| 主权项 |
1. A micro-electromechanical system (MEMS) structure for an angular rate sensor, the structure being positioned between first and second silicon-insulator composite wafers formed of a plurality of structured silicon parts, electrically isolated from each other by an insulator material, the structure comprising:
a mono-crystalline silicon substrate structured to form a sensing system and a frame, the sensing system being completely de-coupled from and surrounded by the frame, which is positioned between engaging surfaces of the first and second composite wafers such that the sensing system is hermetically sealed within a cavity defined by the first and second composite wafers and the frame, the sensing system including:
two seismic masses having front and back surfaces;two driving beams, each having a first end attached to a seismic mass and a second end attached to the first and second composite wafers by means of fixed pedestals provided on the silicon substrate; anda bending spring arranged to directly connect between, and synchronise a primary motion of, the two seismic masses,each of the seismic masses being arranged to have a first degree of rotational freedom about an axis that is substantially perpendicular to the plane of the silicon substrate, andthe seismic masses and driving beams being arranged to have a second degree of rotational freedom about an axis substantially coincident with the longitudinal axis of the driving beams; means for generating and detecting the primary motion consisting of a primary oscillation of the two seismic masses, in opposing phases, in the first degree of rotational freedom; means for detecting a secondary motion consisting of a secondary oscillation of the two seismic masses, in opposing phases, in the second degree of rotational freedom, the means of generating and detecting the primary motion and the means of detecting a secondary motion being provided on both the front and back surfaces of each of the first and second seismic masses, wherein the sensing system is arranged such that, when the structure is subjected to an angular velocity around a third axis that is substantially in the plane of the silicon substrate and perpendicular to the longitudinal axis of the beams, a Coriolis force arises which causes the secondary oscillation of the seismic masses, wherein the engaging surface of the first composite wafer mirrors or matches the engaging surface of the second composite wafer, wherein the seismic masses, the pedestals, the means for generating and detecting the primary motion, and the means for detecting the secondary motion are symmetrically disposed about perpendicular axes, wherein the means for generating and detecting the primary motion involves the use, in a capacitive manner, of at least two fixed electrodes provided above and below each seismic mass, wherein the means for detecting the secondary motion involves the use, in a capacitive manner, of at least two fixed electrodes provided above and below each seismic mass; and means for adjusting the frequency of the oscillations, the adjustment being achieved in a capacitive manner using at least two fixed electrodes located above and below each seismic masses. |
