Thin silicon MEMS contact-stress sensor

Abstract

This thin, MEMS contact-stress (CS) sensor continuously and accurately measures time-varying, solid interface loads in embedded systems over tens of thousands of load cycles. Unlike all other interface load sensors, the CS sensor is extremely thin (< 150 µm), provides accurate, high-speed measurements, and exhibits good stability over time with no loss of calibration with load cycling. The silicon CS sensor, 5 mm2 and 65 µm thick, has piezoresistive traces doped within a load-sensitive diaphragm. The novel package utilizes several layers of flexible polyimide to mechanically and electrically isolate the sensor from the environment, transmit normal applied loads to the diaphragm, and maintain uniform thickness. The CS sensors have a highly linear output in the load range tested (0 – 2.4 MPa) with an average accuracy of ± 1.5 %.