Method of making a high precision microelectromechanical capacitor with programmable voltage source

• US 7,232,699 B1
• Filed: 03/15/2005
• Issued: 06/19/2007
• 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): Geyer; Scott B.
• Assistant Examiner(s): Ullah; Elias
• Application Number:
  US11/081,892
• Time in Patent Office: 826 Days
• Field of Search: 438/455, 438/456, 438/48, 438/106
• US Class Current: 438/48
• 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 Method of Making a High Precision Microelectromechanical Capacitor with Programmable Voltage Source includes steps for forming 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 method of forming a monolithic microelectromechanical device comprising the steps of:

(a) forming a trim capacitor having a continuously-adjustable capacitance value on a substrate;

(b) forming a capacitance actuator on said substrate mechanically coupled to and electrically isolated from said trim capacitor, said capacitance actuator for adjusting said continuously-adjustable capacitance value responsive to a voltage potential, the step of forming a capacitance actuator including the step of coupling a dielectric layer to the trim capacitor for continuously-adjusting the capacitance value; and

(c) forming a programmable voltage source on said substrate for generating said voltage potential corresponding to a control signal.

2. The method of forming a monolithic microelectromechanical device as recited in claim 1, wherein step (c) further comprises the steps of:

(c1) forming an amplifier, on said substrate, having an input and output terminal;

(c2) forming a floating-gate transistor, on said substrate, coupled to said input terminal for storing a charge value;

(c3) forming means for selectively causing electrons to inject onto said floating-gate, on said substrate, thereby increasing said stored charge value and said voltage potential; and

(c4) forming means for selectively causing electrons to tunnel from said floating-gate, on said substrate, thereby decreasing said stored charge value and said voltage potential.

3. The method of forming a monolithic microelectromechanical device as recited in claim 2, wherein step (c) further comprises forming a feedback capacitor, on said substrate, coupled between said input and output terminals.

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

(a) an injection control signal for initiating said electron injection; and

(b) a tunneling control signal for initiating said electron tunneling.

5. The method of forming a monolithic microelectromechanical device as recited in claim 1, wherein step (a) further comprises the steps of:

(a1) forming a first electrode on said substrate; and

(a2) forming a movable second electrode laterally disposed a first distance from said first electrode, said first distance adjustable by said capacitance actuator to change said continuously-adjustable capacitance value.

6. The method of forming a monolithic microelectromechanical device as recited in claim 5, wherein step (b) further comprises the steps of:

(b1) forming a third electrode on said substrate; and

(b2) forming a movable fourth electrode laterally disposed a second distance from said third electrode, said second distance adjustable responsive to an electrostatic force between said third and fourth electrodes corresponding to said voltage potential.

7. The method of forming a monolithic microelectromechanical device as recited in claim 6, wherein the step of coupling the dielectric layer comprises the step of forming the dielectric layer so that the dielectric layer is disposed between said first and second electrodes and extending between said third and fourth electrodes, said dielectric layer being flexibly movable with respect to a substrate.

8. The method of forming a monolithic microelectromechanical device as recited in claim 7, 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.

9. The method of forming a monolithic microelectromechanical device as recited in claim 1, wherein said monolithic microelectromechanical device includes a digital to analog converter.

10. The method of forming a monolithic microelectromechanical device as recited in claim 9, further comprising the steps:

(a) repeating steps (a)–

(c), thereby forming a plurality of said trim capacitors, said capacitance actuators, and said programmable voltage sources; and

(b) forming a plurality of fixed capacitors on said substrate each coupled to at least one of said trim capacitors.

11. The method of forming a monolithic microelectromechanical device as recited in claim 10, further comprising the step of adjusting each said programmable voltage source, such that the relative capacitance of each combination of said trim capacitor coupled with said fixed capacitor is substantially C, 2C, 4C, 8C, . . . , 2ⁱ⁻

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

12. The method of forming a monolithic microelectromechanical device as recited in claim 11, further comprising the steps of:

(a) applying a sine wave, in digital format, to said monolithic microelectromechanical device;

(b) generating an output signal responsive to measurements of quantization error, signal-to-noise ratio, and distortion ratio; and

(c) adjusting said programmable voltage source responsive to said measurements, thereby changing said continuously-adjustable capacitance value.