JPH07177763A - Electrostatic actuator, information processing device, and scanning tunneling microscope - Google Patents

Abstract

(57) [Abstract] [Purpose] An electrostatic actuator that is used to control the position of a probe in a scanning tunneling microscope (STM) or an information processing device using the principle of STM, and that can obtain a large displacement with a small driving voltage. I will provide a. [Structure] A dielectric thin film 104 is laminated on a fixed electrode 103. The movable piece 107 is arranged via the space 106. The movable piece 107 is rotatable by a beam 121 and is supported by a doubly supported beam structure. An electrostatic attractive force is generated by applying a voltage to the fixed electrode 103, and the one end 10 of the movable piece 107 is
7a contacts the dielectric thin film 104. When the voltage applied to the fixed electrode 103 is raised in this state, the contact area between the movable piece 107 and the dielectric thin film 104 increases, and in response to this, a rotational force acts on the movable piece 107 to move the movable piece 107. The other end 107b is displaced in the direction away from the substrate 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine electrostatic actuator used in a scanning tunneling microscope, an information processing apparatus using the electrostatic actuator, and a scanning tunneling microscope.

[0002]

2. Description of the Related Art Recently, a scanning tunneling microscope (Scanning Tunneling Microscope) capable of directly observing the electronic structure of surface atoms of a conductor.
Microscope; hereinafter abbreviated as STM) was developed [G. Bin
nig, et al., Phys. Rev. Lett., 49 , 57 (1982)], real-space images can be measured with high resolution regardless of single crystal or amorphous. The STM has the advantage that it can be observed at low power without damaging the medium (sample) with an electric current, and also operates in the atmosphere or in a liquid, and can be used for various materials. For this reason, STM is expected to have a wide range of applications.

In the STM, a voltage is applied between a metal probe (probe electrode) having a pointed tip and a conductive substance so that both of them are set to 1
The fact that a tunnel current flows between the two is used when they are brought close to a distance of about nm. This current is very sensitive to changes in the distance between the two, and by scanning the probe electrode in the in-plane direction while keeping the tunnel current value constant,
We can read various information about all electron clouds in real space. At this time, the resolution in the in-plane direction is about 0.1 nm. Therefore, if the principle of STM is applied, it is possible to sufficiently perform high density recording / reproducing on the atomic order (sub-nanometer).

For example, there is a method in which recording / reproducing is performed by STM using a thin film layer of a material having a memory effect with respect to voltage-current switching characteristics, such as a conjugated π-electron organic compound or chalcogen compound, as a recording layer. Proposed [JP-A-63-161552, JP-A-63-1]
No. 61553]. According to this method, if the recording bit size is 10 nm, a large-capacity recording / reproduction of 10 ¹² bit / cm ² is possible.

In the recording / reproducing apparatus utilizing the principle of the STM, as the recording layer used in the recording medium, the information written in the recording layer can be detected by the tunnel current flowing between the probe electrode and the recording layer. Any material can be used as long as it is a material. For example, if unevenness is formed on the surface for recording, HOPG
(Highly Oriented Pyrolithic Graphite) cleaved substrate, Si wafer, Au, Ag, Pt, Mo, C by vacuum deposition or epitaxial growth
Examples thereof include metal thin films such as u and glassy metals such as Rh ₂₅ Zr ₇₅ and Co ₃₅ Tb ₆₅ . Materials recorded by the electronic state of the surface include amorphous Si, thin film layers of conjugated π-electron organic compounds and chalcogen compounds.

Further, for the purpose of downsizing the device, it has been considered to form a plurality of probe electrodes and an extremely small movable mechanism on a semiconductor substrate by a micromechanics technique by a semiconductor lithography process. An actuator using an electrostatic cantilever, a piezoelectric bimorph cantilever (see, for example, US Pat. No. 4,906,840), etc. has been proposed as a typical micromachine used for such a movable mechanism. An electrostatic actuator using an electrostatic cantilever is provided with a drive electrode facing the cantilever, and an electrostatic attraction between the drive electrode and the cantilever generated by applying a voltage to the drive electrode is used to displace the cantilever. It is what On the other hand, a piezoelectric bimorph actuator using a piezoelectric bimorph cantilever constitutes a cantilever by laminating an electrode and a piezoelectric body, and is displaced based on mechanical deformation of the piezoelectric body caused by applying a voltage to the electrode. . These micromachines are manufactured by a semiconductor photolithography process, can be easily arrayed and reduced in cost, and can be expected to have high-speed response because they are miniaturized.

[0007] In particular, in comparison with a piezoelectric bimorph actuator based on self-displacement, an electrostatic actuator displaces a cantilever by an electrostatic attractive force due to a voltage applied from the outside, so that it is possible to perform a large displacement relative to its size. Is. In addition, since the step of removing the substrate from the back surface when manufacturing the piezoelectric bimorph actuator can be formed by using the sacrificial layer for the electrostatic actuator, the step of removing the substrate from the back surface is not required, which is simple and easy. It can be manufactured with high precision and small size.

FIG. 8 is a sectional view showing the structure of a conventional cantilever type electrostatic actuator. The insulating layer 907 is provided over the substrate 908, and the substrate 9 is provided through the insulating layer 907.
A drive electrode 906 is provided at a substantially central portion of 08. A dielectric thin film 905 is provided so as to cover the surfaces of the drive electrode 906 and the insulating layer 907.
The cantilever 903 is arranged so as to project above the drive electrode 906, and the fixed end of the cantilever 903 is fixed to the substrate 908 via the spacer 904. In this electrostatic actuator, a voltage is applied between the cantilever 903 and the drive electrode 906 on the substrate 908 to generate an electric field between them, whereby an electrostatic force is generated and the cantilever 903 bends, and the cantilever 903 and the substrate 908 are deflected. The distance from 908 becomes smaller. Therefore, the movement of the cantilever 903 can be controlled by controlling the voltage applied to the drive electrode 906,
It can be used as an actuator.

When such an electrostatic actuator is used for STM or the like, as shown in FIG. 8, a conical projection is formed on the surface near the tip of the free end of the cantilever 903 and opposite to the substrate 908. The probe 901 is provided.
In the case of STM, the sample 902 is arranged so as to face the probe 901. Since the electrostatic force between the cantilever 903 and the drive electrode 906 is only attractive force, the cantilever 90
3 is displaced only with respect to the drive electrode 906 in the direction of narrowing the distance between the two. Therefore, the sample 902 and the probe 9
01 To control the distance to the tip and prevent the portion other than the tip of the probe 901 from coming into contact with the sample 902, as shown in FIG. It must be bent and made well.

[0010]

When the electrostatic actuator described above is used in the recording / reproducing apparatus using the STM or the STM, it is necessary to bend the cantilever portion in the direction opposite to the substrate (driving electrode). And the distance between the cantilevers increases. Therefore, the electrostatic force generated between the drive electrode and the cantilever portion is weakened, and it is necessary to increase the drive voltage in order to secure the operation amount (displacement amount) as the actuator. Therefore, it is necessary to take measures such as increasing the (electrical) withstand voltage of each part, which hinders miniaturization of the actuator itself and causes a cost increase. Moreover, since a power supply with a high output voltage is required, it has been an obstacle to downsizing of the entire device.

An object of the present invention is to provide an electrostatic actuator having a large displacement amount even when driven by a low voltage, an information processing device and a scanning tunneling microscope using the electrostatic actuator.

[0012]

An electrostatic actuator according to the present invention comprises a fixed electrode, a movable piece made of a conductor and opposed to the fixed electrode with a gap therebetween, and a support portion for supporting the movable piece. And a dielectric thin film provided between the fixed electrode and the movable piece, and when the voltage applied to the fixed electrode reaches a predetermined value, part of the movable piece is the dielectric thin film. The fixed electrode is brought into contact with the fixed electrode via the electrode, and the area of the contact portion between the movable piece and the fixed electrode is increased or decreased according to the change in the voltage applied to the fixed electrode.

A first information processing apparatus of the present invention uses the electrostatic actuator of the present invention, has a probe as an object to be displaced, and controls the position of the probe by the electrostatic actuator while applying the probe to the probe. Perform processing based on the physical interaction that acts.

A second information processing apparatus of the present invention includes the electrostatic actuator of the present invention, a probe as an object to be displaced, a recording medium arranged to face the probe, the recording medium and the probe. At least from the recording medium based on a physical interaction between the probe and the recording medium, a moving means for moving the recording medium in an in-plane direction of the recording medium, a voltage applying means for applying a drive voltage to the fixed electrode. And a reproducing means for reproducing information.

The scanning tunneling microscope of the present invention comprises the electrostatic actuator of the present invention, a probe provided as a displacement object and facing the sample, and a movement for moving the sample and the probe in the in-plane direction of the sample. Means, voltage applying means for applying a drive voltage to the fixed electrode, and detecting means for applying a voltage between the probe and the sample to detect a tunnel current flowing between the probe and the sample. Have.

[0016]

In the electrostatic actuator of the present invention, the fixed electrode and the movable piece are arranged through the gap, and the dielectric thin film is provided between the fixed electrode and the movable piece. When applied, electrostatic attraction acts on the movable piece. Here, for example, the position of the support portion for supporting the movable piece is shifted with respect to the fixed electrode, and the distance between the fixed electrode and the movable piece is made relatively small, so that a fixed voltage at the fixed electrode is maintained. When applied, a partial region of the movable piece (usually one end of the movable piece) comes into contact with the fixed electrode via the dielectric thin film. When the voltage applied to the fixed electrode is changed from this state, the movable piece bends and the contact area between the fixed electrode and the movable piece through the dielectric thin film changes, which causes the movable part to move about the axis. Rotational force is generated in one piece. The electrostatic actuator of the present invention utilizes the displacement due to this rotational force. The electrostatic actuator of the present invention will be referred to as a torsion lever type electrostatic actuator. Obviously, the amount of displacement of the movable piece is maximum at the end opposite to the contact part across the support part, so it is desirable to dispose the displacement object at this part.

In the electrostatic actuator of the present invention, the distance between the fixed electrode (driving electrode) and the movable piece (cantilever portion) can be effectively reduced, and the supporting portion serves as a fulcrum, as compared with the conventional one. Since the lever is configured, a large displacement amount can be achieved with a small driving voltage. Further, in the electrostatic actuator of the present invention, the constant voltage in the above description is 0 V, that is, one end of the movable piece is in contact with the fixed electrode via the dielectric thin film in the state where no voltage is applied to the fixed electrode. Some of them are included.

In the present invention, it is desirable to use, as the movable piece, an electrically conductive and appropriate piece.
For example, an aluminum thin film can be used.

As the dielectric thin film, SiO ₂ , SiN, Z
rO ₂ , TiO ₂ , MgO, Al ₂ O ₃ , SiC, SiON, Al
An inorganic material such as N, ZnO or an organic polymer material such as polyimide, polyamide, PMMA (polymethylmethacrylate) can be used. In order to reduce the drive voltage for controlling the displacement amount, it is effective to use a ferroelectric material for the dielectric thin film. Examples of the ferroelectric material include titanic acid-based ferroelectrics such as barium titanate, lead titanate, and lead zirconate titanate, and organic high-molecular materials such as polyvinylidene fluoride and vinylidene fluoride-trifluoroethylene copolymer. Molecular ferroelectrics can be mentioned.

In the information processing apparatus of the present invention, since the probe is attached to the electrostatic actuator described above, it is possible to reduce the drive voltage for controlling the position of the probe.
It is possible to reduce the size and cost of the entire device. Typically, when the probe and the recording medium are opposed to each other and the information is processed based on the physical interaction between the two, the distance between the probe and the recording medium can be controlled at a low voltage, And this control can be done accurately. Further, in the scanning tunneling microscope of the present invention, since the probe for detecting the tunnel current is attached to the above-mentioned electrostatic actuator, the voltage for controlling the distance between the sample and the probe can be reduced and the control can be performed. Will be able to do it accurately.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings.

<< First Embodiment >> FIG. 1 (A) is a top view of an electrostatic actuator (torsion lever type electrostatic actuator) of the first embodiment of the present invention, and FIG. 1 (B) is a view of FIG. 1 (A). A sectional view taken along the line AA ', and FIG. 1C is a sectional view taken along the line AA' during operation of this electrostatic actuator.

The electrostatic actuator 100 is an STM.
It is used in an information processing device utilizing the principle of (scanning tunneling microscope), and a conical probe 150 is formed in advance. The insulating layer 102 is provided on the entire upper surface of the substantially rectangular substrate 101.
The fixed electrode 103 is provided on the insulating layer 102 at a position approximately in the center of the surface of the. A dielectric thin film 104 is formed so as to cover the insulating layer 102 and the fixed electrode 103. Further, wall-shaped spacers 105 are formed upward along the respective sides of the substrate 101. A flat plate-shaped support 108 having a rectangular center opening 119 is provided so as to cover the upper surface of the spacer 105.

The mechanically movable portion of the electrostatic actuator 100 is constructed as a movable piece (lever) 107. The movable piece 107, together with the beam 121 that is a support portion of the movable piece 107, is formed of a conductive member as an integral part of the support body 108. That is, the movable piece 107 has a rectangular shape smaller than the central opening 119, and is arranged so that one end 107 a side in the longitudinal direction thereof completely extends above the fixed electrode 103. The short side of the movable piece 107 is substantially equal to the length of the corresponding side of the fixed electrode 103, the long side is longer than the corresponding side of the fixed electrode, and the center of the fixed electrode 103 and the center of the movable piece 107 are Movable piece 10
7 is displaced toward the other end 107b in the longitudinal direction. Beam 121
Are provided in correspondence with both long sides of the movable piece 107, and these beams 121 are arranged substantially on a straight line. Further, the position where the beam 121 supports the movable piece 107 is a position far from the center of the movable piece 107 on the other end 107b side in the longitudinal direction of the movable piece 107. Beam 12
1 supports the movable piece so that the movable piece 107 can rotate about the beam 121 as a rotation axis.

On the upper surface of the movable piece 107 (the surface not on the substrate 108 side), the wiring layer 152 is provided with the silicon oxide film 151 interposed therebetween.
And the probe 150 is provided on the wiring layer 152.
Are arranged. The arrangement position of the probe 150 is the other end 107b of the movable piece 107 in the longitudinal direction. With this configuration, the movable piece 107 and the dielectric thin film 10
A void 106 is formed between the voids 4 and 4.

Next, the operating principle of the electrostatic actuator 100 will be described. Here, the movable piece 107 and the fixed electrode 103 are insulated, and the movable piece 107 is grounded.

By applying the voltage V _b to the fixed electrode 103, an electrostatic attractive force acts between the fixed electrode 103 and the movable piece 107, and the beam 121 is provided so as to be displaced from the center of the movable piece 107. As a result, as shown in FIG. 1C, the beam 121 is twisted, and one end 107a in the longitudinal direction of the movable piece 107 comes into contact with the surface of the dielectric thin film 104. With the rotation of the movable piece 107, the movable piece 107
b is displaced in a direction away from the substrate 101 (upward in the drawing). Here, the angle between the surface of the substrate 101 and the movable piece 107 is θ
And

When the voltage V _b applied to the fixed electrode 103 is increased in this state, as shown in the schematic diagram of FIG.
The movable piece 107 bends to increase the contact area with the dielectric thin film 104.
Further rotation about 21 causes the other end 107b in the longitudinal direction to be further displaced in the direction away from the substrate 101. By increasing the voltage V _b , the movable piece 10
As the contact area of No. 7 increases, the deflection angle of the beam 121 also increases, and the displacement amount of the other end 107b of the movable piece 107 increases.

Here, when the contact distance from the one end side of the movable piece 107 is represented by L, the contact distance L and the fixed electrode 1
The relationship with the applied voltage V _b to the signal 03 is as shown in FIG. 3, for example. In this example, not in contact with the one end 107a and the dielectric thin film 104 of the movable piece 107 in a state where the fixed electrode 103 without applying a voltage V _b, the applied voltage V _b is 30V
Then, the one end 107a of the movable piece 107 and the dielectric thin film 104 come into contact with each other for the first time. Of course, the voltage V _b is 0
Even when it is between V and 30 V, an electrostatic attractive force according to the voltage V _b acts on the movable piece 107, the beam 121 is twisted according to this electrostatic attractive force, and the other end 107 b of the movable piece 107 is moved. It is displaced. The contact distance L increases as the applied voltage V _b is increased from 30V.

In this electrostatic actuator 100, when the movable piece 107 is in contact with a part of the dielectric thin film 104, the movable piece 107 is stronger against mechanical vibration and has a larger electrostatic attraction. Can be given to. Therefore, a voltage V _b (30 V in the example of FIG. 3) such that one end 107 a of the movable piece 107 in the longitudinal direction is in contact with the dielectric thin film 104 is constantly applied as a bias voltage, and a drive voltage for adjusting the displacement amount is applied. It is desirable that the displacement amount be controlled by superimposing this on the bias voltage.

Next, an example of the manufacturing process of the electrostatic actuator 100 will be described with reference to FIG.

First, the substrate 10 made of silicon (Si)
A silicon nitride film having a thickness of 300 nm was formed on the substrate 1 by low pressure CVD (LPCVD) to form an insulating layer 102 (FIG. 4A). A polysilicon film to be the fixed electrode 103 is formed by LPCVD to a thickness of 300 nm, and then,
Phosphorus (P) ions are implanted into the polysilicon film at a density of 1 × 10 ¹⁶ / cm ² by an ion implantation method, and the temperature is set to 1100 ° C.
Diffusion treatment was performed for 1 hour in the nitrogen atmosphere. As a result,
The sheet resistance of the polysilicon film was 12 Ω / cm ² . Photoresist is applied to this polysilicon film, and the photoresist is patterned using a photolithography process of exposing and developing, and then the polysilicon film is patterned with a mixed aqueous solution of hydrofluoric acid and nitric acid. It peeled and the fixed electrode 103 was formed (FIG.4 (B)).

Next, a silicon oxide layer is deposited on the entire surface to a thickness of 200 nm by a sputtering method, and the dielectric thin film 10 is formed.
4 was formed. Then, a photoresist 141 is formed by a spin coater as a layer to be the spacer 105.
It was applied over the entire surface in a thickness of μm (FIG. 4 (C)). Photoist 1
As 41, a positive photoresist AZ1350J (trade name) manufactured by Hoechst was used. A thickness of 300 n is formed on the photoresist 141 by vacuum deposition.
m aluminum (Al) layer 142 is deposited (see FIG.
(D)), a silicon oxide film 151 was deposited to a thickness of 200 nm on the aluminum layer 142 by sputtering (FIG. 4 (E)).

Then, an aluminum layer to be the wiring layer 152 is formed by a vacuum deposition method, a photoresist 143 is applied thereon, and the photoresist 143 is patterned by a photolithography process.
The wiring layer 152 is formed by patterning the aluminum layer.
Was formed (FIG. 4 (F)). The patterning of the aluminum layer was performed by using an etchant made of a mixed aqueous solution of phosphoric acid, nitric acid and acetic acid, and heating the etchant at 50 ° C.

Next, patterning was performed by a photolithography process, and the silicon oxide film 151 was etched into a predetermined shape by a reactive ion etching method using CF ₄ gas (FIG. 4G). Subsequently, patterning was performed by a photolithography process, and the aluminum layer 142 was etched with a mixed aqueous solution of phosphoric acid, nitric acid and acetic acid to form the movable piece 107, the support 108 and the beam 121 (FIG. 4H).

Then, a probe 150 is formed on the wiring layer 152 by a method of depositing a metal through a shadow mask (see US Pat. No. 4,906,840), and a reactive ion etching method using oxygen plasma is used. Then, the photoresists 141 and 143 are etched. At this time, the photoresist 143 is completely removed, and with respect to the photoresist 141, the portion sandwiched between the movable piece 107 and the fixed electrode 103 and the portion in the vicinity of this portion are removed to remove the spacer 105 and the gap. 106 was formed. The etching conditions at this time were such that the oxygen flow rate was 100 ccm or more and the gas pressure during etching was 20 Pa or more, so that the side etching could easily proceed.

Through the above manufacturing steps, the torsion lever type electrostatic actuator shown in FIG. 4 (I) could be obtained. In the manufactured electrostatic actuator 100, the beam 121 had a width of 3.5 μm and a length of 10 μm, and the movable piece 107 had a length of 42 μm in the longitudinal direction and a width of 30 μm.

Next, an information processing apparatus using the above electrostatic actuator 100 will be described with reference to FIG. This information processing apparatus records and reproduces information on the recording medium 205.

The recording medium 205 comprises a recording layer 203 exposed on the surface, a lower electrode layer 202 provided on the lower side of the recording layer 203, and a tracking groove 204 provided on the surface of the recording medium 205. The recording medium 205 is mounted on the stage 201 for driving the recording medium 205 in the in-plane directions (XY directions). The electrostatic actuator 100 has a movable piece 10 to the extent that a tunnel current flows between the recording layer 203 and the probe 150.
The tip of the probe 150 formed on the recording layer 20 is the recording layer 20.
The recording layer 203 is arranged so as to approach the surface of the recording layer 203. Here, in the electrostatic actuator 100, the size of the movable piece 107 is 340 μm in length and 50 in width.
The one having a thickness of 15 μm and a thickness of 15 μm was used. Here, for the sake of simplicity, a structure supporting the electrostatic actuator 100 is not shown.

The probe 150 is the electrostatic actuator 1.
00 is connected to the input of the current-voltage conversion amplifier 207. The output of the current-voltage conversion amplifier 207 is input to the high-pass filter (HPF) 208, the edge detection comparator 210, and the error amplifier 213. The output of the high pass filter 208 is the comparator 2
It is input to the data modulator / demodulator 211 via 09. The reference voltage of the comparator 209 is the voltage threshold V ₂ .
The error amplifier 213 compares the reference voltage V _ref with the input voltage (output of the current-voltage conversion amplifier 207) and generates an output according to the error component.
The output of No. 3 is amplified by the gain amplifier 214 and applied to the fixed electrode 103 of the electrostatic actuator 100. With this configuration, the electrostatic actuator 100 is feedback-controlled according to the tunnel current value so that the tunnel current value becomes constant.
That is, the distance between the tip of the probe 150 and the surface of the recording layer 203 is controlled so as to maintain a constant value.

A recording controller 222 is provided inside the data modulator / demodulator 211, and a data modulation output from the recording controller 222 is connected to a pulse generator 212 for generating a recording pulse. The output of the pulse generator 212 is connected to the lower electrode layer 203 of the recording medium 205 via the capacitor C ₁ . The lower electrode layer 203 has a power supply 2 that generates a DC bias voltage V _B1 via a resistor R _1.
23 is also connected.

A tracking controller 215 for controlling the movement of the stage 201 in the X and Y directions is provided. From the tracking controller 215, a track movement status signal, an up control signal, a down control signal, and wobbling are provided. A voltage signal is output. The edge detection comparator 210 uses the reference voltage as the threshold voltage V _3, and its output is input to the AND circuit 216 together with the track movement status signal. The output of the AND circuit 216 is input to the OR circuit 217 together with the up control signal, and the output of the OR circuit 217 is input to the up input terminal of the up / down counter 218. Further, the down control signal is input to the down input terminal of the up / down counter 218.
A D / A converter 219 is provided on the output side of the up / down counter 218. The output of the D / A converter 219 is used for controlling the stage 201 in the X direction via the amplifier 221. Also, the wobbling signal is the resistance R ₂
An amplifier 220 for inputting via the
The output of 0 is used to control the stage 201 in the Y direction. Further, a variable resistance V controlled by the scanning direction control signal
R ₁ is inserted between the input terminals of the amplifiers 220 and 221.

Next, the operation during reproduction will be described. The tunnel current detected by the probe 150 in a state where the probe 150 two-dimensionally scans the recording medium 205 is amplified by the current-voltage conversion amplifier 207, and then the Takashiro pass filter 208 converts the high frequency component, that is, the data information component. To be extracted. Then, it is compared with the voltage threshold value V ₂ by the comparator 209, converted into binarized data, and input to the data modulation / demodulation unit 211. On the other hand, the writing (recording) of information to the recording medium 205 is performed by the recording medium 2
In the state in which the probe 150 is two-dimensionally scanned on 05, a write pulse is generated from the pulse generator 212 at a position corresponding to the positive of the recording information according to a command from the recording control unit 222, and a position corresponding to the negative of the recording information is generated. Then, it is done by letting it pass as it is.

By the way, the tunnel current (voltage) signal is
It is compared with the threshold voltage V ₃ by the edge detecting comparator 210. The probe 150 is the recording medium 20.
Since the tunnel current changes abruptly when approaching the edge portion of 5, the edge position can be detected by detecting the change. A signal notifying the detection will be called an edge detection signal. At the time of recording / reproducing, the edge detection signal forcibly switches the up / down counter 218 to the up-count operation. Further, after counting up to a certain count value, it is switched to counting down again.

With this configuration, when the track is moved to move the probe 150 over the track, the presence or absence of the tracking groove 204 is ignored and the scanning direction is not changed, and the tracking controller 215 also controls the up / down counter 218. Up / down operation can be controlled. The count output of the up / down counter 218 is converted into an analog voltage by the D / A converter 219, and the stage 201 is driven by ΔX. Furthermore, D /
The output of the A converter 219 drives the stage 201 by ΔY via the variable resistor VR ₁ controlled by the scanning direction control signal. To adjust the scanning direction of the probe 150 in the XY plane, the variable resistor VR ₁ is changed to change the ΔX / of the stage 201.
This is done by changing the drive ratio of ΔY. Also,
The scanning azimuth that appropriately traces the recording bit string on the recording medium 205 is detected by performing the ΔY drive by the wobbling voltage and monitoring the envelope signal of the tunnel current (voltage) signal at that time.

Although the silicon oxide film is used as the dielectric thin film in the first embodiment described above, other materials such as SiN, ZrO ₂ , TiO ₂ , MgO and Al are used as the material of the dielectric thin film.
A material having electrical insulation such as ₂ O ₃ , SiC, SiON, AlN and ZnO can be used. The reduction of the drive voltage for displacement control in the electrostatic actuator is
This can be achieved by using a material having a large dielectric constant for the dielectric thin film. That is, since the electrostatic attraction when the movable piece is in contact with the dielectric thin film is proportional to the dielectric constant of the dielectric thin film, it is possible to reduce the driving voltage by using an insulating thin film material with a large dielectric constant. Is possible. Such ferroelectric materials include TiBaO, PbZrTiO, P
A material capable of forming a thin film, such as bTiO, can be used. Further, an organic polymer thin film is formed on the fixed electrode, and a thin film such as a silicon oxide film that prevents etching of the organic polymer thin film when the movable piece and the void below the beam is formed on the thin film. It is also possible to use an organic polymer thin film as the dielectric thin film by forming Polyimide, polyamide, PMMA as organic polymer thin film
It is possible to reduce the driving voltage by using a polymer material such as PVDF or P (VDF-TrFE) that exhibits ferroelectricity. Further, although the dielectric thin film is provided on the fixed electrode in this embodiment, it goes without saying that it may be provided on the surface of the movable piece on the substrate side.

In the information processing apparatus using the above-mentioned electrostatic actuator, it is possible to extremely miniaturize and lightweight the array of probes, that is, the multi-probe configuration. In this case, the electrostatic actuator is provided for each probe, and the displacement amount is independently controlled.

<< Second Embodiment >> Next, an electrostatic actuator according to a second embodiment of the present invention will be described. FIG. 6 is a fragmentary perspective view showing the electrostatic actuator 180. The electrostatic actuator 180 is of a torsion lever type and is used in a scanning tunneling microscope, and has the same configuration as that of the first embodiment, but is provided with a spacer and a support. There is no difference. Therefore, the support member 18 that supports the end portion of the beam 121
1 is provided on the dielectric thin film 104. The support member 181 is L-shaped, and is for allowing the movable piece 107 to be arranged with respect to the dielectric thin film 104 via a gap. Further, the movable piece 107 is provided with a probe (probe electrode) 150 as in the first embodiment.

Next, a scanning tunneling microscope using this electrostatic actuator 180 will be described. Figure 7
FIG. 3 is a block diagram showing the configuration of this scanning tunneling microscope.

The conductive sample 305 for observing the surface is placed on a fine movement mechanism 306 for finely moving the sample 305 in the XY directions (in-plane directions of the sample 305). on the other hand,
The electrostatic actuator 180 is the electrostatic actuator 18.
It is attached to the coarse-movement piezoelectric element 303 for driving 0 in the Z direction (sample direction) so as to face the sample 305. The coarse-movement piezoelectric element 303 has an approach mechanism 304 for bringing the coarse-movement piezoelectric element 303 close to the sample surface.
Is attached to. The approach mechanism 304 is a Z-direction moving stage, and is driven manually or by a motor.

A bias circuit 308 for applying a bias voltage between the sample 305 and the probe 150, and a sample 305.
A tunnel current detection circuit 309 for detecting a tunnel current flowing between the probe 150 and the probe 150 is provided. The output of the tunnel current detection circuit 309 is input to the control circuit 312 and the Z-direction servo circuit 310. The Z-direction servo circuit 310 is for feedback-controlling the electrostatic actuator 180, and is configured to apply a voltage between the movable piece 107 and the fixed electrode 103 according to the tunnel current value. Further, a Z-direction coarse movement drive circuit 307 and an XY fine movement drive circuit 311 which drive the coarse movement piezoelectric element 303 and the fine movement mechanism 306, respectively, are provided. The Z direction coarse movement drive circuit 307 and the XY fine movement drive circuit 311 are controlled by the control circuit 312. A display 313 is connected to the control circuit 312.

Next, the operation of this scanning tunneling microscope will be described. First, the approach mechanism 304 is operated so that the probe 150 enters the stroke of the coarse-motion piezoelectric element 303 with respect to the surface of the sample 305. Coarse movement piezoelectric element 303
Drive control is performed using the Z-direction coarse movement drive circuit 307, servo control is performed on the electrostatic actuator 180, and the coarse movement piezoelectric element 303 is extended, and the probe 180 and the sample 3 are moved.
The expansion is stopped when it is detected that a tunnel current flows between the signal and the signal. By operating in this way,
The observation is ready.

When observing the sample 305, the bias circuit 3
08, a bias voltage is applied, and at this time, the sample 30
The tunnel current detection circuit 309 detects the tunnel current flowing between the probe 5 and the probe 180. The Z-direction servo circuit 310 applies a voltage such that the tunnel current is constant to the electrostatic actuator 180, thereby controlling the position of the probe 180 in the Z-direction. In this state, the fine movement mechanism 306 is moved to the XY fine movement driving circuit 31.
By scanning in the XY directions by the sample 1
The servo voltage changed by the minute unevenness on the surface is detected. If the change in the servo voltage is taken into the control circuit 312 and processed in synchronization with the XY scanning signal, an STM image (topographic image) in the constant current mode can be obtained. When changing the observation location, the fine movement mechanism 806 is moved in the XY directions by the XY fine movement drive circuit 811, and the observation is performed so that the probe 180 comes to a desired area.

It goes without saying that this scanning tunnel microscope can also be applied to the constant height mode in which the tunnel current that changes due to minute irregularities on the surface of the sample 305 is detected. By using the scanning tunneling microscope of the present embodiment, it becomes possible to observe the sample surface accurately and stably.

[0055]

As described above, in the electrostatic actuator of the present invention, the fixed electrode and the movable piece are arranged with a gap, and the dielectric thin film is provided between the fixed electrode and the movable piece. When the applied voltage reaches a predetermined value, one end side of the movable piece comes into contact with the fixed electrode through the dielectric thin film, so that the contact area changes according to the applied voltage and the movable piece responds accordingly. Since the other end side of will be displaced,
There is an effect that a large displacement amount can be obtained with a small driving voltage. As a result, it is not necessary to increase the electric breakdown voltage of each part, and the device can be downsized.

In the information processing apparatus of the present invention, by using the electrostatic actuator of the present invention, the driving voltage can be lowered and the apparatus can be downsized, thereby reducing the cost and easily forming a multi-probe. There is an effect that can be achieved.

By using the electrostatic actuator of the present invention, the scanning tunnel microscope of the present invention has the effect of lowering the drive voltage and downsizing the device, thereby reducing the cost.

[Brief description of drawings]

1A is a top view of an electrostatic actuator of a first embodiment of the present invention, FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. 1A, and FIG.
[Fig. 6] is a sectional view taken along line AA 'during operation.

FIG. 2 is a schematic cross-sectional view explaining the operating principle of the electrostatic actuator of FIG.

FIG. 3 is a characteristic diagram showing a relationship between an applied voltage and a contact distance in the electrostatic actuator of FIG.

4A to 4I are schematic cross-sectional views showing a manufacturing process of the electrostatic actuator of FIG.

5 is a block diagram showing a configuration of an information processing device using the electrostatic actuator of FIG.

FIG. 6 is a fragmentary perspective view showing a configuration of an electrostatic actuator according to a second embodiment of the present invention.

7 is a block diagram showing a configuration of a scanning tunneling microscope using the electrostatic actuator of FIG.

FIG. 8 is a sectional view showing a configuration of a conventional cantilever type electrostatic actuator.

[Explanation of symbols]

 100,180 Electrostatic actuator 101 Substrate 102 Insulating layer 103 Fixed electrode 104 Dielectric thin film 105 Spacer 106 Gap 107 Movable piece 108 Support 119 Center opening 121 Beam 150 Probe 181 Support member 201 Stage 202 Lower electrode layer 203 Recording layer 205 Recording medium 205 207 Current-voltage conversion amplifier 208 High-pass filter 211 Data modulator / demodulator 212 Pulse generator 213 Error amplifier 214 Gain amplifier 215 Tracking control unit 218 Up-down counter 222 Recording control unit 223 Power supply 303 Coarse-motion piezoelectric element 304 Approach mechanism 305 Sample 306 Fine movement Mechanism 307 Z-direction coarse movement drive circuit 308 Bias circuit 309 Tunnel current detection circuit 310 Z-direction servo circuit 311 XY fine movement drive circuit 312 Control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01B 21/30 Z

Claims (10)

[Claims] 1. A fixed electrode, a movable piece made of a conductor and opposed to the fixed electrode with a gap therebetween, a support portion for supporting the movable piece, and between the fixed electrode and the movable piece. With a dielectric thin film provided, when the voltage applied to the fixed electrode reaches a predetermined value, a part of the movable piece contacts the fixed electrode via the dielectric thin film,
An electrostatic actuator in which an area of a contact portion between the movable piece and the fixed electrode increases or decreases according to a change in a voltage applied to the fixed electrode. 2. The supporting part supports the movable piece as a doubly supported beam so that the movable piece can rotate about an axis lying in a plane parallel to the surface of the fixed electrode. 1. The electrostatic actuator according to 1. 3. The electrostatic actuator according to claim 1, wherein the object to be displaced is held at a portion on the movable piece, which is opposite to the contact portion with respect to the support portion. 4. The electrostatic actuator according to claim 1, wherein the dielectric thin film is made of a ferroelectric material. 5. The electrostatic actuator according to claim 1, wherein the dielectric thin film is an organic polymer thin film. 6. The electrostatic actuator according to claim 1, wherein the movable piece is made of an aluminum thin film. 7. The physical interaction using the electrostatic actuator according to claim 3, having a probe as the object to be displaced, and acting on the probe while controlling the position of the probe by the electrostatic actuator. An information processing device that performs processing based on. 8. The electrostatic actuator according to claim 3, a probe as the displacement object, a recording medium arranged to face the probe, the recording medium and the probe, At least information is reproduced from the recording medium based on a physical interaction between the moving means for moving in the in-plane direction, the voltage applying means for applying a drive voltage to the fixed electrode, and the probe and the recording medium. An information processing apparatus having a reproducing means. 9. The information processing apparatus according to claim 7, wherein a plurality of the electrostatic actuators are provided, and each of the electrostatic actuators is independently controlled. 10. The electrostatic actuator according to claim 3, a probe that is provided as the displacement object and faces the sample, and a moving unit that moves the sample and the probe in an in-plane direction of the sample. Scanning type having a voltage applying means for applying a drive voltage to the fixed electrode and a detecting means for applying a voltage between the probe and the sample to detect a tunnel current flowing between the probe and the sample Tunnel microscope.