JPH0862245A - Electrostatic servo type acceleration sensor - Google Patents

Abstract

PURPOSE: To provide an electrostatic servo type acceleration sensor of which sensitivity and offset can be easily adjusted electronically. CONSTITUTION: A mass part 13 is supported by beams 121-124 whose respective one edges are connected to respective anchors 111-114 protruding on a substrate, thin-piece shaped movable electrodes 21a-23b protrude from the mass part 13, and fixed electrodes 31a-33d are provided on both sides of the movable electrodes 21a-23b, thus constituting an electrostatic servo type acceleration sensor. A first voltage Vg is supplied to the movable electrodes 21a-23b, one of a first voltage Vg, a second voltage +Vr, and a third voltage -Vr is selected by selection switches 41a-43d and is fed to each of the fixed electrodes 31a-33d, and the area between the movable electrode and the fixed electrode where electrostatic force operates is variably adjusted by the switches 41a-43d, thus adjusting sensitivity and offset.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention sets a fixed electrode pair in proximity to a movable electrode, which is suitable for, for example, a rotation angle sensor or an electrostatic servo actuator device. On the other hand, the present invention relates to an electrostatic servo type acceleration sensor in which an electrostatic force is applied according to acceleration.

[0002]

2. Description of the Related Art Semiconductor acceleration sensors and electrostatic actuators have been developed to which surface micromachining technology for semiconductor substrates is applied. For example, an acceleration sensor disclosed in Japanese Patent Publication No. 4-504003 is known. ing.
In such an acceleration sensor, capacitors and circuit elements that make up the sensor are formed monolithically by a precise manufacturing process. Cannot be completely eliminated.

Therefore, in order to correct such an error, it is necessary to adjust the sensitivity and the offset, and therefore trimming is performed in the manufacturing process. As the trimming method, for example, a method of adjusting the resistance value of the thin film resistor with a laser is generally used. However, such a trimming method not only takes a lot of time, but also requires dedicated equipment.

FIG. 4 shows the configuration of a conventionally known electrostatic capacitance type acceleration servo acceleration sensor, which is projected on a substrate surface of a semiconductor or the like (not shown) and has, for example, a quadrilateral shape. Forming four anchors 111-114 at each vertex,
Beams 121 to 124 that constitute a support member are set so that one end is supported by each of the anchors 111 to 114. Then, each of the beams 121 to 124 supports the four corner portions to set the rectangular mass portion 13 that is floated from the substrate surface. Anchor 111
.About.114, beams 121 to 124, and the mass portion 13 are integrally cut out from, for example, a polysilicon member, and the mass portion 13 is movably supported by an acting acceleration.

The rectangular mass portion 13 has a plurality of strip-shaped movable electrodes 21a, 21b, 22a, 22b, 23a, which are formed so as to project laterally from opposite long sides thereof. 23b
Are integrally formed. Then, these movable electrodes 21
a to 23b, fixed electrodes 31a, 31b, 32a, 32b, 33 fixedly formed on the substrate in proximity to one side surface of each.
a, 33b are provided, and the fixed electrodes 31a, 31b, 32a are further provided near the other side surfaces of the movable electrodes 21a-23b.
, 32b, 33a, 33b Fixed electrode 31c paired with it
, 31d 1, 32c 2, 32d 2, 33c 2, 33d 2 are arranged.
That is, the fixed electrode pair is arranged on both sides of each of the plurality of movable electrodes 21a to 23b.

A first power supply unit having a voltage value Vg is connected to each of the movable electrodes 21a to 23b integrally provided on the mass unit 13 through one anchor 111 that supports the mass unit 13 as described above. , The movable electrodes 21a-23b are both set to the first voltage Vg. Furthermore, these movable electrodes 21a
~ 23b Fixed electrodes set close to one side of each
31a, 31b, 32a, 32b, 33a and 33b are voltage values + Vr
Fixed electrodes 31c, 31d, 32 which are connected to the second power source of the movable electrodes 21a-23b and are set on the other side surfaces of the movable electrodes 21a-23b.
A third power supply unit having a voltage value -Vr is connected to c, 32d, 33c and 33d.

That is, the capacitance formed between the movable electrodes 21a-23b and the fixed electrodes 31a, 31b, 32a, 32b, 33a, 33b, and the movable electrodes 21a-23b and the fixed electrodes 31c, 31d, 32c, A differential capacitance is formed by the capacitance formed between 32d, 33c, and 33d, and acceleration is detected by a change in this capacitance.

The electrostatic servo type acceleration sensor configured as described above suppresses the displacement of the mass portion 13 by generating an electrostatic force that balances the acceleration, so that the acceleration can be detected with high accuracy. I'm trying to do it.

In the case of this acceleration sensor, the following expression is given, and acceleration can be detected because the voltage applied to the movable electrode becomes proportional to the acceleration. However, in order to change the sensitivity, it is necessary to change the voltage Vr or amplify Vg with an appropriate amplification factor. For this reason, adjustment is made by trimming circuit elements or the like.

[0010]

[Equation 1]

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and the sensitivity and offset can be easily adjusted by electrical control, and the mass portion that is integrally displaced with the movable electrode can be controlled. The electrostatic servo type acceleration sensor is configured so that the electrostatic force can be variably set to eliminate the need for adjustment such as trimming, and for example, an acceleration sensor or the like that can perform acceleration detection with high accuracy can be configured. It is the one we are trying to provide.

[0012]

In an electrostatic servo type acceleration sensor according to the present invention, a movable electrode is integrally provided on a mass portion supported so as to be displaced, and the movable electrode is arranged in a displacement direction opposite to the movable electrode. In the mechanism configured by setting the fixed electrode pairs in close proximity to each other, the voltage sources respectively supplied to the pair of fixed electrodes forming the fixed electrode pair are controlled to be switched to different voltage values.

For example, the first voltage source is connected to the movable electrode, and the pair of fixed electrodes forming the fixed electrode pair are
The first voltage source or the second or third voltage source having a voltage value different from that of the first voltage source is selectively connected. In addition, in each combination of the movable electrode and the fixed electrode pair, the shape of the movable electrode or the fixed electrode is set so that the facing area between the side surface of the movable electrode and each fixed electrode forming the fixed electrode pair can be set differently. I am trying to adjust.

[0014]

In the electrostatic servo type acceleration sensor having the above-mentioned structure, the movable electrode is movable relative to the electric potential set on the movable electrode. An electric potential equal to the electric potential of the electrode or a second or third electric potential different from this is applied and set,
For example, with the voltage Vg applied to the movable electrode,
When this voltage Vg is similarly applied to the pair of fixed electrodes sandwiching the movable electrode, the facing area which causes a potential difference between the movable electrode and the fixed electrode becomes "0" substantially. On the other hand, when the voltages + Vr and −Vr on both sides of the voltage Vg are set to be applied to the pair of fixed electrodes located on both sides of the movable electrode, the potential difference between the movable electrode and the fixed electrode is set. The generated area becomes maximum, a large electrostatic force acts, and the sensitivity and offset can be adjusted without performing adjustment such as trimming.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an acceleration sensor driven by an electrostatic servo. The main body of this acceleration sensor is shown in FIG.
Similarly to the conventional example shown in (1), the rectangular mass portion 13 is displaceably supported by the beams 121 to 124 coupled to the anchors 111 to 114. The strip-shaped movable electrodes 21a, 21b, 22a, 22b are integrally formed on both edge portions facing the mass portion 13.
, 23a, 23b are formed in a protruding manner, and these movable electrodes 21a
~ 23b fixed electrode 31a close to one side of each,
31b, 32a, 32b, 33a, 33b, and movable electrodes 21a, 21b, 22a, 22b, 23a, 23.
Fixed electrodes 31c, 31d close to the other side of b
, 32c, 32d, 33c, 33d. That is, the fixed electrode pair is arranged on both sides of each of the plurality of movable electrodes 21a to 23b.

Here, the mass portion 13 is provided with a gate electrode protruding from the opposite side portion thereof and displaced together with the mass portion 13.
141 and 142 are projected, and the gate electrodes 141 and 14 are
2 diffusion layers 15a and 15b serving as a source and a drain, and 16a and 16b serving as drains, respectively, are formed on the substrate surface located on both sides of 2 and MOSFETs 171 and
172 are configured. That is, the mass part 13
When the gate electrodes 141 and 142 are displaced, the amount by which the gate electrodes 141 and 142 overlap the source region and the drain region respectively changes, and the channel region formed between these source region and drain region is controlled, so that the mass of the MOSFETs 171 and 172 is reduced. An output signal corresponding to the displacement amount of the portion 13 is derived.

Fixed electrodes 31a to 33d located on both sides of the movable electrodes 21a to 23b are provided with changeover switches 41a to 41d, 42a to 42d, 43a to 43d, respectively. ~ 33
The voltage applied to d is + Vr or -Vr
The voltage Vg equal to that of the movable electrodes 21a-23b is selectively switched and applied.

In the illustrated state, the fixed electrodes 31a, 31b, 32a
, 32b is applied with voltage + Vr, and fixed electrode 31c
, 31d, 32c, and 32d, a voltage -Vr is applied and set, and a voltage Vg is applied to the fixed electrodes 33a to 33d. This voltage Vg is applied to the movable electrodes 21a-23b integrated with the mass portion 13 via the anchor 111.

In the state shown in FIG. 1, the fixed electrode 31a
, 31b, 32a, 32b are applied with voltage + Vr, and fixed electrodes 31c, 31d, 32c, 32d are applied with voltage -Vr, respectively, and with respect to fixed electrodes 331 to 33d. Is applied with the same voltage Vg as that of the movable electrodes 23a and 23b. Therefore, in such a state, the changeover switches 43a to 43d are switched from the state shown in the figure, the voltage + Vr is applied to the fixed electrodes 33a and 33b, and the voltage -Vr is applied to the fixed electrodes 33c and 33d. In comparison, the electrode area that produces a potential difference is 2/3
Therefore, the electrostatic force acting becomes 2/3.

Here, the changeover switches 41a to 43d are appropriately constituted by semiconductor switch elements, and the states of the changeover switches 41a to 43d are set to Vg, + Vr, -Vr before shipment by appropriately using a memory element. Can be set to select any of the. Also, in actual use, the sensitivity may be dynamically changed by switching the changeover switches 41a to 43d depending on the magnitude of the acting acceleration.

For example, when the acting acceleration is smaller than a certain level, the changeover switches 41a to 41d are further changed from the state shown in this figure (the changeover of these switches is preferably as symmetrical as possible),
The same voltage V as that of the movable electrodes 21a and 21b is applied to the fixed electrodes 31a to 31d.
When g is applied, the area of the electrode on which the electrostatic force acts becomes 1/3, and V calculated by the equation (3) is calculated.
g is tripled. Therefore, even if the acceleration is small, the change in Vg is large, but the detection range is 1/3. In this case, the electrostatic force for damping the gates 141 and 142 does not change before and after the electrode area is changed because Vg increases as the electrode area decreases.

In the embodiment shown in FIG. 1, the movable electrodes 21a ...
The lengths of the fixed electrodes 31a to 33d facing the 23b are kept constant, but if the fixed electrode length is weighted to a power of 2 as shown in FIG. Since the facing area is weighted to the power of 2, it is weighted to the power of 2 by switching the changeover switches 41a to 43d. That is, the electrostatic force is D
It is possible to obtain a state of / A conversion, and various conversion characteristics can be obtained by adjusting the electrode length so as to obtain a predetermined area ratio. 2, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In the embodiment shown in FIG. 3, voltage + Vr
Also, the voltage source for setting -Vr can be constituted by a variable voltage source such as D / A converters 51 and 52. In this way, the electrostatic force applied can be electronically adjusted with high precision, and the fixed electrodes 31a to 33d are weighted to the power of 2 as shown in the embodiment of FIG. If so, the electrostatic force is adjusted in a wider range. In FIG. 3, the same components as those in FIG.

By constructing the voltage source by the D / A converters 51 and 52 as in this embodiment, the voltage ± Vr can be adjusted by setting a predetermined digital value, and the sensitivity and offset can be digitally adjusted. Can be adjusted. In this case, a voltage corresponding to the offset may be applied between the movable electrode and the fixed electrode.

That is, by digitally varying the electrostatic force, the sensitivity and offset of the servo sensor such as an acceleration sensor can be adjusted, and the electrostatic force can be used for adjusting the driving force of the electrostatic actuator. Further, as a means for varying the electrostatic force, a means using this D / A converter and a means for weighting the electrode length to a power of 2 can be combined.

The sensitivity described here is the amount of change in the output voltage Vg per 1G, and changing this sensitivity means setting the amount of change in the output voltage Vg per 1G to a desired value. Is. Regarding the offset, by constantly generating an electrostatic force corresponding to the offset amount, Vg is set so as to pull back the movable part against the electrostatic force.
The offset can also be adjusted due to the change in.

Further, in the movable gate type MOSFET for detecting acceleration, the sensitivity as a sensor is changed by changing the gate area. However, in the case of the electrostatic servo type, the output voltage Vg is irrelevant to the sensitivity of the sensor as shown in the equation (3), and therefore the sensitivity of the output voltage Vg (the amount of change in voltage per 1G). Does not change. However, it affects the reaction rate and the like.

In the acceleration sensor shown in the above embodiments, when the power is turned on, a part or all of the changeover switch is connected to the power supply side of the voltage Vg, or the output of the D / A converter is connected to the movable electrode. If the digital value input to the D / A converter is set so that the potentials are the same, the electrostatic force can be weakened or eliminated, and malfunctions such as sticking of electrodes due to noise when the power is turned on. Can be prevented. Such means for varying the electrostatic force can be applied not only to the acceleration sensor but also to various electrostatic actuators, and a rotation angle sensor or the like can be configured with the same idea.

[0029]

As described above, according to the electrostatic servo type acceleration sensor of the present invention, the mass that is integrally displaced with the movable electrode can be easily adjusted by the electric control so that the sensitivity and the offset can be easily adjusted. It is possible to configure an acceleration sensor that makes it possible to perform acceleration detection with high accuracy by making it possible to variably set the electrostatic force that controls the parts, and eliminate the need for adjustments such as trimming. Is also suitable.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an electrostatic servo type acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a configuration diagram for explaining an electrostatic servo type acceleration sensor according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram for explaining an electrostatic servo type acceleration sensor according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a conventional acceleration sensor.

[Explanation of symbols]

111-114 ... Anchor, 121-124 ... Beam, 13 ... Mass part,
171, 172 ... MOSFET, 21a-23b ... Movable electrode, 31
a ~ 33d ... fixed electrode, 41a ~ 43d ... changeover switch,
51, 52 ... D / A converter.

Claims (6)

[Claims] 1. A displaceablely supported mass part, a movable electrode integrally provided on the mass part, and a fixed electrode pair set close to each other in displacement directions opposite to the movable electrode. In a sensor mechanism provided, an electrostatic servo acceleration sensor, wherein voltage sources for applying a voltage to the fixed electrodes forming the fixed electrode pair are controlled to be switched to different voltage values. 2. A first voltage source is connected to the movable electrode, and the fixed electrodes forming the fixed electrode pair have a voltage value different from that of the first voltage source or the first voltage source. The electrostatic servo type acceleration sensor according to claim 1, wherein the second or third voltage source for which is set is selectively connected. 3. A first voltage source is connected to the movable electrode, and the fixed electrodes forming the fixed electrode pair are provided with the first voltage source selected by a changeover switch.
The electrostatic servo acceleration sensor according to claim 1, wherein one of a second voltage source and a third voltage source having a voltage value different from that of the first voltage source is connected. 4. A first voltage source is connected to the movable electrode, and a second voltage source or a third voltage source is connected to each of the fixed electrodes forming the fixed electrode pair. The electrostatic servo acceleration sensor according to claim 1, wherein the third voltage source is constituted by a D / A conversion means. 5. A plurality of strip-shaped movable electrodes are integrally projectingly formed on the mass portion, and fixed electrodes constituting the fixed electrode pair are arranged close to both sides of each of the plurality of movable electrodes. The electrodes are set individually, and for each combination of the movable electrode and fixed electrode pair, the side surface of the movable electrode and the fixed electrode forming each fixed electrode pair are set to have different facing areas. The electrostatic servo acceleration sensor according to claim 1, wherein the shape of the movable electrode or the fixed electrode is adjusted so as to be adjustable. 6. The electrostatic servo acceleration sensor according to claim 5, wherein the length of the portion of the fixed electrode facing the movable electrode is set to be different by weighting a power of two.