RU2347190C1 - Micromechanical gyroscope - Google Patents

Abstract

FIELD: physics; measuring.

SUBSTANCE: invention concerns to the devices measuring angular velocity, in particular, to micromechanical gyroscopes (MMG) of vibrating type. The MMG contains the basis made from silicon with stators mounted on it through isolating stratums and a seat on which with the help torsions the curl is suspended, and a cover from silicon with the isolating stratum superimposed on it on which electrodes are located and the electronic block with the power supply. The basis and a cover are welded on perimetre. The signal outputs of the electronic block are joined to deductions from stators, a curl and electrodes, deductions, at least, from the basis or cover silicon are joined to a blanket deduction of the power supply. Besides, on an outside surface of silicon of a cover and/or the basis the metallisation stratum is superimposed. Introduction of an additional deduction from the basis and-or cover silicon and as drawing of an additional stratum of metallisation by an outside surface of silicon of a cover and/or the basis allow to reduce influence of spurious couplings between power and signal electrodes of the MMG.

EFFECT: reduction of influence of spurious couplings between power and signal electrodes of the MMG.

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Description

The proposed device relates to devices that measure angular velocity, in particular to micromechanical gyroscopes (MMG) of vibration type.

Currently developed and widely used MMG vibration type. They include moving mass (PM), a system for measuring PM movements along two axes, a system for exciting vibrations at the resonant frequency of the suspension (Fres) along one axis, which are sometimes called primary and the axis, respectively, is the axis of primary vibrations. Under the action of Coriolis acceleration along the other axis (orthogonal to the first), PM oscillations arise, called secondary [Peshekhonov et al. Results of the development of a micromechanical gyroscope. XII St. Petersburg International Conference on Integrated Navigation Systems May 23-25, 2005 p. 268-274, Fig. 1, Raspopov V.Ya. Micromechanical devices, 2nd edition. Tool Gos. University - Tula, 2004, 475 pp, 325-462 pp]. The motion axes of the PM have fixed electrodes (or stators). These stators with a conductive PM form capacitors whose capacitances depend on the position of the PM.

The power electrodes located along the axis of excitation of primary vibrations in the MMG receive alternating voltages that create forces or moments at the resonant frequency of the PM suspension with the help of an electric field, which can be considered as power voltages. Their level can be from 0.1 to 10 V, depending on the quality factor of the suspension. In MMG, the level of power signals exceeds the level of the measured signals by three or more orders of magnitude.

When using conductive silicon as the base in MMG, as shown in FIG. p.1092-1101) between the electrodes to which power voltages are supplied and the electrodes forming capacitive PM displacement sensors, spurious connections arise, the equivalent circuit of which is a series connection of capacitors and a resistor. To reduce the influence of these spurious bonds, compensating signals can be used, the value of which is determined experimentally. However, it is difficult to introduce such corrections for a large number of electrodes because of the complicated procedure for determining the numerical values of these corrections. In addition, when changing environmental parameters (for example, temperature), the parameters of the equivalent circuit describing these parasitic bonds can change.

To reduce the influence of spurious bonds, MMG electrodes can be placed on a dielectric base (see M.E. Ash et al. Micromechanical Inertial Sensor Development at Draper Laboratory With Recent Test Results. Symposium Gyro Technology 1999, Stuttgart, Germany, p. 3.0- 3.12, fig. 2, fig. 3). These figures show that MMG is assembled from two parts (“wafers”), one of which is used to make glass and the other is silicon. However, this design is low-tech, because involves the use of two different types of materials.

As an example of a commercially available MMG design made entirely on a silicon crystal and having a large number of electrodes on one substrate, we can use Bosch MMG, in which both the power electrodes of the primary oscillation excitation channel and the measuring electrodes of the output channel are located on the substrate (see the book Raspopova p. 344-345).

As another example, MMG described in [Peshekhonov et al. Results of the development of a micromechanical gyroscope. XII St. Petersburg International Conference on Integrated Navigation Systems May 23-25, 2005 p.268-274]. The design of the MMG is shown in Fig. 2,3, and the manufacturing technology is shown in Fig. 5. In contrast to the Bosch MMG, the measuring electrodes of the output channel are not located on the base, but on the MMG cover. However, such a placement does not eliminate the passage of interference caused by power voltages. This is due to the fact that in this design there is a connection between the base and the MMH cover through metallization layers deposited along the perimeter of the silicon crystal (see the aforementioned Fig. 5, where the metallization layers are highlighted in white in Figs. 5g and 5c). And although there is an insulating layer under the metallization layer on the cover, which is used as silicon dioxide, the connection between the upper and lower silicon crystals (between the base and the cover) on alternating current exists and has a significant value - at the level of tens of picofarads.

The presence of capacitive coupling between the base and the cover with measuring electrodes, which form a capacitive PM displacement sensor along the output channel, leads to the fact that the inputs of capacitance-voltage converters, for example, transresistive amplifiers (see Fig. 6 of the mentioned article Peshekhonov and others) In addition to the high-frequency current, currents arrive at the resonant frequency of the PM suspension from the power electrodes of the drive, which increases the noise and interference at the output of the demodulator in this channel. In addition, the signals supplied to the power or feedback electrodes can also pass through stray capacitors to the input of the capacitance-voltage converter. Ultimately, this degrades the accuracy of MMG.

As a prototype, the MMG described in the aforementioned work by Peshekhonov [Peshekhonov V.G. et al. Results of the development of a micromechanical gyroscope. XII St. Petersburg International Conference on Integrated Navigation Systems May 23-25, 2005 p.268-274]. This MMG contains a silicon base with stators installed on it through insulating layers and a support on which a rotor is suspended using torsions, a silicon cover with an insulating layer deposited on it, on which electrodes are applied, leads from stators, rotor and electrodes, an electronic unit and its power source, while the signal terminals of the electronic unit are connected to the terminals from the stators, rotor and electrodes, and the power terminals of the electronic unit are connected to the terminals of the power source, including the common terminal.

The disadvantage of MMG is not high enough accuracy due to the passage of power signals from the drive channel (voltages at the electrodes of the comb engine) to the output channel of the MMG through doped silicon and thin layers of silicon oxide.

The objective of the invention is to improve the accuracy of MMG.

The problem is solved in that a micromechanical gyroscope containing a silicon base with stators installed on it through the insulating layers and a support on which a rotor is suspended using torsions, a silicon cover with an insulating layer deposited on it, on which the electrodes are located, and the base and the lid is welded around the perimeter, the electronic unit with a power source, while the signal leads of the electronic unit are connected to the leads from the stators, rotor and electrodes, the leads, at least from silicon Considerations or covers that are connected to the common terminal of the power source. In addition, the problem is solved in that a metallization layer is applied to the outer surface of the silicon of the lid and / or base, which is connected to a common terminal of the power source.

Essentially, in the proposed micromechanical gyroscope, it is proposed to reduce the influence of power electrodes on the measuring ones by connecting the silicon base and cover with a common output of the power source. An additional effect of this is manifested in the fact that the electrodes and the disk are shielded by conductive silicon and an additional metallization layer of the lid and base.

The inventive device is illustrated by drawings.

Figure 1 shows a design variant MMG. In figure 1, the following notation:

1 - base;

2 - support;

3 - torsion bars;

4 - moving mass (PM);

4 - stators located in the plane of the primary oscillations.

Figure 2 shows the electrodes and the conclusions from them. In figure 2, the following notation:

2 - support;

5 - stators located in the plane of the primary oscillations;

6 - a pair of electrodes diametrically located on the lid;

7 - another pair of electrodes diametrically located on the lid;

8 - electrical leads from MMG structural elements (electrodes, stators and supports)

Figure 3 shows the design of the micromechanical part of the MMG. In figure 3, the following notation:

4 - PM;

9 - silicon base 1;

10 - silicon cap;

11 - an insulating layer deposited on the base 1;

12 - metallization layer;

13 - an insulating layer between the metallization layer and the silicon cap.

Figure 4 shows a simplified equivalent electrical circuit MMG. In figure 4, the following notation:

4 - PM, which is shown in the form of an electric current conductor;

8 - electrical conclusions from the structural elements of MMG;

9 - silicon base 1;

10 - silicon cap;

14 - the output of the electronic unit MMG;

15 - 18 - capacitors formed by electrodes 7, 6 and PM 4;

19 - 22 - capacitors formed by the stators 5 and PM 4;

23 - capacitors formed by electrodes 7, 6 and silicon cap 10;

24 - capacitors formed by the stators 5 and silicon base 9;

25 is equivalent resistors representing resistances between the silicon region of the lid 10 near the insulating layer on which the electrodes 7, 8 are placed and the silicon region of the lid near the metallization layer 12;

26 is equivalent resistors representing resistances between the silicon region of the base near the insulating layer 11 on which the stators 5 are placed and the silicon region of the base near the outer surface of the base;

27 - equivalent resistors representing the resistance between the areas of the silicon cap near the insulating layers on which the electrodes 7, 8 are placed;

28 is equivalent resistors representing resistances between areas of the silicon base near the insulating layers on which the stators 5 are placed;

29 is a capacitor formed by a support 2 and silicon base 1;

30 is an equivalent resistor representing the resistance between the silicon base region near the insulating layer on which the support 2 is placed and the silicon base region near the outer surface of the base;

31 is an equivalent resistor representing the ohmic resistance of the torsion bars;

32 - electronic block MMG;

33 - power source electronic block MMG;

34 - the General conclusion of the power source 33;

35 is a capacitor formed by silicon of the cover 10, an insulating layer 13 and a metallization layer 12;

36 is a capacitor formed by silicon of the base 9, an insulating layer 11 located along the perimeter of the base 1 and a metallization layer 12;

37 - an additional layer of metallization on top of the silicon cover 10;

38 - an additional layer of metallization below the silicon base 9;

39 - an additional conclusion from the silicon base 9;

40 - additional output from silicon cap 10.

41 - source of control voltage.

42 - current from the source of control voltage 41.

The proposed device operates as follows.

For the manufacture of vibration-type MMG, two silicon wafers are used, the first of which is (see FIG. 1) the base 1 on which the support 2 is mounted. On this support 2 is suspended by means of torsion 3 3 PM 4 (made in the form of a disk). Stators 5 are also installed on the base. PM 4 and stators 5 have a comb structure, forming a comb motor and a PM 4 angular displacement sensor in the plane of primary vibrations.

The electrodes 6 (see figure 2) used to measure the displacements of PM 4 in the plane of the secondary vibrations are deposited on a second silicon wafer (cover). The electrodes 7, which can be used to introduce feedback and adjust the resonant frequency of the suspension along the axis of the secondary vibrations, are also formed on the lid. Conclusions 8 from the stators 5, electrodes 6, 7 and supports 2 allow you to apply electrical signals to them from the electronic unit that ensures the functioning of the MMG.

The support 2, on which the PM 4 is suspended, and the stators 5 are mounted on the base 1 of silicon 9 through an insulating layer of silicon oxide 11 (see figure 3). A cover made of silicon 10 is attached to the base by welding metallization layers 12 previously deposited on the base and on the cover. The metallization layer 12 on the lid is applied after the formation of an insulating layer 13 on the periphery of the lid.

As a result of the described technological operations in the micromechanical assembly MMG, a comb motor and capacitive displacement sensors PM 4 are formed, which on a simplified electrical diagram of the connections between different nodes of the micromechanical assembly MMG are (see Fig. 4) capacitors 19-22 formed by PM 4 and stators 5, and capacitors 15-18 formed by PM 4 and electrodes 6, 7. Pin 8 through the resistance of torsion 3 (resistor 31) is connected to PM 4. The electrical resistance of the support itself compared to the resistance of thin torsions can be neglect. In addition to these elements and bonds, which can be considered useful, in the micromechanical assembly of the MMG there are parasitic bonds, which are depicted by capacitors 23, 24, 29 and 35 and resistors 25-28, 30. The capacitors are formed by the conductive layers of silicon, of which the stators 5 are made, electrodes 6, 7 and the support 2, or layers of metallization 12 and layers of silicon oxide 11, 13 between the conductors. It should be noted that the dielectric constant of silicon oxide is 3.9 times higher than vacuum. Therefore, with the same values of the gap between PM 4 and electrodes 6, 7 and the thickness of this oxide layer between the electrodes and silicon of the cover 11, the stray capacitance values are about 4 times more useful. So, for example, if the capacitance of the capacitor 15 is 2 pF, then the capacitance of the capacitor 23 will be approximately 8 pF. Note that for smaller values of the thickness of the oxide layer (as a rule, it is chosen equal to 0.5 μm), these parasitic capacitances turn out to be correspondingly larger, which further increases the level of interference. The total area of the metallization layers 12 located along the perimeter of the crystal is also large, which, taking into account the dielectric constant of silicon oxide, gives a value of the order of 15-20 pF, i.e. significantly more capacitance of the electrodes. To the terminals 8 shown in FIG. 2, an electronic unit 32 is connected to the MMH, which is connected to a voltage source 33 by the power terminals, which has two terminals, for example, 5 V and a common terminal 34. In order not to clutter the connection diagram in FIG. 3, not all connections of terminals 8 with the corresponding inputs and outputs of block 32 are shown. In the proposed device from silicon of the cover 10 and base 9, an additional terminal 39 and 40 is made, respectively, which is connected to the common terminal 34 of the source 33. An additional effect of reducing spurious connections is achieved by applying an additional layer of metallization 37 and 38 over the entire surface of the silicon cap 10 and base 9, which leads to a significant reduction equivalent resistors 25 and 26. Also, an additional layer of metallization 37 and 38 acts as a shield for the electrodes 4 and PM from electromagnetic environmental influences.

Figure 4 shows the passage of current 42 from a source of control voltage 41 to the inputs of the electronic unit 32 through the measuring electrodes.

Thanks to the introduced metallization layer 38 and 37, which leads to a decrease in the resistances 25 and 26 and additional terminals 39 and 40 from silicon connected to the common terminal 34, the fraction of the current from the source U1 passing through the resistor 26 increases, and the fraction of the current passing through the electronic unit 32 is reduced. Thus, the influence of spurious connections and the level of interference in the proposed MMG are reduced.

Thus, in the proposed device in comparison with the prototype, an increase in accuracy is achieved.

Claims (2)

1. A micromechanical gyroscope containing a silicon base with stators installed on it through insulating layers and a support on which a rotor is suspended using torsions, a silicon cover with an insulating layer deposited on it, on which electrodes are located, while the base and cover are welded to perimeter, an electronic unit with a power source, while the signal terminals of the electronic unit are connected to the leads from the stators, rotor and electrodes, characterized in that the leads from the silicon base and / or cover, which are unified with a common power supply wiring. 2. The micromechanical gyroscope according to claim 1, characterized in that a metallization layer is applied onto the outer surface of the silicon of the lid and / or base, which is connected to a common terminal of the power source.

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