JPH01116940A - Method for recording and reproducing information - Google Patents

Abstract

PURPOSE:To perform recording and reproduction with extremely high density by implanting an element different from elements constituting a recording medium according to information and varying the work function between a recorded part and an unrecorded part, and detecting a tunnel current which varies as the work function varies and flows through a probe. CONSTITUTION:When information is recorded, the element different from the elements constituting the recording medium is implanted in the surface (conductive film) 2 of the discoid recording medium according to the information to be recorded to vary the work function of the implanted part (recorded part) 9. Then the conductive probe 13 is set at a predetermined distance from the surface 2 of the discoid recording medium where the information is recorded and a constant voltage of several mV - several V is applied between the probe 13 and recording medium. Then when the recording medium is rotated, the probe 13 scans on the surface of the recording medium and the tunnel current corresponding to the variation of the work function of the surface of the recording medium flows to the probe 13, so that the variation of this tunnel current is detected. Consequently, recording with extremely high density and sure reproduction are performed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for recording and reproducing information, and in particular, a method for recording information suitable for use in a system that requires high-density recording such as an AI (artificial intelligence) system. This relates to a reproduction method.

[Conventional technology]

Various methods have been known for high-density recording, and typical examples include magnetic recording and optical recording.

However, these recording densities are 0.0.
5 to 1 μmφ (i.e., when recording 1 bit of information,
The area of a circle with a diameter of 0.5 to 1 μm is required. ) is the limit.

In other words, in magnetic recording, the minimum domain diameter that can exist in a ferromagnetic material, that is, 10 nm, is considered to be the theoretically possible recording density, but in reality, there are restrictions on the device side such as the magnetic head used for recording and reproduction. 0.7 to 1 per bit from
It is approximately μmφ. Further, in optical recording, the recording density is limited by the spot diameter of the light used for recording and reproduction, and is approximately 0.5 to 1 μmφ per bit.

For this reason, various researchers are rushing forward with methods for recording and reproducing higher-density information, and recently, in particular, methods for recording and reproducing higher-density information have been developed as memory for AI (artificial intelligence) systems. is required.

As a method for recording at a higher density than magnetic recording or optical recording, a method using an electron beam has been proposed as described in Japanese Patent Application Laid-Open No. 59-221846.

Since the beam diameter of the electron beam can be narrowed down to about 1 to 2 nm, the recording pit diameter can be reduced. However, electrons are easily scattered due to their small mass, and the pit diameter and pit spacing cannot be reduced due to the proximity effect, which reduces the contrast between adjacent bits, and the recording density is 60 nm per bit.
The limit is approximately φ. Furthermore, if we consider its use as a memory for an AI system, its capacity must be approximately 100 GB, which is the capacity of a human brain cell, and in order to achieve this large capacity in a small area of approximately 100 mmφ, At least a recording density of about 30 nmφ per bit is required.

On the other hand, recently, scanning tunneling microscope Cscanning
tuneLing m1croscope; hereinafter abbreviated as STM. ) is rapidly developing a high-resolution microscopy technique known as microscopy.

STM utilizes a tunneling current that flows between a pair of electrodes (i.e., between a deep metal needle and a conductive sample) by allowing electrons to seep through a thin potential barrier (e.g., a vacuum layer) to Since it is possible to analyze the surface state of a conductive sample (that is, a conductive sample) with an extremely high resolution of 0.5 nm in horizontal resolution and 0.01 nm in vertical resolution, it is becoming an innovative analysis method in solid surface analysis and the like. Therefore, considering the high resolution of STM, it is considered possible to record and reproduce information at a recording density several orders of magnitude higher than that of conventional methods.

Regarding such STM, for example, "Scanning Tunneling Microscope" (Solid State Physics vol. 1.22. k3゜P17
6-P186 (1987)).

[Problem that the invention seeks to solve]

As described above, conventional magnetic recording, optical recording, and electron beam recording have a problem in that the recording density is limited by the recording spot diameter or spread due to scattering, and high-density recording cannot be achieved.

Therefore, an object of the present invention is to solve the problems of the prior art described above and provide an information recording method that can record information at an extremely high recording density, and a reproduction method for reproducing the information. It's about doing.

[Means for solving problems]

In order to achieve the above object, the present invention injects an element different from the element constituting the recording medium into the surface of a disk-shaped recording medium according to the information to be recorded, and creates a recording area and an unrecorded area. The information is recorded by changing the work function of the recording medium, and while applying a constant voltage between the deep needle located at a predetermined distance from the surface of the recording medium and the recording medium, the work function is changed. The information is reproduced by detecting the tunnel current flowing through the deep needle, which changes with the change.

[Effect]

First, the information recording method according to the present invention will be explained.

Information is recorded by injecting elements different from the elements constituting the disk-shaped recording medium onto the surface of a disk-shaped recording medium (hereinafter referred to as disk-shaped recording medium) according to the information to be recorded. This is done by changing the work function of the part. Specifically, there are the following two methods.

(1) A resist such as PMMA (polymethyl methacrylate) is applied to the surface of the disk-shaped recording medium, the beam diameter of the ion beam is narrowed down to about 30 nm using an electromagnetic optical system, and ion beam exposure is performed according to the information to be recorded. After that, remove the resist in the exposed area,
A thermal diffusion method in which the element to be implanted is implanted into the exposed area by performing heat treatment in an atmosphere containing the element.

(2) Beam diameter of ion beam is 30n by electromagnetic optical system
m, and on the surface of the disk-shaped recording medium,
An ion implantation method that implants ionized elements according to the information to be recorded.

Of these two methods, the ion implantation method is more preferable than the thermal diffusion method because it is superior in doping amount accuracy, uniformity, and concentration distribution control.

By the way, ions have a larger mass than electrons and are hardly scattered within the resist and disk-shaped recording medium. Therefore, as mentioned above, when an ion beam is used, the beam system and pattern diameter match, making it possible to irradiate them closely. You can also do it. Moreover, it is currently possible to narrow down the beam diameter of the ion beam to about 30 nm using an electromagnetic optical system.
For example, the bit diameter (see Figure 2 (a) below) is 30
nm.

If the track pitch is 60 nm, the recording density is 5
0 Gbits/cm” can be obtained.

Next, a method for reproducing information according to the present invention will be explained. The above-mentioned STM (ie, scanning tunneling microscope) technique is used to reproduce the information.

That is, as described above, a conductive deep needle is set at a predetermined distance from the surface of a disk-shaped recording medium on which information is recorded, and a voltage of several mV to several square meters is applied between the deep needle and the disk-shaped recording medium. Apply a constant voltage of

By rotating the disc-shaped recording medium, the deep needle scans the surface of the disc-shaped recording medium, and a tunnel current is applied to the deep needle according to a change in the work function of the surface of the disc-shaped recording medium. flows. Information is reproduced by detecting fluctuations in this tunnel current.

By the way, in STEM technology, methods for measuring the surface state of a solid can be roughly divided into two modes: a constant current mode and a variable current mode.

Therefore, two methods based on these two modes can be considered as detection methods for detecting changes in the work function on the surface of a disk-shaped recording medium.

That is, one method is based on the constant current mode, in which the position of the probe is controlled using a piezoelectric drive device or the like so that the tunnel current flowing through the probe is always constant. One possible method is to detect the change in the work function described above by detecting the distance between the probe and the surface of the disk-shaped recording medium.Another method is to use a method based on a variable current mode to The position of the probe is set in advance so that the distance between it and the surface of the shaped recording medium is a predetermined distance,
One possible method is to detect the change in the work function described above by detecting the tunnel current flowing through the probe.

Note that the information reproducing method described above is based on the latter method based on the variable current mode, but similar results can be obtained using the former method based on the constant current mode. Needless to say.

Furthermore, when considering the case where a disk-shaped recording medium is used as a memory, in order to obtain a high transfer rate (that is, perform high-speed playback), it is necessary for the probe to scan the surface of the disk-shaped recording medium at high speed. Therefore, it can be said that the latter method based on the variable current mode is more preferable.

By reproducing as described above, information can be reliably reproduced even if the recording surface density is 50 Gbits/cm'' as described above.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of an information recording apparatus that records information using a recording method according to the present invention.

In Figure 1, l is glass, plastic or S.
The surface of the substrate is flat and smooth. Reference numeral 2 denotes a conductive film made of W, which is formed with good uniformity on the substrate l by vacuum evaporation or sputtering. Note that the thickness of the conductive film 2 is not particularly strict, and it is sufficient as long as the surface is smooth.

Further, in this embodiment, the conductive film 2 is made of W as described above, but other constituent elements include C, Mo, etc.
etc. are suitable.

A disk is constituted by the substrate 1 and the conductive film 2 as described above.

Further, 3 is an ion implantation device, which generates an extremely fine ion beam with an energy of 20 to 200 keV. Reference numeral 4 denotes an ion beam focusing device, which focuses the ion beam to a beam diameter of about 30 nm.

5 is a beam modulator, which controls the intensity of the ion beam according to the recording signal. 6 is a disk rotation motor for rotating the disk described above, 7 is a vacuum chamber, and 8 is a vacuum pump.

Now, the recording method of this embodiment will be explained.

First, a tracking groove for performing tracking control is provided on the disk. The appropriate width of the tracking groove is 30 nm to 50 nm, and the groove depth is 0.5 nm. Tracking control is possible in principle if it is Inm or more, but considering the margin of processing technology, Inm
More preferably n or more. Therefore, in this embodiment, the groove width is 30 nm, and the groove depth is 1 nm.

Therefore, first of all, the inside of the vacuum chamber 7 is evacuated to about 1X10-'pa using the vacuum pump 8.

Next, the disk consisting of the substrate 1 and the conductive film 2 is rotated by the disk rotation motor 6. And beam modulator 5
With the beam intensity kept constant by
The Ga'' ion beam is irradiated onto the conductive film 2 of the disk through the Ga'' ion beam, and etched to form a tracking groove having a groove width of 30 nm and a groove depth of 1 nm.

After the tracking grooves are formed on the disk in this way, information is then recorded.

Therefore, first, the inside of the vacuum chamber 7 is evacuated to lXl0-'pa using the vacuum pump 8. next,
The disk is rotated by a disk rotation motor 6. Then, while controlling the beam intensity by the beam modulator 5 according to the recording signal, a Cs ion beam is irradiated from the ion implantation device 3 onto the conductive film 2 of the disk via the ion beam focusing device 4 to implant ions. I do. At this time,
The beam diameter of the Cs ion beam is determined by the ion beam focusing device 4.
It is focused to about 30 nm.

Note that the type of ion beam to be irradiated can be easily changed by simply replacing the target for generating the ion beam in the ion implantation device 3.

FIG. 2(a) is an enlarged plan view showing a portion of the tracking groove and recording portion formed on the surface of the conductive film 2 in FIG. A in Figure 2 (a)
- It is a sectional view in the A' line direction.

In FIGS. 2(a) and 2(b), numeral 9 is a recording portion into which ions are implanted by a Cs ion beam, and numeral 10 is a recording portion of Ga.
This is a tracking groove formed by etching with a positive ion beam.

That is, in the manner described above, the conductive film 2 is coated as shown in FIG. 2(a).
, by forming a tracking groove 10 as shown in (b) and implanting an element (i.e. Cs) different from the element (i.e. W) constituting the conductive film 2, , the work function of the recording section 9 shown in FIG. 2(a) is changed.

Table 1 below shows the relationship between substances and work functions.

In other words, as is clear from Table 1, when the element constituting the conductive film 2 of the disk is W and the implanted element is Cs as in this example, the work function of W constituting the conductive film 2 is 4.55 (eV), but by injecting Cs into W, the injected part, that is, the recording part 9 becomes an alloy W-C.
s, the work function of that part changes to 1.36 (eV).

As described above, information is recorded in this embodiment.

According to this embodiment, the bit diameter (see FIG. 2(a)) is 3
0 nm, so if the l rank pitch is set to 60 nm and the disk diameter is set to 10 cm, the recording surface density is 50 nm.
Gbits/cm” and recording capacity of 100
You can get 0 bytes.

Next, the reproduction method of this embodiment will be explained.

FIG. 3(a) is a perspective view showing an example of an information detecting part of an information reproducing apparatus that reproduces information by the reproducing method according to the present invention, and FIG. 3(b) is a perspective view of FIG. 3(a) in direction B. This is a side view when viewed from above.

In FIGS. 3(a) and 3(b), 11 and 12 are tracking probes, 13 is a reproduction probe, and 14 is a piezoelectric drive device.

The probes 11, 12, and 13 are each made of metal such as w or pt, and the radius of curvature R at the tip is about 1100n. However, there is a difference between the radius of curvature R at the tip and the horizontal resolution δ, δL
:xR"" Therefore, in order to read the recording part 9 with a bit diameter of 30 nm, the radius of curvature R of the tip of the reproducing deep needle 13 only needs to be R<900 nm.

In addition, in FIGS. 3(a) and 3(b), for convenience of explanation, the probes 11, 12, and 13 are shown in the recording section 9. It is drawn much smaller than the actual size ratio of the tracking groove 10.

Furthermore, the piezoelectric drive device 14 displaces each probe 11, 12° 13 in two-dimensional directions of the radial direction α and the perpendicular direction β of the disk.

Therefore, first, by the piezoelectric drive bag 't 14,
The reproduction probe 13 is placed at a distance Z from the surface of the conductor film 2 of the disk.
=0.5 nm. Next, playback probe 1
A constant voltage V=0.9 (V) is applied between 3 and the conductive film 2. The disk is then rotated by a disk rotation motor (not shown). As a result, each probe 11.
12 and 13 scan the conductive film 2. At this time, a tunnel current flows through the reproduction probe 13 in accordance with a change in the work function of the surface of the conductive film 2. Therefore, information is reproduced by detecting fluctuations in this tunnel current.

Here, the current density of the detected tunnel current is J y
(A/n m ”) and the work function of the surface of the conductor film 2 is φ (eV), the voltage V applied between the reproduction probe 13 and the conductor film 2 is 0.9 (V), Since the distance #Z between the probe 13 and the surface of the conductive film 2 is 0.5 nm, J t = 5.69X 10-'-JT・EXP (
−5,13J).

Current density J7 of tunnel current led by this second
The relationship between φ and work function φ is shown in FIG.

As mentioned above, when Cs is injected onto the conductive layer 112 of the disk made of W, the injected portion, that is, the recording portion 9
The work function of the area is 1.36 (eV), and the work function of the other part is 4.55 (eV), so the current density of the detected tunnel current is 1 to 1, as is clear from Figure 4.
This will result in a two-digit change. Therefore, it is possible to sufficiently reproduce recorded information.

Next, tracking control in this embodiment will be explained.

In this embodiment, tracking control is also performed by detecting tunnel current.

First, as shown in FIG. 3(b), the two tracking needles 11 and 12 are positioned so that the reproduction needle 13 is in the correct position in the disk radial direction (that is, the reproduction needle 13 is in the recording section 9).
The center lines of the tracking grooves 10 are set to be equidistant to the left and right when the center of the tracking groove 10 is at the scanning position. However, the tracking groove 10 is not necessarily
It does not have to be a mirror image of the center line of That is, the tracking needles 11 and 12 may be offset in the direction along the center line of the tracking groove 10 as long as they are equidistant from the center line. Further, from the center line of the tracking groove 10, each tracking deep needle 11.
The distance to 12 is 1/1 of the groove width of the tracking groove 10.
It may be less than 2, and is not particularly limited.

Next, a constant voltage is applied between the two tracking needles 11 and 12 provided as described above and the conductive film 2. As described above, when the disk is rotated by a disk rotation motor (not shown), each deep needle 1
1.12.13 scans the conductive film 2.

Therefore, the difference between the tunnel currents flowing through each of the tracking needles 11 and 12 is detected, and the piezoelectric drive device 14 is driven based on the difference to correct the tracking deviation of the reproduction needle 13 in the disk radial direction. In addition, the absolute value of the tunnel current flowing through the tracking deep needle 11 and 12 is detected,
Based on this, the piezoelectric drive device 14 is driven to correct the distance deviation between the reproduction deep needle 13 and the surface of the conductive film 2.

As shown in FIGS. 3(a) and 3(b), the servo system can be simplified if the two tracking needles 11, 12 and one reproducing needle 13 are integrated. , more preferred.

Further, in order to protect the surface of the disk from contamination by dust and the like from the outside world, it is more preferable that the disk and the deep needle be integrally sealed.

〔Effect of the invention〕

As explained above, according to the recording method according to the present invention,
It can record information at an extremely high recording density of 50 Gbits/cm", which is equivalent to 10 times that of conventional optical discs, making it a high-density, large-capacity memory suitable for AI (artificial intelligence) systems, etc. It is also possible to realize

Further, according to the reproducing method of the present invention, even information recorded at extremely high recording density as described above can be reliably reproduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a specific example of an information recording device that records information using the recording method according to the present invention, and FIG.
) is a plan view showing an enlarged part of the tracking groove and the recording part formed on the surface of the conductive film in FIG.
FIG. 2(b) is a sectional view taken along line AA' in FIG. 2(a), and FIG. 3(a) is information detection of an information reproducing/reproducing device that reproduces information by the reproducing method according to the present invention. A perspective view showing a specific example of the part, FIG. 3(b) is a perspective view of FIG. 3(a)
FIG. 4 is a side view when viewed from the direction, and is a characteristic diagram showing the relationship between the current density of tunnel current and work function in one embodiment of the present invention. Explanation of symbols 1... Substrate, 2... Conductive film, 3... Ion implanter, 4... Ion beam focusing device, 5... Beam modulator, 6... Disk rotation motor, 7... Vacuum chamber, 8... Vacuum pump, 9... Recording section, IO
... Tracking groove, 11.12... Tracking deep needle, 13... Reproducing deep needle, 14... Piezoelectric drive device. Agent Patent Attorney Akio Namiki Ml S (Neem 1 cycle device) Sufu mouth & use 7-push 2 Figure (α) (b)

Claims (1)

[Claims] 1. By locally implanting an element different from the elements constituting the recording medium onto the surface of the recording medium according to the information to be recorded, and changing the work function of the implanted portion, Information is recorded, and while applying a constant voltage between a probe disposed at a position away from the surface of the recording medium and scanning the surface of the recording medium, and the recording medium, the probe and the recording medium are Detecting the tunnel current flowing through the probe (or the distance between the probe and the surface of the recording medium) when the distance between the probe and the surface of the medium (or the tunnel current flowing through the probe) is constant. A method for recording and reproducing information, characterized in that the information is reproduced by detecting a change in the work function of the surface of the recording medium. 2. The method for recording and reproducing information as set forth in claim 1, wherein the element is implanted into the surface of the recording medium during recording by an ion implantation method. Method. 3. The method for recording and reproducing information as set forth in claim 1, wherein the element is implanted into the surface of the recording medium during recording by a thermal diffusion method. Method. 4. In the method for recording and reproducing information according to any one of claims 1 to 3, when reproducing the information, a Two tracking probes are prepared to scan over tracking grooves provided in advance on the surface of a recording medium, and while applying a constant voltage between these tracking probes and the recording medium, each tracking probe is By detecting a tunnel current flowing through the recording medium and controlling the position of the probe based on the detection result, the probe scans a portion of the surface of the recording medium where information is recorded. An information recording and reproducing method characterized by: 5. A method for recording and reproducing information according to any one of claims 1 to 4, wherein the recording medium has a disk shape.