MEMS device with two axes comb drive actuators

• US 7,872,394 B1
• Filed: 12/12/2002
• Issued: 01/18/2011
• Est. Priority Date: 12/13/2001
• Status: Active Grant

• Current Assignee: Crossfiber Inc., Iande Group, LLC
• Original Assignee: Joseph E. Ford
• Inventors: Fan, Li, Chen, Richard, Bang, Christopher A., Gritters, John, Klaassen, Erno, Yeh, Hsin-Chih, Kruglick, Ezekiel John Joseph
• Primary Examiner(s): Tamai; Karl I
• Application Number:
  US10/319,403
• Time in Patent Office: 2,959 Days
• Field of Search: 310/309, 385/18, 359223-226, 359/290, 359/291
• US Class Current: 310/309
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H02N 1/006 of the gap-closing type H02N1/004 takes precedence

Abstract

In certain embodiments, a MEMS actuator is provided comprising a frame and a movable structure coupled to the frame. A vertical comb drive is provided between the frame and the movable structure to actuate the movable structure.

Claims

1. A MEMS device comprising:

A) a movable structure comprising two shaft portions, defining a first shaft portion and a second shaft portion, extending in opposite directions,

B) a movable frame comprising two shaft portions, defining a third shaft portion and a fourth shaft portion, extending in opposite directions,

C) a first set of two torsional members, co-aligned with each other, each of said two torsional members connecting the movable structure to the movable frame and passing through at least a portion of one of said first or second shaft portions such that the movable structure is capable of rotation about a first axis defined by the first set of two torsional members,

D) a first set of at least four vertical comb drives, each vertical comb drive defining a plurality of stationary comb teeth extending from said movable frame and a plurality of movable comb teeth extending from said movable structure, two of which vertical comb drives are electrostatically coupled to one of said first and second shaft portions and two of which are each electrostatically coupled to the other of said first and second shaft portions,

E) an outer fixed frame structure,

F) a second set of two torsional members co-aligned with each other, each of said two torsional members connecting the movable frame to the support structure and passing through one of the two shaft portions extending from the movable frame such that the movable frame is capable of rotation about a second axis defined by the second set of two torsional members, and

G) a second set of at least four vertical comb drives, each vertical comb drive defining a plurality of stationary comb teeth extending from said outer fixed frame structure and a plurality of movable comb teeth extending from said movable frame, two of which vertical comb drives are electrostatically coupled to one of said third and fourth shaft portions and two of which are coupled to the other of said third and fourth shaft portions;

wherein said movable structure, said movable frame, said first set of two torsional members, said first set of at least four comb drives, said outer fixed frame structure, said second set of two torsional members, said second set of at least four comb drives are all fabricated from a single multi-layer semi-conductor structure of semiconductor material and insulator material using a single mask to define, during a series of processing steps, the location and width of both movable comb teeth and stationary comb teeth so as to assure self alignment of the comb teeth of the first and second sets of vertical comb drives,

wherein said multi-layer semi-conductor structure is comprised of at least two silicon layers, defining an upper semi-conductor layer and an intermediate semi-conductor layer, and at least one additional semiconductor layer, defining a bottom layer, said top layer, said intermediate layer and said bottom layer being separated by at least two insulator layers defining a first lower insulator layer and a second intermediate insulator layer, portions of said second intermediate insulator layer separating said stationary comb teeth into first electric potential regions and second electric potential regions and other portions of said second intermediate insulator layer being removed to define a top surface of said movable comb teeth,

wherein a hardmask material is applied to the upper semi-conductor layer and etched utilizing a first photoresist pattern to form overwidth hardmask portions for etching the stationary comb teeth,

wherein a second photoresist pattern is formed on the overwidth hardmask portions to define location and a cross section of the stationary comb teeth and on portions of the upper semi-conductor layer between the overwidth hardmask portions to define location and a cross section of the movable comb teeth to define distances between the fixed and movable comb teeth,

wherein excess portions of the overwidth hardmask portions are removed utilizing the second photoresist pattern and then the unmasked portions of the upper semi-conductor layer is etched away utilizing the same second photoresist pattern forming deep gaps in the upper semi-conductor layer with the upper insulator layer acting as an etch stop material for the upper semi-conductor layer etch to define exposed portions of the upper insulator layer, and then the exposed portion of the upper insulator layer is removed utilizing the same second photoresist pattern;

wherein after removal of the exposed portion of the upper insulator layer, the second photoresist pattern is removed and exposed portions of the upper semiconductor layer and the exposed portions of the second semiconductor layer are etched away down to the first lower insulator layer to define the stationary comb teeth comprising portions of the first semiconductor layer and the second semiconductor layer separated by portions of the second intermediate insulator layer and to define the movable comb teeth comprising portions of the intermediate semiconductor layer with vertical gaps between the teeth; and

wherein a backside etch is performed to etch portions of the bottom layer and the first lower insulator layer to permit the movable teeth to move relative to the stationary teeth.

2. A MEMS device as in claim 1 wherein said first and second torsional members are aligned orthogonally to said third and fourth torsional members.

3. A MEMS device as in claim 1 wherein each of said third and fourth torsional members comprise an upper member and a lower member separated from each other along sections of the upper and lower members.

4. A MEMS device as in claim 1 wherein said movable frame comprises an upper portion and a lower portion separated by an insulator portion wherein the upper portion is electrically separated into two segments defining a first segment and a second segment.

5. A MEMS device as in claim 4 wherein said first segment is adapted to provide electric power to one of the two comb drives coupled to the first shaft portion and one of the two comb drives coupled to the second shaft portion and the second segment is adapted to provide electric power to the other of the two comb drive coupled to the first shaft portion and the other of the two comb drive coupled to the second shaft portion.

6. A MEMS device as in claim 1 wherein deep trench reactive ion etch is utilized to etch both the upper semi-conductor layer and the intermediate semi-insulator layer to ensure well defined etch profiles with said hard mask layer acting as an etch stop material for the silicon etch process.

7. A process for fabricating a MEMS device comprising:

A) a movable structure comprising two shaft portions, defining a first shaft portion and a second shaft portion, extending in opposite directions,

B) a movable frame comprising two shaft portions, defining a third shaft portion and a fourth shaft portion, extending in opposite directions,

C) a first set of two torsional members, co-aligned with each other, each of said two torsional members connecting the movable structure to the movable frame and passing through at least a portion of one of said first or second shaft portions such that the movable structure is capable of rotation about a first axis defined by the first set of two torsional members,

D) a first set of at least four vertical comb drives, each vertical comb drive defining a plurality of stationary comb teeth extending from said movable frame and a plurality of movable comb teeth extending from said movable structure, two of which vertical comb drives are electrostatically coupled to one of said first and second shaft portions and two of which are each electrostatically coupled to the other of said first and second shaft portions,

E) an outer fixed frame structure,

F) a second set of two torsional members co-aligned with each other, each of said two torsional members connecting the movable frame to the support structure and passing through one of the two shaft portions extending from the movable frame such that the movable frame is capable of rotation about a second axis defined by the second set of two torsional members, and

G) a second set of at least four vertical comb drives, each vertical comb drive defining a plurality of stationary comb teeth extending from said outer fixed frame structure and a plurality of movable comb teeth extending from said movable frame, two of which vertical comb drives are electrostatically coupled to one of said third and fourth shaft portions and two of which are coupled to the other of said third and fourth shaft portions;

wherein said movable structure, said movable frame, said first set of two torsional members, said first set of at least four comb drives, said outer fixed frame structure, said second set of two torsional members, said second set of at least four comb drives are all fabricated from a single multi-layer semi-conductor structure of semiconductor material and insulator material using a single mask to define, during a series of processing steps, the location and width of both movable comb teeth and stationary comb teeth so as to assure self alignment of the comb teeth of the first and second sets of vertical comb drives, and

wherein said multi-layer semi-conductor structure is comprised of at least two silicon layers, defining an upper semi-conductor layer and an intermediate simi-conductor layer, and at least one additional semiconductor layer, defining a bottom layer, said top layer, said intermediate layer and said bottom layer being separated by at least two insulator layers defining a first lower insulator layer and a second intermediate insulator layer, and

wherein said process of fabricating said MEMS device comprises the steps of;

A) applying a hardmask material to the upper semi-conductor layer and etching the hardmask material utilizing a first photoresist pattern to form overwidth hardmask portions for etching the stationary comb teeth,

B) forming a second photoresist pattern on the overwidth hardmask portions to define location and a cross section of the stationary comb teeth and on portions of the upper simi-conductor layer between the overwidth hardmask portions to define location and a cross section of the movable comb teeth and to define distances between the fixed and movable comb teeth,

C) removing excess portions of the overwidth hardmask portions utilizing the second photoresist pattern and then etching away the unmasked portions of the upper semi-conductor layer utilizing the same second photoresist pattern forming deep gaps in the upper semi-conductor layer with the upper insulator layer acting as an etch stop material for the upper semi-conductor layer etch to define exposed portions of the upper insulator layer, and then removing the exposed portion of the upper insulator layer utilizing the same second photoresist pattern;

D) after removal of the exposed portion of the upper insulator layer, removing the second photoresist pattern and exposed portions of the upper semiconductor layer and etching away the second semiconductor layer to define (i) the stationary comb teeth comprising portions of the first semiconductor layer and the second semiconductor layer separated by portions of the second intermediate insulator layer and (ii) the movable comb teeth comprising portions of the intermediate semiconductor layer with vertical gaps between the teeth; and

E) performing a backside etch to etch portions of the bottom layer and the first insulator layer to permit the movable teeth to move relative to the stationary teeth.

8. A process as in claim 7 wherein deep trench reactive ion etch is utilized to etch both the upper semi-conductor layer and the intermediate semi-insulator layer to ensure well defined etch profiles with said hard mask layer acting as an etch stop material for the silicon etch process.