Electrothermal Microactuators Research Articles

Position Feedback-Control of an Electrothermal Microactuator Using Resistivity Self-Sensing Technique.

The self-sensing technology of microactuators utilizes a smart material to concurrently actuate and sense in a closed-loop control system. This work aimed to develop a position feedback-control system of nickel electrothermal microactuators using a resistivity self-sensing technique. The system utilizes the change in heating/sensing elements' resistance, due to the Joule heat, as the control parameter. Using this technique, the heating/sensing elements would concurrently sense and actuate in a closed loop control making the structures of microactuators simple. From a series of experiments, the proposed self-sensing feedback control system was successfully demonstrated. The tip's displacement error was smaller than 3 µm out of the displacement span of 60 µm. In addition, the system was less sensitive to the abrupt temperature change in surroundings as it was able to displace the microactuator's tip back to the desired position within 5 s, which was much faster than a feed-forward control system.

Improving displacement of silicon V-shaped electrothermal microactuator using platinum sputter deposition process

PurposeThis paper aims to propose a method to reduce the resistance of silicon-based V-shaped electrothermal microactuator (VEM) by applying a surface sputtering process.Design/methodology/approachFour VEM’s samples have been fabricated using traditional silicon on insulator (SOI)-Micro-electro-mechanical System (MEMS) technology, three of them are coated with a thin layer of platinum on the top surface by sputtering technique with different sputtered times and the other is original. The displacements of the VEM are calculated and simulated to evaluate the advantages of sputtering method.FindingsThe measured results show that the average resistance of the sputtered structures is approximately 1.16, 1.55 and 2.4 times lower than the non-sputtering sample corresponding to the sputtering time of 1.5, 3 and 6 min. Simulation results confirmed that the maximum displacement of the sputtered VEM is almost 1.45 times larger than non-sputtering one in the range of voltage from 8 to 20 V. The experimental displacements are also measured to validate the better performance of the sputtered samples.Originality/valueThe experimental results demonstrated the better displacement of the VEM structure after using the platinum sputtering process. The improvement can be considered and applied for enhancing displacement as well as decreasing the driving voltage of the other electrothermal microactuators like U- or Z-shaped structures while combining with the low-cost SOI-MEMS micromachining technology.

Modeling of multiphysics coupling and performance analysis of Z-shaped electrothermal microactuator

Electrothermal microactuators have a very promising future in micro-electro-mechanical systems applications since they can generate large displacement and force with low actuating voltages and small device areas. In this paper, a temperature distribution and unload displacement model of a Z-shaped electrothermal microactuator is presented. In order to prove the accuracy of the model, finite element analysis (FEA) and experimental results are provided to make comparison. The results of temperature profile and unload displacement output, which are from the model calculation, FEA and experimental test, agree well with each other. It gives an indirect proof that the model is correct and FEA calculation is practicable. It can be shown that the shape of the actuator has no effect on the maximum temperature, and the unload displacement and output force depend on the beam length and inclined angle of the actuator.

Effects of Sidewall Inclination on Performance of Electrothermal Micro-Actuator

As an important part of Micro-Electro-Mechanical systems (MEMS), micro-actuators have a direct impact on the performance of MEMS devices. This paper presents the effects of sidewall inclination of deep reactive ion etching (DRIE) on the performance of U-shaped electrothermal micro-actuators. The electrothermal micro-actuator models with sidewall inclination angles from -5° to 5° are simulated through finite element method (FEM) by ANSYS to study the influences on the output displacement and the highest node temperature. The simulation results show that electrothermal micro-actuator with larger sidewall inclination angle has more displacement deviation. In addition, larger voltage amplifies the deviation of displacement. The highest node temperature decreases with the increase of the sidewall inclination, and the deviation is small.

An Alternative Approach to Investigate V-Shaped Electrothermal Microactuators in Vacuum

In this work, we use a simplified version of Young’s solution for the steady-state Joule-heating, that uses temperature dependent thermal and electrical conductivities, to find the temperature and displacement behavior of a V-shaped electrothermal microactuator (ETMA) device. In order to test and validate our approach we performed FEM simulations and actually built an ETMA device by microfabrication. The experimental device displacement was measured in vacuum, with a scanning electron microscope. Our numerical results agree quite well with the FEM simulation and experimental results up to a displacement of (0.8 ± 0.2) $\mu \text{m}$ and applied current of 30 mA. Above 35 mA, an abrupt variation of the resistivity is observed followed by surface degradation at 50 mA and device melting at 52 mA. The validity of our approach is discussed of the device geometry and material parameters. [2019-0208]

Engineering microscale systems for fully autonomous intracellular neural interfaces

Conventional electrodes and associated positioning systems for intracellular recording from single neurons in vitro and in vivo are large and bulky, which has largely limited their scalability. Further, acquiring successful intracellular recordings is very tedious, requiring a high degree of skill not readily achieved in a typical laboratory. We report here a robotic, MEMS-based intracellular recording system to overcome the above limitations associated with form factor, scalability, and highly skilled and tedious manual operations required for intracellular recordings. This system combines three distinct technologies: (1) novel microscale, glass–polysilicon penetrating electrode for intracellular recording; (2) electrothermal microactuators for precise microscale movement of each electrode; and (3) closed-loop control algorithm for autonomous positioning of electrode inside single neurons. Here we demonstrate the novel, fully integrated system of glass–polysilicon microelectrode, microscale actuators, and controller for autonomous intracellular recordings from single neurons in the abdominal ganglion of Aplysia californica (n = 5 cells). Consistent resting potentials (<−35 mV) and action potentials (>60 mV) were recorded after each successful penetration attempt with the controller and microactuated glass–polysilicon microelectrodes. The success rate of penetration and quality of intracellular recordings achieved using electrothermal microactuators were comparable to that of conventional positioning systems. Preliminary data from in vivo experiments in anesthetized rats show successful intracellular recordings. The MEMS-based system offers significant advantages: (1) reduction in overall size for potential use in behaving animals, (2) scalable approach to potentially realize multi-channel recordings, and (3) a viable method to fully automate measurement of intracellular recordings. This system will be evaluated in vivo in future rodent studies.

Optimal Design of Electrothermal Microactuators for Many Criteria by Means of an Immune Game Theory Multiobjective Algorithm

The paper presents the application of the IMGAMO (immune game theory multiobective algorithm) in the optimal design of electrothermal microactuators. Several numerical tests on the mathematical benchmark test functions were performed, showing the superiority of the IMGAMO, when a large number of criteria are considered, in comparison to other multiobjective optimizers. A parametric numerical model of an electrothermal microactuaror was developed and verified. Six functionals, which depend on various thermal and mechanical quantities of the microactuator, were proposed, formulated and numerically implemented. These functionals represent real requirements asked of microactuators. The boundary-value problem of an electro-thermo-mechanical field was solved multiple times during the course of optimization by way of the finite element method (FEM). A numerical example of multiobjective optimization of chevron-type electrothermal actuators is included in the paper. Representation of the multi-dimensional Pareto fronts by means of scatter plot matrices, aided by self-organizing maps (SOMs), is presented. The novel method of selecting interesting, compromise-solutions is proposed and described.

Izdelava elektrotermičnih aktuatorjev na osnovi mikro-elektronsko-mehanskih sistemov, izdelanih z dodajnimi tehnologijami

Izdelava elektrotermičnih aktuatorjev na osnovi mikro-elektronsko-mehanskih sistemov, izdelanih z dodajnimi tehnologijami

Review of Electrothermal Actuators and Applications

This paper presents a review of electrothermal micro-actuators and applications. Electrothermal micro-actuators have been a significant research interest over the last two decades, and many different designs and applications have been investigated. The electrothermal actuation method offers several advantages when compared with the other types of actuation approaches based on electrostatic and piezoelectric principles. The electrothermal method offers flexibility in the choice of materials, low-cost fabrication, and large displacement capabilities. The three main configurations of electrothermal actuators are discussed: hot-and-cold-arm, chevron, and bimorph types as well as a few other unconventional actuation approaches. Within each type, trends are outlined from the basic concept and design modifications to applications which have been investigated in order to enhance the performance or to overcome the limitations of the previous designs. It provides a grasp of the actuation methodology, design, and fabrication, and the related performance and applications in cell manipulation, micro assembly, and mechanical testing of nanomaterials, Radio Frequency (RF) switches, and optical Micro-Electro-Mechanical Systems (MEMS).

Optimized V-Shaped Beam Micro-Electrothermal Actuator Using Particle Swarm Optimization (PSO) Technique

Background:Electrothermal microactuators are very promising for wide range of Microelectromechanical Systems (MEMS) applications due to the low voltage requirement and large force produced.Method:A new optimized V-beam electrothermal micro actuator was implemented in variable optical attenuator. In this work, Particle Swarm Optimization (PSO) technique is proposed to design the Vshaped beam.Result:The approach has successfully improved both angular displacement &amp; output force of the microactuator. Entropy generation rate was used as optimization criteria.

Modeling of multiphysics coupling and performance analysis of V-shaped electrothermal microactuator

Electrothermal microactuators have a very promising future in MEMS applications since they can generate large displacement and force with low actuating voltages and small device areas. In this paper, a temperature distribution and unload displacement model of a V-shaped electrothermal microactuator are presented. In order to prove the accuracy of the model, finite element analysis (FEA) and experimental results are provided for comparison. The results of temperature profile and unload displacement output, which are from the model calculation, FEA and experimental test, agree well with each other. It gives an indirect proof that the model is correct and FEA calculation is practicable. It can be shown that the shape of the actuator has no effect on the maximum temperature, and the unload displacement and output force depend on the beam length and inclined angle of the actuator.

Theoretical modal analysis and parameter study of Z-shaped electrothermal microactuators

This paper presents a comprehensive modal analysis of Z-shaped beam electrothermal microactuators for the first time. Both longitudinal and lateral vibrations are taken into account to obtain the vibration equations of the unique geometric feature: a Z-shaped beam with a shuttle in the middle. The natural frequencies and the associated mode shapes of the Z-shaped beams are calculated based on the vibration equations subjected to both boundary and continuity conditions. Finite element simulations are performed using ANSYS software to verify the analytically calculated natural frequencies and mode shapes of the Z-shaped beams. Based on the modal analysis, this paper also investigates the relationship between the natural frequencies and volume scale of the Z-shaped beam electrothermal microactuators. In addition, comprehensive parameter analysis is conducted to provide insights and guidance on designing and optimization of the Z-shaped beam electrothermal microactuators.

Vibration Modes and Parameter Analysis of V‐Shaped Electrothermal Microactuators

Comprehensive analysis on the modal characteristics of V‐shaped electrothermal microactuators is presented in this paper for the first time. Considering the unique geometric characteristics of the V‐shaped beam, that is, two inclined beams supporting a movable shuttle, both the lateral and longitudinal deflections are taken into account in the modal analysis. Boundary and continuity conditions are employed to obtain the frequency equation. Natural frequencies are then obtained by solving the frequency equation. Mode shapes corresponding to their natural frequencies are also calculated analytically. The theoretical modal analysis is verified with the finite element analysis using ANSYS software. Based on the model analysis, this paper further investigates the relationship between natural frequencies and the volume scaling of the V‐shaped beam. Finally, comprehensive parametric studies in terms of material properties and structural dimensions are conducted to provide insights and guidance in designing the V‐shaped beam electrothermal microactuators.

MEMS measurements of single cell stiffness decay due to cyclic mechanical loading.

The goal of this study was to measure the mechanical stiffness of individual cells and to observe changes due to the application of repeated cell mechanical loads. 28 single baker's yeast cells (Saccharomyces cerevisiae) were fatigue tested and had their stiffness measured during repetitive loading cycles performed by a MEMS squeezer in aqueous media. Electrothermal micro-actuators compressed individual cells against a reference back spring; cell and spring motions were measured using a FFT image analysis technique with ~10nm resolution. Cell stiffness was calculated based on measurements of cell elongation vs. applied force which resulted in stiffness values in the 2-10N/m range. The effect of increased force was studied for cells mechanically cycled 37 times. Cell stiffness decreased as the force and the cycle number increased. After 37 loading cycles (~4min), forces of 0.24, 0.29, 0.31, and 0.33 μN caused stiffness drops of 5%, 13%, 31% and 41% respectively. Cells force was then set to 0.29 μN and cells were tested over longer runs of 118 and 268cycles. After 118cycles (~12min) cells experienced an average stiffness drop of 68%. After 268cycles (~25min) cells had a stiffness drop of 77%, and appeared to reach a stiffness plateau of 20-25% of the initial stiffness after approximately 200cycles.

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.

Dynamic modelling and analysis of V- and Z-shaped electrothermal microactuators

This paper presents a dynamic model and design analysis for V- and Z-shaped electrothermal microactuators operating in vacuum and in air conditions. The model is established with a coupled-field analysis combining the electrothermal and thermomechanical analyses for both heating and cooling processes. The electrothermal behaviors that dominated the overall dynamics are described by hybrid partial differential equations for three serially connected segments. The equations are solved subjected to the boundary, continuity, and initial conditions, and a unique method based on Fourier series is utilized to solve the temperature increase in each arms. The thermomechanical responses, i.e., the displacement and force, of the actuator are then calculated under the assumptions of quasi-static inertia. The analytical evaluations of the temperature and displacement are compared with the ones from finite element analysis via ANSYS software. A good agreement is found between analytical and simulation results. By virtual of the finite-element simulation, local high-frequency low-amplitude vibrations are demonstrated along the overall dynamic response for both V- and Z-shaped actuators with specific dimensions. Moreover, distinct dynamic behaviors between U- and V- and Z-shaped beams are observed and discussed using a proposed comparison benchmark. Finally, based on the dynamic model, the influences of structural as well as material parameters on the dynamic behaviors are analyzed to pave the way for improving the design and optimizing the dimensions of V- and Z-shaped electrothermal microactuators.

Thermal behavior modeling and characteristics analysis of electrothermal microactuators

Electrothermal microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators, but these performances come at the expense of large input energy and relatively low frequencies because of the time necessary to reach thermal equilibrium. These characteristics provide motivation for improving thermal actuator designs that are more energy efficient and better suited for high-frequency applications. To this end, models describing the combined electrothermal and thermomechanical behavior of thermal actuators are developed in this thesis. The temperature distribution of the actuator is analyzed and the influence of the actuator’s geometrical parameters on its force and displacement is studied. Steady-state and transient thermal responses of the actuator operating in air and a vacuum are investigated by creating finite-difference model with temperature-dependent parameters, this model allows temperatures throughout the actuator to be simulated as a function of time. Results demonstrate that the efficiency of the actuator can be improved significantly by operating in a vacuum environment and providing short-duration, high-current pulse inputs. A set of parametric studies and design changes are evaluated through thermomechanical models, strategies gained from modeling analysis result in significant improvements in operational efficiency of the thermal actuator.

Electrothermomechanical modeling of out-of-plane deformation in single-stepped beams actuated by resistive heating

An analytical model for the electrothermomechanical analysis of out-of-plane deformation in resistively heated single-stepped beams is presented. The model takes into account the conductive heat transfer from the beam to the substrate in which it is anchored. It also considers the temperature dependence of the beam material properties and accounts for the locally enhanced resistive heating effect around the release holes in the beam to predict temperature distribution along the beam. Energy method and Euler–Bernoulli beam theory are used for the prediction of out-of-plane deformation and stress distribution of the beam, as well as the out-of-plane rotation at the middle of the beam. The model considers the nonuniformity of the air gap between the beam and the substrate and captures the resultant asymmetric temperature distribution along the beam. The out-of-plane rotations in the middle of the single-stepped beam predicted by the analytical model and measured experimentally agree within 10%. The analytical model is then used to predict the maximum actuation current, which results in high temperature plastic deformation and agrees with the experiments within 5%. The proposed analytical model provides a good approach for systematic design and analysis of out-of-plane electrothermal microactuators based on single-stepped beam design.