JP2019049434A - Acceleration sensor - Google Patents

Abstract

To provide an acceleration sensor with which it is possible to widen the range of detectable acceleration.SOLUTION: Provided is an X-axis sensor 21(acceleration sensor), comprising: a support part 11 for a substrate having a cavity 12; a pair of stationary electrodes 51, 51 arranged in the cavity 12 and fixed to the support part 11; a first movable electrode 61 and a second movable electrode 62 arranged between the pair of stationary electrodes 51, 51 and capable of moving in the direction of an axis X in which the pair of stationary electrodes 51, 51 are in a row; and a stationary plate 81 arranged between the first movable electrode 61 and the second movable electrode 62 and fixed to the support part 11.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a capacitive acceleration sensor.

  BACKGROUND ART An acceleration sensor for measuring an acceleration acting on an object is widely used, for example, in order to grasp an attitude, a movement, a vibration state or the like of the object. Further, there is a strong demand for miniaturization of acceleration sensors. In order to meet such a demand, miniaturization of an acceleration sensor is achieved by using a so-called MEMS (Micro Electro Mechanical System) technology. For example, Patent Document 1 discloses a capacitive acceleration sensor using MEMS technology.

  In addition, acceleration sensors are required to widen the range of detectable accelerations so that high accelerations can be detected, and to widen the bandwidth so that even if acceleration changes occur at high frequencies, they can be detected. There is. In order to improve these two characteristics, it is necessary to increase the resonance frequency of the vibration of the movable portion of the acceleration sensor.

  FIG. 13 is a simplified view schematically showing elements of the mechanical part of the capacitive acceleration sensor. The acceleration sensor movably supports a weight 630 by springs 640 and 650 so that two movable electrodes 610 and 620 fixed to the weight 630 move between the two fixed electrodes 510 and 520 fixed. It has become. The acceleration sensor has a capacitance C1 of a capacitor including the movable electrode 610 and the fixed electrode 510 (the fixed electrode 510 on the left side in the drawing) moved by the movement of the weight 630, and the fixed electrode 510 adjacent to the movable electrode 620. The capacitance C2 of the capacitor formed of (the fixed electrode 510 on the right side in the figure) changes. By electrically detecting changes in the capacitances C1 and C2, an acting acceleration can be detected. In order to widen the acceleration sensor, the spring constants of the springs 640 and 650 may be increased to increase the resonant frequency of the vibration of the weight 630.

  FIG. 14 shows the relationship between the frequency of vibration of the weight 630 and the change in amplitude when the spring constant is changed. In order to detect acceleration correctly, it is necessary to suppress the change in amplitude to about ± 3 dB. As shown in FIG. 14, as the spring constant is increased (k1 <k2 <k3 <k4), the position of the peak indicating the resonance frequency is shifted to the high frequency side. As a result, the frequency band in which the change in amplitude is 3 dB or less is wider as the spring constant is larger.

  However, on the other hand, as the spring constant is increased, the height of the peak at the resonance frequency is increased. This prevents the spread of the frequency band in which the change in amplitude is 3 dB or less.

JP 2012-88083 A

  An object of the present invention is to provide an acceleration sensor which can widen the range of detectable acceleration in view of the above-mentioned circumstances.

  An acceleration sensor provided by the first aspect of the present invention is disposed between a substrate having a cavity, a pair of fixed electrodes disposed in the cavity and fixed to the substrate, and the pair of fixed electrodes. A pair of movable electrodes movable in the detection direction in which the pair of fixed electrodes are arranged, and a fixed plate disposed between the pair of movable electrodes and fixed to the substrate.

  In a preferred embodiment of the present invention, the fixed plate is electrically insulated from the fixed electrode and the movable electrode.

  In a preferred embodiment of the present invention, the fixing plate is made of an insulator.

  In a preferred embodiment of the present invention, the acceleration sensor comprises a movable base portion to which the pair of movable electrodes is fixed, and a spring portion which fixes the movable base portion to the substrate in a movable state in the detection direction. And further.

  In a preferred embodiment of the present invention, the pair of fixed electrodes and the pair of movable electrodes are made of conductive silicon.

  In a preferred embodiment of the present invention, the substrate is made of conductive silicon.

  In a preferred embodiment of the present invention, the apparatus further comprises a lid fixed to the substrate to seal the cavity.

  In a preferred embodiment of the present invention, the pair of fixed electrodes are electrically connected, different voltage signals are input to the pair of movable electrodes, and electric signals of the pair of fixed electrodes are output. Be done.

  In a preferred embodiment of the present invention, the pair of movable electrodes are electrically connected, different voltage signals are input to the pair of fixed electrodes, and electric signals of the pair of movable electrodes are output. Be done.

  In a preferred embodiment of the present invention, the acceleration in the detection direction acts on the distance between each of the movable electrodes and the fixed plate, and the distance between each of the movable electrodes and the fixed electrode adjacent to the movable electrode. In the non-operating state, all are the same.

  In a preferred embodiment of the present invention, each of the movable electrodes, each of the fixed electrodes, and the fixed plate has a rectangular plate shape orthogonal to the detection direction.

  In a preferred embodiment of the present invention, the dimensions of the movable electrodes, the fixed electrodes, and the fixed plate in the depth direction of the cavity are all equal.

  In a preferred embodiment of the present invention, the acceleration sensor includes a comb-like first electrode and a second electrode which are engaged with each other at an interval, and the first electrode includes the pair of fixed electrodes. The second electrode includes the pair of movable electrodes.

  According to the present invention, the fixed plate damps the vibration in the detection direction of the pair of movable electrodes. As a result, the change in the amplitude at the resonance frequency of the vibration is reduced, and the range of detectable acceleration can be made wider.

  Other features and advantages of the present invention will become more apparent from the detailed description given below based on the attached drawings.

It is a schematic plan view which shows the acceleration sensor concerning 1st Embodiment of this invention. It is a schematic plan view which shows an X-axis sensor. It is a principal part enlarged plan view of FIG. It is sectional drawing in alignment with the IV-IV line of FIG. FIG. 3 is a simplified view schematically showing elements of mechanical parts of the X-axis sensor of FIG. 2; It is an electrical equivalent circuit schematic of the X-axis sensor of FIG. It is a figure which shows the relationship of the change of the frequency of vibration, and an amplitude at the time of changing Q value by making a spring constant and mass of a weight constant, and making a damping coefficient large. It is a schematic plan view which shows the X-axis sensor of the acceleration sensor concerning 2nd Embodiment of this invention. It is a schematic plan view which shows the X-axis sensor of the acceleration sensor concerning 3rd Embodiment of this invention. It is a schematic plan view which shows the X-axis sensor of the acceleration sensor concerning 4th Embodiment of this invention. It is a principal part enlarged plan view of FIG. It is an electrical equivalent circuit schematic of the X-axis sensor of FIG. It is an element simplification figure showing briefly the element of the mechanical part of a capacitive type acceleration sensor. It is a figure which shows the relationship of the frequency of vibration of a weight, and a change of an amplitude when a damping coefficient and mass of a weight are made constant and a spring constant is changed.

  DESCRIPTION OF EMBODIMENTS A mode for carrying out the present invention (hereinafter, referred to as “embodiment”) will be described based on the attached drawings.

First Embodiment
FIG. 1 is a schematic plan view showing an acceleration sensor A1 according to a first embodiment of the present invention. The acceleration sensor A1 is a so-called three-axis acceleration sensor, and outputs signals for detecting accelerations acting in three axial directions orthogonal to each other. The acceleration sensor A1 includes a substrate 1 having a rectangular shape in plan view, a sensor unit 2 disposed at the center of the substrate 1, an electrode pad 3 disposed to the side of the sensor unit 2 in the substrate 1, and a lid 4 . Although the size of the acceleration sensor according to the present invention is not limited, in the present embodiment, a relatively small acceleration sensor A1 using a so-called MEMS technology will be described.

  The sensor unit 2 includes an X-axis sensor 21, a Y-axis sensor 22, and a Z-axis sensor 23. The Z-axis sensor 23 is for detecting an acceleration acting in the Z-axis direction which is the thickness direction of the substrate 1. The X-axis sensor 21 is for detecting an acceleration acting in the X-axis direction (the x1-x2 direction shown in the drawing) which is a direction along one side of the substrate 1 which is orthogonal to the Z-axis direction. The Y-axis sensor 22 is for detecting the acceleration in the Y-axis direction (the y1-y2 direction shown in the figure) orthogonal to the Z-axis direction and the X-axis direction. Substrate 1 and sensor unit 2 are made of a semiconductor substrate made of conductive silicon (for example, a low resistance substrate having a resistivity of 5 Ω · m to 500 Ω · m) using a microfabrication technique used for manufacturing a semiconductor integrated circuit. It is formed by processing. A hollow portion is formed in the substrate 1, and the X-axis sensor 21, the Y-axis sensor 22, and the Z-axis sensor 23 are supported in a floating state from the bottom surface of the hollow portion. The X-axis sensor 21 and the Y-axis sensor 22 are arranged in the X-axis direction at intervals. The Z-axis sensor 23 is disposed so as to surround each of the X-axis sensor 21 and the Y-axis sensor 22.

  The electrode pad 3 is connected to an external electronic component (for example, ASIC (Application Specific Integrated Circuit) element) to input a signal to each sensor 21 to 23 or output a signal from each sensor 21 to 23 And the necessary number (five in FIG. 1) are provided. The lid 4 is made of, for example, a silicon substrate, and is bonded to the surface of the substrate 1 to seal each of the sensors 21 to 23 in the hollow portion formed in the substrate 1.

  Next, details of the X-axis sensor 21 will be described with reference to FIGS.

  FIG. 2 is a schematic plan view showing the X-axis sensor 21. As shown in FIG. FIG. 3 is an enlarged plan view of the main part of FIG. FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. FIG. 5 is a simplified diagram showing elements of mechanical parts of the X-axis sensor 21 in a simplified manner. FIG. 6 is an electrical equivalent circuit diagram of the X-axis sensor 21. As shown in FIG.

  In a hollow portion formed in the substrate 1, a support portion 11 for supporting the sensors 21 to 23 in a floating state is formed. The X-axis sensor 21 is disposed on the inner side of a support 11 formed in an annular shape in a square shape in plan view. The X-axis sensor 21 is supported in a floating state from the bottom of the cavity 12 inside the support 11 (see FIG. 4). The X-axis sensor 21 includes a fixed portion 5 fixed to the support portion 11 and a movable portion 6 supported movably in the X-axis direction with respect to the fixed portion 5. The dimensions in the Z-axis direction of the fixed portion 5 and the movable portion 6 are the same (see FIG. 4).

The fixed portion 5 is fixed to the support portion 11 and arranged in a comb-tooth shape with a fixed base portion 52 extending in the X-axis direction along the inner wall on the y2 side of the cavity 12 and spaced equally along the fixed base portion 52 And a plurality of fixed electrodes 51 extending in the Y-axis direction (y1 direction). The fixed base portion 52 is formed in a ladder shape in plan view to increase strength, and is fixed to the spring portions 64 and 65 (see FIG. 3). Since the fixed base portion 52 is fixed to the spring portions 64 and 65 via the insulating portion 521 made of silicon oxide (SiO ₂ ), the fixed base portion 52 is electrically insulated from the spring portions 64 and 65. The shape of the fixed base portion 52 is not limited to this. The fixed electrode 51 has a rectangular plate shape orthogonal to the X-axis direction.

  The movable portion 6 has a movable base portion 63 extending along the inner wall of the cavity 12 on the y1 side, and two spring portions 64 and 65 having one end fixed to the movable base portion 63 and the other end fixed to the support portion 11 and extending in the Y axis direction. And a plurality of first movable electrodes 61 and second movable electrodes 62 extending in the Y-axis direction (y2 direction) from the movable base portion 63 so as to be disposed one by one between the two adjacent fixed electrodes 51, respectively. Is equipped. The first movable electrode 61 and the second movable electrode 62 have a rectangular plate shape orthogonal to the X-axis direction. In the present embodiment, the first movable electrode 61 is disposed on the x2 side between the two fixed electrodes 51, and the second movable electrode 62 is disposed on the x1 side. When no acceleration is applied, the distance between the first movable electrode 61 and the fixed electrode 51 adjacent thereto is equal to the distance between the second movable electrode 62 and the fixed electrode 51 adjacent thereto. There is.

  The movable base portion 63 is formed in a lattice shape in plan view, and in the movable base portion 63, the plurality of first movable electrodes 61 are electrically connected to each other, and the plurality of second movable electrodes 62 are respectively connected to each other It is electrically connected. On the other hand, the first movable electrode 61 and the second movable electrode 62 are electrically insulated. In addition, the structure of the movable base part 63 is not limited, The electrical connection mentioned above is performed, and it should just be a structure which has a certain amount of weight. The spring portion 64 disposed on the x1 side is electrically connected to the first movable electrode 61 in the movable base portion 63. That is, the spring portion 64 functions as a current path for inputting a voltage signal to each first movable electrode 61. The spring portion 65 disposed on the x2 side is electrically connected to the second movable electrode 62 in the movable base portion 63. That is, the spring portion 65 functions as a current path for inputting a voltage signal to each second movable electrode 62. The two spring portions 64 and 65 also function as a spring for supporting the movable base portion 63 so as to be movable in the X-axis direction. The movable base portion 63, the first movable electrode 61, and the second movable electrode 62 also function as a weight movably supported in the X-axis direction by the two spring portions 64 and 65.

Further, the X-axis sensor 21 is provided with a fixing plate 81 which is disposed at an intermediate position between two adjacent fixed electrodes 51 and extends from the fixed base portion 52 in the Y-axis direction (y1 direction). The fixing plate 81 has a rectangular plate shape orthogonal to the X-axis direction. Each fixed plate 81 is disposed between the first movable electrode 61 and the second movable electrode 62. When no acceleration is applied, the distance between the first movable electrode 61 and the fixed plate 81 is equal to the distance between the second movable electrode 62 and the fixed plate 81. Further, in the present embodiment, the distance between the first movable electrode 61 and the fixed plate 81 (the distance between the second movable electrode 62 and the fixed plate 81) is the distance between the first movable electrode 61 and the fixed electrode 51 adjacent thereto. It is equal to the spacing (the spacing between the second movable electrode 62 and the fixed electrode 51 adjacent thereto). That is, the fixed electrode 51, the first movable electrode 61, the fixed plate 81, the second movable electrode 62, and the fixed electrode 51 are arranged at equal intervals in this order. The fixing plate 81 is fixed to the fixing base portion 52 via the insulating portion 82 made of silicon oxide (SiO ₂ ) (see FIG. 3), and thus, the fixing plate 81 is electrically insulated from the fixing base portion 52. Therefore, the fixed plate 81 is in a high impedance state in which no current flows when it is not electrically connected anywhere. The entire fixing plate 81 may be formed of an insulator (silicon oxide).

  On the surface of the substrate 1 including the fixed portion 5, the movable portion 6 and the fixed plate 81, an insulating film (not shown) made of, for example, silicon oxide is formed. An interconnection (not shown) made of, for example, Al is formed at a predetermined position on the insulating film. Further, the side surfaces of the fixed portion 5, the movable portion 6 and the fixed plate 81 are covered with a protective film (not shown) made of, for example, silicon oxide.

  In the present embodiment, the X-axis sensor 21 has dimensions of, for example, about 300 μm in the X-axis direction and Y-axis direction and, for example, about 50 μm in the Z-axis direction. The fixed electrode 51, the first movable electrode 61, and the second The dimension of the movable electrode 62 in the Z-axis direction is, for example, about 15 to 30 μm. In addition, each dimension is not limited.

  In the X-axis sensor 21, when acceleration in the X-axis direction acts, the movable base portion 63 supported by the two spring portions 64 and 65 vibrates in the X-axis direction. Accordingly, the first movable electrode 61 and the second movable electrode 62 extending from the movable base portion 63 also vibrate in the X-axis direction between the two fixed electrodes 51 adjacent to each other. When the movable base portion 63 moves in the x1 direction, the first movable electrode 61 moves to a position away from the adjacent fixed electrode 51, and the second movable electrode 62 moves to a position approaching the adjacent fixed electrode 51. Conversely, when the movable base portion 63 moves in the x2 direction, the first movable electrode 61 moves to a position approaching the adjacent fixed electrode 51, and the second movable electrode 62 moves to a position away from the adjacent fixed electrode 51 Do.

  FIG. 5 is a simplified diagram showing elements of mechanical parts of the X-axis sensor 21 in a simplified manner. Assuming that the mass of the movable portion 6 is m, and the spring constant of the spring portions 64 and 65 is k, when the acceleration a in the X-axis direction acts in the x2 direction, the movable portion 6 is only x = ma · a / k in the x1 direction Moving. In this case, the distance between the first movable electrode 61 and the adjacent fixed electrode 51 (the left fixed electrode 51 in the figure) changes to d + x, where d is the distance when acceleration in the X-axis direction is not acting. . On the other hand, the distance between the second movable electrode 62 and the adjacent fixed electrode 51 (the fixed electrode 51 on the right side in the drawing) changes to dx. Since the capacitance of the capacitor is inversely proportional to the distance between the electrodes, the capacitance C1 of the capacitor formed of the first movable electrode 61 and the adjacent fixed electrode 51 decreases, and the fixed electrode 51 adjacent to the second movable electrode 62 decreases. The capacitance C2 of the capacitor consisting of Therefore, the acting acceleration a can be detected by electrically detecting the changes in the capacitances C1 and C2.

  FIG. 6 is an electrical equivalent circuit diagram of the X-axis sensor 21. As shown in FIG. As shown in FIG. 6, a variable capacitor of electrostatic capacitance C1 consisting of the first movable electrode 61 and the fixed electrode 51, and a variable capacitor of electrostatic capacitance C2 consisting of the second movable electrode 62 and the fixed electrode 51, It is connected in series between the spring portion 64 connected to the input terminal P1 and the spring portion 65 connected to the input terminal P2. The connection point of the two variable capacitors is connected to the output terminal P3 via the fixed base portion 52. Further, between the input terminal P1 and the input terminal P2, a variable capacitor formed of the first movable electrode 61 and the fixed plate 81 and a variable capacitor formed of the second movable electrode 62 and the fixed plate 81 are connected in series. (Part A surrounded by a broken line). Since the fixed plate 81 has high impedance and can be neglected in terms of electrical connection, the part A is equivalent in electrical connection to one fixed capacitor of electrostatic capacitance Cp (see B surrounded by a broken line). That is, in terms of electrical connection, the X-axis sensor 21 is equivalent to a conventional acceleration sensor (see FIG. 13) that does not include the fixed plate 81. Therefore, in the X-axis sensor 21 as well, acceleration can be detected using the same detection method as that of the conventional acceleration sensor.

  Specifically, an AC square wave signal is input from the input terminal P1, and a signal obtained by inverting the square wave signal is input from the input terminal P2. When no acceleration is applied, the first movable electrode 61 and the second movable electrode 62 are not moved, and the electrostatic capacitance C1 and the electrostatic capacitance C2 become the same. In this case, the signal output from the output terminal P3 becomes a zero signal because the signal from the input terminal P1 and the signal from the input terminal P2 cancel each other. On the other hand, when acceleration is acting, the first movable electrode 61 and the second movable electrode 62 move, and a difference occurs between the electrostatic capacitance C1 and the electrostatic capacitance C2. In this case, the signal output from the output terminal P3 is a square wave signal which differs depending on the direction and magnitude of the acceleration. The acceleration can be detected based on this output signal.

  On the other hand, in the present embodiment, by disposing the fixed plate 81 between the first movable electrode 61 and the second movable electrode 62, a damping element conforming to the squeeze film damping model is added. That is, the fixed plate 81 generates a resistance due to the flow and compression of the lean gas with respect to the vibration of the first movable electrode 61 and the second movable electrode 62 in the X-axis direction, and the damping of the vibration becomes large. This corresponds to increasing the damping coefficient in the damping vibration.

  FIG. 7 shows the relationship between the frequency of vibration and the change in amplitude when the Q value is changed by keeping the spring constant and the mass of the weight constant and increasing the damping coefficient. Assuming that the mass of the movable portion 6 is m, the spring constant of the spring portions 64 and 65 is k, and the damping coefficient is c, the resonance frequency f is f = √ (k / m) / (2 * π), and the Q value is Q = √ (m · k) / c, and the Q value is inversely proportional to the attenuation coefficient c. As the attenuation coefficient c is increased, the Q value decreases and the peak height at the resonance frequency decreases. This can further broaden the frequency band in which the change in amplitude falls within ± 3 dB. The damping coefficient c (and the Q value) can be adjusted by changing the dimension of the fixed plate 81 in the Y-axis direction or the dimension in the X-axis direction. If the area of the surface of the fixed plate 81 perpendicular to the X-axis direction is increased by increasing the dimension of the fixed plate 81 in the Y-axis direction, the damping factor due to squeeze film damping is increased, and the damping coefficient c is increased ( Q value becomes smaller). When the dimension of the fixed plate 81 in the X-axis direction is increased, the distance between the fixed plate 81 and the first movable electrode 61 (second movable electrode 62) is narrowed. Therefore, the damping factor due to the squeeze film damping between the fixed plate 81 and the first movable electrode 61 (the second movable electrode 62) is increased, and hence the attenuation coefficient c is increased (Q value is decreased). When adjusting with the dimension of the fixed plate 81 in the X-axis direction, the attenuation coefficient c can be adjusted without affecting the other characteristics such as the resonance frequency since the mass m of the movable portion 6 is not affected.

  In the present embodiment, the spring constant k of the spring portions 64 and 65 is increased by making the dimension in the X-axis direction of the spring portions 64 and 65 larger than that of the conventional one. Thereby, the frequency band where the change in amplitude is 3 dB or less is broadened (see FIG. 14). Although the Q value is increased by increasing the spring constant k, the Q value is decreased by adding the fixed plate 81 to increase the damping coefficient c. As a result, the frequency band in which the change in amplitude is 3 dB or less is further expanded (see FIG. 7).

  The Y-axis sensor 22 has substantially the same configuration as that obtained by rotating the X-axis sensor 21 by 90 ° in plan view, and thus detailed description will be omitted. In the Y-axis sensor 22, the fixed electrode 51, the first movable electrode 61, the second movable electrode 62, and the fixed plate 81 respectively extend in the X-axis direction, and the movable base is moved when acceleration in the Y-axis direction is applied. The portion 63 vibrates in the Y-axis direction. Thereby, the first movable electrode 61 and the second movable electrode 62 also vibrate in the Y-axis direction between the two fixed electrodes 51 adjacent to each other. Therefore, the electrostatic capacitance of the capacitor formed of the first movable electrode 61 and the fixed electrode 51 adjacent thereto, and the change of the capacitance of the capacitor formed of the fixed electrode 51 adjacent to the second movable electrode 62 are electrically detected. Thus, the acceleration acting in the Y-axis direction can be detected. In the Y-axis sensor 22 as well, by disposing the fixed plate 81 between the first movable electrode 61 and the second movable electrode 62, the attenuation coefficient can be increased, and the range of detectable acceleration is broadened. ing.

  The Z-axis sensor 23 also detects acceleration based on a change in capacitance of a capacitor composed of a movable electrode and a fixed electrode, but not a change in the distance between the electrodes of the capacitor, but the electrodes of the capacitor face each other The acceleration is detected based on the change in capacitance due to the change in area of the part. The Z-axis sensor 23 includes, for example, a fixed electrode and a movable electrode which have a rectangular plate shape orthogonal to the X-axis direction. When acceleration in the Z-axis direction acts, the movable electrode vibrates in the Z-axis direction. Thereby, the area of the overlapping region of the movable electrode and the fixed electrode changes when viewed in the Z-axis direction. By electrically detecting the change in capacitance due to the change in area, the acceleration acting in the Z-axis direction can be detected. The detailed description of the configuration of the Z-axis sensor 23 is omitted.

  The X-axis sensor 21 and the Y-axis sensor 22 correspond to the "acceleration sensor" of the present invention. Further, it can be said that the acceleration sensor A1 also corresponds to the "acceleration sensor" of the present invention.

  Next, a method of manufacturing the acceleration sensor A1 will be described.

  First, the surface of a semiconductor substrate made of conductive silicon is thermally oxidized (for example, at a temperature of 1100 to 1200 ° C., a film thickness of 5000 Å). Thus, the insulating film is formed on the surface of the semiconductor substrate. Next, the insulating film is patterned by a known patterning technique to form an opening in the region where the insulating portion is to be embedded. The insulating portion includes an insulating portion 82 for insulating the fixed plate 81 from the fixed base portion 52, an insulating portion 521 for insulating the fixed base portion 52 and the spring portions 64 and 65, and the first movable electrode 61 in the movable base portion 63. And a portion for insulating the second movable electrode 62 from each other. Next, the semiconductor substrate is dug down by anisotropic deep RIE (Reactive Ion Etching) using the insulating film as a hard mask, specifically by the Bosch process. Thereby, a trench is formed in the semiconductor substrate. Subsequently, the inside of the trench formed in the semiconductor substrate and the surface of the semiconductor substrate are thermally oxidized (for example, at a temperature of 1100 to 1200 ° C.), and then the surface of the oxide film is etched back (for example, the film thickness after etch back) Is 21800 Å). Thereby, the insulating layer filling up the trench is simultaneously formed.

  Next, an insulating film made of silicon oxide is stacked on the semiconductor substrate by the CVD method. Next, the insulating film is etched to form a contact hole, and a contact plug which fills the contact hole is formed, and then aluminum is deposited (for example, 7000 Å) on the insulating film and patterned by sputtering. Thus, the wiring is formed on the insulating film.

  Next, the insulating film on the region where the cavity portion is to be formed in the semiconductor substrate is removed by etching. Then, a resist having an opening in a region other than the region where the fixed portion 5, the movable portion 6 and the fixed plate 81 are to be formed is formed on the insulating film. Subsequently, the semiconductor substrate is dug down by anisotropic deep RIE using the resist as a mask, specifically by the Bosch process. Thereby, the surface portion of the semiconductor substrate is formed into the shape of the fixed portion 5, the movable portion 6 and the fixed plate 81, and a trench is formed therebetween. After deep RIE, the resist is peeled off.

  Then, a protective film made of silicon oxide is formed on the entire surface of the fixed portion 5, the movable portion 6 and the fixed plate 81 and the entire inner surface of the trench (that is, the side and bottom defining the trench) by thermal oxidation or PECVD. Be done. Then, a portion of the protective film on the bottom of the trench is removed by etch back. Thus, the bottom of the trench is exposed.

  Then, the bottom of the trench is further dug down by anisotropic deep RIE. Thus, an exposed space in which the crystal plane of the semiconductor substrate is exposed is formed at the bottom of the trench. Following this anisotropic deep RIE, reactive ions and etching gas are supplied to the exposed space of the trench by isotropic RIE. Then, the semiconductor substrate is etched in the direction parallel to the surface of the semiconductor substrate while being etched in the thickness direction of the semiconductor substrate starting from each exposed space by the action of reactive ions or the like. As a result, all the exposed spaces adjacent to each other are integrated to form the cavity 12 in the semiconductor substrate, and the fixed portion 5, the movable portion 6 and the fixed plate 81 float in the cavity 12. .

  Through the above steps, the acceleration sensor A1 shown in FIG. 1 is obtained. Alternatively, a sacrificial layer may be formed on the semiconductor substrate, a conductive silicon layer may be stacked on the sacrificial layer, and the sacrificial layer may be selectively etched and removed to form the cavity 12.

  Next, the function and effect of the acceleration sensor A1 will be described.

  According to the present embodiment, the X-axis sensor 21 includes the fixed plate 81 fixed at an intermediate position between the two adjacent fixed electrodes 51 and disposed between the first movable electrode 61 and the second movable electrode 62. There is. By disposing the fixed plate 81 between the first movable electrode 61 and the second movable electrode 62, a damping element according to the squeeze film damping model is added to the damping vibration of the movable portion 6, and the damping coefficient Becomes larger. As the attenuation coefficient increases, the Q value decreases and the peak height at the resonance frequency decreases. Therefore, it is possible to further broaden the frequency band in which the change in amplitude falls within ± 3 dB (see FIG. 7). As a result, the range of acceleration that can be detected by the X-axis sensor 21 can be made wider. Similarly, since the Y-axis sensor 22 also includes the fixed plate 81, the damping coefficient of the movable portion 6 is increased. As a result, the range of acceleration that can be detected by the Y-axis sensor 22 can be made wider. Therefore, the detectable range of the acceleration acting in the X-axis direction and the acceleration acting in the Y-axis direction in the acceleration sensor A1 can be made wider.

  Further, according to the present embodiment, in the state where the fixing plate 81 is not electrically connected anywhere, it is in a high impedance state in which no current flows. Therefore, in terms of electrical connection, the fixed plate 81 can be ignored, so that the acceleration can be detected using the same detection method as a conventional acceleration sensor not provided with the fixed plate 81.

  According to this embodiment, in the state where acceleration is not applied, the distance between the first movable electrode 61 and the fixed plate 81 (the distance between the second movable electrode 62 and the fixed plate 81) is equal to that of the first movable electrode 61 Is equal to the distance between the fixed electrode 51 adjacent thereto and the distance between the second movable electrode 62 and the fixed electrode 51 adjacent thereto. That is, the attenuation coefficient between the fixed plate 81 and the first movable electrode 61 (second movable electrode 62), and the attenuation coefficient between the fixed electrode 51 and the first movable electrode 61 (second movable electrode 62) are , And the dimensions of the fixed plate 81 and the fixed electrode 51 in the Y-axis direction. Therefore, in order to obtain a desired attenuation coefficient, it is only necessary to adjust the ratio of the dimensions of the fixed plate 81 and the fixed electrode 51 in the Y-axis direction. This makes it easy to adjust the attenuation coefficient. Moreover, although it is not a simple proportionality relation, a damping factor can also be adjusted with flat plate intervals. At that time, if only the distance between the fixed plate 81 and the first movable electrode 61 and the distance between the fixed plate 81 and the second movable electrode 62 are adjusted, only the attenuation coefficient can be adjusted without affecting other characteristics. . The relationship between the plate interval and the damping coefficient conforms to the squeeze film damping model.

  8 to 12 show another embodiment of the present invention. In these figures, the same or similar elements as or to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

Second Embodiment
FIG. 8 is a schematic plan view showing an X-axis sensor 21 of an acceleration sensor A2 according to a second embodiment of the present invention. The X-axis sensor 21 of the present embodiment differs from the X-axis sensor 21 (see FIG. 2) of the first embodiment in that the movable base portion 63 is disposed on the y2 side.

  In the X-axis sensor 21 according to the second embodiment, the two spring portions 64 and 65 are U-shaped in plan view, and movably support the movable base portion 63 disposed on the y2 side in the X-axis direction. . The first movable electrode 61 and the second movable electrode 62 extend from the movable base portion 63 in the y1 direction. The fixed base portion 52 is disposed on the y1 side, and the fixed electrode 51 extends from the fixed base portion 52 in the y2 direction. The fixing plate 81 also extends from the fixing base portion 52 in the y2 direction.

  Also in the present embodiment, the same effects as in the first embodiment can be obtained. In addition, the shape of the spring parts 64 and 65 is not limited.

Third Embodiment
FIG. 9 is a schematic plan view showing an X-axis sensor 21 of an acceleration sensor A3 according to a third embodiment of the present invention. The X-axis sensor 21 of the present embodiment differs from the X-axis sensor 21 (see FIG. 2) of the first embodiment in that the movable base portion 63 is disposed at the center in the Y-axis direction.

  In the X-axis sensor 21 according to the third embodiment, the two spring portions 64 and 65 have a J shape in plan view, and movably support the movable base portion 63 disposed at the center in the Y-axis direction in the X-axis direction. doing. The first movable electrode 61 and the second movable electrode 62 extend from the movable base portion 63 in both the y1 direction and the y2 direction. Further, two fixing portions 5 are provided. The fixed base portion 52 of one fixed portion 5 is disposed along the inner wall of the cavity 12 on the y2 side, and the fixed electrode 51 and the fixed plate 81 extend from the fixed base portion 52 to the front of the movable base portion 63 in the y1 direction It extends to In the other fixed portion 5, the fixed base portion 52 is disposed along the inner wall on the y1 side of the cavity 12, and the fixed electrode 51 and the fixed plate 81 extend from the fixed base portion 52 to the front of the movable base portion 63 in the y2 direction It extends to The first movable electrode 61 and the second movable electrode 62 extending from the movable base portion 63 in the y1 direction are disposed between the fixed electrode 51 and the fixed plate 81 of the fixed portion 5 on the y1 side, and from the movable base portion 63 in the y2 direction The extending first movable electrode 61 and the second movable electrode 62 are disposed between the fixed electrode 51 and the fixed plate 81 of the fixed portion 5 on the y2 side. The fixed portion 5 on the y1 side and the fixed portion 5 on the y2 side are electrically connected, and both fixed electrodes 51 have the same potential. In addition, the fixed plate 81 fixed to the fixed portion 5 on the y1 side is disposed between the first movable electrode 61 and the second movable electrode 62 extending in the y1 direction from the movable base portion 63 and is fixed to the fixed portion 5 on the y2 side. The fixed plate 81 fixed is disposed between the first movable electrode 61 and the second movable electrode 62 extending from the movable base portion 63 in the y2 direction.

  Also in the present embodiment, the same effects as in the first embodiment can be obtained. In addition, the shape of the spring parts 64 and 65 is not limited.

Fourth Embodiment
FIGS. 10 to 12 show an X-axis sensor 21 of an acceleration sensor A4 according to a fourth embodiment of the present invention. 10 is a schematic plan view (corresponding to FIG. 2 in the first embodiment), FIG. 11 is an enlarged plan view of the main part of FIG. 10 (corresponding to FIG. 3 in the first embodiment), and FIG. Equivalent circuit diagram (corresponding to FIG. 6 in the first embodiment). The X-axis sensor 21 according to the present embodiment includes two types of electrodes in which the fixed portion 5 is electrically separated from each other, and all the electrodes of the movable portion 6 are electrically connected. It differs from the X-axis sensor 21.

  The movable portion 6 has a movable base portion 63 extending along the inner wall of the cavity 12 on the y1 side, and two spring portions 64 and 65 having one end fixed to the movable base portion 63 and the other end fixed to the support portion 11 and extending in the Y axis direction. And a plurality of movable electrodes 66 arranged in a comb shape along the movable base portion 63 and extending in the Y-axis direction (y2 direction). In the present embodiment, the movable base portion 63 is formed in a lattice shape in plan view, and in the movable base portion 63, the plurality of movable electrodes 66 are electrically connected to each other. The shape of the movable base portion 63 is not limited. For example, it may be a rectangular parallelepiped shape (a rectangular shape in plan view) without a gap.

  The fixed portion 5 is fixed to the support portion 11 and fixed to the first fixed base portion 54 extending in the X-axis direction along the inner wall on the y2 side of the cavity 12 and to the support portion 11. The second fixed base portion 56 extending in the X-axis direction is arranged in a comb shape at equal intervals along the first fixed base portion 54 so as not to connect with each other and extends in the Y-axis direction (y1 direction) And a plurality of first fixed electrodes 53, and a plurality of second fixed electrodes 55 arranged in a comb shape at equal intervals along the second fixed base portion 56 and extending in the Y-axis direction (y1 direction) There is. The movable electrode 66 is not disposed between the second fixed electrode 55 and the first fixed electrode 53 closest to the second fixed electrode 55, and the first fixed electrode 53 second closest to the second fixed electrode 55 Two movable electrodes 66 are disposed between them.

  Further, between the two movable electrodes 66 disposed between the first fixed electrode 53 and the second fixed electrode 55, the Y-axis direction (y1 direction) from the first fixed base portion 54 or the second fixed base portion 56. ) Is arranged. The fixing plate 81 is fixed to the first fixing base portion 54 or the second fixing base portion 56 via the insulating portion 82. In the present embodiment, in a state where acceleration is not applied, the first fixed electrode 53, the movable electrode 66, the fixed plate 81, the movable electrode 66, and the second fixed electrode 55 are arranged at equal intervals in this order. There is.

  In the X-axis sensor 21, when acceleration in the X-axis direction acts, the movable base portion 63 supported by the two spring portions 64 and 65 vibrates in the X-axis direction. Accordingly, the movable electrode 66 extending from the movable base portion 63 also vibrates in the X-axis direction between the adjacent first fixed electrode 53 and second fixed electrode 55. When the movable base portion 63 moves in the x1 direction, the movable electrode 66 adjacent to the first fixed electrode 53 moves to a position away from the first fixed electrode 53, and the movable electrode 66 adjacent to the second fixed electrode 55. Moves to a position approaching the second fixed electrode 55. Therefore, the electrostatic capacitance C1 of the capacitor formed of the first fixed electrode 53 and the movable electrode 66 adjacent thereto decreases, and the electrostatic capacitance C2 of the capacitor formed of the second fixed electrode 55 and the movable electrode 66 adjacent thereto increases. Conversely, when the movable base portion 63 moves in the x2 direction, the movable electrode 66 adjacent to the first fixed electrode 53 moves to a position approaching the first fixed electrode 53, and movable adjacent to the second fixed electrode 55. The electrode 66 moves to a position away from the second fixed electrode 55. Therefore, the electrostatic capacitance C1 of the capacitor formed of the first fixed electrode 53 and the movable electrode 66 adjacent to it increases, and the electrostatic capacitance C2 of the capacitor formed of the second fixed electrode 55 and the movable electrode 66 adjacent thereto decreases. Therefore, the acting acceleration can be detected by electrically detecting the changes in the capacitances C1 and C2.

  FIG. 12 is an electrical equivalent circuit diagram of the X-axis sensor 21 of the fourth embodiment. As shown in FIG. 12, a variable capacitor of electrostatic capacitance C1 consisting of a first fixed electrode 53 and a movable electrode 66, and a variable capacitor of electrostatic capacitance C2 consisting of a second fixed electrode 55 and a movable electrode 66, It is connected in series between the first fixed base portion 54 connected to the input terminal P1 and the second fixed base portion 56 connected to the input terminal P2. The connection point of the two variable capacitors is connected to the output terminal P3 via the movable base portion 63 (and the spring portions 64 and 65). Further, two variable capacitors composed of the movable electrode 66 and the fixed plate 81 are connected in series, and both ends thereof are connected to the output terminal P3 (portion A surrounded by a broken line). Since the fixed plate 81 has high impedance and can be neglected in terms of electrical connection, the part A is one in which both terminals of one fixed capacitor are at the same potential, which is substantially the same as one that is not electrically. Therefore, also in the X-axis sensor 21 of the fourth embodiment, the acceleration can be detected using the same detection method as that of the conventional acceleration sensor.

  According to the present embodiment, the X-axis sensor 21 includes a fixed plate 81 disposed between two adjacent movable electrodes 66. Therefore, a damping element conforming to the squeeze film damping model is added to the damping vibration of the movable portion 6, and the damping coefficient becomes large. As a result, the range of acceleration that can be detected by the X-axis sensor 21 can be made wider. Similarly, since the Y-axis sensor 22 also includes the fixed plate 81, the damping coefficient of the movable portion 6 is increased. As a result, the range of acceleration that can be detected by the Y-axis sensor 22 can be made wider. Therefore, the detectable range of the acceleration acting in the X-axis direction and the acceleration acting in the Y-axis direction in the acceleration sensor A1 can be made wider.

  Further, according to the present embodiment, in the state where the fixing plate 81 is not electrically connected anywhere, it is in a high impedance state in which no current flows. Therefore, in terms of electrical connection, the fixed plate 81 can be ignored, so that the acceleration can be detected using the same detection method as a conventional acceleration sensor not provided with the fixed plate 81.

  According to the present embodiment, in the state where acceleration is not applied, the distance between the movable electrode 66 and the fixed plate 81 is the distance between the first fixed electrode 53 and the movable electrode 66 adjacent thereto (the second fixed electrode 55 Distance to the adjacent movable electrode 66). This makes it easy to adjust the attenuation coefficient.

  According to the present embodiment, since all the movable electrodes 66 of the movable portion 6 have the same potential, the structure of the movable base portion 63 is simplified as compared with the case where two types of electrodes electrically separated from each other are provided. Can. Therefore, the manufacturing process can be simplified.

  In the first to fourth embodiments, the acceleration sensors A1 to A4 are relatively small acceleration sensors using the MEMS technology. However, the present invention is not limited to this. The acceleration sensors A1 to A4 may be relatively large acceleration sensors that do not use the MEMS technology. Even in this case, the fixed plate 81 is disposed between the first movable electrode 61 and the second movable electrode 62 (between the two movable electrodes 66), whereby the viscosity resistance of the gas filled in the cavity 12 is obtained. Will increase. Therefore, since the attenuation coefficient is increased, the range of detectable acceleration can be made wider. In this case, the materials of the fixed portion 5, the movable portion 6, the fixed plate 81, and the substrate 1 are not limited. Also, the structure of each part is not limited. It is sufficient to include at least a pair of fixed electrodes, a pair of movable electrodes movable between the pair of fixed electrodes, and a fixed plate disposed between the pair of movable electrodes and fixed to the fixed electrode.

  The acceleration sensor according to the present invention is not limited to the embodiments described above. The specific configuration of each part of the acceleration sensor according to the present invention can be varied in design in many ways.

A1 to A4: Acceleration sensor 1: Substrate 11: Support 12: Cavity 2: Sensor 21: X-axis sensor 22: Y-axis sensor 23: Z-axis sensor 3: Electrode pad 4: Lid 5: Fixing portion 51: Fixed electrode 52: fixed base portion 521: insulating portion 53: first fixed electrode 54: first fixed base portion 55: second fixed electrode 56: second fixed base portion 6: movable portion 61: first movable electrode 62: second movable Electrode 63: movable base portion 64, 65: spring portion 66: movable electrode 81: fixed plate 82: insulating portion

Claims (13)

A substrate having a cavity,
A pair of fixed electrodes disposed in the cavity and fixed to the substrate;
A pair of movable electrodes disposed between the pair of fixed electrodes and movable in a detection direction in which the pair of fixed electrodes are arranged;
A fixed plate disposed between the pair of movable electrodes and fixed to the substrate;
An acceleration sensor comprising: The fixed plate is electrically insulated from the fixed electrode and the movable electrode.
The acceleration sensor according to claim 1. The fixing plate is made of an insulator.
The acceleration sensor according to claim 1. A movable base portion to which the pair of movable electrodes are fixed;
A spring portion for fixing the movable base portion to the substrate in a movable state in the detection direction;
Further equipped with,
The acceleration sensor according to any one of claims 1 to 3. The pair of fixed electrodes and the pair of movable electrodes are made of conductive silicon.
The acceleration sensor according to any one of claims 1 to 4. The substrate is made of conductive silicon.
The acceleration sensor according to any one of claims 1 to 5. The apparatus further comprises a lid fixed to the substrate to seal the cavity.
The acceleration sensor according to any one of claims 1 to 6. The pair of fixed electrodes are electrically connected,
Different voltage signals are input to the pair of movable electrodes,
Electrical signals of the pair of fixed electrodes are output,
The acceleration sensor according to any one of claims 1 to 7. The pair of movable electrodes are electrically connected,
Different voltage signals are input to the pair of fixed electrodes, respectively.
Electrical signals of the pair of movable electrodes are output,
The acceleration sensor according to any one of claims 1 to 7. The distance between each of the movable electrodes and the fixed plate, and the distance between each of the movable electrodes and the fixed electrode adjacent to the movable electrode are the same in a state where acceleration in the detection direction is not applied. ,
The acceleration sensor according to any one of claims 1 to 9. Each of the movable electrodes, the fixed electrodes, and the fixed plate has a rectangular plate shape orthogonal to the detection direction.
The acceleration sensor according to any one of claims 1 to 10. The dimensions of the movable electrodes, the fixed electrodes, and the fixed plate in the depth direction of the cavity are all equal.
The acceleration sensor according to any one of claims 1 to 11. And a comb-like first electrode and a second electrode which are engaged with each other at intervals.
The first electrode includes the pair of fixed electrodes,
The second electrode includes the pair of movable electrodes,
The acceleration sensor according to any one of claims 1 to 12.