Acceleration sensor with protrusions facing stoppers

Abstract

An integrally micromachined acceleration sensor has a mass with a surface facing a stopper. At least one protrusion projects from this surface toward the stopper. In the absence of acceleration, the protrusion is spaced apart from the stopper, but by limiting motion of the mass toward the stopper, the protrusion improves the shock resistance of the acceleration sensor. The protrusion also prevents the mass from sticking to the stopper during the fabrication process. The stopper may have a pattern of holes surrounding the protrusion, so that the protrusion is produced naturally during the wet etching process that separates the mass from the stopper. The holes also shorten the wet etching time.

1 . A method for fabricating an acceleration sensor, comprising:
 preparing a substrate having a first layer, a second layer, and a joining layer through which the first layer is joined to the second layer;   patterning the first layer to form a mass attachment section, a peripheral attachment section surrounding and spaced apart from the mass attachment section, at least one beam flexibly linking the mass attachment section to the peripheral attachment section, and at least one stopper contiguously joined to the peripheral attachment section and spaced apart from the mass attachment section and the beam;   patterning the second layer to form a mass spaced apart from the stopper and having a surface facing the stopper, and a frame surrounding and spaced apart from the mass; and selectively removing a part of the joining layer to leave a first joining layer joining the mass to the mass attachment section, a second joining layer joining the frame to the peripheral attachment section, and at least one protrusion protruding from the surface of the mass toward the stopper, the protrusion being spaced apart from the stopper.   
     
     
         2 . The method of  claim 1 , wherein the selectively removing a part of the joining layer is carried out by wet etching. 
     
     
         3 . The method of  claim 1 , wherein the patterning the first layer further includes forming a plurality of holes facing respective areas on the surface of the mass, and the at least one protrusion is formed between at least two of the areas in the step of selectively removing a part of the joining layer. 
     
     
         4 . The method of  claim 1 , wherein the at least one protrusion is formed so as to have a square pyramidal shape, a triangular pyramidal shape, a hexagonal pyramidal shape, or an octagonal pyramidal shape.