METHOD OF USING A PLURALITY OF SMALLER MEMS DEVICES TO REPLACE A LARGER MEMS DEVICE

• US 20100116632A1
• Filed: 11/09/2009
• Published: 05/13/2010
• Est. Priority Date: 11/07/2008
• Status: Active Grant

• Current Assignee: Qorvo US, Inc. (Qorvo, Inc.)
• Original Assignee: Cavendish Kinetics Inc (Qorvo, Inc.)
• Inventors: Gaddi, Roberto, Unamuno, Anartz, Van Kampen, Robertus Petrus, Knipe, Richard L., Joshi, Vikram, SMITH, CHARLES GORDON
• Granted Patent: US 8,861,218 B2
• Time in Patent Office: Days
• US Class Current: 200/181
• CPC Class Codes: B81B 2201/0221 Variable capacitors
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2207/053 of movable structures
• CPC Class Codes: B81B 7/04 Networks or arrays of similar microstructural devices
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass
• 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

Embodiments disclosed herein generally include using a large number of small MEMS devices to replace the function of an individual larger MEMS device or digital variable capacitor. The large number of smaller MEMS devices perform the same function as the larger device, but because of the smaller size, they can be encapsulated in a cavity using complementary metal oxide semiconductor (CMOS) compatible processes. Signal averaging over a large number of the smaller devices allows the accuracy of the array of smaller devices to be equivalent to the larger device. The process is exemplified by considering the use of a MEMS based accelerometer switch array with an integrated analog to digital conversion of the inertial response. The process is also exemplified by considering the use of a MEMS based device structure where the MEMS devices operate in parallel as a digital variable capacitor.

Claims

1. A device structure, comprising:

a substrate;

a plurality of layers formed over the substrate, a first layer of the plurality of layers bounding one or more cavities formed within the structure between the substrate and the plurality of layers; and

a plurality of micro electromechanical devices disposed over the substrate and within each of the one or more cavities.

2. The device structure of claim 1, further comprising a pull up electrode within at least one of the one or more cavities and coupled with the first layer above the plurality of micro electromechanical devices.

3. The device structure of claim 2, further comprising a via connection from the substrate to one or more layers disposed over the one or more cavities.

4. The device structure of claim 3, wherein at least one of the one or more cavities has a length, a width and a height where at least one of the length or width is between about 20 microns and about 30 microns.

5. The device structure of claim 1, wherein the one or more cavities and plurality of micro electromechanical devices are embedded within a complementary metal oxide semiconductor.

6. The device structure of claim 1, wherein a first device of the plurality of devices has a different design than a second device of the plurality of devices.

7. The device structure of claim 1, further comprising:

a first electrode;

a second electrode; and

a plurality of cantilevers that are each movable from a position in contact with the first electrode to a position spaced from both the first electrode and the second electrode to a position in contact with the second electrode.

8. The device structure of claim 7, wherein the device structure is a digital variable capacitor.

9. The device structure of claim 8, further comprising a third electrode, wherein each of the plurality of cantilevers is coupled to the third electrode.

10. A method of using a device structure, the device structure having one or more cavities and a plurality of devices disposed within each of the one or more cavities, the method comprising:

applying a first electrical bias to one or more landing electrodes to move the plurality of devices from a first position spaced from the one or more landing electrodes into a second position in contact with the one or more landing electrodes;

moving one or more of the plurality of devices by applying an acceleration;

detecting a number of devices that remain in contact with the one or more landing electrodes following the acceleration; and

applying a second electrical bias to the plurality of landing electrodes to move the plurality of devices into the second position.

11. The method of claim 10, wherein the detecting comprises detecting presence or absence of electrical continuity between the one or more landing electrodes and corresponding device.

12. The method of claim 11, wherein the plurality of devices comprise a torsion spring, a proof mass coupled to and rotatable about the torsion spring, and a resistive contact coupled to the torsion spring opposite to the proof mass, and wherein the device structure further comprises one or more of a pull up electrode disposed above the proof mass and a pull down electrode disposed below the proof mass, the method further comprising:

applying an electrical bias to one or more of the pull up electrode and the pull down electrode, the electrical bias sufficient to overcome a stiction force between the plurality of devices and the plurality of landing electrodes.

13. The method of claim 10, further comprising applying a pull up force to one or more of the plurality of devices, wherein the pull up force is insufficient to move all of the plurality of devices from contact with the landing electrode, wherein applying a pull up force is separate from the moving one or more of the plurality of devices.

14. The method of claim 10, wherein the plurality of devices comprise a torsion spring, a proof mass coupled to and rotatable about the torsion spring, and a resistive contact coupled to the torsion spring opposite to the proof mass, and wherein the device structure further comprises one or more of a pull down electrode disposed above the proof mass and a pull up electrode disposed below the proof mass, the method further comprising, wherein the detecting comprises:

measuring a change in capacitance between the proof mass and one of the pull down electrode or the pull up electrode for each device.

15. The method of claim 10, wherein the one or more cavities includes a plurality of cavities with each cavity having one or more devices therein.

16. A method of operating a digital variable capacitor, the digital variable capacitor having a plurality of micro electromechanical devices formed within a cavity, the method comprising:

moving a plurality of cantilevers from a first position spaced a first distance from an RF electrode to a second position spaced a second distance from the RF electrode, the first distance is greater than the second distance;

moving the plurality of cantilevers to the first position; and

moving the plurality of cantilevers to a third position spaced a third distance from the RF electrode, the third distance is greater than the first distance.

17. The method of claim 16, further comprising applying an electrical bias to one or more first electrodes to move the plurality of cantilevers from the first position to the second position.

18. The method of claim 17, further comprising applying an electrical bias to one or more second electrodes to move the plurality of cantilevers to the third position.

19. The method of claim 18, wherein the plurality of micro electromechanical devices operate in parallel.

20. The method of claim 16, wherein the plurality of micro electromechanical devices operate in parallel.