JPH01133239A - Information recording and reproducing system and information recording medium - Google Patents

Abstract

PURPOSE:To enable high-speed transfer at a high recording density by subjecting the spacing between a conductive needle and information recording layer to servo control so as to obtain a reference value with the average value of tunnel current as a reference at the time of reproducing and the average value of the tunnel current before intensification for the purpose of recording as a reference at the time of recording. CONSTITUTION:A servo system for controlling the spacing between the information recording layer 15 and the information recording layer 4 controls the spacing between the conductive needle 15 and the information recording medium 1 in the perpendicular direction thereof by driving piezo-electric ceramics 45c to expand or contact in such a manner that the average value of the tunnel current attains the specified value. The spacing between the conductive needle 15 and the recording layer 4 is so maintained and controlled as to attain the reference value with the average value of the tunnel current obtd. by averaging the tunnel current fluctuating according to the presence or absence of recording as a reference at the time of recording. The spacing between the conductive needle and the recording layer 4 is maintained with the average value of the tunnel current at the point of the time before intensification of the tunnel current for the purpose of recording as a reference and is subjected to the servo control by the piezo-electric ceramics 45c so as to obtain the reference value at the time of recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-density information recording/reproducing system and an information recording medium used therefor.

[Conventional technology]

The most important issue in current information recording technology is improving recording density. Compared to conventional horizontal magnetic recording technology, optical recording using optical recording devices that use laser light or magneto-optical recording devices that use a combination of laser light and magnetic fields can reduce the recording spot to the wavelength of light (about 1 μm). (As a result, the recording density has improved by almost two orders of magnitude. However, in order to further increase the density of optical recording, it is necessary to use a laser beam with a shorter wavelength and an optical system that can be used for it.) As far as optical recording is concerned, it is difficult to significantly improve recording density with current technology.

In recent years, scanning tunneling microscopes (S(anning Tu
A high-resolution microscope using tunneling effect called tunneling microscope HSTM has been developed.

A discussion of STM can be found in ``Proceedings of the 1st International Conference on Scanning Tunneling Microscopy Technology.
s of The First International
nal Conference on Scanning
Tunneling Microscopy), 5
surface science, volume 181.
Nos, 1/2. March (1) 1987 J. STM is several angstroms horizontally,
In the vertical direction, it is possible to analyze material surface features with a high resolution of 1 angstrom or less. Therefore ST
The recording density of an apparatus that reproduces information recorded on the surface of a recording medium using the principle of M can be several orders of magnitude higher than the recording density of the information recording and reproducing apparatus that uses the laser beam.

An information recording/reproducing apparatus utilizing the principle of STM having such characteristics is described by Kazan et al. in Japanese Patent Application Laid-open No. 80536/1982, and will be briefly explained below.

That is, the recording medium is composed of at least a conductor layer and a signal recording layer stacked one on top of the other. When the conductive layer is brought close to a conductive needle serving as a pickup with an extremely small distance therebetween, a tunnel current flows between the two. At this time, if the signal recording layer is located between the two, the tunnel current flows through the signal recording layer.

When the tunnel current is strengthened, a change in the work function or a change in the surface shape of the signal recording layer occurs, and this is utilized for recording. Also, during playback, when the conductive layer is brought close to the conductive needle with an extremely small gap, the tunnel current that flows between the two causes the work function of the signal recording layer located between the two. Since a current change occurs due to a change in the current or a change in the surface shape, it is possible to reproduce the recording (change in work function or change in the surface shape) in the signal recording layer.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology that utilizes the STM principle, no consideration is given to tracking control for the track on the information recording medium of the pickup, and tracking control is not required when actually configuring an information recording/reproducing apparatus that utilizes the STM principle. There seems to be a problem with. Further, in the above-mentioned conventional technology, the pickup is servo-controlled to move up and down depending on whether or not there is recording on the surface of the recording medium. That is, although the strength of the tunnel current varies depending on the presence or absence of recording on the surface of the recording medium, servo control is performed by applying feedback control such as moving the pickup up and down so that the tunnel current remains constant.
If the presence or absence of recording on the surface of a recording medium is expressed by unevenness, the pickup is servo-controlled to maintain a constant distance from the surface of the recording medium by moving up and down to follow the unevenness. It turns out. Because of this vertical movement, the control speed of the pickup cannot be made very fast, and as a result, it has been difficult to make the signal readout speed high.

An object of the present invention is to provide an information recording/reproducing method using the STM principle that has high information recording density, high signal readout speed, and stable tracking control, and an information recording medium used therein. It is in.

[Means for solving problems]

Among the above purposes, in order to increase the signal recording and reproducing speed, the interval is controlled using the average value of the tunnel current so that the average interval between the pickup and the information recording medium becomes a predetermined value. That is, instead of moving the pickup up and down depending on whether recording is being performed or not, servo control is applied to maintain the pickup at the average position of the up and down movement.

In addition, for tracking control of the pickup to perform stable tracking, an information recording medium with a structure that can apply a tracking signal to the track of the information recording medium is used, and the position in the track direction is determined by the tracking signal detected from the track by the pickup. control.

[Effect]

Since the pickup is controlled so that the average distance between the pickup and the information recording medium is a predetermined value, there is no need to move the pickup depending on the strength of the tunnel current depending on whether recording is being performed or not, and the read signal speed is controlled by the pickup servo system. It is possible to read out high frequency signals because there is no restriction on the frequency band. In addition, tracking is performed so that the magnitude of the tracking signal guided from the target track of the information recording medium is maximized, or the magnitude of the tracking signal guided from two tracks adjacent to the target track is equal. Through this control, stable tracking is possible without deviating from the target track.

〔Example〕

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

FIG. 1 is a block diagram showing the configuration of an information recording and reproducing system as an embodiment of the present invention. In the figure, reference numeral 1 denotes an information recording medium, and the figure shows a cross-sectional view of the medium in a direction perpendicular to its tracks. The information recording medium 1 is provided by, for example, embedding a conductor layer 3 of polysilicon, metal, semiconductor, etc. on the surface of an insulating substrate 2 of glass, silicon, sapphire, etc., and further has an information recording layer 4 thereon. When viewed from above, it is shaped like a disk or a card. The information recording layer 4 is a material whose properties change and work function changes due to a tunnel current flowing between the conductive layer 3 and the conductive needle 15 as a pickup during recording, and whose state is maintained. It may be any material that has a surface shape that changes due to tunnel current during recording and maintains that state. The conductive needle 15 serving as a pickup is used for recording and reproducing information signals with the information recording medium 1, and is a tungsten needle whose tip is etched to a thickness of 061 μm or less. By making the tip of the needle 15 thinner in this way, high-density recording and reproduction becomes possible.

In order to record and reproduce information, the distance between the information recording medium 1 and the conductive needle 15 as a pickup needs to be large enough to detect a tunnel current due to the tunnel effect. Therefore, the distance and relative position between the needle 15 and the information recording medium 1 are controlled by an actuator 40 to which the needle 15 as a pickup is attached.

The actuator 40 has a fixed base 48a.

48b, a movable base 48c, and piezoelectric ceramics 45a, 45b, 45c, etc., such as PLZT and PZT. That is, the bases 48a and 48b are each fixed at appropriate fixed positions by means not shown. The movable base 48c is connected to the fixed base 48a via the piezoelectric ceramic 45a and the insulator 47, and is also connected to the fixed base 48b via the piezoelectric ceramic 45b and the insulator 47. Furthermore, the movable base 48c has a piezoelectric ceramic 45
c and is connected to a conductive needle 15 as a pickup via an insulator 47.

Therefore, if a control voltage is now applied between the electrodes 4a afl and 46 b'' to expand and contract the piezoelectric ceramic 45c, the needle 15 can be moved up and down with respect to the information recording medium 1 to adjust the distance between them. Also, the electrodes 46a' and 46
b' or between the electrodes 46a and 46b to expand and contract the piezoelectric ceramic 45b or the piezoelectric ceramic 45a, the needle 15 can be moved in the left-right direction with respect to the information recording medium 1. Tracking control can be performed by

Next, a method of generating a signal for driving the actuator 40 in order to control the distance between the needle 15 as a pickup and the information recording medium 1 will be explained.

The tunnel current 16 flowing between the conductive needle 15 and the information recording medium 1 changes depending on the distance between the conductive needle 15 and the information recording layer 4, the work function of the surface of the recording layer 4, the bias voltage 41, etc. Further, the work function of the surface of the information recording layer 4 changes depending on the written signal. However, by using a modulation method that does not have a DC component, such as 8-14 modulation ffl (EFM), which is used in compact discs, as a signal modulation method when recording information, the average value of the tunnel current (or low frequency components) can be made unaffected by the recording signal. Further, by keeping the bias voltage 41 constant, variations in the tunnel current 16 due to variations in the bias voltage 41 can be prevented. In that case, the low frequency component of the tunnel current 16 changes depending only on the distance between the conductive needle 15 as a pickup and the information recording layer 4. Since the magnitude of the tunnel current 16 is minute, ranging from several nA to several hundred nA, it is converted into a voltage by a current-voltage conversion amplifier (I-V converter) 37 and amplified, and then a voltage signal (hereinafter referred to as a voltage signal) corresponding to the tunnel current is generated. , a detection signal), and this detection signal 42 is used in subsequent processing.

The detection signal 42 is input to a low pass filter (LPF) 17 and a bypass filter (HPF) 1B, and is separated into a low frequency component used for controlling the distance between the conductive needle 15 and the information recording medium 1 and a high frequency component used for information reproduction. do. The average value (low frequency component) of the tunnel current signal separated by the LPF 17 is subjected to necessary processing in the detector 26, phase compensation circuit 39, and amplifier 28, and then applied to the actuator 40 (more specifically, the electrode 46a''). Front-end hold circuit 49
You may or may not use a prefix hold, but
When reproducing the signal, the electrode 46 is directly connected without pre-holding.
In addition to "A", when recording, the pre-hold circuit 4 uses the recording control signal as the hold control signal 50 as described later.
In addition to 9, perform a pre-hold.

A servo system for controlling the distance controls the vertical position (distance) of the conductive needle 15 with respect to the information recording medium 1 by driving the piezoelectric ceramic 45C to expand and contract so that the average value of the tunneling current is constant. Therefore, the average distance between the conductive needles 15 and the information recording layer 4 can be controlled to be substantially constant.

On the other hand, the information recorded in the information recording layer 4 is
The high frequency component of the detection signal separated by 8 is input to the signal processing circuit 43 for demodulating the recorded information, and the recorded information can be reproduced by being processed.

As explained above, the conductive needle 15 as a pickup
By controlling the distance between the information recording medium 1 and the information recording medium 1, it is no longer necessary to control the tunnel current 16 so that it always remains constant in response to changing signals, as was done in the past. can be made wider than the response frequency band of the servo system. As a result, the bit rate of the recording signal can be significantly increased.

Although not shown in the figure, signal recording is performed by superimposing a recording signal on the bias voltage 41 to increase the tunnel current 16 and cause a change in the information recording layer 4. In addition, to control the distance between the conductive needle 15 and the information recording medium 1 during recording, a pre-hold circuit is used to control the average tunnel current immediately before applying the recording signal. 4
9 and used to drive the piezoelectric ceramic 45c to expand and contract during recording, the distance between the conductive needle 15 and the information recording medium 1 can be controlled in the same manner as during signal reproduction.

Next, tracking control will be explained using FIG. In the information recording medium 1, a tracking signal 20 is applied to a target track 19, and a tracking signal 23 and a tracking signal 24 are applied to tracks 21 and 22 adjacent to the target track, respectively. Conductive needle 15
The distance between the information recording medium 1 and the information recording medium 1 is controlled by the method described above. A band pass filter (BPF) 25 converts the target tracking signal 20 into another tracking signal 2.
This is for frequency separation from 3.24 and detector 2.
6 is for knowing the magnitude of the tracking signal. The signal source 27 generates a wobbling signal for wobbling the conductive needle 15 as a pickup,
Phase compensation performs phase compensation of the servo system. Also, the amplifier 28
performs signal calculation and amplification.

Tracking control of the conductive needle 15 with respect to a target track 19 of the information recording medium 1 is performed using a tracking signal detected from the information recording medium 1 by the needle 15. Next, a specific tracking control method will be explained. As mentioned above, the magnitude of the tunnel current 16 changes depending on the distance between the conductive needle 15 and the information recording medium 1, and the wider the distance, the smaller the tunnel current 16 becomes. The diameter of the tip of the conductive needle 15 is approximately equal to or smaller than the track pitch, and therefore the tracking signal of the track with the shortest distance to the conductive needle 15 is larger than the tracking signal of the other tracks. Therefore, the target track 1 separated in frequency by the bandpass filter 25
Using a tracking control signal 29 obtained by adding a wobbling signal for stable tracking to the tracking signal 20 of 9, the piezoelectric ceramic 45 is controlled so that the magnitude of the tracking signal 20 of the target track 19 is maximized.
Tracking can be performed on the track 19 by driving the conductive needles 15a and 45b to extend and retract and control the position of the conductive needle 15 in the left and right direction.

Next, another embodiment of the present invention will be described. FIG. 2 is a block diagram showing the configuration of another embodiment of the present invention. In this embodiment as well, the distance between the conductive needle 15 and the information recording medium 1 is controlled in the same manner as described with reference to FIG.

In the information recording medium 1, a tracking signal 31 is applied to a target track 30, and a tracking signal 34 and a tracking signal 35 are applied to tracks 32 and 33 adjacent to the target track, respectively. Conductive needle 15
The detection signals 42 detected using the above are input to band pass filters BPF25a, 25b, and 25c in order to separate them from other tracking signals in terms of frequency. In other words, the tracking signal 34 is separated by the BPF 25a,
The tracking signal 31 is separated by a BPF 25b,
It is assumed that the tracking signal 35 is separated by the BPF 25C. The separated tracking signal is sent to a detector 26.
a, 26b, and 26c, respectively, and a signal corresponding to the magnitude of the tracking signal is obtained as an output. Operational amplifiers 28a, 28b, and 28c operate and amplify this signal.

In this embodiment, tracking is not done by maximizing the magnitude of the tracking signal of the target track as in the previous embodiment, but by making the magnitudes of the tracking signals of two tracks adjacent to the target track equal. Perform tracking control as follows. For example, when a tracking signal 31 is applied to a target track 30 as shown in FIG. 2, the tracking control signal 29 is controlled so that the magnitude of the tracking signal 34 is equal to the magnitude of the tracking signal 35. The switch 36 is set to the C position so that the operation can be performed.

Note that when the three sets of signals applied to each track are fixed, the set of tracking signals used for tracking control changes depending on the target track, so a changeover switch 36 is used to switch the set of tracking control signals accordingly. It is necessary to use There are also three sets of tracking signal powers applied to each track (if variable,
Tracking signal 31 is always sent to the target track, and tracking signal 3 is sent to tracks adjacent to the target track.
It is clear that if the tracking signals 35 and 4 are applied, tracking control can be performed without switching the set of tracking signals with a switch. That is, in this embodiment, the point is that the conductive needle 15 can be controlled so that the magnitudes of the tracking signals of two tracks adjacent to the target track are equal.

FIG. 3 is a sectional view showing an embodiment of the information recording medium according to the present invention. Figure 3 shows tracking signal 6 on track 5.
, tracking signal 6 is applied to each track 7 except track 5.
1 and 2 respectively show an information recording medium 1 configured to be able to apply tracking signals 8 of different frequencies.

FIG. 4 is a sectional view showing another embodiment of the information recording medium according to the present invention. Figure 4 shows that tracking signals with different frequencies are applied between three adjacent tracks, and the three
1 shows an information recording medium 1 configured so that a tracking signal of the same frequency can be applied to each track. Track 9.9A.

Tracking signal 10 with a frequency of 9B, track 1
1. Tracking signal 1 of other frequencies to IIA and IIB
2. Tracks 13. A tracking signal 14 of another frequency is applied to 13A and 13B.

Although the connection between the conductive layer 3 (see FIG. 1) constituting each track and the tracking signal source is not shown in FIGS. 3 and 4, for example, the connection between the conductor layer 3 (see FIG. This can be done by selectively forming a conductive pattern on the surface or inside of an insulating substrate by irradiation or the like. In addition, the tracking signal can be applied from a connector contact prepared in advance if the information recording medium is in the form of a card, or via a spindle or clamper for supporting the disk if the information recording medium is in the form of a disk. can. In addition, when silicon is used as the insulating substrate 2 (see Figure 1), the connection to the tracking signal source can be made by forming a conductive pattern such as polysilicon using IC manufacturing technology, or by using a semiconductor pattern. It is also possible to form a .

Further, in that case, since an electronic circuit can be formed on the information recording medium, the necessary signals can also be generated by the electronic circuit on the information recording medium.

Note that here we used signal sources with different frequencies as tracking signals, but it may also be a signal that generates pulses at different pulse timings than other tracks, as long as it is a signal that can be distinguished from the tracking signals of adjacent tracks. good.

5 and 6 are cross-sectional views of other embodiments of the information recording medium according to the present invention, and both are cross-sectional views taken in a direction perpendicular to the tracks of the information recording medium 1. FIG. As already explained in the previous embodiment, the information recording medium 1 has an insulating substrate 2.
A conductive layer 3 is provided on the surface of the conductor layer 3, and an information recording layer 4 is further provided thereon
It has been established. The information recording layer 4 is a material whose work function changes due to the tunnel current during recording and maintains that state, or the shape of its surface changes due to the tunnel current during recording and the state changes. Any substance that can be retained may be used. The changed part (recorded part)
is denoted as S.

The difference between the embodiment shown in FIG. 5 and the embodiment shown in FIG. 6 is that in the embodiment shown in FIG. In the embodiment, the conductor layer 3 is embedded in the insulating substrate 2.

7 and 8 are cross-sectional views of still other embodiments of the information recording medium according to the present invention, and both are cross-sectional views taken in a direction perpendicular to the tracks of the information recording medium 1. FIG.

The information recording medium 1, the insulating substrate 2, and the conductive layer 3 are shaped like a disk or a card, as in the previous embodiment. The conductor layer 3 is a material whose work function changes due to the tunnel current during recording and maintains that state, or the shape of its surface changes due to the tunnel current during recording and the state changes. Any substance that can be retained may be used. The differences between the embodiment shown in FIG. 7 and the embodiment shown in FIG. 8 are the same as the differences between the embodiment shown in FIG. 5 and the embodiment shown in FIG.
In the embodiment shown in FIG. 8, the conductive layer 3 is formed on the insulating substrate 2, whereas in the embodiment shown in FIG. The point is that there is.

Although the embodiments shown in FIGS. 1 and 2 are explained using the information recording medium shown in FIG. 5, the present invention is not limited to this, and information recording media shown in other drawings may be used in the same way. Of course it is a thing.

〔Effect of the invention〕

According to the present invention, there is an advantage that it is possible to realize an information recording/reproducing device that has a high recording density on a molecular level in the area required to store one bit and has a high information transfer rate.

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams showing the configuration of an embodiment of the information recording and reproducing method according to the present invention, and FIGS.
Each figure is a cross-sectional view showing a tracking signal source of an embodiment of an information recording medium according to the present invention, and FIGS. 5 to 8 are cross-sectional views each showing the structure of an information recording medium according to the present invention. Explanation of symbols■...Information recording medium, 2...Insulating substrate, 3...
Conductor layer, 4... Information recording layer, 5... Track, 6
...tracking signal, 7...track, 8...
Tracking signal, 9... Track, 10... Tracking signal, 11... Track, 12... Tracking signal, 13... Track, 14... Tracking signal, 15... As pickup Conductive needle, 16... Tunnel current, 17... Low pass filter, 18... Bypass filter, 19... Track, 20... Tracking signal, 21... Track,
22... Track, 23... Tracking signal, 2
4... Tracking signal, 25... Band pass filter, 26... Detector, 27... Wobbling signal source, 28... Operational amplifier, 29... Tracking control signal, 30... Track , 31... Tracking signal, 32... Track, 33... Track, 34
... Tracking signal, 35 ... Tracking signal, 36 ... Switch, 37 ... Current-voltage conversion amplifier, 38 ... Interval control signal, 39 ... Phase compensation circuit,
40... Actuator, 41... Bias voltage,
42... detection signal, 43... signal processing circuit, 45.
...Piezoelectric ceramic, 46... Electrode, 47... Insulator, 48... Base, 49... Pre-hold circuit, 5
0...Hold control signal agent Patent attorney Akio Namiki Figure 3

Claims (1)

[Claims] 1. In a recording medium formed by overlapping at least a conductive layer and a signal recording layer, the conductive layer is placed at a minute distance from a conductive needle as a pickup through the signal recording layer. Utilizing the tunnel current that flows between the conductive layer and the conductive needle through the signal recording layer when they are brought close to each other so as to separate them, the tunnel current is intensified and applied to the signal recording layer during recording. , recording is performed by causing a change in the work function or surface shape of the recording layer, and during reproduction, due to the change in the work function or surface shape of the signal recording layer, the conductor layer and the pickup act as a pickup. In an information recording and reproducing method in which reproduction is performed by causing a change in a tunnel current flowing between the conductive needle and the signal recording layer through the signal recording layer, the distance between the conductive needle and the conductive layer is changed during reproduction. ,
a servo control means for maintaining and controlling the tunnel current average value obtained by averaging the fluctuations of the tunnel current depending on the presence or absence of recording, and maintaining and controlling the tunnel current so as to obtain the reference value; The distance between the body layers,
The method is characterized by comprising a servo control means for maintaining and controlling an average value of the tunnel current at a time point before the tunnel current is strengthened for recording as a reference so that the reference value is obtained. Information recording and reproducing method. 2. In a recording medium formed by overlapping at least a conductive layer and a signal recording layer, the conductive layer is brought close to a conductive needle serving as a pickup by a minute distance through the signal recording layer. At the time of recording, the tunnel current flowing through the signal recording layer between the conductive layer and the conductive needle is utilized. Recording is performed by causing a change in function or a change in surface shape, and during reproduction, due to the change in work function or change in surface shape in the signal recording layer, the contact between the conductive layer and the conductive needle as a pickup is In an information recording and reproducing method in which reproduction is performed by causing a change in a tunnel current flowing through the signal recording layer between the two, a signal source that applies a tracking signal to a track on the recording medium, and a signal current from the signal source. an information recording and reproducing system, comprising: tracking control means for detecting by the conductive needle using the tunneling current and controlling tracking of the needle. 3. In the information recording and reproducing system as set forth in claim 2, the signal source includes a plurality of signal sources that apply different signals to each track, and the tracking control means receives signals from the signal source corresponding to the target track. An information recording and reproducing system comprising means for detecting a signal with a conductive needle and controlling tracking of the needle so that the signal is maximized. 4. In the information recording and reproducing system according to claim 2, the signal source comprises a plurality of signal sources that apply different signals for each track, and the tracking control means:
It consists of a means for detecting two signals from two signal sources corresponding to two tracks adjacent to the target track with a conductive needle, and controlling the tracking of the needle so that the magnitudes of both signals are approximately equal. An information recording and reproducing method characterized by: 5. A conductor layer is provided on an insulating substrate, and a signal recording layer is further provided on the conductor layer, and the signal recording layer is configured to cause a tunnel current to flow through the signal recording layer to the conductor layer. An information recording medium comprising a material that causes a change in its work function or a change in surface shape, and comprising a signal source that applies a tracking signal to the conductive layer using the tunnel current. 6. The information recording medium according to claim 5, wherein the conductive layer forms concentric or spiral tracks. 7. The information recording medium according to claim 5, wherein the signal source is comprised of different signal sources that output different signals for a certain track and tracks in the vicinity thereof. 8. The information recording medium according to claim 5, characterized in that the signal source is composed of three different signal sources that output different signals for a certain track and its two adjacent tracks. Information recording medium.