Electrothermal Actuators Research Articles

Design and characterization of solid articulated four axes microrobot for microfactory applications

In this paper, we present the design and experimental evaluation of a 3-dimensional microrobot called Solid Articulated Four Axes Microrobot (sAFAM). The sAFAM is fabricated using Microelectromechanical System (MEMS) technology, then assembled to achieve out-of-plane motion and perform micro and nano manipulation tasks relevant to future microfactories such as pick and place and applying controlled forces onto the environment. The paper discusses the design, fabrication and assembly processes for constructing sAFAM. Four in-plane electrothermal actuators drive the end-effector through a complaint mechanical coupling. The microrobot structure was simulated by finite element analysis (FEA), predicting a 13 μm × 47 μm × 115 μm workspace and verifying appropriate concentration of stresses during actuation. The resolution, repeatability, and workspace of the microrobot were then measured experimentally via optical microscopy and laser ranging, indicating a 16 μm × 20 μm × 118 μm dimension workspace. Experiments also indicate that the motion resolution and repeatability of the microrobot varies depending on the location of the end-effector in space, but generally range between 20 nm (minimum) and 150 nm (maximum). With FEA simulation result, the force output of sAFAM falls in the range of tens of micro Newtons. Thus, sAFAM has the potential for future use as an assist micro/nano manipulation tool in the scanning electron microscope (SEM) or in conjunction with an atomic force microscope (AFM).

A Two-Terminal Bistable Electrothermally Actuated Microswitch

An improved design of an electrothermally actuated two-terminal bistable microswitch is the focus of this paper. The proposed design has bimodal bistability which is obtained by using a pair of arches, a V-beam electrothermal actuator, and a novel initially retracting actuator. All these elements are monolithically integrated in a single planar releasable layer. The salient feature of the design is the usage of only a single pair of electrodes to switch between ON and OFF states, even though there are two actuators. In order to reduce the stress, the two actuators are mechanically decoupled but are electrically coupled to satisfy the two-terminal actuation. The switch design is experimentally verified by realizing on a silicon-on-insulator (SOI) wafer using a single-layer micro-fabrication technique. An actuation voltage of 11.8 V with 200-ms pulse-width, drives the switch from OFF to ON state and a 50-ms pulse of the same voltage across the same terminals, brings it back. [2018-0293]

Modeling and Thermal Metrology of Thermally Isolated MEMS Electrothermal Actuators for Strain Engineering of 2D Materials in Air

We present electrothermal microelectromechanical (MEMS) actuators as a practical platform for straining 2-D materials. The advantages of the electrothermal actuator are its high output force and displacement for low input voltage, but its drawback is that it is actuated by generating high amounts of heat. It is crucial to mitigate the high temperatures generated during actuation for reliable 2-D material strain device implementation. Here, we implement a chevron actuator design that incorporates a thermal isolation stage in order to avoid heating the 2-D material from the high temperatures generated during the actuation. By comparing the experiment and simulation, we ensure our design does not compromise output displacement while keeping the 2-D material strain device stage cool. We also provide a simple analytical model useful for quickly evaluating different thermal isolation stage designs.

An actuator–sensor hybrid device made of carbon-based polymer composite for self-sensing systems

This paper presents the concept, design, and characterization of a new type of integrated device with a hybrid structure. The proposed device is hybridized with an electrothermal actuator and a bending sensor with temperature-compensating ability, which can serve as a self-sensing system. The sensor displays a parallel change in the electrical resistance upon the temperature alteration, resulting enables a cancellation of cross talk. The actuator exhibits a visible maximum strain of 1.2% at an electric power intensity of around 1.05 mW/mm3, and the bending sensor can display the curvature without the need for an external monitoring system such as a laser displacement meter. The traceability of the motion is represented well while power is supplied, but a slight delay occurs when the power is switched off, this being due to the difference in thermal conductivity between the composite of the actuator and the sensor. This proposed hybrid device realizes a simple self-sensing operation using a simple power supply and monitoring reading lines. It offers ease of fabrication and promising practical applications in remote sensing/operating devices.

An Electrothermal Cu/W Bimorph Tip-Tilt-Piston MEMS Mirror with High Reliability.

This paper presents the design, fabrication, and characterization of an electrothermal MEMS mirror with large tip, tilt and piston scan. This MEMS mirror is based on electrothermal bimorph actuation with Cu and W thin-film layers forming the bimorphs. The MEMS mirror is fabricated via a combination of surface and bulk micromachining. The piston displacement and tip-tilt optical angle of the mirror plate of the fabricated MEMS mirror are around 114 μm and ±8°, respectively at only 2.35 V. The measured response time is 7.3 ms. The piston and tip-tilt resonant frequencies are measured to be 1.5 kHz and 2.7 kHz, respectively. The MEMS mirror survived 220 billion scanning cycles with little change of its scanning characteristics, indicating that the MEMS mirror is stable and reliable.

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 & output force of the microactuator. Entropy generation rate was used as optimization criteria.

Laser fabrication of graphene-based electrothermal actuators enabling predicable deformation.

Electrothermal actuators (ETAs) that can convert electric energy into mechanical works have been extensively studied for their great potential in artificial muscles and robotics. However, the production of ETAs that enable complex and predictable deformation is still challenging. In this Letter, an ETA based on reduced graphene oxide (RGO) and polyethylene (PE) bimorph is developed through a facile laser-scribing method. Since the laser-scribing technology permits flexible patterning, conductive RGO electrodes with complex circuit patterns can be readily produced on a thermally active PE film, forming an ETA capable of fast and reversible deformation. In addition, the laser-scribed ETA demonstrated orientation-defined bending performance, enabling more sophisticated deformation control. The laser scribing of graphene oxide has opened up a new way to produce ETAs towards cutting-edge applications such as soft robotics and intelligent systems.

An Electro-Thermal Actuation Method for Resonance Vibration of a Miniaturized Optical-Fiber Scanner for Future Scanning Fiber Endoscope Design

Medical professionals increasingly rely on endoscopes to carry out many minimally invasive procedures on patients to safely examine, diagnose, and treat a large variety of conditions. However, their insertion tube diameter dictates which passages of the body they can be inserted into and, consequently, what organs they can access. For inaccessible areas and organs, patients often undergo invasive and risky procedures—diagnostic confirmation of peripheral lung nodules via transthoracic needle biopsy is one example from oncology. Hence, this work sets out to present an optical-fiber scanner for a scanning fiber endoscope design that has an insertion tube diameter of about 0.5 mm, small enough to be inserted into the smallest airways of the lung. To attain this goal, a novel approach based on resonance thermal excitation of a single-mode 0.01-mm-diameter fiber-optic cantilever oscillating at 2–4 kHz is proposed. The small size of the electro-thermal actuator enables miniaturization of the insertion tube. Lateral free-end deflection of the cantilever is used as a benchmark for evaluating performance. Experimental results show that the cantilever can achieve over 0.2 mm of displacement at its free end. The experimental results also support finite element simulation models which can be used for future design iterations of the endoscope.

Essential design and fabrication considerations for the reliable performance of an electrothermal MEMS microgripper

Over the past years, microelectromechanical systems (MEMS) have become a vital component within a wide range of technologies, making the study of their performance and operational reliability a very critical aspect for their correct functionality. Microgrippers are one such type of MEMS devices with one of their key applications being the manipulation of biological tissues and cells. This paper presents a microgripper design based on the ‘hot and cold arm’ electrothermal actuation mechanism that is suitable to study the deformability properties of human red blood cells under healthy and pathological conditions. The main scope of this paper is to highlight a number of failure mechanisms that are typical of surface micromachined MEMS microgrippers. These include out-of-plane buckling of the hot arm, stress concentrations, device stiction, and residual stresses. The studied polysilicon microgripper structures were designed and fabricated in line with the specifications of the commercial fabrication process PolyMUMPsTM. The microgripper design was numerically modelled and electrothermomechanically studied using finite element analysis in CoventorWare $$^{\circledR }$$ . Experimental testing on the fabricated structures was used to demonstrate reliable microgripper performance as well as instances of the considered failure mechanisms. Results for the reliable microgripper performance show that the microgripper arms deflected as expected when actuated, with the obtained simulation and experimental results in good agreement. The investigated failure mechanisms have led to the identification of essential design and fabrication considerations whose thorough investigation, with the aid of appropriate modelling approaches, is essential to define improvement solutions and best practices to mitigate the failure or malfunction of the microgripper during operation.

Design and Analysis of a High-Gain and Robust Multi-DOF Electro-thermally Actuated MEMS Gyroscope.

This paper presents the design and analysis of a multi degree of freedom (DOF) electro-thermally actuated non-resonant MEMS gyroscope with a 3-DOF drive mode and 1-DOF sense mode system. The 3-DOF drive mode system consists of three masses coupled together using suspension beams. The 1-DOF system consists of a single mass whose motion is decoupled from the drive mode using a decoupling frame. The gyroscope is designed to be operated in the flat region between the first two resonant peaks in drive mode, thus minimizing the effect of environmental and fabrication process variations on device performance. The high gain in the flat operational region is achieved by tuning the suspension beams stiffness. A detailed analytical model, considering the dynamics of both the electro-thermal actuator and multi-mass system, is developed. A parametric optimization is carried out, considering the microfabrication process constraints of the Metal Multi-User MEMS Processes (MetalMUMPs), to achieve high gain. The stiffness of suspension beams is optimized such that the sense mode resonant frequency lies in the flat region between the first two resonant peaks in the drive mode. The results acquired through the developed analytical model are verified with the help of 3D finite element method (FEM)-based simulations. The first three resonant frequencies in the drive mode are designed to be 2.51 kHz, 3.68 kHz, and 5.77 kHz, respectively. The sense mode resonant frequency is designed to be 3.13 kHz. At an actuation voltage of 0.2 V, the dynamically amplified drive mode gain in the sense mass is obtained to be 18.6 µm. With this gain, a capacitive change of and is achieved corresponding to the sense mode amplitude of and at atmospheric air pressure and in a vacuum, respectively.

Design and Simulation of a Miniaturized RF-MEMS Reconfigurable Microstrip Combline Band Pass Filter

Reconfigurable bandpass filter (RBPF) is crucial in various radio frequency (RF) applications. However, the use of lumped element filters have failed to show tuneable integrated solutions with low insertion loss in the high frequency range. Most reconfigurable filter designs are faced with the challenges of narrow bandwidth, high losses, bulkiness, high voltage and high power consumption. To overcome these issues, this research undertakes to develop a miniaturized reconfigurable radio frequency micro-electro-mechanical system (RF MEMS) band-pass filter designed for wireless communication at the center frequency of 30 GHz. The filter is optimized for low insertion loss, broad bandwidth, low applied voltage, lower power consumption and high linearity. The design consists of 3rd order tapped input microstrip combline transmission lines structure integrated with in-plane tunable parallel capacitors and electrothermal actuator. The transmission lines are patterned on a silicon dioxide (Si02) of thickness 1 μm placed on a silicon (Si) substrate with the dielectric constant of ε,. = 11.9. The filter occupies chip area of 1.1 mm x 0.9 mm without the dummy substrate. The 3D structure is designed and simulated in Computer Simulator Technology (CST). The result shows the achieved inband insertion loss of less than 1 dB and the return loss better than 8 dB. The proposed reconfigurable bandpass filter can tune its center frequency with relatively constant absolute bandwidth.

Design of a novel three arm electrothermal microgripper with multiple degrees of control

A novel three arm microgripper design is presented in this paper. It is a SU-8 based design with integrated microheaters. It is composed of three microactuators: two are based on a design for bi-directional beam deflection and the other is a tri-directional actuator. The actuators are simulated and analyzed using COMSOL Multiphysics tool. The first actuator has displacement of about 12 μm and 35 μm respectively when heaters h1 and h2 are used in operation and the heater temperature is about 200°C. The second actuator has a displacement of about 12 μm in all three directions. This microgripper is flexible and can be used to grasp a wide range of sizes of micro-particles. In addition, it has more freedoms of control by using the different combinations of the 8 embedded microheaters for electrothermal actuation.

Post-Release Deformation and Motion Control of Photonic Waveguide Beams by Tuneable Electrothermal Actuators in Thick SiO₂.

Photonic packaging, which includes high-precision assembly of photonic sub-systems, is currently a bottleneck in the development of commercially-available integrated photonic products. In the pursuit of a fully-automated, high-precision, and cost-effective photonic alignment scheme for two multi-channel photonic chips, this paper explores different designs of the on-chip electrothermal actuators for positioning mechanically-flexible waveguide structures. The final alignment goal is ∼100 nm waveguide to waveguide. The on-chip actuators, particularly for out-of-plane actuation, are built in a 16 μm-thick SiO photonic-material stack with 5 μm-thick poly-Si as an electrothermal element. A major challenge of out-of-plane positioning is a 6 μm height difference of the waveguides to be aligned, due to different built-up material stacks, together with a misalignment tolerance of 1 μm–2 μm from the pre-assembly (flip-chip) process. Therefore, the bimorph-actuator design needs to compensate this height difference, and provide sufficient motion to align the waveguides. We propose to exploit the post-release deformation of so-called short-loop bimorph actuator designs to meet these joint demands. We explore different design variants based on the heater location and the integration of actuator beams with waveguide beams. The actuator design (with 30 μm poly-Si and 900 μm SiO in length) has ∼8 μm out-of-plane deflection and is able to generate ∼4 μm motion, which meets the design goal.

Design and research on large displacement bidirectional MEMS stage with interlock mechanism

The design, fabrication and characterization of a large displacement bidirectional MEMS stage is presented in this paper. The V-shape electro-thermal actuator, micro lever, pawl and slider are investigated respectively. With 11 V driven voltages, these basic components can generate 15 mN output force and realize pulling, disengaging and reengaging to move the stage forward and backward smoothly (1 mm displacement in bi-direction). The rack and interlock mechanism formed by the pawl and slider make the device to have the features of linear output displacement, low power consumption, input signal recognition and displacement sustaining. SOI wafer is introduced in the fabrication process, and the 1.2 × 3.5 mm2 movable plate can be actuated successfully.

Thermal Reliability Study of an Electrothermal MEMS Mirror

Micro-electrical-mechanical mirrors based on electrothermal bimorph actuators have unparalleled advantages of large scan range, low driving voltage, and high fill factor, but their reliability issues are not well understood. One of the main failure phenomena is the burnout of the refractory metal resistor embedded in electrothermal bimorph actuator structures. In this paper, the burnout process was thoroughly studied via both electrical and optical testing. In particular, the current passing through the embedded resistor was monitored throughout the entire burnout process. It was found that the burnout was caused by multiple steps of anomalies, including electrical breakdown at poor step coverage, short circuit, overheating, and electromigration. Electrical models and lumped-element thermal models were established and electrothermomechanical finite-element method simulations were performed. The modeling and simulation results are all in good agreement with the experimental results. These findings will help greatly improve future design for better reliability.

A novel scanning force microscopy probe with thermal-electrical actuation and piezo-resistive sensing

This work presents a novel scanning force microscopy probe with electro-thermal actuation and piezo-resistive detection. The fabricated probe of 270 × 58 × 2.5 μm3 can generate a force between 1.05 μN and 16.52 μN with a resolution of nano-newton, and can detect the nanometer-scale deflection. The minimum detectable output signal of the probe could be down to 20 μV and the sensitivity reaches 4.92 mV μm−1. This is a straight-forward technique for characterizing the mechanical properties of micro/nano-structures and devices.

An investigation into the mechanical behavior of multi- input and multi-output MEMS resonators

We investigate theoretically and experimentally the mechanical behavior of Micro electromechanical systems MEMS resonators with multiple input (actuation) and output (detection) methods. The devices are based on a compound resonator consisting of an in-plane clamped-guided arch beam that is mechanically coupled from its guided side to another T-shaped resonant beam. Tensile and compressive bi-directional electrostatic axial forces are induced on the T-shaped resonator, which modulate the stiffness of both the arch and the T-shaped beams resonators, thereby changing their resonance frequencies to lower or higher values. At the coupling point of the two resonators, additional two flexure beams are attached, which provide another electrothermal tuning capability. The electrothermal actuators can be configured in various ways to adjust, as desired, the mechanical stiffness of the resonators; thereby controlling their resonance frequency. Therefore, this structure offers various electrothermal and electrostatic actuation and read-out possibilities, which can lead to complex device functionalities based on multiple inputs and outputs. As an example, we experimentally demonstrate an electromechanical resonant 1:2 DEMUX logic element. The logic operation is based on the linear frequency modulation. This study demonstrates that with such compound MEMS resonators, it is possible to build more complex logic functionalities.

Fabrication and modal characterisation of large‐area polymer membranes for acoustic micro‐electromechanical systems devices

Bilayer polymer/metal suspended membranes made of poly(methyl methacrylate) (PMMA) and aluminium (Al) have been fabricated using a wet transfer technique where a polyelectrolyte (polydiallyldimethylammonium chloride - PDAC) has been employed as sacrificial layer to facilitate the detachment of the thin PMMA/Al layers from the substrate holders. In this way, free-standing PMMA/Al membranes with outstanding diameter (3.5 mm) to thickness (400 nm) ratios of ~10 4 have been obtained. The membranes have been actuated mechanically and electrothermally and their modal behaviour characterised using laser Doppler vibrometry. The first five modes of vibrations have been detected in the range of 2-25 kHz. The second and fifth degenerate modes have been seen to split, probably due to non-uniform tension or mass density. The membranes can achieve vibration amplitudes in the order of few tens of microns. When performing electro-thermal actuation, it has been observed that the amplitude of a single mode can be tuned by controlling the path of the electric current across the membrane.

Biomimetic Color Changing Anisotropic Soft Actuators with Integrated Metal Nanowire Percolation Network Transparent Heaters for Soft Robotics

AbstractTo add more functionalities and overcome the limitation in conventional soft robots, highly anisotropic soft actuators with color shifting function during actuation is demonstrated for the first time. The electrothermally operating soft actuators with installed transparent metal nanowire percolation network heater allow easy programming of their actuation direction and instantaneous visualization of temperature changes through color change. Due to the unique direction dependent coefficient of thermal expansion mismatch, the suggested actuator demonstrates a highly anisotropic and reversible behavior with very large bending curvature (2.5 cm−1) at considerably low temperature (≈40 °C) compared to the previously reported electrothermal soft actuators. The mild operating heat condition required for the maximum curvature enables the superior long‐term stability during more than 10 000 operating cycles. Also, the optical transparency of the polymer bilayer and metal nanowire percolation network heater allow the incorporation of the thermochromic pigments to fabricate color‐shifting actuators. As a proof‐of‐concept, various color‐shifting biomimetic soft robots such as color‐shifting blooming flower, fluttering butterfly, and color‐shifting twining tendril are demonstrated. The developed color‐shifting anisotropic soft actuator is expected to open new application fields and functionalities overcoming the limitation of current soft robots.

Fabrication and Properties of Composite Artificial Muscles Based on Nylon and a Shape Memory Alloy

This paper focuses on the design, fabrication and investigation of the mechanical properties of new artificial muscles formed by twisting and annealing. The artificial muscles designed by twisting nylon have become a popular topic in the field of smart materials due to their high mechanical performance with a large deformation and power density. However, the complexity of the heating and cooling system required to control the nylon muscle is a disadvantage, so we have proposed a composite artificial muscle for providing a direct electricity-driven actuation by integrating nylon and a shape memory alloy (SMA). In this paper, the design and fabrication process of these composite artificial muscles are introduced before their mechanical properties, which include the deformation, stiffness, load and response, are investigated. The results show that these composite artificial muscles that integrate nylon and a SMA provide better mechanical properties and yield up to a 44.1% deformation and 3.43 N driving forces. The good performance and direct electro-thermal actuation make these composite muscles ideal for driving robots in a method similar to human muscles.