JP2004286554A - Semiconductor dynamic quantity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a wide range of acceleration with a small size. <P>SOLUTION: Three beams 41, 42, 43 having different lengths are formed in respective end parts of a weight 3, the longest beam 41 is displaced when low G is impressed, the beam 42 having the middle length is displaced when middle G higher than the low G is impressed, the beam 43 having the shortest length is displaced to a space d3 when high G higher than the middle G is impressed, and a distance between a fixed electrode 1 and a movable electrode 2 is changed followed thereto within a range from the low G to the high G. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor dynamic quantity sensor that detects a dynamic quantity such as acceleration based on a capacitance between a fixed electrode and a movable electrode.
[0002]
[Prior art]
As a conventional example of this kind, there is one disclosed in, for example, Patent Document 1 below. Here, a capacitive acceleration sensor in one axis direction (X direction) will be described with reference to FIG. 3A is a plan view, FIG. 3B is a bb cross-sectional view of FIG. 3A, and FIG. 3C is a cc cross-sectional view of FIG. By forming a groove 11 in the semiconductor layer of the semiconductor substrate 10, a plurality of sets of the fixed electrode 1 and the movable electrode 2 face each other in the X direction to form a capacitor. A plurality of sets of movable electrodes 2 are formed in a comb shape in the ± Y direction with respect to the weight 3 extending in the X direction. Both ends of the weight 3 are formed on the semiconductor substrate 10 so as to be displaceable in the X direction, and beams 4 that are displaceable according to acceleration are formed at both ends of the weight 3. The fixed electrodes 1 arranged in the ± Y direction so as to face the movable electrode 2 are respectively connected to pads 5a and 5b made of Al or the like, and the movable electrode 2 is connected to a pad 5c. The pads 5a, 5b, and 5c are connected to the outside through the pads 6a, 6b, and 6c of another circuit chip 6 such as a mother board by bonding with wires W.
[0003]
Here, the movable electrode 2a is disposed between the adjacent fixed electrodes 1a and 1b. In such a configuration, when acceleration in the X direction is applied to the sensor, the beam 4 moves in the X direction. The displacement changes the distance between the fixed electrodes 1a and 1b and the movable electrode 2a, and the capacitance CS1 between the fixed electrode 1a and the movable electrode 2a and the capacitance CS2 between the fixed electrode 1b and the movable electrode 2a are changed. Change. An equivalent circuit of this semiconductor dynamic quantity sensor is shown on the left side of FIG. A pulse voltage Vcc is applied to the fixed electrodes 1a and 1b. Then, the change ΔC (= CS1−CS2) of the generated capacitances CS1 and CS2 is taken out from the movable electrode 2a, and for example, the voltage = (CS1−CS2) · Vcc / by the switched capacitor circuit 5 as shown on the right side of FIG. The acceleration can be detected by converting the acceleration into Cf.
[0004]
Here, conventionally, when it is possible to detect from a relatively low acceleration (low G) to a relatively high acceleration (high G), a plurality of beams in which the dimensions of the comb-shaped beam 4, the electrodes 1, 2, and the weight 3 are changed. This is supported by using a sensor. FIG. 3A shows, as an example, a conventional example in which two sensors having different lengths of the beam 4 are arranged in the same direction. Since the beam 4a of the sensor shown on the left side is relatively long, it is displaced at a low G, Since the beam 4b of the sensor shown on the right side is relatively short and is displaced at a high G, it is possible to detect two ranges of low G and high G.
[0005]
[Patent Document 1]
JP-A-5-304303
[Problems to be solved by the invention]
However, in the above conventional example, since a plurality of sensors in which dimensions of the beam 4, the electrodes 1, 2 and the weight 3 of the comb structure are changed to detect a wide range of acceleration, the size of the whole sensor becomes large. There are points.
[0007]
An object of the present invention is to provide a semiconductor dynamic quantity sensor capable of detecting a wide range of acceleration with a small size in view of the problems of the conventional example.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized in that a beam displaced according to acceleration is constituted by a plurality of beams having different spring constants.
According to the above configuration, since the beam having the spring constant corresponding to the acceleration is displaced, a wide range of acceleration can be detected by one sensor.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view and a sectional view showing an embodiment of a semiconductor dynamic quantity sensor according to the present invention, and FIG. 2 is a graph showing an acceleration-electrode distance between a conventional example and the semiconductor dynamic quantity sensor of FIG.
[0010]
1A is a plan view, FIG. 1B is a bb cross-sectional view of FIG. 1A, and FIG. 1C is a cc cross-sectional view of FIG. FIG. 1 shows an example in which a beam displaced in accordance with acceleration is composed of a plurality of beams having different spring constants, and three beams 41, 42, and 43 having different lengths are formed at each end of the weight 3. In this example, the beam 41 is longest and the beam 43 is shortest. The weight 3 is supported on the semiconductor substrate 10 via the anchor 7 so as to be able to hold three beams 41, 42, 43. The other configuration is the same as the configuration of the conventional sensor shown in FIG. 3, and a detailed description thereof will be omitted.
[0011]
Each of the beams 41, 42, and 43 has a two-piece structure in the acceleration detection direction (X direction). Each of the intervals d1, d2, and d3 inside the beams 41, 42, and 43, and the electrode interval (the fixed electrode and the The relationship between the movable electrodes)
d1 <d2 <d3 = electrode spacing.
[0012]
In the above configuration, when a low G is applied, the longest beam 41 is displaced, and when displaced up to the distance d1, the two beams 41 come into contact with each other, so that no further displacement occurs. Further, when a medium G higher than the low G is applied, the second longest beam 42 is displaced. When the medium G is displaced up to the interval d2, the two beams 42 come into contact with each other, so that no further displacement occurs. Further, when a high G higher than the medium G is applied, the shortest beam 43 is displaced to the interval d3. When the three beams 41, 42, and 43 having different lengths are displaced in this way, as shown in FIG. 2B, the distance between the fixed electrode 1 and the movable electrode 2 is in a range from low G to high G. Since it changes following, a single sensor can detect a wide range of acceleration. By the way, FIG. 2A shows the acceleration-electrode interval when three sensors having different lengths of the beam 4 are used. At low G, the electrode interval of the sensor having the longest beam 4 changes. In G, the electrode interval of the sensor having the second beam 4 changes, and at high G, the electrode interval of the sensor having the shortest beam 4 changes.
[Brief description of the drawings]
FIG. 1A is a plan view, FIG. 1B is a bb cross-sectional view, and FIG. 1C is a cc cross-sectional view showing an embodiment of a semiconductor dynamic quantity sensor according to the present invention.
FIG. 2 is a graph showing acceleration-electrode spacing of a conventional example and the semiconductor dynamic quantity sensor of FIG. 1;
3A is a plan view, FIG. 3B is a cross-sectional view taken along line bb, and FIG. 3C is a cross-sectional view taken along line c-c showing a conventional semiconductor dynamic quantity sensor.
FIG. 4 is a circuit diagram showing an equivalent circuit and a switched capacitor circuit of the semiconductor dynamic quantity sensor.
[Explanation of symbols]
1, 1a, 1b Fixed electrode 2, 2a Movable electrode 3 Weight 4, 4a, 4b, 41, 42, 43 Beam 5 Switched capacitor circuit 5a, 5b, 5c, 6a, 6b, 6c Pad 7 Anchor 10 Semiconductor substrate 11 Groove W wire

Claims (2)

In a semiconductor physical quantity sensor that detects acceleration based on a capacitance between a fixed electrode and a movable electrode connected to a beam that can be displaced according to acceleration,
A semiconductor dynamic quantity sensor, wherein the beam is constituted by a plurality of beams having different spring constants. The semiconductor dynamic quantity sensor according to claim 1, wherein the plurality of beams have different lengths in a direction orthogonal to an acceleration detection direction.

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