Micromechanical structure with biaxial actuation and corresponding MEMS device

Patent metadata

Field	Value
Publication number	US-9864187-B2
Application number	US-201615162885-A
Country	US
Kind code	B2
Filing date	May 24, 2016
Priority date	Nov 30, 2015
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

A reflector micromechanical structure includes a frame with a window. The frame is elastically connected to an anchorage structure by first elastic elements. An actuation structure operatively coupled to the frame is configured to generate a first actuation movement of the frame about a first actuation axis. A mobile mass is positioned within the window and elastically coupled to the frame by second elastic elements. A mass distribution is associated to the mobile mass such as to generate, by an inertial effect in response to the first actuation movement, a second actuation movement of rotation of the mobile mass about a second actuation axis.

First claim

The invention claimed is:

1. A micromechanical structure with biaxial actuation, comprising:
a frame including an internally defined window, said frame elastically connected by first elastic elements to an anchorage structure fixed with respect to a substrate;
an actuation structure operatively coupled to said frame and configured to generate a first actuation movement of said frame with respect to a first actuation axis for said frame;
a mobile mass arranged within said window and elastically coupled by second elastic elements of a torsional type to said frame and configured so that said mobile mass is rigidly coupled to said frame in said first actuation movement and further defining a second actuation axis of a torsional type for said mobile mass,
a mass distribution associated to said mobile mass and being asymmetrical at least with respect to said second actuation axis and configured to generate, by an inertial effect as a function of said first actuation movement, a second actuation movement of rotation of the mobile mass about the second actuation axis; and
wherein said mass distribution is configured to generate, in an equation of motion of said micromechanical structure, a mass matrix having terms of inertial coupling between the first actuation movement of said frame and the rotation of said mobile mass.

2. The micromechanical structure according to claim 1 , wherein said mass distribution defines at least one centroid arranged at a distance from the second actuation axis at which an inertial force is originated in response to said first actuation movement so as to generate a twisting moment for rotation of said mobile mass about said second actuation axis.

3. The micromechanical structure according to claim 1 , wherein said first elastic elements are of a torsional type and said first actuation axis defines a rotation axis, said first actuation movement being a rotation of said frame about said first actuation axis.

4. The micromechanical structure according to claim 3 , wherein said first actuation axis and said second actuation axis define a horizontal plane parallel to a main surface of said frame; wherein said mobile mass has in said horizontal plane a geometrical center, and said mass distribution includes a first additional mass portion and a second additional mass portion arranged symmetrically with respect to said geometrical center and aligned in a diagonal direction which is inclined with respect to said first actuation axis and said second actuation axis.

5. The micromechanical structure according to claim 1 , wherein said first actuation movement is a resonant movement, and said actuation structure operates on the basis of an operating principle chosen from: electrostatic; electromagnetic; and piezoelectric.

6. The micromechanical structure according to claim 1 , wherein the mobile mass has a circular shape and a geometrical center and wherein said mass distribution includes a first additional mass portion and a second additional mass portion arranged symmetrically with respect to the geometrical center and aligned in a diagonal direction which is inclined with respect to said first actuation axis and said second actuation axis, said first and second additional mass portions each having a shape of a circular sector.

7. The micromechanical structure according to claim 6 , wherein said first and second mass portions are joined by a connecting portion at the geometrical center.

8. A micromechanical structure with biaxial actuation, comprising:
a frame including an internally defined window, said frame elastically connected by first elastic elements to an anchorage structure fixed with respect to a substrate;
an actuation structure operatively coupled to said frame and configured to generate a first actuation movement of said frame with respect to a first actuation axis for said frame;
a mobile mass arranged within said window and elastically coupled by second elastic elements of a torsional type to said frame and configured so that said mobile mass is rigidly coupled to said frame in said first actuation movement and further defining a second actuation axis of a torsional type for said mobile mass;
a mass distribution associated to said mobile mass and being asymmetrical at least with respect to said second actuation axis and configured to generate, by an inertial effect as a function of said first actuation movement, a second actuation movement of rotation of the mobile mass about the second actuation axis;
wherein said first elastic elements are of a torsional type and said first actuation axis defines a rotation axis, said first actuation movement being a rotation of said frame about said first actuation axis;
wherein said first actuation axis and said second actuation axis define a horizontal plane parallel to a main surface of said frame;
wherein said mobile mass has in said horizontal plane a geometrical center, and said mass distribution includes a first additional mass portion and a second additional mass portion arranged symmetrically with respect to said geometrical center and aligned in a diagonal direction which is inclined with respect to said first actuation axis and said second actuation axis; and
wherein said mobile mass has in the horizontal plane a circular shape, and each of said first additional mass portion and said second additional mass portion have, in the horizontal plane, a shape of a circular sector and are joined by a connecting portion at the geometrical center.

9. The micromechanical structure according to claim 8 wherein said first actuation movement is a resonant movement, and said actuation structure operates on the basis of an operating principle chosen from: electrostatic and piezoelectric.

10. A micromechanical structure with biaxial actuation, comprising:
a frame including an internally defined window, said frame elastically connected by first elastic elements to an anchorage structure fixed with respect to a substrate;
an actuation structure operatively coupled to said frame and configured to generate a first actuation movement of said frame with respect to a first actuation axis for said frame;
a mobile mass arranged within said window and elastically coupled by second elastic elements of a torsional type to said frame and configured so that said mobile mass is rigidly coupled to said frame in said first actuation movement and further defining a second actuation axis of a torsional type for said mobile mass;
a mass distribution associated to said mobile mass and being asymmetrical at least with respect to said second actuation axis and configured to generate, by an inertial effect as a function of said first actuation movement, a second actuation movement of rotation of the mobile mass about the second actuation axis;
wherein said first elastic elements are of a torsional type and said first actuation axis defines a rotation axis, said first actuation movement being a rotation of said frame about said first actuation axis; and
wherein said mobile mass comprises a body portion formed in a surface layer arranged at a distance from said substrate with respect to a vertical axis, which defines with the first actuation axis and the second actuation axis a set of three Cartesian axes; and said mass distribution includes at least one additional mass portion formed in a structural layer arranged underneath the surface layer with respect to said vertical axis in the direction of said substrate.

11. The micromechanical structure according to claim 10 , wherein the mobile mass has a circular shape and a geometrical center and wherein said mass distribution includes a first additional mass portion and a second additional mass portion arranged

Assignees

• St Microelectronics Srl
• St Microelectronics Srl

Inventors

• Carminati Roberto

Classifications

• B81B2201/042

  Micromirrors, not used as optical switches · CPC title

• B81B3/0083

  Optical properties · CPC title

• G03B21/008

  using micromirror devices · CPC title

• G02B26/0833 Primary

  the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B) · CPC title

• G03B21/28

  Reflectors in projection beam {(in illumination beam G03B21/2066)} · CPC title