JP5333354B2 - Mechanical quantity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the size of dynamic quantity sensor. <P>SOLUTION: The dynamic quantity sensor comprises: an SOI substrate 20; a movable section 2 which is supported by the SOI substrate and displaces parallel to a plane of the SOI substrate responding to an applied acceleration; plural movable pieces 4a-4i formed in a comb-tooth like shape protruding from both sides of the movable section along a displacement direction; plural fixed pieces 6a-6i which are disposed being fixed between the movable pieces so as to form a space between the neighboring movable pieces and are isolated from each other; and plural switches S1-S7 each constituted of a couple of a movable piece and a fixed piece neighboring each other, which are connected in parallel to a power supply E. The dynamic quantity sensor is configured so that, when the movable sections displace according to an applied acceleration, the number of the couples of neighboring movable pieces and the fixed pieces which come into contact with each other varies according to the magnitude of the acceleration, and to generate variable voltage according to the number of the couples. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

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

  Conventionally, a capacitive acceleration sensor is known as this type of mechanical quantity sensor (see Patent Document 1). FIG. 9 is a longitudinal sectional view of a conventional capacitive acceleration sensor (hereinafter referred to as an acceleration sensor) cut in the longitudinal direction. The acceleration sensor 30 is formed by etching an SOI (silicon on insulator) substrate 31. The SOI substrate 31 includes a support substrate 31a made of silicon, a buried oxide film 31b formed on the surface thereof, and a silicon layer 31c formed on the surface thereof.

  The acceleration sensor 30 includes a movable portion 32, a comb-like movable electrode 37 protruding from both side surfaces of the movable portion 32, a fixed portion 36 disposed in the protruding direction of the movable electrode 37, and the fixed portion. Comb-shaped fixed electrodes 38 protruding from the movable portion 32 toward the movable portion 32, beam structures 35 and 35 formed at both ends of the movable portion 32, and anchors for fixing these beam structures to the SOI substrate 31 Parts 33 and 34. By partially removing the buried oxide film 31b, the beam structures 35, 35, the movable portion 32, and the movable electrode 37 have a structure floating from the support substrate 31a. An output terminal 39 for taking out the potential of the movable part 32 is formed on the surface of the anchor part 34, and an output terminal 40 for taking out the potential of the fixed part 36 is formed on the surface of the fixed part 36. Yes.

  FIG. 10 is a circuit diagram showing the main electrical configuration of the acceleration sensor 30 described above. The acceleration sensor 30 includes a signal processing IC 50 configured by CMOS. The signal processing IC 50 includes a known CV conversion circuit 51, a low-pass filter (LPF) 53, an EPROM 54, a D / A conversion circuit 55, and an amplification circuit 52.

  When acceleration is applied to the acceleration sensor 30, the movable portion 32 is displaced in the longitudinal direction, and the distance between the movable electrode 37 and the fixed electrode 38 is changed accordingly, and the capacitance between the movable electrode 37 and the fixed electrode 38 is changed. Changes. The differential capacitances of the electrostatic capacitances C1 and C2 are converted into a voltage according to the differential capacitance by the CV conversion circuit 51, and the high-frequency component is removed by the low-pass filter 53. The signal output from the low-pass filter 53 is amplified by the amplifier circuit 52. The amplifier circuit 52 is capable of gain adjustment and offset adjustment. The D / A conversion circuit 55 performs D / A conversion on the offset adjustment data output from the EPROM 54 and supplies the data to the operational amplifier 52a.

  Conventionally, an acceleration sensor including a plurality of acceleration switches connected in series and a resistor connected in parallel to each acceleration switch is known (see Patent Document 2). Each acceleration switch constituting the acceleration sensor includes a cantilever portion having one end fixed and a free end having a mass portion on the other end, and a conductive portion fixed adjacent to the cantilever portion. Prepare each. The acceleration switch is arranged so that the longitudinal direction of the conductive portion and the acceleration direction are orthogonal to each other. The cantilever portion of each acceleration switch is formed to have a different length for each acceleration switch, and the number of mass portions that come into contact with the conductive portion changes depending on the magnitude of the acceleration, and the output voltage changes. It has become.

Japanese Patent Laying-Open No. 2003-240797 (9th to 10th paragraphs, FIGS. 2 and 5) Japanese Patent Laid-Open No. 10-68742 (paragraphs 35 to 37, FIG. 13)

  The conventional former acceleration sensor described above includes the CV conversion circuit 51 and the low-pass filter 53 in the signal processing IC 50, so that the signal processing IC becomes large, and thus there is a problem that it is difficult to reduce the size of the acceleration sensor 30. Further, since the circuit configuration of the signal processing IC 50 is complicated, there is a problem that the manufacturing cost is increased.

On the other hand, the latter acceleration sensor has a problem that the dimensions of the acceleration sensor are increased in the acceleration direction because the respective acceleration switches are arranged so that the longitudinal direction of the conductive portion and the acceleration direction are orthogonal to each other.
Further, as shown in FIG. 1 of Patent Document 2, the structure of the acceleration switch is a structure in which three substrates are stacked, and a cantilever portion is formed on the central substrate, and the cantilever portion Contact points are formed on the upper and lower surfaces and the upper and lower substrates by vapor deposition of aluminum or copper. In addition, each substrate is insulated by a glass layer. Moreover, each board | substrate is manufactured with a respectively different silicon wafer, The said acceleration switch is obtained by bonding what was obtained by dividing | segmenting each silicon wafer individually. Furthermore, an acceleration sensor is manufactured by connecting a plurality of the obtained acceleration switches.
That is, there is a problem that the manufacturing efficiency of the acceleration sensor is complicated and the manufacturing efficiency is poor.

  Accordingly, the present invention has been made to solve the above-described problems, and aims to reduce the size of a mechanical quantity sensor. Moreover, it aims at improving the manufacturing efficiency of a mechanical quantity sensor.

  In order to achieve the above object, a first feature of the present invention is that a substrate (20) and a substrate supported by the substrate are displaced in parallel with the substrate surface of the substrate in response to application of a mechanical quantity to be detected. A space between the movable part (2) and the plurality of movable pieces (4a to 4i) formed in a comb-like shape protruding from both side surfaces along the displacement direction of the movable part and the adjacent movable pieces. A plurality of fixed pieces (6a to 6i) which are fixedly arranged between the movable pieces so as to be formed and insulated from each other, and each set of the movable piece and the fixed piece adjacent to each other. Thus, a plurality of switches (S1 to S7) connected in parallel to the power source (E) are configured, and the movable piece and the fixed piece that come into contact with each other when the movable portion is displaced according to the application of the mechanical quantity. The number of sets differs according to the magnitude of the mechanical quantity, and according to the number of sets Lies in that is configured to generate a voltage which is.

According to the first feature described above, different voltages are generated according to the number of sets of the movable piece and the fixed piece that are in contact with each other when the movable part is displaced in response to the application of the mechanical quantity. There is no need for a CV conversion circuit and a low-pass filter for converting capacitance to voltage.
Therefore, the mechanical quantity sensor can be reduced in size.

  A second feature of the present invention is that, in the first feature described above, resistors (R1 to R7) are connected in series to the plurality of fixed pieces (6a to 6i), respectively.

According to the second feature described above, since the resistance is connected in series to each of the plurality of fixed pieces, the movable piece and the fixed piece that are in contact with each other receive a voltage via the resistance connected in series to the fixed piece. Can be generated.
Therefore, different voltages can be generated in accordance with the application of the mechanical quantity, so that a plurality of accelerations can be detected.

  A third feature of the present invention is that, in the first or second feature described above, the plurality of movable pieces (4a to 4i) and the fixed pieces (6a to 6i) are each a semiconductor.

According to the third feature described above, since the plurality of movable pieces and fixed pieces are each a semiconductor, the movable pieces and fixed pieces that are in contact with each other can be electrically connected.
Therefore, the movable piece and the fixed piece adjacent to each other can function as a switch.

  A fourth feature of the present invention is that, in the third feature described above, the semiconductor is silicon containing impurities.

  According to the fourth feature described above, since the semiconductor is silicon containing impurities, each movable piece and fixed piece can be formed by processing a silicon layer into which impurities are implanted or diffused.

  A fifth feature of the present invention is that, in the fourth feature described above, the substrate (20) is an SOI substrate, and the movable part (2), by processing a silicon layer containing impurities on the surface of the SOI substrate, A plurality of movable pieces (4a to 4i) and fixed pieces (6a to 6i) are formed.

According to the fifth feature described above, the movable portion, the plurality of movable pieces, and the fixed piece can be formed by processing the silicon layer containing impurities on the surface of the SOI substrate.
Therefore, the mechanical quantity sensor can be manufactured from one SOI substrate, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so that the manufacturing efficiency of the mechanical quantity sensor can be increased.

  A sixth feature of the present invention is that, in the second feature described above, the substrate (20) is an SOI substrate, and the movable part (2), by processing a silicon layer containing impurities on the surface of the SOI substrate. The plurality of movable pieces (4a to 4i), the plurality of fixed pieces (6a to 6i), and the resistors (R1 to R7) are formed.

According to the sixth feature described above, the movable portion, the plurality of movable pieces, the plurality of fixed pieces, and the resistors can be formed by processing the silicon layer containing impurities on the surface of the SOI substrate.
Therefore, the mechanical quantity sensor can be manufactured from one SOI substrate, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so that the manufacturing efficiency of the mechanical quantity sensor can be increased. In addition, since the resistor connected in series to each fixed piece can also be formed in the silicon layer of the SOI substrate, the area of the signal processing circuit can be reduced, so that the mechanical quantity sensor can be further reduced in size.

  According to a seventh feature of the present invention, in the first feature described above, the plurality of fixed pieces (6a to 6i) are each formed of silicon containing impurities, and the movable pieces in contact with each other among the fixed pieces. The piezoresistors (8h) are respectively formed at portions where stress is generated by the pieces.

  According to the seventh feature described above, each piezoresistor can act as a switch because each piezoresistor is formed at a site where stress is generated by the movable piece that is in contact with each of the fixed pieces, and Different voltages can be generated through each piezoresistor. In addition, since it is not necessary to connect a resistor to each fixed piece, the area of the signal processing circuit can be reduced, so that the dynamic quantity sensor can be further reduced in size. Further, if each movable piece serves only to generate stress on each fixed piece and is configured to detect the resistance value of the piezoresistor from each fixed piece, it is not necessary to pass a current through each movable piece.

  An eighth feature of the present invention is that, in the seventh feature described above, the substrate (20) is an SOI substrate, and the movable part (2), by processing a silicon layer containing impurities on the surface of the SOI substrate. The plurality of movable pieces (4a to 4i), the plurality of fixed pieces (6a to 6i), and the piezoresistors (8h) are formed.

According to the eighth feature described above, the movable portion, the plurality of movable pieces, the plurality of fixed pieces, and the piezoresistors can be formed by processing a silicon layer containing impurities on the surface of the SOI substrate.
Therefore, the mechanical quantity sensor can be manufactured from one SOI substrate, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so that the manufacturing efficiency of the mechanical quantity sensor can be increased.

  According to a ninth feature of the present invention, in the first feature described above, the plurality of fixed pieces (6a to 6i) are each formed of silicon containing impurities, and the movable pieces that are in contact with each other among the fixed pieces. The piezoelectric element is formed at each site where stress is generated by the piece.

  According to the ninth feature described above, since each piezoelectric element is formed at a site where stress is generated by the movable piece that is in contact with each fixed piece, each piezoelectric element can serve as a switch, and A different voltage can be generated from each piezoelectric element. Further, if each movable piece plays a role of only generating a piezoelectric effect in each piezoelectric element and is configured to detect the voltage of each piezoelectric element, it is not necessary to pass a current through each movable piece.

  According to a tenth feature of the present invention, in the ninth feature described above, the substrate (20) is an SOI substrate, and the movable part (2), by processing a silicon layer containing impurities on the surface of the SOI substrate. The plurality of movable pieces (4a to 4i), the plurality of fixed pieces (6a to 6i), and the respective piezoelectric elements are formed.

According to the tenth feature described above, the movable portion, the plurality of movable pieces, the plurality of fixed pieces, and each piezoelectric element can be formed by processing the silicon layer containing impurities on the surface of the SOI substrate.
Therefore, the mechanical quantity sensor can be manufactured from one SOI substrate, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so that the manufacturing efficiency of the mechanical quantity sensor can be increased.

  According to an eleventh feature of the present invention, in any one of the first to tenth features described above, the movable pieces that come into contact with each other when the movable portion (2) is displaced in response to the application of the mechanical quantity. The distance between the movable piece and the fixed piece of each set is set so that the number of sets of (4a to 4i) and the fixed pieces (6a to 6i) differs according to the magnitude of the mechanical quantity.

  According to the eleventh feature described above, by adjusting the distance between each set of the movable piece and the fixed piece, the number of sets of the movable piece and the fixed piece that are in contact with each other is changed in accordance with the applied mechanical quantity. Therefore, the mechanical quantity can be detected.

  According to a twelfth feature of the present invention, in any one of the first to eleventh features described above, the movable pieces that come into contact with each other when the movable portion (2) is displaced in response to the application of the mechanical quantity. (4a to 4i) and the fixed pieces (6a to 6i) so that the number of sets differs according to the magnitude of the mechanical quantity, the movable part has a plurality of spring members (3b to 3i) having different spring constants. The movable piece is divided into a plurality of pieces in the displacement direction, and each movable piece is arranged in the divided movable part (2a to 2g).

  According to the twelfth feature described above, by adjusting the spring constant of each spring member, the number of sets of the movable piece and the fixed piece that are in contact with each other can be changed according to the applied mechanical quantity. A mechanical quantity can be detected. Further, by adjusting the combination with the above-described eleventh feature, the distance between the movable piece and the fixed piece of each set, and the spring constant of each spring member, they come into contact with each other according to the applied mechanical quantity. The number of sets of the movable piece and the fixed piece can be changed.

  According to a thirteenth aspect of the present invention, in the twelfth aspect described above, the plurality of spring members (3b to 3i) are the same as the movable pieces (4a to 4i) from both side surfaces of the movable portion (2). The beam structure is formed to protrude in the direction.

  According to the thirteenth feature described above, by adjusting the spring constant of each beam structure, the number of sets of movable pieces and fixed pieces that are in contact with each other can be changed according to the applied mechanical quantity. A mechanical quantity can be detected.

  According to a fourteenth feature of the present invention, in any one of the first to thirteenth features described above, the movable piece (4a to 4i) and the fixed piece (6a to 6i) for detecting a mechanical quantity in a specific range. ) Is larger than the number of sets of the movable piece and the fixed piece for detecting the mechanical quantity outside the specific range.

  According to the fourteenth feature described above, the output voltage difference due to the difference in the mechanical quantity in the specific range can be reduced, so that the detection accuracy of the mechanical quantity in the specific range can be increased.

  According to a fifteenth feature of the present invention, in any one of the first to fourteenth features described above, the movable pieces (4a to 4i) and the fixed pieces (6a to 6i) adjacent to each other are provided on one side. It is in being able to contact each other via the projected part (4j).

  According to the fifteenth feature described above, since the protrusion is provided on one of the movable piece and the fixed piece adjacent to each other, there is a possibility that the movable piece and the fixed piece will not be separated from each other when coming into contact with each other. Absent.

  In addition, the code | symbol in each said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

It is a top view which shows the main structures of the acceleration sensor which concerns on 1st Embodiment of this invention. It is a circuit diagram which shows the main electrical structures of the acceleration sensor shown in FIG. (A) is a top view which shows the model which simplified the structure of the acceleration sensor 1 shown in FIG. 1 with the acceleration direction F1 facing down, (b) is a schematic diagram of (a). It is a circuit diagram which shows the main electrical structures of the model shown to Fig.3 (a). It is a graph which shows the relationship between the output voltage and acceleration of the model shown to Fig.3 (a). It is a graph which shows the relationship between an output voltage and acceleration. It is a top view which shows a part of acceleration sensor which concerns on 2nd Embodiment. It is a top view which shows a part of acceleration sensor which concerns on 3rd Embodiment. It is the longitudinal cross-sectional view which cut | disconnected the conventional sensor in the longitudinal direction. It is a circuit diagram which shows the main electrical structures of the conventional sensor.

<First Embodiment>
A first embodiment according to the present invention will be described with reference to the drawings. In the following embodiments, an acceleration sensor will be described as an example of a mechanical quantity sensor according to the present invention. FIG. 1 is a plan view showing the main structure of the acceleration sensor according to the first embodiment. FIG. 2 is a circuit diagram showing a main electrical configuration of the acceleration sensor shown in FIG.

[Main structure]
The main structure of the acceleration sensor according to this embodiment will be described.
In the acceleration sensor 1, the silicon layer of the SOI substrate 20 is processed by a well-known MEMS (Micro Electro Mechanical System) processing technique, for example, trench etching. The acceleration sensor 1 can be manufactured by substantially the same process as that of the conventional capacitive acceleration sensor shown in FIG. The SOI substrate 20 is a substrate in which a silicon layer is formed on a substrate surface of a support substrate via a buried insulating film. In this embodiment, the support substrate is formed of single crystal silicon, and the silicon layer is an impurity. Is P-type or N-type implanted or diffused. The buried insulating film is a silicon oxide film.

  The acceleration sensor 1 includes an SOI substrate 20, a movable portion 2, a beam structure 3, movable pieces 4 and 5, fixed pieces 6 and 7, and fixed portions 8 and 9. The movable portion 2, the beam structure 3, the movable pieces 4 and 5, the fixed pieces 6 and 7, and the fixed portions 8 and 9 are formed by trench etching of the silicon layer of the SOI substrate 20. The lower part of the movable part 2, the beam structure 3, and the movable pieces 4 and 5 have a structure floating from the support substrate by removing the silicon oxide film by etching, and the SOI is applied according to the application of the acceleration to be detected. The substrate 20 is displaced parallel to the substrate surface.

  An arrow F1 in the figure indicates the direction of acceleration to be detected. The movable part 2 is formed in a longitudinal shape along the acceleration direction F1. The movable part 2 is divided into a plurality of movable parts 2a to 2g along the acceleration direction F1. The divided movable parts 2a to 2g are connected to each other via beam structures 3b to 3i. The movable portion 2a at the front end is connected to the front end portion 10 via the beam structure 3a, and the movable portion 2g at the rear end is supported by the SOI substrate 20 by the anchor portion 11 via the beam structure 3j. . That is, the movable part 2 has a rear end that is a fixed end and a front end that is a free end.

From one side surface along the displacement direction of each movable part 2a-2g, the movable pieces 4a-4i are protrudingly formed in the direction orthogonal to the acceleration direction F1. From the other side surface along the displacement direction of each movable part 2a-2g, movable piece 5a-5i protrudes in the direction orthogonal to the acceleration direction F1. That is, a plurality of movable pieces orthogonal to the acceleration direction F1 are formed in a comb-like shape from both side surfaces along the displacement direction of the movable portion 2.
In this embodiment, each movable piece 4, 5 is formed in a shape (plate wall shape) in which a plate-like member is erected, and is formed with the same protruding length and protruding height.

The beam structures 3a to 3j are formed so as to protrude from both side surfaces along the displacement direction of the movable portion 2 in a direction orthogonal to the acceleration direction F1. In this embodiment, the beam structures 3a to 3j make the standing plate-like members face each other, connect the protruding side ends of the plate-like members, and the base ends of the plate-like members are mutually connected. It is formed in a structure connected across adjacent movable parts. In other words, the movable parts adjacent to each other are connected by the open ends of the U-shaped members that are long horizontally. Since it has such a structure, each beam structure 3a-3j has a spring property which can be expanded-contracted with respect to the acceleration direction F1 and its reverse direction.
The movable parts 2a to 2g, the beam structures 3a to 3j, and the anchor parts 10 and 11 are integrally formed by processing the silicon layer of the SOI substrate 20.

  A fixed part 8 is provided on the side of one side of the movable part 2, and a fixed part 9 is provided on the side of the other side. A fixed piece 6 is formed to protrude from the fixed portion 8 so as to face the movable piece 4, and a fixed piece 7 is formed to protrude from the fixed portion 9 to face the movable piece 5. The fixed part 8 includes fixed parts 8a to 8g, and fixed pieces 6a to 6i are formed so as to protrude from the fixed parts 8a to 8g so as to be adjacent to the movable pieces 4a to 4i. The fixed part 9 is composed of fixed parts 9a to 9g, and fixed pieces 7a to 7i are projected from the fixed parts 9a to 9g so as to be adjacent to the movable pieces 5a to 5i.

  Each movable piece 4a-4i and each fixed piece 6a-6i are arrange | positioned so that a space may be formed between the mutually adjacent movable piece and fixed piece. Each movable piece 5a-5i and each fixed piece 7a-7i are arrange | positioned so that space may be formed between the mutually adjacent movable piece and fixed piece. The fixing portions 8a to 8g and the fixing portions 9a to 9g are insulated from each other, whereby the fixing pieces are also insulated from each other.

In this embodiment, each fixed piece is formed in a shape in which a plate-like member is erected, and the plate surface faces the plate surface of the adjacent movable piece.
When the acceleration is applied, each movable piece is displaced in the acceleration direction F1 against the spring force of each beam structure. When the acceleration is no longer applied, each movable piece is moved to the position before the displacement by the restoring force of each beam structure. Return. Of the movable pieces 4a to 4i and the fixed pieces 6a to 6i, the movable pieces and the fixed pieces adjacent to each other constitute a switch. That is, when a movable piece and a fixed piece adjacent to each other are taken as one set, a total of seven sets constitute the switches S1 to S7 connected in parallel to the power source E (FIG. 2).

  An electrode pad 14 is provided outside the fixed part 8 on one side, and an electrode pad 15 is provided outside the fixed part 9 on the other side. The electrode pad 14 includes electrode pads 14a to 14g, and each electrode pad is electrically connected to the fixing portions 8a to 8g. The electrode pad 15 includes electrode pads 15a to 15g, and each electrode pad is electrically connected to the fixing portions 9a to 9g. The electrode pads 14a to 14g are electrically connected in series with the resistors R1 to R7 (FIG. 2) by wire bonding or the like.

  That is, the resistors R1 to R7 are electrically connected in series to the fixed pieces 6a to 6i. An electrode pad 12 is provided in the vicinity of the anchor portion 10, and an electrode pad 13 is provided in the vicinity of the anchor portion 11. A power source E (FIG. 2) is electrically connected to the electrode pad 12, and an output terminal Go is electrically connected to the electrode pad 13.

  As shown in FIG. 2, the acceleration sensor 1 includes a power supply E, a switch circuit 21, and a signal processing circuit 22. The switch circuit 21 includes seven switches S1 to S7 connected in parallel between the power supply E and the output terminal Go. The signal processing circuit 22 includes resistors R1 to R7 connected in parallel between the power supply E and the output terminal Go. Is provided. Connected between the signal processing circuit 22 and the output terminal Go is a pull-down resistor R8 for maintaining the output voltage at 0 V when no acceleration is applied. When the movable piece comes into contact with the adjacent fixed piece, the switch by the movable piece and the fixed piece is turned on, a current flows through a resistor connected to the fixed piece, and an output voltage Go corresponding to the acceleration is generated.

  The spring constants of the beam structures 3a to 3j are different in the number of sets (the number of switches to be turned on) of the movable pieces 4a to 4i and the fixed pieces 6a to 6i that are in contact with each other according to the magnitude of the applied acceleration. Is set as follows. Since the movable piece and the fixed piece that are in contact with each other are energized via a resistor connected to the fixed piece, the acceleration sensor 1 has different voltages depending on the number of sets of the movable piece and the fixed piece that are in contact with each other. Is generated. The resistance values of the resistors R1 to R7 are set so that the output voltage of the output terminal Go varies depending on the magnitude of the applied acceleration.

Here, a method for determining the spring constant of each beam structure, the mass of each movable part, and the interval between the movable piece and the fixed piece adjacent to each other will be described.
For ease of explanation, the acceleration sensor 1 shown in FIG. 1 will be described using a simplified model. FIG. 3A is a plan view showing a simplified model of the structure of the acceleration sensor 1 shown in FIG. 1 with the acceleration direction F1 facing downward, and FIG. 3B is a schematic diagram of FIG. FIG. 4 is a circuit diagram showing the main electrical configuration of the model shown in FIG. FIG. 5 is a graph showing the relationship between the output voltage and acceleration of the model shown in FIG.

  A set including the movable piece 4a and the fixed piece 6a is referred to as a switch S1, a set including the movable piece 4b and the fixed piece 6b is referred to as a switch S2, and a set including the movable piece 4c and the fixed piece 6c is referred to as a switch S3. Also, the spring constants of the beam structures 3b to 3d are k1 to k3, the masses of the movable parts 2a to 2c (including the movable pieces protruding from both side surfaces) are m1 to m3, and between the movable piece 4a and the fixed piece 6a. Assume that the interval is ΔX1, the interval between the movable piece 4b and the fixed piece 6b is ΔX2, and the interval between the movable piece 4c and the fixed piece 6c is ΔX3. The acceleration is detected in three stages G1 to G3 (G1, G2, and G3 increase in order).

  The spring constants k1 to k3, the masses m1 to m3, and the intervals ΔX1 to ΔX3 are determined so that different switches are turned on at the respective accelerations G1 to G3. For example, only the switch S3 is turned on when the minimum acceleration G1 is applied, only the switches S3 and S2 are turned on when the acceleration G2 is applied, and the switches S3, S3, and S1 are applied when the maximum acceleration G3 is applied. Each value is determined so that becomes ON.

It is not necessary for the spring constant, mass, and interval to be all different, and any one or more may be determined to be different. That is, the combination of switches that are turned on at each acceleration may be different.
In this embodiment, in the model shown in FIG. 3A, the spring constants k1 to k3 of the beam structures are made different by making the protruding lengths L1 of the beam structures 3b to 3d different. In the illustrated example, the protruding length L1 of the beam structures 3b to 3d is the shortest in the beam structure 3b that connects the movable parts 2a and 2b, and the beam structure 3d that connects the movable part 2c and the anchor part 11 Longest.

That is, assuming that the direction of the acceleration direction F1 is the front, the spring constant k1 of the beam structure 3b provided at the front is the largest, and the spring constant k3 of the beam structure 3d provided at the rear is the smallest.
The spring constant of the beam structure is made different by changing the structure of the beam structure from other beam structures in addition to the protruding length of the beam structure as shown in the beam structures 3d and 3g in FIG. You can also.

  The resistance values of the resistors R1 to R3 electrically connected to the fixing portions 8a to 8c are set so that the output voltage of the output terminal Go varies depending on the magnitude of the applied acceleration. For example, it is assumed that the voltage V1 of the power source E is 6V and acceleration of 0 to 6G is to be detected in 2G increments. In this case, the resistance values of the resistors R1 to R3 are set so that the switch S1 is turned on when the acceleration 2G is detected, the switch S2 is turned on when the acceleration 4G is detected, and the switch S3 is turned on when the acceleration 6G is detected. To do. In this example, the resistor R1 is set to 2Ω, the resistor R2 is set to (2/3) Ω, and the resistor R3 is set to 0Ω.

  By setting the resistance values of the resistors R1 to R3 in this way, as shown in FIG. 5, the output voltage Go becomes 2V when 2G acceleration is applied, and when 4G acceleration is applied. Becomes 4V, and when 6G acceleration is applied, it becomes 6V. That is, since three levels of voltage can be output for three levels of acceleration, the acceleration can be detected in three levels.

  In addition, the number of sets of the movable piece and the fixed piece for detecting the acceleration in a specific range is made larger than the number of sets of the movable piece and the fixed piece for detecting an acceleration outside the specific range. It is also possible to improve the detection accuracy of the range acceleration. For example, by adjusting one or more of the spring constant of the beam structure, the mass of the movable part, and the distance between the movable piece and the fixed piece, the switch is turned on in more stages for a specific range of acceleration. Like that.

  FIG. 6 is a graph showing the relationship between output voltage and acceleration. In the illustrated example, the range of accelerations G3 to G6 is to be detected with higher accuracy than the range of accelerations G1 to G2. For this reason, the detection width of acceleration in the range of accelerations G3 to G6 is set smaller than the detection width of acceleration in the range of accelerations G1 to G2. The output voltage is set so as to increase in response to the increase in acceleration. Voltages V1 to V2 are output for the accelerations G1 to G2, and voltages V1 to V2 for the accelerations G3 to G6. Voltages V3 to V6 having a smaller increase width are output.

Thus, when detecting the range of the acceleration G3 to G6 with higher accuracy than the range of the acceleration G1 to G2, one of the spring constant of the beam structure, the mass of the movable part, and the interval between the movable piece and the fixed piece. By adjusting the above, a voltage of V3 to V6 is output in the range of accelerations G3 to G6.
For example, if the acceleration sensor 1 is used for detecting the acceleration at the time of a vehicle collision, the range in the vicinity of acceleration serving as a trigger for operating the airbag in the event of a collision can be detected with high accuracy. Can be controlled.

[Effect of the first embodiment]
(1) If the acceleration sensor 1 according to the first embodiment described above is implemented, a set of movable pieces 4a to 4i and fixed pieces 6a to 6i that come into contact with each other when the movable portion 2 is displaced according to the application of acceleration. Since different voltages can be output according to the number, a CV conversion circuit and a low-pass filter for converting electrostatic capacitance to voltage as in the prior art are unnecessary.
Therefore, the acceleration sensor can be reduced in size.

(2) Since the movable pieces 4a to 4i and the fixed pieces 6a to 6i are semiconductors formed by processing a P-type or N-type silicon layer, respectively, the movable pieces and the fixed pieces that are in contact with each other are electrically connected. Can be connected.
Therefore, the movable piece and the fixed piece adjacent to each other can function as the switches S1 to S7.

(3) Furthermore, the movable part 2, the anchor parts 10 and 11, the movable pieces 4 and 5, the fixed pieces 6 and 7, and the fixed parts 8 and 9 can be formed by processing the silicon layer on the surface of the SOI substrate 20. it can.
Therefore, the acceleration sensor 1 can be manufactured from one SOI substrate 20, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so that the acceleration sensor manufacturing efficiency can be increased.

(4) Further, any one or more of the spring constants of the beam structures 3a to 3j, the masses of the movable portions 2a to 2g and the movable pieces 4 and 5, and the interval between the movable piece and the fixed piece adjacent to each other are adjusted. As a result, the switches S1 to S7 that are turned on according to the applied acceleration can be made different and the output voltage can be made different, so that the acceleration can be detected in multiple stages.

Second Embodiment
Next explained is the second embodiment of the invention. FIG. 7 is a plan view showing a part of the acceleration sensor according to this embodiment. Note that the acceleration sensor according to this embodiment has the same configuration and function as the acceleration sensor 1 according to the first embodiment except that the shapes of some of the movable pieces are different.

  Each movable piece of the acceleration sensor according to this embodiment is formed with a protrusion at a portion facing a fixed piece adjacent to each other, and can be contacted with each other via the protrusion. In the example shown in FIG. 7, the movable piece 4a is formed with a protrusion 4j at a portion facing the adjacent fixed piece 6a. By forming the protrusions on each movable piece in this way, the contact area when the movable piece and the fixed piece come into contact can be reduced, so that the movable piece and the fixed piece are in close contact with each other when no acceleration is applied. This prevents the phenomenon of not being separated.

Therefore, when the movable piece and the fixed piece are brought into close contact with each other and are not separated from each other, a state where the switch is turned on is maintained, and a situation in which an error occurs in the output voltage Go can be avoided.
Instead of forming the protrusion on each movable piece, the protrusion may be formed on the fixed piece.

<Third Embodiment>
Next explained is the third embodiment of the invention. FIG. 8 is a plan view showing a part of the acceleration sensor according to this embodiment.

  Each fixed piece of the acceleration sensor according to this embodiment is formed with a piezoresistor for detecting the displacement of the fixed piece. A pair of electrodes (not shown) for detecting a change in the resistance value of the piezoresistor is formed at both ends of each piezoresistive element. In the example shown in FIG. 8, a piezoresistor 8h is formed at the base (base) of the fixed piece 6a. When the movable piece 4a contacts the fixed piece 6a, the stress generated at the base of the fixed piece 6a due to the contact is transmitted to the piezoresistor 8h, and the resistance value of the piezoresistor 8h changes. By detecting this change in resistance value, it is possible to detect that the movable piece 4a and the fixed piece 6a are in contact with each other, and to detect acceleration.

  That is, the piezoresistors formed on each fixed piece can serve as the switches S1 to S7 and the resistors R1 to R7 of the first embodiment. As described above, the acceleration sensor according to this embodiment does not need to be provided with the resistors R1 to R7 in the signal processing circuit, and can be further downsized. Further, each movable piece has a role of only generating a stress in each fixed piece and changing the resistance value of the piezoresistor, so that it is not necessary to pass a current through each movable piece.

Moreover, the movable part 2, each movable piece 4,5, each fixed piece 6,7, and each piezoresistor can be formed by processing the silicon layer containing impurities on the surface of the SOI substrate.
Therefore, the acceleration sensor can be manufactured from one SOI substrate 20, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so the manufacturing efficiency of the acceleration sensor can be increased.

<Other embodiments>
(1) The resistors R1 to R7 provided in the signal processing circuit 22 of the acceleration sensor 1 according to the first embodiment may be formed in the silicon layer of the SOI substrate 20. For example, each resistor can be formed by controlling the amount of impurities implanted or diffused into the silicon layer. Moreover, each resistance can also be built in each fixing | fixed part 8a-8g.
If this structure is used, since the area of the signal processing circuit 22 can be reduced, the acceleration sensor 1 can be further downsized.

(2) A piezoelectric element is formed in a portion where stress is generated by the movable piece that is in contact with each fixed piece, and a change in voltage generated by each piezoelectric element is detected, so that the movable piece and the fixed piece are in contact with each other. It is also possible to detect the acceleration. The piezoelectric element can be formed by laminating a piezoelectric film and an electrode film on a silicon layer. The electrode film can be formed of aluminum, nickel, or the like. The piezoelectric film can be formed by sputtering or vapor deposition using a material such as zinc oxide (ZnO) or lead zirconate titanate (PZT).

  That is, each piezoelectric element can serve as the switches S1 to S7 of the first embodiment. In addition, each movable piece has a role of only generating a piezoelectric effect in each piezoelectric element, so that it is not necessary to pass a current through each movable piece.

Moreover, the movable part 2, each movable piece 4,5, each fixed piece 6,7, and each piezoelectric element can be formed by processing the silicon layer containing impurities on the surface of the SOI substrate.
Therefore, the acceleration sensor can be manufactured from one SOI substrate 20, and it is not necessary to manufacture from three different silicon wafers as in the prior art, so the manufacturing efficiency of the acceleration sensor can be increased.

(3) Each movable piece and fixed piece can be formed of a material other than a semiconductor material as long as it has conductivity. In addition, each movable piece and fixed piece is formed of a non-conductive material, and an electrode pattern is provided on the surface and wall surface of each movable piece and fixed piece so that the movable piece and the fixed piece in contact with each other are electrically connected. The structure to form may be sufficient.

(4) When an acceleration in an acceleration direction different from the acceleration direction F1 by 180 ° is applied, different voltages are output according to the number of movable pieces 5a to 5i and fixed pieces 7a to 7i that are in contact with each other. You can also. In this case, the fixing portions 9a to 9g are electrically connected to the electrode pads 15a to 15g, and the electrode pads 15a to 15g are electrically connected to the resistors R1 to R7 in series by wire bonding or the like.

  The mechanical quantity sensor according to the present invention can be applied to a yaw rate sensor, an angular velocity sensor, and the like in addition to the acceleration sensor described above.

1 .... acceleration sensor (mechanical quantity sensor), 2 .... movable part,
3 .. Beam structure (spring member), 4, 5 .... Movable piece, 6, 7 .... Fixed piece,
8, 9 .. Fixing part, 10, 11, .. Anchor part, 12 to 15 .. Electrode pad,
20 ... SOI substrate.

Claims (15)

A substrate,
A movable part supported by the substrate and displaced parallel to the substrate surface of the substrate in response to application of a mechanical quantity to be detected;
A plurality of movable pieces that are formed in a comb-like shape from both side surfaces along the displacement direction of the movable portion, and
It is fixedly arranged between each movable piece so that a space is formed between adjacent movable pieces, and includes a plurality of fixed pieces insulated from each other.
Each set of movable pieces and fixed pieces adjacent to each other constitutes a plurality of switches connected in parallel to the power source,
The number of sets of the movable piece and the fixed piece that come into contact with each other when the movable portion is displaced in accordance with the application of the mechanical quantity varies depending on the magnitude of the mechanical quantity, and the voltage varies depending on the number of sets. A mechanical quantity sensor configured to generate   The mechanical quantity sensor according to claim 1, wherein a resistance is connected in series to each of the plurality of fixed pieces.   The mechanical quantity sensor according to claim 1, wherein each of the plurality of movable pieces and the fixed piece is a semiconductor.   The mechanical quantity sensor according to claim 3, wherein the semiconductor is silicon containing impurities.   5. The substrate according to claim 4, wherein the substrate is an SOI substrate, and the movable portion, the plurality of movable pieces, and the fixed piece are formed by processing a silicon layer containing impurities on the surface of the SOI substrate. Mechanical quantity sensor.   The substrate is an SOI substrate, and the movable portion, the plurality of movable pieces, the plurality of fixed pieces, and the resistors are formed by processing a silicon layer containing impurities on the surface of the SOI substrate. Item 3. A mechanical quantity sensor according to Item 2.   The plurality of fixed pieces are each formed of silicon containing impurities, and piezoresistors are respectively formed in portions where stress is generated by the movable pieces in contact with each other among the fixed pieces. Item 2. The mechanical quantity sensor according to Item 1.   The substrate is an SOI substrate, and the movable portion, the plurality of movable pieces, the plurality of fixed pieces, and the piezoresistors are formed by processing a silicon layer containing impurities on the surface of the SOI substrate. The mechanical quantity sensor according to claim 7.   The plurality of fixed pieces are each formed of silicon containing impurities, and piezoelectric elements are respectively formed in portions of the fixed pieces where stress is generated by the movable pieces that are in contact with each other. Item 2. The mechanical quantity sensor according to Item 1.   The substrate is an SOI substrate, and the movable portion, the plurality of movable pieces, the plurality of fixed pieces, and the piezoelectric elements are formed by processing a silicon layer containing impurities on the surface of the SOI substrate. The mechanical quantity sensor according to claim 9.   Each set of the movable piece and the fixed piece so that the number of sets of the movable piece and the fixed piece that come into contact with each other when the movable part is displaced in accordance with the application of the mechanical quantity varies depending on the magnitude of the mechanical quantity. The mechanical quantity sensor according to any one of claims 1 to 10, wherein an interval is set.   Each of the movable parts has a spring constant so that the number of sets of the movable piece and the fixed piece that come into contact with each other when the movable part is displaced in accordance with the application of the mechanical quantity varies depending on the magnitude of the mechanical quantity. 12. The apparatus according to any one of claims 1 to 11, wherein the movable piece is divided into a plurality of different displacement directions via a plurality of different spring members, and each movable piece is disposed in a divided movable section. The mechanical quantity sensor according to one.   The mechanical quantity sensor according to claim 12, wherein the plurality of spring members are beam structures that are formed to project from both side surfaces of the movable portion in the same direction as the movable piece.   The number of sets of movable pieces and fixed pieces for detecting a mechanical quantity in a specific range is greater than the number of sets of movable pieces and fixed pieces for detecting a mechanical quantity outside the specific range. The mechanical quantity sensor according to any one of claims 1 to 13.   The mechanical quantity according to any one of claims 1 to 14, wherein the movable piece and the fixed piece adjacent to each other can contact each other via a protrusion provided on one side. Sensor.

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