JP5101820B2 - Mechanical quantity sensor - Google Patents

Description

  The present invention relates to a mechanical quantity sensor that detects a mechanical quantity such as acceleration and angular velocity.

In a wide range of fields such as a camera shake correction device for a video camera, an in-vehicle airbag device, and a posture control device for a robot, a mechanical amount sensor for detecting a mechanical amount acting on an object is used.
One of these mechanical quantity sensors is, for example, a semiconductor sensor formed by processing a semiconductor substrate.
In this semiconductor sensor, a silicon substrate is etched to form a weight portion, which is a mass body, in the central portion. The weight portion is structured to be elastically supported by the frame (fixed portion) by a flexible beam portion.

And when a semiconductor sensor receives external forces, such as acceleration and angular velocity, a stress will act on the weight part which is a movable body. Then, the weight portion is tilted by the action of stress, and its posture changes.
By analyzing the change in the posture of the weight part, the direction and magnitude of the acting external force can be detected.
Such a mechanical quantity sensor requires a plurality of wirings for leading out signals detected inside (inside) the sensor to the outside (outside) of the sensor. These wirings are connected to the inside of the sensor. It is disposed through a through hole penetrating the outside.

In addition, in such a sensor that detects the mechanical quantity based on the posture change of the weight part, in order to reduce the air resistance when the weight part operates and to increase the detection sensitivity (detection accuracy), the inside is more in a vacuum state. It is desirable to be close to
However, when the inside of the sensor is brought close to a vacuum state, it is necessary to hermetically seal the wiring through hole so that the gas does not leak.
Conventionally, a technique for appropriately hermetically sealing a through hole in such a sensor has been proposed in the following patent documents.
JP-A-7-245417

  In Patent Document 1, a conductive thin film is disposed inside a connection hole (through hole) provided in a fixed substrate, and the connection hole is sealed at the end face in a state where electrical contact is made with the conductive thin film. A technique for providing a truncated cone-shaped independent region (post structure) that stops is proposed.

By the way, in the sensor described in Patent Document 1, an independent region (post structure) is provided on a support portion (frame) including a weight portion (weight).
In another conventional sensor, as shown in FIG. 6, the post structure 100 is disposed in a region partitioned by a beam 120 between the weight 130 and the frame 110.
In such a sensor, the size of the weight is limited in order to secure the formation region of the post structure, and thus it is difficult to improve the sensitivity of the sensor.
Therefore, an object of the present invention is to provide a mechanical quantity sensor that can further improve the sensitivity of the sensor.

In the invention according to claim 1, a frame having a hollow portion, a weight, a beam for supporting the weight by the hollow portion of the frame, a first substrate for sealing the hollow portion of the frame, and a center of the weight A post structure having an end surface bonded to the first substrate, a posture detecting means for detecting a change in posture of the weight, and the posture detecting means Output means for outputting a mechanical quantity that acts on the basis of the detection results of the plurality of post structures, and a plurality of the post structures are disposed in the center of the weight, and each of the post structures is adjacent to the penetrating through. It is partitioned by a partition wall formed between the holes , further provided with a step portion in the longitudinal direction, the maximum aspect ratio in a specific etching process is a, and the depth of the through hole in the step portion is γ If each step In, alpha> by an inner surface opposed to Rukoto of the through hole through a distance that satisfies the relation of (γ / a) α to achieve the object.
According to a second aspect of the present invention, an electrode disposed opposite to the weight is provided, and the posture detection means is configured to change the weight of the weight based on a change in capacitance between the weight and the electrode. A change in posture is detected, the first substrate has a via hole that draws the potential of the electrode to the outside, and the post structure seals the via hole .
In the invention 請 Motomeko 3, wherein in dynamic quantity sensor according to claim 1 or 2, wherein the first substrate, the second substrate and the third substrate provided to face through the weight Thus, the post structure electrically connects the second substrate and the third substrate.
According to a fourth aspect of the present invention, in the mechanical quantity sensor according to any one of the first to third aspects, the mechanical sensor includes an electrode provided on the first substrate, and the posture detection unit includes the electrode and the electrode. A change in posture of the weight is detected based on a change in capacitance with the weight, and the post structure is electrically connected to at least a part of the electrode.
According to a fifth aspect of the present invention, in the mechanical quantity sensor according to any one of the first to fourth aspects, the post structure is made of a columnar member having conductivity.

  According to the present invention, by providing the post structure at a position penetrating through at least one of the central portion of the weight and the beam, the weight can be formed larger, so that the sensitivity of the sensor can be improved. .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
(1) Outline of Embodiment A mechanical quantity such as acceleration or angular velocity acting on an object is detected based on a change in posture of the weight 13 supported by the beam 12.
The beam 12 is composed of a member that can be easily deformed (bent, warped, bent), such as a silicon substrate. The beam 12 is fixed to the frame 11, and a weight 13 is fixed to the center thereof. When a force such as acceleration or angular velocity acts on the weight 13, the posture of the weight 13 changes.
The posture change of the weight 13 is caused by the amount of change in capacitance between the upper surface of the weight 13 and the fixed electrodes 21a to 21d facing the upper surface of the weight 13 and the electrostatic capacity between the fixed electrodes 31a to 31d facing the lower surface of the weight 13. Detection is based on the amount of change in capacity.
The fixed electrodes 21 a to 21 d are provided on the inner surface of the upper glass substrate 2 that vacuum seals the inside of the sensor, and the fixed electrodes 31 a to 31 d are provided on the inner surface of the lower glass substrate 3.

In the acceleration sensor according to the present embodiment, through holes 16a to 16d are provided in the center part (weight part 130e) of the weight 13, and the post structures 14a to 14d are provided through these holes. Yes. Moreover, the through-holes 17a-d are provided in the beam 12, and the post structures 15a-d are penetrated and provided in these.
The potentials of the fixed electrodes 31a to 31d are taken out to the via holes 431a to 431d provided in the upper glass substrate 2 through the post structures 15a to 15d, and the potentials of the fixed electrodes 21a to 21d are taken to the via holes 421a to 421d.

An internal signal of the sensor is connected to a signal processing unit (C / V conversion circuit or the like) provided outside the sensor through via holes 421a to 431d and 431a to 431d provided in the upper glass substrate 2.
The post structures 14a to 14d and 15a to 14d have a function of sealing the via holes 421a to 421d provided in the upper glass substrate 2.
According to the present embodiment, the post structures 14 a to 14 d and 15 a to d are formed in the central portion (the weight portion 130 e) of the weight 13 and the region of the beam 12, so that the weight 13 is at the limit of the hollow portion of the frame 11. This range (region), that is, the vicinity of the inner wall surface of the frame 11 can be effectively formed. Thereby, size reduction of a sensor can be achieved.

(2) Details of Embodiment In this embodiment, a capacitance detection type acceleration sensor (hereinafter referred to as an acceleration sensor) will be described as an example of a mechanical quantity sensor.
FIG. 1 is a perspective view showing a schematic structure of the acceleration sensor according to the present embodiment.
In FIG. 1, in order to express the structure of the acceleration sensor in an easy-to-understand manner, the structure of each layer is shown separately, but in actuality, each layer is configured in a stacked state.
The acceleration sensor according to the present embodiment is a semiconductor sensor element formed by processing a semiconductor substrate. The processing of the semiconductor substrate can be performed using MEMS (micro electro mechanical system) technology.

As shown in FIG. 1, the acceleration sensor has a three-layer structure in which a movable part structure 1 is sandwiched from above and below by an upper glass substrate 2 and a lower glass substrate 3.
The same direction as the stacking direction of the layers in the substrate constituting the acceleration sensor is defined as the vertical direction, that is, the z-axis (direction). The axes orthogonal to the z-axis and orthogonal to each other are defined as an x-axis (direction) and a y-axis (direction). That is, the x axis, the y axis, and the z axis are three axes that are orthogonal to each other.

FIG. 2A is a plan view showing the upper surface portion of the movable part structure 1, and FIG. 2B is a plan view showing the upper surface portion of the lower glass substrate 3.
FIG. 3A is a plan view showing an upper surface portion of the upper glass substrate 2, and FIG. 3B is a plan view showing a lower surface portion of the upper glass substrate 2.
In addition, FIG.3 (b) shows the permeation | transmission figure seen from the outer side (upper surface side) of the upper glass substrate 2 in order to avoid complication of description.
As shown in FIG. 2A, in the movable part structure 1, a frame 11, a beam 12, and a weight 13 are formed by etching a silicon substrate.
The frame 11 is a fixed part provided on the peripheral edge of the movable part structure 1 so as to surround the weight 13, and constitutes the framework of the movable part structure 1.
The beams 12 are four strip-shaped thin members extending in the cross direction in the radial direction (in the direction of the frame 11) from the center of the weight 13, and have flexibility.

The weight 13 includes a prismatic weight portion 130e located at the center, and prismatic weight portions 130a to 130d arranged in a balanced manner at four corners of the weight portion 130e. The weight portions 130a to 130e are integrally formed as a continuous solid.
The weight 13 is a mass body fixed to the frame 11 by four beams 12. The weight 13 can be vibrated or twisted by the force applied from the outside by the action of the beam 12. The weight 13 has conductivity, and its side surface functions as a movable electrode.

In the acceleration sensor according to the present embodiment, through holes 16a to 16d that penetrate the weight 13 in the thickness direction (z-axis direction) are formed in the central portion of the weight 13, that is, the weight portion 130e.
Further, through holes 17a to 17d penetrating in the thickness direction (z-axis direction) are formed in respective portions of the beam 12 extending in all directions.
In addition, prismatic post structures 14a to 14d and 15a to 15d are disposed inside the through holes 16a to 16d and 17a to 17d, respectively.
The post structures 14a to 14d and 15a to d are loosened so that gaps are formed between the outer side surfaces thereof and the outer wall surfaces of the through holes 16a to 16d and 17a to 17d.
Further, the end surfaces (end portions) of the post structures 14 a to 14 d and 15 a to 15 d are joined to the upper glass substrate 2 and the lower glass substrate 3.
The post structures 14a to 14d and 15a to 14d may be formed by etching the silicon substrate in the same manner as the frame 11, the beam 12 and the weight 13, or may be formed using separate members. May be.

As shown in FIG. 2B, on the upper surface of the lower glass substrate 3 (the surface facing the movable part structure 1), the fixed electrode 31a and the weight part 130b are opposed to the part facing the weight part 130a. A fixed electrode 31c is provided at a portion facing the fixed electrode 31b and the weight portion 130c, and a fixed electrode 31d is provided at a portion facing the weight portion 130d.
The lower glass substrate 3 is provided with electrode pads 331a to 331d that function as relay portions for taking out (drawing out) the potentials of the fixed electrodes 31a to 31d outside the acceleration sensor.
The post structures 15a to 15d shown in FIG. 2A are joined to the lower glass substrate 3 in electrical contact with the electrode pads 331a to 331d.
The fixed electrodes 31a to 31d and the electrode pads 331a to 331d are connected by a conductive pattern.

As shown in FIG. 3 (b), on the lower surface of the upper glass substrate 2 (the surface facing the movable part structure 1), the fixed electrode 21a and the part facing the weight part 130b are arranged on the part facing the weight part 130a. A fixed electrode 21c is provided at a portion facing the fixed electrode 21b and the weight portion 130c, and a fixed electrode 21d is provided at a portion facing the weight portion 130d.
The upper glass substrate 2 is provided with electrode pads 221a to 221d that function as relay portions for taking out (drawing out) the potentials of the fixed electrodes 21a to 21d outside the acceleration sensor.
The post structures 14a to 14d shown in FIG. 2A are bonded to the upper glass substrate 2 in a state of being in electrical contact with the electrode pads 221a to 221d.
Note that the fixed electrodes 21a to 21d and the electrode pads 221a to 221d are connected by a conductive pattern.

On the lower surface of the upper glass substrate 2 (the surface facing the movable part structure 1), an electrode pad that functions as a relay part for taking out (drawing out) the potential of the movable part structure 1 (weight 13) to the outside of the acceleration sensor. 210 is provided.
Further, the potential of the fixed electrodes 31a to 31d provided on the lower glass substrate 3 via the post structures 15a to 15d is applied to the lower surface of the upper glass substrate 2 (the surface facing the movable part structure 1) of the acceleration sensor. Electrode pads 231a to 231d that function as relay portions for taking out (drawing out) are provided.
The post structures 15a to 15d shown in FIG. 2A are bonded to the upper glass substrate 2 and the lower glass substrate in an electrical contact with the electrode pads 331a to d and the electrode pads 231a to 231d.

As shown in FIG. 3A, the upper glass substrate 2 is provided with via holes 410, 421a to d, 431a to d for extracting (extracting) signals from the acceleration sensor to the outside.
The via hole 410 is a lead electrode that takes out (leads out) the potential of the movable part structure 1 (weight 13) to the outside of the acceleration sensor via the electrode pad 210.
The via holes 421a-d take out the potentials of the fixed electrodes 21a-d through the electrode pads 221a-d to the outside of the acceleration sensor, and the via holes 431a-d have the electrode pads 331a-d and the post structures 15a-d. And a lead electrode that takes out (draws) the potential of the fixed electrodes 31a to 31d outside the acceleration sensor via the electrode pads 231a to 231d.

FIG. 4A is a view showing a cross section of the acceleration sensor in the AA ′ portion shown in FIG.
As shown in FIG. 4A, the via holes 410, 421a to d and 431a to d are through-holes provided in the portions where the electrode pads 210, 221a to d and 231a to d on the upper glass substrate 2 are provided. The conductive film is formed along the inner wall and bottom surface of the through hole.
The through hole is a tapered through hole having an opening area with a small diameter from the outside to the inside of the upper glass substrate 2, that is, toward the electrode arrangement surface.
In addition, the conductive film provided inside the through hole ensures electrical contact (conduction) with the electrode pads 210, 221a-d, 231a-d when the movable part structure 1 and the upper glass substrate 2 are joined. It is configured to be taken.

Further, as shown in FIG. 4A, a movable gap for making the weight 13 movable between the upper surface of the beam 12 and the weight 13 (the surface facing the upper glass substrate 2) and the upper glass substrate 2. 18 is formed. The upper glass substrate 2 is bonded so as to seal the movable gap 18.
A weight is also provided between the lower surface of the beam 12 (the surface facing the lower glass substrate 3) and the bottom surface of the weight 13, that is, the lower surface (the surface facing the lower glass substrate 3) and the lower glass substrate 3, and also at the periphery of the weight 13. A movable gap 19 for making 13 movable is formed. The lower glass substrate 3 is bonded so as to seal the movable gap 19.
The movable gaps 18 and 19 are in a state closer to a vacuum. Thus, by making the inside of the sensor in a vacuum state, air resistance when the weight 13 operates can be reduced, and detection sensitivity (detection accuracy) of the acceleration sensor can be improved.

In addition, when forming the frame 11, the beam 12, and the weight 13 of the movable part structure 1, a D-RIE (Deep-Reactive Ion Etching) technique for performing a deep trench etching with a plasma on a silicon substrate is used. Do it.
Note that the post structures 14a to 14d and 15a to 15d are simultaneously formed using the D-RIE technology. In the acceleration sensor according to the present embodiment, the movable part structure 1 is formed of a silicon substrate. However, the forming member of the movable part structure 1 is not limited to this. For example, an SOI (silicon on insulator) substrate in which an oxide film is embedded in an intermediate layer of a silicon substrate may be used.

In this case, since the intermediate oxide film layer functions as an etching blocking layer (stop layer) in the etching process when the beam 12 and the weight 13 are processed, the processing accuracy in the thickness direction can be improved.
When the movable part structure 1 is formed using an SOI substrate, the weight 13 is formed using a support layer in the SOI substrate, and the beam 12 is formed using one active layer.
The upper glass substrate 2 and the lower glass substrate 3 are fixed substrates joined so as to seal the movable part structure 1. The upper glass substrate 2 and the lower glass substrate 3 are bonded to each other by anodic bonding in the frame 11 of the movable part structure 1.

Next, the operation of the acceleration sensor configured as described above will be described.
In the acceleration sensor according to the present embodiment, as shown in FIG. 4B, when acceleration is applied, stress acts and the posture of the weight 13 changes. That is, the weight 13 is inclined with respect to the stationary state shown in FIG.
By detecting changes in the posture of the weight 13 (inclination and twisting amount), the direction and magnitude of the acting acceleration are detected.
The acceleration sensor according to the present embodiment has a structure in which the weight 13 is supported in the hollow portion of the frame 11 by the beam 12 extending from the inner wall surface of the frame 11 toward the center of the sensor (weight 13). In this way, by supporting the weight 13 from the inner wall surface of the frame 11, that is, from the outside, the weight 13 can obtain a large displacement when an external force such as acceleration acts.

For example, as shown in FIG. 4B, when acceleration acts in the x-axis direction and the posture of the weight 13 is inclined with respect to the x-axis, the fixed electrodes 21a to d and 31a to d and the movable electrode (weight 13). And the distance changes.
Specifically, the distance between the fixed electrodes 21a, 21b, 31c, 31d and the movable electrode is reduced, while the distance between the fixed electrodes 21c, 21d, 31a, 31b and the movable electrode is increased.
Such a change in the distance between the electrodes appears as a change in the capacitance between the electrodes, and the posture change of the weight 13 can be detected based on the change in the capacitance.

A change in the distance between the electrodes, that is, a change in the capacitance between the electrodes is electrically detected using a C / V (capacitance / voltage) conversion circuit in a signal processing unit (control unit) (not shown).
The acceleration sensor according to the present embodiment is configured such that a detection signal of the capacitance between the electrodes is input to the C / V conversion circuit via the via holes 410, 421a to d and 431a to d described above. .
Based on the detected change in the posture of the weight 13 (inclination direction, degree of inclination, etc.), the signal processor converts the amount of change in the posture of the weight 13 into an electrical signal that is an acceleration detection signal.

As described above, in the acceleration sensor according to the present embodiment, the post structures 14a to 14d are arranged in the formation region of the center part (the weight part 130e) of the weight 13, and the post structures 15a to 15d are arranged on the beam 12. Arranged in the formation area.
Therefore, the post structures 14a to 14d and 15a to 15d are not limited as in the prior art (FIG. 6), and the weight 13 is connected to the marginal range (region) of the hollow portion of the frame 11, that is, the frame 11 It can be effectively formed up to the vicinity of the inner wall surface.
Therefore, when the frame 11 having the same size as the conventional one is used, the weight 13 having a larger movable electrode can be formed.
In this way, by increasing the size of the weight 13, the detection portion of the weight 13 can be provided at a position further away from the center of the weight 13, that is, a portion where the displacement amount of the weight 13 becomes larger. The detection sensitivity (detection accuracy) of the sensor can be further improved.

In the acceleration sensor according to the present embodiment, the through holes 16a to 16d for penetrating the post structures 14a to 14d are independently formed without overlapping. That is, the post structures 14a to 14d are arranged in a state of being separated by the through holes 16a to 16d.
Therefore, the partition wall formed between the adjacent through holes 16a to 16d can act as a shield for suppressing (reducing) capacitive coupling between the post structures 14a to 14d, and the acceleration sensor Detection sensitivity (detection accuracy) can be further improved.
When providing a plurality of post structures inside one through hole, it is preferable to provide a shielding means such as a shield plate (wall) between the post structures.

(Modification)
In the acceleration sensor according to the present embodiment, as described above, the post structures 14a to 14d and 15a to 15d can be formed by processing the same silicon substrate simultaneously with the frame 11, the beam 12 and the weight 13. .
However, when these portions are formed by performing an etching process on a silicon substrate (or SOI substrate), the interval between the portions is limited by the aspect ratio in the etching process.
The aspect ratio is an index indicating a relative thickness with a vertical (height): horizontal (width) dimension ratio of a three-dimensional shape.
The aspect ratio in the etching process is a depth of progress of etching and an opening width ratio of holes and grooves. For example, an aspect ratio of a groove having a depth of 5 μm and a width of 1 μm is 5. The aspect ratio of the shape produced by the silicon process is approximately 10 and therefore it is difficult to produce a thick three-dimensional shape.

The acceleration sensor according to the present embodiment has a structure in which through holes 16a to 16d and post structures 14a to 14d are formed in the center part (weight part 130) of the weight 13, and the through holes 16a to d and The play interval (gap) between the post structures 14a to 14d, that is, the minimum set value of the distance between the inner surface of the through holes 16a to 16d and the outer surface of the post structures 14a to 14d is limited by the aspect ratio in the etching process. The
In the acceleration sensor according to the present embodiment, in order to properly form the post structures 14′a to d in the through holes 16a to d, that is, to ensure a sufficient gap with the through holes 16a to d. Further, as shown in FIG. 5, the post structures 14′a to d have a two-stage structure having shoulders (steps).

Specifically, as shown in FIG. 5, the post structures 14a to d ′ and the through holes 16a from the upper surface (the surface facing the upper glass substrate 2) to the depth γ at the center portion (weight portion 130e) of the weight 13 are provided. ˜d, and the post structures 14a to d ′ and the through holes 16a from the lower surface (the surface facing the lower glass substrate 3) to the depth ε at the center portion (weight portion 130e) of the weight 13. The gap with ~ d is set to β.
Note that the gap lengths α and β satisfy the following conditions.
(Gap length α)> (depth γ) / (maximum aspect ratio)
(Gap length β)> (depth ε) / (maximum aspect ratio)

The maximum aspect ratio is a value that depends on the current state of etching technology for silicon substrates, and increases as the etching technology develops.
The etching process of the silicon substrate is performed using, for example, an anisotropic etching technique such as D-RIE, which is a kind of dry etching, and allows the etching to proceed only in a specific direction.
In the acceleration sensor according to the present embodiment, the gap length α is set to, for example, 1 to 10 μm, more preferably about 1 to 5 μm. The weight thickness ε is set to about 500 μm.
When an SOI substrate is used, it is preferable that the active layer side is etched with a gap length α and a depth γ, and the support layer side is etched with a gap length β and a depth ε. However, in this case as well, the relationship between the gap length α and the gap length β is α <β as shown in FIG.

It is the perspective view which showed schematic structure of the acceleration sensor which concerns on this Embodiment. (A) is the top view which showed the upper surface part of the movable part structure, (b) is the top view which showed the upper surface part of the lower glass substrate. (A) is the top view which showed the upper surface part of the upper glass substrate, (b) is the top view which showed the lower surface part of the upper glass substrate. (A) is the figure which showed the cross section of the acceleration sensor in the A-A 'part shown to Fig.3 (a). It is the figure which showed the modification of the post structure. It is the figure which showed the example of arrangement | positioning of the post structure of the conventional acceleration sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Movable part structure 2 Upper glass substrate 3 Lower glass substrate 11 Frame 12 Beam 13 Weight 14a-d Post structure 15a-d Post structure 16a-d Through-hole 17a-d Through-hole 18, 19 Movable gap 21a-d Fixed Electrode 31a-d Fixed electrode 130a-e Weight part 210 Electrode pad 221a-d Electrode pad 231a-d Electrode pad 331a-d Electrode pad 410 Via hole 421a-d Via hole 431a-d Via hole

Claims (5)

A frame having a hollow portion;
A weight,
A beam for supporting the weight by a hollow portion of the frame;
A first substrate for sealing the hollow portion of the frame;
A post structure that penetrates a through hole provided in at least one of the central portion of the weight and the beam, and has an end surface bonded to the first substrate;
Posture detection means for detecting posture change of the weight;
Based on the detection result of the posture detection means, an output means for outputting the acting mechanical quantity;
With
In the central portion of the weight, a plurality of the post structures are disposed,
Each of the post structures is partitioned by a partition wall formed between the adjacent through holes , further provided with a stepped portion in the longitudinal direction, the maximum aspect ratio in a specific etching process being a, When the depth of the through-hole in the portion is γ, each step portion is opposed to the inner surface of the through-hole through an interval α that satisfies a relationship of α> (γ / a). Quantity sensor. Comprising an electrode disposed opposite the weight;
The posture detecting means detects a change in posture of the weight based on a change in capacitance between the weight and the electrode;
The first substrate has a via hole for extracting the potential of the electrode to the outside,
The mechanical sensor according to claim 1, wherein the post structure seals the via hole. The first substrate includes a second substrate and a third substrate provided to face each other via the weight,
The post structure, dynamic quantity sensor according to claim 1 or 2, characterized in that electrically connecting the third substrate and the second substrate. Comprising an electrode provided on the first substrate;
The posture detecting means detects a change in posture of the weight based on a change in capacitance between the electrode and the weight;
The mechanical sensor according to any one of claims 1 to 3 , wherein the post structure is electrically connected to at least a part of the electrode. The post structure, dynamic quantity sensor according to any one of claims 1-4, characterized in that it consists of columnar members having conductivity.

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