Source: http://www.google.com/patents/US6928872?dq=6,272,646
Timestamp: 2015-04-01 10:55:05
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Patent US6928872 - Integrated gyroscope of semiconductor material with at least one sensitive ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn integrated gyroscope, including an acceleration sensor formed by: a driving assembly; a sensitive mass extending in at least one first and second directions and being moved by the driving assembly in the first direction; and by a capacitive sensing electrode, facing the sensitive mass. The acceleration...http://www.google.com/patents/US6928872?utm_source=gb-gplus-sharePatent US6928872 - Integrated gyroscope of semiconductor material with at least one sensitive axis in the sensor planeAdvanced Patent SearchPublication numberUS6928872 B2Publication typeGrantApplication numberUS 10/443,647Publication dateAug 16, 2005Filing dateMay 21, 2003Priority dateApr 27, 2001Fee statusPaidAlso published asUS20040035204Publication number10443647, 443647, US 6928872 B2, US 6928872B2, US-B2-6928872, US6928872 B2, US6928872B2InventorsGuido Spinola Durante, Sarah Zerbini, Angelo MerassiOriginal AssigneeStmicroelectronics S.R.L.Export CitationBiBTeX, EndNote, RefManPatent Citations (19), Referenced by (26), Classifications (6), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetIntegrated gyroscope of semiconductor material with at least one sensitive axis in the sensor plane
US 6928872 B2Abstract
a first driving assembly; a first sensitive mass extending in a first direction and a second direction, said first sensitive mass being moved by said driving assembly in said first direction; a first capacitive sensing electrode, facing said first sensitive mass, the first driving assembly, first sensitive mass, and first sensing electrode being components of a first part of the acceleration sensor; a second driving assembly; a second sensitive mass extending in the first direction and the second direction, said second sensitive mass being moved by said second driving assembly in said first direction; and a second capacitive sensing electrode, facing said second sensitive mass, the second driving assembly, second sensitive mass, and second sensing electrode being components of a second part of the acceleration sensor, symmetrical to the first part, the first and second driving assemblies being connected by central springs; wherein said acceleration sensor has a rotation axis parallel to said second direction, and said first and second sensitive masses are sensitive to forces acting in a third direction perpendicular to said first and second directions. 2. The gyroscope according to claim 1 wherein said first capacitive sensing electrode comprises a conductive material region extending underneath and at a distance, in said third direction, from said first sensitive mass.
a sensitive mass extending in a first direction and a second direction, a driving assembly, said sensitive mass being moved by said driving assembly in said first direction, said driving assembly including a driving element connected to said sensitive mass through a mechanical linkage, which enables, at least to one part of said sensitive mass, a movement having a component in a third direction perpendicular to said first and second directions; and a capacitive sensing electrode, facing said sensitive mass; wherein said acceleration sensor has a rotation axis parallel to said second direction, and said sensitive mass is sensitive to forces acting in the third direction. 4. The gyroscope according to claim 3 wherein said sensitive mass can be translated parallel to said third direction.
a driving assembly; a sensitive mass extending in a first direction and a second direction, said sensitive mass being moved by said driving assembly in said first direction; and a capacitive sensing electrode, facing said sensitive mass; wherein said acceleration sensor has a rotation axis parallel to said second direction, and said sensitive mass is sensitive to forces acting in a third direction perpendicular to said first and second directions; the gyroscope comprising two symmetrical parts connected by central springs and each including an own driving assembly, an own sensitive mass, and an own capacitive sensing electrode. 18. A device, comprising:
a semiconductor substrate; an electrode formed in a first layer of the substrate; a driving element, mechanically coupled to the substrate and configured to oscillate along a first axis lying in a first plane parallel to the first layer; and a sensing mass, mechanically coupled to the driving element and capacitively coupled to the first electrode, formed in a second layer of the substrate, the sensing mass being configured to oscillate with the driving element along the first axis lying in the first plane parallel to the first layer, and further configured to move along a second axis perpendicular to the first layer in response to angular movements of the substrate about a third axis perpendicular to the first axis and lying in the first plane. 19. The device of claim 18, further comprising a processing circuit configured to detect a magnitude of angular velocity of the substrate about the third axis by detecting changes in the capacitive coupling of the sensing mass and the electrode.
a semiconductor substrate; a first, second, third, and fourth electrodes formed in a first layer of the substrate; a first sensing mass, mechanically coupled to the substrate and capacitively coupled to the first and second electrodes, formed in a second layer of the substrate, the first sensing mass being configured to oscillate along a first axis lying in a first plane parallel to the first layer, and further configured to oscillate about a second axis lying in the first plane in response to forces acting along a third axis perpendicular to the first and second axes, the first sensing mass and first and second electrodes forming first and second sensing capacitors; and a second sensing mass, mechanically coupled to the substrate and capacitively coupled to the third and fourth electrodes, formed in the second layer of the substrate, the second sensing mass configured to oscillate along the first axis lying in the first plane, and further configured to oscillate about a fourth axis, parallel to the second axis, in response to forces acting along the third axis; the second sensing mass and third and fourth electrodes forming third and fourth sensing capacitors. 22. The device of claim 21, further comprising a processing circuit configured to process signals from the first, second, third, and fourth sensing capacitors to separate forces acting on the device due to coriolis effect from forces acting on the device due to momenta.
oscillating a driving element in a first axis lying in a first plane relative to a surface of a semiconductor material body, the driving element mechanically couple to the body; moving the semiconductor material body about a second axis perpendicular to the first axis and lying in the same plane; and detecting the movement of the semiconductor material body by detecting changes in a capacitive coupling between a sensing mass mechanically coupled to the driving body and an electrode formed on the surface of the semiconductor body, due to movements of the body in an axis perpendicular to the first plane. 24. A device, comprising:
a semiconductor material body; a driving element coupled to the semiconductor material body and movable with respect to the semiconductor material body in a first axis; a sensing mass mechanically couple to the driving element and movable with respect to the driving element in a second axis, perpendicular to the first axis; and a capacitive electrode positioned between the semiconductor material body and the sensing mass and configured to detect movement of the sensing mass in the second axis. 25. The device of claim 24 wherein the sensing mass is movable with respect to the driving element in a third axis, perpendicular to the first and second axes, the second axis being perpendicular to a face of the semiconductor material body, the device further comprising:
a plurality of sensing electrodes configured to detect movement of the sensing mass in the third axis. 26. The device of claim 24 wherein the driving element, sensing mass, and capacitive electrode are components of a first part of the device, the device further comprising:
a second part, symmetrical to the first part and coupled thereto by spring elements. 27. The device of claim 24 wherein the sensing mass is a first sensing mass and the capacitive electrode is a first capacitive electrode, the device further comprising:
a second sensing mass, the first and second sensing masses each being eccentrically, rotatably, coupled to the driving element, the first and second sensing masses configured to rotate around the second and a third axes, respectively, the second and third axes being parallel to each other; and second, third, and fourth capacitive electrodes, the first and second capacitive electrodes being positioned between the semiconductor material body and the first sensing mass, and the third, and fourth capacitive electrodes being positioned between the semiconductor material body and the second sensing mass.
As is known, integrated gyroscopes of semiconductor material, manufactured using MEMS (Micro-Electro-Mechanical Systems) technology, operate on the basis of the theorem of relative accelerations, exploiting Coriolis acceleration. In particular, when a linear velocity is applied to a movable mass rotating with angular velocity, the movable mass �feels� an apparent force, called Coriolis force, which determines a displacement thereof in a direction perpendicular to the linear velocity and to the axis of rotation. The apparent force can be hence detected by supporting the movable mass through springs which enable a displacement thereof in the direction of the apparent force. On the basis of Hooke's law, this displacement is proportional to the apparent force itself and, thus, detection of the displacement of the movable mass enables detection of Coriolis force and, hence, of the angular velocity.
U.S. Pat. No. 5,955,668 and WO 99/19734 provide for an external oscillating mass connected to an internal sensing mass and, i.e., two independent mechanical parts which can be appropriately calibrated. However, in case of the gyroscope of circular shape (described in the patent U.S. Pat. No. 5,955,668), the structure is sensitive to stresses due to the fabrication steps and to thermal drift, since the suspension springs of the sensing element internal to the oscillating external mass are very rigid in the direction of the axis of the angular velocity, and it is not possible to anchor the detection element centrally, in so far as the gyroscope would �feel� the velocity of a number of axes simultaneously and would become unusable. Instead, for the gyroscope of rectangular shape (described in the patent WO 99/19734), the system is not optimized since it uses suspension springs which involve undesired rotational contributions; moreover, the described gyroscope does not enable rejection of linear accelerations. In either case, but in particular in case of a translation gyroscope, numerous interconnections are present which pass underneath the mass, and the interconnections are quite long, with the risk of capacitive couplings with the sensing structures and hence of false or imprecise reading.
FIG. 3 is a cross-section taken along line III�III of FIG. 1;
FIG. 4 is a cross-section taken along the line IV�IV of FIG. 2;
FIG. 8 is a cross-section taken along the line VIII�VIII of FIG. 7; and
FIG. 9 is a cross-section taken along the line IX�IX of FIG. 7.
This previous gyroscope enables detection of the Coriolis force acting parallel to the second direction, in the sensor plane, and due to a rotation about an axis (hereinafter referred to as �sensitive axis�) extending in the third direction, perpendicular to the sensor plane. By setting two gyroscopes rotated by 90� one with respect to the other on an appropriate board, it is possible to detect the apparent forces acting along two Cartesian axes parallel to the plane of the gyroscope, and hence the corresponding angular accelerations. It is not, however, possible to detect the apparent force and the corresponding angular acceleration along the third Cartesian axis, since in this case the third gyroscope should be mounted perpendicular to the board.
FIGS. 1 to 3 illustrate a gyroscope 1 according to a first embodiment of the invention. As shown in detail in FIG. 1, the gyroscope 1 comprises an acceleration sensor 23 formed by two parts 2 a, 2 b, which are symmetrical with respect to a central axis of symmetry designated by A and connected together by two central springs 3, configured to be symmetrical with respect to a horizontal centroidal axis designated by B. Furthermore, each part 2 a, 2 b has a vertical centroidal axis designated by C. The axes A and C are parallel to the axis Y, while the axis B is parallel to the axis X. The intersection between the horizontal centroidal axis B and the vertical centroidal axis C constitutes the centroid G1 of each part 2 a, 2 b. The acceleration sensor 23 is sensitive to an angular velocity directed parallel to the axis Y.
The driving element 5, the movable driving arms 12, the movable driving electrodes 13, the fixed driving arms 14 a, 14 b, and the fixed driving electrodes 15 a, 15 b together form a driving system 16 for each part 2 a, 2 b. The sensitive mass 6 has a basically plane shape, with the main extension in the direction of the axes X and Y. In the example illustrated, each sensitive mass 6 is rectangular in shape, with the length 11 in the Y direction, the width 12 in the X direction, and with a centroid G2, and is surrounded on three sides by the respective driving element 5.
In this way, if two gyroscopes 1 of the type described are available in a single chip, the two gyroscopes being rotated through 90� (one with driving direction parallel to the axis X and the other with driving direction parallel to the axis Y) and hence having two sensitive axes in the plane of the sensitive mass 6, but staggered by 90� with respect to one another, and if, moreover, there is available a gyroscope of a known type on the same chip, this gyroscope having a sensitive axis perpendicular to the plane of the sensitive mass 6, it is possible with a single device to detect the angular velocities along all three Cartesian axes.
In the gyroscope 40 of FIG. 5, as illustrated in FIG. 6, the Coriolis force F acting on the centroid G3 of each sensitive mass 42 a, 42 b determines opposite rotations of the suspended masses 42 a, 42 b connected to a same driving element 5, since they have the centroid G3 on opposite sides with respect to the respective supporting elements 46 a, 46 b. This rotation determines an opposite variation in the capacitance of the capacitors formed by each portion 43 a, 43 b of the suspended masses 42 a, 42 b and the respective sensing electrode 46 a, 46 b. With the structure described, it is possible to eliminate the influence of external momenta acting on the suspended masses 42 a, 42 b. In fact, as shown in the simplified diagram of FIG. 6 and as explained above, the couple generated by the Coriolis force F, designated by M2, has the same value, but opposite sign, in the two accelerometers 42 a, 42 b carried by the same driving element 5. In particular, the couple M2 cause the more massive larger portions 43 b of the suspended masses 42 a, 42 b to drop downward or rise upward together as they rotate in opposite directions about their respective support elements 46 a, 46 b. This results in opposite-polarity changes of the capacitance of the capacitors formed by the two accelerometers 42 a, 42 b and the respective sensing electrode 48 a, 48 b, and thus an opposite change in the signals supplied by the sensing electrodes 48 a, 48 b of each part 2 a, 2 b. Instead, a possible external couple, designated by M1, acts in a concordant direction on both of the suspended masses 42 a, 42 b. In particular, the couple M1 will result in rotation of the suspended masses 42 a, 42 b about their respective supporting elements 46 a, 46 b in the same direction. This results in same-polarity changes of the capacitance of the capacitors formed by the two accelerometers 42 a, 42 b and the respective sensing electrode 48 a, 48 b, and thus a same change in the signals supplied by the sensing electrodes 48 a, 48 b of each part 2 a, 2 b. Consequently, by subtracting the signals supplied by the sensing electrodes 48 a, 48 b of each part 2 a, 2 b of the gyroscope 40 from one another, the effect due to the external momentum M1 is cancelled, while the effect due to the Coriolis force is summed. In this way, it is possible to determine the magnitude of the angular velocity in the direction Y, eliminating the noise due to external momenta. In addition, a more symmetrical reading is obtained, which provides a non-negligible advantage during calibration and matching of the sensing resonance frequencies.
The gyroscope 40 illustrated in FIG. 5 is less sensitive than the gyroscope 1 of FIG. 1, since the variation in capacitance due to rotation of the suspended masses 42 a, 42 b is less than the variation that may be obtained as a result of translation in the direction Z of the suspended masses 6, given the same external force F. The gyroscope 40 is, however, less subject to electrostatic pull-in due to mechanical shocks. In fact, in the gyroscope of FIG. 1, on account of the biasing of the driving elements 5 and the sensing electrodes 20, it may happen that, following upon a mechanical shock, the driving elements 5 adhere to, and remain attracted by, the respective sensing electrodes 20, this being facilitated by the large facing area. Instead, with the gyroscope 40, a possible mechanical shock, such as might cause rotation of the suspended masses 42 a, 42 b, does not in general cause a condition of �sticking�, given that in this case each sensitive mass 42 a, 42 b touches the respective sensing electrode 48 a, 48 b only along one edge instead of with the entire surface.
The gyroscope 50 of FIGS. 7 to 9 is able to detect forces acting in the direction Z (sensitive axis parallel to the axis Y) as has been described with reference to FIG. 1. In addition, the gyroscope is able to detect forces acting in the direction of the axis Y (sensitive axis parallel to the axis Z), in so far as any displacement in the direction Y is detected as a variation in capacitance between the movable sensing electrodes 18 and the fixed sensing electrodes 19 a, 19 b. In the gyroscope 50 it is possible to distinguish the effects of forces or of components thereof acting in the three directions. In fact, the displacements in the direction X (due to driving or to external forces) are not detected by the sensing electrodes 20, as mentioned with reference to FIG. 1, and cause a same capacitive variation on the fixed sensing electrodes 19 a and 19 b and can thus be rejected. The displacements along the axis Y are not detected by the sensing electrodes 20, as mentioned previously with reference to the embodiment of FIG. 1, but are detected by the fixed electrodes 19 a and 19 b, as explained above. The displacements along the axis Z are detected by the sensing electrode 20, as mentioned previously with reference to FIGS. 1-3. Their effect on the fixed sensing electrodes 19 a and 19 b can, instead, be rejected since they detect a same capacitive variation with respect to the movable sensing electrodes 18, as for the displacements in the direction X.
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