JPH10339638A - Angular speed sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection sensitivity by forming a piezoelectric body of a drive vibration part thinner than that of a detection vibration part for larger drive displacement of the drive vibration part and also for higher inspec tion voltage of the detection vibration part. SOLUTION: At a root side of a cantilever vibrator extending from a base body 1, a common electrode 4a, a thick zinc oxide layer 5a and a pair of detection vibration parts 6 and 7 comprising a pair of detection electrodes 6a and 7a are formed. In addition, on a tip end side of the cantilever vibrator 2, a drive vibration part 8 comprising a common electrode 4b, a thin zinc oxide layer 5b, and a drive electrode 8a is formed. Then, a thickness t2 of the zinc oxide layer 5b of the drive vibration part 8 is formed thinner than a thickness t1 of the zinc oxide layer 5a of the detection vibration parts 6 and 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric angular velocity sensor which is mounted on a moving body such as an automobile and detects the rotational angular velocity.

[0002]

2. Description of the Related Art As a conventional angular velocity sensor of this type, FIG. 11 shows a structure including a cantilever vibrator disclosed in Japanese Patent Application Laid-Open No. 7-113463. A cantilever vibrator 32 extending from the silicon substrate 31 to one side is formed. A silicon oxide layer 33 is formed on the cantilever vibrator 32,
On this silicon oxide layer 33, three elongated divided electrodes 3
6a, 37a, 38a are formed in the longitudinal direction.
A piezoelectric body 34 is formed on these divided electrodes 36a, 37a, 38a and the like. Also, this piezoelectric body 3
A common electrode 35 is formed on 4. Then, with the piezoelectric body 34 interposed, the common electrode 35 and the split electrode 36a,
The detection vibration unit 36, the drive vibration unit 37, and the detection vibration unit 38 are configured by 37a and 38a, respectively.

A conventional angular velocity sensor has the above-described structure, and the operation will be described next. An AC voltage is applied between the lower divided electrode 37a of the center driving vibration section 37 and the upper common electrode 35 to vibrate the cantilever vibrator 32 in the Z-axis direction. When the cantilever vibrator 32 is vibrating in this way, the angular velocity sensor (cantilever vibrator 32)
When rotated about the axis, the cantilever vibrator 3
2 comes to vibrate also in the Y-axis direction. Then, compressive stress and tensile stress are alternately generated in the detection vibration portions 36 and 38 on both sides, and voltages of opposite polarities are generated in the detection vibration portions 36 and 38, respectively. The rotational angular velocity is obtained by differentially amplifying the generated voltage.

[0004]

However, FIG.
In the conventional angular velocity sensor shown in FIG. 5, when the piezoelectric body 34 of the cantilever vibrator 32 is thin as a whole, the drive displacement of the cantilever vibrator 32 by the drive vibrator 37 increases, but the detection vibrators 36 and 38 Are lower. On the other hand, when the piezoelectric body 34 of the cantilever vibrating body 32 is thick as a whole, the driving displacement of the cantilever vibrating body 32 by the driving vibrating section 37 is small, but the detection voltage of the detecting vibrating sections 36 and 38 is high. .

In any case, looking at the output characteristics of the driving vibration section 37 and the detection driving sections 36 and 38, if one is good, the other is bad, and if the other is good, one is bad, and the angular velocity sensor The detection sensitivity (output voltage for 1 ° / s) was reduced.

Accordingly, an object of the present invention is to provide an angular velocity sensor having improved detection sensitivity by forming the thickness of the piezoelectric body of the piezoelectric vibrating section smaller than the thickness of the piezoelectric body of the detecting vibrating section.

[0007]

According to the first aspect of the present invention, a cantilever vibrator extending from a base is divided into two in the beam width direction from the root to the center of the cantilever vibrator. A pair of detection vibrators are formed from a pair of detection electrodes, a layer of a piezoelectric body and a common electrode, and from the center of the cantilever vibrator to a tip thereof, from the layer of the drive electrode, the piezoelectric body and the common electrode. A driving vibration portion is formed, and a wiring pattern is led out from the pair of detection electrodes to a pair of detection pads formed on the piezoelectric body of the base, and a wiring pattern is formed between the driving electrode and the pair of detection electrodes. Through the drive pad formed on the piezoelectric body of the base, and the thickness of the piezoelectric body interposed between the drive electrode and the common electrode is increased by the piezoelectric intervening between the pair of detection electrodes and the common electrode. Thinner than body thickness Are those formed.

According to the present invention, for example, an AC voltage of 5 to 50 kHz is applied between the driving pad (driving electrode) and the common electrode. Then, the cantilever vibrating body is vertically vibrated by the area vibration of the piezoelectric body. Thus, if the angular velocity sensor rotates around the axis of the cantilever vibrator while the cantilever vibrator is bending and vibrating, the cantilever vibrator also vibrates in the horizontal direction due to Coriolis force. I will be. Due to the horizontal vibration, voltages of opposite polarities are generated on the detection electrodes of the pair of detection vibrators. By differentially amplifying the voltage of the opposite polarity, the rotational angular velocity based on the Coriolis force can be detected.

In particular, according to the present invention, the thickness of the piezoelectric body of the drive vibrating section is set to １ ／ of the thickness of the piezoelectric body of the detecting vibrating section.
In addition to being formed thin below, 1/10 of the thickness of the support beam
By selecting a value of 1/20, the drive amplitude of the cantilever vibrator is increased. In addition, the detection voltage of the detection vibrating portion increases as the thickness of the piezoelectric body increases. Thereby, the detection sensitivity of the angular velocity sensor is improved.

According to a second aspect of the present invention, a pair of bifurcated beam vibrators, each of which has two nodes of bending vibration supported by four supporting beams, are divided into two in the beam width direction between the nodes. Detection electrode,
A pair of detection vibrating portions each formed of a piezoelectric body and a common electrode layer are formed, and a driving electrode formed of a driving electrode, a piezoelectric body, and a common electrode layer are provided outside the two nodes on the doubly supported vibrating body. A vibrating portion is formed, a wiring pattern is led out from the pair of detection electrodes and the two drive electrodes through the support beam, and the thickness of the piezoelectric body interposed between the two drive electrodes and the common electrode is reduced. , Formed thinner than the thickness of the piezoelectric body interposed between the pair of detection electrodes and the common electrode.

According to the present invention, for example, an AC voltage of 5 to 50 kHz is applied between the two drive electrodes and the common electrode. Then, the cantilever vibrator is moved by the area vibration of the piezoelectric body to 2
Bending vibration is performed in the vertical direction with two nodes as fulcrums. Thus, if the angular velocity sensor is rotated around the axis of the doubly supported beam vibrator while the doubly supported beam vibrator is bending and vibrating, the doubly supported beam vibrator is also bent horizontally by Coriolis force. It starts to vibrate. Due to this horizontal bending vibration,
Voltages of opposite polarities are generated on the detection electrodes of the pair of detection vibrators, respectively. By differentially amplifying the voltage of the opposite polarity, the rotational angular velocity based on the Coriolis force can be detected.

Further, in the present invention, the thickness of the piezoelectric body of the drive vibrating section is formed smaller than the thickness of the piezoelectric body of the detecting vibrating section, similarly to the first aspect of the present invention. This is the same as the invention described in 1.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a piezoelectric angular velocity sensor 10 having a cantilever vibrator structure will be described as a first embodiment of the present invention with reference to FIG. Reference numeral 1 denotes a base made of silicon or the like, and a cantilever vibrator 2 made of silicon extends from a part of the base 1 at right angles. An insulating film, for example, a silicon oxide film 3 is formed on the front and back surfaces of the base 1 and the cantilever vibrator 2.

On the silicon oxide film 3 from the base to the center of the base 1 and the cantilever vibrator 2, a common electrode 4a serving as a lower electrode of a pair of detection vibrators described later is formed. A piezoelectric material, for example, a zinc oxide layer (Zn) is formed on the common electrode 4a and the silicon oxide film 3 on the tip side of the cantilever vibrator 2.
O) 5 is formed. On the tip side of the cantilever vibrating body 2, a common electrode 4b serving as a lower electrode of a driving vibrating unit, which will be described later, is buried in an upper layer portion that is at least 1/2 from the bottom surface of the piezoelectric body 5. The common electrodes 4a and 4b are connected to each other at a central portion of the cantilever vibrator 2, for example, via holes 4c. In addition, a PZT (lead zirconate titanate) -based material can be used as the piezoelectric body.

From the root to the center of the cantilever vibrating body 2, on the piezoelectric body 5, a pair of detection electrodes 6 which are divided into two in the beam width direction and are long in the beam axis direction and opposed to the common electrode 4a.
a and 7a are formed. These pair of detection electrodes 6a,
7a is led out by a wiring pattern to pads 6b and 7b provided on the piezoelectric body 5 formed on the base 1. The layer composed of the pair of detection electrodes 6a, 7a, the piezoelectric body 5, and the lower electrode 4a forms a pair of the detection vibrator 6,
7 is constituted.

A drive electrode 8a opposing the common electrode 4b is formed on the piezoelectric body 5 from the center to the tip of the cantilever vibrator 2. The drive electrode 8a is led to a pad 8c provided on the piezoelectric body 5b of the base 1 via a wiring pattern 8b formed in a gap between the pair of detection electrodes 6a, 7a. The layer including the drive electrode 8a, the piezoelectric body 5, and the common electrode 4b constitutes the drive vibration unit 8.

Here, the thickness t1 of the piezoelectric body 5 of the pair of detection vibrators 6 and 7 is formed to be 3 to 8 μm, and the thickness t2 of the piezoelectric body 5 of the drive vibration section 5 is larger than the thickness t1 of the piezoelectric body 5. , 1
薄 く 3 μm.

Next, the operation of the angular velocity sensor 10 shown in FIG. 1 will be described. An AC voltage of 5 to 50 kHz is applied between the pad 8c (drive electrode 8a) and the common electrode 4b (4a). Then, the drive vibrating unit 8 vibrates the cantilever vibrator 2 in the Z-axis direction with the base of the cantilever vibrator 2 as a fulcrum, as the thickness of the thin piezoelectric body 5 expands and contracts and at the same time the area is reduced and expanded. . As described above, when the angular velocity sensor 10 rotates around the Y axis while the cantilever vibrator 2 is vibrating, the support beam 2 also vibrates in the X axis direction due to Coriolis force. Then, the pair of detection vibrators 6 and 7 alternately receive the tensile stress and the compressive stress, and the detection electrodes 6a and 7
Voltages of opposite polarities are generated at a, and the rotational angular velocity based on the Coriolis force can be detected by differentially amplifying these voltages of opposite polarities.

Next, with reference to FIG. 2, a description will be given of a piezoelectric angular velocity sensor 20 having a structure of a doubly supported vibrator as a second embodiment of the present invention. Reference numeral 11 denotes a doubly supported beam vibrator made of silicon or the like. One node n1 of the bending vibration is supported by support beams 11a and 11b, and the other node n2 is supported by support beams 11c and 11d. The end faces of the four support beams 11a to 11d are respectively connected to the concave side walls of the base (not shown). An insulating film, for example, a silicon oxide film 12 is formed on the doubly supported beam vibrator 11 and the four support beams 11a to 11d.

A common electrode 13 is formed on the silicon oxide film 12 between the nodes n1 and n2 of the cantilever vibrating body 11. The common electrode 13 is led out to, for example, one support beam 11a by the wiring pattern 13a.

The silicon oxide film 1 including the common electrode 13
2, a zinc oxide layer (ZnO) 14 is formed.
Between the nodes n1 and n2 of the doubly-supported vibrator 11, a pair of detection electrodes 15a and 16a which are divided into two in the beam width direction and long in the beam axis direction are formed on the zinc oxide layer. And
The pair of detection electrodes 15a, 16a, the zinc oxide layer 14, and the common electrode 13 form a pair of detection vibrators 15, 1
6 are configured.

Outside the nodes n1 and n2 of the cantilever vibrating body 11, common electrodes 17a and 7b are embedded in upper layers of the zinc oxide layer 14 at a half or more of the thickness thereof. The common electrodes 17a and 17b are connected to the common electrode 13 via via holes and the like in the manner shown in FIG. Driving electrodes 18a and 19a opposing the common electrodes 17a and 17b are formed on the zinc oxide layer 14 above the common electrodes 17a and 7b, respectively. Then, the drive electrode 18a, the zinc oxide layer 14, and the common electrode 1
The drive vibration unit 18 is constituted by 7a. Further, the driving vibration section 19 is constituted by the driving electrode 19a, the zinc oxide layer 14, and the common electrode 17b.

Here, the thickness t1 of the zinc oxide layer 14 of the pair of detection vibrating portions 15 and 16 is formed to be 3 to 8 μm, and the thickness t2 of the zinc oxide layer 14 of the driving vibrating portions 18 and 19 is Is formed as thin as 1 to 3 μm with respect to the thickness t1.

The drive electrodes 18a and 19a and the pair of detection electrodes 15a and 16a are connected to the nearest support beams 11a to 11a.
It is led out through a wiring pattern formed on d.

Next, the operation of the angular velocity sensor 20 shown in FIG. 2 will be described. Common electrode 13 (17a, 17b)
An AC voltage of 5 to 50 kHz is applied between the driving electrodes 18a and 19a. Then, the driving vibration units 18 and 19
At the same time as the thickness of the thin piezoelectric body 14 expands and contracts, the area is reduced and expanded, and the two-sided beam vibrating body 11 bends and vibrates in the Z-axis direction with the two nodes n1 and n2 of the doubly supported beam vibrating point as fulcrums. As described above, when the angular velocity sensor 20 rotates around the Y axis while the doubly supported beam vibrator 11 is bending and vibrating, the doubly supported beam vibrator 11 also bends and vibrates in the X axis direction due to Coriolis force. become. Then, the pair of detection vibrators 15,
16 alternately receives a tensile stress and a compressive stress, and generates voltages of opposite polarities on the detection electrodes 15a and 16a, respectively.
The rotational angular velocity based on the Coriolis force can be detected by differentially amplifying these voltages of opposite polarities.

Next, a method of manufacturing the angular velocity sensor shown in FIG. 1 will be described with reference to FIGS. In FIG. 3, thermal oxidation, sputtering, and C
The silicon oxide film 3 is formed by VD (chemical vapor deposition) or the like.
a and 3b are respectively formed.

Referring to FIG. 4, a photoresist is applied on oxide films 3a and 3b using a photolithography technique, and a resist mask m1 is formed on the entire surface of oxide film 3a on the front surface. A resist mask m2 is formed on the side.

Then, using the resist masks m1 and m2, the silicon substrate 1 is immersed in an etching solution of BHF (buffer / hydrofluoric acid), and the oxide film 3b at the center of the back surface of the silicon substrate 1 is removed by etching.

In FIG. 5, resist masks m1, m2
, The silicon substrate 1 is immersed in an etching solution of TMAH (tetramethylammonium hydroxide), and the silicon oxide films 3a and 3b are used as masks to etch away the center of the back surface of the silicon substrate 1; The thickness is 50-100 μm
Is formed.

In FIG. 6, the silicon substrate 1 is immersed in a BHF etchant using photolithography technology, and the silicon oxide film 3a on the surface is patterned into the planar shape shown in FIG. Then, aluminum (Al), gold (Au) / chromium (C
A metal such as r) is deposited, and a resist mask is formed at a position corresponding to the common electrode 4a. Then, using this resist mask, Au is aqua regia and Cr is a chrome etchant.
Al is wet-etched with 50 ° C. hot phosphoric acid to form a common electrode 4a.

In FIG. 7, a zinc oxide layer 5a having a thickness of 2 to 5 μm is formed on the entire surface of the silicon oxide film 3a including the common electrode 4a by using the RF magnetron sputtering method. Then, the zinc oxide layer 5a is patterned into the shape of the silicon oxide film 3 by wet etching or dry etching with an acidic water such as hydrochloric acid or nitric acid, and an opening 5a for a via hole reaching the tip of the common electrode 4a is formed. It is formed on the zinc oxide layer 5a.

In FIG. 8, aluminum (Al), gold (Au) / chromium (C) are formed on the zinc oxide layer 5a and the like.
r) or the like, and a common electrode 4b connected to the common electrode 4a is formed using a resist mask. And
By a process similar to that of FIG. 7, a zinc oxide layer 5b having a thickness of 1 to 3 μm is entirely formed.

In FIG. 9, a metal such as aluminum (Al), gold (Au) / chromium (Cr) is vapor-deposited on the zinc oxide layer 5b, and as shown in FIG. The detection electrodes 6a, 7a, the drive electrode 8a, the wiring pattern 8b, and the pads 6b, 7b, 8c are formed.

In FIG. 10, a planar resist mask shown in FIG. 1 is formed on a zinc oxide layer 5b including an electrode 8a and the like, and the membrane 2a of the silicon substrate 1 is vertically etched by dry etching using the mask. Process it,
Unnecessary portions are removed to manufacture the angular velocity sensor 10 shown in FIG.

[0035]

According to the first aspect of the present invention, in the angular velocity sensor having the structure of the cantilever vibrating body, the thickness of the piezoelectric body of the driving vibrating section is formed smaller than the thickness of the piezoelectric body of the detecting vibrating section. Therefore, the driving displacement of the driving vibrating part becomes large and the detection voltage of the detecting vibrating part becomes high, so that both can improve the detection sensitivity.

Further, since a pair of detection vibrating portions are formed at the base of the cantilever vibrating body having a large generated stress, a displacement based on a minute Coriolis force can be detected, and the detection sensitivity can be improved. it can.

According to a second aspect of the present invention, there is provided an angular velocity sensor having a structure of a cantilever vibrating body, wherein the thickness of the piezoelectric body of the driving vibrating section is detected similarly to the first aspect of the invention. Since it is formed thinner than the thickness of the body, the driving displacement of the driving vibrating part is increased, and the detection voltage of the detecting vibrating part is increased, and together with this, the detection sensitivity can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment of an angular velocity sensor according to the present invention.

FIG. 2 is a perspective view of a second embodiment of the angular velocity sensor of the present invention.

FIG. 3 is a view showing a method of manufacturing the angular velocity sensor according to the first embodiment of the present invention shown in FIG. 1 and showing a process of forming oxide films on both surfaces of a silicon substrate.

FIG. 4 is a process diagram for etching and removing a silicon oxide film on the back surface of the silicon substrate.

FIG. 5 is a process diagram of forming a membrane by etching the center of the back surface of the silicon substrate.

FIG. 6 is a process diagram of patterning a silicon oxide film on the surface of a silicon substrate and forming a common electrode.

FIG. 7 is a process diagram of patterning by sputtering a zinc oxide layer.

FIG. 8 is a process diagram of depositing and patterning a metal for a common electrode and sputtering a zinc oxide layer.

FIG. 9 is a process diagram of forming a detection electrode, a drive electrode, and the like by depositing a metal.

FIG. 10 is a process diagram of removing unnecessary portions by etching a silicon substrate.

FIG. 11 is a perspective view of a conventional angular velocity sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 11 Substrate 2 Cantilever vibrator 2a Membrane 3, 12 Silicon oxide film 4a, 4b, 13, 17a, 17b Common electrode 5, 14 Zinc oxide layer 5a First zinc oxide layer 5b Second zinc oxide layer 6 , 7, 15, 16 Detecting vibrating parts 6a, 7a, 15a, 16a Detecting electrodes 8, 18, 19 Driving vibrating parts 8a, 18a, 19a Driving electrodes 10, 20 Angular velocity sensors 11a to 11d Supporting beams

Claims (2)

[Claims] 1. A cantilever vibrator extending from a base is provided with a pair of a detection electrode, a piezoelectric body, and a common electrode divided in two in a beam width direction from a root portion to a center portion of the cantilever vibrator. A pair of detection vibrating portions are formed, and a driving vibrating portion including a layer of a driving electrode, a piezoelectric body, and a common electrode is formed from a central portion to a tip portion of the cantilever vibrating member, and the pair of detecting electrodes A driving pad formed on the piezoelectric body of the base from the drive electrode, wherein a wiring pattern is respectively led out to a pair of detection pads formed on the piezoelectric body of the base. An angular velocity sensor wherein a thickness of a piezoelectric body interposed between the drive electrode and the common electrode is formed smaller than a thickness of a piezoelectric body interposed between the pair of detection electrodes and the common electrode. 2. A pair of a detection electrode, a piezoelectric body, and a common electrode divided into two in the beam width direction, between two nodes of a doubly supported vibrator in which two nodes of bending vibration are supported by four support beams. A pair of detection vibrating portions formed of an electrode layer are formed, and a driving vibrating portion formed of a driving electrode, a piezoelectric body, and a common electrode layer is formed outside each of the two nodes on the doubly supported beam vibrating body. A wiring pattern is led out from the pair of detection electrodes and the two drive electrodes through the support beam, and the thickness of the piezoelectric body interposed between the two drive electrodes and the common electrode is reduced by the pair of the drive electrodes and the common electrode. An angular velocity sensor formed to be thinner than the thickness of the piezoelectric body interposed between the detection electrode and the common electrode.