A MEMS micro-reed switch designed for portable applications

Abstract

This paper presents the design, the fabrication and the characterization of a novel MEMS micro-reed switch, which consists of two Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> magnetic plates as micro-reeds. One is embedded in a silicon trench. The other is suspended above the substrate and supported by a pair of crab-leg flexures from the two sides. Both Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> plates are split into two long, narrow strips to improve the sensitivity. The switch is actuated by bringing an external magnet closer to the switch. The magnetic field required to turn on the switch can be as low as 1 mT. The contact force is estimated to ~20 μN and the initial contact-resistance is <;10 Ω with gold contacts. The switch has been tested to pass more than 40 million hot switching cycles at 2 mA current at room temperature when packaged at wafer level with SU-8 sealing. The die size is 1.7×1.8×1.1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The proposed micro-reed switch can be used as the proximity sensor to sense the magnetic field. It also has the potential to replace the conventional reed switch in portable electronics, such as cellular phones, hearing aids and laptops, where conserving battery power and device size is critical.