Process for the fabrication of an inertial sensor with failure threshold

Abstract

A process for the fabrication of an inertial sensor with failure threshold includes the step of forming, on top of a substrate of a semiconductor wafer, a sample element embedded in a sacrificial region, the sample element configured to break under a preselected strain. The process further includes forming, on top of the sacrificial region, a body connected to the sample element and etching the sacrificial region so as to free the body and the sample element. The process may also include forming, on the substrate, additional sample elements connected to the body.

1 . A process for the fabrication of an inertial sensor with failure threshold, comprising the steps of: 
 forming, on top of a substrate of a semiconductor wafer, at least one sample element embedded in a sacrificial region;    forming, on top of said sacrificial region, a body connected to said sample element; and    etching said sacrificial region, so as to free said body and said sample element.    
     
     
         2 . The process according to  claim 1 , in which the step of forming said sample element comprises: 
 forming a first layer of a first material, which coats said substrate;    forming a second layer of a second material, which coats said first layer;    shaping said second layer, so as to define said sample element; and    forming a third layer of said first material coating said first layer and said sample element.    
     
     
         3 . The process according to  claim 2 , in which said first material is a dielectric material and said second material is a conductive material.  
     
     
         4 . The process according to  claim 3 , in which said first material is silicon dioxide and said second material is polysilicon.  
     
     
         5 . The process according to  claim 1  wherein the step of forming at least one sample element comprises the step of making at least one weakened region of said sample element.  
     
     
         6 . The process according to  claim 5 , in which the step of making at least one weakened region comprises the step of defining a narrowing of said sample element.  
     
     
         7 . The process according to  claim 6  in which said step of defining a narrowing portion comprises forming notches in said sample element.  
     
     
         8 . The process according to  claim 5  in which the step of making at least one weakened region comprises making a groove extending between opposite edges of said sample element.  
     
     
         9 . The process according to  claim 8 , in which the step of making a groove comprises performing an etch of controlled duration of said sample element.  
     
     
         10 . The process according to  claim 8  in which the step of making a groove comprises: 
 forming a stop layer inside said sample element; and  
 etching said sample element until said stop element is reached.  
 
     
     
         11 . The process according to  claim 1  wherein the step of forming at least one sample element comprises defining at least one anchoring pad of said sample element.  
     
     
         12 . The process according to  claim 11 , in which the step of etching said sacrificial region is interrupted before removing residual portions of said sacrificial region underlying said anchoring pad.  
     
     
         13 . The process according to  claim 1 , further comprising making, before performing the step of forming said body, at least one first opening through said sacrificial region, which exposes one end of said sample element, and making second openings, which expose respective portions of said substrate.  
     
     
         14 . The process according to  claim 13 , in which the step of forming said body comprises: 
 growing an epitaxial layer, which extends on top of said sacrificial region and through said first opening and said second openings; and    etching said epitaxial layer until said sacrificial region is reached.    
     
     
         15 . The process according to  claim 14 , in which, during the step of etching said epitaxial layer there are defined anchorages connected to said substrate and elastic elements connecting said body to said anchorages.  
     
     
         16 . A method for manufacturing an inertial sensor, comprising: 
 forming, on a semiconductor substrate, a sample element having a first end coupled to the substrate, the sample element being configured to break under a preselected strain; and    forming, above the semiconductor substrate, a semiconductor material body coupled to a second end of the sample element.    
     
     
         17 . The method of  claim 16  wherein the sample element has a T shape, the first end forming a cross-bar portion of the T and being coupled to the substrate at extreme ends of the crossbar, the second end extending from a central portion of the crossbar to form the T.  
     
     
         18 . The method of  claim 16 , further comprising forming an additional sample element having a first end coupled to the substrate, a second end coupled to the semiconductor material body, and configured to break under the preselected strain.  
     
     
         19 . The method of  claim 16 , further comprising forming a weakened region on the sample element, and wherein the sample element is configured to break at the weakened region under the preselected strain.  
     
     
         20 . The method of  claim 19  wherein the weakened region comprises a narrowed region of the sample element.  
     
     
         21 . A method of measuring movement of a device, comprising: 
 providing, in the device, a circuit configured to permanently change a conductive state of a conductive path in the event the device is subjected to an acceleration exceeding a preselected level;    applying a potential at first and second ends of the conductive path; and    detecting a change in the conductive state of the conductive path.    
     
     
         22 . The method of  claim 21  wherein the circuit is configured to break the conductive path.  
     
     
         23 . The method of  claim 21  wherein the device is a cellular phone.  
     
     
         24 . The method of  claim 21  wherein the preselected level corresponds to an acceleration caused by a drop of the device to an unyielding surface from a preselected height.  
     
     
         25 . The method of  claim 21  wherein the preselected level is selected to be equal to or less than an acceleration sufficient to damage the device.  
     
     
         26 . The method of  claim 21 , further comprising breaking a semiconductor structure through which the conductive path passes in the event the device is subjected to the acceleration.  
     
     
         27 . The method of  claim 26  wherein the breaking step comprises moving a first semiconductor body relative to a second semiconductor body in response to inertial forces resulting from the acceleration, the semiconductor structure being coupled at a first end thereof to the first body and at a second end to the second body, the movement of the first body causing a flexion of the structure, resulting in the breaking thereof.  
     
     
         28 . The method of  claim 27  wherein the second semiconductor body is rigidly coupled to the device.