High precision microelectromechanical capacitor with programmable voltage source

• US 7,388,247 B1
• Filed: 05/28/2003
• Issued: 06/17/2008
• Est. Priority Date: 05/28/2003
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Lagnado, Isaac, de la Houssaye, Paul R.
• Primary Examiner(s): Warren; Matthew E
• Application Number:
  US10/446,615
• Time in Patent Office: 1,847 Days
• Field of Search: 257/312, 257/532, 257/595, 257/600, 257/602, 257/E27.048, 257/E29.325, 257/E29.343, 257/E29.344, 361/277, 361/278, 361/290
• US Class Current: 257/312
• CPC Class Codes: H01G 5/019 Means for correcting the capacitance characteristics
• CPC Class Codes: H01G 5/16 using variation of distance between electrodes
• CPC Class Codes: H01L 23/5223 Capacitor integral with wiring layers
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A high precision microelectromechanical capacitor with programmable voltage source includes a monolithic MEMS device having a capacitance actuator, a trim capacitor, and a high precision, programmable voltage source. The trim capacitor has a variable capacitance value, preferably for making fine adjustments in capacitance. The capacitance actuator is preferably mechanically coupled to and electrically isolated from the trim capacitor and is used to control the capacitance value of the trim capacitor. The capacitance adjustment of the trim capacitor is non-destructive and may be repeated indefinitely. The trim capacitor may be adjusted by mechanically changing the distance between its electrodes. The programmable voltage source provides a highly accurate and stable output voltage potential corresponding to control signals for controlling the capacitance actuator. The programmable voltage source may optionally include a floating-gate transistor coupled to an amplifier for storing charge and therefore, providing a non-volatile, stable, and adjustable output voltage potential.

Claims

1. A monolithic microelectromechanical device comprising:

a trim capacitor having a continuously-adjustable capacitance value;

a capacitance actuator coupled to control said continuously-adjustable capacitance value;

wherein said trim capacitor further comprises;

a first electrode; and

a movable second electrode disposed a first distance from said first electrode, said first distance adjustable by said capacitance actuator to change said continuously-adjustable capacitance value;

wherein said capacitance actuator comprises;

a third electrode; and

a movable fourth electrode disposed a second distance from said third electrode, said second distance adjustable responsive to an electrostatic force between said third and forth electrodes corresponding to said voltage potential;

a programmable voltage source for generating a voltage potential corresponding to a control signal, wherein said voltage potential controls said capacitance actuator,

wherein said programmable voltage source includes;

an amplifier having an input and output terminal; and

a floating-gate transistor wherein a floating gate of said transistor is coupled to said input terminal for storing a charge value; and

a shared flexible dielectric layer disposed between said first and second electrodes and extending between said third and fourth electrodes, said dielectric layer being movable with respect to a substrate, said dielectric layer comprising a first surface with a first roughness disposed between said electrodes;

wherein,

said first electrode has a second surface with a second roughness;

such that said first surface opposes said second surface, thereby forming an effective area of substantial contact, said area of substantial contact being responsive to movements of said second electrode, thereby changing said continuously-adjustable capacitance value.

2. The monolithic microelectromechanical device as recited in claim 1, wherein said programmable voltage source further comprises:

means for selectively causing electrons to inject onto said floating-gate, thereby increasing said stored charge value and said voltage potential; and

means for selectively causing electrons to tunnel from said floating-gate, thereby decreasing said stored charge value and said voltage potential.

3. The monolithic microelectromechanical device as recited in claim 1, wherein said programmable voltage source further comprises a feedback capacitor coupled between said input and output terminals.

4. The monolithic microelectromechanical device as recited in claim 2, wherein said control signal comprises:

an injection control signal for initiating said electron injection; and

a tunneling control signal for initiating said electron tunneling.

5. The monolithic microelectromechanical device as recited in claim 1, wherein said capacitance actuator is mechanically coupled to and electrically isolated from said trim capacitor.

6. The monolithic microelectromechanical device as recited in claim 1, wherein said capacitance actuator has a capacitance value, said capacitance value being larger than said continuously-adjustable capacitance value.

7. The monolithic microelectromechanical device as recited in claim 1, wherein said first and third electrodes are fixed with respect to said substrate and said second and fourth electrodes are attached to said flexible dielectric layer, wherein movement of said fourth electrode causes movement of said second electrode.

8. The monolithic microelectromechanical device as recited in claim 1, wherein said capacitance actuator further comprises piezoelectric material.

9. The monolithic microelectromechanical device as recited in claim 1, wherein said programmable voltage source is non-volatile.

10. The monolithic microelectromechanical device as recited in claim 1, wherein said monolithic microelectromechanical device includes a digital to analog converter.

11. The monolithic microelectromechanical device as recited in claim 10, wherein said digital to analog converter further comprises a capacitor network comprising:

a plurality of said trim capacitors;

a plurality of said capacitance actuators;

a plurality of said programmable voltage sources; and

a plurality of fixed capacitors each coupled to at least one said trim capacitor;

wherein, the relative capacitance of each combination of said trim capacitor coupled with said fixed capacitor is substantially C, 2C, 4C, 8C, . . . , 2i−

1C, respectively, where i is the number of binary bits.

12. The monolithic microelectromechanical device as recited in claim 1, wherein said monolithic microelectromechanical device includes a SIGMA-DELTA analog to digital converter.

13. The monolithic microelectromechanical device as recited in claim 12, wherein said SIGMA-DELTA analog to digital converter further comprises:

(a) a voltage comparator for generating an output signal responsive to an analog input signal;

(b) a first integrator operably coupled to said voltage comparator, said integrator for receiving said output signal of said comparator;

(c) an analog to digital converter operably coupled to said first integrator for generating a first digital output signal responsive to said analog input signal;

(d) a digital to analog converter operably coupled to said analog to digital converter for generating an analog feedback signal to said comparator, said analog feedback signal responsive to said first digital output signal, said digital to analog converter comprising;

a plurality of said trim capacitors;

a plurality of said capacitance actuators;

a plurality of said programmable voltage sources; and

a plurality of fixed capacitors each coupled to at least one said trim capacitor;

wherein, the relative capacitance of each combination of said trim capacitor coupled with said fixed capacitor is substantially C, 2C, 4C, 8C, . . . , 2i−

1C, respectively, where i is the number of binary bits.

14. The monolithic microelectromechanical device as recited in claim 13, wherein said digital to analog converter further comprises a second integrator operably disposed between said first integrator and said analog to digital converter.

15. The monolithic microelectromechanical device as recited in claim 13, wherein said digital to analog converter further comprises a digital decimator operably coupled to said analog to digital converter for generating a second digital output signal responsive to said first digital output signal.

16. A monolithic microelectromechanical device comprising:

a trim capacitor having a continuously-adjustable capacitance value;

a capacitance actuator coupled to control said continuously-adjustable capacitance value;

wherein said trim capacitor further comprises;

a first electrode; and

a movable second electrode vertically disposed a first distance from said first electrode, said first distance adjustable by said capacitance actuator to change said continuously-adjustable capacitance value;

wherein said capacitance actuator comprises;

a third electrode; and

a movable fourth electrode vertically disposed a second distance from said third electrode, said second distance adjustable responsive to an electrostatic force between said third and forth electrodes corresponding to said voltage potential;

a programmable voltage source for generating a voltage potential corresponding to a control signal, wherein said voltage potential controls said capacitance actuator,

wherein said programmable voltage source includes;

an amplifier having an input and output terminal; and

a floating-gate transistor wherein a floating gate of said transistor is coupled to said input terminal for storing a charge value; and

a shared flexible dielectric layer disposed between said first and second electrodes and extending between said third and fourth electrodes, said dielectric layer being movable with respect to a substrate, said dielectric layer comprising a first surface with a first roughness disposed between said electrodes;

wherein,

said first electrode has a second surface with a second roughness;

such that said first surface opposes said second surface, thereby forming an effective area of substantial contact, said area of substantial contact being responsive to movements of said second electrode, thereby changing said continuously-adjustable capacitance value.