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 cap wherein the cap is attached to the base at the surface defined by 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 flexures will not deform beyond their breaking point,   wherein piezoresistors are deposited or implanted on the bottom surface of the base beneath the flexures to create a Wheatstone bridge, and arranged such that the Wheatstone bridge will output a voltage signal proportional to the strain induced in the piezoresistors.   
     
     
         2 . The force sensor from  claim 1 , comprising:
 an etched shelf around the perimeter of the base to serve as a channel for extraction of debris during wafer dicing.   
     
     
         3 . The force sensor from  claim 1 , comprising:
 machined holes in the cap to serve as a channel for extraction of debris during wafer dicing.   
     
     
         4 . The force sensor from  claim 1 , comprising:
 a retaining wall around the periphery of the base released by slots etched into the base.   
     
     
         5 . The force sensor from  claim 1 , comprising:
 wherein at least one flexure is formed in the corners of the base.   
     
     
         6 . A wafer section of force sensors from  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 from  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 . A force sensor, comprising:
 a cap attached to a base at the surface defined by at least one rigid boss and an outer wall, forming a sealed cavity,   at least one flexure formed in the base and around the at least one rigid boss to convert force applied to the cap into strain,   a gap between the base and the cap that narrows with the application of force to the cap such that the flexures will not deform beyond their breaking point,   a means to sense strain on the bottom surface of the base.   
     
     
         9 . The force sensor of  claim 8 , wherein the flexure is formed in the base and around the at least one rigid boss by etching. 
     
     
         10 . The force sensor of  claim 8 , wherein the means to sense strain consist of piezoresistive, piezoelectric, or capacitive transducers. 
     
     
         11 . The force sensor of  claim 8 , wherein the means to sense strain produce an electrical voltage, current, or charge signal proportional to the strain. 
     
     
         12 . The force sensor of  claim 8 , wherein the electrical signal produced by the means to sense strain are routed to electrical terminals on the bottom surface of the base. 
     
     
         13 . The force sensor of  claim 8 , wherein the electrical terminals on the bottom surface of the base consist of solder bumps. 
     
     
         14 . The force sensor of  claim 8 , wherein the base has grooves to focus mechanical strain on one or more center flexure.