Bimorph Structure Research Articles

2538 カーボンナノチューブ/イオン液体ゲルからなる高分子アクチュエータの電気化学特性(J10-9 高分子・薄膜,J10 知的材料・構造システム)

We have reported a novel low-voltage driven dry polymer actuators based on single-walled carbon nanotube gels (bucky gels) of ionic liquids. The actuator has a bimorph structure composed of polymer-supported bucky gel electrodes and a polymer-supported ionic-gel electrolyte. In order to improve the performance of the actuator, we further explored the preparation method of the bucy-gel electrode and internal ionic liquid species. Herein we report details of improved response of our bucky gel actuator.

Energy harvesting MEMS device based on thin film piezoelectric cantilevers

A thin film lead zirconate titanate Pb(Zr,Ti)O3 (PZT), energy harvesting MEMS device is developed to enable self-supportive sensors for in-service integrity monitoring of large social and environmental infrastructures at remote locations. It is designed to resonate at specific frequencies of an external vibrational energy source, thereby creating electrical energy via the piezoelectric effect. Our cantilever device has a PZT/SiNx bimorph structure with a proof mass added to the end. The Pt/Ti top electrode is patterned into an interdigitated shape on top of the sol-gel-spin coated PZT thin film in order to employ the d 33 mode. The base-shaking experiment at the first resonant frequency of the cantilever (170 × 260 μm) generates 1 μW of continuous electrical power to a 5.2 MΩ resistive load at 2.4 V DC. The effect of proof mass, beam shape and damping on the power generating performance are modeled to provide a design guideline for maximum power harvesting from environmentally available low frequency vibrations. A spiral cantilever is designed to achieve compactness, low resonant frequency and minimum damping coefficient, simultaneously.

Methods and apparatus to increase sound quality of piezoelectric devices

A piezoelectric transducer comprises a piezoelectric component, an acoustic member attached to one of the surfaces of the piezoelectric component and a dampening material of low elastic modulus attached to one or both surfaces of the piezoelectric transducer. The piezoelectric component may comprise either an unimorph or a bimorph structure including a piezoceramic wafer made of lead zirconate titanate and a layer of dampening material sandwiched between the piezoelectric component and the acoustic member. The acoustic member comprises a surrounding wall portion and an end portion which form an acoustic chamber when the member is mounted on a surface of the piezoelectrie component. The end portion has an orifice to form a passageway from the chamber through the end portion to the outside of the member.

1P1-C17 バイモルフ型静電マイクロアクチュエータの力特性

Four types of bimorph electrostatic microactuators having different structure and size were fabricated and tested. They consist of bimorph structure beams made of poly-Si and Au/Cr, and their performance is achieved by using several beams connected in series and bending them sequentially with electrostatic force. Forces generated by the microactuators were measured with a Si cantilever and a laser displacement meter. The relationship between applied voltage and generated force showed that the actuator which had longer beams located closer to a substrate generated larger force by applying lower voltage.

Novel Bimorph-Structured Hydrogel Containing Segregated Polymer Surfactant

Bimorph-structured NIPA/NIPA–PMDP gel was fabricated from a NIPA gel containing a polymer surfactant (PMDP) by an electrophoretic method. The gel showed clearly bending motions when heating in 1 M NaCl solution. Directions of the bending motions can be changed by switching from pure water to the salt solution. It was verified that the NIPA–PMDP gel was more active material to the stimuli and NIPA gel was less active one in the bimorph structure, which resulted in the bending motions.

Micromirror structure actuated by TiNi shape memory thin films

TiNi films were deposited by co-sputtering TiNi and Ti targets. Results from differential scanning calorimetry and curvature measurement revealed martensitic transformation and shape memory effect upon heating and cooling. Two types of TiNi/Si micromirror structures with a Si mirror cap (40 µm thick) and TiNi/Si actuation beams were designed and fabricated. For the first design, a V-shaped cantilever based on the TiNi/Si bimorph structure was used as the actuation mechanism for the micromirror. In the second design, three elbow-shaped Si beams with TiNi electrodes were used as the arms to actuate the mirror. The TiNi/Si microbeams were flat at room temperature and bent up by applying voltage in the TiNi electrodes (due to phase transformation and shape memory effect), thus causing changes in angles of the micromirror.

Focused ion beam fabrication of thermally actuated bimorph cantilevers

Focused ion beam (FIB) technology was used to fabricate thermally actuated cantilever arrays using silicon nitride membrane chips for microelectromechanical systems (MEMS) applications. Sequential modification and test is made possible by the dualbeam FIB/SEM. A fabrication route based largely on the use of FIB etch and deposition steps applied to a silicon nitride membrane chip resulted in the formation of readily released bimorph structures with lengths <10 μm. Device deflection sensitivity better than 500 nm/mW was observed. Short-circuiting and hence non-functionality of some devices was attributed to the platinum halo overlap between deposited tracks, which limits the potential for miniaturisation of FIB-MEMS prototypes. Potential applications for these cantilever arrays include scanning probe microscope (SPM) systems and resonant gas sensors.

Fabrication and characterization of diamond-like carbon/Ni bimorph normally closed microcages

Normally closed microcages based on highly compressively stressed diamond-like carbon (DLC) and electroplated Ni bimorph structures have been simulated, fabricated and characterized. Finite-element and analytical models were used to simulate the device performance. It was found that the radius of curvature of the bimorph layer can be adjusted by varying the DLC film stress, the total layer thickness and the thickness ratio of the DLC to Ni layers. The angular deflection of the bimorph structures can also be adjusted by varying the finger length. The radius of curvature of the microcage was in the range of 18–50 µm, suitable for capturing and confining micro-objects with sizes of 20–100 µm. The operation of this type of device is very efficient due to the large difference in thermal expansion coefficients of the DLC and the Ni layers. Electrical tests have shown that these microcages can be opened by ∼90° utilizing a power smaller than 20 mW. The operating temperatures of the devices under various pulsed currents were extracted through the change in electrical resistance of the devices. The results showed that an average temperature in the range of 400–450 °C is needed to open this type of microcage by ∼90°, consistent with the results from analytical simulation and finite-element modelling.

Polarisation kinetics of electrically connected electroconductive ferroelectric multilayer structures

In this article, the polarisation kinetics of an electrically connected ferroelectric bimorph structure is described with an electric model by means of equivalent circuit analysis. This model results in a system of ordinary differential equations (ODEs) that can be solved numerically. A bimorph model structure consisting of wire-connected layers of barium–titanate–stannate ceramics was poled. The conductivities of the layers can be estimated by comparing of the measured electric field in the layers and the results of the poling model. In order to consider hysteretic effects, the Preisach model of hysteresis is included into the poling model. Within the ODEs, the slope of the hysteresis loop is needed. An algorithm for estimating it via the Preisach model was developed. This approach is based upon linear interpolation between adjacent grid points of the discretised electric field within the Preisach model. An example shows the capabilities of this method for considering poling, switching effects and depolarisation.

Normally closed microgrippers using a highly stressed diamond-like carbon and Ni bimorph structure

A normally closed microgripper with a radius of curvature of 18–50 μm using a diamond-like carbon (DLC) and stress free electroplated Ni bimorph structure has been demonstrated. The large curvature in the fingers of the microgrippers is due to the high compressive stress of the DLC layer. The radius of curvature of the figures can be adjusted by the thickness ratio, and the closure of the devices can also be adjusted by varying the finger length. This device works much more efficiently than other bimorph structures due to the large difference in thermal expansion coefficients between the DLC and the Ni layers. Preliminary electrical tests have shown these microgrippers can be opened by 60°–90° at an applied power of &amp;lt;20mW.

Analytical and Numerical Modelling of Laminated Composites with Piezoelectric Elements

We propose an accurate and efficient approach to laminated piezoelectric plates based on a refinement of elastic displacement and electric potential through the plate thickness. More precisely, the model accounts for a shearing function and a layerwise approximation for the electric potential. The layerwise approach becomes a necessity in order to accommodate electric potential at the electrode interfaces. The equations of motion for the piezoelectric composite are deduced from a variational formulation incorporating the continuity conditions at the layer interfaces by using Lagrange multipliers. Different situations are investigated among them (i) bimorph and (ii) sandwich structures for two kinds of electro-mechanical loads applied (density of force and electric potential) and are compared to the finite element computations performed on the 3D model. The vibration problem is also presented and the frequencies for the axial and flexural modes are obtained. At last performance and effectiveness of the model are also discussed and applications to control of the structure shape and vibration are proposed.

A self-organized bending-beam electrochemical actuator

Abstract Recent new technologies of electromechanical conversion devices have been reviewed. Especially, the electrochemical properties of anisotropic actuators using polypyrrole have been reported in detail and the realization of the bimorph (or bending-beam) structure without artificial adhesive agent is introduced.

Improved photothermal deflection design of an integrated microbeam for application to anexternal-cavity tunable laser diode

This paper presents analytical results showing that the photothermal deflectionof a microbeam greatly increases by employing an antireflection-coatedbimorph structure. We expect this deflection to exceed half a wavelength,which is required for a tunable laser diode, by increasing the temperature by100 °C with an optical absorption rate above 98%. An antireflection coating ofAu/Si3N4/Au on theAu and Si3N4 bimorph structure semiconductor microbeam provides enhanced deflection about 500 timesgreater than that of the solitary semiconductor microbeam at off-resonant frequencies.The designed microbeam monolithically integrated on gallium arsenide (GaAs at0.83 µm wavelength) or indiumphosphide (InP at 1.3 µm wavelength) platform will be used for a variable-length external-cavity edge-emittingtunable laser diode.

Capacitive-type chemical sensors using thin silicon/polymer bimorph membranes

Capacitive-type chemical sensing devices based on a silicon/polymer bimorph structure have been fabricated and evaluated. Upon exposure to analytes, the polymer covering the thin silicon membrane swells, inducing a deflection on the membrane, which is measured as a capacitance change between membrane and substrate. Five different polymer layers [poly-hydroxy-ethyl-methacrylate (PHEMA), poly-methyl-methacrylate (PMMA), poly-vinyl-acetate (PVAc), epoxydized novolac (EPN) and poly-dimethylsiloxane (PDMS)] were used. Exposure to water, methanol and ethanol vapors was used for evaluating performance. Sensitivities ranging from 4.5fF/%RH for PDMS to 29fF/%RH for PHEMA-covered devices are reported. Devices covered with PHEMA, PVAc and PMMA also exhibit strong response upon exposure to methanol and ethanol atmospheres.

Fabrication of chemical sensors based on Si/polymer bimorphs

The fabrication and first results of a capacitive type chemical sensor based on a silicon/polymer bimorph structure are described. Upon exposure to analytes the polymer covering the thin silicon membrane swells inducing a deflection on the membrane which is measured as a capacitance change between membrane and substrate. Five different polymer layers [poly-hydroxy-ethyl-methacrylate (PHEMA), poly-methyl-methacrylate (PMMA), poly-vinyl-acetate (PVAc), epoxy-novolac (EPN) and poly-dimethylsiloxane (PDMS)] are examined. Exposure to water, methanol and ethanol vapors is used to evaluate performance. Sensitivities ranging from 4.5fF/%RH for PDMS up to 29fF/%RH for PHEMA covered devices are reported. Devices covered with PHEMA, PVAc and PMMA also exhibit strong response upon exposure to methanol and ethanol atmospheres. Differences in sensitivities between these layers may be exploited in constructing an effective chemical discriminating array.

Analytical and numerical modelling of laminated composites with piezoelectric layers

An accurate and efficient modelling for laminated piezoelectric plates is presented. The approach is based mostly on a refinement of the elastic displacement including a shear correction and accounting for a layerwise approximation for the electric potential. The equation of the model are deduced from a variational formulation accounting for continuity conditions at the layer interfaces by using Lagrange multipliers. The resolution of different situations is considered for various types of electromechanical loads : (i) density of applied forces and (ii) applied electric potential. The results for bimorph and sandwich structures are given and compared to the finite element computations performed on the 3D model. The problem of vibration of piezoelectric laminated composites is also discussed. A quite good accuracy is shown for the electromechanical local (the trough-the-thickness variation) and global (deflection, frequencies, etc.) responses of the present plate model.

Fabrication of chemical sensors based on Si/polymer bimorphs

The fabrication and first results of a capacitive type chemical sensor based on a silicon/polymer bimorph structure are described. Upon exposure to analytes the polymer covering the thin silicon membrane swells inducing a deflection on the membrane which is measured as a capacitance change between membrane and substrate. Five different polymer layers [poly-hydroxy-ethyl-methacrylate (PHEMA), poly-methyl-methacrylate (PMMA), poly-vinyl-acetate (PVAc), epoxy-novolac (EPN) and poly-dimethylsiloxane (PDMS)] are examined. Exposure to water, methanol and ethanol vapors is used to evaluate performance. Sensitivities ranging from 4.5fF/%RH for PDMS up to 29fF/%RH for PHEMA covered devices are reported. Devices covered with PHEMA, PVAc and PMMA also exhibit strong response upon exposure to methanol and ethanol atmospheres. Differences in sensitivities between these layers may be exploited in constructing an effective chemical discriminating array.

Au/poly-Siバイモルフ構造を用いた静電マイクロアクチュエータの駆動特性の改善(J21-2 静電アクチュエータ・MEMS技術応用,J21 マイクロメカトロニクス)

An electrostatic microactuator with Au/poly-Si bimorph structure was driven with low voltage of 5.2 V, and it was vibrated repeatedly with amplitude of 10μm and frequency of 160 Hz. Its performance is achieved by using several cantilevers connected in series and bending them repeatedly with electrostatic force. The fabricated microactuators were tested by applying voltages with various frequencies and amplitudes, and its deflections were measured using a laser displacement meter. As a result, the deflection of an actuator was found to be the maximum at a frequency of up to 160 Hz when the actuator size was 300μm. The hysteresis of characteristics of the fabricated microactuator became smaller when the actuator size was decreased. Also, the frequency band where the maximum deflection was obtained became wider with reduction of the actuator size.

Dynamic peak amplitude analysis and bonding layer effects of piezoelectric bimorphcantilevers

An analytical prediction of dynamic performance for piezoelectric bimorph structures wasinvestigated. A damping ratio was assumed and employed to determine dynamic peakamplitudes at resonances by finding the frequency with of the peak amplitude. Finite element simulations were used to validate the proposedimprovement strategy. Results show that the peak amplitude determination method is goodenough to predict the dynamic performance of piezoelectric bimorphs. The effects ofbonding layers were also analysed by both static and dynamic methods. The bondinginfluence can be minimized by selecting appropriate bonding materials and dimensions ofstructures.

Instability in micromachined curved thermal bimorph structures

For the micromachined thermal bimorph structure, there is often initial deflection, or so-called geometrical imperfection, which may affect the stability of the structure. Here, finite element simulations and experiments are conducted to study the influences of initial deflection and actuating region on mechanical behaviors of a curved bimorph structure with clamped boundary condition. Devices are fabricated by adjusting the internal stresses of polysilicon layers on bimorph structures to achieve various initial deflections. Various actuation regions are achieved by designing different sizes of top layers covering the bottom layers of the bimorph structures. Stable and unstable regions in terms of two design factors, initial deflection ratio and bimorph ratio, are characterized by simulations and experiments. It is found that the curved bimorph structure is stable when the bottom layer is fully covered with the top layer or the initial deflection is much smaller than the structure thickness. The stable device is found to deflect in one direction only. The bimorph structure becomes unstable while the initial deflection is close to or larger than structure thickness. For unstable curved bimorph structures, we find the snap buckling effect with two-way deflections and a hysteresis loop.