Information recording unit and method for information recording/reproduction

A method and apparatus for recording information on an information recording medium and/or reproducing information from the recording medium. Probes for recording and/or reproducing information and a support for supporting the probes are arranged so that the probes are positioned to face the information recording medium. The support and the information recording medium are relatively moved by sliding on sliding surfaces thereof. The distance between the support and the recording medium is roughly set by projections formed between the support and the recording medium, and is finely adjusted during operation by a mechanism for moving the probes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an information recording unit and information 
recording and/or reproduction apparatus. Specifically, the present 
invention can suitably be applied to an improvement in a 
recording/reproduction apparatus using a scanning tunneling microscope. 
2. Related Background Art 
A scanning tunneling microscope (hereinafter referred to as STM) which is 
capable of directly observing the electron structure at the surface of a 
substance or in the vicinity of the surface has been developed [G. Binnig 
et al., Helvetica Physica Acta, 55,726 (1982) ]. This microscope enables 
high-resolution measurement of a real-space image of monocrystals and 
amorphous materials and enables observation using a low electric power 
such that the medium is not damaged by current. Also, it can be used to 
examine various materials because it can be operated in atmospheric air or 
solutions as well as in ultra-high vacuum. A wide range of application of 
this microscope is therefore expected. 
Recently, recording/reproduction apparatuses to which an STM is applied 
have also been developed (Japanese Patent Laid-Open Publication Nos. 
63-161552 and 63-161553). 
These conventional recording reproduction apparatuses have a construction 
such as that shown in FIG. 1. 
In the apparatus, a DC voltage high enough to cause a tunnel current is 
applied to a recording medium 8 by using a voltage applying circuit 5 and, 
in this state, the distance between a probe electrode (probe) 6 and the 
recording medium 8 is controlled so that the tunnel current is constant. 
Also, a pulse voltage is applied to the recording medium 8 having a 
switching memory effect with respect to electrical characteristics at a 
recording position to locally create a portion having a different 
electrical resistance in the recording portion. 
For reproduction, the distance between the probe 6 and the recording layer 
is constantly maintained by using a current amplifier 7, a servo circuit 3 
and a three-dimensional (3-D) driving mechanism 2 while applying a low 
voltage. An XY scan driving circuit 4 and the 3-D driving mechanism 2 are 
used to scan over the recording medium surface to make the probe 6 follow 
the surface so that a detection current is constant, thereby reproducing 
the recorded information from the amounts of control in the direction of 
the Z-axis corresponding to changes in electrical resistance created by 
recording operation and from the position of the probe on the surface. 
These operations are controlled by a microcomputer 1. The tunnel current 
starts flowing when the distance between the probe electrode 6 and the 
recording medium is reduced to 1 nm. High-precision working/production 
techniques are therefore required for components for finely controlling 
the probe electrode 6 and the recording medium 8. 
For this recording/reproducing process, as described above, it is necessary 
to control the distance between the probe electrode and the recording 
medium with high accuracy. At the same time, there is a need to simplify 
this distance control for the purpose of improving the 
recording/reproducing apparatus for wide use. 
SUMMARY OF THE INVENTION 
The present invention has been achieved generally based on the 
above-described prior art, and an object of the present invention is to 
provide an information recording medium, an information recording unit, 
and apparatus and method for information recording and/or reproduction, 
wherein even during a relative movement of the probe and the recording 
medium parallel to the surface of the medium, the distance therebetween 
can be set as desired and maintained constantly with accuracy by a simple 
means. 
Other objects of the present invention will become apparent from the 
following detailed description of embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 schematically shows a recording/reproduction apparatus in accordance 
with the first embodiment of the present invention. The apparatus includes 
a microcomputer 401 for conducting overall control of the apparatus, servo 
circuits 403, XY scan driving circuits 404, voltage applying circuits 405 
for applying voltages between probe electrodes and a recording medium, 
probe electrodes 406 formed of tungsten, current amplifiers 407, recording 
medium 408 formed by laminating four layers of SOAZ 
(squalirium-bis-6-octyl-azulene) by the Langmuir-Blodgett technique, a 
substrate electrode 409 formed by depositing Cr to 50 .ANG. by vacuum 
deposition and further depositing Au to 300 .ANG. thereon by vacuum 
deposition, a quartz glass substrate 410, an up-down mechanism 411 formed 
of laminated piezoelectric elements, an up-down mechanism driving circuit 
412, an XY driving mechanism 413, an XY driving circuit 414, and a 
container 415 for retaining probe electrodes 406, recording medium 408, 
substrate electrode 409 and substrate 410. For simplification, only three 
probe electrodes 406 are illustrated. For each of the plurality of probe 
electrodes 406, the servo circuits 403, the XY scan driving circuits 404, 
the voltage applying circuits 405, and the current amplifiers 407 are 
provided, respectively, as illustrated. Later-described three-dimensional 
driving mechanisms (not shown in FIG. 2) are provided in the container 415 
to respectively drive the probes. The container 415 is detachably attached 
to the body of the recording/reproduction apparatus. 
To record information on recording medium 408, each probe electrode 406 is 
brought closer to recording medium 408, and a voltage having, for example, 
a rectangular pulse waveform with a peak voltage of 3.5 V and a width of 
50 ns is applied by voltage applying circuit 405 to thereby change a 
characteristic of recording medium 408 to create a portion (corresponding 
to one bit) reduced in electrical resistance. The unillustrated 
three-dimensional driving mechanism and XY driving mechanism 413 are used 
to scan each recording medium 408 with each probe 406 in the X-Y 
directions (parallel to the surface of the recording medium), and a pulse 
is independently applied to a desired position from each probe electrode, 
thereby recording the information. 
For reproduction, the recording medium surface is scanned two-dimensionally 
in the same manner as recording, while applying a DC voltage lower than 
the recording voltage, e.g., 200 mV between probe electrodes 406 and 
recording medium 408 and while feedback-controlling the driving of the 
three-dimensional driving mechanism in the z direction (the direction of 
the distance between probe electrodes 406 and recording medium 408) 
independently with respect to each probe electrode so that a current 
detected by using current amplifier 407 and servo circuit 403 is 
maintained constant at, for example, 0.1 nA. At this time, the amount of 
feedback (the amount of driving in the z direction) corresponds to the 
recorded information on the recording medium, and the information is 
reproduced in correspondence with the recording position. Erasing is 
performed by applying, for example, a triangular wave pulse voltage of 5 V 
having a pulse width of 1 .mu.s as in the case of recording. These 
operations are controlled by the microcomputer 401. 
FIG. 3 shows an appearance of the container 415 taken out of the 
recording/reproduction apparatus in accordance with the first embodiment. 
A plurality of probe electrodes and a recording medium are disposed in 
this container so as to face each other. The container 415 is provided 
with electrodes 627 for connection of signals with the main unit of the 
apparatus, and a window 731 through which XY driving mechanism 413 enters 
the container. When the container 415 is inserted into the main unit of 
the apparatus, electrodes 627 are brought into contact with electrodes 
(not shown) provided on the apparatus, thereby completing the wiring as 
shown in FIG. 1. 
FIG. 4 schematically shows the three-dimensional driving mechanism for 
driving the probe electrodes in the direction of the Z axis (perpendicular 
to the surface of the recording medium) and in the X-Y directions. Bimorph 
beams 800 and a driving wiring region 802 are arranged. Bimorph beams 800 
and probe electrodes 406 were produced by a well-known method called 
micromechanics or micromachining. (Reference Documents: K. E. Petersen, 
Proc. IEEE 70, 420 (1982) and T. R. Albrecht, et al., 4th International 
conference on STM/STS (STM 1989) P1-29, S10-2) 
In the beam 800 are laminated two upper electrodes (Au) arranged in the 
widthwise direction, an insulating layer (Si.sub.3 N.sub.4), a 
piezoelectric layer (ZnO), an insulating layer (Si.sub.3 N.sub.4), an 
intermediate electrode (Au), an insulating layer (Si.sub.3 N.sub.4), a 
piezoelectric layer (ZnO), an insulating layer (Si.sub.3 N.sub.4), and two 
lower electrodes (Au) arranged in the widthwise direction. Each beam 800 
has a length of 750 .mu.m, a width of 150 .mu.m, and a thickness of 7.5 
.mu.m. If the two piezoelectric layers are polarized in the same 
direction, a voltage with same polarity + (-) is applied to both the two 
upper electrodes and the two lower electrodes relative to the intermediate 
electrode to displace the end of the bimorph beam 800, i.e., the probe 
electrode in the direction of the Z axis. The extent of this displacement 
is about 5 .mu.m when the voltage is .+-.15 V. It is possible to displace 
the probe in each of the directions of the X and Y axes by selecting the 
voltages to the two upper electrodes and the two-lower electrodes relative 
to the intermediate layer. Conductors from probes 406 formed of tungsten 
are led over bimorph beams 800 to the circuit on the wiring region 802 and 
are finally connected respective electrodes 627. A circuit for supplying 
control signals for bimorph beams 800 from electrodes 627 is also formed 
on the wiring region 802. 
Setting of container 415 on the apparatus will be described below with 
reference to the figures including cross sections of container 415. 
FIGS. 5 and 6 are diagrams of details of container 415 in accordance with 
the present embodiment. 
FIG. 5 is a cross-sectional view showing the relationship between the 
positions of the probe electrode and the recording medium. Bimorph beams 
800 are fixed on bases 801. Bases 801 are bonded and fixed to a frame 616 
which is formed as a structure member for the information recording 
carrier. A member 700 is a recording substrate formed of the 
above-mentioned substrate electrode 409 for recording medium 408 and 
substrate 410. Projections 700a are formed on the recording substrate 700. 
The recording substrate 700 is fixed on a frame 617 which is connected to 
XY driving mechanism 413. The lower surfaces of bases 801 and the upper 
surfaces of projections 700a are finished as flat planes with high 
accuracy. The upper surfaces or projections 700a are also covered by the 
recording medium 408. The height of projections 700a is determined by 
high-accuracy working so that the distance between bases 801 supporting 
bimorph beams 800 and surface portions of recording medium 408 other than 
the projections (i.e., surfaces used for recording/reproduction) is set to 
a predetermined value. The recording medium on projections 700a and bases 
801 slide on slides surfaces 609. This close contact between the recording 
medium on projections 700a and bases 801 ensures that the distance between 
probe electrodes 406 and the portions of recording medium 408 at which 
recording or reproduction is actually effected is adjusted to some degree, 
that is, this state is that rough adjustment of the distance has been 
completed. When the plurality of probe electrodes 406 are displaced 
relative to recording medium 408 in the X-Y directions to a large extent 
at a time, XY driving mechanism 413 drives recording medium 408 in X-Y 
directions through frame 617 while maintaining recording medium 408 on 
projections 700a and bases 801 in close contact. Recording medium 408 on 
projections 700a and bases 801 thereby slide on slide surfaces 609. Thus, 
the probe electrodes 406 and the surfaces of recording medium 408 actually 
used for recording or reproduction continue to maintain said state of the 
rough adjustment of the distance during the driving of XY driving 
mechanism and after the driving. There is, threfore, no need for a 
time-consuming operation for adjusting the distance between probe 
electrodes 406 and recording medium 408 each time they are moved to a 
large extent in X-Y directions for recording or reproduction. 
FIG. 6 shows a state in which an information recording cartridge is set in 
an apparatus body 630 and XY driving mechanism 413 formed of an inchworm 
arrangement of piezoelectric elements is inserted through window 731 by 
up-down mechanism 411. Frame 617 on which the recording substrate is fixed 
has a surface for connection to XY driving mechanism 413 on the opposite 
side from the recording medium 408. An electrode connector 629 is provided 
to supply signals and power from the control system in the main body of 
the apparatus to the internal circuit of the container, i.e., the 
information recording cartridge. The container is sealed by a 
mechanical-seal packing 770 to form a closed internal space. This closed 
space is defined by bases 801, frames 616 and 617, packing 770, recording 
substrate 700 and recording medium 408. 
Container 415 can be attached to or detached from the apparatus body 630 as 
indicated by the arrows. At the time of attachment or detachment, up-down 
mechanism 411 moves XY driving mechanism 413 downward to a position to 
avoid interference of XY driving mechanism 413 with attachment or 
detachment of container 415. 
When container 415 is inserted into the apparatus body 630, electrode 
connector 629 and electrodes 627 are brought into contact and electrically 
connected to each other to complete the circuit shown in FIG. 2. At the 
time of recording or reproduction, the voltage applied to each bimorph 
beam 800 is controlled to control the distance between each probe 
electrode 406 and recording medium 408 and a x-y direction fine scanning 
condition. Scanning of a large distance within the recording medium 408 
surface is effected at a time by xy driving mechanism 413. 
Since the slide portion with projection is formed on the recording medium 
surface side, it is possible to prevent the damage caused by contact of 
portions of the probe electrodes, the bimorph beams and the bases with the 
recording/reproduction regions of the medium. 
As described above, this embodiment is directed to a unit carrying an 
information recording medium on which information is recorded and/or from 
which information is reproduced by an information recording/reproduction 
apparatus. The unit includes probes for recording information on the 
information recording medium and/or reproducing information from the 
information recording medium, a support for supporting the probes so that 
the probes are positioned to face the information recording medium, and 
slide surfaces formed on the support to enable a relative movement between 
the support and the information recording medium while the distance 
between the support and the information recording medium is maintained 
constant. Also, this embodiment is directed to an apparatus for recording 
information on an information recording medium and/or reproducing 
information from the information recording medium. The apparatus includes 
probes for recording information on the information recording medium 
and/or reproducing information from the information recording medium, a 
support for supporting the probes so that the probes are positioned to 
face the information recording medium, and slide surfaces formed on the 
support to enable a relative movement between the support and the 
information recording medium while the distance between the support and 
the information recording medium is maintained constant. Also, the 
embodiment is directed to a method for recording information on an 
information recording medium and/or reproducing information from the 
information recording medium. The method includes the step of relatively 
moving the information recording medium and a support for supporting 
probes for information recording and/or information reproduction so that 
the probes are positioned to face the information recording medium, with 
sliding on sliding surfaces thereof while the distance between the support 
and the information recording medium is maintained constant, and the step 
of recording information on the information recording medium with the 
probes and/or reproducing information from the recording medium. Further, 
the embodiment is directed to an information recording medium for 
information recording and/or information reproduction using probes 
provided in an information recording/reproduction apparatus to record 
information and/or reproduce information. The information recording medium 
includes recording regions in which information recording and/or 
information reproduction is effected with the probes, and slide surfaces 
which enable relative movement between the recording regions and a support 
for supporting the probe while the distance between the recording regions 
and the support is maintained constant. 
By these means, the desired distance between the medium and the probes 
relatively moved parallel to the surface of the medium can easily be 
maintained constant with high accuracy. 
A second embodiment of the present invention will now be described below. 
In this embodiment, a high polymer containing fluorine atoms, i.e., 
polyimide formed by polyaddition-polymerizing pyromellitic anhydride, 
2,2-bis-(4-aminophenoxyphenyl)-1,3-hexafluoropropane is used as a 
recording medium material instead of SOAZ used in the first embodiment. 
The apparatus of this embodiment is not illustrated because it is the same 
as that of the first embodiment. Recording, reproduction and erasing can 
be performed in the same manner as the first embodiment. By the use of 
polyimide containing fluorine atoms for the recording layer, the surface 
energy of the slide portions is reduced so that the recording substrate 
can be moved smoothly. 
Thus, polyimide, in particular, a polyimide containing fluorine atoms is 
used for the recording medium and this material is also applied to the 
slide surface to form a slide layer for sliding on the support in 
accordance with this embodiment, whereby it is possible to form a suitable 
lubrication layer on the sliding surface simultaneously with the formation 
of the recording medium. 
A third embodiment of the present invention will be described below with 
reference to FIG. 7. Components corresponding to those of the first 
embodiment are indicated by the same reference numerals. In this 
embodiment, all XY scan driving circuits 404 and all servo circuits 403 
shown in FIG. 1 are incorporated in container 415 as a drive circuit 613. 
Except for this, the construction is the same as that of the first and 
second embodiments, so this embodiment is illustrated in the figure 
corresponding to FIG. 6. A selector for selection of driving of probe 
electrodes 406 may be included in drive circuit 613. Command signals and 
the like from microcomputer 401 are supplied to the drive circuit in 
container 415 through electrode connector 629 and electrodes 627. 
In the above-described embodiments, only probe electrodes 406 and the 
recording medium (and the drive circuit) are accommodated in the container 
and the container is detachably attached to the apparatus body. The 
recording medium can, therefore, be interchanged together with the 
container and there is no need to change the closed state of the interior 
of the container for interchange of the recording medium. Also, the unit 
can be interchanged while maintaining probes 408 and recording medium 408 
in a certain closed state. At the time of X-Y direction position control 
as well, this state can be maintained constant by virtue of the 
above-described slide portions. Therefore, probe electrodes 406 and 
recording medium 408 can be positioned speedily after frame insertion. 
In accordance with the structure of the present embodiments, since 
components to be worked with accuracy, including probe electrodes and 
recording medium 408, can be assembled in one unit, they can be 
manufactured in a process separate from the process for manufacturing 
rough-movement components, circuits and interface units which do not 
require high-precision working. As a result, the assembly of the apparatus 
is facilitated, resulting in improvement in productivity. Since the 
high-precision components can be interchanged by detaching the container, 
the apparatus can easily be maintained with respect to the damage caused 
by an accident. 
In the above-described embodiments, the probe electrodes, bimorph beams and 
parts are produced by micromechanics techniques and can therefore be 
improved in accuracy, and the drive circuit and other components can be 
assembled together with the bimorph beams on the same substrate. 
The recording/reproduction apparatus in accordance with the above-described 
embodiments may be an apparatus having the function for recording, 
reproduction, or 0 information recording, i.e., erasing alone, and may be 
an apparatus having a combination of these functions. 
It is within the scope of the invention that the projections are formed on 
bases or frame 616. Also, the projections can be formed separately of the 
recording substrate and the bases. 
Thus, according to the above-described embodiments, an information 
recording medium, an information recording unit, and apparatus and method 
for information recording and/or reproduction can be provided, wherein 
even during a relative movement of the probe and the recording medium 
parallel to the surface of the medium, the distance therebetween can be 
set as desired and maintained constant with high accuracy in a simple 
manner.