JPH08114456A - Semiconductor yaw-rate sensor - Google Patents

Abstract

PURPOSE: To alleviate temperature dependence and to improve detecting accuracy by providing the respective means of a variable electrode, vibration, vertical-displacement detection and vertical-displacement control, and detecting a yaw rate with the control amount of the variable electrode. CONSTITUTION: When a movable electrode 14 is vibrated in the horizontal direction and a yaw rate is applied on the electrode 14, the electrode 14 is displaced in the vertical direction with respect to a semiconductor substrate 11 by Coriolis force. The displacement is detected, and the displacement of the electrode 14 in the vertical direction is controlled into the direction where the displacement disappears. The interval between the electrode 14 and the substrate 11 is kept constant. At the same time, the yaw rate is detected with the amount of the control for controlling the displacement of the electrode 14 in the vertical direction. The feedback constitution, which keeps the constant interval between the electrode 14 and the substrate 11 with respect to the displacement of the electrode 14 in the vertical direction, is provided. The yaw rate is detected with the control amount. Thus, the highly accurate yaw-rate detection for decreasing the effect of temperature dependence can be performed by using the control amount by the feedback.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor yaw rate sensor using a semiconductor substrate, and more particularly to a semiconductor yaw rate sensor that can be used for vehicle body control and navigation of an automobile.

[0002]

2. Description of the Related Art As a yaw rate sensor for detecting a yaw rate acting on a vehicle body of an automobile, for example, a vibration gyro as disclosed in JP-A-2-113817 is known.

In this vibrating gyro, a piezoelectric element is bonded to a specified surface of a metal square bar to form a vibrating body,
This is configured to be supported by a thin rod. Further, the angular velocity sensor disclosed in Japanese Patent Laid-Open No. 4-142420 is constructed by bonding a piezoelectric element to a metallic sound frame.

That is, in any of these devices for detecting acceleration such as yaw rate, the piezoelectric element vibrates the main body and the distortion caused by the Coriolis force generated by the yaw rate to be measured is detected by the piezoelectric element. It is trying to detect by the change of the voltage.

The performance such as the detection sensitivity in the sensor mechanism constructed as described above depends on the supporting method of the vibrating body and the processing accuracy. Therefore, in order to create a high performance sensor mechanism, the processing is required. It is difficult to assemble, and it is inevitably expensive, and it is not easy to reduce the size of the sensor mechanism due to the restrictions of machining and assembly.

In order to solve such a problem, the applicant of the present application previously applied for a transistor type yaw rate sensor using semiconductor technology by utilizing a transistor type displacement detection mechanism (Japanese Patent Application No. 311762
issue).

This transistor type yaw rate sensor is
A movable electrode having a beam structure arranged at a predetermined distance above the semiconductor substrate, a movable electrode having a beam structure formed on the semiconductor substrate for the movable electrode, and a movable electrode formed on the semiconductor substrate for the movable electrode. When the movable electrode having the source / drain electrodes is vibrated by electrostatic force, the movable electrode is vertically displaced by the action of yaw rate, and the current change between the source / drain electrodes due to this displacement. The yaw rate is detected by.

[0008]

However, in such a transistor type yaw rate sensor, since the transistor type displacement detection mechanism has temperature dependence, the reference position may drift due to temperature, and the angular velocity ω may be changed. There is a problem that the detection accuracy is lowered because the displacement apparently changes due to the temperature change. Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor yaw rate sensor with reduced temperature dependence and improved detection accuracy.

[0009]

In order to achieve the above object, the present invention provides, in the invention described in claim 1, a semiconductor substrate and a movable electrode located above a surface of the semiconductor substrate with a predetermined distance therebetween. A vibrating means for vibrating the movable electrode horizontally with respect to the semiconductor substrate, a vertical displacement detecting means for detecting a displacement of the movable electrode in a vertical direction with respect to the semiconductor substrate, and a vibrating means for vibrating the movable electrode. When displaced in the horizontal direction, the displacement of the movable electrode in the vertical direction is controlled so as to keep the distance between the movable electrode and the semiconductor substrate constant according to the displacement of the movable electrode detected by the vertical displacement detection means. The vertical displacement control means is provided, and the yaw rate is detected by the control amount of the movable electrode by the vertical displacement control means.

According to a second aspect of the present invention, in the first aspect of the invention, the vibrating means is located above the semiconductor substrate and spaced from the surface of the semiconductor substrate by a predetermined distance, and a gap is formed in the movable electrode. It is characterized in that it has a fixed electrode for excitation which is disposed via the above and which vibrates the movable electrode by utilizing static electricity.

According to a third aspect of the invention, in the first or second aspect of the invention, the vertical displacement detection means is formed on the surface of the semiconductor substrate by an impurity diffusion region at a position facing the movable electrode. The vertical displacement of the movable electrode is detected by the electrostatic capacitance between the movable electrode and the lower electrode.

According to a fourth aspect of the invention, in the invention of the third aspect, the vertical displacement control means is provided between the movable electrode and the lower electrode at an initial position of the movable electrode. It is characterized in that the displacement of the movable electrode in the vertical direction is controlled so that the capacitance becomes the reference capacitance by using the capacitance as a reference.

According to a fifth aspect of the invention, in the invention according to any one of the first to fourth aspects, the vertical displacement control means includes a movable electrode for displacement control formed on the movable electrode, and Between the movable electrode for displacement control and the fixed electrode for displacement control provided above the semiconductor substrate so as to face the movable electrode for displacement control, the movable electrode for displacement control is moved according to the displacement of the movable electrode detected by the displacement detection means. A voltage control unit that applies a control voltage between an electrode and the fixed electrode for displacement control, and that keeps the distance between the movable electrode and the semiconductor substrate constant by an electrostatic force between the movable electrode for displacement control and the fixed electrode for displacement control. It is characterized by having and.

[0014]

According to the present invention, when the movable electrode is vibrated in the horizontal direction, when the yaw rate is applied to the movable electrode, the Coriolis force causes the movable electrode to move vertically to the semiconductor substrate. Displace.

Since electrostatic capacitance is used in the present invention as means for detecting this displacement, it is possible in principle to perform highly accurate detection with less influence of temperature dependence. Further, in the present invention, this displacement is detected and the vertical displacement of the movable electrode is controlled in the direction in which the displacement disappears so that the distance between the movable electrode and the semiconductor substrate is kept constant. The yaw rate is detected by the control amount that controls the displacement of.

As described above, the yaw rate is detected by the control amount as a feedback structure for keeping the distance between the movable electrode and the semiconductor substrate constant with respect to the vertical displacement of the movable electrode. By using the feedback control amount instead of the displacement itself, highly accurate yaw rate detection with less influence of temperature dependence can be performed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a planar configuration of the yaw rate sensor. That is, in FIG. 1, the semiconductor substrate 11 is composed of a P-type silicon substrate.

On the semiconductor substrate 11, the anchor portion 1 is formed.
21 to 124 are formed at four places, and this anchor portion 121
131 to 134 whose one ends are respectively supported by
The weight 14 is supported by.

Therefore, the weight 14 is formed by the beam structure as shown in FIG.
It is supported so as to be displaceable in the vertical direction and the horizontal direction (direction of arrow V in FIG. 1) on the plane of FIG. The weight 14 is set to increase the amount of displacement due to the yaw rate.

Further, the weight 14 is formed with projecting movable electrodes 161 to 164 which are located on both sides of the weight 14 in the displacement direction thereof and in which a pair of strips are set parallel to each other in the shape of comb teeth. There is.

The excitation movable electrodes 161 to 164 act to give vibration to the weight 14. These anchor parts 12
1 to 124, the beams 131 to 134, the weight 14, and the excitation movable electrodes 161 to 164 are integrally formed of a heat-resistant metal such as polysilicon or tungsten. Polysilicon is used as the material.

The weight 14 and the excitation movable electrodes 161 to 164 formed integrally with the weight 14 are arranged on the main surface of the semiconductor substrate 11 with a predetermined space therebetween, and the beams 131 to 134.
It is held by the anchor portions 121 to 124 via the.

The weight 14 and the movable electrodes 161 to 164 and the beams 131 to 134 for excitation formed integrally with the weight 14 and the main surface portion of the semiconductor substrate 11 corresponding to each of the movable electrodes. , A lower fixed electrode 151 formed of a diffusion layer formed by introducing N-type impurities by means of ion implantation or the like constitutes a capacitance.

The lower fixed electrode 151 is connected to an external circuit via an aluminum wiring. Further, fixed electrodes for excitation 191 to 194 are arranged corresponding to the respective movable electrodes for excitation 161 to 164.

The excitation fixed electrodes 191 to 194 are respectively movable excitation electrodes 161 on the main surface of the semiconductor substrate 11.
It is fixedly set at the same height position as ~ 164,
Each has comb-shaped strips, and the strips are arranged so as to be in the center of the other strips, and a predetermined interval is formed between the teeth of each comb.

Each of these excitation fixed electrodes 191 to 194 is connected to an excitation power source (not shown) via an aluminum wiring and is supplied with a voltage signal of a predetermined frequency. And the weight 14 and the movable gate electrode 151 are excited by electrostatic force.
Vibrate ~ 154.

The weight 14 integrally provided with the excitation electrodes 161 to 164 is connected to an external circuit via aluminum wiring. The fixed electrode for excitation is 90
Fixed electrodes 171 and 172 for vertical displacement control are formed on both sides of the weight 14 in directions offset from each other.

The fixed electrodes 171 and 17 for controlling the vertical displacement
2 and the weight 14 constitute an electrostatic capacitance. Each of these displacement control fixed electrodes 171 and 172 is connected to an external circuit via an aluminum wiring.

FIG. 2A shows a cross section taken along the line aa of FIG.
That is, in FIG. 2A, a weight 14 which is supported by the insulating film 22 formed on the P-type silicon semiconductor substrate 11 and is made of, for example, polysilicon is set, and the weight 14 serves as the anchor portions 123 and 124. It is held via the beam 133 and the beam 134 between them.

Here, the insulating film 22 is for setting the air gap 24, and is made of SiO ₂ or Si ₃ N ₄ . In addition, the weight 1 as a movable part
4, the lower fixed electrode 151 is formed on the semiconductor substrate 11 below the beams 133 and 134 by ion implantation or the like, and the weight 14 and the lower electrode 151 which are substantially movable electrodes are formed.
Constitutes a capacitance for yaw rate detection.

The insulating film 22 includes the weight 14 and the beams 131 to 13.
4 and the semiconductor substrate 11, which is a sacrificial layer for setting the gap between the semiconductor substrate 11 and the semiconductor substrate 11, and is removed by etching except the portions corresponding to the anchor portions 121 to 124 to form the air gap 24.

In this etching, an etching solution is used which does not etch the polysilicon forming the weight 14, the beams 131 to 134 and the semiconductor substrate 11, but only the insulating film 22 which is a sacrifice layer.

FIG. 2B shows a bb section of FIG. That is, in FIG. 2B, the weight 14 and the semiconductor substrate 1 are
The air gap 24 is set between 1 and 1, and the weight 14 serving as a movable electrode is displaceable in the vertical direction with respect to the semiconductor substrate 11 and the vertical direction with respect to the paper surface.

Further, the weight 14 serving as a movable electrode and the lower fixed electrode 151 constitute an electrostatic capacitance. Further, a gap is set between the excitation fixed electrodes 193 and 194 and the excitation movable electrodes 163 and 164 (not shown), and the excitation fixed electrodes 193 and 194 and the excitation movable electrodes 163 and 164 are formed on the semiconductor substrate 11. It is set to have the same height.

FIG. 2C shows a cc cross section of FIG. That is, in FIG. 2C, the weight 14 and the semiconductor substrate 1 are
The air gap 24 is set between 1 and 2.

Further, fixed displacement control fixed electrodes 171 and 1
An interval is set between 72 and the weight 14, and the vertical displacement control fixed electrodes 171, 172 and the weight 14 are set to have the same height with respect to the semiconductor substrate 11.

Next, a method for manufacturing the yaw rate sensor thus constructed will be described with reference to FIGS. 3 (a) to 3 (e) and FIG.
This will be described with reference to (a) to (d). In these figures, the sensor part is in the left half and the sensor processing circuit is in the right half as M.
Assuming an OSFET, its manufacturing process is also shown.

First, as shown in FIG. 3A, a lower electrode 15 is formed on a semiconductor substrate 11 made of P-type silicon by ion implantation or the like. Next, as shown in FIG. 3B, an insulating film 22 serving as a sacrificial layer is formed on the surface of the semiconductor substrate 11 so as to correspond to the sensor formation portion.

The insulating film 22 may be formed on the entire main surface of the semiconductor substrate 11 and then the insulating film on the transistor formation portion may be removed. And FIG.
As shown in (c), a gate insulating film 25 is formed by gate oxidation on the main surface of the semiconductor substrate 11 corresponding to the transistor formation portion.

Next, as shown in FIG. 3D, the insulating film 2
A film made of polysilicon is formed on 2 and 25, and the weight 14 and the gate 26 of the transistor are subjected to a photolithography process.
To process.

At the same time, the anchor portions 121 to 124, the beams 131 to 134, etc., which are not shown in this figure, are processed. Then, as shown in FIG. 3E, in order to form the source electrode 30 and the drain electrode 31 of the transistor,
Impurities are introduced by ion implantation into the gate electrode 26 in a self-aligned manner to form an N-type diffusion layer.

Next, as shown in FIG. 4A, an interlayer insulating film 32 is formed on the entire surface in order to electrically insulate the movable electrode 14, the gate electrode 26 of the transistor and the like from the aluminum wiring.

Then, as shown in FIG. 4B, contact holes 311 to 313 corresponding to the lower electrode 15, the source electrode 30 and the drain electrode 31 of the transistor are opened in the interlayer insulating film.

After that, as shown in FIG. 4C, aluminum, which is an electrode material, is deposited in correspondence with the contact holes 311 to 313, and the aluminum wiring 32 is formed.
1-323 are formed.

Then, as shown in FIG. 4D, the insulating film 22 under the weight (movable electrode) 14 is etched as a sacrifice layer to form an air gap 24 under the weight (movable electrode) 14. The yaw rate sensor is completed.

In this yaw rate sensor, the beam 131
As a material for forming the layers to 134, a thin film formed on the silicon substrate 11, for example, polysilicon doped with a high concentration of impurities or a material such as a heat resistant metal is used.

Therefore, it is possible to sufficiently reduce the variation in the thickness of the beams 131 to 134. Typically,
When a one-point load is applied to a cantilever beam or a double-supported beam, its displacement is inversely proportional to the cube of the beam thickness and the cube of the width, so the thickness of the beam is greater than that of machining the beam width. Extremely high precision is required for machining.

In addition, a beam-shaped polysilicon layer is formed after forming a sacrificial layer on the semiconductor substrate 11 in advance, and the sacrificial layer is removed by etching, so that a beam having a predetermined interval is set on the surface of the semiconductor substrate 11. 131 to 134 are formed.

Here, the sacrifice layer is a thin film formed in advance for the purpose of finally removing it. In this embodiment, the distance between the movable electrode 14 and the lower fixed electrode 15 is controlled by the thickness of the sacrificial layer. In this case, the controllability of the thickness of the sacrificial layer is good, The controllability of the electrostatic capacitance between the movable electrode 14 and the lower fixed electrode 15 is also improved.

Further, in the manufacturing method for manufacturing this yaw rate sensor, all can be dealt with by the IC manufacturing process itself or its diversion, and the sensor structure can be formed in the IC manufacturing process. Can be easily integrated.

In the yaw rate sensor described in this embodiment, the yaw rate detecting section has a double-supported beam structure. However, this can also be realized by a cantilever beam structure, and the number of beams is four. Does not have to be.

Although the excitation electrode and the vertical displacement control electrode are provided on both sides of the weight, this may of course be provided on one side. Further, although the excitation electrode and the vertical displacement control electrode are provided so as to be offset by 90 degrees, they may be provided on the same side.

Further, although the number of excitation electrodes is two on the movable side and three on the fixed side as shown in the figure, the number of excitation electrodes may be a combination of other numbers. The vertical displacement control electrodes 171 and 172 are shown as being on a straight line parallel to the movable electrode 14 as shown in FIG.
This may be configured like a comb tooth like an excitation electrode.

Further, although the P-type semiconductor substrate is used as the substrate in the above description, it may be formed of an N-type semiconductor substrate. In this case, the diffusion electrode is formed of P-type. Furthermore, the weight 14 does not have to be a quadrangle, but can be configured as a triangle, for example.

Next, the operation of the yaw rate sensor configured as described above will be described. In this yaw rate sensor, a fixed lower electrode 15 is provided on a semiconductor substrate 11 facing a weight (movable electrode) 14 in a vertical direction.
The vertical displacement of 4 changes the capacitance between the movable electrode 14 and the fixed lower electrode 15.

Therefore, the movable electrode 14 and the fixed lower electrode 15
The yaw rate can be detected by detecting the displacement of the movable electrode 14 on the basis of the change in the electrostatic capacitance. Further, when an exciting voltage having a certain frequency is applied between the fixed electrodes for excitation 191 to 194 and the movable electrodes for excitation 161 to 164, horizontal vibration is generated in the movable electrodes for excitation 161 to 164 due to electrostatic force. , The weight (movable electrode) 14 also vibrates.

The Coriolis force generated by the yaw rate is proportional to the speed of this vibration, and it is preferable to select the frequency near the resonance point where the amplitude becomes large in order to increase the vibration speed.

In this way, the excitation movable electrodes 161 to 1
By applying a periodic voltage for excitation between 64 and the fixed electrodes for excitation 191 to 194, the weight (movable electrode) 14 vibrates as shown in FIG.

When a yaw rate ω having an axis which is horizontal to the semiconductor substrate 11 and perpendicular to the vibration is generated, Coriolis force proportional to the vibration speed and the mass of the vibrating body is generated in the direction perpendicular to the semiconductor substrate 11. , Weight (movable electrode) 1
4 is displaced in the direction perpendicular to the semiconductor substrate 11 about Z0.

FIG. 5B shows the displacement when the yaw rate ω is applied. Since the vertical displacement Z of the movable electrode is proportional to the vibration speed, the phase shifts by π / 2 from the horizontal displacement.

Then, the weight (movable electrode) 14 is displaced in the direction perpendicular to the semiconductor substrate 11, whereby the movable electrode 14 is moved.
The capacitance between the fixed lower electrode 15 and the fixed lower electrode 15 changes. In this embodiment, feedback control is performed so that the movable electrode does not move.

That is, the movable electrode 14 and the fixed lower electrode 1
A voltage is applied between the vertical displacement control electrode 171 and the movable electrode 14 so as to keep the electrostatic capacitance between the five constant, and the voltage is controlled to a certain value Z0, and the yaw rate is detected by the control voltage. ing.

This is because the voltage as shown in FIG. 5C is applied between the vertical displacement control electrode 171 and the movable electrode 14,
As shown in (d), the vertical displacement of the movable electrode can be suppressed, and the yaw rate can be detected by the voltage shown in FIG. 5C applied to the vertical displacement control electrode 171.

[0064]

As described above in detail, according to the present invention, the capacitance is used as the means for detecting the displacement of the movable electrode, and in principle the temperature dependence is reduced to improve the detection accuracy. It is possible to provide a semiconductor yaw rate sensor.

[Brief description of drawings]

FIG. 1 is a plan view of a yaw rate sensor according to an embodiment of the present invention.

2A to 2C are respectively aa and a of FIG.
It is a figure which shows bb and cc cross section.

3A to 3E are cross-sectional views sequentially illustrating a manufacturing process of the yaw rate sensor.

4A to 4D are cross-sectional views sequentially illustrating a manufacturing process of the yaw rate sensor.

5A is a diagram showing a horizontal displacement of a movable electrode, FIG. 5B is a diagram showing a displacement of the movable electrode when a yaw rate is applied, and FIG. 5C is a vertical displacement control. FIG. 5D is a diagram showing a change in voltage between the working electrode and the movable electrode, and FIG. 5D is a diagram showing displacement of the movable electrode by the closed loop control.

[Explanation of symbols]

11 ... Semiconductor substrate, 121-124 ... Anchor part, 13
1-134 ... Beam, 14 ... Weight (movable electrode), 151 ... Lower fixed electrode, 161-164 ... Exciting movable electrode, 17
1, 172 ... Fixed electrodes for vertical displacement control, 191-194
... Exciting fixed electrode, 22 ... Insulating film.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G01D 5/16 G01P 9/04 H01L 29/84 F

Claims (5)

[Claims] 1. A semiconductor substrate, a movable electrode positioned above a surface of the semiconductor substrate with a predetermined distance therebetween, a vibrating means for vibrating the movable electrode in a horizontal direction with respect to the semiconductor substrate, and the movable member. Vertical displacement detecting means for detecting displacement of the electrode in the vertical direction with respect to the semiconductor substrate; and displacement of the movable electrode detected by the vertical displacement detecting means when the movable electrode is displaced in the horizontal direction by the vibrating means. Corresponding to the vertical displacement control means for controlling the vertical displacement of the movable electrode so as to keep the distance between the movable electrode and the semiconductor substrate constant. A semiconductor yaw rate sensor, which is adapted to detect a yaw rate. 2. The vibrating means is located above the semiconductor substrate and spaced apart from the surface of the semiconductor substrate by a predetermined distance and with a gap between the movable electrode and the movable electrode using static electricity. The semiconductor yaw rate sensor according to claim 1, wherein the semiconductor yaw rate sensor has a fixed electrode for excitation that vibrates by vibration. 3. The vertical displacement detection means has a lower electrode formed by an impurity diffusion region on a surface of the semiconductor substrate at a position facing the movable electrode, and the vertical displacement of the movable electrode is moved by the movable electrode. The semiconductor yaw rate sensor according to claim 1 or 2, wherein the semiconductor yaw rate sensor is detected by an electrostatic capacitance between an electrode and the lower electrode. 4. The vertical displacement control means is configured such that the electrostatic capacitance serving as the reference is based on the electrostatic capacitance between the movable electrode and the lower electrode at an initial position of the movable electrode. 4. The semiconductor yaw rate sensor according to claim 3, wherein the vertical displacement of the movable electrode is controlled so that the movable electrode has a capacitance. 5. The vertical displacement control means comprises a movable electrode for displacement control formed on the movable electrode, and a fixed displacement control provided above the semiconductor substrate so as to face the movable electrode for displacement control. Between the electrodes, a control voltage is applied between the displacement control movable electrode and the displacement control fixed electrode according to the displacement of the movable electrode detected by the displacement detection means, The semiconductor yaw rate sensor according to any one of claims 1 to 4, further comprising a voltage control unit that keeps a gap between the movable electrode and the semiconductor substrate constant by an electrostatic force between the displacement control fixed electrodes.