JP2004233080A - Semiconductor acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor acceleration sensor having improved shock resistance properties that avoids a decrease in sensitivity characteristics, or the like, to acceleration, and diffuses stress applied to both the ends of a beam to acceleration exceeding a tolerance. <P>SOLUTION: The semiconductor acceleration sensor comprises a frame 1 made of a semiconductor substrate; a weight section 4 that is supported so that it can be floated freely by four beams 2 having elasticity projecting toward the inward from the frame 1; a piezoresistance 3 that is provided at the beam 2 while the resistance is changed according to operating acceleration; and an electrode 5 for extracting signals from the piezoresistance 3. The weight section 4 comprises a main weight section 41 joined to the beam 2; and an auxiliary weight section 42 that is connected to the main weight section 41 and is arranged in a space surrounded by at least two beams 2 and the frame 1. A braking section 43 that comes into contact with nearly the center section of the beam 2 for limiting the floating of the weight section 4 is provided at the gap of the adjacent auxiliary weight section 42. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor acceleration sensor, and more particularly, to a semiconductor acceleration sensor using a piezoresistive element that detects acceleration acting in each of three axial directions.
[0002]
[Prior art]
2. Description of the Related Art As a conventional semiconductor acceleration sensor, for example, there is one proposed in Japanese Patent Application Laid-Open No. 6-109755 (Patent Document 1), which is shown in FIG. FIG. 2A is an overall schematic perspective view, and FIG. 2B is a cross-sectional view taken along line AA. This apparatus includes a substantially rectangular frame 101 made of a silicon substrate, a beam 102, a weight 103, and a pedestal 104 made of glass.
[0003]
Of these, the beam 102 is projected from the upper surface (upper side in FIG. 2) of the four sides constituting the frame 101, respectively, and intersects near the inner center of the frame 101 to form the intersection 102a. Has formed. The beam 102 is formed in a thin shape so as to have elasticity.
[0004]
In addition, a plurality of piezoresistors 105 are provided near the intersection 102a of the beam 102 and on the surface of the four base ends 102b, respectively. These piezoresistors 105 have an X-axis in a direction parallel to any one side of the frame 101, a Y-axis in a direction parallel to the other side crossing the X-axis at an angle of 90 °, and both the X-axis and the Y-axis. When the direction intersecting at 90 ° with the Z axis is defined as the Z axis, a Wheatstone bridge is set as a set of four corresponding to the X axis, Y axis, and Z axis in order to detect acceleration acting in each axis direction. Is composed. These piezo resistors 105 are connected to electrodes 106 formed on the frame 101.
[0005]
The weight portion 103 is joined to the lower surface (the lower side in FIG. 2) of the intersection portion 102a of the beam 102 so that the beam 102 has elasticity and is supported by the frame 101 in a freely movable manner. . The cross-sectional shape is a trapezoid whose width decreases in the Z-axis direction from the silicon substrate toward the pedestal 104.
[0006]
The pedestal 104 has a function of limiting the amount of play of the weight 103. Its shape is a quadrangular shape having substantially the same size as the outer shape of the frame 101 in plan view. Further, a recess 104 a having a range of substantially the same size as the upper surface of the weight portion 103 in a plan view is formed inside the surface of the pedestal 104 joined to the frame 101, and the weight portion 103 is It is provided so that it can move in accordance with the acceleration acting inside.
[0007]
Therefore, according to the semiconductor acceleration sensor having the above configuration, when the acceleration acts on the semiconductor acceleration sensor, the weight portion 103 is supported by the frame 101 and the beam 102 so as to be freely movable. To move back and forth, left and right and up and down. At this time, the beam 102 bends to apply a stress to the plurality of piezoresistors 105, and the resistance values change. As a result, the balance of the Wheatstone bridge is lost, and an electric signal corresponding to the applied acceleration is output from the Wheatstone bridge corresponding to each axis. By extracting this electric signal from the electrode 106, the acceleration can be detected. Further, when an acceleration exceeding the breaking strength of the beam 102 acts, the bottom surface of the concave portion 104a of the pedestal 104 limits the floating of the weight portion 103, so that the breaking can be prevented.
[0008]
[Patent Document 1]
JP-A-6-109755
[Problems to be solved by the invention]
However, with such a semiconductor acceleration sensor, it is difficult to limit the movement of the weight portion 103 in the Z-axis direction (from bottom to top in FIG. 2) from the pedestal 104 to the frame 101. When the above-mentioned acceleration acts, there is a possibility that both ends of the beam 102 where the stress is concentrated may be broken.
[0010]
Further, Patent Document 1 describes that a stopper (not shown) is provided on the surface of the frame 101 on which the piezoresistor 105 is formed. By using this means, the play in the Z-axis direction from the pedestal 104 to the frame 101 can be limited. In this method, when the stopper is joined to the frame 101, the influence on the semiconductor acceleration sensor, The stress generated due to the difference in the coefficient of linear expansion between the beam and the frame 101 causes the beam 102 to be distorted, and as a result, the sensitivity characteristics and the like of the semiconductor acceleration sensor are reduced.
[0011]
The present invention has been made in view of the above points, and an object of the present invention is to suppress a decrease in sensitivity characteristics to acceleration and the like, and to disperse a stress applied to a beam for acceleration exceeding an allowable range. Another object of the present invention is to provide a semiconductor acceleration sensor having excellent shock resistance.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor acceleration sensor according to the first aspect of the present invention comprises a frame made of a semiconductor substrate and four beams having elasticity protruding from the frame toward the inside thereof so as to be freely movable. A semiconductor acceleration sensor having a supported weight portion, a piezoresistor having a resistance value that changes according to acceleration acting on the beam, and an electrode for extracting a signal from the piezoresistance, wherein the weight portion is A main weight portion joined to the beam, and an auxiliary weight portion connected to the main weight portion and disposed in a space surrounded by at least two beams and the frame. In the gap between the sections, there is provided a braking section which abuts a substantially central section of the beam to limit the movement of the weight section.
[0013]
According to this configuration, when the weight portion is displaced by an acceleration exceeding the allowable range, the braking portion provided in the auxiliary weight portion abuts the substantially central portion of the beam, thereby displacing a certain amount or more of the weight portion. Limiting and dispersing the stress applied to the beam by dispersing it from the center to the end of the beam, so that the stress applied to the beam can be suppressed from being concentrated on local parts, especially on the end of the beam That is, breakage can be reduced, that is, impact resistance can be improved. In addition, since there is no component that generates unnecessary stress on the piezoresistor forming surface side of the semiconductor acceleration sensor, it is possible to suppress a decrease in sensitivity characteristics and the like.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
A semiconductor acceleration sensor according to the present embodiment will be described with reference to FIG. FIG. 1A is an overall schematic plan view, and FIG. 1B is a cross-sectional view taken along line AA.
[0015]
This semiconductor acceleration sensor mainly includes a frame 1 made of a semiconductor substrate such as an SOI substrate, a beam 2, a piezoresistor 3, and a weight 4 as main components.
[0016]
The frame 1 is formed by laminating a support layer 11, an intermediate oxide film layer 12, and an active layer 13 of an SOI substrate, and supports a weight portion 4 to be described later joined to a beam 2 to be described later. This is formed by piercing the inside of a rectangular parallelepiped SOI substrate in a state in which the active layer 13 and the intermediate oxide film layer 12 are left in a substantially cross shape so as to be orthogonal to each other at a substantially central portion of the frame 1 and have a substantially frame shape. The outline in a plan view has a substantially square shape. An electrode 5 made of, for example, aluminum (Al) connected to a piezo resistor 3 described later is formed on the frame 1, and the acceleration converted into an electric signal is extracted from the electrode 5.
[0017]
The beam 2 suspends and supports the weight portion 4 so that it can move in accordance with the applied acceleration. This is composed of the active layer 13 in a region which is left in a substantially cross shape when the frame 1 is formed. They are connected to each other at a nearby intersection 21.
[0018]
The piezoresistors 3 are provided on the surface of the beam 2 and are formed at the boundary between one end of the beam 2 and the frame 1 and at the boundary between the other end of the beam 2 and the intersection 21. Of these, the piezoresistor 3 at the boundary with the intersection 21 reacts to acceleration acting on the X-axis and Y-axis directions, and a set of four Wheatstone bridges on the beam 2 parallel to the X-axis. And a set of four Wheatstone bridges on the beam 2 which is also parallel to the Y axis. Further, the piezoresistors 3 at the boundary with the frame 1 respond to acceleration acting in the Z-axis direction, and similarly form four Wheatstone bridges.
[0019]
The weight 4 is supported by the beam 2 so as to be freely movable, and changes the amount of deflection of the beam 2 according to the applied acceleration. In other words, the beam 2 is deflected by converting the acceleration received by the weight 4 into a force derived by Newton's equation of motion (F = mα, F is a force, m is a mass, and α is an acceleration). This is formed on the support layer 11 located in the space inside the frame 1, and has a substantially rectangular outer contour in plan view.
[0020]
More specifically, the weight portion 4 includes a main weight portion 41, four auxiliary weight portions 42, and four braking portions 43. The main weight portion 41 has a substantially square outer shape in plan view, is formed to have a thickness shorter than the thickness of the frame 1 by an allowable displacement amount of the beam 2 with respect to the Z axis, and is formed immediately below the intersection portion 21. ing. Further, this is coupled to the active layer 13 via the intermediate oxide film layer 12 at the intersection 21. At the corner of the main weight portion 41, an auxiliary weight portion 42 having the same thickness as the main weight portion 41 and having a substantially square outer contour in plan view is connected. The auxiliary weight 42 is located in a space surrounded by two adjacent beams 2 and the frame 1 in a state where no acceleration is applied. In addition, a braking portion 43 for connecting the adjacent auxiliary weight portions 42 is formed in this device. The braking portion 43 is formed at a position where it comes into contact with a substantially central portion of the beam 2 when the weight portion 4 is displaced in the Z-axis direction, and has a width of 1/20 to 1 of the length of the beam 2. / 3, and the thickness is substantially equal to that of the auxiliary weight 4.
[0021]
That is, by adopting the configuration as in the present embodiment, when the weight portion 4 is displaced by receiving an acceleration having a component in the Z-axis direction, in particular, the direction from the active layer 13 to the support layer 11 of the SOI substrate, That is, when receiving an acceleration exceeding the allowable displacement amount in the direction from the beam forming surface side of the semiconductor acceleration sensor to the opposite surface side, the braking unit 43 limits the displacement of the weight unit 4 by a certain amount or more, and The contact with the approximate center of the beam 2 distributes the stress applied to the beam 2 evenly over the entire beam 2.
[0022]
Therefore, according to the semiconductor acceleration sensor of the first embodiment described above, the main weight 41 in which the weight 4 is joined to the beam 2, the auxiliary weight 42 connected to the corner of the main weight 41, By providing a braking portion 43 for connecting the matching auxiliary weight portions 42 and providing the braking portion 43 at a position in contact with a substantially central portion of the beam 2, in the Z-axis direction, in particular, from the active layer 13 of the SOI substrate to the supporting layer 11. When the braking portion 43 receives an acceleration exceeding the allowable displacement amount in the direction toward the beam, the braking portion 43 contacts the substantially central portion of the beam 2 to limit the displacement of the weight portion 4, so that the connection portion of the beam 2 with the frame 1 and the beam Stress is not concentrated on the connecting portion between the beam 2 and the intersection 21, and the stress is dispersed throughout the beam 2 to reduce the destruction thereof and improve the impact resistance. Of course, since there is no unnecessary stress on the surface of the frame 1 where the beam 2 is formed, such as the above-described stopper (not shown), the sensitivity characteristics and the like are not reduced.
[0023]
When an acceleration is applied in the direction from the support layer 11 to the active layer 13 of the SOI substrate, the pedestal (not shown) or the package (not shown) bonded to the frame 1 is larger than the allowable amount of the weight 4. Has a function of a stopper against the displacement of, so that the destruction can be reduced and the impact resistance can be improved as described above.
[0024]
【The invention's effect】
The semiconductor acceleration sensor according to the first aspect of the present invention includes a frame formed of a semiconductor substrate, a weight portion movably supported by four elastic beams protruding inward from the frame, and a beam. A piezo-resistor having a resistance value that changes according to an acceleration acting on the electrode, and an electrode for extracting a signal from the piezo-resistor, wherein the weight portion includes a main body joined to the beam. A weight portion, an auxiliary weight portion connected to the main weight portion and disposed in a space surrounded by at least two beams and the frame, and a gap between the adjacent auxiliary weight portions is provided in a gap between the adjacent auxiliary weight portions. Since the brake unit has a braking unit that abuts the substantially central portion to limit the movement of the weight unit, when the weight unit is displaced due to excessively applied acceleration, the braking unit provided on the auxiliary weight unit is activated. By contacting with the approximate center of the beam, it is possible to limit the displacement of the weight portion by a certain amount or more, and to distribute and reduce the stress applied to the beam from the approximate center to the end of the beam, and to apply to the beam. It is possible to suppress the stress from being concentrated on a local portion and reduce the destruction, that is, to improve the impact resistance. In addition, since there is no component that generates unnecessary stress on the piezoresistor forming surface side, it is possible to suppress a decrease in sensitivity characteristics and the like.
[Brief description of the drawings]
FIGS. 1A and 1B show a semiconductor acceleration sensor according to the present invention, in which FIG. 1A is an overall schematic sectional view, and FIG. 1B is a sectional view taken along line AA.
FIGS. 2A and 2B show a conventional semiconductor acceleration sensor, in which FIG. 2A is an overall schematic perspective view, and FIG. 2B is a cross-sectional view taken along line AA.
[Explanation of symbols]
1 Frame 2 Beam 3 Piezoresistor 4 Weight 41 Main weight 42 Auxiliary weight 43 Braking part 5 Electrode

Claims (1)

A frame made of a semiconductor substrate, a weight portion movably supported by four elastic beams protruding inward from the frame, and a resistance value provided in accordance with an acceleration acting on the beam; A semiconductor acceleration sensor having a piezoresistor that changes and an electrode for extracting a signal from the piezoresistor,
The weight portion includes a main weight portion joined to the beam, and an auxiliary weight portion connected to the main weight portion and disposed in a space surrounded by at least two beams and the frame, A semiconductor acceleration sensor having a braking portion in a gap between adjacent auxiliary weight portions to abut a substantially central portion of a beam and to limit play of the weight portion.

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