Enhanced control of shuttle mass motion in mems devices

Abstract

A MEMS device and a method of forming the same. A disclosed method includes: providing a silicon substrate layer, a buried oxide layer and a device silicon layer; using a microfabrication process to pattern a set of device features on the device silicon layer including a shuttle mass and an anchor frame; removing the silicon substrate layer and buried oxide below the shuttle mass; placing a shadow mask on a surface of the device silicon layer, wherein the shadow mask has a microscale opening to expose at least one device feature; and forming a nanoscale stopper on a sidewall of the at least one device feature by depositing a deposition material through the opening in a controlled manner.

What is claimed is: 
     
         1 . A microelectronic mechanical system (“MEMS”) device, comprising:
 a movable feature that moves relative to a fixed feature; 
 a nanoscale stopper that engages and prevents the movable feature from touching the fixed feature as the movable feature moves toward the fixed feature, wherein the nanoscale stopper has a thickness of less than 1000 nanometers; and 
 a soft stopper that engages the movable feature before the movable feature engages the nanoscale stopper, wherein the soft stopper slows the movable feature relative to the fixed feature. 
 
     
     
         2 . The MEMS device of  claim 1 , wherein:
 the movable feature comprises a plurality of movable electrodes extending from a shuttle mass; and   the fixed feature comprises a plurality of fixed electrodes interdigitated with the plurality of movable electrodes.   
     
     
         3 . The MEMS device of  claim 2 , wherein the nanoscale stopper is positioned on sidewalls of the shuttle mass and an adjacent anchor frame. 
     
     
         4 . The MEMS device of  claim 2 , wherein the nanoscale stopper is positioned on sidewalls of the plurality of movable electrodes and plurality of fixed electrodes. 
     
     
         5 . The MEMS device of  claim 1 , wherein the soft stopper comprises at least one cantilever beam positioned on an anchor frame. 
     
     
         6 . The MEMS device of  claim 5 , wherein the at least one cantilever beam includes an end region having a protrusion located to engage a contact zone on the shuttle mass. 
     
     
         7 . The MEMS device of  claim 1 , wherein the nanoscale stopper is fabricated from a material selected from a group consisting of: silicon oxide (“SiO 2 ”), silicon nitride (“SiN”), and paralyne. 
     
     
         8 . A wireless microsensor, comprising:
 a sensor for sensing an environmental condition; and   a microelectronic mechanical system (“MEMS”) device for harvesting energy and powering the sensor, wherein the MEMS device comprises:
 a movable feature that moves relative to a fixed feature; 
 a nanoscale stopper that engages and prevents the movable feature from touching the fixed feature as the movable feature moves toward the fixed feature, wherein the nanoscale stopper has a thickness of less than 1000 nanometers; and 
 a soft stopper that engages the movable feature before the movable feature engages the nanoscale stopper, wherein the soft stopper slows the movable feature relative to the fixed feature. 
   
     
     
         9 . The wireless microsensor of  claim 8 , wherein:
 the movable feature comprises a plurality of movable electrodes extending from a shuttle mass; and   the fixed feature comprises a plurality of fixed electrodes interdigitated with the plurality of movable electrodes.   
     
     
         10 . The wireless microsensor of  claim 9 , wherein the nanoscale stopper is positioned on sidewalls of the shuttle mass and an adjacent anchor frame. 
     
     
         11 . The wireless microsensor of  claim 9 , wherein the nanoscale stopper is positioned on sidewalls of the movable electrodes and fixed electrodes. 
     
     
         12 . The wireless microsensor of  claim 9 , wherein the soft stopper comprises at least one cantilever beam positioned on an anchor frame. 
     
     
         13 . The wireless microsensor of  claim 12 , wherein the at least one cantilever beam includes an end region having a protrusion located to engage a contact zone on the shuttle mass.