Inertial sensor architecture with balanced sense mode and improved immunity to quadrature effects
An inertial sensor including a substrate, sense frames, drive frames configured to put into motion the sense frames, and a sense lever pivotably mounted around a rotation axis. The sense frames, drive frames and sense lever are connected to each other in such a way that when the inertial sensor is subjected to a rotational movement around the rotation axis, the first sense frame, the second sense frame and the sense lever respectively feature a first tilt θ 1 a second tilt θ 2 and a lever tilt θ S relatively to the device plane, and both θ 1 /θ S and θ 2 /θ S are lower than 0.1. The inertial sensor features strain gauges that get stressed when the lever rotates due to the motion of the sense frames.
1 . An inertial sensor comprising:
a substrate which defines a device plane extending along a drive excitation direction (x) and a rotation direction (y) normal to the drive excitation direction (x), the device plane being perpendicular to a detection direction (z),
a sense lever pivotably mounted to the substrate around a rotation axis directed along the rotation direction (y) through a sense-to-substrate elastic device comprising at least one sense-to-substrate spring, the sense lever configured to be tilted at a lever tilt relatively to the drive excitation direction (x),
a first drive frame,
a second drive frame,
a first sense frame connected to the first drive frame through a first sense-to-drive elastic device comprising at least one first sense-to-drive spring and connected to the sense lever through a first sense-to-lever elastic device comprising at least one first sense-to-lever spring, the first sense frame configured to be tilted at a first tilt relatively to the drive excitation direction (x),
a second sense frame connected to the second drive frame through a second sense-to-drive elastic device comprising at least one second sense-to-drive spring and connected to the sense lever through a second sense-to-lever elastic device comprising at least one second sense-to-lever spring, the second sense frame configured to be tilted at a second tilt relatively to the drive excitation direction (x),
a sensing system connected to the sense lever and comprising at least one strain gauge configured to be mechanically stressed by the sense lever when said sense lever is rotating around the rotation axis,
an excitation device configured to force the first drive frame and the second drive frame into opposite motions along the drive excitation direction (x),
wherein the first sense-to-drive elastic device, the first sense-to-lever elastic device, the second sense-to-drive elastic device and the second sense-to-lever elastic device are configured so that upon the inertial sensor being subjected to a rotational movement about the rotation axis, in a transversal plane (xz) extending along the drive excitation direction (x) and the detection direction (z), the ratio of the first tilt to the lever tilt and the ratio of the second tilt to the lever tilt are both lower than 0.1, and
wherein:
both the first sense-to-drive elastic device and the second sense-to-drive elastic device have a sense-to-drive out-of-plane translational stiffness K CD along the detection direction (z), and a sense-to-drive torsional stiffness C CD about the rotation direction (y),
both the first sense-to-lever elastic device and the second sense-to-lever elastic device have a sense-to-lever out-of-plane translational stiffness K SC along the detection direction (z), and a sense-to-lever torsional stiffness C SC about the rotation direction (y),
the sense-to-substrate elastic device has a sense-to-substrate translational stiffness K TOR along the drive excitation direction (x), and a sense-to-substrate torsional stiffness C TOR about the rotation direction (y),
both the centre of rotation of the first sense-to-drive elastic device and the centre of rotation of the second sense-to-drive elastic device are separated from the rotation axis along the drive excitation direction (x) by a distance called sense-drive rotation distance I CD ,
both the centre of rotation of the first sense-to-lever elastic device and the centre of rotation of the second sense-to-lever elastic device are separated from the rotation axis along the drive excitation direction (x) by a distance called sense-lever rotation distance I SC ,
both the centre of mass of the first sense frame and the centre of mass of the second sense frame are separated from the rotation axis along the drive excitation direction (x) by a distance called centre-of-mass distance x C ,
the at least one strain gauge has a translational stiffness along the drive excitation direction (x), called gauge translational stiffness K G ,
the substrate and the at least one strain gauge have respectively a substrate thickness h S and a gauge thickness h G in the detection direction (z),
with
l
CD
-
x
C
=
-
C
OS
K
SC
(
l
SC
-
x
C
)
K
CD
(
C
OS
+
2
(
C
SC
+
K
SC
l
SC
2
)
)
+
2
C
SC
K
SC
x
C
K
CD
(
C
OS
+
2
(
C
SC
+
K
SC
l
SC
2
)
)
±
1
µm
,
with
C
OS
=
C
TOR
+
2
K
G
K
TOR
Z
G
2
2
K
G
+
K
TOR
and
Z
G
=
h
S
-
h
G
2
.
2 . The inertial sensor according to claim 1 , wherein the first sense-to-drive elastic device further comprises at least one first additional sense-to-drive spring, the at least one first sense-to-drive spring connecting the first sense frame to a first portion of the first drive frame extending along the rotation direction (y) and the at least one first additional sense-to-drive spring connecting the first sense frame to a second portion of the first drive frame extending along the drive excitation direction (x).
3 . The inertial sensor according to claim 1 , wherein the second sense-to-drive elastic drive further comprises at least one second additional sense-to-drive spring, the at least one second sense-to-drive spring connecting the second sense frame to a first portion of the second drive frame extending along the rotation direction (y) and the at least one second additional sense-to-drive spring connecting the second sense frame to a second portion of the second drive frame extending along the drive excitation direction (x).
4 . The inertial sensor according to claim 1 , wherein the sense-to-substrate elastic device is accommodated within the sense lever.
5 . The inertial sensor according to claim 1 , wherein the first drive frame and the second drive frame are connected through at least one connection spring.
6 . The inertial sensor according to claim 1 , further comprising at least one compensation electrode extending into a plane parallel to the device plane.
7 . The inertial sensor according to claim 1 , wherein the sensing system is accommodated within the sense lever.
8 . The inertial sensor according to claim 1 , wherein the sense lever comprises a central beam which extends along the rotation axis and to which the sensing system is connected.
9 . The inertial sensor according to claim 1 , wherein the sensing system comprises at least one connection zone configured to electronically connect the at least one strain gauge.
10 . A detection system comprising a plurality of inertial sensors according to claim 1 .
11 . The detection system according to claim 10 , wherein at least two inertial sensors have perpendicular rotation directions.