Bimorph Structure Research Articles

Miniaturization of a Thermally Driven Ni|Si Bimorph

We report on the development of a thermally isolated bimorph structure based on a Ni|Si pair. A 1-mm-long beam of the bimorph was thermally isolated by a polyimide comb from the rest of the Si structure. The Si and Ni layers of the bimorph were 20 µm thick. This geometry enabled us to generate the bending displacement (the stroke) of the free end of the bimorph up to 100 µm at about 100°C with a generated force of about 15 mN. Electrical power consumption for the 100°C working point was lower than 0.2 W and the response time was 0.5 s. This design entitles further miniaturization of micro-electromechanical systems (MEMSs) such as commercial microvalve structures and sensors. The principles of design and experimental results of temperature distribution for the bimorph are presented and discussed.

Bi-ionic actuator by polypyrrole films

A new mechanism for driving the bimorph actuator using polypyrrole (PPy) films has been proposed. This actuator is consisted of two different PPy layers, in which one is electrochemomechanically deformed by the cation insertion and the other is deformed by the anion insertion. The freestanding deformation of each layer is opposite at a certain electrochemical potential with each other. Both deformations, however, cooperate to bend the film into the same direction by forming the bimorph structure. Since synchronized anion insertion and cation deinsertion drive this actuator, it can be expressed as a bi-ionic actuator (BIA). BIA offers its superiority over the conventional one having: (I) the double-active layers for the actuation, (II) the strong adhesive interface by inter-penetrating polymer networking and (III) the available technique for mapping two oppositely bending BIA units into the same film. The bending performance with double-active layer was compared to that with the single-active layer of BIA. The fabrication dependence and the folding performance were also investigated.

Dielectric and pyroelectric properties of PZFNT/PZT bimorph thin films

Pyroelectric Pb1,1(Zr0.58Fe0.2Nb0.2Ti0.02)O3/Pb1.1(Zr0.9Ti0.1)O3 (PZFNT/PZT) bimorph thin films are processed via a modified sol-gel method on highly textured (1 1 1)Pt/Ti/SiO2/Si substrates. XRD and SEM investigations show full pyrochlore to perovskite phase transformation after annealing at 750 °C. XPS depth profiling reveals diffusion of Fe leading to a broad transition layer. The PZT 90/10 bottom layer was shown to be effective for dielectric permittivity control of the bimorph structure. The small signal dielectric constant, e′, was determined as 580 at 10 kHz. The temperature dependence of e′ is shown to exhibit a single maximum at approximately 195 °C. The C–V characteristics of the bimorph structure show the typical behavior of ferroelectric perovskites. These results are attributed to microstructural effects, particularly the presence of a broad transition layer. The pyroelectric properties are reported in the temperature range from 20 to 60 °C and compared to monomorph PZT and PZFNT films. It is shown that the bimorph thin film has higher pyroelectric coefficient and detectivity than the constituent monomorph films.

An electro-thermally driven microactuator with two dimensional motion

In previous literatures, most of the microactuators were designed to deflect in one dimension only. Here, an electro-thermally driven microactuator with out-of-plane and in-plane two dimensional motion is designed, fabricated and tested. This microactuator comprised of a series of bimorph beams, a moving plate, a lateral driven unit, and contact pads. The out-of-plane motion is produced due to the bimorph effect and residual stress between the layers of Au and polysilicon when they are heated. The in-plane motion is obtained by heating the lateral driven unit which consists of two adjacent beams with different cross sections but the same length, then the asymmetrical thermal expansions in two adjacent beams lead to lateral deflection. The microactuator proposed here is fabricated by surface micromaching technique. A two-step releasing method is used here to free the microactuator successfully. The testing results show that the lateral driven unit can produce 10 μm lateral displacements at input voltages of 5 V, and bimorph structures at the same voltage can produce about 12 μm downward displacement. It is also found that this two dimensional motion can be controlled almost independently.

Development of the micro rotary fan

Abstract This paper reports on the design and experimental evaluation of novel MEMS based rotary fans. Both flip-chip and solder self-assembled designs are demonstrated — each utilizing a scratch drive actuator (SDA) rotary motor with forward and reverse control at speeds up to 180 rpm. The SDA motor is powered using a sinusoidal 30–150 V0-P ac signal at frequencies from 2–15 kHz. Resonant mode vibration at 3 kHz allowed the fan motor to be driven using ac signals of less than 30 V0-P. The fan blades are rotated to a specific angle-of-attack using gold coated polysilicon bimorph structures or solder assembly mechanisms. The advantages to each assembly option are discussed with solutions applicable to many electromechanically coupled micro systems. The fabrication and assembly techniques used to create the MEMS fans are well suited for mass production for commercial applications. A versatile flow visualization technique for MEMS based gas flow actuators is also demonstrated using laser illuminated smoke particles introduced into a macro scale chamber containing the fan.

Theory of magnetoelectric effects at microwave frequencies in a piezoelectric/magnetostrictive multilayer composite

A phenomenological theory is proposed to treat the magnetoelectric (ME) coupling at frequencies corresponding to ferromagnetic resonance in a multilayer composite consisting of alternate layers of piezoelectric and magnetostrictive phases. We discuss two models: (i) a simple two-layer (bimorph) structure and (ii) a generalized approach in which the multilayer structure is considered to be a homogeneous medium. Expressions for the stress induced shift $\ensuremath{\delta}H$ in the ferromagnetic resonance field due to an applied electric field E have been obtained for both cases. For a bimorph, $\ensuremath{\delta}H$ is directly proportional to the product of the applied electric field and the ME coupling constant. For a nickel ferrite--lead zirconate titanate (PZT) two layer structure, the theory predicts a factor of 5 stronger effect than in yttrium iron garnet-PZT. When the composite is considered to be a homogeneous medium, the corresponding shift $\ensuremath{\delta}H$ is given by $2{M}_{0}$ ${(B}_{33}\ensuremath{-}{B}_{31})$ E, where ${M}_{0}$ is the composite magnetization and B's are the ME coefficients. For this model, a method for the calculation of magnetoelectric coefficients from experimental data is presented.

PZT and PMN-PT Thin Film Cantilevers: Comparison between Monomorph and Bimorph Structures

AbstractPiezoelectric and electrostrictive materials are potential candidates for integrated micro systems. They can be used in cantilever laminated structures for different applications, e.g. active vibration control or agile transducers [1-3]. Due to the necessity of miniaturization of MEMS devices and the reduction of process costs and time, the use of chemical solution deposition (CSD) technique with microlithography and reactive ion etching (RIE) are essential.Within this work we used these techniques in combination with silicon bulk micro machining technique to fabricate piezoelectric Pb(Zr,Ti)O3 (PZT) and electrostrictive Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT) coated micro cantilevers with different lengths which can be used in micro switch or micro mirror applications. In general PMN shows no elastic hysteresis and a better aging behavior than PZT ceramics. Since the electrostrictive effect is smaller than the piezoelectric effect the tip deflection of PMN-PT coated beams is much lower. Cantilevers with two ceramic thin film layers and an internal electrode (bimorph) were designed and compared to such with single ceramic thin film layers (monomorph). For fabrication control and electrical characterization SEM, polarization hysteresis-, and CV-measurements were performed. Laser interferometry measurements were used to characterize the electromechanic performance of the ceramic thin films and cantilevers.

Two-dimensional modelling of laminated piezoelectric composites: analysis and numerical results

We propose a new approach to laminated piezoelectric plates based on a refinement of the electric potential as function of the thickness coordinate of the laminate and accounting for shear effects. Moreover, the variation of the electric potential as function of the thickness coordinate is modelled for each layer of the laminate. The equation for the laminated piezoelectric plate are then obtained by using a variational formulation involving mechanical surface loads or prescribed electric potential on the top and bottom faces of the plate. In addition to the equations for the generalized stress resultants (due to the shear effects), the equation of the electric charge conservation is also deduced for the 2D model. Particular attention is devoted to the single piezoelectric plate and bimorph structure and the through-thickness distribution of the displacements, electric potential as well as stresses are given for different kinds of electromechanical loads. The results thus obtained are compared to those provided by a finite element method performed for the full 3D model. A good agreement is observed for plates made of layers of PZT-4 piezoelectric material. The comparison ascertains the effectiveness of the present 2D approach to piezoelectric laminates.

Equivalent pyroelectric coefficient of a pyroelectric bimorph structure

A detailed formula for the equivalent pyroelectric coefficient of a bimorph structure acting as a pyroelectric detector was deduced. It is shown that electric fields occur in the structure when it is subjected to a temperature variation, due to the unequal charges generated by the two components. The field dependence of the ferroelectric polarization has to be considered in this case and the (∂P/∂E) derivative appears explicitly in the deduced formula. The effect is that the equivalent pyroelectric coefficient has different values for heating and cooling. This could lead to a redressing effect on the pyroelectric signal if the temperature difference varies periodically. The equivalent pyroelectric coefficient is, also, thickness dependent. This fact offers the possibility of designing structures with high values of pyroelectric coefficient compared with the values of the component phases.

Novel multibridge-structured piezoelectric microdevice for scanning force microscopy

In this article we report the structure and the microfabrication method of a novel micro-scanning force microscopy (SFM) device. It is a lead zirconate titanite (PZT) bimorph structure in the shape of a cantilever supported by bridges. Electric fields applied to the separated sections of the electrodes on the levers can induce lever deflection and actuate the tip in x, y, and z directions. The cantilever can vibrate and sense its own vibration amplitude to detect the surface topography in the cyclic contact SFM mode. In the fabrication process, the sol–gel method is modified for constructing high quality PZT films 3 μm thick. The single bridge device has shown microscopy sensitivity of 0.32 nA/nm in a vertical direction, with actuation sensitivities of 70–80 nm/V in a lateral direction. The multibridged structure has been proven to be effective in elevating the eigenfrequency, which is very important for improving the SPM data rate.

Distributed Sensing and Shape Control of Piezoelectric Bimorph Mirrors

Abstract As part of a collaborative effort between Sandia National Laboratories and the University of Kentucky to develop a deployable mirror for remote sensing applications, research in shape sensing and control algorithms that leverage the distributed nature of electron gun excitation for piezoelectric bimorph mirrors is summarized. A coarse shape sensing technique is developed that uses reflected light rays from the sample surface to provide discrete slope measurements. Estimates of surface profiles are obtained with a cubic spline curve fitting algorithm. Experiments on a PZT bimorph illustrate appropriate deformation trends as a function of excitation voltage. A parallel effort to effect desired shape changes through electron gun excitation is also summarized. A one dimensional model-based algorithm is developed to correct profile errors in bimorph beams. A more useful two dimensional algorithm is also developed that relies on measured voltage-curvature sensitivities to provide corrective excitation profiles for the top and bottom surfaces of bimorph plates. The two algorithms are illustrated using finite element models of PZT bimorph structures subjected to arbitrary disturbances. Corrective excitation profiles that yield desired parabolic forms are computed, and are shown to provide the necessary corrective action.

On droplet formation from capillary waves on a vibrating surface

The formation of sprays from a liquid film on a vibrating surface is used by ultrasonic atomizers for applications ranging from humidification to metal–powder manufacturing. The received opinion in the literature is that droplets are formed periodically from the apexes of an orderly pattern of standing capillary waves, with a wavelength that can be related to vibration frequency by stability analysis. It is described how this assumption may be incorrect in that, after droplet formation commences, the orderliness of the standing–wave pattern is lost due to one or more secondary instability phenomena. These phenomena, which lead to disorderliness, are investigated by using high–speed imaging techniques and a low–frequency vibrating film to model the high–frequency case, because of the difficulty of penetrating clouds of small droplets in the latter case. Different modes of droplet formation are identified and the flow patterns responsible for these modes are discussed. Physical mechanisms are proposed from which it is deduced that only a proportion of standing–wave crests can eject droplets, for a given wall–vibration period, and the identity of these ejecting waves should vary from period to period. The model thus developed demonstrates an apparently random ejection of droplets from one wave cell, even though the model itself is deterministic. The disorder of the capillary waves and the occurrence of several droplet–formation routes are sufficient to explain the range of droplet sizes that is produced by ultrasonic atomization.

光熱作用による微小はりの変位拡大設計と応用

The photothermal deflection of a microcantilever is much increased with a bimorph and an antireflection structure. The deflection is more than half wavelength by the temperature rise of 100°C which is expected by an optical absorption of over 98% for the antireflection coating of Au/Si3N4/Au fabricated on the bimorph structure. The designed cantilever monolithically integrated on gallium arsenide (GaAs, λ=0.83 μm) or indium phosphide (InP, λ=1.3μm) will be used for the external-cavity length change of a tunable laser diode.

A compact and quick-response dynamic focusing lens

A dynamic focusing lens with a completely new mechanism that can be miniaturized and allows for a quick-response has been developed. This lens is structured to directly transform the lens shape as a crystalline lens of the human eye. The lens is comprised of two thin glass diaphragms as a refracting surface, with a transparent working fluid sealed between them, and a new type of piezoelectric bimorph actuator. The displacement of the actuator is enlarged by the bimorph structure. The generated force is determined by the layer number of the bimorph cells. When the actuator is driven to push or pull the glass diaphragm at the actuator side, the other glass diaphragm is transformed into a lens shape (convex lens or concave lens) having various curvatures. The focal length of the lens is controlled by the applied voltage to the actuator. The dynamic focusing lens shows quick response up to 150 Hz. When the lens is operated over 60 Hz, human visual perception cannot recognize the change of the focal length, and we can observe many images having different focal lengths simultaneously.

Design and fabrication of piezoceramic bimorph vibration sensors

A bimorph-type piezoceramic vibration sensor is developed that can make up for the shortcomings of current mass loaded type sensors, such as high price, low sensitivity, and complex structures. For the design, in conjunction with piezoelectric constitutive equations, we derive full analytic response equations of the bimorph sensor to external forces. As the external forces, two representative cases are considered, step and sinusoidal excitation. Based on the results, actual sensors are fabricated and tested for verification of the theoretical results. Thermal stability of the bimorph structure is also checked through experiments. Further, a comparison of performance of the developed sensor is made with that of a commercial reference sensor so that quantitative evaluation of its sensitivity can be made. The sensor developed in this work shows excellent sensitivity and thermal stability in addition to the merits of simple structure and ease of fabrication. The design procedure with the sensor voltage response equations derived in this paper can be applied to develop piezoelectric bimorph sensors to meet any practical specifications.

Piezoelectric sensors for investigations of microstructures

In the paper the application of a piezoelectric bimorph as a sensor to investigate surfaces is considered. The voltage sensitivity and the stiffness of bimorphs with a central metal plate is analysed. This metal plate reinforces the bimorph structure. The derived formulae are used to calculate the parameters of the sensors, which consist of different combinations of metal and ceramic layers. The sensors have been calibrated using the quasistatic method. The experimental results are in good agreement with the calculations. Possible methods for increasing sensor sensitivity are also discussed.

Bimorph-Type Optical Actuator Using PLZT Elements Position Control of Optical Actuator by On-Off Control.

An optical actuator consisting of PLZT elements is a new type of actuator that makes active use of energy and information of light, and is inherently robust to electromagnetic noise. PLZT is an element that produces mechanical strain by the photostrictive effect when irradiated by ultraviolet light. Since displacement of the element is very small, we adopt a bimorph structure for the optical actuator to increase the displacement. In this paper, we propose an effective position control method for the bimorph-type optical actuator ; its validity is confirmed by experiments. A simple on-off control is insufficient to control the optical actuator because the mechanical shutters controlling light irradiation have a large time lag. A new control method, taking into account the dynamic responses of the optical actuator and the shutters, is introduced into the system, and improves the precision and response speed of the optical actuator.

A Study on Optical Actuator Using Bimetal Element. (1st Report. Analysis of Basic Characteristics and Linear Approximation Model).

A new type of optical actuator using bimetal element is presented, which consists of a bimorph structure of the high expansion coefficent material (Ni-Cr-Fe) and the low expansion coefficent material (36Ni-Fe). The fundamental characteristics of the bimetal were investigated experimentally and theoretically, which are of temperature and of displacement versus laser optical beam heating. The experimental setup consists of a laser diode as optical source, a thermocouple and a laser displacement sensor to measure temperature and displacement. The mathematical model of the actuator was also derived. In order to identify some parameters in the system, the finite element method (FEM) was adopted, which analyzes heat trasfer and thermal stress in the actuator. Comparing with the experimental results under various conditions, the simulation by FEM was carried out, and the good agreement with experimental results was obtained. Fainally, the application of linear approximate model with 1st-order lag factor was examined.

Temperature dependence of the pyroelectric voltage in a 2–2 connectivity pyroelectric bimorph

Parallel and series pyroelectric bimorph structures, with 2–2 connectivity, are theoretically analysed to obtain the electric fields inside the two component phases. The proposed model takes into consideration the possibility of an electrical interaction between the two phases. It is demonstrated that the value of the internal electric field, due to the pyroelectric charge generated during heating of the bimorph structure, is considerably different than the case where each of the two phases is heated separately. It is shown that the value and the orientation of the electric fields inside the two phases of the bimorph depend on the value of the pyroelectric coefficients and dielectric constants of the two phases. The most interesting result is obtained in the case of the series bimorph, where the orientation of the electric field inside the phase with a lower pyroelectric coefficent is opposite to the orientation of spontaneous polarisation of this phase.

New Piezoelectric Bimorph Structure Actuators with High Performances

We have developed three types of piezoelectric bimorph structure actuators. The first actuator has a displacement of over 3 mm at 100 Vpk and high reliability by resonance effect of the displacement magnifying part. The second one has a displacement of over 1 mm at 100 Vpk and high stability for change in driving frequency by combined two resonances. The third one has a linearity of displacement until 85% of fracture point and low temperature characteristics by a direct bonding technique that bonds piezoelectric single crystals without using adhesive.