JPH0552507A - Cantilever-type actuator, and scanning tunneling electron microscope and information processing device using the same - Google Patents

Abstract

PURPOSE:To achieve a flexed displacement of a cantilever portion 2 without any elastic body of different substances by allowing a piezoelectric body of a same substance to be two layers with different electrical resistivity in a direction of film thickness. CONSTITUTION:A lower electrode 2 is formed on a substrate 1 and ZnO thin film as a piezoelectric body is used on it. An electrical resistivity is changed due to application of voltage and the electrical resistivity can be changed greatly under growth conditions. Therefore, a low-resistance piezoelectric body 3a and a high-resistance piezoelectric body 3b are constituted in film-thickness direction of the ZnO thin film. An upper electrode 4 is formed on it, thus enabling an unneeded portion to be eliminated. Further, the substrate 1 is etched and a cantilever portion 6 can be formed. In this manner, by changing electrical characteristics of the piezoelectric material Zn thin film in film thickness direction, a portion where deformation is large and a portion where deformation is small in thickness direction of the piezoelectric body are generated, thus enabling a flexed displacement to be generated at a cantilever portion 6 even if there are no elastic bodies due to different substances.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cantilever type actuator formed by laminating a thin film piezoelectric material and a thin film electrode, and an information processing device using the same.

[0002]

2. Description of the Related Art An example of a conventional cantilever type actuator using a thin film piezoelectric material is shown in FIG. 9 (b) is shown in FIG.
It is sectional drawing in the AA surface in (a). As shown in the figure, there is widely known a structure in which a lower electrode 2 is formed on an elastic body 30, a piezoelectric body 3 is provided on the lower electrode 2, and an upper electrode 4 is further laminated thereon.

These are the upper and lower electrodes 2 and 4 of the two sheets.
This is to transform the deformation in the direction perpendicular to the electric field generated when a voltage is applied, that is, the piezoelectric effect defined by d ₃₁ (piezoelectric constant) into bending motion of the cantilever portion 6.

That is, when the piezoelectric body 3 expands or contracts, a difference in length occurs between the piezoelectric body 3 and the elastic body 30, and the cantilever portion 6 is bent and displaced.

[0005]

However, in the above-mentioned conventional example, the elastic body 30 is necessary to generate the bending displacement, and the cantilever portion is warped due to the difference in thermal expansion coefficient between the elastic body and the piezoelectric layer. Sometimes occurs, which deteriorates the positioning accuracy and hinders precision driving.

That is, the object of the present invention is to
A cantilever type actuator capable of eliminating such a point,
Another object of the present invention is to provide a scanning tunnel electron microscope and an information processing device using the same.

[0007]

The structure of the present invention for achieving the above object is a cantilever type actuator in which a thin film piezoelectric material and a thin film electrode are laminated, in which a piezoelectric material layer sandwiched between upper and lower electrodes is used. It is a cantilever type actuator composed of two layers having different electrical resistivities in the film thickness direction.

That is, the piezoelectric body is composed of a low-resistance piezoelectric layer and a high-resistance piezoelectric layer in the film thickness direction. As a result, the electric field strength when a voltage is applied is different between the two, and therefore the displacement of the high-resistance piezoelectric layer becomes larger and bending displacement occurs.

That is, by changing the electric characteristics of the material used as the piezoelectric body in the film thickness direction, a portion having a large deformation and a portion having a small deformation are generated in the thickness direction of the piezoelectric body, and there is no elastic body due to different substances. Even now, it becomes possible to cause bending displacement of the cantilever.

Further, by providing a conductive probe (probe) having a sharp tip at the tip of such a cantilever type actuator and an extraction electrode electrically connected thereto, a small scanning tunnel electron is provided. Microscope (S
(TM) cantilever type probes can be provided.

Further, it is possible to integrate a plurality of the above-mentioned probes on the same substrate in a state having high dimensional accuracy and uniform characteristics, whereby an STM device having multiple probes can be realized.

Further, by observing a medium whose electric resistivity changes by applying a voltage as an STM observation object, a large capacity
A high-density information processing device can be provided.

The zinc oxide (ZnO) thin film used in the present invention has been widely known as a piezoelectric thin film material, but its use as a transparent conductive film has been widespread in recent years.

Such ZnO has a hexagonal wurtzite type crystal structure, and the C axis which is the polarization axis during crystal growth tends to be oriented perpendicular to the substrate.

Further, since it is a kind of II-VI group compound semiconductor, its electrical resistivity can be greatly changed by growth conditions, valence electron control and the like.

The high resistance ZnO used in the present invention will be described below.
The preparation conditions and electrical characteristics of the thin film and the low-resistance ZnO thin film will be described. (1) A high frequency magnetron sputtering apparatus is used as the film forming apparatus, and a zinc oxide sintered body having a diameter of 200 mm is used as the target. (2) The base substrate is provided with a protective film of Si ₃ N _{4 on} its surface.
A Si (100) single crystal substrate formed by the 0Å low pressure CVD method was used. On top of this, a Cr thin film (1
A 0Å) Au thin film (1000Å) was formed by vacuum evaporation. The Cr thin film is formed to secure the adhesion between Si ₃ N ₄ and Au on the substrate surface. The Au thin film is a film that is highly (111) oriented by controlling the deposition conditions. When such an underlayer is used, Zn is added onto the 3-fold symmetry axis of the (111) plane of Au.
The 6-fold symmetry axis (C axis) of O easily grows, and a ZnO thin film having a high degree of C axis orientation can be obtained. (3) Set the above substrate parallel to the target surface,
The substrate was heated to 200 ° C. to grow ZnO. (4) The growth rate of ZnO was about 2Å / sec, and the high frequency output at this time was 350 to 400W. (5) O ₂ and Ar were introduced into the sputtering gas at a ratio of 1: 1 and the total pressure during the ZnO film formation was set to 5 to 30 mtorr. (6) When forming a ZnO film having a low resistivity, a ring-shaped wire made of Al was placed 5 mm above the target. The diameter of the Al ring was set to 150 mm, and the rings were evenly arranged above the circumferential area of the target surface where corrosion was most severe. (7) After the ZnO film was grown, 1000 Å Au was again formed on the ZnO film by vacuum vapor deposition to form an upper electrode, and the electrical characteristics were measured.

Typical electrical characteristics of the high resistance sample and the low resistance sample produced as described above are shown in FIG. A
It is a graph in which the change in electrical resistivity in the case of doping with 1 and in the case of not doping is plotted against the total pressure of sputtering. As you can see from the graph, Z doped with Al
The resistivity of the nO film is 10 ⁻⁶ to 10 ⁻¹⁰ times that of the non-doped one.

By utilizing the property that the resistance values greatly differ by such doping, it is possible to form a high resistivity layer and a low resistivity layer in the thickness direction of the ZnO thin film.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples.

[Embodiment 1] FIG. 1 is a configuration diagram of a cantilever type actuator that best represents the features of the present invention. Incidentally, FIG. 1B is a sectional view taken along the line AA in FIG. In this figure, 1 is a Si single crystal substrate, 2
Is a lower electrode made of a metal thin film, and 3a is a piezoelectric body, which is a low resistivity ZnO thin film. 3b is also a piezoelectric body, and is a ZnO thin film having a larger resistivity than the piezoelectric body 3a. Reference numeral 4 is an upper electrode made of a metal thin film. As shown in the figure, the lower electrode 2 and the upper electrode 4 are separately exposed on the substrate 1, and a voltage can be applied through this portion.

Further, the piezoelectric bodies 3a and 3b have crystal C axes, which are the polarization axis directions thereof, oriented and grown in the direction of arrow 5. The cantilever portion 6 is configured by the above configuration.

Next, the operation principle of the cantilever type actuator according to the present invention will be described with reference to FIG. When a voltage E ₀ is applied to the lower electrode 2 and the upper electrode 4, the piezoelectric layers 3a, 3
Most of the voltage is applied to the high-resistance piezoelectric body 3b due to the difference in the resistivity of b. Therefore, the piezoelectric lateral effect d
_The extension due to ₃₁ becomes larger in the piezoelectric body 3b, so that the cantilever portion 6 is bent and deformed, and the cantilever portion 6 is bent.
Deforms as shown by the dotted line 7.

Even when the voltage application direction is reversed, most of the voltage is applied to the high-resistivity piezoelectric body 3b in the same manner as described above,
The contraction in the lateral direction due to the piezoelectric body lateral effect d ₃₁ in the opposite direction to that described above is larger in the piezoelectric body 3b, and the cantilever portion 6 is bent and deformed in the opposite direction.

As described above, by forming the piezoelectric bodies 3a and 3b made of the same substance as the low resistance layer and the high resistance layer, the cantilever type actuator can be realized without the need for the elastic body layer made of different substances.

Next, an example of a method of manufacturing the cantilever type actuator according to the present invention will be described with reference to FIG.

First, 5 to 10Å of Cr was vacuum-deposited on the single crystal silicon substrate 1 having a plane orientation (100) to secure the adhesion, and then 1000Å of Au was vapor-deposited, and the unnecessary portion of Au / Cr was photolithographically determined. Is removed to form the lower electrode 2 (see FIG. 3A).

Next, ZnO was added to the 2nd layer by the sputter deposition method.
000Å form. At the time of this sputtering, a ring-shaped Al wire is placed near the target surface of the sputtering apparatus, and ZnO of the piezoelectric body 3a is doped with an appropriate amount of Al to reduce the resistance (see FIG. 3B).

Next, the Al wire is removed,
ZnO is sputtered to form 3000 ZnO.
Å to form the piezoelectric body 3b. At the time of this sputter deposition, it is also possible to dope a substance that increases the resistivity from Li, Mn, etc. (see FIG. 3C).

In forming the ZnO film of FIGS. 3B and 3C, the sputtering conditions are selected so that the crystal C-axis of ZnO is oriented perpendicular to the substrate, and a good C-axis oriented film is formed. To form.

Next, 100% Au is again deposited by vacuum vapor deposition.
A 0Å film is formed to form the upper electrode 4 (see FIG. 3D).

Next, by photolithography, the upper electrode 4
Patterning is performed to remove the unnecessary portion by etching. The piezoelectric bodies 3a and 3b are also patterned by photolithography to remove unnecessary portions (see FIG. 3 (e)).

Next, from the back surface of the Si single crystal substrate 1, Si
Si is removed by performing anisotropic etching according to the plane orientation of the single crystal to form the cantilever portion 6 (see FIG. 3F).

As described above, the cantilever type actuator shown in FIG. 1 was manufactured.

The etching solution used in the photolithography was KI: I ₂ aqueous solution for Au and (NH
₄ ) ₂ Ce (NO ₃ ) ₆ : HClO ₄ aqueous solution, acetic acid aqueous solution was used for ZnO, and KOH aqueous solution was used for anisotropic etching of the Si substrate 1.

An example of the dimensions and drive characteristics of each part of the cantilever actuator manufactured according to this example is shown below.

Resistivity of piezoelectric body 3a ... 3 × 10 ^-3 Ωcm Resistivity of piezoelectric body 3b ... 1 × 10 ⁷ Ωcm Cantilever length ... 500 μm Cantilever width ... 50 μm Applied voltage ... ± 3 V Tip amplitude ... ± 2 μm Resonance frequency … 4000 Hz Further, the warp of the cantilever portion after the formation of the cantilever portion without applying a voltage can be set to 0.5 μm or less at the tip portion.

The warp of the cantilever portion generated when the ambient temperature was changed without applying a voltage was very small, and a maximum of 0.1 μm could be realized within the range of 0 ° C. to 100 ° C. ..

In this embodiment, Au / C is used as the electrode.
Although r and Au are used, the electrode material and the etching solution thereof are not limited to these, and other substances can be used. Also, the manufacturing method itself is not limited to this, and it is possible to manufacture by another method.

As described above, the elastic body as shown in the conventional example is removed from the cantilever type actuator and the resistivity is distributed in the film thickness direction of the ZnO piezoelectric layer, so that the warp of the lever due to the temperature change is generated. I was able to suppress it as much as possible.

[Embodiment 2] FIG. 4 shows a second embodiment of the present invention. FIG. 4B is a cross-sectional view taken along the plane AA in FIG.

In this embodiment, in addition to the structure of the first embodiment,
A new extraction electrode 8 was formed on the piezoelectric body 3b, and a probe 9 was formed so as to contact the extraction electrode 8 at the tip of the cantilever portion 6. The upper electrode was divided into 4a and 4b with the extraction electrode sandwiched therebetween, and was configured not to contact the extraction electrode 8.

With this structure, the cantilever actuator according to the present invention can be used as a probe for a scanning tunneling electron microscope (hereinafter abbreviated as STM). That is, the lower electrode 2 and the upper electrodes 4a, 4
A drive voltage is applied to b to displace the cantilever portion 6,
The probe 9 is brought close to the medium to be observed. When the medium has conductivity, a tunnel current flows between the probe 9 and the medium surface when the distance between the probe 9 and the medium surface approaches a few nm. By extracting this current to the outside through the extraction electrode 8, amplifying it, feeding back the cantilever drive voltage, and monitoring the change, the microscopic surface can be observed.

In this case, the displacement direction of the cantilever is only in the Z direction, and an external actuator is used for the fine and coarse movement mechanisms in the x and y directions.

As described above, when the cantilever type actuator of the present invention is used as the probe for STM, since the warpage due to the temperature change is small, the resolution is higher than that when the cantilever type actuator shown in the conventional example is used. It is possible to observe easily.

[Third Embodiment] FIGS. 5 and 6 show a third embodiment of the present invention. FIG. 5 shows an integrated actuator 20 in which a plurality of cantilever actuators having the probe 9 described in the second embodiment are produced on the same silicon substrate.

The structure described above can be manufactured by simply expanding the photolithographic photomask pattern in the manufacturing process shown in the first embodiment. Further, since they can be formed on the same substrate at the same time, the characteristics of each cantilever are uniform and the dimensional accuracy is very high.

Further, since the individual actuators are formed on the Si single crystal substrate, it is possible to integrate transistor elements such as a driver for driving a piezoelectric material and an amplifier for signal amplification on the same substrate.

FIG. 6 shows a multi-head type STM device capable of simultaneously observing a plurality of areas on the surface of the observation medium 22 by using the integrated actuator 20 described in FIG. Reference numerals 21 and 23 denote movable stages having fine movement mechanisms in the x, y, and z directions. The movable actuator 21 is fixed to the movable actuator 21, and the observation medium 22 is fixed to the movable actuator 23.

After having such a structure, the integrated actuator 20 is sufficiently brought close to the observation medium 22, the tunnel current is detected from each probe 9, and the cantilever portion 6 is displaced, whereby the probe 9 and the medium are moved. It drives so that the distance of 22 may be kept constant.

The stages 21 and 23 are replaced by x, y
By finely scanning in the direction, an STM image is obtained from each cantilever portion 6.

As described above, by integrating the cantilever type actuator having the probe 9, STM images can be simultaneously obtained from a plurality of ranges, and the cantilever portion 6 using the present invention can change the temperature and other factors. Since there is little warpage due to, it is possible to obtain a stable two-dimensional image with higher resolution.

An example of the dimensions of the integrated actuator manufactured in this embodiment is shown below.

Integrated actuator: 40 mm × 40 mm × 1 mm Number of cantilever portions 6: 90 Length of cantilever portion 6 500 μm Width of cantilever portion 6 50 μm Length of probe 9 3 μm [Example 4] FIG. 7 An information processing apparatus using the cantilever actuator according to the present invention is shown in FIG. 10 in the figure
Reference numeral 1 is a substrate of the medium, 102 is a metal thin film electrode layer, and 103 is a recording layer. 201 is an XY stage, 202 is an integrated actuator according to the third embodiment, 203 is a support of the integrated actuator, 204 is a linear actuator for coarse movement in the Z-axis direction of the integrated actuator, 20
Reference numerals 5 and 206 denote linear actuators for driving the XY stage in the X and Y directions, and 207 denotes a recording / reproducing bias circuit. Reference numeral 301 denotes a recording / reproducing tunnel current detector that detects a current flowing from the probe to the electrode layer 102 via the recording layer 103. 302 is a servo circuit for moving the cantilever in the Z-axis direction, and 303 is a servo circuit for driving the actuator 204. 304 is a drive circuit for moving a plurality of cantilevers in the Z-axis direction, and 305 is a drive circuit for controlling the position of the XY stage. A computer 306 controls these operations.

By using the integrated actuator according to the present invention in such a system, it is possible to record a large amount of information at a high density, and the occurrence of warpage due to variations in warp of each cantilever and temperature change. Can be reduced, so that the accuracy of writing and reading can be improved.

[0055]

As described above, in a cantilever type actuator using a thin film, by providing a distribution of resistivity in the film thickness direction of the piezoelectric layer, the cantilever can be provided without providing an elastic body in another layer. The part can be bent and displaced.

Further, since another material is not used as the elastic body, there is no warpage caused by the difference in thermal expansion coefficient due to temperature change, and more accurate displacement is possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a cantilever type actuator according to the present invention.

FIG. 2 is a diagram for explaining a displacement operation of the cantilever type actuator according to the present invention.

FIG. 3 is a manufacturing process diagram of the cantilever actuator according to the first embodiment.

FIG. 4 is a configuration diagram showing a second embodiment of the cantilever type actuator according to the present invention.

FIG. 5 is a perspective view of an integrated actuator shown in a third embodiment.

FIG. 6 is a partial cross-sectional view of a scanning tunneling electron microscope using an integrated actuator.

FIG. 7 is a block configuration diagram of an information processing device using an integrated actuator.

FIG. 8 is a graph showing the relationship between the electrical resistivity of a piezoelectric material ZnO and the sputtering pressure.

FIG. 9 is a configuration diagram showing a cantilever type actuator according to a conventional example.

[Explanation of symbols]

 1 Single Crystal Silicon Substrate 2 Lower Electrode 3 Piezoelectric Body 3a Low Resistance Piezoelectric Body 3b High Resistance Piezoelectric Body 4, 4a, 4b Upper Electrode 5 Crystal C Axis 6 Cantilever Part 7 Cantilever Part after Deformation 8 Extraction Electrode 9 Probe 20 Integrated Actuator 21 Movable stage 22 Observation medium 23 Movable stage 30 Elastic body 101 Recording medium substrate 102 Metal electrode layer 103 Recording layer 201 XY stage 202 Integrated actuator 203 Support body 204 Z direction linear actuator 205 X direction linear actuator 206 Y direction linear actuator 207 Recording / reproducing bias circuit 301 Tunnel current detector 302 Servo circuit 303 Servo circuit 304 Cantilever drive circuit 305 Drive circuit 306 Computer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Hirai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (6)

[Claims] 1. In a cantilever type actuator in which a thin film piezoelectric material and a thin film electrode are laminated, a piezoelectric material layer sandwiched between upper and lower electrodes is composed of two layers having different electrical resistivities in the film thickness direction. A cantilever type actuator. 2. The cantilever type actuator according to claim 1, wherein the tip of the cantilever portion is provided with a probe and an extraction electrode electrically connected to the probe. 3. The cantilever type actuator according to claim 1, wherein zinc oxide is used as the thin film piezoelectric body. 4. A cantilever type actuator comprising a plurality of the cantilever type actuators according to claim 1 arranged on the same substrate. 5. A scanning tunneling electron microscope comprising the cantilever type actuator according to any one of claims 1 to 4. 6. An information processing apparatus for recording / reproducing information on / from a recording medium using a tunnel current, comprising at least the cantilever actuator according to any one of claims 1 to 4.