A normally closed MEMS micro reed switch with fill in liquid metal micro hinge structure

This study has successfully designed and implemented the first normally-closed (NC) micro reed switch (Fig.1). The NC-type reed switch consists three separate metal structures (hinge, movable pad/spring, and fixed-pad) and is assembled by an attractive magnetic force exerted by an out-of-plane magnetic field. Furthermore, as applying a strong enough in-plane magnetic field, the spring is deformed by repulsive magnetic force to separate the pads and turn-off the switch (Fig.2). Merits of this NC reed switch: (1) liquid-metal to ensure electrical connection at hinge, (2) UV-gel fixed hinge structure, and (3) magnetized repulsive actuating mechanism. Experiment demonstrates a typical fabricated NC reed switch with driving magnetic field of near 160Gauss (G), and releasing at near 150G. The contact resistance is between 0.2-5Ω. The contact resistance variation is near 13% under a 20G excitation.