JPH02302945A - Recording medium and recording and reproducing device by using this medium - Google Patents

Abstract

PURPOSE:To allow the execution of excellent recording and reproducing by coating the upper part on the surface of the recording medium further with a material having the relatively higher insulating characteristic than the insulating characteristic of the recording medium. CONSTITUTION:The recording medium which has an electrical conductivity and melts and evaporates to cause a local change in surface shape when the medium is locally impressed with electric fields is used. For example, thin films of metals or metal compds., more specifically, Au, Al, Ag, Pt, further, Te-Ti alloy, Te-Se alloy, Te-C, H material or semiconductor thin films consisting of amorphous silicon, etc., are used. The film without having aromaticity consisting of a high-polymer film which is obtd. by polymerizing the monomer selected from the formula I or oxide film or nitride film is used as the film. In the formulas R1 to R4 denote H, halogen, or >=1 and <=10C alkyl group. The recording and reproducing applying the principle of a scanning type tunnel microscope is executed with one unit of the device. The high-density recording and reproducing of particularly several tens to several nm order are executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording medium used in a recording/reproducing apparatus applying the principle of a scanning tunneling microscope (hereinafter referred to as rSTMJ). The present invention also relates to a recording and reproducing method using the medium.

[Conventional technology]

In recent years, the use of memory materials has become the core of the electronics industry, 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 generally high density and large storage capacity are required.

Until recently, magnetic memories and semiconductor memories made of magnetic materials and semiconductors were the main materials, but with the recent advances in laser technology, optical memories have been developed,
Utilizing differences in reflectance, etc., enables high-density recording and reproduction on the order of μm. The recording medium of this optical memory is a thin film of metal or metal oxide, a thin film of organic dye, etc., and the heat of the laser beam is used to create holes or change the reflectance through evaporation, melting, etc. are recorded.

On the other hand, recently, S
TM has been developed [GBinni
ng) and others [Helvetica huizica acta (Hel
vetica Pysica Acta) J 55.7
26 (1982)). This STM has the advantage of being able to measure real-space images with high resolution, regardless of whether they are single crystal or amorphous, using low power without damaging the target due to current, and it can also be used for various materials even in the atmosphere. Because it can be used in many ways, it is expected to have a wide range of applications.

The above-mentioned STM utilizes the fact that a tunnel current flows when a voltage is applied between a metal probe (probe electrode) and a conductive substance to bring them close to a distance of about 1 nm. This current is extremely sensitive to changes in the distance between the two, and by scanning the probe while keeping the tunneling current constant, it is possible to depict the surface structure in real space, and at the same time, it is possible to depict the surface structure in real space. Various information can also be read. At this time, the resolution in the in-plane direction is 0. It is about lnm. Therefore, by applying the principle of STM, high-density recording and reproduction on the nanometer order is possible.

Therefore, in order to enable higher-density recording and reproducing on the nm order, which is even higher than on the μm order, optical memory has conventionally used electron beams, ion beams, or X-rays for recording and reproducing that applies the above-mentioned STM principle.

A method of recording by changing the surface state of a recording medium using electromagnetic waves such as light and reproducing it with STM, and a method of recording using a material that has a memory effect in the switching characteristics of voltage and current, such as a thin film layer of chalcogenide or π, as a recording medium. A method has been proposed in which recording and reproduction are performed using STM using a thin film layer of an electronic organic compound. In addition, a voltage that causes field emission is applied to the probe electrode of the STM, and R
Attempts have also been made to locally melt h-Zr alloy on the sample surface to form cone-shaped protrusions [Nie Stefer (U, 5tafer) et al. [Appl, Phys, Let.
t,) 51 (4).

July 27, 1987].

However, in conventional optical memory, recording and reproduction are performed by converging the laser beam with an optical system, so it is difficult to narrow down the beam diameter to less than the wavelength of the light, and improvements are being made such as using light with a wavelength as short as possible. , recording unit is μm
There is a problem in that the order is limited and it is not possible to increase the density any further.

On the other hand, although the above-mentioned attempts have been made to record and reproduce data using the principles of STM, no practical recording and reproduction apparatus has yet been developed.

Furthermore, the recording medium is made of a material that is electrically conductive and deforms by melting or evaporating when locally heated, but some materials have very low electrical conductivity and are thin films, so the recording medium The resistance value in the in-plane direction of the recording medium increases, and the current value flowing through the probe electrode during recording may vary depending on the location of the recording area, or heat may be generated due to the resistance of the recording medium itself, which may deviate from the optimal recording conditions. There is a problem.

In order to solve the above problems, the present inventors immediately developed a recording medium 2 whose surface shape changes locally by application of a local electric field, as shown in FIG. 4, and a probe electrode l to which a voltage can be applied. They are positioned facing each other and relatively movable in the vertical and horizontal directions, so that the distance between the recording medium 2 and the probe electrode 1 is kept constant during recording, and the distance between the recording medium 2 and the probe electrode 1 is maintained constant during reproduction. We provide a recording and reproducing device that is controlled at intervals that keep the tunnel current constant (Patent Application No. 1983).
-143738).

The symbols in FIG. 4 are the same as those used in FIG. 1.

[Problem to be solved by the invention]

By the way, in the recording medium shown in FIG. 4, if there is an adsorbed object on the surface of the recording medium 2, the current value that causes the recording medium to change its shape will not be uniform in each part of the recording medium, and the recording voltage during recording and reproduction will decrease. , a problem may arise in that the threshold value of the reproduction voltage cannot be specified.

Furthermore, since the surface of the recording medium is exposed to the air, deterioration of the recording medium due to changes over time, changes in humidity, etc. may become a problem.

[Means to solve the problem]

Therefore, the present invention solves the conventional problems by providing a recording medium in which the upper surface of the recording medium described in FIG. Provides a recording and reproducing method.

The recording medium 2 used in the present invention is made of a material that is electrically conductive and whose surface shape locally changes by melting or evaporating when a local electric field is applied. This material is, for example, a thin film of a metal or a metal compound, specifically, for example, Au, Al1. Ag.

Pt, further Te-Ti alloy, Te-3e alloy, Te-
C.

H thread material or a semiconductor thin film such as amorphous silicon can be used.

The film 13 is a non-aromatic polymeric material obtained by polymerizing a monomer selected from the general formula (R1-R4: H, halogen, or an alkyl group having 1 to 10 carbon atoms) or an oxide film. Alternatively, a film made of a nitride film is used.

Examples include polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, polyvinylidene chloride, polytetrafluoroethylene, polybutadiene, polychloroprene, and polyisoprene.

Examples include polyisobutylene and polyoxymethylene.

Polyisobutyl methacrylate, polyisobutyl acrylate, poly-n-octyl methacrylate, poly-n
- Octyl acrylate, etc.

Examples include ethylene oxide and polybischloromethylcyclooxabutane.

In addition, a film made of BN and Si3N4 is used as a nitride film, and a film made of SiO2, ZnO, A, i? 203°In
Films consisting of 2O3, Ti2O5, TiO2, Cr2O3, MgO can be used.

In addition to the vacuum evaporation method, various methods such as a spin code method, a bar code method, and an LB method can be used for producing a film of a polymer material. Sputtering, LPGVD, plasma CVD, and the like can be used as a method for producing the nitride film and oxide film.

The probe electrode 1 is made of tungsten or Pt-Ir.

A sharp needle-like object such as PT is used. In order to improve the resolution of recording and reproduction, it is preferable that the tip of the probe electrode 1 be sharpened by, for example, mechanical grinding, electrolytic polishing, or the like.

In the present invention, the vertical direction refers to the direction in which the recording medium 2 and the probe electrode 1 face each other, and the horizontal direction refers to the direction perpendicular to the vertical direction. Moreover, the relative movement of the recording medium 2 and the probe electrode 1 may be performed by moving only one of them, or by moving both at the same time.

FIG. 1 shows the configuration of a recording/reproducing apparatus using the recording medium of the present invention.

Reference numeral 1 in FIG. 1 is a probe electrode, which is used for recording and reproduction. 2 is a recording medium formed on a substrate 3; 13 is a film coated on the recording medium 2; 4 is a probe current amplifier that detects the tunnel current flowing between the probe electrode 1 and the recording medium 2; A Z-direction servo circuit that controls the movement of the probe electrode l in the Z direction, that is, the vertical direction;
It is a directional fine movement mechanism.

The Z-direction servo circuit 5 uses a Z-direction fine movement mechanism 6 to keep the probe current detected by the probe current amplifier 4 constant.
is driven to control the distance between the probe electrode 1 and the recording medium 2.

Reference numeral 7 denotes an XY direction fine movement mechanism composed of a piezoelectric element and the like that controls the movement of the probe electrode l in the XY directions, that is, in the lateral direction in the figure. Further, 8 is an XY direction coarse movement mechanism, which is driven by a piezoelectric element or electromagnetic means. These XY direction fine movement and coarse movement mechanisms 7 and 8 are controlled by a control circuit (not shown), and the probe electrode 1 can be moved to any position in the recording area of the recording medium 2.

Further, in the present invention, especially when the electrical resistivity of the recording medium 2 is relatively high, it is preferable to provide a base layer 14 having a lower electrical resistivity than the recording medium 2, as shown in FIG. .

Example 1 On a quartz glass substrate 3 on which molybdenum was EB-deposited, Au was deposited as the recording medium 2 by 300 sputtering methods, and a nitride film of Si3N4 was applied as the insulating film 13 by 20 people using the CVD method. was used.

As the probe electrode 1, a tungsten needle with an electrolytically polished tip was used.

Regarding the recording method, see Figure 2 for recording signal 1 to be recorded.
2 and a recording position signal on the recording medium 2 are sent from a control circuit (not shown). At that time, the probe electrode 1 is moved to the designated recording position by the fine and coarse movement mechanisms 7 and 8 in the XY directions.
When the distance to the recording medium 2 is controlled and the recording position is reached, a pulse voltage circuit 11 that generates a pulse voltage corresponding to the recording signal 12 applies a writing pulse voltage (high voltage) to the probe electrode l. 4 volts, width 100n
s) will be given. With this pulse voltage,
An excessive current flowed to the recording position, locally changing the surface shape of the recording medium 2, and a 30 nm image portion having a shape as shown in FIG. 3 was generated and recording was performed. At that time, when a pulse voltage is applied, the probe current changes rapidly, so the Z-direction servo circuit 5 adjusts H so that the output voltage remains constant during that time.
The OLD circuit is controlled to be turned on. Therefore, the distance between the probe electrode 1 and the recording medium 2 did not change significantly during recording, and stable recording was possible.

Next, regarding the reproduction method, the recording position to be reproduced is supported from a control circuit (not shown), and the probe electrode 1 is moved to the specified position by the XY direction fine movement and coarse movement mechanism 7.8, as in the case of recording. and start playback. At this time, the probe electrode 1 is controlled by the Z-direction servo circuit 5 so that a tunneling current is constant (
0,1 nA), the control signal given from the two-direction servo circuit 5 to the Z-direction fine movement mechanism 6 corresponds to the unevenness of the surface of the recording medium 2, and this control signal is sent to the reproduction signal demodulation circuit 9. A reproduced signal 10 was obtained by performing processing such as waveform shaping.

Furthermore, even after repeated use, no change in the S/N ratio was observed over time, and stable recording and reproduction could be performed.

Example 2 Recording medium 2 of Example 1. 13 films on 300 Au
was formed as follows.

0-3% (wt/wt) of polyisobutyl methacrylate using a mixed solvent of benzene/n-hexane (10/1).
(weight) was prepared. This was spread on an aqueous phase of pure water at a water temperature of 20° C., and the surface pressure was increased to 12 mN/m to form a monomolecular film on the water surface.

Using the aforementioned Au substrate, a two-layer monomolecular cumulative film was formed by dipping the substrate at a rate of 5 mm/min in a direction transverse to the water surface and pulling it up while keeping the surface pressure constant.

By repeating this operation, a monomolecular cumulative film of 6 layers (approximately 60 layers) was formed.

The same experiment as in Example 1 was conducted except that the above medium was used.

Recording and playback with good stability over time that can be used repeatedly was achieved.

〔Effect of the invention〕

According to the present invention, a single device can perform recording and reproduction using the STM principle, and in particular, the STM principle enables extremely high-density recording and reproduction on the order of tens to several nanometers. .

In addition, since the recording medium surface is protected by the coating, errors in recording and reproduction due to the presence or absence of adsorbed substances on the recording medium surface, differences, etc. are reduced, and environmental resistance is improved, and deterioration of the S/N ratio due to changes over time is reduced. I can do it.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of an embodiment of the recording/reproducing apparatus according to the present invention, FIG. 3 is a perspective view showing an example of a recording shape, and FIG. 4 is an explanation of the principle of the recording/reproducing apparatus according to the present invention. FIG.

Claims (2)

[Claims] (1) A recording medium whose surface shape changes locally by the application of a local electric field, and furthermore, the surface of the recording medium has general formulas ▲mathematical formulas, chemical formulas, tables, etc.▼, ▲mathematical formulas, chemical formulas,
There are tables, etc. ▼, ▲There are mathematical formulas, chemical formulas, tables, etc.▼ A recording medium on which a film made of a polymeric material, an oxide film, or a nitride film is formed. (2) A step of performing recording on the recording medium according to claim 1 by applying an electric field from a probe electrode to change the surface shape of the recording medium; A recording and reproducing method comprising the step of reproducing a state.