezoelectric constant improved to about −65 pC/N. For realization of a PZT sensor and actuator on a diamond cantilever, the PZT thin film was also successfully patterned by reactive ion etching (RIE) in sulfur hexafluoride (SF 6) plasma using a platinum (Pt) upper electrode layer as an etching mask without any damage on the diamond layer. Based on the fabrication and patterning of PZT thin film together with microfabrication techniques of diamond film formed by chemical vapor deposition (CVD), we demonstrate the diamond AFM probe of 150 μm in length, 50 μm in width, and 5 μm in thickness with a PZT sensor and actuator of 1 μm in thickness. The resolution of image sensing and actuation force were estimated to be about 0.4 nm at a resolution of charge measurement of 1×10 −15 C, and 17 μN at an applied voltage of 8 V, respectively.

Improved Response Time of a Thin Film Hydrogen Storage Alloy Unimorph Structure after Platinum Surface Treatment

In this study, the effect of a platinum surface treatment on the mechanical response of a LaNi5 thin film actuator deposited on polyimide substrates was investigated. Since this actuator could be reversibly driven by hydrogen pressure control, it could function as a sensor and/or controller of the hydrogen gas flux in various hydrogen related devices. In the experiments, the incubation period of the actuation after hydrogen gas exposure was reduced from 100 to 10 s by the platinum surface treatment. This significantly modified mechanical response is attributed to a switching of the reaction rate determining steps. The platinum treatment enhanced the decomposition rate of hydrogen gas molecules at the surface. The platinum treatment should bring about a change of rate determining step to a permeation/diffusion of the hydrogen atoms into the film.

水素吸蔵合金薄膜ユニモルフ構造の白金表面処理による応答性の改善

In this study, the effect of the platinum surface treatment on mechanical response of LaNi5 thin film actuator deposited on polyimide substrates was investigated. Since this actuator could be reversibly driven by hydrogen pressure control, this actuator is expected as a sensor and/or controller of hydrogen gas flux in various hydrogen related devices.In the experiments, initiating time of the actuation after hydrogen gas exposure is reduced from 100 to 10 s by platinum surface treatment. This significantly modified mechanical response is attributed to switching of the reaction rate determining steps. Dissociation of hydrogen gas molecules on the sample surface is considered to be changed to permeation/diffusion of hydrogen atoms in the film by the platinum treatment.

水素吸蔵合金ＬａＮｉ５の薄膜アクチュエータのパラジウム表面処理による高応答性

In this study, the effect of the palladium surface treatment was investigated on the mechanical response of the LaNi5 thin film actuator deposited on polyimide substrates. Since controlling the hydrogen concentration in film by changing the pressure may reversibly drive this actuator, this film actuator can be expected as a sensor and/or a controller of hydrogen gas flux in various hydrogen-related devices. In the present experiments, it was shown that the initiating time for the actuation to be measured after hydrogen gas exposure was reduced from 100 s to 1 s by the palladium surface treatment. This significantly improved mechanical response was attributed to the switching of the reactions in the rate determining steps. The rate determining reaction after the palladium treatment was no longer the dissociation of hydrogen gas molecules on the sample surface, but the hydrogen permeation or diffusion in the film. Furthermore, it was found that the high responsiveness induced by the palladium treatment was also caused by the high permeability of hydrogen in palladium film at room temperature.

進行波を用いた薄膜バルブレスマイクロポンプの開発(J22-3 センサ・アクチュエータシステムとその知能化(3),J22 センサ・アクチュエータシステムとその知能化-実環境で活躍するメカトロニクスを目指して)

Micropumps play a significant role in fluid transportation system of μ-TAS. We propose a peristaltic micropump system composed of a microchannel made of silicon rubber. Bottom surface of the microchannel is deformed by the electrostatic attraction between upper and lower electrodes made of copper thin films. Since the pump has simple structure using the electrostatic thin film actuators without valves, the fabrication process is also as simple as just stacking organic films or layer on PMMA substrate. The micropump is suitable for low-cost disposable applications. We could observe clear deflection of the channel wall which is proportional to the a square of the applied voltage. In addition, we confirmed active motion of microbeads in the fluid by the peristaltic actuation of electrostatic force.

402 マイクロアクチュエータ用PZT圧電薄膜創製技術の開発(GS-16 精密計測・精密加工)

402 マイクロアクチュエータ用PZT圧電薄膜創製技術の開発(GS-16 精密計測・精密加工)