Source: https://patents.justia.com/patent/6928872
Timestamp: 2018-10-15 16:45:16
Document Index: 146304708

Matched Legal Cases: ['arts 2', 'art 2', 'art 2', 'art 2', 'arts 2', 'art 2', 'art 2', 'art 2', 'arts 2', 'art 2', 'art 2', 'art 2', 'art 2']

US Patent for Integrated gyroscope of semiconductor material with at least one sensitive axis in the sensor plane Patent (Patent # 6,928,872 issued August 16, 2005) - Justia Patents Search
Justia Patents Vibratory MassUS Patent for Integrated gyroscope of semiconductor material with at least one sensitive axis in the sensor plane Patent (Patent # 6,928,872)
May 21, 2003 - STMicroelectronics S.r.l.
Multi-device transducer module, apparatus including the transducer module and method of manufacturing the transducer module
Multichannel transducer devices and methods of operation thereof
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 2a, 2b, 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 2a, 2b 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 2a, 2b.
Each part 2a, 2b comprises a driving element 5 of concave shape, here a square C shape, and a sensitive mass 6, completely housed inside the space delimited by the driving element 5 but having a peripheral portion not facing the driving element 5 itself. Both the driving element 5 and the sensitive mass 6 are perforated as shown only in part in FIG. 2.
Each driving element 5 is formed by a first and a second oscillating arms 7, 8, which are parallel to one another and are connected at one end by a central cross member 9 extending perpendicular to the oscillating arms 7, 8. The two cross members 9 of the parts 2a, 2b extend parallel to one another, face one another, and are connected by the central springs 3. The first oscillating arms 7 are aligned together, as also are the second oscillating arms 8.
Anchoring springs 10 extend from each end of the oscillating arms 7, 8 towards the outside of the respective driving elements 5. The anchoring spring 10, which can be seen more clearly in the detail of FIG. 2, are of a folded type, i.e., they comprise at least two non-aligned portions, one connected to the respective driving element 5 and one having an anchoring end 11 fixed to a fixed substrate (as described in greater detail hereinafter with reference to FIG. 3). The anchoring springs 10 are equal and are arranged in pairs symmetrically with respect to the centroidal vertical axis C and the centroidal horizontal axis B, so that the anchoring springs 10 are at equal distances from one another and balanced with respect to the centroid G1 of the respective part 2a, 2b of the gyroscope. The anchoring springs 10 are here made up of four portions extending orthogonally to the arms 7, 8 and connected, in pairs, via short connection portions at their ends.
Associated to each movable driving arm 12 is a first and a second fixed driving arms 14a, 14b (see FIG. 2), which are parallel to the movable driving arms 12 and carry respective fixed driving electrodes 15a, 15b. The fixed driving electrodes 15a, 15b extend perpendicular to the fixed driving arms 14a, 14b towards the respective movable driving arms 12 and are comb-fingered to the movable driving electrodes 13. The first fixed driving arms 14a are arranged all on a same side of the respective movable driving arms 12 (in the example, on the right) and are all biased at a same first potential. Likewise, the second fixed driving arms 14b are all arranged on the other side of the respective movable driving arms 12 (in the example, on the left) and are all biased at a same second potential. For example, it is possible to use a push-pull biasing scheme.
The driving element 5, the movable driving arms 12, the movable driving electrodes 13, the fixed driving arms 14a, 14b, and the fixed driving electrodes 15a, 15b together form a driving system 16 for each part 2a, 2b.
FIG. 3 shows a cross-section through the gyroscope 1. As may be noted, the sensitive mass 6 (as also the driving element 5, the springs 10, 24, the movable driving arms 12, and the fixed driving arms 14a, 14b) is formed in a structural layer, here constituted by an epitaxial layer 29 formed on top of a substrate 30 of monocrystalline silicon. The sensing electrode 20 is formed on top of an insulating layer 31, for example, a deposited oxide layer, which is, in turn, formed on top of the substrate 30.
FIG. 4 shows the cross-section of the gyroscope 1 at one anchoring end 11 of an anchoring spring 10. In particular, the anchoring end 11 has, at the bottom, a reduced portion 11a overlying, and in direct electrical contact with, a first connection region 33 of conductive material, formed in the layer of polycrystalline silicon of the sensing electrode 20 and indicated by a dashed line in FIG. 1. The first connection region 33 enables biasing of the anchoring spring 10 and, more in general, of the driving element 5 and of the sensitive mass 6 at the desired potential. FIG. 4 also shows the non-removed portions 32 of a sacrificial layer, which, where removed, forms the air gap 35. In FIG. 4, the insulating layer 31 and the sacrificial layer 32 extend only underneath the anchoring end 11, and have been removed underneath the movable parts (here the anchoring spring 10). Similar solutions of connection are used for the fixed driving elements 14a, 14b, where, however, the sacrificial area 22 is not generally removed.
The gyroscope 40 of FIG. 5 still comprises a driving system 16 of the type described with reference to FIG. 1, but each driving element 5 is here E-shaped and is provided with two concavities 41a, 41b facing outwards. In practice, each driving element 5 comprises, in addition to the oscillating arms 7, 8 and the central cross member 9, an intermediate arm 45, extending parallel to the axis X. Each driving element 5 is also here supported and biased through an anchoring spring 10 of a folded type, the springs having an anchoring end 11 and being arranged symmetrically with respect to the vertical centroidal axis C.
A sensitive mass 42a, 42b arranged inside each concavity 41a, 41b has a generally rectangular shape and is supported in an eccentric way. In detail, each sensitive mass 42a, 42b is formed by a first smaller rectangular portion 43a and a second larger rectangular portion 43b, these portions being interconnected by a narrow portion 44. Each sensitive mass 42a, 42b has an own centroid G3.
The sensitive mass 42a is supported by two supporting arms 46a extending parallel to the cross member 9 from the narrow portion 44 towards the oscillating arm 7 and towards the intermediate arm 45. Likewise, the sensitive mass 42b is supported by two supporting arms 46b extending parallel to the cross member 9 from the narrow portion 44 towards the oscillating arm 8 and towards the intermediate arm 45. The supporting arms 46a and 46b form torsion springs.
The supporting arms 46a of each sensitive mass 42a are aligned together, as are the supporting arms 46b of each sensitive mass 42b, but, in each part 2a, 2b, the supporting arms 46a of the sensitive mass 42a are misaligned with respect to the supporting arms 46b of the sensitive mass 42b. All of the supporting arms 46a, 46b extend at a distance from the centroid G3 of the respective sensitive mass 42a, 42b. Also here the suspended masses 42a, 42b of the two parts 2a, 2b of the gyroscope 40 are arranged symmetrically with respect to the central axis of symmetry A.
Respective sensing electrodes 48a, 48b extend underneath each portion 43a, 43b of the four suspended masses 42a, 42b. In detail, the sensing electrodes 48a face the smaller portions 43a, and the sensing electrodes 48b face the larger portions 43b. Also here the sensing electrodes 48a, 48b are formed by a polycrystalline silicon layer, separated from the respective portion 43a, 43b by an air gap, and are connected to a processing circuit (not shown).
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 42a, 42b determines opposite rotations of the suspended masses 42a, 42b connected to a same driving element 5, since they have the centroid G3 on opposite sides with respect to the respective supporting elements 46a, 46b. This rotation determines an opposite variation in the capacitance of the capacitors formed by each portion 43a, 43b of the suspended masses 42a, 42b and the respective sensing electrode 46a, 46b.
With the structure described, it is possible to eliminate the influence of external momenta acting on the suspended masses 42a, 42b. 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 42a, 42b carried by the same driving element 5. In particular, the couple M2 cause the more massive larger portions 43b of the suspended masses 42a, 42b to drop downward or rise upward together as they rotate in opposite directions about their respective support elements 46a, 46b. This results in opposite-polarity changes of the capacitance of the capacitors formed by the two accelerometers 42a, 42b and the respective sensing electrode 48a, 48b, and thus an opposite change in the signals supplied by the sensing electrodes 48a, 48b of each part 2a, 2b.
Instead, a possible external couple, designated by M1, acts in a concordant direction on both of the suspended masses 42a, 42b. In particular, the couple M1 will result in rotation of the suspended masses 42a, 42b about their respective supporting elements 46a, 46b in the same direction. This results in same-polarity changes of the capacitance of the capacitors formed by the two accelerometers 42a, 42b and the respective sensing electrode 48a, 48b, and thus a same change in the signals supplied by the sensing electrodes 48a, 48b of each part 2a, 2b.
Consequently, by subtracting the signals supplied by the sensing electrodes 48a, 48b of each part 2a, 2b 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 42a, 42b 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 42a, 42b, does not in general cause a condition of “sticking”, given that in this case each sensitive mass 42a, 42b touches the respective sensing electrode 48a, 48b only along one edge instead of with the entire surface.
The gyroscope 50 has a basic structure similar to that of the gyroscope 1 of FIG. 1, except for the fact that, in each part 2a, 2b, movable sensing electrodes 18 extend from the side of the sensitive mass 6 facing outwards, parallel to the oscillating arms 7, 8. The movable sensing electrodes 18 are comb-fingered to the fixed sensing electrodes 19a, 19b. In detail, each movable sensing electrode 18 is arranged between a fixed sensing electrode 19a and a fixed sensing electrode 19b. The fixed sensing electrodes 19a are all arranged on a first side of the movable sensing electrodes 18 and are electrically connected together at their outer ends through a first anchoring region 51. The fixed sensing electrodes 19b are all arranged on a second side of the movable sensing electrodes 18 and are electrically connected together through respective second anchoring regions 21 formed at their outer ends and connected together through a second connection region 55, represented by a dashed line in FIG. 7 and illustrated in FIG. 8.
The fixed sensing electrodes 19a, 19b form, with the movable sensing electrodes 18, capacitors, the capacitance of which depends upon the distance between them, in a known way. Consequently, any displacement in the direction Y of the sensitive mass 6, due to an oscillation around axis Z, causes a variation of opposite sign in the voltages of the fixed sensing electrodes 19a and 19b, which is detected and processed by an appropriate circuit (not shown) in a known way.
FIG. 8 is a cross-sectional view through the gyroscope at the second anchoring region 21 of the fixed sensing electrodes 19b. Here the second anchoring regions 21, which are formed in the same structural layer as the anchoring springs 10, i.e., the epitaxial layer 29, have at the bottom a reduced portion 21a formed by the epitaxial layer 29 itself, which overlies and is in direct electrical contact with the second connection region 55 formed in the same layer as the sensing electrodes 20 The second connection region 55 is formed on top of the insulating layer 31 and underneath the sacrificial layer 32, of-which only some portions are visible, which have remained after the movable parts of the gyroscope 50 have been freed. The cross-section of FIG. 8 also shows the fixed sensing electrodes 19a and, in a plane set back with respect to the plane of the cross section, the movable sensing electrodes 18, drawn with a dashed line.
FIG. 9 is a cross-section through the gyroscope 50 taken along a fixed sensing electrode 19a. As may be noted, the first anchoring region 51 is formed in the epitaxial layer 29 and has, at the bottom, a reduced portion 51a formed by the epitaxial layer 29, which overlies and is in direct electrical contact with a third connection region 37 of conductive material, formed in the same layer as the sensing electrodes 20 and the second (polysilicon) connection region 55, on top of the insulating layer 31 and underneath the sacrificial layer 32.
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 19a, 19b.
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 19a and 19b 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 19a and 19b, 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 19a and 19b 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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Patent number: 6928872
Patent Publication Number: 20040035204
Inventors: Guido Spinola Durante (Gavirate), Sarah Zerbini (Fontanellato), Angelo Merassi (Vigevano)
Attorney: Seed IP Law Group, PLLC
Application Number: 10/443,647
Current U.S. Class: Vibratory Mass (73/504.04); Capacitive Sensor (73/514.32)