JPH04349243A - Smooth electrode substrate, recording medium and information processor - Google Patents

Abstract

PURPOSE:To improve S/N and to allow high-speed reading out by using a substrate having the difference between the max. value and min. value of surface ruggedness which is below the specific range of specific areas as a smooth electrode substrate and providing rectangular recessed parts or projecting parts having the height or depth of a specific range on the surface of this substrate. CONSTITUTION:The substrate having at least >=1mum square of the smooth surface of <=1nm max. value and min. value of the surface ruggedness is sued as the smooth substrate 101. Such substrate 101 can be formed by using the cleavage plane of crystals, such as mica, MgO, TiC, Si, and graphite. Metals, such as Au, Ag and Pd, are then epitaxially grown on the substrate 101 to form an electrode layer 102. Desired track patterns having 3 to 30nm level difference of tracks are in succession formed by using an ion beam technique and, thereafter, a recording layer 103 consisting of an org. compd. is formed on the layer 102. The smooth electrodes are formed and the S/N is improved. High-speed reading out is thus possible.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high density memory using the principle of a scanning tunneling microscope.

0002

BACKGROUND OF THE INVENTION In recent years, the use of memory materials has become the core of electronics industries such as computers and related equipment, video disks, digital audio disks, etc., and the development of these materials has been extremely active. The performance required of memory materials varies depending on the application, but in general, 1) high density and large storage capacity, 2) fast response speed for recording and playback, 3) low power consumption, and 4) high productivity and low price. etc.

On the other hand, a scanning tunneling microscope (STM) that can directly observe the electronic structure of surface atoms of a conductor has been developed (
G. Binnig et al. Phys. Rev
．． Lett. 49, 57 (1982)), it has become possible to measure real space images with high resolution regardless of whether they are single crystal or amorphous, and it also has the advantage of being able to observe at low power without damaging the medium due to current. However, it also operates in the atmosphere and can be used with various materials, so it is expected to have a wide range of applications.

STM utilizes the fact that a tunnel current flows when a voltage is applied between a metal probe (probe electrode) and a conductive substance and the probe is brought close to a distance of about 1 nm. This current is very sensitive to changes in the distance between the two, and by scanning the probe while keeping the tunneling current constant, it is possible to draw the surface structure in real space and at the same time draw various information about the total electron cloud of surface atoms. You can also read information. At this time, the resolution in the in-plane direction is about 0.1 nm. Therefore, by applying the principle of STM, it is possible to
) enables high-density recording and reproduction. In this case, the recording and reproducing method is particle beam (electron beam, ion beam).
Alternatively, there is a method of recording by changing the surface condition of an appropriate recording layer using high-energy electromagnetic waves such as X-rays and energy rays such as visible and ultraviolet light, and reproducing it with STM, and a method of changing the voltage and current switching characteristics of the recording layer. A method has been proposed in which recording and reproduction are performed using STM using a thin film layer of a material having a memory effect, such as a π-electron organic compound or a chalcogenide.

FIG. 6 shows a configuration diagram of an information processing device to which STM is applied. This will be explained below according to the drawings. 101 is a substrate, 102 is an electrode layer, and 103 is a recording layer. 201 is X
A Y stage, 202 is a probe electrode, 203 is a support for the probe electrode, 204 is a Z-axis linear actuator that drives the probe electrode in the Z direction, and 205 and 206 are linear actuators that drive the XY stage in the X and Y directions, respectively. .

Reference numeral 301 indicates the connection from the probe electrode 202 to the recording layer 1.
This is an amplifier that detects the tunnel current flowing to the electrode layer 102 through the electrode layer 102. 302 is a logarithmic compressor for converting the change in tunnel current into a value proportional to the distance between the probe electrode 202 and the recording layer 103, and 303 is a low-pass filter for extracting the surface unevenness component of the recording layer 103. . 304 is a reference voltage VREF and a low pass filter 303
An error amplifier 305 is a driver that drives the actuator 204. 306 is a drive circuit that controls the position of the XY stage 201. 307 is a high-pass filter that separates data components. A power source 308 applies a pulse voltage for information processing between the probe electrode 202 and the electrode layer 102. When a pulse voltage is applied, the probe current changes rapidly, so
A servo circuit 309 can be used to control rapid displacement of the probe electrode 202 in the Z direction.

FIG. 7 shows a cross section of a recording medium using an electrode substrate and the tip of the probe electrode 202. 101 is a substrate, 10
2 is an electrode layer, 103 is a recording layer, and 104 is a track. 202 is a probe electrode. Further, 401 is a data bit recorded on the recording layer 103, and 402 is a data bit recorded on the substrate 101.
These are crystal grains formed when the electrode layer 102 was formed thereon. The size of the crystal grains 402 is 30 to 30 mm when a normal vacuum evaporation method, sputtering method, etc. is used for manufacturing the electrode layer 102.
It is about 50 nm.

The distance between the probe electrode 202 and the recording layer 103 can be kept constant by the circuit configuration shown in FIG. That is, the tunnel current flowing between the probe electrode 202 and the recording layer 103 is detected, and after passing through the logarithmic compressor 302 and the low-pass filter 303, this value is compared with a reference voltage, and this comparison value approaches zero. Probe electrode 20
By controlling the Z-axis linear actuator 204 supporting the probe electrode 202, the distance between the probe electrode 202 and the recording layer 103 can be made constant.

Further, by driving the XY stage 201, the probe electrode 202 traces the surface of the recording medium, and data on the recording layer 103 can be detected by separating the high frequency component of the signal at point a. The signal strength spectrum of the signal at point a at this time with respect to frequency is shown in FIG.

[0010] Signals with frequency components below f0 are transmitted to the substrate 101.
This is due to the gentle undulations of the medium due to warpage, distortion, etc. The signal centered on f1 is due to the unevenness of the surface of the electrode layer 102, and is mainly due to the crystal grains 402 generated during the formation of the electrode material. f2 is a carrier wave component of recording data, and 403 is a data signal band indicating a data signal band. f3 is a signal component generated from the arrangement of atoms and molecules in the recording layer 103. Further, fT is a tracking signal. Although not shown in the reproducing apparatus of FIG. 6, this tracking signal fT transfers the data string to the probe electrode 20.
This is achieved by forming a step on the medium or writing a signal that can be detected when the medium deviates from the track 104 into the recording layer 103 or the electrode layer 102.

[0011] Furthermore, in order to actually perform recording and reproduction on a memory medium as an apparatus, it is necessary to perform so-called tracking, which is positioning and tracing to a data string. As a tracking method for this type of high-density memory, there are methods using reference markers, crystal atomic arrangement, grooves, etc. on the recording medium.

0012

[Problems to be Solved by the Invention] When the recording medium using the above-mentioned electrode substrate was used, there were the following problems. (1) In order to perform high-density recording by taking advantage of the high resolution that is a feature of STM, the data signal band 403 must be placed between f1 and f3. In this case, a high-pass filter 307 with a cutoff frequency fc is used to separate the data components. However, the base of the signal component of f1 overlaps with the data signal band 403. This is because the signal component of f1 is caused by the crystal grains 402 of the electrode layer 102,
This is because the data recording size and bit interval are close to each other, 1 to 10 nm, compared to 30 to 50 nm of the crystal grains 402. For this reason, the S/N of data reproduction is reduced, and the error rate of read data is significantly increased. (2) When tracking data using a step on the medium, the step is too large and the probe electrode that reads the tracking signal collides with the step, damaging the probe electrode or making it difficult to read data. It may happen.

Furthermore, there are the following problems in tracking.

In the method using a reference marker, the surface of the recording medium must be two-dimensionally scanned to detect the marker, and it takes a considerable amount of time to find the reference marker. In the method using atomic arrangement, it is difficult to obtain a crystal substrate free of lattice arrangement disorder and defects over a recording surface area of 1 cm 2 for high-density recording, for example. Furthermore, when a groove is used, its edge cross section has irregular disturbances, which reduces the detection accuracy of the tracking position in a tracking method using a tunnel current that is very sensitive to distance changes.

[0015]

Means for Solving the Problems and Effects The present invention provides a smooth electrode substrate that enables high S/N ratio and high speed readout using a recording medium. More specifically, the difference between the highest value and the lowest value of the surface unevenness is 1 nm or less over a range of at least 1 μm□, and the surface has rectangular convex portions or concave portions with a height or depth of 3 nm or more and 30 nm or less. Provided is a smooth electrode substrate with characteristics.

The present invention also provides a recording medium in which a recording layer is provided on such a smooth electrode substrate, and an information processing apparatus that performs recording, reproduction, and erasing using such a recording medium.

Furthermore, the present invention provides a recording medium that is low in price, has high productivity, and can be accessed at high speed. More specifically, the recording medium is characterized in that recesses are formed as tracks by anisotropic etching of Si. Further, by performing tracking along the edge portion of the track of such a recording medium and recording and reproducing recorded information two-dimensionally, an information processing device capable of high-density, high-speed access is provided.

FIG. 1 shows a cross-sectional view of a recording medium using a smooth electrode substrate according to the present invention. 101 is a substrate, 102 is an electrode layer having a smooth surface, 103 is a recording layer, and 104 is a track.

FIG. 3 shows a cross-sectional view of a recording medium according to the present invention.

In FIG. 3, a smooth substrate 101 is first prepared. This smooth substrate needs to have a smooth surface with a maximum and minimum surface unevenness of 1 nm or less and at least 1 μm square or more. At the same time, such smooth substrates must be suitable for epitaxial growth of metals. A cleavage plane of a crystal can be used as a smooth substrate that satisfies these conditions. Examples of crystalline materials include mica, MgO, and TiC.
, Si, graphite, etc.

Next, a metal is epitaxially grown as an electrode layer on the smooth substrate. Such metals include Au, A
In addition to Au-Ag, Au-Pd, etc.
Alloys such as these may also be used.

Subsequently, a desired track pattern is formed on the smooth substrate using ion beam technology. Although it is possible to use various conventionally known lithography techniques to form the track pattern, in the present invention, FIB, ion beam etching, etc. Preferably, ion beam technology is used. In addition, in order to distinguish the unevenness of recorded data and prevent damage to the probe electrode during data tracking, the track level difference is 3 nm to 30 nm.
It is nm. Note that after patterning a smooth substrate, metal may be epitaxially grown to form an electrode substrate (
Figure 4(a)). Alternatively, if the smooth substrate itself has conductivity, such as graphite, patterning may be performed directly without epitaxially growing the metal on the smooth substrate (FIG. 4(b)).

[0023] When the surface shape of the electrode layer obtained through the above steps was measured using STM, the surface unevenness was 10
The difference between the maximum and minimum values in the μm□ area is 1 nm to 3
nm, and it was confirmed that it had sufficient smoothness.

Thereafter, a recording layer made of an organic compound is formed on the electrode layer. Methods for forming such a recording layer include conventionally known vacuum evaporation methods, cluster ion beam methods,
Examples include a coating adsorption method, but the Langmuir-Blodgett (LB) method is preferred in order to obtain a uniform film thickness most easily. According to the LB method, it is possible to easily form a monomolecular film of an organic compound or a cumulative film in which such monomolecular films are accumulated.

Furthermore, the recording layer used in the present invention has a current-
Materials that have a memory switching phenomenon (electrical memory effect) in voltage characteristics, such as an organic monomolecular film or an accumulation thereof, in which molecules having both a group with a π electron level and a group with only a σ electron level are laminated on an electrode. It becomes possible to use a membrane. The electric memory effect is a state in which a thin film such as the organic monomolecular film or its cumulative film exhibits two or more different conductivities when placed between a pair of electrodes (Fig. 21
It is possible to reversibly transition (switch) to a low resistance state (ON state) and a high resistance state (OFF state) by applying a voltage that exceeds a threshold that can cause a transition to an ON state or an OFF state. . Further, each state can be maintained (memory) without applying a voltage.

Since most organic materials generally exhibit insulating or semi-insulating properties, the present invention can be applied to a wide variety of organic materials having a group having a π-electron level. Examples of structures of dyes having a π-electron system suitable for the present invention include phthalocyanine, dyes having a porphyrin skeleton such as tetraphenylporphyrin, azulene dyes having squarylium groups and croconic methine groups as bonding chains, quinoline, benzothiazole, Cyanine-based similar dyes in which two nitrogen-containing heterocycles are bonded by a squarylium group and a croconic methine group such as benzoxazole, or cyanine dyes, fused polycyclic aromatics such as anthracene and pyrene, and aromatic and heterocyclic compounds are polymerized chain compounds and polymers of diacetylene groups, as well as derivatives of tetracyanoquinodimethane or tetrathiafulvalene, analogs thereof, and charge transfer complexes thereof,
Further examples include metal complex compounds such as ferrocene and trisbipyridine ruthenium complex.

Examples of polymeric materials suitable for the present invention include condensation polymers such as polyimide and polyamide, and biopolymers such as bacteriorhodopsin.

The electrical memory effect of these compounds having a π-electron level has been observed in films with a thickness of several tens of micrometers or less. Since the distance between them must be close to allow current to flow, the thickness of the recording layer of the present invention is preferably 0.3 nm or more and 10 nm or less, preferably 0.3 nm or more and 3 nm or less.

Furthermore, any material may be used for the probe electrode as long as it exhibits conductivity; for example, Pt, Pt-
Examples include Ir, W, Au, Ag, and the like. The tip of the probe electrode needs to be as sharp as possible to increase the resolution of recording, playback, and erasure. In the present invention, a probe electrode is produced by controlling the shape of the tip of a needle-shaped conductive material using an electropolishing method, but the method and shape of the probe electrode are not limited thereto. Furthermore, there is no need to limit the number of probe electrodes to one; they can be used for position detection and recording.
A plurality of probe electrodes may be used, such as one for reproduction and another.

FIG. 2 shows the frequency spectrum of the signal at point a when the recording medium according to the present invention is used in the information processing apparatus shown in FIG. Signals with frequency components below f0 are due to gentle undulations of the medium due to warping, distortion, etc. of the substrate 101. f2 is a carrier wave component of recording data, and 403 indicates a data signal band. f3 is a signal component generated from the arrangement of atoms and molecules in the recording layer 103. Further, fT is a tracking signal. The signal centered on f1 is due to slight irregularities on the surface of the electrode layer, and these irregularities are created to be equal to or smaller than the data recording signal. This change in unevenness is 1 nm or less in recording and reproducing using STM.

Next, another recording medium of the present invention is shown in FIG.
Shown below.

In the present invention, as shown in the figure, the angle of the edge portion 620 between the side wall of the track and the recording surface is 88° to 90°.
It is preferable that the angle is 2°, and the planar shape may be a right angle such as a stripe or a spiral, a curve, a rectangle, or a circle. Further, a guide portion for drawing the probe electrode 202 into a track on the recording medium may also be provided.

In the recording medium of the present invention, an electrode layer is formed facing the probe electrode, and a recording layer having an electric memory effect is formed on the electrode layer. The recording layer is preferably a monomolecular film of an organic compound or a cumulative film obtained by accumulating the monomolecular film. Such a monomolecular film or a cumulative film thereof can be formed by the LB method, and the organic compound contains It is preferable to use a group having a conjugated π electron level and a group having a σ electron level.

[0034] Furthermore, recording using the recording medium of the present invention
The reproduction and tracking method therefor utilizes the fact that a tunnel current flows when a voltage is applied between a probe electrode and a conductive material and the distance between the two is set to 10 nm or less. Further, in the present invention, the probe electrode detects the first edge portion and reads data by two-dimensionally scanning the probe electrode along the edge portion, so that the data writing area can be accessed at high speed.

Next, a more detailed explanation will be given with reference to the drawings. FIG. 13 shows the main configuration of the recording medium and an information processing apparatus using the same. 101 is a substrate of the recording medium, 102 is a lower electrode, 121 is a recording/reproducing area, and 620 is an edge portion.

201 is a stage that supports the recording medium;
This stage 201 is driven in the Y-axis direction by a linear actuator 206. 203 is a support body that supports the probe electrode 202 and whose position is controlled by actuators 205 and 204 that drive it in the X or Z axis direction, respectively.

The distance between the recording medium surface and the probe electrode 202 is controlled by a tunnel current flowing between the recording medium surface and the probe electrode 202. A tunnel current flowing between recording medium probe electrodes is detected by a bias voltage VB by a load resistor RL, and is amplified by an amplifier 301. A probe height detection circuit 702 determines an appropriate probe height, and a Z-axis drive control circuit 705 determines the probe height. The height is adjusted.

The recording/reproducing area 721 is determined with the edge portion 620 as a reference. That is, the probe electrode 202 is moved by the X-axis drive control circuit 706 and the actuator 205.
Scan in the axial direction. At this time, when the probe electrode 202 approaches the edge portion 620, the tunnel current between the probe electrode 202 and the electrode of the edge portion 620 changes rapidly. The edge detection circuit 70 detects this rapidly changing tunnel current.
Detect with 3. This detection signal causes the X-axis drive control circuit 7 to
06 reverses the scanning direction of the probe electrode 202. Then, after a certain period of time has elapsed, the scanning direction of the probe electrode 202 is reversed again and the probe electrode 202 scans in the direction toward the edge portion 620. At this time, a drive signal is sent to the Y-axis drive control circuit 707 to move the stage 201 by one step in the Y-axis direction.

By repeating the above operations, the probe electrode 202 can always scan the recording/reproducing area 121 along the edge portion 620 and at a certain angle with respect to the edge portion 620.

When recording on a recording medium, the probe electrode 202 detects the edge portion 620 and performs inversion scanning in the
A write voltage is applied from the probe electrode 202 through W. At this time, a series of data pulse trains are recorded until the probe electrode 202 scans in the X-axis direction for a certain period of time and then starts reversing scanning in the edge direction again.

By performing this recording operation every time the probe electrode 202 detects the edge portion 620, a data string having a certain angle with respect to the edge portion is written, and the Y-axis stage 201 sequentially transmits the data in synchronization with this. An area 721 in which data is recorded two-dimensionally is formed.

During reproduction, the probe electrode 202 is scanned with the edge portion 620 as a reference at the same time as during recording. At this time, the direction adjustment between the X-axis scanning direction of the probe electrode 202 and the recorded data string may be performed by a so-called wobbling method as disclosed in Japanese Patent Publication No. 15727/1983, or by two-dimensionally Correction may be made when scanning is performed and data is demodulated by a technique such as pattern matching. FIG. 3 shows how data is recorded on the surface of a recording medium. 401 is a data bit, 641 is a probe electrode 20
2 is the trajectory a of the probe tip when scanning in the direction away from the edge portion 620, and 642 is the trajectory b of the probe tip when the probe electrode 202 moves toward the edge portion 120.

Furthermore, since two-dimensional scanning is performed along this edge portion 620, the probe electrode 202 can be guided to an arbitrary data recording area using this edge portion 620. For example, when a recording medium is first installed in a recording/reproducing apparatus, an error occurs in the positional relationship between the probe electrode 202 and the recording area of the recording medium due to the mechanical precision of the installation. This error is usually about 10 to 100 μm. This is much larger than the data recording area. However, by using this edge detection scan, data areas can be easily found and tracked.

As the recording medium forming method of the present invention, for example, the following method can be considered.

Although it is possible to use a conventionally known lithography technique to form the track, anisotropic etching of Si is used to form the edge angle at right angles. According to this method, regardless of the cross-sectional shape of the mask, the angle between the track side wall and the recording surface is equal to that of Si(110).
It is possible to obtain a track cross section of 88° to 92° depending on the cutting precision. That is, SiO2 as a substrate is 0.
A desired track pattern can be obtained by preparing Si (110) stacked to a thickness of 1 μm to 1 μm and performing anisotropic etching of the Si using the SiO 2 of the substrate as a mask.

Next, a conductive material to be an electrode layer is formed on the substrate, and then a recording layer is uniformly laminated over the entire surface. Specifically, the conductive material may be any material having high conductivity, such as Au, Pt, Ag, Pd, Al, In, and Sn.
, Pb, W, and alloys thereof, as well as graphite, silicide, and conductive oxides such as ITO. As a method for forming electrodes using such materials, conventionally known thin film techniques are sufficient. However, the electrode material formed directly on the substrate must be a conductive material that does not form an insulating oxide on the surface, such as noble metals or ITO.
It is desirable to use an oxide conductor such as, and whichever material is used, it is preferable that the surface thereof be smooth.

Further, the manufacturing method of the recording layer, and other conditions such as the material and manufacturing method of the probe electrode of the information processing device using the above recording medium are the same as those of the recording layer of the first recording medium of the present invention described above.

[0048]

[Examples] The present invention will be explained below with reference to Examples.

Example 1 An electrode substrate shown in FIG. 4(c) was produced.

First, a mica plate is cleaved in the atmosphere to form a smooth substrate 101.

Next, Au was epitaxially grown on the smooth substrate using a vacuum evaporation method. The conditions were a deposition rate of 5 Å/sec, an ultimate pressure of 2×10 −6 Torr, a substrate temperature of 400° C., and a film thickness of 5000 Å.

[0052] Next, a focused ion beam is used to create a width of 0.
Tracks of 1 μm, pitch of 1.0 μm, and depth of 5 nm were formed on a smooth electrode substrate. Focused ion beam is Au++
Using ions, acceleration voltage 40kV, ion current 14pA
The conditions were that the dose amount was 1×10 16 /cm 2 .

When the surface of the smooth electrode substrate prepared by the method described above was observed using STM, it was found that the depth of the track was 5 nm at 10 μm square, and the unevenness of the recording surface was less than 1 nm, and the track was clearly distinguishable. did it.

Example 2 A recording medium was manufactured by the manufacturing method shown in FIG.

First, a smooth electrode substrate was prepared in the same manner as in Example 1 (c). After that, a two-layer LB film (30 Å thick) of squarylium-bis-6-octyl azulene (SOAZ) was formed.
A recording layer was formed using (d). Below, SOAZLB
The method for forming the film will be described. A chloroform solution of SOAZ (concentration 0.2 x 10-3M) was spread on the water surface at 20°C, and after the solvent was evaporated, the surface pressure was increased to 20 mN/m to form a monomolecular film of SOAZ on the water surface. was formed. Next, the smooth electrode substrate was placed above the water surface while keeping the surface pressure constant.
The speed was 3 mm/mi in the direction perpendicularly across the OAZ monolayer.
Gently immerse and pull up the SOAZ 2-layer LB.
Form a film and use it as a recording medium.

When the surface of the recording medium prepared by the method described above was observed using STM in the same manner as in Example 1, it was found that the surface of the recording medium was 10 μm.
In m□, the track depth was 5 nm, and the difference between the highest and lowest values of the surface unevenness of the recording surface was 1 nm or less, and the tracks could be clearly distinguished.

FIG. 6 shows the recording medium created as described above.
Information was recorded, reproduced, and erased using the information processing device shown in FIG. The recording/playback method will be described below. The probe electrode 202 was scanned over the track pattern on the recording medium. FIG. 9 is a plan view of a portion of the recording medium. At this time, a bias voltage of -0.5V is applied to the probe electrode (Pt-Rh alloy) 202 with respect to the smooth electrode substrate, and the probe electrode 202 is moved using the driver 305 and actuator 204 so that the tunnel current becomes 0.1 nA. The position of the track 104 is detected by scanning while keeping the distance Z between the track 104 and the electrode layer 102 constant, and the detected track 1
The probe electrode 202 was scanned according to a scanning pattern such as 501 based on the position 04. Such track position detection utilizes the rapid change in track current between the probe electrode 202 and the track 104. A portion of such a scanning pattern, that is, 50% from the step of the track 104.
Recording was performed at a pitch of 10 nm starting at a position of 10 nm. Recording was performed using the electrical memory effect of the recording layer 103. That is, according to the information, a triangular wave pulse voltage having the waveform shown in FIG. 10 is applied to the recording layer 103 using the pulse power source 308,
A low resistance state was created in the application section. At this time, the tunnel current was 2 nA. In FIG. 10, the probe electrode 202 side is a + pole, and the electrode layer 102 side is a - pole. After recording, the recorded information was reproduced again according to the first scanning pattern 501. The reproduction bias voltage is set to 0.5 to avoid recording new information or erasing recorded information.
V, changes in tunnel current were measured, and information was reproduced. In the above playback experiment, the data transfer rate was 1Mb.
The bit error rate when expressed as ps was 1×10 −5 . When the pulse voltage shown in Figure 11 was subsequently applied to the information recording section and the information was reproduced again, it returned to the initial high resistance state (tunnel current = 0.1 nA), confirming that the recorded information had been erased. did it.

Example 3 After forming a smooth electrode substrate in the same manner as in Example 1,
A recording layer of polyimide LB film was formed in the same manner as in Example 2,
It was used as a recording medium.

When recording and reproducing experiments were conducted using such a recording medium in the same manner as in Example 2, the bit error rate was 2×10 −6 and erasing was possible.

Example 4 A mica plate was cleaved in the atmosphere, and a focused ion beam was used on the cleavage plane to form a pattern with a width of 0.1 μm and a pitch of 1.0 μm.
Tracks with a depth of 5 nm were formed on a smooth substrate. The focused ion beam was performed under the same conditions as in Example 1.

Subsequently, an electrode layer made of epitaxially grown Au was formed in the same manner as in Example 1 to obtain a smooth electrode substrate.

A recording layer consisting of two SOAZ layers was formed on the smooth electrode substrate in the same manner as in Example 2 to obtain a recording medium (FIG. 4(a)).

When recording and reproducing experiments were conducted using such a recording medium in the same manner as in Example 2, the bit error rate was 3×10 −5 and erasing was possible.

Example 5 HOPG (Highly-Oriented)
-Pyrolithic-Graphite), and then, in exactly the same manner as in Example 1, using a focused ion beam, it was cleaved to a width of 0.1 μm, a pitch of 1.0 μm, and a depth of 5 nm.
formed a track.

[0065] Thereafter, as a recording layer on the smooth substrate,
Four layers of polyimide LB films were accumulated (FIG. 4(b)). Note that the method for forming the polyimide LB film is as follows.

A dimethylacetamide solution in which polyamic acid (molecular weight approximately 200,000) was dissolved at a concentration of 1 x 10-3% (g/g) was diluted with separately prepared N,N-dimethyloctadecylamine in the same solvent at 1 x 10- 3M solution 1:2 (
v/v) to prepare a polyamic acid octadecylamine salt solution. This solution was spread on an aqueous phase consisting of pure water at a water temperature of 20° C. to form a monomolecular film on the water surface. The surface pressure of this monomolecular film was increased to 25 mN/m, and while keeping this constant, the substrate was stretched 5 m across the water surface.
The Y-type monomolecular film was accumulated by moving at a rate of m/min, dipping and pulling up. The polyamic acid monomolecular cumulative film was heated at 300° C. for 10 minutes to form polyimide.

The thickness of one polyimide layer was determined to be approximately 0.4 nm by ellipsometry.

When recording and reproducing experiments were conducted using such a recording medium in the same manner as in Example 2, the bit error rate was 2×10 −5 and erasing was possible.

Example 6 As shown in FIG. 5, a mica plate is cleaved in the atmosphere to form a smooth substrate 101.

Next, Au was epitaxially grown on the smooth substrate using a vacuum evaporation method to form an electrode layer. The conditions are: evaporation rate 0.5/sec, ultimate pressure 2×10
The temperature was −6 Torr, the substrate temperature was 400° C., and the film thickness was 500 nm.

[0071] Thereafter, an EB resist (PMMA: trade name OEBR-1000, manufactured by Tokyo Ohka) was applied onto the smooth electrode substrate, and a desired resist pattern was formed through exposure and development. EB drawing conditions are acceleration voltage 20kV
, the dose amount was 50 μC/cm2. (width 0.1μm
, pitch 1 μm) Subsequently, the Au electrode layer of the resist pattern was etched by ion etching to obtain a track pattern after the resist was peeled off. The ion etching conditions at this time were an etching gas of Ar, an ion energy of 500 eV, and a current value of 0.5 mV. Furthermore, methyl ethyl ketone was used as a stripping solution.

A recording layer of a polyimide LB film was formed on the smooth electrode substrate in the same manner as in Example 2 to prepare a recording medium.

[0073] Using the recording medium produced as described above,
When a recording/reproduction experiment similar to that in Example 2 was conducted, the bit error rate was 2×10 −6 and erasing was possible.

Comparative Example A smooth electrode substrate was prepared in the same manner as in Example 1. However, the track depth was 50 nm.

When the surface of the smooth electrode substrate was observed by STM in the same manner as in Example 1, the surface unevenness other than the tracks was 1 nm or less, but it was difficult to clearly distinguish the shape of the stepped portions of the tracks. there were. Further, when the tip of the probe electrode on the smooth electrode substrate was observed using an optical microscope, damage was found.

Example 7 First, as a substrate, a Si substrate with a layer of 1 μm of SiO2 was used.
(110) A wafer was prepared and cleaned. Polymethyl methacrylate (PMM), which is an EB resist, is deposited on such SiO2.
A) is applied, subjected to EB exposure and development to form a desired track pattern. The EB writing conditions at this time were an acceleration voltage of 20 kV and a dose of 50 μC/cm 2 . Next, using the resist as a mask, SiO2 was deposited to a depth of 0.1μ.
It was etched to look like m. CF4 for etching
Using gas, gas pressure 5 Pa, etching power 150 W
It was conducted under the following conditions. Thereafter, the resist was removed using methyl ethyl ketone.

Next, using a 40% KOH aqueous solution, SiO
Anisotropic etching of Si was performed at room temperature using No. 2 as a mask. The etching depth was 30 nm.

[0078] On the substrate prepared as described above, Au was formed as an electrode layer to a thickness of 50 nm using a vacuum evaporation method. At this time, a C film with a thickness of 5 nm was used as an undercoat layer.
formed r.

[0079] Thereafter, squarylium was used as a recording layer.
Bis-6-octyl azulene (SOAZ) at a concentration of 0.2
A chloroform solution dissolved at mg/ml was spread on an aqueous phase consisting of pure water at a water temperature of 20°C to form a monomolecular film on the water surface. Wait for the solvent to evaporate, and increase the surface pressure of the monomolecular film to 20
mN/m, and while keeping this constant, the substrate was gently immersed across the water surface at a speed of 5 mm/min, and then pulled up to accumulate two Y-type monomolecular films.

[0080] Recording, reproducing, and erasing experiments were conducted on the recording medium prepared by the method described above using the information processing apparatus shown in FIG. This will be explained below according to the drawings.

101 is a substrate of the recording medium, 201 is a stage, and a probe electrode 202 is placed on an arbitrary recording area on the recording medium.
It can move within a range of 10 mm in each of the X, Y, and Z directions to draw in the object. 801 is a cylindrical PZT (lead zirconate titanate) actuator with a probe electrode (Pt-
Rh alloy) 202 is used to scan along the data string on the recording medium, and is 2μ in each of the X, Y, and Z directions.
It can move up to m.

Probe electrode 202 is connected to current amplifier 810. The output of the current amplifier 810 is sent to the logarithmic compression circuit 8
11 and enters the sample hold circuit 812. The output signal (a) of the sample hold circuit 812 is input to a comparator 813, a peak hold circuit 814, and a high-pass filter 307, respectively.

The output (b) of the peak hold circuit 814 is connected to the error amplifier 304 and the low-pass filter 303. The output of the error amplifier 304 is connected to the ΔZ drive electrode of the cylindrical PZT801. On the other hand, the output of the low-pass filter 303 is passed through the attenuator VR3 to the comparator 81.
7 is input. Output of high-pass filter 307 (d
) is connected to the other input of comparator 817. Further, the output of the comparator 817 is input to a data demodulator of a data modulation/demodulation section 823.

The data modulation output of the data modulation/demodulation section 823 is connected to the pulse generator 821, and the DS bias voltage VB
1 and connected to the recording medium electrode.

The tracking control section 822 drives the cylindrical PZT actuator 801 via an up/down counter 819 and a D/A converter 820. The OR of the output of the comparator 813 for edge detection and the up control signal from the tracking control section 822 is connected to the up input (g) of the up/down counter 819 . On the other hand, the down input (f) of the up/down counter 819 is connected to the down control signal of the tracking control section 822 . The count output of the up-down counter 819 is converted into an analog voltage by the D/A converter 820 and the cylindrical PZT
801 is driven by ΔX.

Assuming a data reproducing operation, the trajectory of the probe electrode 202 on the recording medium is as shown in FIG. When the cylindrical PZT 801 starts data scanning from the probe position initially set by the stage 201 and detects the edge portion 620 along the trajectory represented by 642, the scanning of the probe electrode 202 is reversed and becomes the trajectory 641. After further scanning a certain distance, it is reversed again and proceeds in the direction toward the edge portion 620.

Repeat the above operation to remove the probe electrode 20.
2 detects a data bit string 401, it sequentially scans this data string while adjusting the scanning direction.

The scanning direction of the probe electrode 202 is determined by changing the variable resistor R2 using the scanning direction control signal (l) and changing the drive ratio of ΔX/ΔY of the cylindrical PZT actuator 801. Although not shown in FIG. 15, the detection of the appropriate scanning direction is determined by driving the wobbling voltage (k) by ΔY and monitoring the envelope signal (c) in which the peak of the tunnel voltage is held at this time.

Next, the operation during reproduction will be explained using the timing chart of FIG. 16 showing the states of each signal.

The tunnel current detected by the probe electrode 202 is amplified by the current amplifier 810 in FIG. This sample hold circuit 812 is in a through state during reproduction, and the output of the logarithmic compressor 811 is output as is.

The sample hold output (a) is set to the threshold voltage V by the edge detection comparator 813.
In comparison with B2, it is detected that the probe electrode 202 approaches the edge. However, VB2 is set to be larger than the output voltage due to the data string.

The edge-detected signal forces the up-down counter 819 to switch to up-counting operation, further up-counts a certain count value, and then switches to down-counting again. The up and down control signals of the up/down counter 819 at this time are shown in FIG. 16, respectively. Further, the ΔX drive output is shown in FIG. 16(h).

This operation allows the probe electrode 202 to scan without colliding with the edge portion 620 of the recording medium. The sample-and-hold output (a) is obtained by extracting a high frequency component, that is, a data information component, by a high-pass filter 307, and comparing the envelope signal (c) of the data string with an appropriately attenuated voltage by a comparator 817, and converting it into binary data. Obtain (e). The respective input signals of the comparator 817 at this time are shown in FIGS. 16(c) and 16(d). Further, the binarized signal is shown in FIG. 16(e). Note that the envelope signal (c) is obtained by integrating the peak hold output (b) using a low-pass filter 303.

Next, the operation during recording will be explained using the timing chart of FIG. 17 showing the states of each signal.

Output signal of sample hold circuit 812 (
a) is compared with VB2 by a comparator 813, and when it is detected that the edge portion is approaching, VB3 is first set to a predetermined level and a write operation begins. After waiting for time for the control of the distance between the probe electrode 202 and the recording medium to stabilize, the sample hold control signal (i) is put into a hold state in synchronization with the data write clock, and the pulse generator 821 generates a write pulse (j). . This data pulse is written until the probe electrode 202 performs inversion scanning, and as soon as the probe electrode 202 performs inversion scanning, the data writing operation returns to read scanning and is in a standby state until the next edge portion 120 is detected.

Next, the recording and reproducing method will be explained. A bias voltage of -0.5V is applied to the probe electrode 202 with respect to the substrate, and the probe electrode 202 is scanned while keeping the distance Z between the probe electrode 202 and the recording medium constant so that the tunnel current becomes 0.1 nA. After confirming that the track 104 has been formed, tracking is performed using the method described above, and it has been found that it is possible to scan the probe electrode 202 over any desired track without deviating from the track.

Next, information was recorded at a pitch of 50 nm while scanning the probe electrode 202 on the track. To record such information, the probe electrode 202 is placed on the + side and the electrode layer is placed on the - side so that the electrical memory material is in a low resistance state (ON).
A triangular wave pulse voltage shown in FIG. 18 was applied so as to change the state. Thereafter, the probe electrode 202 was returned to the recording start point and scanned over the track 104 again. As a result, a probe current of about 0.7 mA flows in data bit 401, indicating that it is in an ON state. In the above playback experiment, the bit error rate was 3×
It was 10-6.

Note that after applying the pulse voltage shown in FIG. 19 to the probe electrode 202 so that the electric memory material changes from the ON state to the OFF state, the recorded position was traced again, and as a result, all recorded states were erased. It was also confirmed that it had transitioned to the OFF state.

[0099] The thickness per SOAZ layer is small angle
As determined by line diffraction, it was approximately 1.5 nm.

Example 8 A track pattern and an electrode layer were formed in the same manner as in Example 7. Thereafter, two layers of polyimide LB film were accumulated to form a recording layer. The method for forming the polyimide LB film is as follows.

A dimethylacetamide solution containing polyamic acid (molecular weight approximately 200,000) dissolved at a concentration of 1 x 10-3% (g/g) was diluted with separately prepared N,N-dimethyloctadecylamine at 1 x 10-3% in the same solvent. 3M solution 1:2 (
v/v) to prepare a polyamic acid ontadecylamine salt solution. This solution was spread on an aqueous phase consisting of pure water at a water temperature of 20° C. to form a monomolecular film on the water surface. The surface pressure of this monomolecular film was increased to 25 mN/m, and while keeping this constant, the substrate was stretched 5 m across the water surface.
The Y-type monomolecular film was accumulated by moving at a rate of m/min, dipping and pulling up. The accumulated film was heated at 300° C. for 10 minutes to form polyimide. The thickness of each polyimide layer was determined to be approximately 0.4 nm using ellipsometry.

[0102] When recording and reproducing experiments were conducted in the same manner as in Example 7 using such a recording medium, the bit error rate was 1 x 10-5 and erasing was possible.

Example 9 A recording medium was produced in the same manner as in Example 7. However, a guide portion 901 was also formed for drawing the probe electrode into the track when creating the track pattern (FIG. 9).

[0104] When recording and reproducing experiments were conducted in the same manner as in Example 7 using such a recording medium, the bit error rate was 1 x 10-6 and erasing was possible.

[0105]

[Effects of the Invention] As described above, according to the present invention, the following effects can be obtained.

1) It is possible to form a smooth electrode with a difference of 1 nm or less between the highest and lowest surface irregularities other than tracks, so tracks can be clearly distinguished and data reproduction with a high S/N ratio is possible. Became.

2) Since it is possible to form a smooth electrode in which the difference between the highest and lowest values of surface irregularities other than the track is 1 nm or less, it is possible to obtain a high tracking frequency and to ensure sufficient tracking accuracy. Became.

3) Since the tracks are formed using ion beam technology, it has become possible to form narrow tracks. This has made it possible to perform tracking without sacrificing recording density.

4) Since tracks are formed using ion beam technology, it is now possible to form tracks with small steps. Therefore, the probe electrode is not damaged when it is swept, and the data error rate can be reduced.

5) Since the angle between the edge portion of the track side wall and the recording surface is a right angle, the S/N ratio of the edge detection signal is extremely high, so that the positional accuracy of the probe electrode is improved.

6) Since the conventionally known lithography technique can be used to form the edge portion, it is possible to form the lead-in portion of the probe electrode at the same time, thereby improving the compatibility of recording media.

7) Since the tracking operation based on the edge is performed on a two-dimensional data area, the processing time for the tracking operation is extremely small for one bit of data, and high-speed data reading and writing is possible. It becomes possible.

8) Since the data string is written based on the edge of the recording medium, when the probe electrode scans the data bit string during reading, it is possible to accurately predict the timing at which the data bit is recorded. , wobbling, etc. to ensure the determination of the scanning direction for the data string.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a recording medium according to the present invention.

FIG. 2 is a diagram of the frequency spectrum of a reproduced signal of a recording medium according to the present invention.

FIG. 3 is an example of a cross-sectional view of each manufacturing process of the recording medium according to the present invention.

FIG. 4 is an example of a cross-sectional view of a recording medium and an electrode substrate in the present invention.

FIG. 5 is an example of a cross-sectional view of each manufacturing process of the recording medium according to the present invention.

FIG. 6 is a configuration diagram of a playback device to which STM is applied.

FIG. 7 is a schematic cross-sectional view of a conventional recording medium.

FIG. 8 is a diagram of a frequency spectrum of a conventional reproduction signal.

FIG. 9 is a schematic diagram showing one form of the positional relationship between the probe electrode scanning pattern on the surface of the recording medium and the tracks and recording bits according to the present invention.

FIG. 10 is a diagram showing the waveform of an electric pulse necessary to transition the recording layer of the recording medium of the present invention from a high resistance state to a low resistance state.

FIG. 11 is a diagram showing the waveform of an electric pulse necessary to return a low resistance state region on a recording layer of a recording medium according to the present invention to a high resistance state again.

FIG. 12 is a cross-sectional view of the recording medium of the present invention.

FIG. 13 is a configuration block diagram of an information processing device according to the present invention.

FIG. 14 is a diagram showing the trajectory of the probe electrode of the information processing device according to the present invention on the surface of the recording medium.

FIG. 15 is a diagram showing an embodiment of an information processing device of the present invention.

FIG. 16 is a diagram showing signal waveforms of various parts during reproduction of the information processing apparatus of the present invention.

FIG. 17 is a diagram showing signal waveforms of various parts during recording of the information processing apparatus of the present invention.

FIG. 18 is a diagram showing a pulse signal waveform applied when recording on the recording medium of the present invention.

FIG. 19 is a diagram showing a pulse signal waveform applied when erasing the recording medium of the present invention.

FIG. 20 is a plan view of an embodiment of a recording medium used in the present invention.

FIG. 21 is an explanatory diagram of the electric memory effect.

[Explanation of symbols]

101 Board 102 Electrode layer 103 Recording layer 104 Truck 105 EB resist 201 XY stage 202 Probe electrode 203 Support 204 Z-axis linear actuator 205 X-axis linear actuator 206 Y-axis linear actuator 301 Amplifier 302 Logarithmic compressor 303 Low pass filter 304 Error amplifier 305 Driver 306 Stage drive circuit 307 High pass filter 308 Pulse power supply 309 Servo circuit 401 Data bit 402 Crystal grain 403 Data signal band 501 Scanning pattern 502 Data bit 620 Edge 641 Locus a 642 Trajectory b 702 Probe height detection circuit 703 Edge 705 Z-axis drive control circuit 706 X-axis drive control circuit 707 Y-axis drive control circuit 708 Data modulation circuit 721 Recording and playback area 801 PZT actuator 810 Current amplifier 811 Logarithmic compression circuit 812 Sample hold circuit 813 Comparator 814 Peak hold circuit 817 Comparator 819 Up/down counter 820 D/A converter 821 Pulse generator 822 Tracking control section 823 Data modulation/demodulation section 824 Stage control section 901 Guide part

Claims (17)

[Claims] Claim 1: The difference between the highest and lowest values of surface unevenness is 1 nm or less over a range of at least 1 μm□, and the surface has rectangular convexes or concave portions with a height or depth of 3 nm or more and 30 nm or less. A smooth electrode substrate featuring: 2. The smooth electrode substrate according to claim 1, wherein the surface is a metal thin film epitaxially grown on a cleavage plane of a crystal. 3. The smooth electrode substrate according to claim 1, wherein the rectangular convex portion or concave portion is formed by ion beam technology. 4. A recording medium comprising a recording layer provided on the smooth electrode substrate according to claim 1. 5. The recording medium according to claim 4, wherein the recording layer is made of a monomolecular film of an organic compound having an electric memory effect or a monomolecular cumulative film of the monomolecular film. 6. The recording medium according to claim 5, wherein the monomolecular film or the monomolecular cumulative film has a thickness in the range of 0.3 nm to 10 nm. 7. The monomolecular film or monomolecular cumulative film has L
7. The recording medium according to claim 5, wherein the recording medium is a film formed by method B. 8. The recording medium according to claim 5, wherein the organic compound has a group having a π electron level and a group having a σ electron level in the molecule. 9. A recording medium according to claims 4 to 8,
An information processing device that performs recording, playback, and erasing. 10. In a recording/reproducing method that utilizes a change in current flowing between a recording medium having an electric memory effect and a probe electrode, a recess is formed on the surface of the recording medium by anisotropic etching of Si, and the recess is used for tracking. A recording medium characterized by the following. 11. The recording medium according to claim 10, wherein the angle between the side wall of the track and the edge portion of the recording surface is 88° to 92°. 12. The recording medium according to claim 10, wherein the track is provided with a guide portion for drawing the probe electrode into the recording medium. 13. The recording medium according to claim 10, wherein the recording layer is composed of a monomolecular film of an organic compound having an electrical memory effect or a monomolecular cumulative film of the monomolecular film. 14. The recording medium according to claim 13, wherein the monomolecular film or monomolecular cumulative film has a thickness in the range of 0.3 to 10 nm. 15. The recording medium according to claim 13, wherein the organic compound has a group having a π electron level and a group having a σ electron level in its molecule. 16. The recording medium according to claims 10 to 15, a step of detecting an edge portion of a track provided on the recording medium, and a step of scanning a probe electrode at an angle with the edge portion. An information processing device comprising: a step of moving the recording medium or the probe electrode in a direction along the edge portion. 17. A recording medium according to claims 10 to 15, a step of detecting an edge portion of a track provided on the recording medium, and a step of determining an azimuth angle with respect to the edge of a data string to be recorded and reproduced, An information processing device comprising the step of scanning a probe electrode in a data column direction starting from an edge portion.