Miniaturized and ruggedized wafer level mems force sensors

Abstract

Described herein is a miniaturized and ruggedized wafer level MEMS force sensor composed of a base and a cap. The sensor employs multiple flexible membranes, a mechanical overload stop, a retaining wall, and piezoresistive strain gauges.

1 . A force sensor, comprising:
 a base comprising at least one rigid boss, and   a cap, wherein the cap is attached to the base at a surface defined by the at least one rigid boss,   wherein at least one flexure is formed in the base and around the at least one rigid boss by etching,   wherein a portion of the base is etched to produce an overload stop between the base and the cap such that the at least one flexure will not deform beyond its breaking point,   wherein a plurality of piezoresistors are deposited or implanted on a bottom surface of the base beneath the at least one flexure to create a Wheatstone bridge, and   wherein the piezoresistors are arranged such that the Wheatstone bridge is configured to output a voltage signal proportional to the strain induced in the piezoresistors.   
     
     
         2 . The force sensor of  claim 1 , further comprising:
 an etched shelf around a perimeter of the base to serve as a channel for extraction of debris during wafer dicing.   
     
     
         3 . The force sensor of  claim 1 , further comprising:
 machined holes in the cap to serve as a channel for extraction of debris during wafer dicing.   
     
     
         4 . The force sensor of  claim 1 , further comprising:
 a retaining wall around a periphery of the base released by slots etched into the base.   
     
     
         5 . The force sensor of  claim 1 ,
 wherein the at least one flexure is formed in a corner of the base.   
     
     
         6 . A wafer section of force sensors of  claim 1 , comprising:
 bridges to secure the bosses during attachment of the cap to the base and positioned to be removed during dicing.   
     
     
         7 . A wafer section of force sensors of  claim 1 , comprising:
 etched holes at the edges of the flexures, such that a dicing blade will not come into contact with the flexures.   
     
     
         8 - 14 . (canceled)