JP2001339962A - Electrostatic actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic actuator which stably operates even when an overvoltage is applied momentarily or in a pulse. SOLUTION: In the electrostatic actuator which has a fixed electrode and a movable electrode facing each other and generates an electrostatic attraction between the electrodes by applying a voltage from the outside, the electrostatic actuator has an overvoltage suppression circuit which absorbs an overvoltage applied momentarily or in a pulse from the outside to protect it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electrode for
The present invention relates to an electrostatic actuator that generates a driving force by applying a voltage between the electrodes.

[0002]

2. Description of the Related Art Conventionally, as an example of an electrostatic actuator, a non-dispersive infrared (Non-Dispersive I.
A Fabry-Perot filter used in an nfraRed gas analyzer (hereinafter, referred to as an NDIR gas analyzer) is known. The present applicant has filed Japanese Patent Application No. 2000-412.
No. 87 proposes a Fabry-Perot filter to which semiconductor micromachining technology is applied.

FIG. 4 is a sectional view of a Fabry-Perot filter. In FIG. 4, a fixed mirror 3 is formed on a silicon substrate 1 via a silicon oxide film 2 and a movable mirror 4 is formed.
Is a sacrificial layer 5 made of a silicon oxide film formed on the fixed mirror 3 and a silicon nitride film 6 as an interlayer film, for example.
It is formed on the upper surface and is opposed to the fixed mirror 3.

A gap h corresponding to the thickness of the sacrifice layer 5 is formed between the fixed mirror 3 and the movable mirror 4 by etching and removing the sacrifice layer 5 from the etching holes 7 formed in the movable mirror 4. The movable mirror 4 can be displaced in the direction of the fixed mirror 3 when an external force is applied.

The fixed mirror 3 and the movable mirror 4 are made of, for example, polycrystalline silicon. A fixed electrode 8 is formed on the surface of the fixed mirror 3 by doping a high concentration of impurities. The movable electrode 9 is formed by being doped with an impurity at a concentration.

An external electrode 10a is formed in contact with the movable electrode 9 so as to be able to conduct electricity to the movable electrode 9 from the outside.
An external electrode 10b that enables the external power supply to the fixed electrode 8 is formed in contact with the fixed electrode 8.

Next, the operation will be described. When a potential difference is applied to the fixed electrode 8 and the movable electrode 9 via the external electrodes 10b and 10a, an electrostatic attraction force is generated between the fixed electrode 8 and the movable electrode 9, and the movable mirror 4 moves in the direction of the fixed mirror 3. Displaced to
The length of the gap h changes. By changing this voltage, it is possible to obtain the length of the gap for transmitting infrared rays in the wavelength band corresponding to the absorption characteristics of the gas to be measured.

[0008]

However, such a Fabry-Perot filter has the following problems. During handling of the Fabry-Perot filter, an excessive voltage exceeding the rating may be instantaneously (pulsely) applied between the external electrodes 10a and 10b due to static electricity or the like. In this case, the application of the excessive voltage causes the movable mirror 4 to approach or come into contact with the fixed mirror 3, causing irreversible characteristic changes and electrostatic breakdown or characteristic deterioration of the interlayer insulating film such as the silicon nitride film 6.

That is, although polycrystalline silicon not doped with impurities is interposed between the movable electrode 9 and the fixed electrode 8 as an insulator, an insulation breakdown occurs due to an excessive voltage, and the movable electrode 9 and the fixed electrode 8 are separated. During this time, a short-circuit current flows. As a result, the movable mirror 4 and the fixed mirror 3 are fused, and even if the applied voltage is returned to zero, the gap h cannot be returned to the original value.

Alternatively, the relationship between the applied voltage and the gap h has a hysteresis characteristic, making it impossible to discriminate the wavelength, and the relationship between the originally designed applied voltage of the Fabry-Perot filter and the transmission wavelength is lost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has an overvoltage suppression circuit for absorbing an overvoltage applied instantaneously or in a pulsed manner between two external electrodes; An object of the present invention is to provide an electrostatic actuator that operates stably even when an excessive voltage is applied by forming the movable electrode 9 and the fixed electrode 8 of the electric actuator on the same substrate.

[0012]

According to a first aspect of the present invention, there is provided a fixed electrode and a movable electrode which are opposed to each other, and a voltage is externally applied between the fixed electrode and the movable electrode to apply electrostatic attraction. In the electrostatic actuator that drives the movable electrode by generating a voltage, an excessive voltage applied instantaneously or in a pulse manner from the outside is absorbed between the outside and the electrostatic actuator, and the electrostatic An electrostatic actuator having an excessive voltage suppression circuit for protecting the actuator.

According to a second aspect of the present invention, in the excessive voltage suppression circuit, a capacitor having one end connected to the fixed electrode and the other end connected to the movable electrode, and a connection between the capacitor and the movable electrode. 2. A first resistor having one end connected to a point and a second resistor having one end connected to the fixed electrode and the other end connected to the other end of the first resistor. It is an electrostatic actuator as described.

According to a third aspect of the present invention, the fixed electrode, the movable electrode and the excessive voltage suppressing circuit are formed on the same substrate. Actuator.

According to a fourth aspect of the present invention, the fixed electrode is formed by processing a conductive silicon layer provided on a silicon substrate, and the movable electrode is formed on the fixed electrode by an interlayer. A conductive silicon layer provided through an insulating film is processed and formed with a gap between the fixed electrode and the conductive silicon layer, and the conductive silicon layer is provided on the silicon substrate. The first resistor and the second resistor are formed by sandwiching the interlayer insulating film between layers or metal layers, and the first resistor and the second resistor are formed by processing a conductive silicon layer provided on the silicon substrate. 4. The electrostatic actuator according to claim 3, wherein:

According to a fifth aspect of the present invention, in the electrostatic actuator according to the fourth aspect, the interlayer film is a silicon nitride film.

According to a sixth aspect of the present invention, the resistance values of the first resistor and the second resistor are controlled by changing an impurity concentration, an impurity diffusion depth and a pattern shape of the silicon layer. The electrostatic actuator according to claim 4, wherein

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a plan layout diagram of the circuit shown in FIG. 1 on a substrate.

1 and 2, reference numeral 8 denotes a Fabry-Perot filter 1 as the electrostatic actuator shown in FIG.
1 is a fixed electrode, 9 is a movable electrode, 10a is an external electrode, and 10b is a grounded external electrode.

The fixed electrode 8 is connected to the external electrode 10b by a fixed electrode wiring and grounded, and is fixed by the fixed electrode 8 and the movable electrode 9 to a capacitor Cf having a capacitance of about 8 pF, for example.
p.

C is a capacitor for suppressing an excessive voltage of, for example, 400 pF. One end of the capacitor is connected to the movable electrode 9 via a wiring resistance Rfp (for example, about 10 kΩ) of the movable electrode wiring. Is the external electrode 10b
Connected to the ground.

R1 is a first resistor for suppressing an excessive voltage of, for example, 400 kΩ. One end of the first resistor is connected to a connection point between the capacitor C and the movable electrode 9 via a wiring resistor Rfp, and the other end of the first resistor R1 is connected to the other end. It is connected to the external electrode 10a via a wiring resistance R0 (for example, about 10 kΩ).

R2 is a capacitor C and a capacitor Cf
A second resistor of, for example, 100 kΩ for discharging the charge stored in p, one end of the second resistor R2 is connected to the external electrode 10b and grounded, and the other end is connected to the external electrode 10a via the wiring resistance R0. Have been.

The above-mentioned capacitor C and first resistor R
1. The excessive voltage suppression circuit 12 is constituted by the first and second resistors R2.

C0 is, for example, 200 pF, connected between the external electrodes 10a and 10b as a static electricity application model.
The capacitor C0 is a 200 V capacitor, and the discharge of the capacitor C0 is a model of pulse-like static electricity applied instantaneously between the external electrodes 10a and 10b.

Next, the operation of the circuit shown in FIG. 1 will be described.
FIG. 3 is a characteristic diagram showing a change with time of the voltage V0 between the external electrodes 10a and 10b and the voltage Vfp across the capacitor Cfp.

In FIG. 1, when a pulse-like excessive voltage due to static electricity or the like is instantaneously applied to the external electrodes 10a and 10b (when the capacitor C0 is discharged), the direction of R0 → R2, R0 → R1 only at that moment. → C direction, R0 → R1
Although the current flows in the direction of → Rfp → Cfp, the current stops flowing immediately when the supplied electric charge is exhausted, and the voltage V0 between the external electrodes depends on the resistance value of each resistor and the capacitance of the capacitor as shown in FIG. It attenuates based on the determined time constant and drops from 200V at a stretch.

In this case, since the capacity of the capacitor C is much larger than the capacity of the capacitor Cfp, the charge due to the excessive voltage is mainly absorbed by the capacitor C, and the stored charge is discharged in the direction of R1 → R2.

The capacitor Cfp stores an electric charge that is much smaller than the amount charged to the capacitor C by the excessive voltage, and the capacitor Cfp during the storage is stored.
The voltage Vfp at both ends rises to about 20 V after the excessive voltage 200 V is suppressed, and thereafter, Rfp → R1 → R2
, And Vfp gradually decreases to 0V.

In this case, by adjusting the resistance values of the first resistor R1 and the second resistor R2 and the capacitance of the capacitor C, the voltage Vfp across the capacitor Cfp can be suppressed to a desired value or less. Can be adjusted.

For example, when the electrostatic actuator is driven at about 1 Hz, the delay of the time constant due to the addition of the excessive voltage suppression circuit 12 is on the order of milliseconds or less, and does not affect its operation.

In a normal operation in which a DC voltage V is applied between the external electrodes 10a and 10b, the current I flowing through the circuit of FIG. 1 is I = V / (R0 + R2). Therefore,
The voltage drop due to the addition of the excessive voltage suppression circuit 12 is I × R0, the value is extremely small, and does not significantly affect the operation of the electrostatic actuator.

In the manufacture of the excessive voltage suppression circuit 12, for example, the silicon nitride film 6 as an interlayer film shown in FIG. 4 is used as a dielectric, and is used for forming the fixed electrode 9 and the movable electrode 8. The capacitor C is formed by patterning the silicon nitride film 6 with polycrystalline silicon or another metal having conductivity.

Incidentally, the silicon nitride film 6 as the interlayer film may be a silicon oxide film. The first resistor R1 and the second resistor R2 are formed by patterning, for example, conductive polycrystalline silicon used for forming the fixed electrode 9 and the movable electrode 8.

In order to suppress an excessive voltage, a PN junction diode is often used in parallel with the element to be protected, but the above-described excessive voltage suppressing circuit 12 is formed simultaneously during the manufacturing process of the Fabry-Perot filter 11. Electrostatic actuator that can be inexpensively protected from excessive voltage without complicating the manufacturing process for forming a PN junction because it is composed of the capacitor C and the first and second resistors R1 and R2. Can be realized.

The resistance values of the first and second resistors R1 and R2 and the capacitance of the capacitor C are determined by the thickness of the silicon nitride film 6,
By changing parameters such as the depth of impurity diffusion into the polycrystalline silicon, the amount of impurity ions implanted, and the pattern shape, it is possible to easily and accurately adjust.

[0037]

As described above, according to the first aspect of the present invention,
According to the present invention, since the excessive voltage suppressing circuit for absorbing the excessive voltage applied instantaneously or in a pulse manner between the two external electrodes is provided, the excessive voltage is applied instantaneously or in a pulse manner. Also in this case, it is possible to provide an electrostatic actuator that operates stably.

According to the third to sixth aspects of the present invention, an excessive voltage suppressing circuit for suppressing an excessive voltage applied instantaneously or in a pulse manner between two external electrodes and an electrostatic actuator are provided. Since the movable electrode and the fixed electrode are simultaneously formed on the same silicon substrate, it is possible to provide an inexpensive electrostatic actuator that operates stably even when an excessive voltage is applied instantaneously or in a pulsed manner.

[0039]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a plan layout view on a silicon substrate according to an embodiment of the present invention.

FIG. 3 is an operation characteristic diagram of the circuit shown in FIG. 1;

FIG. 4 is a sectional view of a Fabry-Perot filter.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 3 fixed mirror 4 movable mirror 6 silicon nitride film 8 fixed electrode 9 movable electrode 10a, 10b external electrode 12 excessive voltage suppression circuit R1 first resistor R2 second resistor C capacitor h gap

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kentaro Suzuki 2-9-132 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Corporation (72) Inventor Masayuki Kashida 2-9-132 Nakamachi, Musashino-shi, Tokyo Next to Kawa Electric Co., Ltd.

Claims (6)

[Claims] 1. An electrostatic device having a fixed electrode and a movable electrode disposed opposite to each other, and applying an external voltage between the fixed electrode and the movable electrode to generate an electrostatic attraction, thereby driving the movable electrode. In the actuator, between the outside and the electrostatic actuator, an excessive voltage suppression circuit that protects the electrostatic actuator by absorbing an excessive voltage applied instantaneously or in a pulse from the outside is provided. Characteristic electrostatic actuator. 2. The excessive voltage suppression circuit, wherein one end is connected to the fixed electrode and the other end is connected to the movable electrode, and one end is connected to a connection point between the capacitor and the movable electrode. 2. The electrostatic actuator according to claim 1, comprising: a first resistor; and a second resistor having one end connected to the fixed electrode and the other end connected to the other end of the first resistor. 3. The electrostatic actuator according to claim 1, wherein the fixed electrode, the movable electrode, and the excessive voltage suppression circuit are formed on a same substrate. 4. The fixed electrode is formed by processing a conductive silicon layer provided on a silicon substrate, and the movable electrode is provided on the fixed electrode via an interlayer insulating film. A conductive silicon layer is processed and formed with a gap between the fixed electrode and the fixed electrode, and the capacitor is formed between the conductive silicon layer and the metal layer provided on the silicon substrate. 4. The semiconductor device according to claim 3, wherein the first resistor and the second resistor are formed by sandwiching an insulating film, and the first resistor and the second resistor are formed by processing a conductive silicon layer provided on the silicon substrate. An electrostatic actuator as described. 5. The electrostatic actuator according to claim 4, wherein said interlayer film is a silicon nitride film. 6. The resistance value of the first resistor and the second resistor is:
5. The electrostatic actuator according to claim 4, wherein the control is performed by changing an impurity concentration, an impurity diffusion depth, and a pattern shape of the silicon layer.