JPH04232875A - Acceleration sensor - Google Patents

Abstract

PURPOSE: To provide a better acceleration sensor by improving a sensor constituted of and produced from a silicon carrier so that at least one set frame and at least one deformable seismic mass member fixed to the inside of the frame protrude and provided with a means for detecting the deflection within the plane of the carrier of the seismic mass member and detecting acceleration, especially, angular velocity. CONSTITUTION: Sesmic mass members 20 are arranged in a left and right symmetric state and connected to a frame 10 through at least two webs 21, 22, 23, 24 capable of being curved within the plane of a carrier and the deflection of the seismic mass members within the plane of the carrier is detected at least on two mutually opposed sides of the seismic mass members 20.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a sensor for detecting acceleration, in particular an angular acceleration sensor, manufactured from a silicon carrier, which comprises at least one
one stationary frame and at least one deformable seismic mass fixed within the frame, configured to protrude, for detecting a deflection of the seismic mass in the plane of the carrier. Relates to a form in which means are provided.

0002

[Prior Art] Federal Republic of Germany Patent No. 4000903
The specification discloses an acceleration sensor consisting of a single-crystal two-layer carrier. This acceleration sensor has a tongue that vibrates parallel to the surface of the carrier, on which a stationary electrode is arranged against the direction of vibration. In this sensor, acceleration is detected via a capacitance change between a movable tongue and a stationary electrode.

“Laterally Driven P
olysiliconResonant Micros
"Lateral-driven polysilicon resonant microstructures""W.C. Tange, T.H. Nau
Yen, R. T. Howe; Sensorand
Actuators, 20 (1989) 25-30
A sesimo mass suspended in an Archimedean helix and equipped with an electrostatic cam transmission is known. This publication states that such a structure is realized by polysilicon technology.

0004

SUMMARY OF THE INVENTION It is an object of the invention to improve the conventional acceleration sensors of the type mentioned at the outset in order to make them even better.

[0005]

[Means for Solving the Problem] According to the present invention, which solves this problem, a seismic mass is connected to a frame via at least two symmetrically arranged webs that are bendable in the plane of the carrier. The deflection of the seismic mass in the plane of the carrier is detected on at least two mutually facing sides of the seismic mass.

[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 vary in the same direction or in opposite directions. By comparing these signals, it is possible to distinguish between rotational motion and linear acceleration in a very simple manner. Furthermore, the seismic mass of the sensor is advantageously deflectable in the carrier plane and does not project out of the carrier plane. In this case, the carrier itself advantageously serves as a protection element against mechanical overload. By suspending the seismic mass on at least two sides via a thin web, the stability of the sensor against overloads is increased, while at the same time
Very high measurement sensitivity can be obtained. At the same time, sensitivity to lateral acceleration is reduced. With regard to lateral sensitivity, it is also 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 standard manufacturing methods allow particularly small structures to be obtained. Furthermore, it is also advantageous to integrate the evaluation circuit of the sensor into the silicon carrier.

[0007] Advantageous developments of the acceleration sensor according to claim 1 are possible with the measures set forth in claim 2 and below.

The detection of the deflection of the sesimo mass can particularly advantageously be carried out piezoresistively by means of two piezoresistors which are respectively mounted on the left and right sides of the web axis on the suspension web. When the sesimo mass is accelerated linearly, at least two piezoresistors in each suspension web change in the same direction. When a rotational movement occurs, one side of each suspension web stretches while the other side contracts. This causes the resistance of each suspension web to vary in opposite directions. Piezoresistive signal detection can also advantageously be used for sensors manufactured from single-layer carriers. If the entire carrier is constituted by a narrow suspension web, this will predominate the deflection of the seismic masses in the plane of the carrier, while the deflection of the seismic masses in the direction perpendicular to the plane of the carrier will be suppressed; It's advantageous.

In order to produce and insulate the substructure of the sensor, a biaxial silicon carrier is used and a doped junction, preferably a pn junction, is formed between the upper layer and the lower layer. This is particularly advantageous. The carrier may consist of a single crystal, in which case the upper layer can be produced by diffusion of impurity atoms, or it may be a separate epitaxial layer on the carrier. Depending on the structure of the sensor, it may be advantageous to use a silicon carrier with a separate polysilicon layer. In this case, the insulation takes place, for example, via silicon oxide between the monocrystalline silicon layer and the polycrystalline silicon layer.

Another advantageous possibility is to perform capacitive signal detection. For this purpose, it is advantageous to construct the stationary electrodes from a silicon carrier so that they protrude starting from two sides of the frame facing each other and parallel to the suspension web. The stationary electrodes each form a capacitor in cooperation with a suspension web which serves as a movable electrode. In order to amplify the signal, another stationary electrode is configured to protrude from the frame, starting from the seismic mass parallel to this stationary electrode and cooperating with the stationary electrode to generate a built-in digital signal. It is advantageous to provide movable electrodes forming a capacitor. According to another advantageous refinement of the invention, the capacitor can be used as a position control element, by which the seismic mass is brought back into its rest position by supplying a variable voltage. A combination of a capacitive position control element, a capacitive signal detection element and a piezoresistive signal detection element is also advantageous. Insulating the movable electrodes with respect to the stationary electrodes is useful when the seismic mass is constructed only in the upper layer.
It can be realized particularly well. 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 carried out by dielectric diffusion. or by etching recesses completely through the upper layer.

According to another embodiment of the acceleration sensor according to the invention, the sesimo mass is suspended in two interdigitated Archimedean spirals, these two spirals having a movable web in the outermost windings. ing. This 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 interdigitating finger structure can advantageously be used for signal measurement or also for position control. The additional signal pickup is preferably performed piezoresistively by means of a piezoresistor arranged on a spiral.

[0012] In order to increase the sensitivity of the sensor, the sesimo mass may be arranged over the entire width of the carrier. If the seismic mass has the same thickness as the suspension part, the moment of inertia or lateral sensitivity is increased.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the structure of the present invention will be specifically explained 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.
A sensor is shown. In this embodiment, the seismic mass 20 consists of four thin webs 21, 22, 23
, 24 in a symmetrical manner. This structure consists of a single or double layer silicon carrier. The carrier is monocrystalline or comprises a polysilicon layer. Webs 21, 22, 23, 24 and seismic mass 2
0 may consist of the entire thickness of the carrier or may reduce its thickness. In order to increase the sensitivity, it is advantageous to construct the seismic mass 20 as large as possible, that is to say over the entire thickness of the carrier. In a seismic mass 20 in which the width dimension of the webs 21, 22, 23, 24 is larger than the thickness dimension (that is, for example, the web is constructed over the entire thickness of the carrier), variations in the plane of the carrier are The direction is predominant over the direction perpendicular to the carrier. In the embodiment shown in FIG. 1, two piezoresistors 81, 82 are attached to each web 21-24, respectively. These piezoresistors 81 and 82 are arranged on the left and right sides of the web axis, respectively. Linear acceleration in the plane of the carrier or perpendicular to the plane of the carrier results in a constant length change in the same direction of the two halves of the suspended web, i.e. the left and right halves about the web axis, i.e. the web A resistance change occurs in the same direction of the piezoresistors. On the contrary, a rotational movement about an axis of rotation perpendicular to the plane of the carrier causes a curvature of the web halves in the same direction and thus a change in the resistance of the piezoresistors in the web in the same direction. By comparing the resistance values in the webs or by corresponding circuit connections, linear accelerated movements can be easily distinguished from rotary movements.

FIG. 2 shows a sensor structure comparable to FIG. In this embodiment of FIG. 2, the signal measurement is performed capacitively rather than piezoresistively. For this purpose, a stationary electrode 1 projects parallel to the suspension webs 21, 22, 23, 24 from the stationary frame 10 of the carrier.
1, 12, 13, and 14 are configured. These stationary electrodes 11, 12, 13, 14 cooperate with suspension webs 21, 22, 23, 24, which serve as movable electrodes, to form a capacitance. stationary electrodes 11, 12,
13, 14 are arranged with respect to movable electrodes 21, 22, 23, 24 in such a way that linear acceleration in the plane of the carrier causes mutually opposite capacitance changes in two mutually opposite capacitances. There is. Only a rotational movement about an axis of rotation perpendicular to the carrier plane causes a capacitance change in the same direction in the at least two mutually opposite capacitances. This sensor structure consists of a two-layer silicon carrier 1, an upper layer 2 and a lower layer 3.
A doped junction is formed between the two. web 21
, 22, 23, and 24 are formed only in the upper layer 2. The frame 10 is provided with an insulating diffusion 30 around the bonding area of the web. These insulating diffusions 30 are
stationary electrodes 11, 12, 13, 14 protrude;
They may be provided at locations on the frame 10 in any suitable manner. These insulating diffusions 30 cooperate with the pn-junction between the upper layer 2 and the lower layer 3 to connect the suspended webs 21, 22, 23, 24, which act as movable electrodes, to the stationary electrodes 11, 12
, 13, 14. FIG. 3 shows a cross-sectional view of the area of the webs 22, 24 of the sensor. The stationary frame 10, like the seismic mass 20, is formed over the entire thickness of the carrier. The seismic mass 20 may have a reduced thickness or may be provided only in the upper layer 2.

Another possibility of insulating the structural parts and measuring the signal is shown in FIG. The etched recess completely through the upper layer 2 is designated by 45. Thereby, the stationary electrode 41 starting from the frame in FIG. 4 is electrically isolated from the movable electrode 42 starting from the seismic mass 20. The movable electrode 42 together with the stationary electrode 41 forms a built-in digital capacitor connected in parallel that amplifies the signal. The mode of operation of the sensor shown in FIG. 4 corresponds to the mode of operation of the sensor shown in FIGS. 2 and 3. All combinations of the illustrated signal detection methods are possible. For example, integrated digital capacitors can be combined with diffuse isolation as shown in FIG. 2 and/or with piezoresistive signal detection as shown in FIG. Furthermore, the capacitor structure shown in FIGS. 2 and 4 is useful not only for signal detection, but also for the seismic mass 2 by providing a variable voltage.
It is also conceivable to provide it to perform zero position control. In this way, overloads are better prevented and the service life is increased. The linearity of the starting signal is thereby also improved.

FIGS. 5 to 7 show a lower layer 3 configured as a substrate, an insulating layer 5 applied to this substrate 3, and a polysilicon layer applied to this insulating layer 5. an upper layer 2 configured as a polysilicon layer 2;
It consists of a silicon carrier 1 with an insulating layer 5 applied thereon. 6 and 7 are cross-sectional views along the axes indicated by A and B in FIG. 5. FIG. Protruding from the polysilicon layer 2 is an anchor point 55 , which is firmly connected to the substrate 3 via the insulating layer 5 . Starting from this anchor point 55 as a central point are two spirals 50, 60 that interpenetrate. These 2
The two helices 50, 60 are formed only in the polysilicon layer 2, are not connected to the substrate 3 except at the anchor point 55, and are configured to be movable like a spiral spring. In the outermost turns of the spirals 50, 60, a movable ground 51, 61, respectively, is likewise constructed only in the polysilicon layer 2. This polysilicon layer 2
are arranged in a star shape with the anchor point 55 at the center. These movable earths 51, 61 have comb-like finger structures 511, 611 on both sides thereof. Similarly, an anchor point 55 is connected between the movable earths 51 and 61.
Stationary electrodes 71 are arranged in a star shape with .
These electrodes 71 are connected to the substrate 3 and/or the frame (not shown in FIGS. 5, 6 and 7). The fixed electrode 71 also has a comb-like finger structure 7
It has 11. The finger structures 511, 611 of the movable ground 51, 61 and the finger structures 711 of the stationary electrode 71 are interdigitated. These finger structures 511, 611, 711 together form a built-in digital capacitor or electrostatic magnetoresistive drive which is also used for position control and signal detection. Moreover, signal detection in this structure requires only a helix 50
, 60 is also possible.

With this sensor, angular accelerations about an axis perpendicular to the carrier plane can be detected particularly well. In this case, Archimedes' spiral 50
, 60 act like a spiral spring that expands or compresses depending on the direction of rotation, thereby movable earths 51, 6
1 changes relative to the stationary electrode 71, which changes the electrical value of the built-in digital capacitor.

[Brief explanation of the drawing]

1 shows a schematic top view of a sensor with a piezoresistive signal measuring device; FIG.

FIG. 2 shows a schematic top view of a sensor with a capacitive signal measuring device;

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

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

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

FIG. 6 is a sectional view taken along the line A in FIG. 5;

FIG. 7 is a sectional view taken along the line B in FIG. 5;

[Explanation of symbols]

1 silicon carrier, 2 upper layer (polysilicon layer), 3 lower layer (substrate),
5 insulating layer, 10 frame, 11, 12
, 13, 14 electrodes, 20 seismomer mass,
21, 22, 23, 24 web, 30 insulation diffusion, 41, 42 electrode, 45 etching recess, 50, 60 spiral, 51, 61 ground, 55 anchor point, 71 electrode,
81,82 piezoresistor, 511,611,7
11 Finger structure

Claims (14)

[Claims] 1. A sensor for detecting acceleration manufactured from a silicon carrier, comprising at least one stationary frame and at least one deformable size model fixed in the frame. The seismic mass body (2) is configured to protrude and is provided with means for detecting a change in orientation of the seismic mass body (2) in the plane of the carrier.
0) at least two symmetrically arranged webs (21, 22, 23, 24) bendable in the plane of the carrier;
is connected to the frame (10) via a frame (10), such that a deflection of said seismic mass (20) in the carrier plane is detected on at least two mutually facing sides of the seismic mass (20). An acceleration sensor characterized by: 2. The frame (10) is rectangular, the seismic mass (20) has a rectangular cross section, and the seismic mass (20) is attached to the frame (10) on four sides or on two sides. ) and is connected to the seismic mass (2
The upper edge of the rectangle 0) is arranged parallel to the inner surface of the frame (10), and the seismic mass body (20)
is suspended in the center of the frame (10), and the suspension webs (21, 22, 23, 24) are connected to the seismic mass body (
20) Projecting perpendicularly from the center of the upper edge of the acceleration sensor of claim 1. 3. Two piezoresistors (81, 82) are respectively attached to the left and right sides of the web axis on the web (21, 22, 23, 24), or
, 22, 23, 24).
Or the acceleration sensor according to 2. 4. From claim 1, wherein the web (21, 22, 23, 24) and/or the seismomer mass (20) are arranged in whole or in part over the entire thickness of the silicon carrier (1). 3. The acceleration sensor according to any one of items 3 to 3. 5. The silicon carrier (1) is the upper layer (2).
5. Acceleration sensor according to claim 1, characterized in that it has a lower layer (3) and a lower layer (3). 6. Acceleration sensor according to claim 6, characterized in that a doped junction is formed between the upper layer (2) and the lower layer (3). 7. The silicon carrier (1) is single crystal,
The acceleration sensor according to claim 5 or 6. 8. Acceleration sensor according to claim 5, wherein the upper layer (2) is a polysilicon layer. 9. The silicon carrier (1) is attached to the upper layer (2).
9. Acceleration sensor according to claim 8, further comprising an insulating layer (5) between the lower layer (3) and the lower layer (3). 10. Projecting from the mutually facing inner sides of the frame (10) consisting of the silicon carrier (1),
At least two stationary electrodes (11, 12, 13, 14
), and these electrodes (11, 12, 13
, 14) are the suspension webs (21, 22, 2), respectively.
Suspension webs (21, 22, 23,
10. The acceleration sensor according to claim 5, wherein the acceleration sensor forms a capacitor together with 24). 11. Projecting from the mutually facing inner sides of the frame (10) consisting of the silicon carrier (1),
At least two stationary electrodes (11, 12, 13, 14
) are arranged, and projecting from the seismic mass (20) parallel to these electrodes are arranged at least two movable electrodes (42), the stationary electrodes and the movable electrodes 11. Acceleration sensor according to one of claims 5 to 10, characterized in that they cooperate to each form a capacitor. [Claim 12] Suspension web (21, 22, 23
, 24) are constructed only on the upper layer (2), and stationary electrodes (11, 12, 13, 14, 41) are arranged by pn-junctions or between the upper layer (2) and the lower layer. (3) and by an insulating diffusion (30) in the upper layer (2) and/or by an etched recess (45) completely through the upper layer (2). The acceleration sensor according to claim 10 or 11. 13. A sensor for detecting acceleration made of a silicon carrier (1), the silicon carrier (1) comprising a lower layer (3) configured as a substrate and a lower layer (3) configured as a substrate. In the type with an insulating layer (5) placed on a substrate and an upper layer (2) configured as a polysilicon layer placed on this insulating layer (5), The upper layer as a silicon layer (
An anchor point (55) is formed protruding from 2), the anchor point (55) is connected to the lower layer (3) as a substrate via the insulating layer (5), and the central point protrudes from the anchor point (55) and is not connected to the substrate (3);
It consists of two spirals (50, 60) that interpenetrate and are each connected to at least one movable earth (5) in the outer wall.
1,61), and the movable ground (51,61)
) has a finger structure (511, 611) on one or both sides and a stationary electrode (7) surrounding the anchor point (55) between said movable earths (51, 61) in a star shape
1) is connected to the substrate (3) via an insulating layer (5), a stationary electrode (71) has a finger structure (511, 611) on one or both sides, and a movable earth (51,61) finger structure (511,611)
) and a finger structure (711) of a stationary electrode (71) interdigitate. [Claim 14] Piezoresistance is a spiral (50, 60)
14. The acceleration sensor of claim 13, wherein the acceleration sensor is located above.