JPH0869640A - Recording medium - Google Patents

Abstract

PURPOSE: To unnecessitate an imidating process and to simplify producing processes by using a prescribed polyimide film formed by the Langmuir-Blodgett's(LB) technique as a recording layer. CONSTITUTION: An electrode layer and a recording layer are laminated. The recording layer is made of a monomolecular film of soluble polyimide having <=100Å thickness formed by the LB technique. An imidating process requiring chemical treatment and heating and liable to cause the entering of a residual mixture into a recording layer and deformation due to difference in thermal expansion by heating is unnecessitated and the objective high quality recording medium is produced while simplifying producing processes.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the recording and / or recording of information.
The present invention relates to a recording medium and a recording / reproducing device that reproduce information.

[0002]

2. Description of the Related Art In recent years, with the development of an information-oriented society, the development of large-capacity memory has been extremely active. Generally, the performance required for memory is 1) high density and large recording capacity 2) fast recording / reproducing response speed 3) low power consumption 4) high productivity and low price, etc. The development of memory systems and memory media that realize such performance is extremely active.

Conventionally, the mainstream of memories has been magnetic memories and semiconductor memories using magnetic materials and semiconductors as materials.
In recent years, with the progress of laser technology, inexpensive and high-density optical memories using organic thin films such as organic dyes and photopolymers have appeared.

At present, technical development is underway toward miniaturization of unit memory bits in order to make these memories higher in density and larger in capacity, but based on a completely different principle from these conventional memories. A memory proposal has also been made. For example, one of them is the concept of a molecular electronic device in which each organic molecule has the function of a logic element or a memory element. It can be seen that molecular electronic devices have advanced the miniaturization of unit memory bits to the utmost limit, but until now, how to access individual molecules has been a problem.

On the other hand, recently, a scanning tunneling microscope (S
TM) was developed (G. Binning et al.
Phys. Rev. Lett. 49, 57 (198
2)) High resolution measurement in real space is now possible regardless of whether it is single crystal or amorphous. The STM utilizes the fact that a tunnel current flows when a voltage is applied between a metallic probe (probe electrode) and a conductive substance to bring them close to a distance of about 10 Å. This current is very sensitive to changes in the distance between the two, and the surface structure in real space can be drawn by scanning the probe so that the tunnel current is kept constant. Information can also be read. The resolution in the in-plane direction at this time is about 1Å. Therefore, if the principle of STM is applied, it is possible to perform high-density recording / reproducing sufficiently in atomic order (several Å). As a recording / reproducing method at this time, high-energy electromagnetic waves such as particle beam (electron beam, ion beam) or X-ray and visible
A method of recording by changing the surface state of an appropriate recording layer using energy rays such as ultraviolet light and reproducing by STM, or a material having a memory effect on the switching characteristics of voltage and current as the recording layer, for example, π-electron organic A method and the like have been proposed in which recording / reproduction is performed using STM using a thin film layer of a compound or chalcogenide. In addition, there is a proposal of a method and a device for capturing molecules on a substrate from a fluid by applying a voltage pulse, selectively writing data bits, and reading and erasing the data bits (JP-A-1-19675).
No. 1).

[0006]

In the recording / reproducing method as described above, when a thin film layer of a π-electron organic compound is used, polyimide may be used from the viewpoint of heat resistance. In this case, from the viewpoint of thinning, it is preferable to use a monomolecular film of polyimide or a monomolecular cumulative film formed by using the Langmuir-Blodgett method (hereinafter abbreviated as LB method) as the recording medium. Conventionally, in order to form a polyimide monomolecular film or a monomolecular cumulative film using the LB method, first,
By mixing long-chain alkylamines for introducing an appropriate degree of hydrophobicity to polyamic acid, a film is formed as a polyamic acid amine salt, and then by chemical treatment or heating and baking,
A method has been employed in which a polyimide film is formed by performing a dehydration cyclization (imidization) reaction and a deamination reaction. However, in the case of the imidization method by chemical treatment, there is a risk that residual impurities contained in the imidization solution may be mixed in the recording medium with the imidization treatment. In the case of imidization by heat treatment, depending on the combination of the heating conditions and the electrode substrate, there is a concern that defects may occur due to the difference in coefficient of thermal expansion between the polyimide film and the substrate, or the electrode substrate may be deformed or deteriorated. It is an object of the present invention to provide a recording medium having a recording layer made of a polyimide film, which does not have the drawbacks of the conventional techniques, and a recording / reproducing apparatus having the recording medium.

[0007]

According to the present invention, there is provided a recording medium having at least an electrode layer and a recording layer laminated, the recording layer comprising a soluble polyimide film, and the recording medium. This is a recording / reproducing device.

In the present invention, by using the soluble polyimide for the recording layer, the step of chemical treatment or heat treatment using an imidizing solution for converting the polyamic acid amine salt formed on the electrode substrate into polyimide can be omitted. Therefore, it is possible to eliminate mixing of residual impurities contained in the imidization solution, and it is possible to provide a recording medium free from defects and deformation by not performing heat treatment at high temperature.

Polyamic acid, which is a precursor of polyimide, is generally obtained by subjecting a carboxylic acid anhydride and a diamine to a condensation reaction. The soluble polyimide used in the present invention is a carboxylic acid anhydride moiety and / or a diamine. Dimethylacetamide (DMA) because it contains siloxane bond, fluoride, alkyl group, etc.
C), N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), dimethylformamide (DMF) and other aprotic polar solvents, and low-boiling point solvents such as chloroform and acetone. is there. Such soluble polyimides are synthesized from the carboxylic acid anhydrides and diamines listed below. As carboxylic acid anhydride

[0010]

Embedded image And the like. As the diamine,

[0011]

Embedded image And the like. It is also possible to use a copolymer using a carboxylic acid anhydride and / or diamine having two or more kinds of polymer main chains.

In the present invention, the above-mentioned soluble polyimide is dissolved in the above-mentioned solvent at a desired concentration, and a monomolecular film or a monomolecular cumulative film is formed on the electrode substrate by the LB method.
It is preferable to use a recording medium from the viewpoint of thinning and controlling the film thickness.

In this case, the concentration is not particularly limited, but it is preferably in the range of 1 × 10 ⁻⁷ to 1 × 10 ⁻³ M from the viewpoint of developability.

To form a polyimide monolayer, a solution of soluble polyimide adjusted to a desired concentration is gently spread on the surface of water. Here, the water phase is 2 to 25 ° C.
Pure water is generally used, but various metal ions may be added or the pH may be adjusted by adding acid or alkali. Next, the soluble polyimide spread on the water surface is compressed to form a soluble polyimide monomolecular film on the water surface.

While keeping the surface pressure of this monomolecular film constant, a solid substrate is immersed in a direction crossing the monomolecular film on the water surface,
By continuously pulling up, two layers of Y-type monomolecular film can be accumulated on the solid substrate.

In order to transfer a monomolecular film of soluble polyimide onto a substrate, in addition to the above-mentioned vertical dipping method, horizontal deposition method,
It is also possible to use a method such as a rotating cylinder method.

The MIM structure element (FIG. 6) in which the above-mentioned monomolecular cumulative film 43 is sandwiched between the metal electrodes 41 and 42 is shown in FIG.
The current-voltage characteristic as shown in FIG. 8 is shown. Two states (O
The N state and the OFF state) are transited to each other by applying a voltage equal to or higher than the threshold value, and each state is maintained at the threshold voltage or lower. These characteristics range from a few Å to a few hundred
Although it is expressed in a film thickness of 0Å, a film thickness of several Å to 500Å is preferable, and a film thickness of 10Å to 200Å is most preferable.

Any electrode material may be used as long as it has a high electric conductivity. For example, Au, Pt, Ag, Pd, Al, I.
Numerous materials including metals such as n, Sn, Pb, and W, alloys thereof, graphite and silicide, and conductive oxides such as ITO can be cited, and they can be applied to the present invention. As a method of forming an electrode using such a material, a conventionally known thin film technique can be adopted.
However, the surface of the electrode material formed directly on the substrate is LB.
When forming the film, it is preferable to use a conductive material that does not form an insulating oxide film, for example, a noble metal or an oxide conductor such as ITO.

The metal electrode of the recording medium is preferably used when the insulating property of the recording layer is high, but the metal electrode may not be used as long as the recording layer exhibits semiconductor properties.

The distance between the probe electrode and the recording medium is controlled by a repulsive force acting between the probe electrode and the recording medium, scanning is performed on the surface of the recording medium in a close state until the repulsive force acts, and a voltage is applied between the two. Recording, reproduction, and erasing can be performed by applying a desired voltage by a circuit. However, when recording, reproducing, or erasing using the recording medium of the present invention, the distance between the probe electrode and the recording medium can be controlled only by repulsive force. Alternatively, tunneling current or field emission current may be used.

[0021]

【Example】

 Example 1 A recording medium was prepared as follows.

The cleaved mica substrate 101 is heated to a substrate temperature of 45.
The temperature was kept at 0 ° C., and Au was epitaxially grown to a film thickness of 1000 Å to obtain an electrode substrate.

Next, equation (1)

[0024]

[Chemical 3] Soluble polyimide represented by the following formula is dissolved in dimethylacetamide (DMAC) (concentration converted to monomer: 1 × 10
^-3 M), this solution was spread on an aqueous phase made of pure water having a water temperature of 15 ° C. to form a monomolecular film on the water surface. After evaporation of the solvent, the surface pressure was increased to 5 mN / m. Keeping the surface pressure constant, speed 3mm in the direction across the surface of the substrate.
After gently immersing the film at 3 min / min, the film was gently pulled up at 3 mm / min to form a two-layer Y-type monomolecular cumulative film. By repeating such an operation, a four-layer polyimide monomolecular cumulative film 103 was formed.

The recording medium formed in this manner is used as an AFM.
When the surface property was evaluated using, it was found to have a uniform and smooth surface.

In order to know the film thickness of this polyimide film, 40 layers of polyimide monomolecular cumulative film were formed on the Si substrate by the above-mentioned method, and the film thickness per layer was obtained by using the ellipsometry method. It was 4Å / layer.

The above recording medium was installed in the recording / reproducing apparatus shown in FIG. Reference numeral 1 is a recording medium, 2 is a probe electrode provided facing the recording medium 1, 3 is a cantilever to which the probe electrode 2 is attached, and 4 is a support for the cantilever 3. The probe electrode 2 implants Si ions at one end of the cantilever 3 and selectively grows Si on this Si to form a pyramidal crystal 201 having a sharp tip, and then A
u is vapor-deposited to a thickness of 300Å by a vacuum vapor deposition method to form a conductive layer
2 was formed and created. The cantilever 3 allows the probe electrode 2 to be displaced in the Z-axis direction. The medium 1 can be moved by a small amount in the x, y and z-axis directions by the xyz fine movement device 5, and further can be moved by the xyz coarse movement device 6. Cantilever support 4 and xyz
The coarse movement device 6 is fixed to the base 7. The base 7 is installed on a seismic isolation table (not shown).

Next, recording and reproduction were carried out in this recording / reproducing apparatus.

While the detection current is being monitored, the distance between the probe electrode 2 and the recording medium 1 is brought close to the state shown as a region in FIG. 3, and in this state, the control circuits 8 of the xyz fine movement device 5 and the xyz coarse movement device 6, After applying the triangular wave pulse voltage having the waveform shown in FIG. 4 which is the threshold voltage V _th ON or higher for holding the output of No. 9 and generating the ON state between the probe electrode 2 and the Au electrode layer 102. , Again 100 mV
When a measurement was performed by applying a bias of No. 2, a current of about 8 μA flowed, and it was shown that it was in an ON state.

Next, a triangular wave pulse voltage having a waveform shown in FIG. 5, which is a voltage equal to or higher than the threshold voltage V _th OFF changing from the ON state to the OFF state, is applied to the above described recording bit in the ON state, and then again. It was confirmed that when a bias of 100 mV was applied, it returned to the OFF state at a current value of about 1 nA.

Example 2 The recording medium used in this example has a recording layer 103 on an Au electrode layer 102 formed in the same manner as in Example 1. The recording layer 103 was formed as follows.

In the same manner as in Example 1, a solution prepared by dissolving the soluble polyimide represented by the formula (2) in a monomer-converted concentration of 1 × 10 ⁻³ M with chloroform was prepared.

[0033]

[Chemical 4] Six layers of soluble polyimide monomolecular films were formed from this solution in the same manner as in Example 1 to form recording layers.

The recording medium formed in this manner is used as an AFM.
When the surface property was evaluated using, the film had a uniform and smooth surface, and the film thickness per layer was determined in the same manner as in Example 1, and it was 4Å / layer.

In this embodiment, the recording medium is applied to the recording / reproducing apparatus as shown in FIG. In this device, a Si substrate 4 having a plurality of cantilever beams is fixed to a support base 13,
The support 13 is attached to the base 7 via at least three piezoelectric elements 14. These piezoelectric elements 14 are individually driven by the piezoelectric element control circuit 12 controlled by the micro computer 11. Further, a voltage is applied to each probe electrode 2 by the voltage application / current detection circuit 10 ′, and the current flowing between each probe electrode 2 and the recording medium 1 is detected separately. The other structure is the same as that used in the first embodiment.

The recording medium 1 is set in the xyz fine movement device 5, and both are brought close to each other with a bias of 100 mV applied between the probe electrode 2 and the Au electrode 102. At this time, the piezoelectric element 14 is controlled and adjusted so that all the probe electrodes uniformly approach the recording medium 1, and all the probe electrodes are brought closer to the state of area a in FIG. Under this condition, while the medium 1 was moved in the x direction by the xyz fine movement device 5, recording, reproducing, and erasing operations similar to those in Example 1 were performed in parallel for each probe electrode 2, and recording with each probe electrode I was able to play and erase.

[0037]

According to the present invention, by using a soluble polyimide for the recording layer, the imidization step can be omitted, and as a result, (1) the recording layer from the imidization solution in the imidization step. It is possible to avoid the risk of contamination with residual impurities and the generation of defects due to heating, and the risk of deformation of the electrode layer or the substrate due to heating is eliminated, and (2) because the imidization step is unnecessary, It has become possible to simplify the manufacturing process of the recording medium.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of an information recording / reproducing apparatus of the present invention.

FIG. 2 is an explanatory view schematically showing another example of the information recording / reproducing apparatus of the present invention.

FIG. 3 is a characteristic diagram showing changes in a current flowing between the probe electrode and the surface of the recording layer obtained when the distance between the probe electrode and the surface of the recording layer is changed, and a change in force acting between the two.

FIG. 4 is a diagram showing a pulse voltage waveform for recording.

FIG. 5 is a diagram showing a pulse voltage waveform for erasing.

FIG. 6 is an M in which the recording layer used in the present invention is sandwiched between metal electrodes.
6 is a schematic diagram of the configuration of an IM element.

7 is a diagram showing current-voltage characteristics obtained by the device of FIG.

FIG. 8 is a diagram showing current-voltage characteristics representing the memory effect obtained by the device of FIG.

[Explanation of symbols]

 1 recording medium 2 probe electrode 3 cantilever 4 cantilever support 5 xyz fine movement device 6 xyz coarse movement device 7 base 8 xyz control device for fine movement device 9 xyz coarse movement device control circuit 10 voltage application and current detection circuit 11 Microcomputer 12 Control Circuit of Piezoelectric Element 13 Support 14 Piezoelectric Element 41 Metal Electrode 42 Metal Electrode 43 Monomolecular Accumulation Film 101 Substrate 102 Electrode Layer 103 Recording Layer 201 Si Crystal 202 Conductive Layer

Claims (8)

[Claims] 1. A recording medium in which at least an electrode layer and a recording layer are laminated, wherein the recording layer comprises a soluble polyimide film. 2. The recording medium according to claim 1, wherein the soluble polyimide film is a monomolecular film formed by the Langmuir-Blodgett method. 3. The recording medium according to claim 1, wherein the soluble polyimide film is a monomolecular cumulative film formed by the Langmuir-Blodgett method. 4. The recording medium according to claim 1, wherein the recording layer has a thickness of 100 Å or less. 5. A recording / reproducing apparatus comprising a recording medium in which at least an electrode layer and a recording layer are laminated, and the recording layer is made of a soluble polyimide film. 6. The recording / reproducing apparatus according to claim 5, wherein the soluble polyimide film is a monomolecular film formed by the Langmuir-Blodgett method. 7. The recording / reproducing apparatus according to claim 5, wherein the soluble polyimide film is a monomolecular cumulative film formed by the Langmuir-Blodgett method. 8. The recording / reproducing apparatus according to claim 5, wherein the recording layer has a thickness of 100 Å or less.