# US 9,040,854 B2 · MEMS electrostatic actuator

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- Number: US 9,040,854 B2
- Document ID: US9040854B2
- Status: Granted
- Kind: B2
- Application number: 13/614,936
- Filed: 2012-09-13
- Published: 2014-03-20
- Granted: 2015-05-26
- Earliest claimed: 2011-09-13
- Assignees: Texas Instruments Incorporated
- Applicants: Arun K. Gupta; William C. McDonald
- Inventors: Arun K. Gupta; William C. McDonald
- Web page: https://patentgrep.com/patent/US9040854B2

## CPC

- H02N 2/12: Constructional details
- B81B 3/0008: {Structures for avoiding electrostatic attraction, e.g. avoiding charge accumulation}
- B81B 3/001: {Structures having a reduced contact area, e.g. with bumps or with a textured surface}
- B81B 3/0013: {Structures dimensioned for mechanical prevention of stiction, e.g. spring with increased stiffness}
- B81B 7/02: containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] (B81B7/04 takes precedence)
- B81B 2201/016: having a bridge fixed on two ends and connected to one or more dimples
- B81B 2201/0221: Variable capacitors
- B81B 2203/0109: Bridges
- B81B 2203/0181: See-saws
- B81B 2203/053: Translation according to an axis perpendicular to the substrate
- B81B 2203/058: Rotation out of a plane parallel to the substrate
- B81B 2203/06: Devices comprising elements which are movable in relation to each other, e.g. slidable or rotatable
- H02N: ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)

## Abstract

A MEMS electrostatic actuator includes a bottom plate affixed to a substrate and a top plate suspended above the bottom plate. The top plate has a parallel plate center section and two rotating members electrically connected to the center section. Each rotating member is attached centrally of the rotating member for rotation about an axis of rotation to a set of anchor posts. The attachment includes at least one pair of torsional springs attached along each axis, each spring comprising a rectangular metal square that twists as the rotational members rotate. Electrostatic pull-down electrodes are underneath each rotational member.

## Claims

### Claim 1

A MEMS electrostatic actuator, comprising:
a bottom plate affixed to a substrate;
a top plate suspended above the bottom plate; the top plate comprising a parallel plate center section and two rotating members electrically connected to the center section;
each rotating member is attached centrally of the rotating member for rotation about an axis of rotation to a set of anchor posts; the attachment including at least one pair of torsional springs attached along each axis, each spring comprising a rectangular metal square that twists as the rotational members rotate; and
electrostatic pull-down electrodes underneath each rotational member.

### Claim 2 (depends on 1)

The MEMS electrostatic actuator of claim 1, wherein the rotating members include raised portions to provide rigidity.

### Claim 3 (depends on 1)

The MEMS electrostatic actuator of claim 1, wherein the parallel plate center section includes undulations to impart rigidity.

### Claim 4 (depends on 1)

The MEMS electrostatic actuator of claim 1, wherein the rotating members include spring tips at an end of each rotating member.

### Claim 5 (depends on 1)

The MEMS electrostatic actuator of claim 1, wherein the bottom plate has a rough surface due to large grains formed in a metal of the bottom plate.

### Claim 6 (depends on 5)

The MEMs electrostatic actuator of claim 5, wherein the bottom plate has a peak-to-valley surface roughness of around 800 Å.

### Claim 7 (depends on 1)

The MEMS electrostatic actuator of claim 1, wherein the bottom plate has notches at the edges.

### Claim 8 (depends on 7)

The MEMs electrostatic actuator of claim 7, wherein the top plate has notches at the edges of the parallel plate center section.

### Claim 9

A MEMS electrostatic actuator, comprising:
a bottom plate affixed to a substrate;
a top plate above the bottom plate, the top plate comprising a parallel plate center section and two rotating members electrically connected to the center section;
each rotating member is attached centrally of the rotating member for rotation about an axis of rotation to a set of anchor posts; the attachment including at least one pair of springs attached along each axis, each spring comprising a rectangular metal square that twists as the rotational members rotate;
the rotating members including spring tips at inner ends;
the parallel plate center section having notches at edges adjacent the rotating members; and
electrostatic pull-down electrodes underneath each rotational member.