Electrostatically actuated oscillating structure with oscillation starting phase control, and manufacturing and driving method thereof

Patent metadata

Field	Value
Publication number	US-9921405-B2
Application number	US-201715401681-A
Country	US
Kind code	B2
Filing date	Jan 9, 2017
Priority date	Dec 12, 2013
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

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.

First claim

What is claimed is:

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;
said first and second regions of actuation of the mobile element including a respective plurality of first and second elongated elements, which extend in cantilever fashion towards the first and second stator subregions, respectively;
said 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
at least an element of structural asymmetry comprising a recess extending, at least in part, in the fourth elongated elements for reducing the extension of the fourth elongated elements, in such a way that a 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.

2. The oscillating structure according to claim 1 , wherein the reduced extension of said element of structural asymmetry is made in a second direction orthogonal to said first direction and having 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.

3. The oscillating structure according to claim 1 , wherein the second stator subregion comprises a main body from which said fourth elongated elements extend in cantilever fashion, the recess further extending in the area of a surface region of the main body of the second stator subregion contiguous to the fourth elongated elements.

4. 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.

5. 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.

6. 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.

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;
wherein step (d) includes forming a respective plurality of first and second elongated elements which extend in cantilever fashion towards the first stator subregion and the second stator subregion, respectively;
wherein step (c) includes forming a respective plurality of third and fourth elongated elements comb-fingered to the first and second elongated elements, respectively;
(e) forming an element of structural asymmetry by forming a recess at least in part in the fourth elongated elements so that a 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.

8. The method according to claim 7 , wherein the step of forming the element of structural asymmetry includes forming the element of structural asymmetry 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 subject during manufacturing thereof.

9. The method according to claim 7 , wherein the second 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 said recess further including forming the recess in a position corresponding to a surface region of the main body of the second stator subregion contiguous to the fourth elongated elements.

10. 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.

Assignees

• St Microelectronics Srl
• St Microelectronics Int Nv

Inventors

• Vigna Benedetto
• Ferrera Marco
• Costantini Sonia
• Salina Marco

Classifications

• H04N9/3129

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• B81C1/00198

  comprising elements which are movable in relation to each other, e.g. comprising slidable or rotatable elements · CPC title

• H04N9/3135

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• B81B2203/0154

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• H02N1/002

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