Linear accelerometer

Abstract

A linear accelerometer is provided having a support substrate, fixed electrodes having fixed capacitive plates, and a movable inertial mass having movable capacitive plates capacitively coupled to the fixed capacitive plates. Adjacent capacitive plates vary in height. The accelerometer further includes support tethers for supporting the inertial mass and allowing movement of the inertial mass upon experiencing a linear acceleration along a sensing axis. The accelerometer has inputs and an output for providing an output signal which varies as a function of the capacitive coupling and is indicative of both magnitude and direction of vertical acceleration along the sensing Z-axis. A microsensor fabrication process is also provided which employs a top side mask and etch module.

1 . A linear accelerometer comprising: 
 a support substrate;    a first fixed electrode comprising one or more first fixed capacitive plates fixed to the support structure and having a first height;    a second fixed electrode comprising one or more second fixed capacitive plates fixed to the support structure and having a second height;    a movable inertial mass comprising one or more first movable capacitive plates capacitively coupled to the one or more first fixed capacitive plates and one or more second movable capacitive plates capacitively coupled to the one or more second fixed capacitive plates, wherein the one or more first movable capacitive plates have a third height greater than the first height of the one or more first fixed capacitive plates, and the one or more second movable capacitive plates have a fourth height less than the second height of the one or more second fixed capacitive plates;    a support structure for supporting the movable inertial mass and allowing linear movement of the inertial mass relative to the support substrate upon experiencing a linear acceleration along a sensing axis;    an input for providing input signals to one of the first and second fixed and first and second movable capacitive plates; and    an output for receiving an output signal from the other of the first and second fixed and first and second movable capacitive plates which varies as a function of capacitive coupling and is indicative of magnitude and direction of acceleration along the sensing axis.    
   
   
       2 . The linear accelerometer as defined in  claim 1 , wherein the input comprises a first input signal applied to the first fixed electrode and a second input signal applied to the second fixed electrode, and wherein the output is electrically coupled to the movable inertial mass.  
   
   
       3 . The linear accelerometer as defined in  claim 1 , wherein the first fixed capacitive plates are arranged substantially parallel to the first movable capacitive plates, and the second fixed capacitive plates are arranged substantially parallel to the second movable capacitive plates.  
   
   
       4 . The linear accelerometer as defined in  claim 1 , wherein the support structure comprises a plurality of tethers.  
   
   
       5 . The linear accelerometer as defined in  claim 4 , wherein the plurality of tethers comprises four L-shaped tethers.  
   
   
       6 . The linear accelerometer as defined in  claim 1 , wherein the substrate comprises a silicon substrate.  
   
   
       7 . The linear accelerometer as defined in  claim 1 , wherein the first and second fixed capacitive plates each comprises a plurality of capacitive plates, and wherein the first and second movable capacitive plates each comprises a plurality of capacitive plates.  
   
   
       8 . The linear accelerometer as defined in  claim 7  further comprising: 
 a third fixed electrode comprising one or more third fixed capacitive plates; and    a fourth fixed electrode comprising one or more fourth fixed capacitive plates, wherein the movable mass further comprises one or more third movable capacitive plates forming a capacitive coupling with the third fixed capacitive plates, and one or more fourth movable capacitive plates forming a capacitive coupling with the fourth fixed capacitive plates, and further wherein a height of the third fixed capacitive plates is greater than a height of the third movable capacitive plates and a height of the fourth fixed capacitive plates is less than a height of the fourth movable capacitive plates.    
   
   
       9 . The accelerometer as defined in  claim 1 , wherein the sensing axis is perpendicular to the support substrate.  
   
   
       10 . The accelerometer as defined in  claim 1 , wherein adjacent fixed and movable capacitive plates are separated by first and second gaps.  
   
   
       11 . A linear accelerometer comprising: 
 a support substrate;    a first bank of variable capacitors formed of one or more first fixed capacitive plates and one or more first movable capacitive plates, wherein the first fixed capacitive plates have a height greater than a height of the first movable capacitive plates;    a second bank of variable capacitors formed of one or more second fixed capacitive plates and one or more second movable capacitive plates, wherein the second movable capacitor plates have a height greater than a height of the second fixed capacitive plates;    an inertial mass that is linearly movable in response to linear acceleration along a sensing axis, wherein the inertial mass includes the first and second movable capacitive plates;    a support structure for supporting the inertia mass and allowing linear movement of the inertial mass upon experiencing a linear acceleration along the sensing axis;    a first input for supplying an input signal to the first bank of variable capacitors;    a second input for supplying an input signal to the second bank of variable capacitors; and    an output for sensing an output signal from the first and second variable capacitors indicative of magnitude and direction of linear acceleration sensed along the sensing axis in response to linear movement of the inertial mass.    
   
   
       12 . The linear accelerometer as defined in  claim 11  further comprising: 
 a third bank of variable capacitors formed of a third plurality of fixed capacitive plates and a third plurality of movable capacitive plates, wherein the third plurality of fixed capacitive plates have a height greater than a height of the third plurality of movable capacitive plates; and    a fourth bank of variable capacitors formed of a fourth plurality of fixed capacitive plates and a fourth plurality of movable capacitive plates, wherein the fourth plurality of movable capacitive plates have a height greater than a height of the fourth plurality of fixed capacitive plates.    
   
   
       13 . The linear accelerometer as defined in  claim 11 , wherein the first and second input signals are clocked signals that are out-of-phase with each other.  
   
   
       14 . The linear accelerometer as defined in  claim 11 , wherein the first fixed capacitive plates are arranged substantially parallel to adjacent ones of the first movable capacitive plates and the second fixed capacitive plates are arranged substantially parallel to adjacent ones of the second movable capacitive plates.  
   
   
       15 . The linear accelerometer as defined in  claim 11 , wherein the support structure comprises a plurality of tethers.  
   
   
       16 . The linear accelerometer as defined in  claim 15 , wherein the plurality of tethers comprises four L-shaped tethers.  
   
   
       17 . The linear accelerometer as defined in  claim 11 , wherein the substrate comprises a silicon substrate.  
   
   
       18 . The accelerometer as defined in  claim 11 , wherein the sensing axis is perpendicular to the support substrate.  
   
   
       19 . The accelerometer as defined in  claim 11 , wherein adjacent fixed and movable capacitive plates are separated by first and second gaps.