Performance enhancement of electromagnetic microrelay matrices
Creators: name: Dahari, Zuraini
Publisher: name: RMIT University
Year: 2024

description: Although MEMS technology has enabled batch fabrication of hundreds of microrelays on a single substrate, the majority of the reported designs of electromagnetic micro relays were intended for use as individual units. However, matrix arrays of microrelays can be very useful in many applications. Switching of individual relays in a matrix with dedicated control circuits becomes problematic when the size of the matrix is large. For such a scheme to succeed, very narrow manufacturing tolerances will have to be achieved in the parameters of the relay. In a typical commercial microfabrication environment it is impossible to achieve the required narrow tolerances in the thickness and the initial free end position of the cantilever. The work reported in this thesis was concerned with the performance enhancement of the electromagnetic microrelays to achieve robust array operation. Following an extensive literature review, the set of desirable design features to enhance the performance and operational reliability of electromagnetic microrelays were identified as bistability, bidirectional actuation, fixed on and off positions for the moving contact element, latching of the moving contact element to fixed surfaces in both switching states, rotational motion of the moving element about its centre of mass, a compact torsional flexure to support the moving element akin to a central pivotal joint but amenable to microfabrication, use of most of the stored energy in the spring element to switch between states, use of external permanent magnets for latching purpose, and use of narrow current pulse as the switching signal. A novel design incorporating the above features and amenable to the planar microfabrication processes was then developed. Magneto-mechanical analyses of the electromagnetic microrelay were performed by considering the mechanical and magnetic subsystems separately and combining the results to determine the interaction between the two subsystems. Both analytical studies and FEA were carried out and the results were found to be reasonably close. Advantageously, the relay exhibited high stiffness in the switched state and low stiffness during its travel from one switched state to the other. The relay was found capable of generating both attractive and repulsive magnetic forces at the two ends of the rigid beam. Remarkably close polynomial fits were found to the magnetic torque results obtained by the FEA. The models along with the scaling laws for electromagnetic systems were then used to extrapolate the finite element analyses results for geometrically similar but different sizes of the magnetic structure and for different currents. As AuNi5 and Rh are considered good contact materials for microrelays, optimum design parameters were determined for each case. Tolerances for such key design parameters as the thickness of the cantilever spring element were determined, and the minimum current pulse width required for switching the relay estimated. Much broader reliability margins were demonstrated for the microrelay. A scaled-up model was fabricated and successfully tested as proof of concept. Processing steps for the microfabrication of the relay was also given. The thesis is concluded with a discussion on the performance of the proposed microrelay and suggestions for further research.