Electrothermal Microactuator Research Articles

Characterization and optimization of an electro-thermal microactuator for precise track positioning

ABSTRACTThis paper presents a MEMS mirror actuated by four suspended electro-thermal bimorphs. The dimension of the mirror platform is 250 µm × 250 µm. The MEMS mirror design is created based on process modeling following strict fabrication constraints. Transient and dynamic characteristics of the micromirror device are analyzed using coupled electro-thermal-mechanical finite element models and schematic behavior models, respectively. The design is optimized using experimental design and response surface methodology to achieve large actuation displacement and small lateral shift. The micromirror device is shown to have a uniform mirror platform deflection, a large resonant frequency adequate to support the high servo bandwidth control, as well as an excellent linear relation between the micromirror deflection and the input electric power. The proposed electro-thermal MEMS mirror is capable of generating a mirror displacement of 8.25 µm under a 3 V pulse voltage input, and can potentially be used as a fine...

Fabrication and investigation of low actuation voltage curved beam bistable MEMS switch

Fabrication and characterization of a novel bistable MEMS (MicroElectroMechanical Systems)-based switch is reported in this paper. The bistable switch is fabricated on SOI wafer with 10 µm thick device Si layer using Silicon-On-Insulator Multi User MEMS Process with three masks. The proposed device is comprised of a centrally clamped parallel curved beams (switching element) and a pair of electrothermal V-beam microactuators (actuating element). The bistability is achieved through the buckling of centrally clamped parallel curved beams and the critical buckling load is provided by the electro-thermal expansion of the V-beam microactuators. Hinges, latches, membranes are not used in the proposed design and thus the fabrication complexity is reduced to a greater extent. A maximum displacement of 20.7 µm is achieved at 14 V DC supply for the V-beam microactuator and this thermal expansion of the V-beam microactuator acted as the critical buckling load for the centrally clamped parallel curved beam. Electrical and mechanical characterization of switch is performed and after the analysis, it is verified that the nonlinear property (elasticity) of silicon material is poor and that is the reason for comparatively higher actuation voltage to simulation results. A novel optimized redesign for the electrothermal V-beam microactuator based on POLYMUMPs process is proposed in order to overcome the uncertainties endured.

Closed-form modelling and design analysis of V- and Z-shaped electrothermal microactuators

This paper presents the modelling and design analysis of V- and Z-shaped electrothermal microactuators. First, a comprehensive but concise closed-form multiphysical analytical model is developed to predict the output displacement and force of both V- and Z-shaped electrothermal microactuators operating either in vacuum or in air conditions. The analytical model is verified by finite element analysis and experimental testing. Then, a novel comparison benchmark is proposed for the design and analysis of the V- and Z-shaped microactuators. With the multiphysical model and comparison benchmark, comprehensive performance comparison and analysis of the V- and Z-shaped beams are performed with the aim of providing insight and guidance on selection and design of the two typical types of electrothermal microactuators. Finally, the application of the comparison model into the design analysis is demonstrated using a design example of an electrothermal microactuator, and the detailed investigation is conducted to examine the effects of the material properties and structural parameters on the microactuator outputs.

Material and performance characterization of Z-shaped nickel electrothermal micro-actuators

The ultimate goal of this work was to develop a novel electrothermal micro-actuator, with ease of fabrication and low-cost, using a nickel electroplating technique. In this work, the properties of the nickel films deposited at an electroplating current density of 7.0mA/cm2 using two electrolytes, i.e. nickel sulfate and nickel sulfamate solutions, were compared. From the material testing, the nickel sulfamate solution provided a nickel film with a rougher but softer surface; therefore, the solution was chosen in a process to fabricate the micro-actuators. The micro-actuators with a Z-shaped driving mechanism were designed with a variation in the gap between small and large arms. Within the range of experimental conditions, i.e. applying DC current of 3–5A for 30s, average temperature of the driving mechanism was less than 100°C, at which the micro-actuator with the gap of 200μm provided the largest displacement of around 250±32μm and the magnitude of the force higher than 4.5±0.8mN. All micro-actuators could appropriately respond to a driving frequency up to 1Hz. In addition, no significant decrement of the magnitude of the exerting force was observed within 21,600 actuating cycles. Lastly, the micro-gripper was fabricated and tested. The successful gripping of an asymmetrical sesame seed was demonstrated.

Electrothermal MEMS parallel plate rotation for single-imager stereoscopic endoscopes.

This work reports electrothermal MEMS parallel plate-rotation (PPR) for a single-imager based stereoscopic endoscope. A thin optical plate was directly connected to an electrothermal MEMS microactuator with bimorph structures of thin silicon and aluminum layers. The fabricated MEMS PPR device precisely rotates an transparent optical plate up to 37° prior to an endoscopic camera and creates the binocular disparities, comparable to those from binocular cameras with a baseline distance over 100 μm. The anaglyph 3D images and disparity maps were successfully achieved by extracting the local binocular disparities from two optical images captured at the relative positions. The physical volume of MEMS PPR is well fit in 3.4 mm x 3.3 mm x 1 mm. This method provides a new direction for compact stereoscopic 3D endoscopic imaging systems.

Electrothermal MEMS fiber scanner for optical endomicroscopy.

We report a novel MEMS fiber scanner with an electrothermal silicon microactuator and a directly mounted optical fiber. The microactuator comprises double hot arm and cold arm structures with a linking bridge and an optical fiber is aligned along a silicon fiber groove. The unique feature induces separation of resonant scanning frequencies of a single optical fiber in lateral and vertical directions, which realizes Lissajous scanning during the resonant motion. The footprint dimension of microactuator is 1.28 x 7 x 0.44 mm3. The resonant scanning frequencies of a 20 mm long optical fiber are 239.4 Hz and 218.4 Hz in lateral and vertical directions, respectively. The full scanned area indicates 451 μm x 558 μm under a 16 Vpp pulse train. This novel laser scanner can provide many opportunities for laser scanning endomicroscopic applications.

Design and simulation of an optimized electrothermal microactuator with Z-shaped beams

The displacement of the central shuttle of a Z-shape chevron actuator can be calculated using a developed approach from other authors. Who demonstrated that the actuators with this geometry offer a larger displacement compared with V-shape actuators. Z-shape offers a larger stiffness and output force for the case of only one arm. This paper is focused on the optimization of the Z-shaped beams of a chevron actuator of eight beams, which seeks to increase the previously described response. The structure is designed in parametric solid modeling 3D software Autodesk Inventor, and simulated by finite element method in Ansys 15.0. These simulations were implemented considering several modifications on the length of the Z-shaped beams in order to choose the most appropriate length. The electric potential applied in all cases was from 0.2 V up to 5 V. The Z-shape length of the arms for the case of the optimized Z-shape actuator increases the shuttle’s displacement in approximately 50% compared to V-shape actuator, and 38% compare to the original Z-shape. Analytical adjusted approach is extremely matched with the simulations results. Length of the Z-shape beam is the determinant factor of the displacement. The low stiffness of the optimized Z-shape actuator (89% lower than the original V-shape and 58% compared to Z-shape) can allow its use as load sensor.

Robust design optimization of electro-thermal microactuator using probabilistic methods

Micromachining of microelectromechanical systems which is similar to other fabrication processes has inherent variation that leads to uncertain dimensional and material properties. Methods for optimization under uncertainty analysis can be used to reduce microdevice sensitivity to these uncertainties in order to create a more robust design, thereby increasing reliability and yield. In this paper, approaches for uncertainty and sensitivity analysis, and robust optimization of an electro-thermal microactuator are applied to take into account the influence of dimensional and material property uncertainties on microactuator tip deflection. These uncertainties include variation of thickness, length and width of cold and hot arms, gap, Young modulus and thermal expansion coefficient. A simple and efficient uncertainty analysis method is performed by creating second-order metamodel through Box-Behnken design and Monte Carlo simulation. Also, the influence of uncertainties has been examined using direct Monte Carlo Simulation method. The results show that the standard deviations of tip deflection generated by these uncertainty analysis methods are very close to each other. Simulation results of tip deflection have been validated by a comparison with experimental results in literature. The analysis is performed at multiple input voltages to estimate uncertainty bands around the deflection curve. Experimental data fall within 95 % confidence boundary obtained by simulation results. Also, the sensitivity analysis results demonstrate that microactuator performance has been affected more by thermal expansion coefficient and microactuator gap uncertainties. Finally, approaches for robust optimization to achieve the optimal designs for microactuator are used. The proposed robust microactuators are less sensitive to uncertainties. For this goal, two methods including Genetic Algorithm and Non-dominated Sorting Genetic Algorithm are employed to find the robust designs for microactuator.

Sequential Design Method for Geometric Optimization of an Electrothermal Microactuator Based on Dynamic Kriging Models

This paper proposes a sequential optimization methodology for designing an electrothermal polysilicon actuator in the presence of a fabrication tolerance. In the proposed method, a deterministic optimum is first sought from an initial design, and then a reliability-based robust design is obtained launching at the deterministic point. This serial design strategy can enhance numerical efficiency through minimizing the use of computationally expensive reliability-based design optimization. To effectively perform the robust design of very complex multiphysics problems, elaborate surrogate models based on the local window concept are exploited comprehensively. The proposed method is applied to an electrothermal polysilicon actuator with seven design random variables, and then three different nominal designs are examined in terms of maximum deflection, consumed power, and confidence level.

The Model and Application of Bi-directional Electrothermal Microactuator

As the power producer, the microactuator is an important part of Micro Electro Mechanical Systems, which is used for the energy conversion, motion and force producion. The function and performance of MEMS are deeply affected by the micro-actuator's output ability of displacement and force. In this paper, a bi-directional electrothermal microactuator which can generate displacements in both x and y direction is designed. Static theoretical model of bi-directional actuator is established via electro-thermal analysis and thermal-structural analysis. The static theoretical model is preliminary validated by comparing the theoretical values with simulation and experimental results. We also study the application of micro transmission mechanism based on bi-directional electrothermal microactuator.

Improved design of polymeric composite electrothermal micro-actuator for high track density hard disk drives

Recently, we have developed a polymeric composite electrothermal micro-actuator for dual-stage applications in hard disk drives (HDDs). The polymer composite was demonstrated with a larger thermal expansion as compared to silicon. Yet, the previous design of polymeric composite thermal actuator was stiff, having a high mechanical resonant frequency at 33 kHz and a moderate static displacement stroke of 50 nm at 4 V. An even larger stroke above 100 nm is generally required to meet the need of HDD dual-stage systems. To meet the requirement for a large stroke, we presented an improved design of polymeric composite electrothermal micro-actuator by increasing flexibility of the composite thermal benders. As compared to the previous design, the new design doubled the displacement stroke up to 106 nm at 4 V while it maintained a high mechanical resonant frequency of 31 kHz, slightly below that of the previous design. In addition, a finite element analysis showed that electrothermal activation of the micro-actuator is rather localized and it causes only a small temperature rise of the neighbouring parts of head gimbal assembly. These good performances suggested that this improved design of thermal micro-actuator is promising for high bandwidth dual-stage positioning systems in future high track density HDDs.

Constrained Structural Optimization of Electro-Thermal Microactuator Using Double Chromosome Genetic Evolution

This paper presents two design optimization models for U-type electro-thermal microactuator. The result shows that the unequal arm model has better performance than the equal arm model. The models were solved by finite element analysis that are verified and comparison to publish paper and then are utilized in optimum design. The feature of presenting work contains temperature constraints to avoid the harm of operating object and decrease stress concentration on flexure. For handling design constraints, a method named double chromosome genetic evolution (DCGE) is developed in gene based algorithm. The idea of the presenting constrained strategy was inspired from the gene evolved by double helix chromosome of expressing certain traits. The constrained evolutionary algorithm proposed in this work is efficient and reliable. It can be integrated into a broad field of engineering optimization.

Design, Modeling and Optimization of a Novel Two DOF Polymeric Electro-Thermal Micro-Actuator

In this paper, design, simulation and optimization of a novel electrothermally-activated polymeric microactuator capable of generating combination of bidirectional lateral and rotational motions are presented. The composite structure of this actuator is consisted of a symmetric meandered shape silicon skeleton, a SU8 thermal expandable polymer and a thin film chrome layer heater. This actuator is controlled by applying appropriate voltages on its four terminals. With the purpose of dimension optimization, a numerical parametric study is executed. The modeled actuator which is 1560 μm long, 156 μm wide and 30 μm thick, demonstrates a remarkable lateral displacement of 23 μm at power consumption of 38 mW and a considerable rotation of about 7.5° at the same power consumption but with excitation of different terminals.

Precisely rectilinear electro-thermal microactuator using a high-aspect ratio microstructured Si/SU-8 composite

This paper presents a Si/SU-8 composite electro-thermal microactuator that can generate a precisely rectilinear in-plane stroke. The microactuator consists of a pair of electro-thermally activated composite bimorphs which are joined at their tips through a central Si beam. When activated, the central beam deflects and outputs an in-plane rectilinear stroke at its center. The central stroke is precisely rectilinear along the plane of symmetry due to very high stiffness in the orthogonal directions to the stroke. This composite thermal microactuator produces a much larger rectilinear stroke and blocked force per unit temperature rise compared to an all-silicon one. At a temperature rise below 87 °C (driven below 8.0 V), the stroke increases linearly with the temperature rise up to 8.0 µm. Analytical and finite element models are developed for this range of actuation. Beyond an 87 °C temperature rise, the stroke was further enhanced by Poisson's ratio effect on SU-8 which increases the effective coefficient of thermal expansion of the composite. The microactuator could produce a maximum rectilinear stroke of 42 µm and a maximum estimated blocked force of 60 mN at a driving voltage of 14.5 V which causes a SU-8 average temperature rise of 266 °C.

An electro-thermal micro-actuator based on polymer composite for application to dual-stage positioning systems of hard disk drives

This paper presents an electro-thermal micro-actuator based on polymer composite for dual-stage head positioning systems in hard disk drives (HDDs). This micro-actuator has a pair of benders, which are made of silicon–polymer composite. When electro-thermally activated by resistive heating, the composite expands and consequently the benders produce a lateral bending motion to drive a femto slider, which carries a magnetic read/write head. The micro-actuator has been fabricated by deep silicon etching and polymer patterning. Experiment shows that the micro-actuator can drive up to 35nm peak-to-peak displacement when it is activated by a 3.25V half-sine input voltage at 500Hz under a moderate temperature rise. The first in-plane mechanical resonant frequency is measured to occur at 36.8kHz. Analytical and finite element models were developed to simulate the micro-actuator performance. It is noted that the simulation results agree well with the experimental measurement. With good performance, the electro-thermal micro-actuator are useful for high bandwidth dual-stage positioning systems in future high-density HDDs.

Modeling and characterization of a SOIMUMP’s hybrid electro thermal actuator

A hybrid electro thermal microactuator is designed and its analytical model is developed. An existing hot and cold beam actuator is added with a gold layer of 0.5 μm thickness, so that the performance of the hybrid electro thermal actuator is improved. The analytical model is validated by comparing the results with 3D finite element model. Further the device is fabricated using SOIMUMPs process and characterized to validate the proposed analytical model. The shape of cold beam is also modified such that it improves the displacement. The results obtained from analytical and experimental models are in good agreement.

Improved Designs for an Electrothermal In-Plane Microactuator

Reported presently are two design approaches to improve the performance of an electrothermal in-plane microactuator with “chevron” beams. One incorporates beams with uniform cross sections but nonuniform lengths or tilt angles to accommodate the thermally induced expansion of the “shuttle”; the other incorporates beams with nonuniform cross sections to widen the high-temperature “expansion” zones. It is derived analytically, verified using finite-element simulations, and tested by microfabricating actuators occupying a constrained device area that the incorporation of one or the other proposed features leads to an improved performance figure-of-merit, defined to be the product of the actuation displacement and force. An increase in the figure-of-merit by up to 65% per beam has been measured.

Vibration Characteristic Analysis of V-Shaped Electrothermal Microactuator

This paper is focused on the finite element analysis (FEA) and theoretical calculation of vibration characterization of V-shaped electrothermal microactuator. A vibration mechanical model about V-shaped electrothermal microactuator is presented. By having a comparison between FEA and theoretical calculation about natural frequencies of V-shaped electrothermal microactuator, the maximum error is within 0.19 %. This paper also analyzes the influences of microactuator geometric parameters on natural frequency. The length and thickness have larger effect on the natural frequency of the actuator, while the angle and width have less effect on the natural frequency.

具有三层结构的SU-8胶V形微电热驱动器

To eliminate the out-of plane actuation of a SU-8 electrothermal micro-actuator,a novel SU-8 chevron electrothermal micro-actuator with a copper/SU-8/copper symmetrical structure was proposed.The mechanical model of the micro-actuator which contains the stiffness of a driven structure was established by using the stiffness matrix method.The geometric parameters of the micro-actuator were designed for a microgripper by using the established model.The designed micro-actuator was simulated by Ansys software and the simulation results verified the reasonability of the mechanical model.Then,the micro-actuator and the microgripper were fabricated by a simple process followed with a performance test.The test results show that when the temperature of the micro-actuator only increases 32.93℃ in a driving voltage of 150 mV,the output displacement is 2.5 μm and jaw gap change is 126 μm.During the operation processes,the out-of plane displacement of the tip is always lower than 500 nm.Finally,the micro-manipulation sequence of a SU-8 micro-part with a size of 1.4 mm×135 μm×50 μm was carried out to verify the driving ability of the micro-actuator.

An electrothermal microactuator with Z-shaped beams

This paper introduces a Z-shaped thermal microactuator for in-plane motion, which could be complementary to the well-established comb drives and V-shaped thermal actuators. The Z-shaped actuators share many features in common with the V-shaped ones, but offer certain advantages such as smaller feature size and larger displacement. They also offer a large range of stiffness and output force that is between those of the V-shaped actuators and comb drives. In particular, they can achieve smaller stiffness without buckling, which renders them as simultaneous load sensors. The Z-shaped actuator was modeled analytically and verified by multiphysics finite element analysis. Among all the design parameters, the beam width and the length of the central beam were identified as the major ones in tuning the device displacement, stiffness, stability and output force. Experimental measurements of three arrays of Z-shaped thermal actuators agreed well with the finite element analysis. In addition, the quasi-static and dynamic performances of individual Z-shaped thermal actuators were measured. The average temperature in the device structure was estimated from the electric resistivity at each actuation voltage. The bandwidth of the Z-shaped thermal actuators can be increased for devices with a substrate underneath.