Micromachined wafer strain gauge

Abstract

A micromachined strain gauge comprising a plastically deformable piezoresistive microstructure formed on a surface of a substrate so that deformation of the substrate plastically deforms the microstructure to thereby change the resistance of the microstructure. The stress in the substrate can be determined from the change in the resistance of the microstructure.

1 . A micromachined strain gauge comprising a plastically deformable piezoresistive microstructure formed on a surface of a substrate so that deformation of the substrate plastically deforms the microstructure to thereby change the resistance of the microstructure, wherein stress in the substrate can be determined from change in the resistance of the microstructure.  
   
   
       2 . The micromachined strain gauge of  claim 1 , wherein the microstructure is connectable to a resistance measuring circuit.  
   
   
       3 . The micromachined strain gauge of  claim 2 , wherein the microstructure is formed on the surface of the substrate by surface micromachining.  
   
   
       4 . The micromachined strain gauge of  claim 3 , wherein the surface micromachining is by at least one of film deposition, photolithography and etching.  
   
   
       5 . The micromachined strain gauge of  claim 4 , wherein the microstucture is formed on the surface of the substrate in a meander.  
   
   
       6 . The micromachined strain gauge of  claim 5 , wherein the microstructure comprises gold.  
   
   
       7 . The micromachined strain gauge of  claim 6 , wherein the substrate comprises a portion of a semiconductor wafer.  
   
   
       8 . The micromachined strain gauge of  claim 7 , wherein the portion of the semiconductor wafer comprises a die of the semiconductor wafer.  
   
   
       9 . A method of determining stress in a substrate comprising the steps of: forming a plastically deformable piezoresistive microstructure on a surface of the substrate so that deformation of the substrate plastically deforms the microstructure to thereby change the resistance of the microstructure; 
 measuring change in the resistance of the microstructure;    determining stress in the substrate from change in the resistance of the microstructure.    
   
   
       10 . A method of determining stress induced in a wafer by wafer processing, the method comprising the steps of: 
 micromachining at least one plastically deformable piezoresistive strain gauge microstructure on at least one die of the wafer so that deformation of the die plastically deforms the strain gauge microstructure to thereby change the resistance of the strain gauge microstructure;    measuring the resistance of the strain gauge microstructure before wafer processing;    measuring the resistance of the strain gauge microstructure after wafer processing;    determining stress induced in the die by wafer processing from change in the resistance of the strain gauge microstructure.    
   
   
       11 . The method of  claim 10 , wherein a plurality of plastically deformable piezoresistive strain gauge microstructures are respectively micromachined on a corresponding plurality of die of the wafer.  
   
   
       12 . The method of  claim 11 , further comprising the step of generating a wafer map of the stress induced in individual die by wafer processing.  
   
   
       13 . The method of  claim 12 , wherein the wafer processing comprises processing wafers to fabricate microelectromechanical systems (MEMS) thereon.