Method of fabricating a high Q - large tuning range micro-electro mechanical system (MEMS) varactor for broadband applications

Abstract

A Micro Electro-Mechanical System (MEMS) varactor ( 100, 200 ) having a bottom electrode ( 116 ) formed over a substrate ( 112 ) and a dielectric material ( 130 ) disposed over the bottom electrode ( 116 ). A pull-down electrode ( 122 ) is formed over spacer ( 120 ) and the dielectric material ( 130 ). The MEMS varactor ( 100, 200 ) is adapted to operate in a stiction mode, with at least a portion of pull-down electrode ( 122 ) in contact with dielectric material ( 130 ). The MEMS varactor ( 100, 200 ) has a high Q, large tuning range, and high sensitivity.

What is claimed is:  
     
         1 . A Micro Electro-Mechanical System (MEMS) varactor, comprising: 
 a bottom electrode formed over a substrate;    a dielectric material disposed over said bottom electrode;    a spacer proximate said bottom electrode; and    a pull-down electrode over said spacer and said dielectric material, wherein said varactor is adapted to operate in a stiction mode.    
     
     
         2 . The MEMS varactor according to  claim 1  wherein a first voltage signal applied across said bottom electrode and said pull-down electrode produces a first capacitance.  
     
     
         3 . The MEMS varactor according to  claim 2  wherein said a second voltage signal applied across said bottom electrode and said pull-down electrode produces a second capacitance.  
     
     
         4 . The MEMS varactor according to  claim 3  wherein said pull-down electrode maintains contact with said dielectric materal over a range of voltage signals.  
     
     
         5 . The MEMS varactor according to  claim 4  wherein said range of voltage signals is from approximately 3 V to 10 V, wherein a capacitance in the range of 13 to 25 pF is produceable by said MEMS varactor in response to said range of voltage signals.  
     
     
         6 . The MEMS varactor according to  claim 4  further comprising an insulating layer disposed over said substrate beneath said bottom electrode, wherein a distance D 1  is defined between said insulating layer and said pull-down electrode.  
     
     
         7 . The MEMS varactor according to  claim 6  wherein said distance D 1  is approximately 0.5-2.0 micrometers.  
     
     
         8 . The MEMS varactor according to  claim 6  wherein said distance D 1  is greater than 2.0 micrometers.  
     
     
         9 . A Micro Electro-Mechanical System (MEMS) varactor, comprising: 
 a bottom electrode formed over a substrate;    a dielectric material disposed over said bottom electrode;    a spacer proximate said bottom electrode; and    a pull-down electrode over said spacer and said dielectric material, wherein said varactor is adapted to operate in a stiction mode, wherein a voltage signal applied across said bottom electrode and said pull-down electrode produces a capacitance.    
     
     
         10 . The MEMS varactor according to  claim 9  wherein said pull-down electrode maintains contact with said dielectric materal over a range of voltage signals in said stiction mode.  
     
     
         11 . The MEMS varactor according to  claim 10  wherein said range of voltage signals is from approximately 3 V to 10 V, wherein a capacitance in the range of 13 to 25 pF is produceable by said MEMS varactor in response to said range of voltage signals.  
     
     
         12 . The MEMS varactor according to  claim 11  further comprising an insulating layer disposed over said substrate beneath said bottom electrode, wherein a distance D 1  is defined between said insulating layer and said pull-down electrode.  
     
     
         13 . The MEMS varactor according to  claim 12  wherein said distance D 1  is approximately 0.5-2.0 micrometers.  
     
     
         14 . The MEMS varactor according to  claim 12  wherein said distance D 1  is greater than 2.0 micrometers.  
     
     
         15 . A method of manufacturing a MEMS varactor, comprising: 
 depositing an insulator on a substrate;    forming a bottom electrode on said insulator;    depositing a dielectric material over said bottom electrode;    forming a spacer over said insulator;    forming a pull-down electrode over said spacer and said dielectric material, wherein said varactor is adapted to operate in a stiction mode.    
     
     
         16 . The method according to  claim 15  wherein said pull-down electrode contacts at least a portion of said dielectric material in said stiction mode.  
     
     
         17 . The method according to  claim 15  wherein a distance D 1  is defined between said insulating layer and said pull-down electrode.  
     
     
         18 . The MEMS varactor according to  claim 6  wherein said distance D 1  is approximately 0.5-2.0 micrometers.  
     
     
         19 . The MEMS varactor according to  claim 6  wherein said distance D 1  is greater than 2 micrometers.  
     
     
         20 . A method of operating a MEMS varactor having a bottom electrode formed on a substrate, a dielectric material disposed over the bottom electrode, a spacer formed on the substrate supporting a pull-down electrode, wherein a voltage applied across the bottom electrode and the pull-down electrode responsively changes the capacitance of the varactor, comprising: 
 applying a voltage signal across the bottom electrode and the pull-down electrode to produce a predetermined capacitance across said bottom and pull-down electrode, wherein at least a portion of said pull-down electrode is adapted to contact said dielectric material during a stiction mode.    
     
     
         21 . The method according to  claim 20  wherein the area of said pull-down electrode portion in contact with said dielectric material varies responsively to changes in said voltage signal.  
     
     
         22 . The method according to  claim 21  wherein said applying a voltage signal comprises applying a voltage of approximately 3 V to 10 V to produce a varactor capacitance in the range of 13 to 25 pF.