Electrothermal Microactuators Research Articles

A Nodal Analysis Method for Laterally-Driven Electrothermal Microacutators

This paper introduces a novel method for the simulation and verification of the laterally-driven electrothermal microactuator. A nodal analysis model of the electrothermal microactuator was built without meshing. This model may simulate the static and dynamic behaviour of the electrothermal microactuators with variational thermal conductivity, electrical resistivity and thermal expansion coefficient. There are only three stages of ODEs in the model, but its static relative error is below 5% in comparison with the results of the nonlinear model of ANSYS with the nonlinear geometrical options turned on. The equivalent circuit was then built to present the capability of co-simulating with the control and feedback circuits.

Modelling & Simulation of Novel Three Arm MEMS Actuators & Its Application

This paper presents the design and Finite Element Model (FEM) simulation of a novel electrothermal microactuators and arrays. It is a single material microactuator which deflects at its tips by differential thermal expansion of its constituent parts. The electrothermal actuator consists of three thin arms, three thin blades and two electrical connection pads. The goal of this coupled electrothermal actuator design was to multiply the force by adding the individual contributions of all the three actuators. The difference in magnitude of blade deflections depends on the geometrical characteristics of the actuators. The thermal deformation and thermal stability are easily controllable. The simulation employing ANSYS/Multiphysics software results include force, deflection, thermal stress, ideal electrothermal actuator and array geometries. The main advantage of this electrothermal actuator is large deflection of blades with very low actuation voltage in comparison with electrostatic actuators. A typical application in a micromirror is shown to illustrate the utility of these actuators and arrays.

Performance Improvement of an Electrothermal Microactuator Fabricated Using Ni-Diamond Nanocomposite

In this paper, a low-temperature stress-free electrolytic nickel (EL) deposition process with added dispersed diamond nanoparticles (diameter <0.5 /spl mu/m) is developed to synthesize Ni-diamond nanocomposite for fabricating electrothermal microactuators. Device characterization reveals dramatic performance improvements in the electrothermal microactuator that is made of the nanocomposite, including a reduction in the input power requirement and enhanced operation reliability. In comparison with the microactuator made of pure nickel, the nanocomposite one can save about 73% the power for a 3 /spl mu/m output displacement and have a longer reversible displacement range, which is prolonged from 1.8 /spl mu/m to more than 3 /spl mu/m. Furthermore, the nanocomposite device exhibits no performance degradation after more than 100 testing cycles in the reversible regime. The enhancements increase with the incorporation of the nanodiamond in a nickel matrix, so the Ni-diamond nanocomposite has potential for application in MEMS fabrication.

Ni-carbon nanotubes nanocomposite for robust microelectromechanical systems fabrication

This article presents a novel fabrication process to enhance the operational performance and reliability of electrothermal microactuators. Carbon nanotubes (CNTs) (outer diameter: 10–20nm, inner diameter: 5–10nm, length: 0.5–200μm) are incorporated in an electrolytic nickel deposition process in which a well-dispersed Ni-CNTs colloidal solution is made by a special acid oxidative method to synthesis a Ni-CNTs nanocomposite for device fabrication. Measurement results show that the microactuator plated with CNTs (0.028g∕L) needs the power requirement less 95% than the pure nickel device at the same output displacement of 3μm. The performance improvement of the electrothermal microactuator made of the nanocomposite, including device strength and power efficiency, has shown to be similar to the Ni-diamond composites (L. N. Tsai, G. R. Shen, Y. T. Cheng, and W. S. Hsu, The 54th Electronic Components and Technology Conference, June 2004, pp. 472–476)). In addition, the E∕ρ ratio of the Ni-CNTs composite can be enhanced to 1.47 times higher than that of pure nickel, which is a fascinating result for resonant device fabrication.

Precision bi-directional motion of a linear mechanical shuttle with an electrothermal microengine

This research is focused on the design and experimental characterization of an electrothermal microengine that is capable of precise bi-directional motion. The microengine is operated with arrays of microelectromechanical systems (MEMS) asymmetrical electrothermal microactuators that are synchronously activated. The fundamental MEMS polysilicon electrothermal microactuator uses resistive (Joule) heating to generate thermal expansion and movement. In a conventional planar asymmetrical electrothermal microactuator, the “hot” arm is positioned parallel to the “cold” arm, but since the “hot” arm is narrower than the “cold” arm, the electrical resistance of the “hot” arm is greater. When an electrical current passes through the electrothermal microactuator (through the series connected electrical resistance of the “hot” and “cold” arms), the “hot” arm is heated to a higher temperature than the “cold” arm. This temperature increase causes the “hot” arm to expand along its length, thus forcing the tip of the device to rotate about its mechanical flexure element. The practical integration of arrays of MEMS electrothermal microactuators to realize a monolithic microengine is presented. The microengine has been operated to control the position of a linear mechanical shuttle.

Operation of electrothermal and electrostatic MUMPs microactuators underwater

Surface-micromachined actuators made in multi-user MEMS processes (MUMPs) have been operated underwater without modifying the manufacturing process. Such actuators have generally been either electro-thermally or electro-statically actuated and both actuator styles are tested here for suitability underwater. This is believed to be the first time that thermal and electrostatic actuators have been compared for deflection underwater relative to air performance. A high-frequency ac square wave is used to replicate a dc-driven actuator output without the associated problem of electrolysis in water. This method of ac activation, with frequencies far above the mechanical resonance frequencies of the MEMS actuators, has been termed root mean square (RMS) operation. Both thermal and electrostatic actuators have been tested and proved to work using RMS control. Underwater performance has been evaluated by using in-air operation of these actuators as a benchmark. When comparing deflection per volt applied, thermal actuators operate between 5 and 9% of in-air deflection and electrostatic actuators show an improvement in force per volt applied of upwards of 6000%. These results agree with predictions based on the physical properties of the surrounding medium.

Electrothermal properties and modeling of polysilicon microthermal actuators

This work addresses a range of issues on modeling electrothermal microactuators, including the physics of temperature dependent material properties and Finite Element Analysis (FEA) modeling techniques. Electrical and thermal conductivity are a nonlinear function of temperature that can be explained with electron and phonon transport models, respectively. Parametric forms of these equations are developed for polysilicon and a technique to extract these parameters from experimental data is given. A modeling technique to capture the convective and conductive cooling effects on a thermal actuator in air is then presented. Using this modeling technique and the established polysilicon material properties, simulation results are compared with measured actuator responses. Both static and transient analyzes have been performed on two styles of actuators and the results compare well with measured data.

Single- and double-hot arm asymmetrical polysilicon surface micromachined electrothermal microactuators applied to realize a microengine

This research focuses on the design and experimental characterization of two types of MEMS asymmetrical electrothermal microactuators. The motivation is to present a description of the behavior of the electrothermal microactuator to facilitate its adaptation to a variety of MEMS applications. Both MEMS polysilicon electrothermal microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. In a conventional electrothermal microactuator, the ‘hot’ arm is positioned parallel to a ‘cold’ arm, but since the ‘hot’ arm is narrower than the ‘cold’ arm, the electrical resistance of the ‘hot’ arm is larger. When an electrical current passes through the microactuator (through the series connected electrical resistance of the ‘hot’ and ‘cold’ arms), the ‘hot’ arm is heated to a higher temperature than the ‘cold’ arm. This temperature increase causes the ‘hot’ arm to expand along its length, thus forcing the tip of the device to rotate about a mechanical flexure element. A new electrothermal actuator design eliminates the parasitic electrical resistance of the ‘cold’ arm by incorporating an additional ‘hot’ arm. The second ‘hot’ arm results in an improvement in electrical efficiency by providing an active return current path. Additionally, the ‘cold’ arm can now have a narrower flexure compared with the conventional single-‘hot’ arm device because it does not have to pass an electric current. A narrower flexure element manifests improved mechanical efficiency. Deflection and force measurements of both electrothermal actuators as a function of applied electrical power are presented. Also described is the practical integration of the electrothermal microactuators in a monolithic microengine that is capable of rotating a set of gears.

Design and Performance of a Microengine Realized with Arrays of Asymmetrical Electrothermal Polysilicon Surface Micromachined Microactuators

ABSTRACTThis research focuses on the design and experimental characterization of two types of MEMS asymmetrical electrothermal microactuators. Both microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. Deflection and force measurements of both microactuators as a function of applied electrical power are presented. Also described is the practical integration of the electrothermal microactuators in a monolithic microengine that is capable of rotating a set of gears.

Bent-beam electrothermal actuators-Part I: Single beam and cascaded devices

This paper describes electrothermal microactuators that generate rectilinear displacements and forces by leveraging deformations caused by localized thermal stresses. In one manifestation, an electric current is passed through a V-shaped beam anchored at both ends, and thermal expansion caused by joule heating pushes the apex outward. Analytical and finite element models of device performance are presented along with measured results of devices fabricated using electroplated Ni and p/sup ++/ Si as structural materials. A maskless process extension for incorporating thermal and electrical isolation is described. Nickel devices with 410-/spl mu/m-long, 6-/spl mu/m-wide, and 3-/spl mu/m-thick beams demonstrate 10 /spl mu/m static displacements at 79 mW input power; silicon devices with 800-/spl mu/m-long, 13.9-/spl mu/m-wide, and 3.7-/spl mu/m-thick beams demonstrate 5 /spl mu/m displacement at 180 mW input power. Cascaded silicon devices using three beams of similar dimensions offer comparable displacement with 50-60% savings in power consumption. The peak output forces generated are estimated to be in the range from 1 to 10 mN for the single beam devices and from 0.1 to 1 mN for the cascaded devices. Measured bandwidths are /spl ap/700 Hz for both. The typical drive voltages used are /spl les/12 V, permitting the use of standard electronic interfaces that are generally inadequate for electrostatic actuators.

In-plane tip deflection and force achieved with asymmetrical polysilicon electrothermal microactuators

Several microactuator technologies have recently been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion are the most common modes of microactuator operation. This research focuses on the design and experimental characterization of two types of asymmetrical MEMS electrothermal microactuators. The motivation is to present a unified description of the behavior of the electrothermal microactuator so that it can be adapted to a variety of MEMS applications. Both MEMS polysilicon electrothermal microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. In a conventional electrothermal microactuator, the ‘hot’ arm is positioned parallel to a ‘cold’ arm, but because the ‘hot’ arm is narrower than the ‘cold’ arm, the electrical resistance of the ‘hot’ arm is higher. When an electric current passes through the microactuator (through the series connected electrical resistance of the ‘hot’ and ‘cold’ arms), the ‘hot’ arm is heated to a higher temperature than the ‘cold’ arm. This temperature increase causes the ‘hot’ arm to expand along its length, thus forcing the tip of the device to rotate about a mechanical flexure element. The new thermal actuator design eliminates the parasitic electrical resistance of the ‘cold’ arm by incorporating an additional ‘hot’ arm. The second ‘hot’ arm results in an improvement in electrical efficiency by providing an active return current path. Additionally, the ‘cold’ arm can have a narrower flexure than the flexure in a conventional single-‘hot’ arm device because it does not have to pass an electric current. The narrower flexure element manifests improved mechanical efficiency. Deflection and force measurements of both actuators as a function of applied electrical power have been presented in this work.

Asymmetrical Polysilicon Electrothermal Microactuators for Achieving Large In-Plane Mechanical Forces and Deflections

ABSTRACTThis research focuses on the design and experimental characterization of two types of asym- metrical MEMS electrothermal microactuators. Both MEMS polysilicon electrothermal microac- tuator designs use resistive (Joule) heating to generate thermal expansion and movement. Deflection and force measurements as a function of applied electrical power are presented.

Electrothermal actuators fabricated in four-level planarized surface micromachined polycrystalline silicon

This paper presents the results of tests performed on a variety of electrothermal microactuators and arrays of these actuators. The results are intended to aid designers of thermally actuated mechanisms, and they would apply to any surface micromachined polysilicon MEMS processes. Results presented include force and deflection vs. input power, maximum operating frequency, and the effects of long term operation. The end result is a set of proposed ideal actuator and array geometries for different applications' force requirements. In addition, various methods of arraying these actuators together are presented. Comparisons of these arraying methods allow the designer to choose which method best matches the fabrication process available and the application requirements. Finally, a thermally actuated stepper motor is used to demonstrate a useful application of these arrays.