Triaxial inertial switch with multiple thresholds and resistive ladder readout

We describe the design, modeling, fabrication, and testing of a MEMS inertial switch that can detect accelerations in the x, y, and z axes using a single mass/spring assembly (first reported in Ref. [1]). A spiral spring suspension is used which is compliant in all directions. The inertial switch approach offers zero power draw until an acceleration event occurs. Arrays of individual triaxial sensors are created on a single chip, with each switch designed to close at a different acceleration threshold between 50 g and 250 g. A resistor ladder connects each switch together in series such that the number of pinouts from the chip is substantially reduced. The response of the switch array to half-sine acceleration pulses of 5–8 ms duration is reported, with multiple switches in the array closing and opening in sequence for higher magnitude acceleration pulses. The switch closure time under these conditions is consistently less than 200 μs, and bounce is minimal for applied accelerations lower than 200 g.