Selectable capacitance circuit

• US 20060067028A1
• Filed: 05/20/2005
• Published: 03/30/2006
• Est. Priority Date: 09/27/2004
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Floyd, Philip D.
• Granted Patent: US 7,657,242 B2
• Time in Patent Office: Days
• US Class Current: 361/278
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833
• CPC Class Codes: G09G 3/3466 based on interferometric effect
• CPC Class Codes: G09G 3/3473 based on light coupled out of a light guide, e.g. due to scattering, by contracting the light guide with external means
• CPC Class Codes: H01G 5/18 due to change in inclination, e.g. by flexing, by spiral wrapping
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations

Abstract

A voltage-controlled capacitor and methods for forming the same are described. A mechanical conductor membrane of the voltage-controlled capacitor is movable to and from a first position and a second position. An amount of capacitance can vary with the movement of the mechanical conductor membrane. A microelectromechanical systems (MEMS) voltage-controlled capacitor can be used in a variety of applications, such as, but not limited to, RF switches and RF attenuators.

Claims

1. A voltage-controlled capacitor comprising:

a substrate assembly with an input terminal, a control terminal, and a voltage reference terminal;

voltage reference lines disposed on the substrate assembly, wherein at least one of the voltage reference lines is coupled to the voltage reference terminal;

a mechanical conductor membrane spaced above the substrate assembly and coupled directly or indirectly to one or more of the voltage reference lines at opposing ends of the mechanical conductor membrane so that the opposing mechanical conductor membrane is anchored at two or more ends and so that the mechanical conductor membrane is AC coupled to the one or more voltage reference lines, wherein at least a portion of the mechanical conductor membrane is movable to and from a first position a first distance from a surface of the substrate assembly and a second position a second distance from the surface of the substrate assembly;

one or more posts disposed between the substrate assembly and the mechanical conductor membrane and disposed between the two or more ends anchoring the mechanical conductor membrane, where the one or more posts support the mechanical conductor membrane;

a signal conductor disposed on the substrate assembly, where the signal conductor is DC coupled to the control terminal, wherein a voltage on the control terminal at least partially controls the position of the mechanical conductor membrane;

a layer of dielectric material disposed between a top surface of the signal conductor and the mechanical conductor membrane, where a gap exists between at least one of (a) the mechanical conductor membrane and the layer of dielectric material or (b) the layer of dielectric material and the signal conductor when the mechanical conductor membrane is in the first position, and substantially no gap exists when the mechanical conductor membrane is in the second position; and

a coupling capacitor with a first terminal and a second terminal, where the first terminal is coupled to the input terminal and where the second terminal is coupled to the signal conductor.

2. The capacitor as defined in claim 1 wherein the signal conductor comprises a non-transparent material.

3. The capacitor as defined in claim 1 wherein a material for the signal conductor comprises at least one of silver, copper, gold, aluminum, or combinations thereof.

4. The capacitor as defined in claim 1 wherein a material for the signal conductor has a resistivity of less than 1×

10<sup>−

6</sup> ohm-meters (Ω

-m).

5. The capacitor as defined in claim 1 wherein a material for the signal conductor has a resistivity of less than 0.1×

10<sup>−

6</sup> ohm-meters (Ω

-m).

6. The capacitor as defined in claim 1 wherein the layer of dielectric material is disposed directly on the top surface of the signal layer.

7. The capacitor as defined in claim 1, further comprising an insulator disposed between at least one end of the mechanical conductor membrane and a corresponding voltage reference line.

8. The capacitor as defined in claim 7 wherein the voltage reference line corresponds to a signal ground but is configured to have a DC bias.

9. The capacitor as defined in claim 1 wherein the voltage reference terminal is configured to be coupled to a signal ground reference.

10. The capacitor as defined in claim 1, further comprising an output terminal coupled to an opposite end of the signal conductor than the input terminal.

11. The capacitor as defined in claim 1, wherein the capacitor is embodied in an RF attenuator.

12. The capacitor as defined in claim 1, wherein the layer of dielectric material disposed between the top surface of the signal conductor and the mechanical conductor membrane has a thickness in the range of 0.1 to 0.5 micrometers.

13. The capacitor as defined in claim 1, wherein the signal conductor has a thickness in the range of 0.5 to 5 micrometers.

14. A capacitor having a selectable capacitance comprising:

a substrate assembly;

a signal conductor on the substrate assembly, wherein the signal conductor forms a first electrode for the capacitor;

a layer of dielectric material covering at least an upper surface of the signal conductor; and

one or more mechanical conductor membranes spaced above the substrate assembly such that the signal conductor is disposed between the substrate assembly and the one or more mechanical conductor membranes, where the one or more mechanical conductor membranes form a second electrode for the capacitor, wherein at least two or more portions of the one or more mechanical conductor membranes are at least partially independently movable from a low capacitance position and a high capacitance position such attainable positions include a low capacitance position for at least a selected two portions of the mechanical conductor membranes, a high capacitance position for the selected two portions of the mechanical conductor membranes, and an intermediate capacitance configuration in which one of the selected two portions is in the high capacitance position and the other is in the low capacitance position, wherein the selected position is at least partially determined by a voltage on the signal conductor.

15. The capacitor as defined in claim 14, wherein at least two or more portions correspond to a single continuous segment of the mechanical conductor membrane, and wherein the two or more portions differ by at least one of (a) a presence or absence of posts disposed between the substrate assembly and the segment of the mechanical conductor membrane, (b) a difference in height of posts, (c) a difference in spacing among posts, or (d) combinations thereof.

16. The capacitor as defined in claim 14, wherein at least two or more portions of the one or more mechanical conductor membranes correspond to separate segments of the mechanical conductor membrane forming a common electrode coupled to a signal ground, where the separate segments are DC isolated from another and coupled to separate biases for independent control of the separate segments.

17. The capacitor as defined in claim 14, wherein a plurality of signal conductors and a plurality of multiple segments of the mechanical conductor membranes are arranged in rows and columns.

18. An RF device, comprising:

a conductive line configured to carry an RF signal; and

a deformable membrane having at least two actuatable positions for selectively filtering the RF signal.

19. The RF device as defined in claim 18, wherein the deformable membrane comprises two or more separate membranes.

20. The RF device as defined in claim 18, wherein the RF device is configured such that the at least two actuatable positions are independently actuatable.

21. The RF device as defined in claim 18, further comprising:

a display;

a processor that is in electrical communication with said display, said processor being configured to process image data;

a memory device in electrical communication with said processor.

22. The RF device as defined in claim 21, further comprising:

a first controller configured to send at least one signal to said display; and

a second controller configured to send at least a portion of said image data to said first controller.

23. The RF device as defined in claim 21, further comprising an image source module configured to send said image data to said processor.

24. The RF device as defined in claim 23, wherein said image source module comprises at least one of a receiver, transceiver, and transmitter.

25. The RF device as defined in claim 21, further comprising an input device configured to receive input data and to communicate said input data to said processor.

26. A capacitor having a selectable capacitance, the capacitor comprising:

at least two electrodes spaced apart by a gap; and

means for adjusting the gap to select the capacitance.

27. The capacitor as defined in claim 26, wherein the means for adjusting the gap further comprises:

means for selecting a DC bias; and

means for applying the DC bias to the at least two electrodes.

28. The capacitor as defined in claim 26, wherein the means for adjusting the gap comprises means for adjusting a plurality of gaps between a conductive line configured to carry an RF signal and a plurality of electrodes.