A silicon force sensor for large magnitude impact loads

We present a novel force sensor to measure large forces over a wide bandwidth (from static loads to 100's of kHz) for use as a shock sensor in challenging environments. The sensor is configured as a washer with embedded MEMS (Microelectromechanical Systems) piezo-resistive doped polysilicon sensing elements. The silicon sensing elements utilize photolithographically patterned strain gages on deforming sense plates to provide a high sensitivity linear response (1-10 mV/1000 lbf, 0.2-2 mV/kN) to input loads of up to 10,000 lbf (45,000 N). Higher loads are achievable by implementing relatively simple design changes, for instance a thicker or smaller diameter sense plate. Very small silicon sensor elements (as small as 10-100 μm in diameter) allow multiple sensors to be embedded in the washer to provide redundant load measurement and the determination of load direction. Readily available engineering materials FR4 (epoxy circuit board), copper, Kapton (polyimide), and steel are used to package the silicon sensor die in a sandwich that protects the brittle silicon allowing it to survive high magnitude impact loads. The design procedures presented allow the sensor designer to control the stress level at the silicon sensor die and therefore the effective load range of the sensor, while maintaining a high signal to noise ratio (>100:1).