SUSPENDED MASSES IN MICRO-MECHANICAL DEVICES

• US 20130205901A1
• Filed: 02/10/2012
• Published: 08/15/2013
• Est. Priority Date: 02/10/2012
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Homeijer, Brian D.
• Granted Patent: US 8,984,942 B2
• Time in Patent Office: Days
• US Class Current: 73/514.33
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: G01P 2015/0871 using stopper structures for limiting the travel of the seismic mass

Abstract

The micro-mechanical device includes a substrate with an internal cavity, a first surface, and an opposing second surface. A first trench is formed from the first surface of the substrate into the internal cavity. The first trench at least partially defines flexures. A second trench is formed from the second surface of the substrate into the internal cavity and at least partially defines a suspended mass. The suspended mass is connected by the flexures to the substrate.

Claims

1. A micro-mechanical device comprising:

a substrate comprising an internal cavity, a first surface, and an opposing second surface;

a first trench formed through the first surface of the substrate into the internal cavity, the first trench at least partially defining flexures; and

a second trench formed through the second surface of the substrate into the internal cavity, the second trench at least partially defining a suspended mass, in which the suspended mass is connected by the flexures to the substrate, in which the flexures are sandwiched between sides suspended mass and the surrounding substrate.

2. The device of claim 1, in which the flexures are symmetrically disposed about a center of mass of the suspended mass such that the tendency of the suspended mass to twist under acceleration is reduced.

3. The device of claim 1, in which the second trench is a release trench formed around the perimeter of the suspended mass.

4. The device of claim 1, in which the second trench defines additional flexures.

5. The device of claim 1, in which the flexures are to allow preferential motion of the suspended mass in an in-plane direction.

6. The device of claim 1, in which the device is to sense in-plane accelerations.

7. The device of claim 1, further comprising bumpers formed by the release trench.

8. The device of claim 1, in which the first trench is formed into a first portion of the internal cavity and the second trench is formed into a different second portion of the internal cavity.

9. The device of claim 1, in which the suspended mass as the same thickness as the substrate and includes a portion of the first surface and a portion of the second surface.

10. The device of claim 1, in which the substrate is a silicon-on-insulator substrate.

11. The device of claim 10, in which the silicon-on-insulator substrate comprises a handle layer, an oxide layer, and a device layer, in which the second trench is a release trench formed in the device layer and the flexures are formed in the handle layer.

12. The device of claim 11, in which the release trench is narrower than the flexure trench such that under acceleration the release trench closes before the flexure trench and limits motion of the suspended mass.

13. The device of claim 1, in which the flexures comprise a rectangular cross section with the major axis of the rectangular cross section being perpendicular to the first and second surfaces.

14. A micro-mechanical acceleration sensor comprising:

a silicon-on-insulator substrate comprising, an internal cavity, a first surface, and an opposing second surface, in which a thickness of the substrate is defined by the distance between the first surface and opposing second surface;

flexure trenches formed from the first surface of the substrate into the internal cavity, the flexure trenches defining flexures with a rectangular cross section and major axis of the rectangular cross section is perpendicular to the first and second surfaces; and

a release trench formed from the second surface of the substrate into the internal cavity, the release trench at least partially defining a suspended mass and releasing the suspended mass so that the suspended mass is connected to the substrate by the flexures, the flexures being formed around the perimeter of the suspended mass and being sandwiched between the suspended mass and surrounding substrate,

in which the flexures exhibit a first spring force in response to motion in plane with the substrate and a second higher spring force in response to motion of the suspended mass out-of-plane of the substrate, in which the sensor measures accelerations that are in the plane of the substrate.

15. A method for forming a suspended mass comprising:

obtaining a substrate with at least one cavity, the substrate comprising a first surface and an opposing second surface;

etching a first trench through the first surface of the substrate and into a first portion of the at least one cavity, the first trench at least partially defining a first flexure; and

etching a second trench through the second surface of the substrate and into a second portion of the at least one cavity to at least partially define a proof mass, in which the first flexure is sandwiched between the proof mass and surrounding substrate and the proof mass is suspended from the substrate by the first flexure, in which the proof mass comprises a portion of the first surface and a portion of the second surface.