JP3261539B2 - Manufacturing method of electrode substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode substrate, and more particularly to a method for manufacturing an electrode substrate used in a recording medium of an information processing apparatus utilizing the principle of a scanning tunneling microscope (hereinafter abbreviated as STM).

[0002]

2. Description of the Related Art In recent years, the use of memory materials is at the core of the electronics industry such as computers and related equipment, video disks, digital audio disks, and the like, and the development of such materials is extremely active. The performance required for memory materials varies depending on the application, but in general, high density, large recording capacity, fast response time for recording and reproduction, low power consumption, high productivity, low price, etc. Can be raised.

Conventionally, semiconductor memories and magnetic memories using a magnetic material or a semiconductor as a material have been mainly used. However, with the recent development of laser technology, inexpensive optical memories using organic thin films such as organic dyes and photopolymers have been used. High-density recording media have appeared.

On the other hand, recently, a scanning tunneling microscope (hereinafter abbreviated as STM) capable of directly observing the electronic structure of surface atoms of a conductor has been developed [G. Binnig et al. P
hys. Rev .. Lett, 49, 57 (198
2)], it is possible to measure a real space image with high resolution regardless of whether it is single crystal or amorphous, and has the advantage that it can be observed with low power without damaging the sample by current. It is expected to have a wide range of applications because it operates and can be used for various materials.

[0005] The STM utilizes the fact that a tunnel current flows when a voltage is applied between a metal probe (probe electrode) and a conductive material to approach a distance of about 1 nm. This current is very sensitive to changes in the distance between them. By scanning the probe so as to keep the tunnel current constant, it is possible to read various kinds of information on all electron clouds in the 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,
High-density recording and reproduction on the atomic order (sub-nanometer) can be performed sufficiently. For example, JP-A-61
In the recording / reproducing apparatus disclosed in JP-A-80536, atomic particles adsorbed on the medium surface are removed by an electron beam or the like, writing is performed, and this data is reproduced by STM.

A method has been proposed in which recording / reproduction is performed by STM using a material having a memory effect on the switching characteristics of voltage and current, for example, a thin film layer of a π-electron organic compound or chalcogen compound as a recording layer. [Japanese Patent Laid-Open No. 63-
161552, JP-A-63-161553]. According to this method, the recording bit size is set to 10n.
Assuming that m, a large capacity recording / reproducing of 10 ¹² bit / cm ² is possible.

FIG. 3 shows a configuration example of an information processing apparatus to which the STM is applied. This will be described below with reference to the drawings.

Reference numeral 101 denotes a substrate; 102, a metal electrode layer;
03 is a recording layer. 201 is an XY stage, 202 is a probe electrode, 203 is a support for the probe electrode, 204
Denotes a Z-axis linear actuator for driving the probe electrode in the Z direction, and 205 and 206 denote XY stages, respectively.
A linear actuator 207 driven in the Y direction is a pulse voltage circuit.

Reference numeral 301 denotes a signal from the probe electrode 202 to the recording layer 1.
This is an amplifier that detects a tunnel current flowing to the electrode layer 102 via the gate electrode 103. Reference numeral 302 denotes a logarithmic compressor for converting a change in tunnel current into a value proportional to the gap distance between the probe electrode 202 and the recording layer 103, and reference numeral 303 denotes a low-pass filter for extracting a surface unevenness component of the recording layer 103. . 304, a reference voltage V _REF and a low-pass filter 303
An error amplifier 305 detects an error with respect to the output of the actuator 305. A driver 305 drives the Z-axis linear actuator 204. A drive circuit 306 controls the position of the XY stage 201. 307 is a high-pass filter for separating data components.

FIG. 4 shows a cross section of a conventional recording medium and the tip of a probe electrode 202. As shown in FIG.

Reference numeral 401 denotes data bits recorded on the recording layer 103, and 402 denotes crystal grains formed when the electrode layer 102 is formed on the substrate 101. The size of the crystal grains 402 is about 30 to 50 nm when a normal vacuum deposition method, a sputtering method, or the like is used as a method for manufacturing the electrode layer 102.

The gap between the probe electrode 202 and the recording layer 103 can be kept constant by the circuit configuration shown in FIG. That is, after detecting a tunnel current flowing between the probe electrode 202 and the recording layer 103 and passing through a logarithmic compressor 302 and a low-pass filter 303, this value is compared with a reference voltage so that the comparison value approaches zero. Probe electrode 2
The gap between the probe electrode 202 and the recording layer 103 can be made constant by controlling the Z-axis linear actuator 204 that supports the actuator 02.

Further, by driving the XY stage 201, the probe electrode 202 traces the surface of the recording medium, and the data of the recording layer 103 can be detected by separating the high frequency component of the signal at the point (a).

FIG. 5 shows a signal intensity spectrum with respect to the frequency of the signal at the point (a).

The signal of the frequency component of f ₀ or less is
This is due to the gradual undulation of the medium due to warpage, distortion and the like. signal centered on f ₁ is due to unevenness of the surface of the recording layer 103, it is due to the crystal grain 402 primarily occurs during electrode material formed. f ₂ is a carrier component of the recording data, 403 is a data signal band. f ₃ is the recording layer 1
03 is a signal component generated from the atomic and molecular arrangement.

[0017]

When the recording medium shown in the conventional example is used, there are the following problems.

In order to perform high-density recording utilizing the high resolution characteristic of STM, the data signal band 403 must be set to f ₁ and f ₃
Must be placed between In this case, the high range cutoff frequency f _c to separate the data components pass filter 307
Is used.

However, the tail of the signal component of f ₁ overlaps with the data signal band 403. This is because the signal components of f ₁ is due to the grain 402 of the electrode layer 102, the recording size and the bit interval of the data to 30~50nm grain 402 is close to the 1~10nm by. For this reason, a case may occur where the S / N ratio for data reproduction is reduced.

In order to enable a high S / N ratio and high-speed reproduction, it is important to suppress the spread of the signal component of f ₁ to a small value. For this purpose, an electrode substrate having a smooth surface having a surface unevenness of 1 nm or less and a size of 1 μm □ or more is desired.

As one means for obtaining such an electrode substrate, the surface unevenness is 1 nm or less and the size is 1 μm square.
An electrode layer is formed on a first substrate having a smooth surface as described above by an evaporation method or the like, and then a second substrate is prepared, and an adhesive is applied to the second substrate. A method of forming an intended electrode substrate by bringing the electrode formed on the first substrate into close contact with the first substrate, transferring the electrode formed on the first substrate to the second substrate, and copying the first smooth surface. There is
In such a method, a process for obtaining an electrode substrate having a smooth surface is complicated, and there are restrictions such as selecting an electrode material having low adhesion to the first substrate in order to transfer an electrode layer. Further, a more efficient and simple manufacturing method has been desired.

That is, the object of the present invention is as follows.
An object of the present invention is to provide a method for manufacturing an electrode substrate which eliminates the complexity of the manufacturing process as described above and is simpler.

[0023]

The constitution of the present invention for achieving the above object is as follows.

That is, the principle of the scanning tunneling microscope is
For manufacturing an electrode substrate used in an information processing apparatus using the same
Has a surface roughness of 1 nm or less and a size of 1 μm.
The present invention is directed to a method for manufacturing an electrode substrate, wherein an amorphous metal layer is formed on a base material having a smooth surface of not less than m □.

Here, as the base material, it is preferable to use a crystal substrate whose main surface is cleaved, or a glass substrate whose main surface is formed by melting.
In the formation of the amorphous metal layer, a manufacturing method in which the amorphous metal layer is formed by directly adhering to a base material from a gas phase is preferable.

According to such a manufacturing method, an electrode substrate having a smooth surface can be manufactured efficiently and simply as compared with the related art.

Hereinafter, the present invention will be described in detail. First, a smooth substrate 101 is prepared. This substrate has a surface irregularity of 1n.
It must have a smooth surface of not more than m and not less than 1 μm □. Here, the surface roughness is measured by bringing the tip of the microprobe close to the sample substrate surface, measuring the interatomic force acting between the tip atom of the microprobe and the atom on the sample substrate surface, and observing the sample surface shape. AFM (Atomic-Force)
-Microscopy).

Using such an AFM, the conductivity of the sample,
The surface shape of a sample can be measured with atomic-order resolution regardless of insulation. The present inventors evaluated the surfaces of various materials using AFM, and found that the following materials were suitable as the smooth substrate in the present invention. . Cleavage plane of crystal: A very smooth surface can be easily obtained as the cleavage plane of the crystal.
gO, TiC, Si, HOPG (highly oriented graphite), and the like. . Melted glass surface ... for example, float glass, #
7059 fusion, fused quartz, and the like.

The surface profile of the above-mentioned material was measured by AFM.
nm or less. In particular, the mica cleavage plane has few steps of the lattice plane generated at the time of cleavage, and is suitable as a smooth substrate used in the present invention.

Next, as shown in FIG. 1, an electrode layer 102 is formed on the smooth substrate 101. Electrode layer 10 according to the present invention
As 2, a material having conductivity and being amorphous is desired. Metals that can be amorphous metal layers include A
u-Si, Au-Ge, Au-Sn, Au-Pb, Au
-Si-Ge, Au-Pb-Si, Ag-Pb, Ag-
Cu, Ag-Pb-Si, Cu-Zr, Pd-Si, P
d-Cu-Si, Pt-Sb, Pt-Ge, Pt-T
a, Rh-Nb, Rh-Ta, Re-Si, Ir-N
There are many materials such as b, Ir-Ta, Ir-Ta-B, and transition metal alloys. Many of these amorphous metals can be considered depending on the combination of the constituent elements and compositions, and the degree of freedom is increased depending on the forming method.

As a method of forming an amorphous metal layer, there are well known a method of forming an amorphous metal by directly attaching a substrate from a gas phase such as vapor deposition or sputtering, and a method of rapidly cooling a liquid. However, liquid quenching is difficult to form directly on a smooth substrate, and methods such as vapor deposition, ion plating, cluster ion beam, and sputtering, which form an amorphous metal directly on a substrate from the gas phase, are suitable. ing.

The above-mentioned forming method is conventionally known as a thin film forming technique. Even when an amorphous metal layer is formed, it can be sufficiently formed by this technique, but preferably, an amorphous metal is formed. At this time, it is desirable that the smooth substrate 101 be sufficiently cooled. This is because, by cooling, the range of the composition of the constituent elements to form the amorphous metal layer film can be increased. In addition, the formed electrode layer 1
The fact that 02 is amorphous can be confirmed by X-ray diffraction.

The electrode layer 102 made of an amorphous metal layer obtained as described above has no crystal grains, so that the substrate 1
01, and a smooth electrode substrate having a smooth surface of 1 μm square or more with a surface unevenness of 1 nm or less can be obtained.

Next, as shown in FIG. 1, a recording layer 103 is formed on the electrode layer 102 of the smooth electrode substrate. As the recording layer 103, a material having a memory switching phenomenon (electric memory effect) in current-voltage characteristics, for example, a molecule having both a group having a π-electron level and a group having only a σ-electron level is formed on an electrode. It is possible to use a laminated organic monomolecular film or its accumulated film. The electric memory effect is a state in which a thin film such as the above-mentioned organic monomolecular film and its cumulative film is disposed between a pair of electrodes, and shows a state (ON state and OFF state in FIG. 6) showing two or more different conductivity. By applying a voltage exceeding a threshold value at which a transition can be made, a transition (switching) to a low resistance state (ON state) and a high resistance state (OFF state) can be performed reversibly. In addition, each state can be held (memory) without applying a voltage.

In general, most of organic materials have insulating or semi-insulating properties, so that organic materials having a group having a π-electron level applicable in the recording layer are remarkably diversified. Examples of the structure of the dye having a π electron system suitable for the recording layer include, for example, a dye having a porphyrin skeleton such as phthalocyanine and tetraphenylporphyrin, an azulene dye having a squarylium group and a croconic methine group as a binding chain, quinoline, and benzothiazole. , Benzoxazole and other two nitrogen-containing heterocycles bonded by a squarylium group and a croconic methine group, or cyanine dyes, or condensed polycyclic aromatics such as cyanine dyes, anthracene and pyrene, and aromatic rings and heterocycles A chain compound obtained by polymerization of a compound and a polymer of a diacetylene group, further a derivative of tetracyanoquinodimethane or tetrathiafulvalene and an analog thereof and a charge transfer complex thereof, or even ferrocene,
Metal complex compounds such as a trisbipyridine ruthenium complex are exemplified.

Examples of suitable polymer materials for the recording layer include biopolymers such as addition polymers such as polyacrylic acid derivatives, condensation polymers such as polyimide, and ring-opening polymers such as nylon. .

For the formation of the recording layer 103, specifically, a vapor deposition method, a cluster ion beam method, or the like can be applied. However, Langmuir is a known conventional technique because of its controllability, easiness and reproducibility. Blodget method (LB)
The method is very suitable.

According to the LB method, a monomolecular film of an organic compound having a hydrophobic portion and a hydrophilic portion in one molecule or a cumulative film thereof can be easily formed on a substrate, and the thickness on the order of molecules can be obtained. And a uniform and homogeneous organic ultrathin film can be stably supplied over a large area.

In the LB method, in a molecule having a structure having a hydrophilic site and a hydrophobic site in a molecule, when the balance between the two (balance of amphipathicity) is appropriately maintained,
This is a method of forming a monomolecular film or a cumulative film thereof by utilizing the fact that molecules form a monomolecular layer with the hydrophilic group facing downward on the water surface.

Examples of the group constituting the hydrophobic site include various generally known saturated and unsaturated hydrocarbon groups, condensed polycyclic aromatic groups, and linear polycyclic phenyl groups. Each of these constitutes a hydrophobic site alone or in combination with a plurality thereof.

On the other hand, the most typical constituents of the hydrophilic site are, for example, carboxyl group, ester group, acid amide group, imide group, hydroxyl group, and amino group (1, 2, tertiary and quaternary). ) And the like.

An organic molecule having both a hydrophobic group and a hydrophilic group in a well-balanced manner can form a monomolecular film on the water surface, and is a very suitable material for the present invention. .

Although the electric memory effect of these compounds having a π-electron level has been observed at a film thickness of several tens nm or less, the thickness should be 5 to 300 ° from the viewpoint of film formability and uniformity. Is preferred.

FIG. 2 shows the frequency spectrum of the signal at point (a) when the recording medium using the smoothing electrode substrate according to the present invention is used in the information processing apparatus of FIG. The signal of the frequency component equal to or lower than f ₀ is due to the gradual undulation of the medium due to the warpage or distortion of the substrate 101. f ₂ is a carrier component of the recording data, 403 denotes a data signal band. f ₃ is a signal component generated from the arrangement of atoms and molecules in the recording layer 103.

The signal centered at f ₁ is obtained by transferring slight irregularities on the surface of the base material to the surface of the electrode layer 102, and these irregularities are made equal to or smaller than the data recording signal. The change in the unevenness is 1 nm or less in recording and reproduction using STM. In the recording medium using the electrode substrate of the present invention, the size of the smooth surface of the recording layer 103 is 1 μm square or more. As a result, the following operation and effect can be obtained. . The signal component f ₁ due to the unevenness of the surface of the recording layer 103 and the data signal band 403 do not overlap, and the S / N does not decrease due to the spread of the spectrum of f ₁ . That is, the data error rate can be reduced. . Since there is no unevenness on the surface of the recording layer 103,
The displacement of the probe electrode 202 in the Z-axis during XY scanning while keeping the gap between the surface of the probe electrode 202 and the probe electrode 202 constant is small. For this reason, the XY stage 201 can be driven very quickly. . Since there is no unevenness on the surface of the recording layer 103, the tip of the probe electrode 202, that is, the position of the tip atom through which the tunnel current flows is stably selected. The probe electrode 202 as seen on the surface of the recording layer 103 having irregularities
The so-called ghost phenomenon in which a tunnel current flows between the plurality of atoms and the recording layer 103 is eliminated.

[0046]

Embodiments of the present invention will be specifically described below.

Example 1 As shown in FIG. 1, a mica plate is cleaved in the air to form a smooth substrate 101. Subsequently, a Pt-Ta alloy (Pt50%, Ta50
%) To form an electrode layer 102. The electrode layer 10
2 is to maintain the substrate temperature at room temperature, Ar pressure is 2 mTorr,
Film formation rate 300Å / min, ultimate pressure 5 × 10 ^-7 Torr
r, the film thickness was 2000 °.

The X of the electrode layer 102 thus obtained is
The line diffraction measurement revealed no amorphous layer except for the peak of the mica plate. When the surface was observed by STM, the surface unevenness was 1 nm or less at 10 μm square.

Next, a four-layer polyimide LB film was formed on this smooth electrode substrate to form a recording layer 103. Hereinafter, a method for forming the recording layer 103 using the polyimide LB film will be described.

A polyamic acid represented by the formula (1) is mixed with an N, N'-dimethylacetamide-benzene mixed solvent (1: 1 V /
V) (concentration in terms of monomer: 1 × 10 ⁻³ M)
A separately prepared 1 × 10 ⁻³ M solution of N, N-dimethyloctadecylamine in the same solvent was mixed at 1: 2 (V / V) to prepare a polyamic acid octadecylamine salt solution represented by Chemical Formula 2.

[0051]

Embedded image

[0052]

Embedded image This solution was spread on an aqueous phase composed of pure water at a water temperature of 20 ° C., and a monomolecular film was formed on the water surface. After removing the solvent by evaporation, the surface pressure was increased to 25 mN / m. While maintaining the surface pressure constant, the smooth electrode substrate is moved at a speed of 5
After immersion gently at a speed of 5 mm / min,
The film was gently pulled up with n to produce a two-layer Y-type monomolecular cumulative film. By repeating this operation, a four-layer monomolecular cumulative film of polyamic acid octadecylamine salt was formed.

Next, the substrate is decompressed (up to 1 mmHg).
Heating and baking at 300 ° C. for 10 minutes to imidize the octadecylamine polyamic acid salt (Formula 3)

[0054]

Embedded image Four layers of polyimide single molecule cumulative films were obtained.

Next, when the surface shape of the recording medium produced by the above-described method was examined by the information processing apparatus shown in FIG. 3, the surface of the recording medium reflected the smooth surface of the electrode. The surface unevenness was 1 nm or less.

Next, a recording / reproducing experiment was performed. As the probe electrode 202, a probe electrode 202 made of platinum / rhodium was used. The probe electrode 202 controls the distance (Z) from the surface of the recording layer 103 by a piezoelectric element so that the current is kept constant by controlling the distance (Z).
Is finely controlled. Further, the linear actuators 204, 205, 206 keep the distance Z constant,
It is designed so that fine movement control can be performed also in the in-plane (X, Y) direction.

The probe electrode 202 can perform recording / reproduction / erasing directly. The recording medium is placed on the high-precision XY stage 201 and can be moved to any position.

A recording medium having a recording layer 103 in which four polyimide layers were accumulated was placed on an XY stage 201. Next, the probe electrode 202 and the electrode layer 1 of the recording medium
A voltage of +1.5 V was applied between the probe electrodes and the distance (Z), and the distance (Z) between the probe electrode 202 and the surface of the recording layer 103 was adjusted while monitoring the current. At this time, the probe current Ip for controlling the distance Z between the probe electrode 202 and the surface of the recording layer 103 was set to be 10 ⁻¹⁰ A ≧ Ip ≧ 10 ⁻¹¹ A.

Next, the probe electrode 202 is connected to the recording layer 103.
While scanning on the above, information was recorded at a pitch of 100 °. The recording of such information is performed by setting the probe electrode 202 to +
With the electrode layer 102 on the negative side, a rectangular pulse voltage (first pulse voltage) _exceeding a threshold voltage V _th ON at which the electric memory material (four polyimide LB films) changes to a low resistance state (ON state) Was added. Thereafter, the probe electrode 202 was returned to the recording start point, and the recording layer 103 was scanned again.
At this time, adjustment was made so that Z = constant at the time of reading the recording. As a result, a probe current of about 10 nA flowed through the data bit 401, indicating that the data bit 401 is in the ON state.

The probe voltage is changed to a threshold voltage V _th OFF at which the electric memory material changes from the ON state to the OFF state.
The voltage was set to 10 V (second pulse voltage) exceeding the threshold value, and the recording position was traced again. As a result, it was confirmed that all the recording states were erased and the state transited to the OFF state. Further, when the error rate of the read data was examined with the reading speed kept constant, the error rate was 10 ⁻⁴ in the conventional example, but 10 ⁻⁴ in the present embodiment.
It became possible to remarkably reduce it to ^-7 .

(Example 2) A fused quartz plate was converted to a smooth substrate 101.
And Pt-Ta on the smooth substrate 101 by sputtering.
An alloy (Pt 50%, Ta 50%) is formed into a film and the electrode layer 10
Form 2 The electrode layer 102 is maintained at a substrate temperature of room temperature, an Ar pressure of 2 mTorr, and a film formation rate of 300 ° / mi.
n, the ultimate pressure was 5 × 10 ⁻⁷ Torr, and the film thickness was 2000 °.

The X of the electrode layer 102 thus obtained is
A line diffraction measurement was performed, but no crystalline peak was observed. When the surface was observed by STM, 10
In μm □, the surface unevenness was 1 nm or less. Further, a recording layer was formed in the same manner as in Example 1, and experiments for recording, reproduction, and erasing were performed. As a result, the same results as in Example 1 were obtained.

(Embodiment 3) A fused quartz plate was converted to a smooth substrate 101.
Then, an Au—Y alloy (Au 80%, Y20%) is formed on the smooth substrate 101 by a sputtering method, and the electrode layer 102 is formed. The electrode layer 102 is cooled by liquid nitrogen at a substrate temperature, an Ar pressure of 2 mTorr, and a film forming speed of 300 ° /
min, ultimate pressure 5 × 10 ^-7 Torr, film thickness 2000Å
Was performed under the following conditions.

The X of the electrode layer 102 thus obtained is
A line diffraction measurement was performed, but no crystalline peak was observed. When the surface was observed by STM, 10
In μm □, the surface unevenness was 1 nm or less. Further, a recording layer was formed in the same manner as in Example 1, and experiments for recording, reproduction, and erasing were performed. As a result, the same results as in Example 1 were obtained.

[0065]

As described above, according to the manufacturing method of the present invention, a smooth electrode substrate can be easily obtained in one step without any complicated steps, and since there is no electrode layer separation step. It is not necessary to consider the adhesiveness, and as a result, the degree of freedom in material selection is expanded, and an industrially advantageous electrode substrate used for an information processing device or the like to which the STM is applied can be provided.

[Brief description of the drawings]

FIG. 1 shows a schematic sectional view of an electrode substrate obtained according to the present invention.

FIG. 2 shows a diagram of a frequency spectrum of a recording medium using an electrode substrate obtained by the present invention.

FIG. 3 shows a configuration diagram of an information processing apparatus to which STM is applied.

FIG. 4 shows a schematic cross-sectional view of a conventional electrode substrate.

FIG. 5 shows a diagram of a frequency spectrum of a reproduction signal of a recording medium using an electrode substrate obtained by a conventional example.

FIG. 6 shows a current-voltage characteristic graph when recording is performed on a recording medium.

[Explanation of symbols]

 Reference Signs List 101 substrate 102 electrode layer 103 recording layer 201 XY stage 202 probe electrode 203 support 204 Z-axis linear actuator 205 X-axis linear actuator 206 Y-axis linear actuator 207 pulse voltage circuit 301 amplifier 302 logarithmic compressor 303 low-pass filter 304 error amplifier 305 Driver 306 Drive circuit 307 High-pass filter 401 Data bit 402 Crystal grain 403 Data signal band

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-241350 (JP, A) JP-A-2-114643 (JP, A) JP-A-3-71452 (JP, A) JP-A-60-1985 214436 (JP, A) Jikken 63-50002 (JP, Y1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/10 G11B 9/00

Claims (3)

(57) [Claims] 1. Use of the principle of a scanning tunneling microscope
In manufacturing method of electrode substrate used in information processing equipment
And forming an amorphous metal layer on a base material having a smooth surface having a surface unevenness of 1 nm or less and a size of 1 μm □ or more. 2. The method for manufacturing an electrode substrate according to claim 1, wherein a substrate made of a crystal whose main surface is cleaved or glass formed by melting is used as the base material. 3. The method for manufacturing an electrode substrate according to claim 1, wherein the amorphous metal layer is formed by directly attaching the amorphous metal layer to a base material from a gas phase.