Laterally Vibrating Bulk Acoustic Wave Resonator

Abstract

A laterally vibrating bulk acoustic wave (LVBAW) resonator includes a piezoelectric plate sandwiched between first and second metal layers. The second metal layer is patterned into an interdigital transducer (IDT) with comb-shaped electrodes having interlocking fingers. The width and pitch of the fingers of the electrodes determine the resonant frequency. A combined thickness of the first and second metal layers and the piezoelectric layer is less than the pitch of the interlocking fingers.

What is claimed is: 
     
         1 . A method of fabricating a microelectromechanical system (MEMS) device, comprising:
 forming a piezoelectric layer on a substrate;   forming a metal layer on a portion of the piezoelectric layer; and   patterning a portion of the metal layer into an interdigital transducer (IDT) and a reflector on a side of the IDT, in which the IDT and the reflector are part of a laterally vibrating bulk acoustic wave (LVBAW) resonator, the IDT includes a comb-shaped electrode having fingers, the reflector is spaced from the IDT by a distance based on a sum of first and second terms, the first term is an odd multiple of a quarter of a wavelength of a signal having a target resonant frequency of the LVBAW resonator, and the second term is half of a spacing between the fingers.   
     
     
         2 . The method of  claim 1 , wherein the portion of the metal layer is a first portion, the LVBAW resonator is a first LVBAW resonator, the IDT is a first IDT, the reflector is a first reflector, the side is a first side, the comb-shaped electrode is a first comb-shaped electrode, the distance is a first distance, the wavelength is a first wavelength, the target resonant frequency is a first target resonant frequency, the fingers are first fingers, and the method further comprises:
 patterning a second portion of the metal layer into a second IDT and a second reflector on a second side of the second IDT, in which the second IDT and the second reflector are part of a second LVBAW resonator, the second IDT includes a second comb-shaped electrode having second fingers, the second reflector is spaced from the second IDT by a second distance based on a sum of third and fourth terms, the third term is an odd multiple of a quarter of a second wavelength of a signal having a second target resonant frequency of the second LVBAW resonator, and the fourth term is half of spacing between the second fingers.   
     
     
         3 . The method of  claim 2 , wherein patterning the first portion of the metal layer and patterning the second portion of the metal layer are performed with a metal mask. 
     
     
         4 . The method of  claim 2 , wherein patterning the first portion of the metal layer and patterning the second portion of the metal layer are performed simultaneously. 
     
     
         5 . The method of  claim 2 , wherein patterning the first portion of the metal layer and patterning the second portion of the metal layer are performed on different batches of LVBAW resonator devices. 
     
     
         6 . The method of  claim 1 , wherein patterning the portion of the metal layer is performed by a lithographic process. 
     
     
         7 . The method of  claim 1 , wherein patterning the portion of the metal layer is performed by a direct write lithographic process. 
     
     
         8 . The method of  claim 1 , wherein the reflector is a first reflector, the metal layer is a first metal layer, and the method further comprises:
 forming a second reflector on a portion of the substrate; and   forming a second metal layer on a portion of the second reflector,   wherein the piezoelectric layer is formed on the second metal layer.   
     
     
         9 . The method of  claim 8 , wherein the second reflector includes a Bragg mirror. 
     
     
         10 . The method of  claim 8 , wherein the second metal layer includes a non-electrified floating plate, the IDT includes first and second electrodes, and the method further comprises coupling one of the first or second electrodes to a ground terminal. 
     
     
         11 . The method of  claim 8 , further comprising coupling the second metal layer to a ground terminal. 
     
     
         12 . The method of  claim 1 , wherein the comb-shaped electrode has a finger to finger pitch based on half of the wavelength. 
     
     
         13 . The method of  claim 1 , wherein a respective width of each finger is less than half of the wavelength of the signal. 
     
     
         14 . The method of  claim 1 , wherein the wavelength is based on a propagation speed of the signal between the IDT and the reflector. 
     
     
         15 . The method of  claim 1 , wherein the reflector include metal strips that are electrically isolated from each other. 
     
     
         16 . The method of  claim 1 , wherein adjacent fingers are separated by a space; and
 wherein a width of each finger is wider than the space.   
     
     
         17 . The method of  claim 1 , wherein adjacent fingers are separated by a space; and
 wherein a width of each finger is narrower than the space.