JPH06235733A - Acceleration sensor and angular speed sensor - Google Patents

Abstract

PURPOSE:To provide an acceleration sensor having simple structure where complicated operating process is eliminated without increasing any cost and to provide an extremely downsized angular speed sensor. CONSTITUTION:A cantilever upper electrode 3 is disposed on an insulator 15 provided on a substrate 1 having a lower electrode 2 and a power supply E is connected between the electrodes 2 and 3. Under a state where a constant voltage for generating field radiation continuously is applied from the power supply E, the upper electrode 3 is flexed upon application of force and a current corresponding to the flexure is detected thus determining acceleration immediately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor using a micro vacuum element and an angular velocity sensor using a cantilever structure.

[0002]

2. Description of the Related Art In recent years, an air bag system for the purpose of safety measures for vehicles has become widespread, and an acceleration sensor is often used for such an air bag system. This acceleration sensor operates to detect a change corresponding to the amount of deflection as an electrical signal when mechanical deflection occurs due to a shock or the like applied to the sensor element.

FIG. 9 shows an example of a conventional acceleration sensor. For example, a lower electrode 42 is provided on a silicon substrate 41, and an upper electrode 43 is supported by a support 44 so as to approach and face the lower electrode 42. It is provided in a cantilever structure, and when a mechanical force acts on the substrate 1, the distance d between the electrodes 42 and 43 changes as in the following equation. d = ε / C C = ε · 1 / d where C: capacitance between electrodes ε: permittivity of insulator between electrodes C can be measured by applying a voltage between the electrodes 42 and 43. , Acceleration can be obtained based on the d.

FIG. 10 shows an example of a conventional acceleration sensor, which shows a diaphragm structure in which a weight portion 55 is provided on a silicon substrate 51 and a diffusion bridge compensation resistor 56 is provided on the substrate 51. The acceleration is detected at X. Also, FIG.
1 shows an example of another conventional acceleration sensor, which is a piezoelectric acceleration sensor in which a ZnO piezoelectric element 68 is provided on a silicon substrate 61. 69 is P channel MO
SFET, 70 is a P-type diffusion resistance, 71 is a power supply section, 72 is a ground section, and 73 is a ZnO temperature compensation section.

Further, in recent years, a piezoelectric vibrating gyroscope (hereinafter referred to as "piezoelectric gyro") has been actively developed as an angular velocity sensor. This piezoelectric gyro utilizes the fact that when a rotating angular velocity is applied to a vibrating object, Coriolis force is generated in the direction perpendicular to the vibrating direction. Recently, it has been used to prevent the touch of navigation systems and VTR cameras. Has been done. Some of the small piezoelectric gyros used for these are vibrators made of Elinvar material, a small piece of PZT ceramics bonded as a drive source with an adhesive, or a piezoelectric vibrator itself using PZT ceramics. Further, in order to detect the Coriolis force efficiently, two detectors are installed for one oscillator, and the difference in the detection voltage between them is used to improve the sensitivity to the rotational angular velocity.

FIG. 12 shows an example of the basic principle of a conventional piezoelectric gyro, and shows a structure called a Watson type, where 81 is a tuning fork type oscillator and 82 is a tuning fork type oscillator 81. The piezoelectric element for driving is provided, and the reference numeral 83 is a piezoelectric element for detecting. When the tuning fork vibrator 81 is vibrated in the x-axis direction by the driving piezoelectric element 83, when the angular velocity ω is applied to the central axis (z axis) of the tuning fork vibrator 81, the original vibration axis (x axis) is returned. On the other hand, Coriolis force is generated in the y-axis direction which is the direction orthogonal to the y-axis. When the Coriolis force is detected by the detecting piezoelectric element 83 in the y-axis direction, the angular velocity ω can be obtained. It is necessary to provide a driving power supply unit and a signal processing unit in these piezoelectric gyros.

[0007]

The piezoelectric acceleration gyro which is the conventional acceleration sensor and angular velocity sensor has the following problems, respectively. (1) First, in the acceleration sensor having a cantilever structure shown in FIG.
Since the inter-electrode distance d must be calculated based on the change in capacitance, the acceleration must be obtained, which complicates the calculation process. (2) The diaphragm structure of FIG. 10 and the piezoelectric type acceleration sensor of FIG. 11 require a special process for processing, which increases the cost. (3) Next, in the piezoelectric gyro of FIG. 12, the vibrator itself has a length of several tens of mm due to manufacturing restrictions.
Since it is necessary to provide the driving power supply unit and the signal processing unit, it is difficult to achieve miniaturization.

The present invention has been made to solve the above problems, and an acceleration sensor having a simple structure and a microminiaturization which does not require a complicated calculation process without increasing the cost is intended. It is an object to provide an angular velocity sensor.

[0009]

In order to achieve the above object, the present invention according to claim 1 is such that one electrode is supported by a cantilever structure on an insulator on a substrate and the other electrode is a substrate. It includes a pair of electrodes provided above, a power supply connected to generate electric field emission between the pair of electrodes, and a detection circuit for detecting a current flowing between the pair of electrodes by the power supply, the current being one of It is characterized in that it is configured to flow in accordance with the amount of deflection of the electrode.

According to a second aspect of the present invention, a driving piezoelectric element for vibrating the cantilever vibrator and a detecting piezoelectric element for detecting an external force acting on the cantilever vibrator are formed. It is characterized in that a plurality of cantilever oscillators are installed in the same chip.

[0011]

According to the structure of the present invention as set forth in claim 1, when a detecting circuit detects a current flowing by connecting a power source between a pair of electrodes, when one electrode bends, a current corresponding to the amount of deflection is obtained. Is detected by the detection circuit. Thus, the acceleration can be immediately obtained by observing the change in the current.

According to the second aspect of the present invention, there is provided a driving piezoelectric element for vibrating the cantilever vibrator and a detecting piezoelectric element for detecting an external force acting on the cantilever vibrator. A plurality of cantilever vibrators having the above are formed in the same chip, and the detecting piezoelectric element detects the angular velocity corresponding to the Coriolis force generated by vibrating the driving piezoelectric element.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of the acceleration sensor of the present invention, in which 1 is a silicon substrate and PSG (Phos
An insulator 15 made of pho-Silicate-Glass), SiO ₂ (silicon dioxide), or the like is formed by a CVD (Chemical-Vapor-Deposition) method, a sputtering method, or the like. An upper electrode 3 made of polycrystalline silicon doped with phosphorus is supported on the insulator 15 in a cantilever structure, and the upper electrode 3 corresponds to the magnitude of this force when it receives a mechanical force. It has the property of flexing easily.

Reference numeral 2 is a lower electrode made of Mo, W or the like, which is combined with the upper electrode 3 to form a pair of electrodes. A power source E is connected between the pair of electrodes 2 and 3 via a resistor R. It The acceleration sensor of this embodiment, which is composed of the substrate 1, the insulator 15, the upper electrode 3, and the lower electrode 2, has an upper electrode 3 corresponding to the cathode and a lower electrode 2 corresponding to the anode when viewed from the surface of the micro vacuum element. It can be seen as a bipolar tube consisting of.

When the electric field strength at the tip of the upper electrode 3 (cathode) made of polycrystalline silicon exceeds a certain level by the power source E connected between the pair of electrodes 2 and 3, electric field emission occurs and a current I based on the electric field emission occurs. Flows like the following equation. I = (EV) / R where V is the terminal voltage of the resistor R. This field emission current characteristic changes depending on the electric field strength of the upper electrode 3. On the other hand, since the electric field strength changes depending on the distance between the electrodes 2 and 3 as well as the voltage from the power source E, when the upper electrode 3 is bent by a mechanical force, the electric field strength between the upper electrode 3 and the lower electrode 2 is increased. As the distance changes, the electric field strength changes, so that the field emission current characteristics change.

As a result, a constant voltage having a temperature at which field emission is always generated by the power source E is applied between the electrodes 2 and 3,
By measuring the field emission current characteristic, it is possible to detect the mechanical force applied from the outside, that is, the acceleration.

Next, a method of manufacturing the acceleration sensor of this embodiment will be described in the order of steps. First, as shown in FIG. 2, using a silicon substrate 1, PSG and SiO as described above are formed on the silicon substrate 1.
_The insulator 15 made of ₂ or the like is formed by a CVD method, a sputtering method, or the like. Next, a phosphorus-doped polycrystalline silicon layer 16 to be an upper electrode is formed on the insulator 15 by a CVD method, and a photoresist 17 is further applied thereon. Subsequently, by using the photoresist 17 as a mask, the unnecessary polycrystalline silicon layer 16 (broken line portion) is photoetched and removed to form the upper electrode 3.

Next, as shown in FIG. 3, the insulator 15 under the upper electrode 3 is photoetched with a hydrofluoric acid solution using the photoresist 17 as a mask. At this time, by performing excessive etching, the insulator 15 is undercut, and the cantilever structure of the upper electrode 3 is formed. continue,
As shown in FIG. 4, using the photoresist 17 as a mask, a metal layer 18 of Mo, W, or the like is formed from above by evaporation. At this time, since the upper electrode 3 is covered with the photoresist 17, the metal layer 18 does not adhere. next,
As shown in FIG. 5, by removing the photoresist 17 together with the unnecessary metal layer 18, the lower electrode 2 is formed by leaving the metal layer only on the substrate 1, and the acceleration sensor of this embodiment is obtained. .

According to this embodiment, the following effects can be obtained. (1) The upper electrode 3 is bent when a mechanical force is applied to the pair of electrodes 2 and 3 with a constant voltage applied by the power source E to the extent that field emission is always generated, to cope with this deflection amount. Since the acceleration can be immediately obtained by detecting the current, it is possible to eliminate the conventional complicated calculation process. (2) The cantilever structure can be formed by a photolithography technique or a thin film forming technique used in a usual semiconductor industry, and a special process as in the past is not required, so that the cost does not increase.

FIG. 6 is a perspective view showing an embodiment of the angular velocity sensor of the present invention, showing an example applied to a piezoelectric gyro.
Reference numeral 21 is a silicon substrate that constitutes a chip, 22 is a drive power source portion formed on the silicon substrate 21, and 23 is a signal processing portion formed on the silicon substrate 21. A,
A1 is a piezoelectric sensor having a cantilever structure formed on the silicon substrate 21. The piezoelectric sensor A1 receives a Coriolis force with respect to the rotation about the rotation axis (z axis) and torsionally vibrates. B and B1 are silicon substrates 21 so as to be orthogonal to the piezoelectric sensors A and A1.
With the cantilever structure piezoelectric sensor formed above, torsional vibration does not occur with respect to rotation about the rotation axis (z axis), and only the amplitude changes. The piezoelectric sensors A1 and B1 vibrate with a phase difference from the piezoelectric sensors A and B. x, y,
z and ω have the same meaning as in FIG.

FIG. 7 is a perspective view schematically showing a piezoelectric sensor having a cantilever structure in the piezoelectric gyro of FIG.
1, C2 and C3 indicate Pt / PZT / Pt capacitors as described later, and P indicates a drive / signal detection pad. FIG. 8 shows a manufacturing process of the cantilever structure. This cantilever structure is formed using the well-known lift-off method.

First, in step A, S is formed on the silicon substrate 21.
After forming iO ₂ 25, polysilicon 1 to be a sacrifice layer
-Form 25. In this method, for example, polysilicon 1 is previously formed on the entire surface by a known sputtering method or the like, and then an unnecessary portion is removed by photoetching. Next, in step B, a polysilicon 2 is formed on the polysilicon 1/25.
-26 is formed and the circumference thereof is covered with SiO ₂ 27. This forming method can be easily formed by utilizing a well-known technique. Then, in step C, Pt / PZT / Pt capacitors C1 and C are formed on the polysilicon 2.27.
2 and C3 are formed. This is Pt29, PZT3
After forming 0 and Pt31 by a well-known technique, the whole is PSG
It is formed by covering with 32. PZ as a piezoelectric body
T is formed by the sol-gel method. Next, the polysilicon 1.26 is removed by etching with an aqueous solution of ethylenediaminepyrocatechol, whereby the cantilever structure is completed by the lift-off method. C1 operates as a driving source piezoelectric capacitor, and C2 and C3 are external forces (Coriolis force)
It operates as a piezoelectric capacitor for detection. According to such a manufacturing method, the piezoelectric gyro of FIG. 6 can be formed on one silicon substrate 21 by the IC technique.

In FIG. 6 and FIG. 7, let us consider a case of rotation at an angular velocity ω around the rotation axis (z axis). In the piezoelectric sensor A having a cantilever structure which is vibrated in the x-axis direction by the drive voltage, the Coriolis force F acts in the y-axis direction due to the rotation of the angular velocity ω about the z-axis, and the cantilever beam is torsionally vibrated.
Here, the Coriolis force F is expressed by the following equation. F = 2 mvω For this reason, the voltage v generated in the piezoelectric capacitor C1 or C2 becomes larger than that when it is not rotating. At this time, the Coriolis force unlike the piezoelectric sensor A does not act on the piezoelectric sensor B (which vibrates in the x-axis direction) positioned at right angles to the piezoelectric sensor A (does not cause torsional vibration). However, the voltage generated in the piezoelectric capacitor C2 or C3 of the piezoelectric sensor B changes as compared to when it is not rotating.

Here, when the piezoelectric sensors B and B1 are vibrated with drive voltages having different phases, the vibration amplitudes of B and B1 at the same time are different corresponding to the left and right rotations about the z axis. come. Therefore, the rotation direction around the z axis can be detected by taking the difference between the output voltages of the detecting piezoelectric capacitors C2 or C3 of the piezoelectric sensors B and B1. As described above, when the rotation around the z-axis is considered, the angular velocity can be detected by the piezoelectric sensor A, and the rotation direction can be detected by the piezoelectric sensors B and B1.

As described above, according to the present embodiment, by using the IC technology, the drive power source unit is provided in one silicon substrate 21 together with the Coriolis force detecting piezoelectric capacitors C2 and C3 and the drive source piezoelectric capacitor C1. Since 22 and the signal processing unit 23 are formed, the piezoelectric gyro that operates as an angular velocity sensor can be miniaturized.
In addition, since it becomes possible to mass-produce the IC, cost reduction can be achieved.

[0026]

As described above, according to the present invention as set forth in claim 1, the electrode is deflected when a force is applied without a special process, and the current corresponding to the amount of deflection is detected. Since the acceleration is immediately obtained by using the acceleration sensor, it is possible to provide an acceleration sensor having a simple structure. Therefore, a complicated calculation process can be eliminated without increasing the cost.
According to the second aspect of the present invention, since the drive power supply section and the signal processing section can be formed in one substrate, it is possible to provide an angular velocity sensor that is miniaturized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an acceleration sensor of the present invention.

FIG. 2 is a cross-sectional view showing the manufacturing process of the acceleration sensor of this embodiment.

FIG. 3 is a cross-sectional view showing another manufacturing process of the acceleration sensor of this embodiment.

FIG. 4 is a cross-sectional view showing another manufacturing process of the acceleration sensor of this embodiment.

FIG. 5 is a cross-sectional view showing another manufacturing process of the acceleration sensor of this embodiment.

FIG. 6 is a perspective view showing an embodiment of an angular velocity sensor of the present invention.

FIG. 7 is a perspective view showing an outline of a piezoelectric sensor having a cantilever structure, which is one of the angular velocity sensors of this embodiment.

FIG. 8 is a cross-sectional view showing the manufacturing process of the angle sensor of the present embodiment.

FIG. 9 is a sectional view showing a conventional acceleration sensor.

FIG. 10 is a perspective view showing another conventional acceleration sensor.

FIG. 11 is a perspective view showing another conventional acceleration sensor.

FIG. 12 is a schematic diagram showing the basic principle of a conventional angular velocity sensor.

[Explanation of symbols]

 1, 21 Substrate 2 Lower electrode 3 Upper electrode 15 Insulator 17 Photoresist 22 Drive power supply section 23 Signal processing section 25 Polysilicon 1 26 Polysilicon 2 29, 31 Pt 30 PZT A, A1, B, B1 Cantilever structure Piezoelectric sensor C1 Drive source piezoelectric capacitor C2, C3 Detection piezoelectric capacitor

Claims (2)

[Claims] 1. A pair of electrodes in which one electrode is supported by a cantilever structure on an insulator on a substrate and the other electrode is provided on the substrate, and field emission is generated between the pair of electrodes. An acceleration sensor including a power supply connected to the power supply and a detection circuit for detecting a current flowing between a pair of electrodes by the power supply, wherein the current flows according to a deflection amount of one electrode. . 2. A cantilever vibrator having a driving piezoelectric element for vibrating the cantilever vibrator and a detecting piezoelectric element for detecting an external force acting on the cantilever vibrator.
An angular velocity sensor characterized in that a plurality of them are installed in the same chip.