Method for making micromechanical structures having at least one lateral, small gap therebetween and micromechanical device produced thereby

Abstract

A method and resulting formed device are disclosed wherein the method combines polysilicon surface-micromachining with metal electroplating technology to achieve a capacitively-driven, lateral micromechanical resonator with submicron electrode-to-resonator capacitor gaps. Briefly, surface-micromachining is used to achieve the structural material for a resonator, while conformal metal-plating is used to implement capacitive transducer electrodes. This technology makes possible a variety of new resonator configurations, including disk resonators and lateral clamped-clamped and free-free flexural resonators, all with significant frequency and Q advantages over vertical resonators. In addition, this technology introduces metal electrodes, which greatly reduces the series resistance in electrode interconnects, thus, minimizing Q-loading effects while increasing the power handling ability of micromechanical resonators.

What is claimed is:  
     
         1 . A method for making micromechanical structures having at least one lateral gap therebetween, the method comprising: 
 providing a substrate;    surface micromachining the substrate to form a first micromechanical structure having a first vertical sidewall and a sacrificial spacer layer on the first vertical sidewall;    forming a second micromechanical structure on the substrate, the second micromechanical structure including a second vertical sidewall separated from the first vertical sidewall by the spacer layer; and    removing the spacer layer to form a first lateral gap between the first and second micromechanical structures.    
     
     
         2 . The method as claimed in  claim 1  wherein the step of surface micromachining further forms a third vertical sidewall on the first micromechanical structure with the sacrificial spacer layer thereon and wherein the method further comprises forming a third micromechanical structure including a fourth vertical sidewall separated from the third vertical sidewall by the spacer layer and wherein the step of removing further forms a second lateral gap between the first and third micromechanical structures.  
     
     
         3 . The method as claimed in  claim 1  wherein the second micromechanical structure includes an electrode.  
     
     
         4 . The method as claimed in  claim 3  wherein the first micromechanical structure includes a resonator and wherein the first lateral gap is an electrode-to-resonator capacitive gap.  
     
     
         5 . The method as claimed in  claim 1  wherein the step of forming includes the step of plating metal on the substrate and wherein the second micromechanical structure is a plated metal electrode.  
     
     
         6 . The method as claimed in  claim 5  further comprising preventing metal from being plated on the first micromechanical structure.  
     
     
         7 . The method as claimed in  claim 1  wherein the first lateral gap is a submicron gap.  
     
     
         8 . A micromechanical device comprising: 
 a substrate;    a first micromechanical structure supported on the substrate and having a first vertical sidewall;    a second micromechanical structure supported on the substrate and having a second vertical sidewall; and    a first submicron lateral gap between the first and second vertical sidewalls to increase electromechanical coupling of the first and second micromechanical structures.    
     
     
         9 . The device as claimed in  claim 8  wherein the second micromechanical structure comprises an electrode.  
     
     
         10 . The device as claimed in  claim 9  wherein the electrode is a metal electrode.  
     
     
         11 . The device as claimed in  claim 10  wherein the metal electrode is a plated metal electrode.  
     
     
         12 . The device as claimed in  claim 8  wherein the first micromechanical structure is a lateral resonator.  
     
     
         13 . The device as claimed in  claim 8  wherein the first micromechanical structure has a third vertical sidewall and wherein the device further comprises a third micromechanical structure supported on the substrate and having a fourth vertical sidewall and a second submicron lateral gap between the third and fourth vertical sidewalls to increase electromechanical coupling of the first and third micromechanical structures.  
     
     
         14 . The device as claimed in  claim 12  wherein the lateral resonator is a polysilicon resonator.  
     
     
         15 . The device as claimed in  claim 12  wherein the lateral resonator is a flexural-mode resonator beam.  
     
     
         16 . The device as claimed in  claim 8  wherein the substrate is a semiconductor substrate.  
     
     
         17 . The device as claimed in  claim 16  wherein the semiconductor substrate is a silicon substrate.  
     
     
         18 . The device as claimed in  claim 8  wherein the first submicron lateral gap is a capacitive gap.  
     
     
         19 . The device as claimed in  claim 13  wherein the second and third micromechanical structures are electrodes.  
     
     
         20 . The device as claimed in  claim 19  wherein the electrodes are metal electrodes.  
     
     
         21 . The device as claimed in  claim 20  wherein the metal electrodes are plated metal electrodes.  
     
     
         22 . The device as claimed in  claim 13  wherein the first and second submicron lateral gaps are capacitive gaps.  
     
     
         23 . The method as claimed in  claim 3  wherein the step of forming includes the step of growing the electrode via selective epoxy growth.  
     
     
         24 . The method as claimed in  claim 3  wherein the step of forming includes the steps of depositing polysilicon and etching the polysilicon to form the electrode.  
     
     
         25 . The device as claimed in  claim 9  wherein the electrode is a polysilicon electrode.  
     
     
         26 . The device as claimed in  claim 9  wherein the electrode is an SEG-grown electrode.