JP3199775B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for measuring acceleration, which is provided with a seismic mass, which can be bent so as to be displaced by acceleration in a plane of a carrier. A movable electrode connected to the seismic mass, a fixed electrode connected to the carrier, and the fixed electrode together with the movable electrode, the capacitance of which varies with acceleration. Of the form that forms

[0002]

2. Description of the Related Art German Patent No. 40000093.
The specification discloses an acceleration sensor composed of a single-crystal two-layer carrier. This acceleration sensor has a tongue that vibrates parallel to the surface of the carrier, and stationary electrodes are arranged on the tongue against the vibration direction. In this sensor, the acceleration is detected via a change in capacitance between a movable tongue and a stationary electrode.

"Laterally Driven Polysilicon Resonant
Microstructures ”(WCTange, THNauyen, RTHowe; Senso)
According to rand Actuators, 20 (1989) 25-30, seismic masses are known which are suspended on an Archimedes helix and have an electrostatic cam transmission. This publication states that such a structure is realized by polysilicon technology.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve a conventional acceleration sensor of the type mentioned at the outset to provide a better one.

[0005]

According to the present invention which solves this problem, the carrier has an upper layer and a lower layer of polycrystalline silicon, and these two layers are They are insulated from each other, and the seismic mass and the web, the carrier
Means are formed in the plane that are continuous with the upper layer and insulate the stationary electrode from the movable electrode.

[0006]

The acceleration sensor of the present invention has the advantage that rotational motion can be distinguished from linear acceleration by detecting deflections of the seismic mass on multiple sides of the seismic mass. Depending on the type of acceleration, the measurement signals detected on different sides of the seismic mass change in the same direction or in opposite directions. By comparing these signals, it is possible, in a very simple manner, to distinguish between rotational movement and linear acceleration. Also, the seismic mass of the sensor can advantageously be deflected in the carrier plane, without projecting out of the carrier plane at this time. In this case, the carrier itself advantageously serves as a protection against mechanical overload. By having the seismic mass suspended on at least two sides via a thin web, the stability of the sensor against overload is increased,
Very high measurement sensitivity is obtained. At the same time, the sensitivity to lateral acceleration is reduced. With regard to lateral sensitivity, it is particularly advantageous to suspend the seismic mass on four sides. It is particularly advantageous if the sensor is manufactured from a silicon carrier. This is because a particularly small structure can be obtained by the standard manufacturing method. Further advantageously, the evaluation circuit of the sensor can be integrated in the silicon carrier.

[0007] Advantageous variants of the acceleration sensor according to claim 1 are possible by means of the second and subsequent measures.

[0008] The detection of the deflection of the seismic mass can be effected particularly advantageously in a piezoresistive manner by means of two piezoresistors each mounted on the suspension web on the left and right of the web axis. When the seismic mass is accelerated linearly, at least two piezoresistors in each suspension web change in the same direction. If a rotational movement occurs, one side of each suspension web will expand while the other side will contract.
Thereby, the resistance value of each suspension web changes in the opposite direction. Piezoresistive signal detection can also be used advantageously for sensors made from carriers having a single-layer structure. If the entire carrier is constituted by a narrow suspension web, this will predominate the deflection of the seismic mass in the plane of the carrier, while suppressing the deflection of the seismic mass in a direction perpendicular to the plane of the carrier, It is advantageous.

To manufacture and insulate the substructure of the sensor, a biaxial silicon carrier is used to form a doping junction, preferably a pn junction, between the upper and lower layers. This is particularly advantageous. The carrier is composed of a single crystal, in which case the upper layer can be produced by the diffusion of impure atoms, or the upper layer can be a separate epitaxial layer on the carrier. Depending on the structure of the sensor, it is advantageous to use a silicon carrier with a separate polysilicon layer. In this case, the insulation is performed, for example, via silicon oxide between the single-crystal silicon layer and the polycrystalline silicon layer.

Another advantageous possibility is to perform capacitive signal detection. For this purpose, it is advantageous if the stationary electrodes consist of a silicon carrier, projecting starting from two sides facing each other of the frame and parallel to the suspension web. The stationary electrodes cooperate with the suspension web used as the movable electrode to form a capacitor in each case. In order to amplify the signal, another stationary electrode is constructed to protrude from the frame, parallel to this stationary electrode, starting from the seismic mass, and in cooperation with the stationary electrode, the built-in digital It is advantageous to provide a movable electrode forming a capacitor. According to another advantageous embodiment of the invention, the capacitor can be used as a position control element by supplying a variable voltage so that the seismic mass is again brought to its stop position. A combination of a capacitive position control member, a capacitive signal detection member and a piezoresistive signal detection member is also advantageous. Insulating a movable electrode against a stationary electrode
This can be realized particularly well if the seismic mass is only configured in the upper layer. In this way, the pn-junction between the upper layer and the lower layer forms the insulation of the electrode with respect to the lower layer; the insulation in the upper layer is advantageously provided by insulation diffusion Or by etching recesses completely penetrating the upper layer.

According to another embodiment of the acceleration sensor according to the invention, the seismic mass is suspended on two Archimedes spirals penetrating each other, the two spirals comprising a movable web on the outermost winding. ing. The movable web has a cam-like finger structure which, together with the finger structure starting from the stationary web, forms an electrostatic magnetoresistive drive.
The interdigitated finger structures can advantageously also be used for signal measurement or for position control. The additional signal pick-up takes place preferably in a piezoresistive manner by means of piezoresistors arranged on the helix.

In order to increase the sensitivity of the sensor, the seismic mass may be arranged over the entire width of the carrier. If the seismic mass is constructed with the same thickness as the suspension, the moment of inertia or lateral sensitivity is increased.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the configuration of the present invention will be specifically described with reference to the embodiments shown in the drawings.

FIG. 1 shows a stationary frame 10 and a deflectable seismic mass 20 fixed within the frame 10.
And a sensor comprising: In this embodiment, the seismic mass 20 comprises four thin webs 21, 22, 2
It is symmetrically suspended via 3, 24. This structure is composed of a single-layer or two-layer silicon carrier. The carrier is monocrystalline or comprises a polysilicon layer. The webs 21, 22, 23, 24 and the seismic mass 20 may be constructed over the entire thickness of the carrier or may be reduced in thickness. In order to increase the sensitivity, the seismic mass 20 may be configured as large as possible, ie over the entire thickness of the carrier. Web 21, 22, 23, 24
In the seismic mass 20 in which the width dimension of the carrier is greater than the thickness dimension (i.e., for example, the web is formed over the entire thickness of the carrier), the deflection in the carrier plane is perpendicular to the carrier. Dominates over direction changes. In the embodiment shown in FIG. 1, two piezoresistors 81 and 82 are attached to each of the webs 21 to 24, respectively. These piezoresistors 81 and 82 are arranged on the left and right of the web axis, respectively. Due to linear acceleration in the plane of the carrier or in a direction perpendicular to the plane of the carrier, the two halves of the suspended web, i.e. the left and right halves about the web axis, always have the same length change, i.e. the web. Of the piezoresistors in the same direction. Conversely, rotational movement about an axis of rotation perpendicular to the plane of the carrier results in the same-direction bending of the web halves and, consequently, the same-direction resistance change of the piezoresistors in the web. By comparing the resistance values on the web or by connecting the circuits accordingly, linear acceleration movements can be easily distinguished from rotational movements.

FIG. 2 shows a sensor structure comparable to that of FIG. In the embodiment of FIG. 2, the signal measurement is performed in a capacitive manner, not in a piezoresistive manner. For this purpose, the support electrodes 21, 22, 23, 24 project from the fixed frame 10 of the carrier in parallel to the fixed electrodes 1.
1, 12, 13, and 14 are configured. These stationary electrodes 11, 12, 13, 14 cooperate with suspension webs 21, 22, 23, 24 used as movable electrodes to form capacitance. Stationary electrodes 11, 12,
13 and 14 are arranged with respect to the movable electrodes 21, 22, 23 and 24 such that linear acceleration in the carrier plane causes opposite capacitance changes in the two opposite capacitances. I have. Only a rotational movement about an axis of rotation perpendicular to the carrier plane causes a capacitance change in at least two opposite capacitances in the same direction.
This sensor structure is composed of two layers of a silicon carrier 1, the upper layer 2 and the lower layer 3 of the silicon carrier 1.
, A doping junction is formed. Web 2
1, 22, 23 and 24 are formed only on the upper layer 2. The frame 10 is provided with an insulating diffusion 30 around the area where the web is joined. These insulating diffusions 30
May be provided in a suitable manner at the location of the frame 10 where the stationary electrodes 11, 12, 13, 14 protrude.
These insulating diffusions 30 cooperate with a pn-junction between the upper layer 2 and the lower layer 3 to place the suspended webs 21, 22, 23, 24 acting as movable electrodes on the stationary electrodes 11, 1
2, 13 and 14 are electrically insulated. In FIG.
A sectional view of the area of the sensor webs 22, 24 is shown. The stationary frame 10, like the seismic mass 20, is formed over the entire thickness of the carrier. The seismic mass 20 may be reduced in thickness or provided only on the upper layer 2.

Another possibility for the insulation of the structural parts and the signal measurement is shown in FIG. The etched recess completely penetrating the upper layer 2 is designated by the reference numeral 45. Thereby, the stationary electrode 41 starting from the frame in FIG. 4 is electrically separated from the movable electrode 42 starting from the seismic mass 20. The movable electrode 42, together with the stationary electrode 41, forms a parallel connected internal digital capacitor for amplifying the signal. The operation mode of the sensor shown in FIG. 4 corresponds to the operation mode of the sensor shown in FIGS. All combinations of the illustrated signal detection methods are possible. For example, a built-in digital capacitor can be combined with the diffusion isolation shown in FIG. 2 and / or with piezoresistive signal detection as shown in FIG. 2 and 4
May be provided not only for signal detection but also for controlling the position of the seismic mass 20 by supplying a variable voltage.
In this manner, overload is well prevented and the service life is increased. The linearity of the starting signal is also improved by this.

FIGS. 5 to 7 show a lower layer 3 configured as a substrate, an insulating layer 5 provided on the substrate 3, and a polysilicon layer provided on the insulating layer 5. Upper layer 2 configured as
A sensor comprising a silicon carrier 1 comprising an insulating layer 5 applied thereon is shown. FIG. 6 and FIG.
FIG. 5 shows a cross-sectional view along the axis indicated by reference numerals A and B. An anchor point 55 protrudes from the polysilicon layer 2.
Are firmly connected to the substrate 3 via the insulating layer 5. Starting from this anchor point 55 as the center point, two spirals 50, 60 penetrating each other depart. These two spirals 50 and 60 are formed only in the polysilicon layer 2 and have anchor points 55.
In other cases, it is not connected to the substrate 3 and is configured to be movable like a spiral spring. Spiral 50,6
The outermost windings of 0 have movable masses 51, 6 respectively.
1 is similarly configured only in the polysilicon layer 2.
The polysilicon layer 2 is arranged in a star shape with the anchor point 55 as the center. These movable masses 51,
61 is a comb-like finger structure 511, 611 on both sides thereof
have. Between the movable mass bodies 51 and 61, similarly, the electrode 7 fixed in a star shape with the anchor point 55 as the center.
1 are arranged and these electrodes 71 are connected to the substrate 3 and / or the frame (not shown in FIGS. 5, 6 and 7). The stationary electrode 71 also has a comb-shaped finger structure 711. The finger structures 511 and 611 of the movable mass bodies 51 and 61 and the finger structure 711 of the stationary electrode 71 are inserted into each other. These finger structures 511, 611, 711
Work together to form a built-in digital capacitor or electrostatic magnetoresistive drive that is also used for position control and signal detection. Moreover, signal detection in this structure is also possible by piezoresistors arranged on the spirals 50 and 60.

With this sensor, an angular acceleration about an axis perpendicular to the plane of the carrier can be detected particularly well. In this case, the Archimedes spiral 5
0, 60 act like a spiral spring which expands or compresses depending on the direction of rotation, whereby the movable masses 51, 60
The position of 61 changes with respect to the stationary electrode 71, thereby changing the electrical value of the built-in digital capacitor.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a sensor including a piezoresistive signal measuring device.

FIG. 2 is a schematic plan view of a sensor having a capacitive signal measuring device.

FIG. 3 is a schematic sectional view of the sensor shown in FIG. 2;

FIG. 4 is a schematic plan view of a sensor having a built-in digital capacitor.

FIG. 5 is a schematic plan view of a sensor with an Archimedes spiral suspension.

FIG. 6 is a cross-sectional view along the reference symbol A in FIG.

FIG. 7 is a cross-sectional view along the reference numeral B in FIG.

[Explanation of symbols]

Reference Signs List 1 silicon carrier, 2 upper layer (polysilicon layer), 3 lower layer (substrate), 5 insulating layer, 10 frame, 11, 12, 13, 14 electrodes, 20 seismic mass, 21, 22, 23 , 2
4 webs, 30 insulation diffusion, 41, 42 electrodes,
45 Etching recess, 50, 60 spiral, 5
1,61 mass, 55 anchor points, 71
Electrodes, 81,82 piezoresistors, 511,611,
711 finger structure

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-123361 (JP, A) JP-A-60-159658 (JP, A) JP-A-61-63167 (JP, U) 500475 (JP, A) UK Patent Application Publication 2240178 (GB, A) West German Patent Application Publication 3742385 (DE, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/12-15 / 125

Claims (11)

(57) [Claims] 1. A sensor for measuring acceleration, comprising a seismic mass (20), which can be bent such that the seismic mass (20) is displaced by acceleration in the plane of the carrier. Thin web (21,22,2
3,24) and suspended in a seismic mass (20)
The movable electrode (42) is connected to the fixed electrode (11,12,13,14,41) and the fixed electrode (11,12,13,14,41) is connected to the carrier.
Together with the movable electrode (42) form a capacitor whose capacitance varies with acceleration, wherein the carrier comprises an upper layer (2) and a lower layer (3) made of polycrystalline silicon. ) has a, these two layers (2, 3) are insulated from each other, the seismic mass (20) and web (21, 22, 23, 24), but responsible
Means are formed in the body plane and continuous with the upper layer (2) and insulate the stationary electrodes (11, 12, 13, 14, 41, 41) from the movable electrodes (42). An acceleration sensor, characterized in that: 2. Between the upper layer (2) and the lower layer (3).
2. The process according to claim 1, wherein a doping junction is formed in the substrate.
Speed sensor . 3. The carrier (1) comprises an upper layer (2) and a lower layer (2).
2. An insulating layer (5) between said layer and said layer.
The acceleration sensor according to any one of the preceding claims . 4. A fixed electrode (11,12,13,14,
41) to insulate the movable electrode (42).
4. The method according to claim 1, wherein an edge diffusion is provided.
The acceleration sensor according to any one of the preceding claims . 5. A fixed electrode (11, 12, 13, 14,
41) to insulate the movable electrode (42) from
2. The method according to claim 1, wherein an etching recess is provided.
The acceleration sensor according to any one of claims 3 to 3 . 6. At least two stationary electrodes (41).
And parallel to these stationary electrodes (41) and
At least two projecting from the seismic mass (20)
The movable electrode (42) is protruded and formed.
The stationary electrode (41) and the movable electrode cooperate with each other.
2. The method according to claim 1, wherein each of the capacitors forms one capacitor.
The acceleration sensor according to any one of the preceding claims. 7. A multiple capacitors are connected in parallel
The acceleration sensor according to claim 6, wherein 8. A sensor for measuring acceleration, comprising a movable mass (51, 61), said movable mass being displaced by acceleration in the plane of a carrier (1). As described above, the movable finger structures (511, 611) are suspended from the movable springs (50, 60), and the movable bodies (51, 61) are connected to the masses (51, 61). 71) is connected to the fixed electrode (7).
1) with movable finger structures (511, 611)
In a type in which a capacitor whose capacitance is changed by acceleration is formed, a carrier (1) has an upper layer (2) made of polycrystalline silicon and a lower layer (3). These two layers (2, 3) are insulated from each other and have a movable mass (51, 61), a movable spring (50, 60), a stationary electrode (71) and a movable finger structure (511, 61). 611) are formed continuously with the upper layer (2) in the plane of the carrier . 9. The combination of an upper device (2) and a lower layer (3).
9. The method according to claim 8, wherein a doping junction is formed therebetween.
Acceleration sensor . 10. A carrier (1) comprising an upper layer (2) and a lower layer (2).
And an insulating layer (5) between the first and second layers (3).
8. The acceleration sensor according to 8 . 11. The fixed electrode (71) has a finger structure.
(711), and the finger structure (711)
Movable finger structures (511, 611) penetrate each other
And forming a capacitor.
Acceleration sensor .