MEMS electrostatic actuator

• US 9,263,973 B2
• Filed: 04/21/2015
• Issued: 02/16/2016
• Est. Priority Date: 09/13/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Gupta, Arun Kumar, McDonald, William Craig
• Primary Examiner(s): Barrera, Ramon M
• Application Number:
  US14/691,962
• Publication Number:
  US 20150229241A1
• Time in Patent Office: 301 Days
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/016 having a bridge fixed on two ends and connected to one or more dimples
• CPC Class Codes: B81B 2201/0221 Variable capacitors
• CPC Class Codes: B81B 2203/0109 Bridges
• CPC Class Codes: B81B 2203/0181 See-saws
• CPC Class Codes: B81B 2203/053 Translation according to an axis perpendicular to the substrate
• CPC Class Codes: B81B 2203/058 Rotation out of a plane parallel to the substrate
• CPC Class Codes: B81B 2203/06 Devices comprising elements which are movable in relation to each other, e.g. slidable or rotatable
• CPC Class Codes: B81B 3/0008 Structures for avoiding electrostatic attraction, e.g. avoiding charge accumulation
• CPC Class Codes: B81B 3/001 Structures having a reduced contact area, e.g. with bumps or with a textured surface
• CPC Class Codes: B81B 3/0013 Structures dimensioned for mechanical prevention of stiction, e.g. spring with increased stiffness
• CPC Class Codes: 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
• CPC Class Codes: H02N 2/12 Constructional details

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

1. A MEMS electrostatic actuator device comprising an array of MEMS actuators, each MEMS actuator comprising:

a bottom plate affixed to a substrate, wherein the bottom plate is a signal electrode;

a top plate suspended above the bottom plate;

the top plate comprising a parallel plate center section and two rotating drive members electrically connected to the center section, wherein the center section has openings to reduce stiction;

each rotating drive member is attached to a set of anchor posts, wherein the rotating drive members enable vertical movement of the center section; and

electrostatic pull-down electrodes underneath each rotating drive member.

2. The MEMS electrostatic actuator device of claim 1, wherein the rotating drive members have an outer end width that is less than an inner end width so that MEMS actuators of the array of MEMs actuators may be interdigitated.

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

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

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

.

7. The MEMs electrostatic actuator device of claim 1, wherein the top plate has notches at the edges of the parallel plate center section.

3. The MEMS electrostatic actuator device of daft wherein the parallel plate center section includes undulations to impart rigidity.

8. A MEMS electrostatic actuator device comprising an array of MEMS actuators, each MEMS actuator comprising:

a bottom plate affixed to a substrate, wherein the bottom plate is a signal electrode;

a top plate above the bottom plate, the top plate comprising a parallel plate center section and two rotating drive members electrically connected to the center section, wherein the center section has openings to reduce stiction;

each rotating drive 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 rotating drive members rotate;

the rotating drive members including spring tips at inner ends;

the rotating drive members having an outer end width that is less than an inner end width wherein the MEMS actuators of the array of MEMS actuators are interdigitated;

the parallel plate center section having notches at edges adjacent the rotating drive members;

a pivot pin member traversing the notches allowing relative pivotal motion of rotating drive members; and

electrostatic pull-down electrodes underneath each rotating drive member.