MICRO ELECTRO MECHANICAL SYSTEM

• US 20110138912A1
• Filed: 08/05/2009
• Published: 06/16/2011
• Est. Priority Date: 08/18/2008
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Degawa, Munenori, Jeong, Heewon
• Granted Patent: US 8,683,864 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• CPC Class Codes: B81B 2201/025 Inertial sensors not provided for in B81B2201/0235 - B81B2201/0242
• CPC Class Codes: B81B 2203/0109 Bridges
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/5733 Structural details or topology
• CPC Class Codes: G01P 1/003 used for damping
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

In order to provide a technology capable of suppressing degradation of measurement accuracy due to fluctuation of detection sensitivity of an MEMS by suppressing fluctuation in natural frequency of the MEMS caused by a stress, first, fixed portions 3a to 3d are displaced outward in a y-direction of a semiconductor substrate 2 by deformation of the semiconductor substrate 2. Since a movable body 5 is disposed in a state of floating above the semiconductor substrate 2, it is not affected and displaced by the deformation of the semiconductor substrate 2. Therefore, a tensile stress (+σ₁) occurs in the beam 4a and a compressive stress (−σ₂) occurs in the beam 4b. At this time, in terms of a spring system made by combining the beam 4a and the beam 4b, increase in spring constant due to the tensile stress acting on the beam 4a and decrease in spring constant due to the compressive stress acting on the beam 4b are offset against each other.

Claims

1. A micro electro mechanical system having, formed on a first semiconductor chip,

(a) a first fixed portion,

(b) an elastically deformable first beam, one end of which is connected to the first fixed portion,

(c) a second fixed portion,

(d) an elastically deformable second beam, one end of which is connected to the second fixed portion, and

(e) a displaceable movable body connected to the other end of the first beam and the other end of the second beam,

wherein, when the first fixed portion and the second fixed portion are displaced in the same direction by a stress occurring in the first semiconductor chip, a spring constant of the first beam is increased as compared with that when the first fixed portion is not displaced, and a spring constant of the second beam is decreased as compared with that when the second fixed portion is not displaced.

2. The micro electro mechanical system according to claim 1,

wherein the first fixed portion, the first beam, the second fixed portion and the second beam are disposed on the same side with respect to a center line of the first semiconductor chip.

3. The micro electro mechanical system according to claim 2,

wherein the center line of the first semiconductor chip is a line extending in a direction parallel to a direction of displacement of the movable body.

4. The micro electro mechanical system according to claim 3,

wherein the first beam and the second beam are disposed in directions intersecting the center line of the first semiconductor chip.

5. The micro electro mechanical system according to claim 4,

wherein a connecting portion of the movable body connected to the first beam and the second beam is disposed so as to be sandwiched between the first beam and the second beam.

6. The micro electro mechanical system according to claim 4,

wherein the first beam and the second beam are disposed on opposite sides with respect to the connecting portion of the movable body connected to the first beam and the second beam.

7. The micro electro mechanical system according to claim 5,

wherein the first beam and the second beam are disposed so as to be aligned on a straight line.

8. The micro electro mechanical system according to claim 7,

wherein the first beam has a first turning portion between the one end of the first beam and the other end of the first beam, and the second beam has a second turning portion between the one end of the second beam and the other end of the second beam.

9. The micro electro mechanical system according to claim 8,

wherein a distance between the first fixed portion and the second fixed portion is smaller than a distance between the first turning portion and the second turning portion.

10. The micro electro mechanical system according to claim 8,

wherein the first fixed portion and the second fixed portion are one and the same portion.

11. The micro electro mechanical system according to claim 8,

wherein the first beam has a plurality of beams, and the second beam also has a plurality of beams.

12. The micro electro mechanical system according to claim 11,

wherein the plurality of beams constituting the first beam and the plurality of beams constituting the second beam are equal in number.

13. The micro electro mechanical system according to claim 1,

wherein the first semiconductor chip is mounted on an underlayer substrate via an adhesive agent.

14. The micro electro mechanical system according to claim 13,

wherein the underlayer substrate is a second semiconductor chip on which an integrated circuit is formed.

15. The micro electro mechanical system according to claim 13,

wherein the stress occurring in the first semiconductor chip includes a stress occurring with volume deformation of the adhesive agent.

16. The micro electro mechanical system according to claim 1,

wherein the first semiconductor chip is an SOI substrate made up of a substrate layer, an embedded insulating layer formed on the substrate layer and a silicon layer formed on the embedded insulating layer.

17. The micro electro mechanical system according to claim 16,

wherein the first fixed portion and the second fixed portion are formed by processing the silicon layer and fixed to the substrate layer via the embedded insulating layer existing below the silicon layer;

and

the first beam, the second beam and the movable body are formed by processing the silicon layer and held so as to float above the substrate layer by removing the embedded insulating layer existing below the silicon layer.

18. The micro electro mechanical system according to claim 17,

wherein the stress occurring in the first semiconductor chip includes stresses occurring in the first fixed portion and the second fixed portion formed of the silicon layer fixed to the embedded insulating layer due to a difference in coefficient of thermal expansion between the embedded insulating layer and the silicon layer.