MEMS piezoelectric longitudinal mode resonator

Abstract

A longitudinal mode resonator that includes a substrate and a bar that is suspended relative to the substrate. The bar is suspended such that it is free to expand and contract longitudinally in response to the application of an electric field across its thickness. The expansion and contraction of the bar achieves resonance in response to the field having a frequency substantially equal to the fundamental frequency of the bar.

1 . A method of fabricating a MEMS piezoelectric resonator having a predetermined resonant frequency, the method comprising the steps of: 
 forming a stack of layers on a substrate, the stack having a top layer and comprising at least one piezoelectric material layer;    setting the predetermined frequency of the resonator by selecting a pattern mask having a length that dictates the frequency, and applying the mask to the top layer of the stack; and    etching a plurality of layers of the stack based on the pattern mask, beginning from the top, to shape the resonator.    
   
   
       2 . The method of  claim 1  wherein the stack comprises: 
 a first metal electrode layer;    a piezoelectric bar layer; and    a second metal electrode layer.    
   
   
       3 . The method of  claim 2  wherein the stack further comprises an insulating layer.  
   
   
       4 . The method of  claim 2  further comprising applying an etchant to space at least a part of the stack from the substrate.  
   
   
       5 . The method of  claim 1  wherein after the layers of the stack are etched, the method further comprises etching individual layers of the stack.  
   
   
       6 . The method of  claim 1  further comprising, after the layers of the stack are etched, etching individual layers of the stack to define at least one current stop in one of the first and second metal electrode layers.  
   
   
       7 . The method of  claim 6  wherein the step of etching individual layers of the stack to form a current stop in one of the first and second metal electrode layers further comprises applying a voltage to one of the first and second metal electrodes.  
   
   
       8 . The method of  claim 1  further comprising, after the layers of the stack are etched: 
 etching the first and second metal electrode layers to form at least one current stop and one undesired current stop; and    applying a conducting patch to fill the undesired current stop.