# US 9,753,279 B2 · Electrostatically actuated oscillating structure with oscillation starting phase control, and manufacturing and driving method thereof

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- Number: US 9,753,279 B2
- Document ID: US9753279B2
- Status: Granted
- Kind: B2
- Application number: 14/564,237
- Filed: 2014-12-09
- Published: 2015-06-18
- Granted: 2017-09-05
- Earliest claimed: 2013-12-12
- Assignees: STMicroelectronics S.r.l.; STMicroelectronics International N.V.
- Applicants: STMicroelectronics S.r.l.; STMicroelectronics International N.V.
- Inventors: Benedetto Vigna; Marco Ferrera; Sonia Costantini; Marco Salina
- Web page: https://patentgrep.com/patent/US9753279B2

## CPC

- G02B 26/0841: {the reflecting element being moved or deformed by electrostatic means}
- B81B 3/0045: {Improve properties related to angular swinging, e.g. control resonance frequency}
- B81C 1/00198: {comprising elements which are movable in relation to each other, e.g. comprising slidable or rotatable elements}
- H02N 1/002: {Electrostatic motors}
- H02N 1/006: {of the gap-closing type (H02N1/004 takes precedence)}
- H04N 9/3129: {scanning a light beam on the display screen (scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161)}
- H04N 9/3135: {Driving therefor}
- B81B 2201/042: Micromirrors, not used as optical switches
- B81B 2203/0154: Torsion bars
- G02B 27/1006: {for splitting or combining different wavelengths (G02B27/1086, G02B27/141 take precedence)}
- Y10T 29/49002: Electrical device making
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- H02N: ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

An electrostatically actuated oscillating structure includes a first stator subregion, a second stator subregion, a first rotor subregion and a second rotor subregion. Torsional elastic elements mounted to the first and second rotor subregions define an axis of rotation. A mobile element is coupled to the torsional elastic elements. The stator subregions are electrostatically coupled to respective regions of actuation on the mobile element. The stator subregions exhibit an element of structural asymmetry such that the electrostatic coupling surface between the first stator subregion and the first actuation region differs from the electrostatic coupling surface between the second stator subregion and the second actuation region.

## Claims

### Claim 1

An electrostatically actuated oscillating structure, comprising:
a fixed support body forming a first stator subregion, a second stator subregion, a first rotor subregion and a second rotor subregion;
a first torsional elastic element and a second torsional elastic element mechanically coupled, respectively, to the first and second rotor subregions and defining an axis of rotation parallel to a first direction of an orthogonal reference system; and
a mobile element arranged between, and connected to, said first and second torsional elastic elements, the mobile element being rotatable about the axis of rotation as a result of a torsion of the first and second torsional elastic elements;
wherein the first and second stator subregions are electrostatically coupled to respective first and second regions of actuation of the mobile element, which are diametrically opposite to one another with respect to the axis of rotation,
wherein one of the first and second stator subregions includes at least an element of structural asymmetry such that a surface available for said electrostatic coupling between the first stator subregion and the first actuation region is greater than a surface available for the electrostatic coupling between the second stator subregion and the second actuation region;
wherein said element of structural asymmetry is a bump element of increased thickness housed by the first stator subregion such as to increase a spatial extension, in a second direction orthogonal to said first direction, of a portion of the first stator subregion with respect to a spatial extension in said second direction of a corresponding portion of the second stator subregion;
wherein the first and second regions of actuation of the mobile element include a respective plurality of first and second elongated elements, which extend in cantilever fashion towards the first and second stator subregions, respectively, the first and second stator subregions including a respective plurality of third and fourth elongated elements comb-fingered to the first and second elongated elements, respectively; and
wherein said bump element of increased thickness extending, at least in part, on the third elongated elements, so that the surface available for said electrostatic coupling between the third elongated elements and the first elongated elements is greater than the surface available for the electrostatic coupling between the fourth elongated elements and the second elongated elements.

### Claim 2 (depends on 1)

The oscillating structure according to claim 1, wherein said spatial extension of said bump element is of a value greater than a threshold, said threshold being the maximum value of manufacturing error to which the oscillating structure may be subject during manufacturing thereof.

### Claim 3 (depends on 1)

The oscillating structure according to claim 1, wherein the first stator subregion comprises a main body extending from which in cantilever fashion are said third elongated elements, said bump element of increased thickness further extending in an area corresponding to a surface region, contiguous to the third elongated elements, of the main body of the first stator subregion.

### Claim 4 (depends on 1)

The oscillating structure according to claim 1, further comprising an electronic circuit operatively coupled to the first and second stator subregions and to the mobile element, configured to bias the mobile element at a reference voltage and for biasing the first and second stator subregions by an electrical driving signal including a train of pulses having a voltage value greater, in modulus, than the reference voltage, and such as to generate, and maintain, an oscillation of the mobile element.

### Claim 5 (depends on 4)

The oscillating structure according to claim 4, wherein each between said first and second torsional elastic elements has a first dimension, a second dimension, and a third dimension, measured respectively in a first direction, a second direction, and a third direction, orthogonal to one another, said first dimension being greater than said second and third dimensions, said first and second stator subregions being arranged in such a way that, when they receive the electrical driving signal, the mobile element rotates about the axis of rotation parallel to the first direction.

### Claim 6 (depends on 1)

The oscillating structure according to claim 1, wherein the fixed support body, the first and second torsional elastic elements, and the mobile element are made of semiconductor material.

### Claim 7

A method, comprising:
(a) shaping a fixed support body to form a first stator subregion and a second stator subregion and a first rotor subregion and a second rotor subregion;
(b) forming a first torsional elastic element and a second torsional elastic element, constrained, respectively, to the first and second rotor subregions and defining an axis of rotation;
(c) forming a mobile element set between, and connected to, said first and second torsional elastic elements, the mobile element being rotatable about the axis of rotation as a result of a torsion of the first and second torsional elastic elements; and
(d) forming first and second regions of actuation of the mobile element, which are diametrically opposite to one another with respect to the axis of rotation;
wherein steps (c) and (d) include electrostatically coupling the first and second stator subregions to the first actuation region and to the second actuation region, respectively,
(e) forming, in an area corresponding to one between the first and second stator subregions, an element of structural asymmetry such that a surface available for said electrostatic coupling between the first stator subregion and the first actuation region is greater than a surface available for the electrostatic coupling between the second stator subregion and the second actuation region;
wherein the step of forming said element of structural asymmetry includes forming a bump element of increased thickness in a portion of the first stator subregion, for increasing at least in part a spatial extension, in a second direction orthogonal to said axis of rotation, of the first stator subregion with respect to a spatial extension, in the second direction of a corresponding portion of the second stator subregion;
wherein step (d) includes forming a respective plurality of first and second elongated elements, which extend in cantilever fashion towards the first and second stator subregions, respectively; and
wherein step (c) includes forming a respective plurality of third and fourth elongated elements comb-fingered to the first and second elongated elements, respectively; and
wherein step (e) includes forming said bump element so that the surface available for said electrostatic coupling between the third elongated elements and the first elongated elements is greater than a surface available for the electrostatic coupling between the fourth elongated elements and the second elongated elements.

### Claim 8 (depends on 7)

The method according to claim 7, wherein the step of forming the bump element includes forming the bump element having a spatial extension, in a second direction orthogonal to said first direction, of a value greater than a threshold, said threshold being the maximum value of fabrication error to which the oscillating structure is subj ect during manufacturing thereof.

### Claim 9 (depends on 7)

The method according to claim 7, wherein the first stator subregion comprises a main body, said fourth elongated elements being formed so as extend in cantilever fashion from the main body, the step of forming the bump element further including forming the bump element of increased thickness in an area corresponding to a surface region of the main body of the first stator subregion, contiguous to the third elongated elements.

### Claim 10 (depends on 7)

The method according to claim 7, further comprising:
biasing the mobile element at a reference voltage; and
biasing the first and second stator subregions by an electrical driving signal that includes a train of pulses having a voltage value greater, in modulus, than the reference voltage, for generating, and maintaining, an oscillation of the mobile element.