actuators

R.P.Jourdain and S.A.Wilson
Materials Department, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, United Kingdom

Abstract

Piezoelectric ceramic films in the 20-60 micron thickness range are rarely employed today in commercial micro-mechanical devices, even though their expected force capability suggests that they are well suited to many micro-fluidic and micro-pneumatic applications. Some examples would be micro-scale fuel cells and micro-combustors. Head sliders, radio-frequency (RF) micro-switches and powered micro-optics are further potential application areas. These are only a few and the barriers in bringing them into reality are those of processing compatibility rather than commercial desirability. Such issues are being addressed in the EU Framework 6 Project ‘Q2M’, which focuses on batch-scale fabrication issues for high quality new micromechanical devices that are cost-effective and which have extended capabilities.
This paper discusses a potential batch-scale production route for piezoelectric thick-film bimorph microactuators that combines ultra-precision grinding of ceramics and femto-second laser machining, along with standard micro-fabrication techniques such as wafer bonding. This new method has the key advantage that many different shapes and thicknesses of actuator can be made with only minor process changes, meaning that actuators can be designed to suit their intended application. It contrasts with current practice whereby micro-actuators are often designed around a limited range of standard components, with consequent reduction in their achievable performance. The examples used are a 6mm diameter plane-spiral bimorph actuator for integration into a polymeric micro-valve and 2-5mm long bimorph cantilevers intended for use in
a new type of silicon ‘house’ micro-valve, with pneumatic applications.

D. Clausi, J. Peirs, D. Reynaerts
Katholieke Universiteit Leuven, Department of Mechanical Engineering, Division PMA

Abstract

Shape Memory Alloys have a considerable potential for integration into microsystems, where scaling down of their size allows favorable exploitation of the intrinsic adaptive capabilities, providing an actuation mechanism for applications (e.g. micropneumatics) requiring large force control and large actuator stroke. However, the implementation of these materials into actual structures is rather complex and mostly confined to depositing thin NiTi films onto certain target substrates, resulting in devices having a relatively high cost-per-piece. This paper is aimed at investigating a novel approach for batch integration of SMA to microactuators, which might provide a cost-effective alternative to thin film technology while enhancing functional properties and design flexibility. Indicative requirements for the actuator design have been drawn from typical microvalve applications. In order to evaluate the actuator performance, brass microcantilevers have been produced, with prestrained SMA thin wires bonded on top of them, eccentrically with respect to the cantilever’s neutral plane. The activation of SMA element is obtained by direct heating through electrical current. The bending actuation of the cantilever leads to large strokes, expected to match the requirements of a wide range of applications.

N. Sandström (a), S. Braun (a), T. Grund (b), G. Stemme (a), M. Kohl (b), W. van der Wijngaart (a)
a Microsystem Technology Lab, KTH - Royal Institute of Technology, Stockholm, SWEDEN
b Institut für Mikrostrukturtechnik, Forschungszentrum Karlsruhe GmbH, Karlsruhe, GERMANY

Abstract

This paper demonstrates the concept of wafer-level fabrication and integration of robust bulk SMA microactuators based on adhesive bonding of cold-rolled SMA sheets to silicon wafers. Contact printing of an adhesive polymer ensures a selective bonding when transferring full SMA sheets to silicon structures on a patterned wafer. The induced stress of a thin dielectric film deposited on top of the SMA sheet ensures a stable and built-in reset mechanism of the actuators. The trimorph microactuators can be actuated by indirect resistive heating through a thin metal film. We report on the successful wafer-scale fabrication of actuator cantilevers and their characteristics. First test cantilevers show a cold-state deflection of 300 μm which, however, is limited by the silicon substrate. Upon heating, the cantilever shows a stroke of approx. 80 μm.

J. Matović(a), Z. Jakšić(b)
a: ISAS, Technical University, 1040, Vienna, Austria
b: IHTM, University of Belgrade, 11000, Belgrade, Serbia

Abstract

We present a novel simple and efficient method for the full removal of the influence of ambient temperature variations to the operation of bimaterial-based MEMS actuators and sensors. The removal of the undesired interference is achieved through the very structure of the bimaterial cantilever, by reversing the order of bimaterial constituent materials at a certain length. Thus an extremely simple geometry is obtained for full self-compensation of the structures. We performed the full simulation of our devices by the finite element method. The structures require standard surface micromachining and utilize only Si-technology compatible materials like polyimides or SU-8. A simple rule for the determination of the zero-deflection condition is presented. The described compensation method enables a significantly reduced bimaterial device area and a much higher packaging density in element arrays, as well as an improved signal-to-noise ratio. The method is especially convenient for photodetector arrays for direct conversion of infrared radiation spatial distribution into a visible image.

G. Todorov, K. Kamberov, and L. Dimitrov
CAD/CAM/CAE Laboratory, Technical University of Sofia, Sofia 1000, Bulgaria

Abstract

MEMS actuators are widely used in modern industry. Their main advantage is the concentration of desired mechanical characteristics in a limited space. This paper presents a design and optimization of a flat solid MEMS actuator. The optimization is based of the selection of material properties needed for the achievement of the actuator mechanical characteristics required for good performance. The main goal is to reach necessary output mechanical force with minimal side force effects. The output mechanical force is evaluated by modeling and simulation of the magnetic field and its parameters by the use of FE Analyses. In order to make proper simulations, a finite element model of the complete actuator structure is made up suggested).

Another problem that has been solved in the paper is checking of actuator’s geometry and its dimensions in order to evaluate the effective use of the material. As a result of the study, the optimal output function of the mechanical force versus the stage position has been determined. This has been done on the basis of updated material specifications. The optimal design of a flat solenoid MEMS actuator is proposed.