JP2523144B2 - Information recording / reproducing apparatus and information recording medium - Google Patents

Description

The present invention relates to a high density information recording / reproducing apparatus and an information recording medium used for the same.

[Conventional technology]

The most important issue in the current information recording technology is the improvement of recording density. Compared with conventional horizontal magnetic recording technology, optical recording using an optical recording device that uses laser light or a magneto-optical recording device that uses both a laser light and a magnetic field reduces the recording spot to a light wavelength (about 1 μm). It is possible to improve the recording density by almost two orders of magnitude. However, in order to achieve higher density in optical recording,
A laser beam having a shorter wavelength and an optical system that can be used for the laser beam are required, and as far as optical recording is concerned, it is difficult for the current technology to significantly improve the recording density.

In recent years, Scanning Tunneling Microscope
A high-resolution microscope utilizing the tunnel effect called Microscope (STM) has been developed. For a discussion of STM, see Proceedings of the First International Consortium on Scanning Tunneling Microscopy Technology.
conference on Scanning Tunneling Microscopy), surlace
science, volume 181, Nos. 1/2, March (1) 1987 ”. STM can analyze material surface features with high resolution of several angstroms in the horizontal direction and less than 1 angstrom in the vertical direction. Therefore, the recording density of the device for reproducing the information recorded on the surface of the recording medium by using the principle of STM can be increased by several digits or more as compared with the recording density of the information recording / reproducing device using the laser beam.
An information recording / reproducing apparatus using the principle of STM having such characteristics is described in Japanese Patent Laid-Open No. 61-80636 by Kazan et al., Which will be described briefly below.

That is, the recording medium is composed of at least a conductor layer and a signal recording layer which are superposed. When the conductive layer as a pickup is brought close to the conductive layer with a very small interval, a tunnel current flows between the conductive layer and the conductive layer. At this time, if the signal recording layer is positioned between the two, a tunnel current flows through the signal recording layer. When the tunnel current is increased, the work function or the surface shape of the signal recording layer changes in the signal recording layer, and recording is performed using this. Also, at the time of reproduction, the tunnel current flowing between the conductive needle layer and the conductive needle layer when approaching the conductive layer with a very small space therebetween causes a change in the work function of the signal recording layer located between the two. Since a change in current occurs due to a change in surface shape, recording (change in work function or change in surface shape) in the signal recording layer can be reproduced by this.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technology using the principle of STM, the tracking control for the track on the information recording medium of the pickup is not considered, and the tracking control is actually performed when configuring the information recording / reproducing device using the principle of STM. There seems to be a problem with.
Further, in the above-mentioned conventional technique, the pickup is servo-controlled so as to move up and down according to the presence or absence of recording on the surface of the recording medium. That is, although the tunnel current varies depending on whether or not recording is performed on the surface of the recording medium, the servo control is performed by performing feedback control such that the pickup is moved up and down so that the tunnel current is constant. If the presence or absence of recording on the surface is expressed by unevenness, the pickup is servo-controlled so as to maintain a constant interval with the surface of the recording medium by just moving up and down following the unevenness. Become. Since it moves up and down in this way, the control speed of the pickup cannot be made very fast, and as a result, it was difficult to increase the signal reading speed.

It is an object of the present invention to provide an information recording / reproducing apparatus using the principle of STM which has a high information recording density, a high signal reading speed, and can perform stable tracking control, and an information recording medium used therefor. It is in.

[Means for solving problems]

Among the above objects, in order to increase the signal recording / reproducing speed, the interval is controlled by 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 one by one according to the presence or absence of recording, servo control is performed so as to maintain the pickup at an average position of up and down movement. For tracking control of the pickup for stable tracking, an information recording medium having a structure capable of applying a tracking signal to the tracking 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. Take control.

[Action]

Since the pickup is controlled so that the average distance between the pickup and the information recording medium becomes a predetermined value, it is not necessary to move the pickup according to the strength of the tunnel current depending on the presence or absence of recording, and the read signal speed is the pickup servo. A high frequency signal can be read out without being restricted by the frequency band of the system. In addition, tracking is performed so that the magnitude of the tracking signal induced from the target track of the information recording medium becomes maximum, or the magnitude of the tracking signal induced from two tracks adjacent to the target track becomes equal. By controlling, it becomes possible to perform stable tracking 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 / reproducing apparatus as an embodiment of the present invention. In the figure, 1 is an information recording medium, and the figure shows a cross-sectional view in the direction perpendicular to the track. The information recording medium 1 is provided, for example, by embedding a conductor layer 3 such as polysilicon, metal, or semiconductor on the surface of an insulating substrate 2 such as glass, silicon, or sapphire, and further forming an information recording layer 4 thereon. It is provided and is formed in a disk shape or a card shape as viewed from above. The information recording layer 4 is a substance whose property is changed and its work function is changed by the tunnel current at the time of recording flowing between the conductor layer 3 and the conductive needle 15 as a pickup to maintain the state. It may be any substance that is present or whose surface shape is changed by the tunneling current during recording and that state is maintained. The conductive needle 15 as a pickup is for recording / reproducing information signals to / from the information recording medium 1, and a tungsten needle or the like having a tip thickness of 0.1 μm or less by etching is used. Since the tip of the needle 15 is made thin in this way, high density recording / reproducing is possible.

In order to record / 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 the actuator 40 to which the needle 15 as a pickup is attached.

The actuator 40 includes fixed bases 48a and 48b and a movable base 48c, and piezoelectric ceramics 45a and 45z such as PLZT and PZT.
It consists of b, 45c, etc. That is, the bases 48a and 48b are fixed at appropriate fixing 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. The movable base 48c is made of a piezoelectric ceramic 45c and an insulator.
It is connected via 47 to a conductive needle 15 as a pickup.

Therefore, now, if a control voltage is applied between the electrodes 46a "and 46b" 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. it can. Also, between the electrodes 46a 'and 46b' or the electrodes
If a control voltage is applied between 46a and 46b to expand or contract the piezoelectric ceramic 45b or the piezoelectric ceramic 45a,
Tracking control can be performed by moving the needle 15 in the left-right direction with respect to the information recording medium 1.

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

The tunnel current 16 flowing between the conductive needle 15 and the information recording medium 1 is caused by the distance between the conductive needle 15 and the information recording layer 4 and the recording layer 4.
It changes depending on the work function of the surface of, the bias voltage 41, and the like. The work function of the surface of the information recording layer 4 changes according to the written signal. However, by using a modulation method that does not have a direct current component such as 8-14 modulation (EFM) used in compact discs as a signal modulation method when recording information, the average value of tunnel current (or low The frequency component) can be prevented from being affected by the recording signal. Further, by keeping the bias voltage 41 constant, the fluctuation of the tunnel current 16 due to the fluctuation of 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 as small as several nA to several hundreds nA, it is converted into a voltage by a current-voltage conversion amplifier (IV converter) 37 and amplified, and then a voltage signal corresponding to the tunnel current (hereinafter, (Hereinafter referred to as a detection signal), and this detection signal 42 is used for the subsequent processing.

The detection signal 42 is input to the low pass filter (LPF) 17 and the high pass filter (HPF) 18, and 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 reproducing information. To do. The average value (low frequency component) of the tunnel current signal adjusted by the LPF17 is the detector 26,
After the necessary processing is performed by the phase compensation circuit 39 and the amplifier 28, it is added to the actuator 40 (specifically, the electrode 46a ″).
At this time, the pre-hold circuit 49 may or may not be used for pre-hold, but when the signal is reproduced, the pre-hold is not applied and is applied to the electrode 46a ″ as it is. In addition to the pre-hold circuit 49 as the hold control signal 50, pre-hold is performed.

A servo system for controlling the interval controls the position (interval) in the vertical direction 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 tunnel current becomes constant. Therefore, the average distance between the conductive needle 15 and the information recording layer 4 can be controlled to be substantially constant.

On the other hand, the information recorded on the information recording layer 4 is HPF18.
The high-frequency component of the detection signal separated by is input to the signal processing circuit 43 for demodulating the recorded information and processed to be reproduced.

As described 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 not necessary to control so that the tunnel current 16 is always constant in response to a changing signal, which is the case 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 drawing, the recording of the signal is performed by superimposing the recording signal on the bias voltage 41 and increasing the tunnel current 16 to cause a change in the information recording layer 4. Further, in controlling the distance between the conductive needle 15 and the information recording medium 1 at the time of recording, as described above, the average hold current immediately before the recording signal is applied is determined by the pre-hold circuit. It is stored in 49, and the piezoelectric ceramic 45c is expanded and contracted during recording to control the distance between the conductive needle 15 and the information recording medium 1 as in the case of signal reproduction.

Next, the tracking control will be described with reference to FIG. In the information recording medium 1, the target track 19 has a tracking signal 20, and the track 21 adjacent to the target track 21.
And tracking signal 23, tracking signal on track 22
24 are applied respectively. The distance between the conductive needle 15 and the information recording medium 1 is controlled by the method already described. The band pass filter (BPF) 25 is for separating the target tracking signal 20 from the other tracking signals 23, 24 in terms of frequency, and the detector 26 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, and the phase compensation performs phase compensation of the servo system. The amplifier 28 also operates and amplifies the signal.

Conductive needle for target track 19 of information recording medium 1
The tracking control of 15 is performed using the tracking signal detected from the information recording medium 1 by the needle 15. Next, a specific tracking control method will be described. As described 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 is, the smaller the tunnel current 16 is. The diameter of the tip of the conductive needle 15 is approximately equal to or smaller than the track pitch,
Therefore, the tracking signal of the track with the smallest distance from the conductive needle 15 becomes larger than the tracking signals of the other tracks. Therefore, by using the tracking control signal 29 obtained by adding the wobbling signal for stable tracking to the tracking signal 20 of the target track 19 frequency-separated by the bandpass filter 25, the magnitude of the tracking signal 20 of the target track 19 is increased. The piezoelectric needles 45a, 45b are driven to expand and contract to maximize the
Tracking can be performed on the track 19 by controlling the position of 5 in the left-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. Also in this embodiment, the space between the conductive needles 15 and the information recording medium 1 is controlled by the same method as described with reference to FIG.

In the information recording medium 1, the tracking signal 31 is on the target track 30, and the tracking signal 34 and the tracking signal 35 are on the tracks 32 and 33 adjacent to the target track.
Are respectively applied. The detection signal 42 detected by using the conductive needle 15 is band-pass filter BPFs 25a, 25b, 25c in order to be frequency-separated from other tracking signals.
Is input to That is, the tracking signal 34 is separated by the BPF 25a, the tracking signal 31 is separated by the BPF 25b, and the tracking signal 35 is separated by the BPF 25c. The separated tracking signals are detected by the detectors 26a, 26b,
The signals are respectively detected by 26c, and a signal corresponding to the magnitude of the tracking signal is obtained at the output. The operational amplifiers 28a, 28b, 28c perform operation and amplification of this signal.

In the present embodiment, tracking does not maximize the magnitude of the target tracking signal as in the previous embodiment, but makes the magnitudes of the tracking signals of two tracks adjacent to the target track equal. Tracking control. For example, as shown in FIG. 2, when the tracking signal 31 is applied to the target track 30, the tracking signal is used as the tracking control signal 29.
The switch 36 is set to the position C so that control can be performed so that the size of 34 and the size of the tracking signal 35 become equal.

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. Therefore, the changeover switch 36 for switching the set of tracking control signals is set accordingly. Must be used. When the three sets of tracking signals applied to each track can be changed, the tracking signal 31 is always applied to the target track, and the tracking signal 34 and the tracking signal 35 are applied to the tracks adjacent to the target track. Then, it is obvious that the tracking control can be performed without switching the set of tracking signals with the switch. That is, in the present embodiment, the point is that the conductive needle 15 can be controlled so that the two tracks adjacent to the target track have the same tracking signal magnitude.

FIG. 3 is a sectional view showing an embodiment of the information recording medium in the present invention. FIG. 3 shows an information recording medium 1 configured so that a tracking signal 6 can be applied to the track 5 and a tracking signal 8 having a frequency different from the tracking signal can be applied to each track 7 other than the track 5.

FIG. 4 is a sectional view showing another embodiment of the information recording medium of the present invention. FIG. 4 shows an information recording medium 1 configured such that tracking signals having different frequencies are applied between adjacent three tracks, and tracking signals having the same frequency can be applied for every three tracks. Tracking signal 10 of a certain frequency on tracks 9, 9A, 9B, tracking signal 12 of another frequency on tracks 11, 11A, 11B,
A tracking signal 14 of another frequency is applied to the tracks 13, 13A, 13B.

3 and 4, the connection between the conductor layer 3 (see FIG. 1) constituting each track and the tracking signal source is not shown, but for example, vapor deposition, sputtering, ion beam This can be performed by selectively forming a conductive pattern on the surface or inside of the insulating substrate by irradiation or the like. Further, the tracking signal may be applied from a connector contact or the like prepared in advance when the information recording medium is a card, or via a spindle or a clamper for supporting the disc when the information recording medium is a disk. it can. When silicon is used as the insulating substrate 2 (see FIG. 1), the connection with the tracking signal source is to form a conductive pattern such as polysilicon formed by using the IC manufacturing technique, or a semiconductor pattern. Can also be formed. Further, in that case, since an electronic circuit can be formed on the information recording medium, a necessary signal can be generated by the electronic circuit on the information recording medium.

Although a signal source having a different frequency is used as the tracking signal here, for example, a signal in which a pulse is generated at a pulse timing different from that of another track may be used. good.

5 and 6 are cross-sectional views of another embodiment of the information recording medium of the present invention, both of which are cross-sectional views of the information recording medium 1 in the direction perpendicular to the tracks. The information recording medium 1 is the one in which the conductor layer 3 is provided on the surface of the insulating substrate 2 and the information recording layer 4 is further provided thereon, as already described in the previous embodiment. The information recording layer 4 is a substance whose work function as a property is changed by the tunnel current at the time of recording and maintains its state, or the surface shape is changed by the tunnel current at the time of recording and its state is changed. Any substance that can be retained may be used. The changed portion (recorded portion) is indicated by S.

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

7 and 8 are cross-sectional views of yet another embodiment of the information recording medium according to the present invention, both of which are cross-sectional views of the information recording medium 1 in the direction perpendicular to the tracks.

The information recording medium 1, the insulating substrate 2 and the conductor layer 3 are formed in a disk shape or a card shape as in the previous embodiment. The conductor layer 3 is a substance whose work function as a property changes due to the tunnel current at the time of recording, and its state is maintained, or the surface shape changes due to the tunnel current at the time of recording, and its state changes. Any substance that can be retained may be used. The difference between the embodiment of FIG. 7 and the embodiment of FIG. 8 is the same as the difference between the embodiment of FIG. 5 and the embodiment of FIG. 6, and in the embodiment of FIG. In contrast to being formed on the insulating substrate 2, the conductor layer 3 is embedded in the insulating substrate 2 in the embodiment of FIG.

In the embodiment shown in FIGS. 1 and 2, the information recording medium shown in FIG. 5 is used. However, the present invention is not limited to this, and the information recording medium shown in other figures may be used similarly. Of course, it is a thing.

〔The invention's effect〕

According to the present invention, there is an advantage that it is possible to realize an information recording / reproducing apparatus in which an area required for 1-bit storage has a high recording density on a molecular level and has a high information transfer rate.

[Brief description of drawings]

1 and 2 are block diagrams showing the configuration of an embodiment of the information recording / reproducing apparatus of the present invention, FIG. 3, and FIG.
FIG. 5 is a sectional view showing a tracking signal source of an embodiment of the information recording medium of the present invention, and FIGS. 5 to 8 are sectional views showing the structure of the information recording medium of the present invention. DESCRIPTION OF SYMBOLS 1 ... 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 ... Trucking signal, 13 ... Track, 14 ... Tracking signal, 15 ... Conductive needle as pickup, 16 ... Tunnel current, 17 ... Low pass filter, 18 ... High pass filter, 19 ... … Truck, 20
...... Tracking signal, 21 …… Track, 22 …… Track, 23 …… Tracking signal, 24 …… 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 ceramics, 46 …… Electrodes, 47 …… Insulators, 48 ……
… Base, 49 …… Front hold circuit, 50… Hold control signal

Claims (8)

(57) [Claims] 1. A conductive layer in a recording medium having at least a conductive layer and a signal recording layer superposed on each other, with a minute gap between the conductive layer as a pickup and the signal recording layer. The tunnel current flowing through the signal recording layer between the conductor layer and the conductive needle when being approached is used, and at the time of recording, the tunnel current is strengthened and the recording is performed on the signal recording layer. Recording is performed by causing a change in the work function of the layer or a change in the surface shape, and during reproduction, due to the change in the work function or the surface shape in the signal recording layer, the conductivity of the conductor layer and the pickup is increased. In an information recording / reproducing apparatus for reproducing by changing a tunnel current flowing through the signal recording layer between the needle and the needle, at the time of reproducing, the distance between the conductive needle and the conductor layer is
Servo control means for maintaining and controlling the tunnel current average value obtained by averaging the fluctuation of the tunnel current depending on the presence or absence of recording, so as to obtain the reference value; The distance between the body layers
A servo control unit that holds an average value of the tunnel current as a reference at the time before the tunnel current is strengthened for recording, and maintains and controls so that the reference value is obtained. Information recording / reproducing apparatus. 2. A conductive layer in a recording medium having at least a conductive layer and a signal recording layer superposed on each other, with a minute gap between the conductive layer as a pickup and the signal recording layer. The tunnel current flowing through the signal recording layer between the conductor layer and the conductive needle when being approached is used, and at the time of recording, the tunnel current is strengthened and the recording is performed on the signal recording layer. Recording is performed by causing a change in the work function of the layer or a change in the surface shape, and during reproduction, due to the change in the work function or the surface shape in the signal recording layer, the conductivity of the conductor layer and the pickup is increased. In an information recording / reproducing apparatus which performs reproduction by changing a tunnel current flowing through the signal recording layer between the needle and a needle, a tracking signal is applied to a track on the recording medium. An information recording / reproducing apparatus comprising: a signal source; and tracking control means for detecting a signal current from the signal source by the conductive needle by using the tunnel current and performing tracking control of the needle. . 3. The information recording / reproducing apparatus according to claim 2, wherein the signal source is composed of a plurality of signal sources for applying different signals for each track, and the tracking control means is a signal corresponding to a target track. An information recording / reproducing apparatus comprising a means for detecting a signal from a source by a conductive needle and performing tracking control of the needle so that it becomes maximum. 4. The information recording / reproducing apparatus according to claim 2, wherein the signal source comprises a plurality of signal sources for applying different signals for each track, and the tracking control means is adjacent to the target track. It is characterized in that it comprises means for detecting two signals from two signal sources corresponding to two tracks by a conductive needle and performing tracking control of the needles so that the magnitudes of the two signals become substantially equal. Information recording / reproducing apparatus. 5. A tunnel having an electric conductor layer on an insulating substrate and further having a signal recording layer on the electric conductor layer, the signal recording layer passing through the signal recording layer to the electric conductor layer. Depending on the current
An information recording medium comprising a material that causes a change in its work function or a surface shape and having a signal source for applying a tracking signal to the conductor layer. 6. The information recording medium according to claim 5, wherein the conductor layer forms a concentric circular or spiral track. 7. The information recording medium according to claim 5, wherein the signal source comprises different signal sources for outputting different signals on a certain track and a track in the vicinity thereof. recoding media. 8. The information recording medium according to claim 5, wherein the signal source comprises three different signal sources that output different signals on a certain track and two adjacent tracks. Characteristic information recording medium.